SYMPOSIUM DD
Solid-State Chemistry of Inorganic Materials IV
December 2 { 6, 2002
Chairs
Martha Greenblatt
M. Stanley Whittingham
Miguel A. Alario-Franco
Gregory S. Rohrer
Dept of Chemistry & Chemical Biology
Rutgers Univ
Piscataway, NJ 08854-8087
732-445-3277
Facultad de Ciencias Quimica
Univ of Complutense
Lab de Qimica del Estado Solido
Madrid, E-28040 SPAIN
34-91-394-4338
Dept of Chemistry
SUNY-Binghamton
Science II
Binghamton, NY 13902-6016
607-777-4623
Dept of Materials Science & Engr
Carngie Mellon Univ
WEH 3327
Pittsburgh, PA 15213-3890
412-268-2696
Symposium Support
Donors of the ACS Petroleum Research Fund
National Science Foundation
Proceedings to be published in both book form and online
(see
at www.mrs.org)
as Volume 755
of the Materials Research Society
Symposium Proceedings Series
ONLINE PUBLICATIONS
* Invited paper
637
SESSION DD1: METAL-TO-INSULATOR
TRANSITION - I
Chairs: M. Stanley Whittingham and Peter K. Davies
Monday Morning, December 2, 2002
Back Bay C (Sheraton)
8:45 AM *DD1.1
SOFT X-RAY EMISSION AND RESONANT INELASTIC X-RAY
SCATTERING STUDIES OF ELECTRONIC STRUCTURE IN
METAL OXIDES. Kevin E. Smith, Cormac McGuinness, James E.
Downes, Cristian B. Stagarescu, Philip J. Ryan, Dongfeng Fu,
Department of Physics, Boston University; Steven D. Hulbert,
National Synchrotron Light Source, Brookhaven National Laboratory;
J.M. Honig, Department of Chemistry, Purdue University; Russel
Egdell, Inorganic Chemistry Laboratory, Oxford University.
High resolution synchrotron radiation-excited soft x-ray emission
(SXE) spectroscopy is a powerful probe of the valence band electronic
structure in complex materials. The incident synchrotron radiation
excites a core electron, creating a hole on a core level. Radiative decay
of this core hole via electron transitions from the valence band results
in the emission of a spectrum of x-rays. Due to strong dipole selection
rules and the dominance of intra-atomic over inter-atomic transitions,
the SXE spectrum reects the element and site specic bulk density
of states, resolved into discrete angular momentum components, i.e.
the bulk partial density of states. When the energy of the incident
synchrotron radiation is tuned to a core absorption threshold, the
resulting emission is more accurately described as resonant inelastic
x-ray scattering (RIXS), and the spectra reveal charge transfer and
dipole forbidden excitations. In contrast to photoemission
spectroscopy, SXE/RIXS is not surface sensitive and the spectroscopy
can be performed on samples in external electric or magnetic elds.
We will discuss the instrumentation required to perform SXE/RIXS
experiments, and report the study of a selection of transition metal
oxides. Specically, we will discuss our investigations of the electronic
structure and temperature-induced metal to non-metal transitions in
Cr-doped V2 O3 , and of the electronic structure of the binary
post-transition metal oxides ZnO, CdO, In2 O3 , SnO2 and Sn-doped
In2 O3 . Unique measurements of densities of states, valence band and
shallow core level hybridization, and low energy electron excitations
will be presented. The results will be compared to photoemission data
and to electronic structure calculations. Possible future directions for
the application of this technique in the study of complex materials
will be discussed. Experiments performed at the NSLS. Research
supported in part by the DOE under DE-FG02-98ER45680. The SXE
spectrometer was funded by the US ARO under DAAH04-95-0014.
9:15 AM DD1.2
A Cr(IV) BASED 1212-TYPE CUPRATE. Rocio Ruiz-Bustos,
Myriam H. Aguirre, E. Moran, M.A. Alario-Franco, Laboratorio de
Quimica del Estado Solido, Facultad de Quimica, Universidad
Complutense, Madrid, SPAIN; J.L. Martinez, ICMM, CSIC, Canto
Blanco, Madrid, SPAIN.
The so-called Charge Reservoir Layer (CRL) of the cuprate
superconductors has been the basic play-ground to innovate in the
search of HTSC materials.Once that the room pressure synthesis
possibilities have been worked out, the use of high pressures and
temperatures has opened up a new venue in the search of yet more
substitutions. In this way, elements as dierent as C, S, Ga, P, or Fe,
to quote but a few, have been introduced in the CRL.The case of the
element chromium is particularly interesting in view of the wide
possibilities it oers in both oxidation states and3 coordination
number. Indeed, Cr(III), an octahedral-only t2g ion, is very stable
due to its high Octahedral Crystal Field (OCF) stabilisation energy0
(165 kjul/mol as [Cr(III)-O6 ]) ; in the other extreme, Cr(VI), a d
ion, has no common coordination but the tetrahedral one: [Cr(VI)-O4 ]
and no OCF stabilisation. Yet Cr(VI) has given the wider series of
cuprates: (Cu,Cr) Ba2 Can01 Cun O3n+2 , many of which are
superconducting. But, Chromium has, indeed, some other oxidation
states and, in the present work, we have made a new cuprate with just
Cr(IV) in the CRL: CrSr2 YCu2 O8 . The material is tetragonal, SG
P4/mmm, and unit cell parameters: a = 3.838A & c = 11.30A). This
structure formally derives from Ybco by replacing the so-called
Copper chains [Cu-O4 ]SP by distorted [Cr-O6 ]OCT and is akin to the
relatively novel niobate and ruthenate cuprates MSr2 GdCu2 O8 , of
which the former is non SC while the ruthenates show coexisting
magnetic and superconducting properties Cr(IV) oxides, like CrO2
and SrCrO3 are rather unstable towards decomposition, so that High
Pressure is required for the synthesis.
9:30 AM DD1.3
STUDIES OF THE ELECTRONIC PROPERTIES OF BaV10 O15 :
CRYSTALLOGRAPHIC PHASE TRANSITION, ELECTRICAL
TRANSPORT AND MAGNETIC PROPERTIES. Craig Bridges,
John E. Greedan, McMaster University, Brockhouse Institute for
Materials Research and Department of Chemistry, Hamilton, ON,
CANADA.
BaV10O15 can be regarded as Ba-doped V2 O3 where the Ba ions
substitute in the close packed layers. The Ba2+ions
direct the
occupation of the octahedral sites by the V /3+ ions. The resulting
structure is closely related to that of V2 O3 but with subtle
dierences. A remarkable crystallographic phase transition occurs at
125K from Cmca to Pbca, which, it will be argued, is driven in part
by V-V bond formation resulting in one of the shortest V-V distances,
2.5334(5)A, known in vanadium oxide chemistry. This phase
transition is reected in the transport properties, both resistivity and
Seebeck eect. A complex magnetic phase transition sets in below Tc
= 42K as conrmed by neutron scattering and specic heat studies.
The V-sublattice is geometrically frustrated and the exchange
interactions are strongly antiferromagnetic, 2 = -1141(23)K. Only a
very small fraction of the entropy is removed below Tc , 4% and it is
likely that only a fraction of the spins are ordered. This interpretation
is supported by the neutron data. These results point to a very
heterogenous magnetic ground state.
10:15 AM *DD1.4
VERNIER STRUCTURES IN NOWOTNY CHIMNEY LADDER
PHASES AND -BRASS DERIVATIVES. Stephen Lee, Bernd
Harbrecht, Jianhua Lin, Roald Homann, Mikhail Shatruk, Daniel
Fredrickson, Lan-Feng Yuan and Joshua Teal Schmidt, Departments
of Chemistry, Cornell University, NY; Univ. of Marburg, GERMANY;
Peking University, CHINA.
Both chimney ladder phases (eg., Ru2 Sn3 ) and -brass (Cu5 Zn8 )
structures contain Vernier structures in which there are two sequences
of atoms which are not in simple registry with one another. This can
lead to both commensurate structures with large unit cells (on the
order of 100 A and also incommensurate structures. In these two
families of systems there are also xed electron counting rules which
the experimental structures obey. In the case of chimney ladder
phases, the number of valence electrons per transition metal atom is
often 14. For -brass, electron counts near 21/13 electrons per atom
are often observed. We account for these two features with a two
component model. In both phases there are two dierent
sub-structures which occur in diering amounts, each with their own
preference in valence electron count. Dierent mixtures of these two
phases leads to a host of dierent structures. Both new
crystallographic data and band calculations will be presented.
10:45 AM DD1.5
SOLVING THE STRUCTURE OF THE PHASES IN THE Al-Mg-Si
ALLOY SYSTEM WITH THE HELP OF AB INITIO MODELLING.
Anders Froseth, NTNU, Dept of Physics, Trondheim, NORWAY;
Peter Derlet, Paul Scherrer Institute, Villigen PSI, SWITZERLAND;
Sigmund Andersen and Calin Marioara, SINTEF Materials
Technology, Trondheim, NORWAY.
The Al-Mg-Si 6000-series alloy system is a precipitation hardening
alloy gaining much of of its strenght from precipitate phases acting as
pinning centers for dislocation movement. Recently, Zandbergen,
Andersen and coworkers identied the crystallography of the so-called
"-phase, one of the main hardening phases, using solely electron
microscopy techniques [1]. Later, several other phases have been
identied using high resolution microscopy. To solve the
crystallography of these phases and to get an increased understanding
of the electronic structure and bonding, ab initio modelling has
proven to be a valuable tool. We present results from calculations on
several recently discovered phases and show how ab initio modelling
can give insight into the bonding trends and electronic structure of
the phases in this alloy system. [1] H.W. Zandbergen, S.J. Andersen
and J. Jansen, Science 277, 1221 (1997).
11:00 AM DD1.6
RULES FOR UNDERSTANDING AND DESIGNING NOVEL
MOLECULE-BASED RARE-EARTH MAGNETIC COMPOUNDS.
Lindsay E. Roy, Timothy Hughbanks, Texas A&M University,
Department of Chemistry, College Station, TX.
A fundamental understanding of common magnetic phenomena is
imperative for the deliberate design of novel inorganic materials with
specic properties. Of the elements, open shell 4f rare earth elements
provide the richest region for interesting magnetic and conducting
properties. Despite a copious supply of data from solid state
materials, our ability to predict the magnetic behavior of new
molecular lanthanide compounds is still limited. There is a need for
qualitative tools with sound quantitative basis that can serve as
interpretive and predictive magnetostructural models for
molecule-based lanthanide systems. The RKKY exchange interaction
is commonly cited to describe magnetic coupling in metallic rare earth
systems. Our goal is to provide a basis of correlating structure,
bonding, and magnetic properties with more specic applicability
than the more phenomenological RKKY description. Exploiting
intraatomic exchange between 4f and 5d electrons in lanthanide
638
systems is key to understanding and, ultimately, to designing novel
molecular systems with large magnetic moments at high temperature.
Results of detailed DFT calculations were used to construct and check
features of a generally applicable qualitative approach to
understanding magnetic coupling in rare-earth-rich compounds. We
have studied interatomic exchange, mediated by spin polarization of
both lled and partially-lled bonding orbitals, using basic
perturbation methods. Using fragments based on structures of
metal-rich lanthanide compounds, we have investigated molecular and
low-dimensional extended structures, including Gd3 I6 (OPH3 )12 ,
Gd2 Cl3 , and CaGd6 I12 Mn. Open d-shell clusters can exhibit
ferromagnetic coupling that is many times stronger than that typical
of rare-earth elements and intermetallic compounds.
11:15 AM DD1.7
STABILITY AND HARDNESS OF COVALENT COMPOUNDS.
John Gilman, UCLA, Dept of Materials Science and Engineering, Los
Angeles, CA.
At high temperatures, the hardnesses of covalent crystals are
determined by dislocation mobilities. However, at temperatures below
the Debye temperatures, where dislocation mobilities become very
low, covalent crystals respond to applied stresses by transforming into
new crystal structures, or by fracturing. The critical transformation
stresses depend on the minimum band-gap energies, but not linearly,
and not independent of the valence. It is shown here that a universal
dependence exists if the band-gap energy density is substituted for
the band-gap energy. This is true of the indentation hardness, the
critical transformation pressure, and the elastic shear stiness. The
gap energy per molecular volume is called, the \bonding modulus",
and is closely related to all measures of covalent crystal stability.
These connections and their signicance will be discussed.
11:30 AM DD1.8
HYDROSTATIC PRESSURE INDUCED STRUCTURAL
TRANSITIONS IN MANGANITES WITH ORBITAL ORDERING.
Michael Kaplan, Simmons College, Depts of Chemistry and Physics,
Boston, MA; George Zimmerman, Boston University, Dept of Physics,
Boston, MA.
Hydrostatic pressure may drastically change the electronic structure
of Jahn-Teller crystals. The role of the hydrostatic pressure in the
structural transitions of colossal magnetoresistance manganites is
investigated in the framework of the doublet-triplet model based on
the cooperative Jahn-Teller eect.In this model the eect of the
hydrostatic pressure is mostly attributed to the variation of the energy
gap between the doublet and triplet electronic states. Calculations of
the sublattice and crystal cell spontaneous strains are presented and
the critical temperature-hydrostatic pressure phase diagram is
determined. The results for hydrostatic pressure are compared to
those for uniaxial pressure calculations of the spontaneous crystal
sublattice strains. The major dierence between them is that the
hydrostatic pressure by itself can not induce metaelastic transitions in
the crystals. The magnetoelastic properties of the manganites under
hydrostatic pressure are also discussed. The results can be understood
if we realize that the pressure induced increase of the energy gap
between the ground and excited electronic states in our model is
similar to the rise of crystal's temperature. The results are compared
with experimental X-ray diraction and Raman scattering data.
11:45 AM DD1.9
ORBITAL ORDERING TRANSITION IN La4Ru2 O10 .
Peter Khalifah, Rongying Jin, Solid State Division, Oak Ridge
National Laboratory; David Mandrus, Solid State Division, Oak Ridge
National Laboratory and Dept. of Physics, University of Tennessee;
Raymond Osborn, Materials Science Division, Argonne National
Laboratory; Qingzhen Huang, NIST Center for Neutron Research and
Dept. of Materials and Nuclear Engineering, University of Maryland;
Henny Zandbergen, National Center for High Resolution Electron
Microscopy, Technical University of Delft; Ying Liu, Department of
Physics, The Pennsylvania State University; Robert J. Cava, Dept. of
Chemistry and Princeton Materials Institute, Princeton University.
The study of the interplay between orbital, spin, and charge degrees
of freedom in transition metal oxides is at the forefront of condensed
matter physics. Invariably, the canonical examples of orbitally ordered
compounds (including YTiO3 , YVO3 , KCuF3 , and the perovskite
manganites) contain 3d transition metals because they display large
magnetic moments and strong coupling of orbital and charge
congurations to local coordination polyhedron geometry. Recently,
evidence has been mounting for the importance of orbital physics in
perovskite-related structures containing the 4d transition metal,
ruthenium. Inelastic x-ray scattering experiments have found partial
orbital ordering in the compound Ca2RuO4 , and theoretical models
for treating the orbital eects in this system have been developed.
Experimental evidence for a discrete orbital ordering transition in the
newly discovered lanthanum ruthenate, La4 Ru2 O10 , is presented. This
result is the rst example of a full orbital ordering transition in a 4d
transition metal oxide, and demonstrates that orbital eects are
important to ruthenates.
SESSION DD2: METAL-TO-INSULATOR
TRANSITION - II
Chairs: John E. Greedan and Stephen Lee
Monday Afternoon, December 2, 2002
Back Bay C (Sheraton)
1:30 PM *DD2.1
MANGANITES AND COBALTITES: SIMILARITIES AND
DIFFERENCES. D. Khomskii, Laboratory of Solid State Physics,
Groningen University, Groningen, THE NETHERLANDS.
Colossal magnetoresistance manganites are extensively studied during
last several years, and signicant progress in understanding of their
properties is reached. Cobaltites, on the other hand, are not so
\popular" yet, although these are also very interesting and
perspective materials (e.g. for the battery's applications or as
thermoelectric materials), and their properties are in some respects
even richer than those of manganites. To a large extend this is
connected with the possibility of having dierent spin states in them,
so that, besides charge, spin and orbital ordering present in
manganites, in cobaltites there may also occur spin state transitions,
eventually with corresponding superstructures. In this talk I will
compare the main properties of manganites and cobaltites, paying
main attention to the new specic features of the latter. In particular,
the mechanisms leading to the formation of dierent superstructures
in them will be discussed, and specic properties of quasiparticle
excitations in cobaltites will be analysed.
2:00 PM DD2.2
STRUCTURAL AND MAGNETIC CONSEQUENCES OF
CONTROLLED OXYGEN DEFICIENCY IN LAYERED
MANGANITES AND COBALTATES. J.F. Mitchell, J. Burley, H.
Zheng, S. Short, Materials Science Division, Argonne National
Laboratory, Argonne, IL; P.G. Radaelli, ISIS Facility, Rutherford
Appleton Laboratory, Chilton, UNITED KINGDOM.
We report structural and magnetic studies of oxygen-decient layered
compounds La202x Sr1+2x Mn2 O70x and NdBaCo2O5+y using
neutron powder diraction. By controlling the concentration and
location of these vacancies, the crystal and magnetic structures can be
modied dramatically. We draw links between the observed crystal
structure, the electronic state of the Mn or Co mixed-valent ions, and
magnetic order in these systems.
2:15 PM DD2.3
NUCLEAR AND MAGNETIC STRUCTURES OF K2 NiF4 -TYPE
IRON(III) OXIDES AND OXIDE HALIDES. Andrew L. Hector,
Alexander I. MacDonald, Daniel J. Price and Mark T. Weller,
Department of Chemistry, University of Southampton, UNITED
KINGDOM.
Previous work on K2 NiF4 -type iron(III) oxide magnetic structures has
shown the behaviour commonly observed in this structure type,
antiferromagnetic coupling within the layers combined with
ferromagnetic layer stacking.
We recently reported some unusual
behaviour in Sr2 FeO3 F,1 resulting in a doubling of the c-axis in the
magnetic cell.
The only other example found of such cell doubling was
Ca2MnO4 .2 We have now examined (or re-examined at low
temperature) the magnetic structures of a series of K2 NiF4 -type
iron(III) oxides and oxide halides by PND to look for other examples.
The ferromagnetically stacked magnetic structure was found at 2.4K
in A2FeO3 X (A=Ca,Sr;X=Cl,Br) and BLaFeO4 (B=Ca,Sr,Ba). We
also carried out a variable temperature study of Sr2 FeO3 F and
Ca2MnO4 to try to understand why these phases behave dierently.
Ca2MnO4 has peaks corresponding to two magnetic phases at 2.4K
and 50K. Only antiferromagnetic
stacking (with a doubled c-axis) was
previously reported,2 however ferromagnetic layer stacking was also
observed in our sample. In Sr2 FeO3 F samples which had been
prepared very recently, we observed ferromagnetic stacking with a
small amount of antiferromagnetic stacking. Samples which had been
kept for a period of time had increasing amounts of antiferromagnetic
stacking. Previously we, and others, had believed that Sr2 FeO3 F did
not change in air. However small changes are observed in the lattice
parameters and peak intensities even in powder X-ray data with time.
We believe that Sr2 FeO3 F slowly hydrates with exposure to air.
K2 NiF4 -type structures can intercalate extra anions (and presumably
also water) into sites within the rocksalt layer. This is the obvious
relationship between high pressure Ca2MnO4 and hydrated Sr2 FeO3 F.
There is no superexchange pathway which can explain the layer
stacking within these phases and a through-space dipolar interaction
must be responsible for any 3-dimensional ordering. It is possible that
occupation of the interstitial sites changes this interaction. 1. A.L.
639
Hector, J.A. Hutchings, R.L. Needs, M.F. Thomas and M.T. Weller,
J. Mater. Chem., 2001, 11, 527. 2. D.E. Cox, G. Shirane, R.J.
Birgeneau and J.B. MacChesney, Phys. Rev., 1969, 188, 930.
MAGNETORESISTANCE IN PEROVSKITE RUTHENATES.
Alexander Mamchik, I-Wei Chen, Univ of Pennsylvania, Dept of
Materials Science and Engineering, Philadelphia, PA.
Magnetically doped Ca and Sr ruthenates with perovskite and layered
perovskite structures have been successfully synthesized. Magnetic
frustration in these compounds increases upon doping until the spin
glass state is nally reached. This coincides with a gradual decrease of
electrical conductivity and a metal to insulator transition. In the
compositional region corresponding to the magnetically glassy state, a
large magnetoresistance eect, comparable in magnitude to the CMR
eect, has been observed. In such materials magnetic impurities act as
atomic-level spin valves, which regulates electronic transport in
response to an external magnetic eld. Supported by NSF Grant No.
DMR99-88853 and DMR00-79909.
We have developed a new type of interatomic potential, the rst of its
kind to be able to model ligand eld aects. Previously, interatomic
potentials were typically restricted to \spherical" ions, but by adding
a ligand eld stabilisation energy we are now able to model
\non-spherical" transition metal ions. This allows the possibility of
modelling industrially important catalytic, colossal magneto resistant
and superconducting
materials containing, for example, the Jahn
Teller (JT) Mn3+ and Cu2+ ions. Our model implements an
adaptation of the angular overlap model which includes a
representation of JT eects in a manner which can be readily
implemented in our simulations without a drastic increase in required
CPU time or memory. The resulting parameterised interatomic energy
term and its analytical gradients have been incorporated within the
General Utility Lattice Program (GULP), which is widely used for
modelling ionic solids both in academia and industry. We have
successfully applied our parameterised potential to modelling
lanthanum and rare earth manganates. Studies include the calculation
of oxygen migration paths for LaMnO30 and the structural changes
due to steric and JT eects across the rare earth series LnMnO3 .
3:15 PM *DD2.5
4:15 PM DD2.8
2:30 PM DD2.4
MAGNETIC MATERIALS WITH TRANSITION METALS:
ANALYSISaAND DESIGN USINGa THEORETICAL TOOLS. a
Eliseo Ruiz , Cedric
Desplanches , Antonio Rodridguez-Fortea ,
Santiago Alvareza ; a Departament de Quidmica Inorganica and Centre
de Recerca en Quidmica Terica (CERQT), Universitat de Barcelona,
Barcelona, SPAIN.
During the last years we have employed successfully theoretical
methods based on density functional theory to study10the
magnetic
properties of molecular transition metal compounds. 3 This
approach has been useful for the understanding of the magnetic
properties with more intuitive models as well as an excellent tool to
probe magnetic properties for new compounds that have not yet
synthesized. Here we present an extension of such studies to extend
structures. This rst part of this communication will be devoted to
study and rationalize the magnetic properties of the transition metal
dicyanamides, focusing in the key role of the atomic electronic
conguration. These compounds show a tridimensional structure with
a wide range of magnetic properties. For instance, the C u(II)
compound shows almost no interaction, while the Ni(II) and Cr(II)4
compounds are ferromagnetic and a ntiferromagnetic, respectively. In
the second part, we want to show the application of DFT met hods as
a toolbox that can help us designing new bridging ligands with strong
tailor made exchange coupling between the paramagnetic centers at
very long distances. This kind of bridging ligands will allow buil ding
up new hybrid materials with very large cavities and at the same
time, strong magnetic coupling in t he hosts compound. Finally, we
have explored several combinations of transition metals with cyanide
ligands that can be synthetic
targets to obtain compounds when
higher Tc values than
VII=III [Cr(CN)6]0:086 12.8H2O, reported in 1995
5
by Verdaguer et al., which shows ferrimagnetic order above 315 K.
1) E. Ruiz, P. Alemany, S. Alvarez, J. Cano, J. Am. Chem. Soc.
1997, 119, 1297. 2) E. Ruiz, J. Cano, S. Alvarez, P. Alemany, J. Am.
Chem. Soc. 1998, 120, 11122. 3) Desplanches, C., E. Ruiz, A.
RodridguezFortea, S. Alvarez, J. Am. Chem. Soc. 2002, 124, 5197. 4)
Miller, J.S., Manson, J.L. Acc. Chem. Res. 2001, 34, 563. 5) Ferlay,
S., Mallah, T., Ouahes, R., Veillet, P., Verdaguer, M. Nature, 1995.
378. 70 1.
3:45 PM DD2.6
PREPARATION, ELECTRICAL PROPERTIES AND
MICROSTRUCTURE CHARACTERIZATION OF
MAGNETO-RESISTIVE (La,Ca)MnO3 THIN FILMS. Laurent
Dusoulier, Benedicte Vertruyen, Jean-Francois Fagnard, Jacques
Delwiche, Andre Rulmont, Philippe Vanderbemden, Marcel Ausloos
and Rudi Cloots University of Liege, SUPRAS, Liege, BELGIUM.
We have investigated the preparation of magneto-resistive
(La,Ca)MnO3 thin lms by a sputtering process on dierent
substrates: LaAlO3, MgO and SiO2 . X-ray diraction analysis has
been performed and shows that the lm grown on LaAlO3 single
crystal is perfectly oriented. Electrical and magnetic measurements
have been performed on each sample and can be interpreted on the
basis of their crystallographic texture. Atomic Force Microscopy
reveals the existence of dierent morphologies and can be explained
following the model of Movchan-Demchishin.
4:00 PM DD2.7
DEVELOPMENT AND APPLICATION OF A NEW
INTERATOMIC POTENTIAL FOR THE MODELLING OF
LIGAND FIELD EFFECTS. Scott M. Woodley, C. Richard; A.
Catlow, Royal Institution of Great Britain, London, UNITED
KINGDOM; Peter D. Battle, Oxford Uni, Inorganic Chemistry Lab,
Oxford, UNITED KINGDOM; Julian D. Gale, Imperial College, Dept
of Chemistry, London, UNITED KINGDOM.
A DRASTIC INFLUENCE OF POINT DEFECTS ON PHASE
STABILITY IN MnO2 . Dane Morgan, Dinesh Balachandran, G.
Ceder, MIT, Materials Science and Engineering, Cambridge, MA; A.
van de Walle, Northwestern, Materials Science and Engineering,
Evanston, IL.
MnO2 exists in a remarkably large number of dierent polymorphs,
and the factors that inuence relative energies of each are unclear. We
believe, and demonstrate with rst principles calculations, that part of
the diculty is that defects have a dramatic impact MnO2 structure.
We focus on the -MnO2 polymorphs, which are important for both
primary and secondary battery cathodes. Despite extensive study, the
structure of -MnO2 is still under debate. The most common MnO2
defect, known as a Ruetschi defect, is a Mn vacancy compensated by
four protons. We show that the energetics of the Ruetschi defect
couples strongly to the local Mn arrangement, profoundly aecting
the Mn ordering. It is also shown that many undefected MnO2
structures are very close in energy, making the inuence of defects
even more important in determining structure. We demonstrate that
any realistic understanding of structural stability in MnO2 must
consider the inuence of Ruetschi defects and suggest what types of
structures are likely to be stabilized in highly defected materials.
4:30 PM DD2.9
SINGLE CRYSTAL DIFFRACTION STUDY OF
COMMENSURATE-TO INCOMMENSURATE PHASE
TRANSITION IN CHARGE ORDERED La10x Cax MnO3 BY
ELECTRON NANODIFFRACTION. Jing Tao, J.M. Zuo, Univ. of
Illinois at Urbana-Champaign, Dept. of Materials Science and
Engineering and Materials Research Laboratory, Urbana, IL.
Doped LaMnO3 has strong magnetic dependent electrical properties,
e.g. CMR eect when the doping concentration less than 0.5, which
oers such species as candidates for spintronics applications. It has
been shown strong interactions between magnetic, electronic and
crystal structures are keys to understand the phase transitions
between ferromagnetic metal, charge ordered insulator or
paramagnetic polaron liquid in this system. Chemical inhomogeneity
is also important in local structure. Electron diraction with a probe
of several tens nanometers was used to study the phase transition in
La10x Cax MnO3 of 0.5<x<0.9. The small electron probe is an
advantage that was used to obtain single crystal domain diraction
patterns. The Bragg peaks was used to study the low temperature
ordered structure and charge ordering, while temperature-dependent
diuse scattering was analyzed to understand the transition process.
We focused on the transition in La10x Cax MnO3 with x=1/2, 2/3 and
3/4. The experiment revealed that the
commensurate-to-incommensurate transition in x=1/2 found by
previous experiment also exists in x=2/3 and 3/4. In all cases, we
found the incommensurate phase near the transition temperature
where the average size of charge ordered domain is about a few
nanometers. The diraction intensities of ordered reections also
increase signicantly at the commensurate-to-incommensurate. At
very low temperature, we investigate the symmetry of ordered
structure using convergent-beam electron diraction. The experiment
reveals a glide plane which is consistent with the so-called Wigner
crystal model. The distribution of diraction intensities has the
characteristics of a displacement wave. The full interpretation based
on order parameters and Jahn-Teller distortion vibrational modes will
be discussed in the talk.
4:45 PM DD2.10
STRUCTURE-PROPERTY RELATIONSHIPS OF LanMIn3 n + 2(n
= 1, 2, 1; M = Rh, Ir) and CenMIn3 n + 2(n = 1, 2, 1; M = Rh, Ir).
Robin T. Macaluso and Julia Y. Chan, Dept. of Chemistry, Louisiana
640
State University, Baton Rouge, LA; John L. Sarrao, Condensed
Matter & Thermal Physics Group, Los Alamos National Laboratory,
Los Alamos, NM.
The structure and properties of a new family of intermetallics,
Lnn MIn3n+2 (n = 1, 2, 1; Ln = La, Ce; M = Rh, Ir) will be
presented. The Ce-analogues exhibit antiferromagnetism and
superconductivity in the low-temperature regime. In addition, the
intergrowth homologous series presents a unique opportunity to study
the structure-property relationships. The structures of the
heavy-fermion compounds, CeMIn5 and Ce2MIn8 (M = Rh, Ir), and
the non-magnetic analogues, LaMIn5 and La2MIn8 (M = Rh, Ir) were
determined by single-crystal X-ray diraction. These materials adopt
a tetragonal structure in the space group P 4/mmm with lattice
parameters 4 x 8 A for LnMIn5 and 4 x 12 A for Ln2 MIn8 .
Structural trends, magnetic susceptibility, and transport properties
will be compared for these heavy-fermion compounds. These
structure-property relationships will be discussed in light of
dimensionality for n = 1, 2, 1.
SESSION DD3: POROUS MATERIALS
Chair: Miguel A. Alario-Franco
Tuesday Morning, December 3, 2002
Back Bay C (Sheraton)
8:30 AM *DD3.1
NANOPOROUS NICKEL PHOSPHATES; PROPERTIES AND
POTENTIAL APPLICATIONS. Anthony K. Cheetham, Materials
Research Laboratory, University of California, Santa Barbara, CA.
Nanoporous materials, such as the aluminosilicate zeolites and the
open-framework aluminum phosphates, nd widespread applications
in separation processes, ion-exchange, and catalysis [1], but very few
of the other classes of open-framework materials exhibit interesting
properties because they rarely have sucient thermal stability to be
rendered truly nanoporous. However, the nanoporous nickel
phosphates [2,3] represent an important exception to this general rule
since they are stable to temperatures greater than 500C. They exhibit
unique catalytic properties and will support shape-selective
hydrogenation [3] and dehydrogenation [4] reactions that are not
possible with conventional zeolite catalysts. In addition, they show
interesting sorption properties, especially with respect to hydrogen
storage, where they represent an interesting alternative to carbon
nanotubes and other molecular sieves [5]. We shall discuss some recent
results concerning the applications of these novel materials.
1. A.K. Cheetham, G. Ferey and T. Loiseau, Angew. Chem. Intl. Ed.
38, 3268-3292 (1999).
2. N. Guillou, Q. Gao, M. Nogues, R.E. Morris, M. Hervieu, G. Ferey,
and A.K. Cheetham, C.R. Acad. Sciences (Paris)
Series IIc, 387-392 (1999).
3. N. Guillou, Q. Gao, P.M. Forster, J-S. Chang, M. Nogues, S-E.
Park, G. Ferey, and A.K. Cheetham, Angew. Chem 40, 2831 (2001).
4. J-S. Chang, S-E. Park, Q. Gao, G. Ferey, and A.K. Cheetham,
J.C.S. Chem. Comm. 859-860 (2001).
5. P. Forster, J. Eckert, J-S. Chang, S-E. Park, G. Ferey, and A.K.
Cheetham (to be published)
9:00 AM DD3.2
INORGANIC-INORGANIC MESOPOROUS AND COMPOSITES
MATERIALS BASED ON MINERAL
LIQUID CRYSTALS.
Jean-Christophe P. Gabriely, Franck Camerel, Patrick Batail, Sciences
Moleculaires aux Interfaces, Nantes, FRANCE. yPresent address:
Nanomix, Inc., Emeryville, CA.
We will present our latest, yet unpublished, results on the synthesis of
mesoporous materials using Mineral Liquid Crystals (MLC)* as
templating agents, instead of classical surfactants. The use of MLC
such as V2O5 , that can be oriented under a magnetic eld allowed to
synthesize large single domain monolithic blocks (1 cm) of silicates V2O5 composites. Furthermore, the latter can be remove, aording a
clear and birefringent mesoporous silicate monolith. We will illustrate
this new approach toward mesoporous materials with other examples.
* JCP Gabriel, P. Davidson, Adv. Mater. 12(1) 9-20, 2000.
9:15 AM DD3.3
CATIONIC, NEUTRAL AND ANIONIC MICROPOROUS
MATERIALS BASED ON Ge, Sn AND Pb. Scott R.J. Oliver, State
University of New York at Binghamton, Department of Chemistry,
Binghamton, NY.
In this talk, I will present an overview of our eorts into the
solvothermal synthesis and characterization of late group 14 extended
materials. We synthesize chains, layers and open-frameworks, where
the metal-linking unit is one of a variety of anions: oxygen, uoride,
oxalate or phosphonate. Our primary motivation for this project is
the formation of cationic materials using anionic structure directing
agents (A-SDAs). We have isolated a series of new anionic and neutral
\BING-n" crystal structures from these systems with cationic SDAs.
We have also discovered a layered lead uoride that, unlike
zeolites/zeotypes and the majority of clays, is a cationic host. The
interlamellar nitrate anions can be exhcanged for other anionic
species, such as chromate or benzoate. Examples of anion-exchange,
for a purely inorganic material, are rare. The inherent thermal and
chemical stability of our materials may render them useful in
applications where anion-exchange resins or coordination frameworks
break down. This project therefore open up other potential
anion-based properties, such as new anionic catalytic reactions or
intercalation chemistry.
9:30 AM DD3.4
SYNTHESIS AND CHARACTERIZATION OF NEW MATERIALS
BASED ON LOWER GROUP 14 ELEMENTS: BING-5,6,9,10.
Dat T. Tran, Peter Y. Zavilij, Scott R.J. Oliver, State University of
New York at Binghamton, Dept of Chemistry, Binghamton, NY.
Our research involves the solvothermal synthesis and characterization
of new 3D open-framework and low dimensionality inorganic
materials. The synthesis of open-framework and layered structures has
received a great deal of attention in recent years because of their
relatively straightforward synthetic procedures and their intriguing
properties and applications. We are currently focusing on lower Group
14 elements to prepare structures that are analogous to
aluminosilicate zeolites. We have successfully synthesized a new
layered lead uoride material, Pb3 F5 NO3 , which we denote \BING-5";
a neutral layered lead pyridine phenylphosphonate, which we denote
\BING-6"; a new structure lead metamethylphenylphosphonate,
which we denote \BING-9"; and a new molecular crystal structure
pyridine germanium (IV) tetrauoride, which we denote \BING-10".
These structures are characterized by a variety of solid state
techniques, including: single crystal X-Ray diraction, powder X-Ray
diraction, thermal analyses, electron microscopy, UV-Vis
spectroscopy
and anion-exchange. Some of materials are table up to
450C, which are vastly superior to inorganic and organic resins that
are still the standard for anion-exchange.
10:15 AM *DD3.5
PERIODIC NANOSCALE SEMICONDUCTORS THROUGH
SURFACTANT-DRIVEN SELF-ORGANIZATION OF SOLUBLE
ZINTL CLUSTERS. Sarah Tolbert, Andrew Riley, Dong Sun, Ashley
Cadby, University of California, Los Angeles, Department of
Chemistry and Biochemistry, Los Angeles, CA.
Surfactant driven self-organization of inorganic clusters provides a
simple route to the assembly of complex nanoscale composite
materials. In this work we utilize Zintl clusters, reduced soluble main
group clusters, as building blocks in the formation of periodic
semiconducting phases. A combination of low angle X-ray diraction
and EXAFS are used to probe the properties of the resulting
surfactant/inorganic composites on both the atomic and nanometer
lengthscales. A variety of systems, including pure germanium and
mixed tin/tellurium clusters are employed to produce materials with
band gaps in the near IR. The germanium based materials display
classic quantum connement eects in both their absorption and
luminescence, a result that show that size tunable optical properties
can be combined with complex nanoscale architectures. In some cases,
the surfactant can even be removed to produce periodic, porous,
quantum conned semiconductors.
10:45 AM DD3.6
OPEN FRAMEWORK AND MICROPOROUS TRANSITION
METAL SILICATES. Allan J. Jacobson, Xiqu Wang, Lumei Liu, J.
Huang, Department of Chemistry, University of Houston, Houston,
TX.
The synthesis and structural characterization of several new open
framework and microporous transition metal silicates containing,
vanadium, niobium, copper and uranium will be described. Many of
these new compounds have structures that are based on anionic
three-connected silicate layers that are cross-linked by transition
metal cations to form three-dimensional structures.
Examples of
cross-linkers that we have used include VO2+ , NbOF2+ , Cu(H2 O)2+
2
and UO2+
2 . In each structure, two oxygen atoms from each of two
adjacent layers complete a distorted octahedral environment for the
transition metal cation.
11:00 AM DD3.7
WATER INSERTION IN HYDROPHOBIC POROUS OXIDES. D.
Carriere, S. Sidis, K. Lahlil, M. Moreau, P. Barboux, J.-P. Boilot,
CNRS UMR 7643C, Ecole Polytechnique, Laboratoire de Physique de
la Matiere Condensee, Ecole Polytechnique, Palaiseau, FRANCE.
We have studied the synthesis of porous hydrophobic systems made
641
from sol-gel silica and zirconia. Various silica systems obtained by
sol-gel methods and templating (mesoporous or microporous silica)
have been grafted with alkyl-, vinyl- and phenyl- chlorosilanes.
Similar systems were also obtained by direct synthesis of hybrid
materials starting from functional silicon alkoxides. Alternative
hydrophobic systems were also obtained by synthesis of colloidal
monoclinic zirconia and mesoporous zirconium oxide grafted with
various alkyl phosphonates. The mechanism and the density of
grafting was studied by solid state MAS NMR and nitrogen
adsorption isotherms. The eect of the density of grafting and of the
alkyl chain length on the contact angle with various liquids including
water was measured. The bulk thermodynamic properties of water are
strongly dominated by the interfacial interactions at the surface of
these porous solids. The penetration of water in these porous systems
was studied by high pressure intrusion of water (water porosimetry
between 0 and 100 MPa) into the hydrophobic pores and the resulting
systems were analyzed by dierential scanning calorimetry and by
NMR spectroscopies. We discuss the problems of hysteresis of water
insertion-desinsertion curves as a function of water pressure and pore
size. The amazing mechanical behavior of such water-porous body
mixtures can nd interesting applications for mechanical energy
storage and dissipation.
11:15 AM DD3.8
THE MANIPULATION OF SILICA MESOCELLULAR FOAM
PARTICLE MORPHOLOGY: APPLICATIONS IN FINE
CHEMICAL SYNTHESIS. Thomas M. Lancaster, Jackie Y. Ying,
Massachusetts Institute of Technology, Department of Chemical
Engineering, Cambridge, MA.
Mesocellular foams are a class of high surface area and ultra-large
pore volume silica supports. The silica foams exhibit large pore sizes
and an interconnected mesoporous framework that facilitate the
diusion of large molecules and the hosting of sterically demanding
organometallic complexes within the structure. Thus, silica
mesocellular foams (MCF) are excellent candidates for the catalysis of
bulky pharmaceutical intermediates. We have manipulated MCF
synthesis parameters in an attempt to control the overall particle
morphologies of these materials, while retaining their unique pore
structures, large pores (25-35 nm), and narrow pore size distributions.
These materials have been examined as supports for the asymmetric
Diels-Alder reaction, giving rise to excellent conversions and high
enantioselectivities of greater than 80%.
11:30 AM DD3.9
SYNTHESIS AND CHARACTERIZATION OF NEW IRON AND
ZINC PHOSPHATE MATERIALS WITH OPEN FRAMEWORK.
Yanning Song, Peter Y. Zavalij, M. Stanley Whittingham, State
University of New York at Binghamton, Dept of Chemistry,
Binghamton, NY.
Open framework materials are of great interest due to the applications
in the elds of adsorption, ion exchange, molecular sieving and
catalysis. Metal phosphates are very important open framework
materials due to the rich crystallography. Several new iron phosphate
materials have been synthesized and characterized in our lab. Two
new iron (III) phosphates, FePO4, have been synthesized from the
dehydration of hydrothermally prepared monoclinic and orthorhombic
hydrated phosphates FePO412H2O. On dehydration only bonds
associated with the water molecules are broken, so that both FePO4
phases have essentially the same Fe-P backbone frameworks as the
corresponding hydrates. The electrochemical and magnetic data are
consistent with the structures of these two compounds. The properties
of these new iron phosphate structures are compared with other iron
phosphate phases. Reversible insertion and extraction of lithium into
new iron phosphate hydroxide materials with 3-d rod-packing
framework shows it to be an excellent intercalation material. Several
other transition metals are also incorporated successfully into these
compounds without changing the structure. Interesting magnetic
properties are found in the newly synthesized iron phosphate
materials with ethylene diammonium templates with 1-d chain, 2-d
layered and 3-d network structures. Meanwhile, two new zinc
phosphates with methylammonium templates were also synthesized.
There are innite Zn-O-Zn chains in one of the compounds, while
closed 4-member circuits made up from Zn-O-Zn linkage present in
the other. This work was supported by NSF DMR 9810198.
SESSION DD4: DIELECTRIC MATERIALS
Chairs: Colin Greaves and Susan M. Kauzlarich
Tuesday Afternoon, December 3, 2002
Back Bay C (Sheraton)
1:30 PM *DD4.1
NEW EXAMPLES OF CATION ORDER IN MIXED-METAL
PEROVSKITES. Peter K. Davies, Dept Materials Science &
Engineering, University of Pennsylvania, Philadelphia, PA.
Compared to the many families of A(BI x BII y )O3 perovskites that
adopt a structure with a 1:1 ordered (doubled perovskite)
arrangement of the B-site cations, relatively few
examples are known
with 1:2 or 1:3 type order. Of these the 1:2 A2+ (B2+ 1=3 B5+ 2=3 )O3
alkaline earth based niobates and tantalates (e.g. barium zinc
tantalate) are of considerable commercial importance owing to their
unusually low dielectric losses in the microwave region. Our studies
have focused on the design of B-site chemistries that would enable the
preparation of new families of perovskites with 1:2 or 1:3 order that
themselves may have useful dielectric properties or could be employed
as property enhancing additives to the known microwave materials.
This paper will summarize
examples of new 1:2 ordered chemistries
discovered in the A(B1+ 1=3 B4+ 2=3 )O3 , A(B1+ 1=3 B5+ 2=3 )O3 families.
These include titanate dielectrics such as La(Li1=3Ti2=3 )O3 and
niobate dielectrics such as (Sr2=3 La1=3 )(Li1=3 Nb2=3 )O3 . New
mixed-metal systems have also been prepared with
1:3 type B-site
order. These compounds were found in the A(B2+ 1=4 B5+ 3=4 )O3 ,
1+
5+
2+
4+
A(B 1=4 B 3=4 )O3 and A(B 1=4 B 3=4 )O3 systems. In each case
the details of the structures and the factors aecting the stability of
the cation ordering will be discussed. Results for their dielectric
performance, at low frequencies and in the microwave region, will be
also presented.
2:00 PM DD4.2
DISPLACIVE DISORDER IN BISMUTH ZINC NIOBATES.
Igor Levin, Tammy Amos, Terrell Vanderah, NIST, MSEL,
Gaithersburg, MD; Juan Nino, Clive Randall, Michael Lanagan, Penn
State Univ, CDS, MRL, University Park, PA.
Ternary oxides in the Bi2 O3 -ZnO-Nb2 O5 system exhibit high
dielectric constants, relatively low dielectric losses, and
compositionally tunable temperature coecients of capacitance. Such
properties, combined with sintering temperatures of less than 950C,
render these materials attractive candidates for capacitor and
high-frequency lter applications in multilayer structures co-red with
silver electrodes. The system reportedly features two structurally
distinct ternary compounds Bi1:5 ZnN1:5O7 and Bi2 Zn2=3 Nb4=3 O7
which exhibit very dissimilar dielectric properties. Despite growing
technological interest in these materials, understanding of their
dielectric behavior has been impeded by the lack of detailed structural
information. The Bi1:5 ZnN1:5 O7 compound was claimed to exhibit a
cubic pyrochlore structure, implying that the Zn ions occupy both
A-and B-sites. However, in the absence of detailed
structural/compositional data, the presence of rather small Zn ions on
the eight-fold coordinated A-sites remained controversial. The other
compound, Bi2 Zn2=3 Nb4=3 O7 , was reported to crystallize with a
distorted pyrochlore structure; however, its exact structure has not
been determined. In this presentation, we will discuss the results of a
detailed structural analysis of these compounds using X-ray and
neutron powder diraction combined with transmission electron
microscopy.
2:15 PM DD4.3
CATION ORDERING, DOMAIN GROWTH AND ZINC LOSS IN
THE MICROWAVE DIELECTRIC OXIDE Ba3 ZnTa2 O9 DURING
PROCESSING USING REAL-TIME X-RAY AND NEUTRON
POWDER DIFFRACTION. M. Bieringer, S.M. Moussa,
M.J. Rosseinsky, University of Liverpool, Department of Chemistry,
Liverpool, UNITED KINGDOM; R.M. Ibberson, ISIS Facility, Didcot,
UNITED KINGDOM; A.N. Fitch, ESRF, Grenoble, FRANCE.
The perovskite Ba3 ZnTa2 O9 (BZT) is the parent of a family of high
dielectric constant, low loss oxides currently applied in mobile
telecommunications base stations. The preparation of BZT microwave
dielectric resonators with optimal dielectric properties requires careful
attention to thermal treatment to control the formation of domains in
which the Ta and Zn cations order on the octahedral sites of the
perovskite structure. In this paper we use real-time powder X-ray and
neutron diraction to follow changes in structure and crystal
chemistry during material processing. These studies reveal a complex
interplay between cation ordering and the size of the cation ordered
domains and compositional changes involving phase separation and
ZnO content.
2:30 PM DD4.4
SYNTHESIS AND SINTERING OF (K,Na)NbO3 BASED
CERAMICS. Barbara Malic, Darja Jenko, Janez Bernard, Jena
Cilensek, Marija Kosec, Jozef Stefan Institute, Ljubljana, SLOVENIA.
Piezoelectric materials based on Pb(Zr,Ti)O3 solid solution (PZT)
have been widely used due to their piezoelectric, pyroelectric and
ferroelectric properties. One of the major drawbacks of these materials
is a high lead content and therefore a possible ecological hasard. An
alternative group of lead-free ferroelectric materials are those based
on alkaline niobates. According to the literature (Jae et al.,
642
Piezoelectric Ceramics, 1971) their functional response is satisfactory.
One of the major problems of alkaline niobates is sintering to high
densities (ibid). Our aim was to address in detail the synthesis and
sintering of stoichiometric (K,Na)NbO3 solid solution (KNN). KNN
was prepared by the solid state synthesis from alkaline carbonates and
niobium oxide. KNbO3 (KN) and NaNbO3 (NN) as boundary
compositions of the solid solution were also prepared for comparison.
The thermal decompositions of the alkaline carbonate-niobium oxide
powder mixtures followed
by TG/DTA reveal that the carbonates
decompose below 700C which is approximately 200C lower than
respective alkaline carbonates. The perovskite phase formation
followed by XRD depends on the composition, and requires higher
temperature with increasing Na - content. The dynamic sintering
curves of the as-calcined KNN 50/50, KN and NN powder
compacts
have been recorded. KN and NN start to shrink
at 800C and 1000C,
respectively, that is around 250 C and 400 C below their melting
points.
In the case of KNN the shrinkage interval ranges from around
1000Cup to the melting point at 1140C. After isothermal sintering
at 1100 C relative densities of KNN 50/50 around 92% were attained.
3:15 PM DD4.5
PHASE EQUILIBRIA, CRYSTAL CHEMISTRY, AND DIELECTRIC
BEHAVIOR IN COMPLEX OXIDES. T.A. Vanderah, R.S. Roth, W.
Febo, V. Miller, I. Levin, W. Wong-Ng, NIST, Ceramics Division,
Gaithersburg, MD; S.M. Bell, TRAK Ceramics, Inc., Hagerstown,
MD.
Complex oxide ceramics with interesting and useful dielectric
properties are frequently found in systems based upon TiO2 , Nb2 O5 ,
and/or Ta2 O5 . These ceramics include those used to fabricate a
variety of components in cellular communications circuits that store,
lter, and/or transfer electromagnetic energy with minimal loss (e.g.,
resonators, bandpass lters). Phase equilibria studies of ceramic
systems containing dielectric oxides are conducted to 1) reveal the
existence of new, thermodynamically stable phases, 2) obtain
quantitative information immediately useful for the preparation of
controlled mixtures, and 3) provide systematic data for fundamental
chemistry-structure-properties studies. A review of recent
experimental studies of ternary systems will be presented. Trends in
compound formation, crystal chemistry, and dielectric properties will
be described.
3:30 PM DD4.6
EXTRINSIC CONTRIBUTIONS TO THE DIELECTRIC
RESPONSE IN PbSc1=2 Nb1=2 O3 FROM FIRST PRINCIPLES.
Eric Cockayne, Ceramics Division, NIST, Gaithersburg, MD; Umesh
Waghmare, Theoretical Sciences Unit, JNCASR, Bangalore, INDIA;
Serguei Prosandeev, Physics Department, Rostov State Univ.,
Rostov-on-Don, RUSSIA; Benjamin P. Burton, Ceramics Division,
NIST, Gaithersburg, MD.
PbSc1=2 Nb1=2 O3 (PSN) exhibits relaxor behavior over a range of
temperatures
close to the maximum in its low-frequency dielectric
function 0 (T ). The dielectric properties of PSN, especially the range
of temperatures over which relaxor behavior is observed, are strongly
dependent on extrinsic eects, such as the concentration of Pb
vacancies. We use a rst-principles eective Hamiltonian
to
investigate various extrinsic contributions to 0 (T ): (1) antiphase
boundaries between regions of rocksalt type Sc-Nb chemical ordering;
(2) ferroelectric domain boundaries; (3) nearest neighbor Pb-O
vacancy pairs (Pb vacancies are likely paired with O vacancies to
maintain charge balance). Molecular dynamics simulations show how
the various defects aect the polarization dynamics in their vicinities.
3:45 PM DD4.7
HOW TO DESIGN INTERACTION BETWEEN AND d
ELECTRONS IN CONDUCTING AND MAGNETIC HYBRID
ORGANIC-INORGANIC MOLECULAR MATERIALS.
Lahcene Ouahab, Laboratoire de Chimie du Solide et Inorganique
4:15 PM DD4.9
SYNTHESIS AND CHARACTERISATION OF B-SITE DOPED
COPPER-TANTALATES. Bernd Renner, Stefan Ebbinghaus, Armin
Reller, Universitat Augsburg, Lehrstuhl fur Festkorperchemie,
Augsburg, GERMANY; David Schrupp, Universitat Augsburg,
Lehrstuhl fur Experimentalphysik II, Augsburg, GERMANY;
Hans-Albrecht Krug von Nidda, Monika Heinrich, Peter
Lunkenheimer, Michael Schetter, Universitat Augsburg, Lehrstuhl fur
Experimentalphysik V, Augsburg, GERMANY.
Perovskite-related metal oxides of the general formula ACu3 B4 O12
are known for a long time [1]. A special characteristic of this type of
structure is a collective rotation of BO6 -octahedra giving 3/4 of
A-cation places a quadratic-planar geometry.
For this reason they can
be occupied by Jahn-Teller-active Cu2+ (otherwise a typical
B-cation). The remaining 1/4 of A-sites are occupied by alkali metal-,
alkali earth- or lanthanoid-ions or remain (partially) free, depending
on the valency of the remaining cations. Many of these compounds
reveal interesting physical properties like high electric conductivity or
extraordinary magnetic behaviour. CaCu3 Ti4 O12 , as an example,
shows a very high dielectric constant at low frequencies [2, 3].
Our work concentrates on B-site doped copper-tantalates.
Starting
from CaCu3 Ti4 O12 , the substitution of Ti4+ by pentavalent ions like
tantalum allows us to synthesise A-site decient polycrystaline
phases, ranging from Cu3 Ti2 Ta2 O12 to Cu2 Ta4 O12 . It was also
possible to ux-grow single crystals of Cu2 Ta4 O12 . To further
decrease the copper content in this structure hexavalent ions like
tungsten and molybdenum have been incorporated and single crystals
could be obtained. EXAFS measurements, Rietveld renement data as
well as magnetic and dielectric properties are presented.
4:30 PM DD4.10
STRUCTURE AND PHASE TRANSITIONS IN AURIVILLIUS
PHASE FERROELECTRICS. Philip Lightfoot, Charles Hervoches,
Alan Snedden, University of St. Andrews, School of Chemistry, St.
Andrews, UNITED KINGDOM.
We shall summarise our recent work on the detailed crystallographic
characterisation, by powder neutron diraction methods, of a range of
members of the Aurivillius family of layered bismuth oxide
ferroelectrics. We have shown that the ferroelectric - paraelectric
phase transitions in members of this family containing an even
number of perovskite layers proceed via a `two-step' process, involving
an intermediate paraelectric phase (space group Amam), whereas, for
'odd-layered' analogues the transition is a direct, rst-order transition.
We shall also discuss the nature and extent of cation disorder in the
La-doped Bi4Ti3O12 system, which may have implications for the
observed `fatigure-free' polarisation characteristics in this system.
4:00 PM DD4.8
Moleculaire, UMR 6511 CNRS - Universite de Rennes 1, Rennes,
FRANCE.
In the last few years an increased interest was devoted to hybrid
organic-inorganic multifunctional molecular materials aiming to
obtain synergy between two physical properties. For the particular
class of materials combining electrical conductivity and magnetic
interactions, it is hopped to achieve magnetic coupling between the
localized spin of the inorganic part through the mobile electrons of
the organic part via the so-called -d interactions. In order to match
this mechanism, we are investigating new type of materials where the
two systems interact through a conjugated bridge. This constitutes a
new approach to enable the interactions between and d spins.
According to this idea, we obtained recently, novel molecular bricks,
namely [M(hfac)2 (TTF-py)2 ], M= CuII, MnII, hfac=
hexauoroacetylacetonate; TTF-py=
4-(2-tetrathiafulvalenyl-ethenyl)pyridine in which the conducting and
the magnetic systems are covalently linked (see Figure). After a lot of
eorts, the radical cation salts of these coordination complexes are
now achieved and showed the possible interactions between the spin of
the TTF-py ligand and the spin of the paramagnetic transition
metals. Actually, several compounds are obtained and characterized.
These are [M(hfac)2 (TTF-py)2 ][PF6 ] and
[M(hfac)2 (TTF-py)2 ][PF6 ]2 , in the former only one TTF-py ligand is
oxidized giving rise to a mixed valence complex, while in the second
complex the two TTF-py ligands are oxidized. L. Ouahab, Chem.
Mat., 1997, 9, 1909. F. Iwahori, L. Ouahab, S. Golhen, J.P. Sutter, R.
Carlier, Inorg. Chem., 2001, 40, 6541-6542. L. Ouahab, F. Iwahori, S.
Golhen, R. Carlier, J.P. Sutter Synth. Metal, 2002, in press.
SITE MIXING INVESTIGATIONS IN THREE-LAYER
FERROELECTRIC AURIVILLIUS CERAMICS. M.S. Haluska, S.T.
Misture, New York State College of Ceramics at Alfred University,
Alfred, NY.
Three-layer Aurivillius ceramics Bi2 SrCaNb2TiO12 ,
Bi2 Sr1:5 Ca0:5Nb2 TiO12 , Bi2 Sr2 Nb2 TiO12 , Bi2 Sr1:5 Ba0:5 Nb2 TiO12 ,
Bi2 SrBaNb2 TiO12 were formed via solid-state synthesis and their
structures characterized by Rietveld analysis of powder x-ray
diraction data. Site mixing was observed for all species with the
largest amount of mixing occurring in Bi2 SrBaNb2 TiO12 . Bond
valence sum calculations (BVS) determined that the A-site BVS
increased from underbonded in Bi2 SrCaNb2TiO12 to overbonded in
Bi2 SrBaNb2 TiO12 . The A-site BVS increased linearly with lattice
parameter and average A-site cation radius. Bi-site position relaxation
was observed as the average size of the alkaline earth cation on the
Bi-site increased. Site mixing occurs in these compounds in order to
relieve interlayer strain between the (Bi2 O2 )2+ layer and the
perovskite blocks, between the Nb and Ti-layers of the perovskite
blocks, and to reduce the BVS of the perovskite A-site. A slightly
dierent strain-relief mechanism is observed in the three-layer
Aurivillius phases as opposed to the two-layer phases.
4:45 PM DD4.11
FERROELECTRIC NANOCOMPOSITE WITH HIGH
643
DIELECTRIC CONSTANT. Mai T.N. Pham, B.A. Boukamp, H.J.M.
Bouwmeester, University of Twente, Faculty of Chemical Technology,
Enschede, THE NETHERLANDS.
Ferroelectric materials are of great interest for application as
non-volatile memory and high capacitance capacitors. Through the
dispersion of a metal phase, the dielectric constant of the ferroelectric
composite can be increased substantially. We have investigated the
dielectric properties of lead zirconate titanate (PZT) with dierent
amounts of dispersed platinum. Using a colloidal method, Pt particles
with a grain-size of 3-5 nm were prepared. SEM analysis showed that
Pt was homogeneously dispersed in the PZT matrix. XRD analysis
indicated that between PZT and Pt no unwanted reaction phases were
formed during sintering at 1150 C. Electrical properties were
investigated by impedance spectroscopy measurement. The eective
dielectric constant increased signicantly with increasing Pt volume
content. The observed power law relation follows the prediction by
percolation theory. At 25 vol% of Pt the dielectric constant of the
composite is 4-5 times larger than that of pure PZT. It was found
that the activation energy of the electric conduction decreased with
increasing Pt content.
SESSION DD5: POSTER SESSION
NANOMATERIALS
Chair: Gregory S. Rohrer
Tuesday Evening, December 3, 2002
8:00 PM
Exhibition Hall D (Hynes)
DD5.1
A NEW MECHANISM FOR THE CATALYTIC GROWTH OF
CARBON FIBERS AND METAL DUSTING PHENOMENON.
Zuotao Zeng, and Ken Natesan, Argonne National Laboratory, Energy
Technology Divison, Argonne, IL.
Recently, the growth of carbon nanotubes has attracted a lot of
attention since these carbon bers have many potential applications
in electronic devices and as a hydrogen storage medium. To grow
carbon bers, nanoparticles of Ni and Fe are used as catalysts. The
catalytic growth of carbon ber can also lead to metal dusting
corrosion. The mechanism of metal dusting is not clear, although
research on it has been ongoing for over 50 years. Metal dusting
phenomenon is a metal loss process that occurs in a strong
carburizing gas atmosphere at high temperature. During this process,
corrosion of metals or alloys occurs, accompanied by the formation of
carbon dust, bers, and ne metal carbide and/or pure metal.
Signicant problems with the metal dusting of steel components have
occurred in the petroleum, petrochemical and other industries. Raman
scattering and X-ray diraction were used to study the mechanism of
the catalytic crystallization of carbon and metal dusting. A new
mechanism for metal dusting and the growth of carbon bers is
proposed. Carbon cannot crystallize well by deposition from
carburizing gases at low temperature without catalytic activation
because of its strong C-C bonds and high melting temperature. The
poorly crystalline carbon has higher free energy than that of good
crystalline carbon. To form good crystalline carbon, carbon atoms
have to dissolve, diuse through metal particles, and crystallize on a
proper lattice plane that can act as a template to help the epitaxial
growth of carbon crystals. Metal particles are liberated from the pure
metal and alloys in this process, which leads to metal dusting attack.
The decrease of free energy from highly disordered carbon to well
crystalline carbon is the driving force for metal dusting and carbon
ber growth through metal particles.
DD5.2
CARBON NANOTUBE SIDEWALLS AND END CAPS AS TARGET
SITES FOR CHEMICAL MODIFICATION: CHEMICAL CONTROL
OVER NANOTUBE PROPERTIES. Sarbajit Banerjee, Stanislaus S.
Wong, Department of Chemistry, SUNY at Stony Brook, Stony
Brook, NY, Materials and Chemical Sciences Department,
Brookhaven National Laboratory, Upton, NY.
Single-walled carbon nanotubes (SWNTs) have been the focus of
intensive study due to their unique structure-dependent electronic and
mechanical properties. Understanding the chemistry of single-walled
carbon nanotubes is critical to rational manipulation of their
properties. Chemical modications to these SWNTs through covalent
attachment to metal-containing molecular complexes can have
signicant eects on their properties. In fact, improved solubilization
in organic solvents, charge transfer, and catalytic properties were
noted in SWNTs functionalized with Iridium and Rhodium
complexes. The adducts of SWNTs with these complexes have been
structurally characterized by electron and atomic force microscopy.
Optical properties have been extensively probed by means of
UV-Vis-NIR, mass, and multinuclear NMR spectroscopy as well as by
photoluminescence studies. A further extension of functionalization at
the metal-nanotube interface has been associated with the tethering
of quantum dots (such as CdSe) and oxide nanocrystals (such as
TiO2 ) by oxygenated functional groups on the SWNT surface.
Recently, a more ecient method for functionalizing SWNT sidewalls
with oxygenated functionalities has been developed using ozonolysis
which will enable the attachment of a wide range of dierent
functional moieties with a host of potential applications.
DD5.3
PREFERENTIALLY ORIENTED FILM OF MONOCLINIC
TITANIUM DIOXIDE DERIVED FROM NEGATIVELY CHARGED
TETRATITANATE NANOSHEETS. Wataru Sugimoto, Osamu
Terabayashi, Yasushi Murakami, Yoshio Takasu, Shinshu Univ, Dept
Fine Materials Engineering, Nagano, JAPAN.
Monoclinic titanium dioxide, TiO2 (B) possesses unique properties
compared to other TiO2 polymorhps. TiO2 (B) is a metastable form of
titanium dioxide which is obtained via the so-called `soft chemistry
reaction', which involves a low-energy transformation of
H2 Ti4 O9 xH2 O into TiO2 (B) upon thermal treatment. Due to this
distinctive synthetic method, TiO2 (B) has been obtained only in a
powder form so far. We have applied electrophoretic deposition for the
direct deposition of H2 Ti4 O9 xH2 O from colloidal suspensions of
H2 Ti4 O9 xH2 O nanosheets and its transformation into oriented
TiO2 (B) lm. The dispersion state of a
tetrabutylammonium/H2 Ti4 O9 xH2 O intercalation compound was
studied using various aqueous and non-aqueous solutions. Colloidal
suspensions containing H2 Ti4 O9 xH2 O nanosheets were obtained by
dispersing the tetrabutylammonium/H2 Ti4 O9 xH2 O intercalation
compound in solvents with sucient dielectric constant; for example,
water, methyl alcohol, isopropyl alcohol, acetonitrile,
N,N -dimethylformamide, dimethylsulfoxide. A b-axis oriented
H2 Ti4 O9 xH2 O lm was obtained by electrophoretic deposition using
the colloidal suspension. Thermal treatment of the electrophoretically
deposited lm lead to an oriented TiO2 (B) lm with the (0k0) planes
lying perpendicular to the substrate.
DD5.4
IN-SITU STUDY ON THE NUCLEATION AND GROWTH OF
CERIUM OXIDE NANOPARTICLES AT ROOM TEMPERATURE.
Feng Zhang, Qiang Jin, Jonathan E. Spanier, Richard D. Robinson,
Irving P. Herman, Siu-Wai Chan, Columbia University, Department of
Applied Physics and Applied Mathematics, and Materials Research
Science and Engineering Center, New York, NY.
Cerium oxide nanoparticles are prepared at room temperature with
narrow size distribution. Transmission electron micrographs show that
single-crystal nanoparticles have an octahedral shape with f111g
surfaces or a f200g surfaces truncated octahedral shape. In-situ
ultraviolet-visible light absorption has been performed to monitor the
growth of nanoparticles. The results correlate well with that of the
TEM. In-situ X-ray absorption is performed at Ce LIII edge to
observe
the nucleation and growth of the nanoparticles. The
Ce3+ /Ce4+ ratios in dry powder, supernatant, and total solution are
given from X-ray absorption to explain the chemical reaction. This
work was supported by the MRSEC program of the National Science
Foundation, Award No. DMR-9809687.
DD5.5
LATTICE EXPANSION OF CERIUM OXIDE NANOPARTICLES.
Feng Zhang, Jonathan E. Spanier, Richard D. Robinson, Irving P.
Herman and Siu-Wai Chan.
Mono-dispersed cerium oxide nanoparticles are prepared from solution
at room temperature. Nucleation and growth of particles are
controlled to render a small size distribution. It is found that with
decreasing particle size, the lattice parameter of CeO2 increases,
which has been proven by x-ray diraction and Raman spectroscopy.
This is dierent from what has been observed with noble metals, for
which the lattice parameter shrinks while the particle size decreases.
High temperature x-ray diraction is performed at the National
Synchrotron Light Source on CeO2 nanomaterials with dierent
particle sizes and with dierent atmosphere treatments to study the
lattice parameter change. Possible explanations for the lattice
parameter expansion of ceria will be provided as well. This work was
supported by the MRSEC program of the National Science
Foundation, Award No. DMR-9809687.
DD5.6
COBALT NANOCRYSTAL GROWTH: SIZE, SHAPE AND
STRUCTURE CONTROL. Victor F. Puntes, A. Paul Alivisatos,
Chemistry Dept, UC Berkeley, Berkeley, CA; Can Erdonmez,
Materials Science Department, UC Berkeley, Berkeley, CA;
Daniela Zanchet, Laborat'rio Nacional de Luz Scrotron, Campinas,
BRAZIL.
644
NARROW POLYDISPERSITIES. Susanthri C. Perera, Stephanie L.
Brock, Department of Chemistry, Wayne State University, Detroit,
MI.
Despite considerable interest in nanoparticles of main group pnictides
(pnictogen = group 15 element) such as GaAs and InP, transition
metal analogs have remained essentially unexplored. This is surprising
since bulk materials show a number of properties of signicant
interest including ferromagnetism, magnetoelastic and magnetooptical
properties. Therefore, novel magnetic and electronic properties are
expected from nanoparticle transition metal pnictide systems, and
these materials may have attractive prospects in the design of new
devices. We have developed a procedure based on the reaction of
transition metal (TM) salts or carbonyl complexes with silyl
phosphines to create TM phosphide nanoparticles with control of both
particle size and structure/stoichiometry. The application of this
method to phosphides of Fe and Mn will be described, and the
physical properties of the resultant materials discussed in light of
structure and particle size.
Chemical synthesis is a powerful route to obtain large collections of
monodisperse inorganic nanocrystals with well-dened characteristics,
which have allowed the development of new advanced materials with
properties tuned at the molecular level. It has been observed that
during nucleation and rst stages of growth, small variations in the
synthesis recipe yield crystals of dierent sizes, shapes and structures.
In other words, a large assortment of nanocrystals may be obtained
by slightly perturbing the system at the earlier stages of growth.
Besides, the close relationship between size, shape and crystal
symmetry is also worth the study. The case of Co is of particular
interest: besides the size control, at least three nearly isoenergetic
crystal structures (face-centered cubic, hexagonal close-packed and
epsilon) can be synthesized and shape control (spheres, prisms, cubes,
rods and disks) is also possible. Here, we present our latest results in
the synthesis of Co nanocrystals. Nanocrystals have been obtained by
rapid decomposition of dicobalt octacarbonyl in the presence of
organic ligands under inert atmosphere; by changing temperature and
surfactant mixture composition we have produced nanocrystals of
dierent sizes (between few and few tens of nanometer), structures
(hcp, fcc and epsilon) and shapes (spheres and disks). Ina set of
experiments,
Co nanocrystals have been prepared at 182 C and
110C in the presence and absence of long-chain linear amines. Thus,
hcp and epsilon spheres and hcp disks (which are formed by selective
attachment of surfactants to the (001) facets) have been obtained and
isolated. The competition between crystal symmetry, surface energy
and nanocrystal-solution interaction as a function of temperature,
surfactant attachment and growth time has been followed. The nal
size, shape and crystal structure have been determined by combining
X-Ray Diraction, Electron Diraction and High Resolution
Transmission Electron Microscopy.
DD5.10
DD5.7
SYNTHESIS BY THE OXIDANT PEROXO METHOD (OPM) AND
DYNAMIC CHARACTERIZATION IN SITU BY HRTEM OF THE
CRYSTALLIZATION OF NANOSIZED LEAD TITANATE.
Emerson R. Camargo, Edson R. Leite, UFSCar-Federal University of
Sao Carlos, Dept of Chemistry, LIEC, Sao Carlos, SP, BRAZIL.
We have synthesized nanosized powders of lead titanate (PbTiO3), an
important technological compound that is widely applied by the
industry in several elds, by a new technique called as `the oxidant
peroxo method' (OPM). This chemical method for powder synthesis is
the unique way to obtain nanopowders completely free from carbon
and halides of lead based-perovskites. An amorphous precipitate, with
mole ratio of Pb:Ti = 1:1, was prepared by an oxy-reduction reaction
between Pb(II) and inorganic-peroxo complexes of Ti synthesized
from metallic titanium, in an aqueous solution at high pH. This
precipitate was calcined between 200 and 1000 C in a electrical
furnace using closed alumina boats to crystallize the perovskite
structure without any secondary phase. Crystalline particles with size
in the range from 5 to 50nm were obtained as a function of the
thermal treatment (time and temperature). High-resolution
transmission microscopy (HRTEM) was used to visualize in situ the
dynamic crystallization from the amorphous powder to 5 nm
crystalline particles using the electron bean at 300 kV. The crystalline
structure of the powders was rened by the Rietveld method, and the
nal calcined products were characterized by, thermal analysis, X-ray
diractometry, and Raman spectroscopy.
DD5.8
SYNTHESIS OF MONODISPERSE FERRITE NANOPARTICLES:
XANES (K-EDGE) DETERMINATION OF CATION OXIDATION
STATE AND DISTRIBUTION. Pete Bonitatebus, Mike Larsen, Yan
Gao, GE Global Research Center, PSCT Emerging Technologies,
Niskayuna, NY.
Spinel ferrite nanoparticle synthesis is of value as the resultant
nanomaterials can be used in a wide range of technological
applications including molecular imaging, biomolecular separation,
memory devices, and as materials for high frequency applications
where low core losses are essential. Ferrite nanoparticles are
technologically attractive because the chemical composition, enhanced
by high crystal quality and particle monodispersity, can be tuned to
the particular application. Therefore, a simple, one-pot synthetic
route to produce monodisperse nanocrystalline particles with variable
crystal chemical composition is of worth. The novel method is
non-hydrolytic and uses commercially available precursors in
combination. The exibility of the method has been demonstrated by
its eectiveness in several hydrophobic solvents, using surfactants
bearing pendant polymerizable functional groups. Characterization of
ferrite nanoparticles by TEM, EDX, X-ray and electron diraction,
along with details of the nanostructures as garnered by synchrotron
x-ray source data (XANES) will be included.
DD5.9
SYNTHESIS AND CHARACTERIZATION OF DISCRETE
PHASE-PURE Mn AND Fe PHOSPHIDE NANOPARTICLES WITH
SOLVENT EFFECTS ON THE Au DISTRIBUTION ON Pt-Au/C
CATALYSTS PREPARED BY SURFACE REDOX REACTIONS.
P. Del Angel, J.M. Dominguez, J.A. Montoya, Instituto Mexicano del
Petroleo, Ingenieria Molecular, MEXICO; M.J. Yacaman, P. Santiago,
The University of Texas at Austin, Dept. of Chemical Engineering,
Austin,TX.
The synthesis of Pt-Au/C (graphite) supported bimetallic catalysts
was carried out by surface redox methods using short-chain alcohol
solvents. These methods allowed the low-temperature reduction and
selective deposition of Au species onto Pt(111) crystallographic faces
of Pt crystallites supported on graphite. The Direct Redox method
proceed0 by the reduction \in-situ" of ethyl alcohol solutions of
AuCl4 species using the parent metal (Pt) as the reducing agent,
but the Relling method uses
hydrogen pre-adsorbed on the parent
metal (Pt) to reduce AuCl4 0 species by contact in the Pt-H interface
at room temperature. Thus, the aggregation state of metals in the
Pt-Au/C system was characterized by X-ray diraction, Energy
Dispersive Spectroscopy (EDS) and High Resolution Electron
Microscopy (HREM). The latter techniques were used simultaneously
for assessing the interaction degree between Pt and Au in the
Pt-Au/C system at the nanometer scale. Even at room temperature
most of the small metal particles analyzed showed the presence of
both metals, Pt and Au, however the aggregation state is sensitive to
the preparation method as wellas to the subsequent thermal
treatments at 150, 300 and 500 C under H2 . From room temperature
to about 300 C bimetallic particles are common and the Auo phase
keeps its own nature
at the single particle level. However, after a
treatment at 500C under H2 a Pt-Au solid solution forms readily.
The HREM study shows that Au decoration of Pt particle facets
occurs, which must inuence the catalytic properties of the bimetallic
Pt-Au/C catalysts as well.
DD5.11
NOVEL SYNTHESIS OF METAL OXIDE TUBULAR
STRUCTURES AND NANOFIBERS USING POLYLACTIDE
TEMPLATE. Samuel Lutta, Peter Y. Zavalij, M. Stanley
Whittingham, State University of New York at Binghamton, Institute
for Materials Research and Dept of Chemistry, Binghamton, NY.
Nanobers and tubular structures of several oxides with diameters in
the range 30-100 nm and 200 nm - 800 nm respectively, have been
prepared by a template-directed process. The sol-gel reaction of metal
oxide precursors with acid treated polylactide bers, and subsequent
removal ofthe template by calcination in oxygen at temperatures
above 250 C yielded tubular and nanobrous metal oxide structures.
Hydrothermal treatment of sol-gel mixture results in formation of a -phase vanadium oxide compound for the case of vanadium oxide.A
pure metal oxide phase with a brous morphology is formed when the
product
of hydrothermal reaction is heated at temperatures above
250C in oxygen atmosphere. The oxides include V2O5 , WO3 and
MoO3 . The presented synthesis approach uses a cheap and air-stable
precursor and thus provides an advantageous access to gram
quantities of these novel anisotropic materials. The mechanisms of
formation of the nanobers and tubules are discussed. The materials
have been characterized by SEM, TEM, FTIR, DCP-AES, TGA and
XRD. Optical and electronic properties of these materials will be
studied, which may oer exciting opportunities for their potential
applications in smart windows, battery and catalysis.
DD5.12
SYNTHESIS BY SOFT CHEMISTRY ROUTES AND
CHARACTERIZATION OF Sr2 Bi1:4 Ca0:6O6 NANOPARTICLES.
Isaela Villalpando, Claudia C. Luhrs, Departamento de Quimica,
CUCEI, Universidad de Guadalajara, Jalisco, MEXICO.
645
In recent years nanomaterials has been the focus of attention in many
research centers due to their impact in chemical industry and
technology. They can oer better properties, specially those related
with its chemical and mechanical behavior, compared with traditional
materials, fact that opens a very wide range of possibilities for new
technological applications. The research in this eld has been
stimulated also for the inherent high supercial areas obtained, that
can rise the chemical activity, being the later one of the goals of
industry in order to optimize some processes. The phase
Sr2 Bi1:4 Ca0:6O6 has a perovskite-like structure in which a reversible
redox process takes place, making it suitable for some uses like
catalysis, thermistor devices and solid state gas sensors. In this work,
in order to perform the synthesis at lower temperatures or shorter
reaction times, and to achieve microstructural control that led us to
obtain Sr2 Bi1:4 Ca0:6O6 nanoscale particles, feature needed for some
of those applications, alternative synthesis routes were used instead of
traditional solid state reaction. This report presents the results
obtained when the phase was prepared via coprecipitation of nitrates,
using dierent nitric acid concentrations, and urea or ethylenediamine
as a complexing agents at dierent pH values. X-ray powder
diraction were used to follow the reactions. Scanning and
transmission electron microscopy studies showed the microstructure of
the precursor and nal phases. How the synthesis methods aect the
oxygen content of the subject compound was evaluated with
iodometric titrations. Some reactivity tests in dierent atmospheres
and surface area measurements were also performed.
DD5.13
A NOVEL NANOPARTICLE/LAMELLA OXIDE HYBRID:
TiO2 -PILLARED MoO3 . Seung-Min Paek, Hyun Jung, Jin-Ho Choy,
Seoul National University, Seoul, KOREA.
The intercalation into MoO3 with TiO2 nanoparticles has been
accomplished via the exfoliating and reassembling procedures. The
molybdenum oxide lithiated by LiBH4 is exfoliated in degassed
deionized water. And subsequent restacking of exfoliated MoO3 in the
TiO2 nanoparticle solution results in TiO2 -pillared MoO3 . X-ray
diraction pattern and Fourier transform infrared (FT-IR) spectrum
conrm that the TiO2 nanoparticles are successfully intercalated in
the interlayers of MoO3 . The interlayer expansion of MoO3 with 1d
value of 11.2 A is consistent with the size of TiO2 nanoparticle.
Well-dened (00l) reections reveal highly ordered lamellar character
of TiO2 -pillared MoO3 . Its FT-IR spectrum exhibits the
strong peaks
characteristic of TiO2 in the region of 1500 - 1600 cm01 . The
symmetric stretching vibration (Mo=O) in the TiO2 -pillared MoO3
shifts into a high wavenumber, which suggests the oxidation of MoO3
after TiO2 intercalation. The scanning electron microscopy (SEM)
images show that TiO2 intercalation does not deteriorate the layered
morphology of parent MoO3 . The preedge characteristic of anatase in
the X-ray absorption spectrum of the TiO2 -pillared MoO3 conrms
that guest TiO2 in the interlayer of MoO3 is pillared in the form of
quantum-sized anatase.
DD5.14
STRUCTURE AND ELECTRONIC PROPERTIES OF THE
DIBORIDE NANOTUBES. Leonid A. Chernozatonskii, A.R. Sabirov,
Dept of Material Research, Institute of Biochemical Physics, Moscow,
RUSSIA.
In present work we pay attention
to possible new class of nanotubes
(NT) from diborid material1 . NT atomic structures of MgB2 , CaB2
and ZrB2 have been modeled by means of molecular mechanics and ab
initio methods. Contrary to the familiar carbon NT the dependence of
the strain2energy of MB2 (M=Mg, Zr) tube on its diameter deviates
from 1/D low because the MB2 nanocrust is predominantly rolled up
around the axis parallel to M-M bonds. Thus most stable \armchair"
MgB2 and ZrB2 tubes are that with external hexagonal boron layers,
since most favorable CaB2 NTs have internal boron layers. We used
approach of calculation of electronic spectrum for single wall NT
based on known spectrum
of unfolded layer. This approach was
proposed in work2 and was used for prediction of main properties of
carbon NT. Electronic spectrum of NT can be obtained by applying
the periodic boundary conditions to the electronic wave functions of
corresponding striplike fragment of plane layers. 1D dispersion curves
of a NT in such case are sections of 2D layer spectrum3 along certain
direction in Brilliouin zone. We calculated spectra for a number of
MB2 NTs: (n,n) and(n,0). It was found that in contrary of carbon NT
all considered MB2 nanotubes have high density of states near Fermi
level (<0.2 eV). Furthermore for certain NTs there are high densities
of states on the Fermi level can appear thus one can expect rather
high temperature of transition into superconductive state (for bulk
MgB2 Tc=39 K). For example for (6,6), (20,0), and (21,0) MgB2
nanotubes spectrum there were area where the derivation of energy to
the wave vector was about zero that leads to the high density of
states near the Fermi level, and so such tubes are candidates to
superconductive NT. This work was supported by INTAS (00-237),
Russian Program \Fullerene and Atomic Clusters".
L.A. Chernozatonskii. JETP Lett., 74, 369 (2001).
R. Saito, M. Fujita, G. Dersselhaus, M.S. Dersselhaus. Phys. Rev.
B46, 1804 (1992).
N.I. Medvedeva, Yu.E. Medvedeva, A.L. Ivanovskii, et al. JETP Lett.
73, 366 (2001); J.B. Neaton, A. Perali. Cond-mat/0104098 (2001).
DD5.15
REDOX CHEMISTRY APPROACH TO THE SPONTANEOUS
FORMATION OF NANOTUBE/NANOPARTICLE HYBRID
STRUCTURE. Hee Cheul Choi, Moonsub Shim, Sarunya
Bangsaruntip, Hongjie Dai, Stanford Univ, Dept of Chemistry,
Stanford, CA.
Nanotube/nanoparticle hybrid structures are prepared by forming Au
and Pt nanoparticles selectively on the sidewalls of single-walled
carbon nanotubes. Reducing agent or catalyst free-electroless
deposition purely utilizes redox potential dierence between Au(III),
Pt(II) and carbon nanotube as a main driving force for this reaction.
It is also shown that carbon nanotube roles as a template for wire-like
metal structures. The metal nanoparticles coated carbon nanotube is
simply calcined to obtain well-aligned nanoparticles at the end. The
successful formation of the hybrid structures is monitored by atomic
force microscopy (AFM) and electrical measurements. Since
semiconducting carbon nanotube intrinsically shows hole-doped
property, a simple electrical measurement will directly prove the
direction of charge transfer. As expected, increased current due to
increased hole concentration in carbon nanotube is monitored upon
the formation of nanoparticles on the carbon nanotubes. This novel
route is greatly expected to grant various systems for the further
studies of chemical, physical or electrical properties of nanoscale
heterojunctions.
DD5.16
STRUCTURE, MAGNETIZATION AND MOSSBAUER STUDY OF
NANOSTRUCTURED Ni0:5 Zn0:5 Fe2 O4 FERRITE POWDERS.
Shihui Ge, Zongtao Zhang, Y.D. Zhang, Mingzhong Wu, Inframat
Corporation; D.P. Yang, College of the Holy Cross.
Ferrites have been used as high frequency soft magnetic materials for
a few decades due to its high resistivity and higher permeability.
Nanostructured ferrites possess more advantages than the
conventional ferrite materials and have been a research focus recently.
In this work, a series of nanostructured Ni0:5 Zn0:5 Fe2 O4 were
synthesized by a citrate reaction method followed by calcinating at
various temperatures with the goal of obtaining pure phase
Ni0:5 Zn0:5 Fe2 O4 nanoparticle while keeping the size small. X-ray
diraction, transmission electron microscopy, SQUID magnetometer
and Mossbauer spectroscopy (ME) have been employed to characterize
the crystal structure, phase homogeneity, particle size, the conditions
for chemical reaction completion, and the magnetic properties. The
results show that the saturation magnetization Ms at both 10K and
300K increase with increasing calcination temperature Ta, but particle
size also increases with Ta. Three factors possibly responsible for Ms
decreasing at lower Ta are studied in this work. First, ME experiments
reveal that the reaction forming
Ni0:5 Zn0:5 Fe2 O4 completes only
when calcining above 700C; while for samples calcined at lower Ta,
the reaction is incomplete. This causes lower saturation
magnetization. Secondly, the material in the surface region may be in
an amorphous state, which reduces the saturation magnetization.
Third, the magnetization versus temperature curve for samples
calcined at lower temperatures shows a superparamagnetic-like
behavior. The superparamagnetic relaxation reduces the room
temperature saturation magnetization. A detailed analysis of
nanostructure on the magnetic properties in ferrites will be presented.
Based on these experimental results, an optimal condition for
synthesizing nanostructured Ni0:5 Zn0:5 Fe2 O4 has been established.
DD5.17
TEMPERATURE-DEPENDENT MAGNETIC PROPERTIES OF
SiO2 -COATED Ni75 Fe25 NANOPARTICLES. Mingzhong Wu,
Inframat Corporation, Farmington, CT; University of Connecticut,
Department of Physics and Institute of Materials Science, Storrs, CT;
Y.D. Zhang, S. Hui, Shihui Ge, Inframat Corporation, Farmington,
CT; M.J. Yacaman, University of Texas, Department of Chemical
Engineering, Austin, TX.
SiO2 -coated Ni75 Fe25 nanoparticles were prepared using a wet
chemical method, and their structure and magnetic properties were
investigated using x-ray diraction, high-resolution transmission
electron microscopy, and a superconducting quantum interference
device magnetometer. The SiO2 material was in an amorphous state.
The Ni75 Fe25 nanoparticles were in a simple cubic state and contained
an inner oxide (Ni-oxide and Fe-oxide) core whose size decreased with
increasing calcination temperature. The nanoparticles were basically
in the ferromagnetic state. Their saturation magnetization increased
with increasing calcination temperature, whereas their coercivity
decreased with increasing calcination temperature. The nanoparticles
646
and magnetic properties of synthesized powder were characterized
using x-ray diraction (XRD), high-resolution transmission electron
microscopy (HRTEM), and a superconducting quantum interference
device magnetometer (SQUID). The nano-sized cobalt particles are of
either face centered cubic (fcc) and/or hexagonal close-packed (hcp)
crystalline structures. The average grain size is 14 nm for cobalt
(either fcc or hcp) with a silica coating, and the average grain size is 9
nm for hcp cobalt and 26 nm for fcc cobalt without a silica coating.
The eects of the temperature, time, and coating on the structure and
grain size are discussed. In addition, the eects of grain size on
magnetic properties are also addressed. This work is supported by
DARPA through contract No. F7-6AM945-X05.
exhibited strong temperature-dependent magnetic behaviors. The
Bloch exponent fell from 1.5 for the bulk to smaller values and
decreased with increasing oxide content, while the Bloch constant
were much bigger than that for bulk and increased signicantly with
oxide content. The value of coercivity decreased with increasing
temperature, and this decrease was more pronounced for the
nanoparticles containing high oxide content. The exchange anisotropy
arising from the exchange coupling across the Ni75 Fe25 /oxide
interfaces was examined and was used to interpret the observed
temperature-dependent behaviors. Acknowledgments: The authors
would like to thank Profs. J.I. Budnick and W.A. Hines of the
University of Connecticut for the use of equipment.
DD5.18
OBSERVATION OF NANO-SCALE CLUSTERS IN Nd-Fe-Al
GLASSY HARD MAGNETS BY HIGH RESOLUTION
TRANSMISSION ELECTRON MICROSCOPY. N. Lupu and
H. Chiriac, National Institute of R&D for Technical Physics, Lasi,
ROMANIA.
The development of new and innovative applications in the last
decades resulted in the development of new magnetic materials with
suitable structures and improved physical properties, and if and when
possible the tailoring of the structure depending on the application.
Earlier measurements on Nd-Fe-(Al,Si) bulk amorphous alloys showed
the following general features: (i) fully amorphous structures revealed
by X-ray diraction measurements; (ii) large coercive elds in the
as-cast state for Nd60 Fe30 Al10 bulk amorphous alloys and soft
magnetic behaviour for the similar melt-spun thin ribbons; (iii) large
coercive elds in the as-cast state for both amorphous ribbons and
bulk samples containing less than 60 at. % Nd and for those in which
Al is substituted by Si; (iv) a strong dependence of the coercive eld
on the quenching conditions and temperature; (v) weak ferromagnetic
behaviour after crystallization. All these features suggested that the
microstructure of these easy glass forming amorphous alloys consists
in exchange coupled Fe-Nd magnetic clusters embedded in Nd-rich
amorphous matrix. Our micro-structural data obtained by HRTEM
prove the existence of the very small clusters (or medium-range
ordered regions) with dimensions of 2-3 nm embedded in the
amorphous matrix for Nd50 Fe40 Al10 melt-spun ribbons 25 and 120
m in thickness. The clusters are dispersed more homogeneously in
thick ribbons than in thin ones leading to a higher magnetic
percolation limit, and consequently the larger coercive elds up to 5 T
in the as cast-state for 120 m ribbons in comparison with 1-2 T for
25 m ribbons. These clusters have the composition very close to the
eutectic phase Fe77:2 Nd22:8 . The relationship with the magnetic
response of the system is discussed in detail.
DD5.19
EPITAXIAL GROWTH OF MAGNETIC NICKEL NANODOTS BY
PULSED LASER DEPOSITION. Honghui Zhou, D. Kumar, A. Kvit,
Ashutosh Tiwari and J. Narayan, NSF Center for Advanced Materials
and Smart Structures, Department of Materials Science and
Engineering, North Carolina State University, Raleigh, NC.
Epitaxial nickel magnetic nanodots were obtained by pulsed laser
deposition technique on silicon substrate (Si(100)) using an epitaxial
titanium nitride lm as a template. Eects of substrate and
deposition parameters, such as temperature, laser beam energy
density and template crystalline quality on the epitaxial growth of
nickel nanodots were studied to obtain an optimum deposition
condition. Cross-sectional and plan-view high-resolution transmission
electron microscopy (HRTEM), including electron diraction and
X-ray diraction techniques were used to determine the crystalline
quality of nanodots. The results showed that deposition temperature
in a certain range does not have much inuence on the dots epitaxy
quality, while the crystalline quality of the underlying template is, to
a larger part, responsible for these dierent orientations observed. It
is found that if the template epitaxial quality is good, high percentage
of cube-on-cube orientated nickel nanodots ( Ni (100) k TiN (100) k
Si (100))
can be obtained in a rather wide temperature range (up to
200C). The epitaxial quality deteriorates and other epitaxial
orientations start to form as the number of layers in a multilayered
sample increases. The magnetic measurements were conducted using
superconducting quantum interference device (SQUID)
magnetometer. Results showed that the magnetic properties were
closely related to the epitaxy quality of nanodots.
DD5.20
SYNTHESIS AND CHARACTERIZATION OF STRUCTURE a
CONTROLLED NANO-COBALT PARTICLES. Shiqiang (Rob) Hui ,
a , Mingzhong Wua;b , Dajing Yan, W.A. Hinesb , and T.T.
Y.D. bZhang
Chen ; a Inframat Corporation, Willington, CT; b Dept. of Physics and
Institute of Materials Science, University of Connecticut, Storrs, CT.
Nanostructured cobalt particles with or without a ceramic coating
have been synthesized using a wet chemical method. The structure
SESSION DD6: POSTER SESSION
SYNTHESIS OF MATERIALS
Chair: Gregory S. Rohrer
Tuesday Evening, December 3, 2002
8:00 PM
Exhibition Hall D (Hynes)
DD6.1
MICROSCALE TITANIA MORPHOLOGIES GROWN WITHIN
SWOLLEN PDMS. Arthur Dobley, Scott R.J. Oliver and
Daniel P. Brennan, State University of New York at Binghamton,
Department of Chemistry, Binghamton, NY.
A variety a titania microstructures have been synthesized using a
swollen polymer matrix of polydimethylsiloxane (PDMS). The shapes
and structures grown to date include spheres, \bowls", \nets" and
\brain coral" matrices. The PDMS polymer network is swellable by a
variety of organic solvents. These solvents create internal voids or
spaces within the PDMS, and of particular volume. We then permeate
these spaces with metal alkoxide liquid, and polymerize the inorganic
upon exposure to air or alkaline water. The resultant metal oxide is
thereby shape-templated by the swollen PDMS polymer. The product
is a TiO2 -PDMS composite, and the titania shapes are removed
chemically or mechanically. Methods of characterization include
optical microscopy, TEM, and SEM. Potential applications of these
titania microshapes include catalysts, llers, capsules, and chemical
separators. The synthesis and characterization of these titania
morphologies will be discussed.
DD6.2
PREPARATION OF NEW BISMUTH OXIDES BY HYDROTHERMAL REACTION (111). N. Kumada, T. Takei and N.
Kinomura, Faculty of Engineering, Yamanashi University, Kofu,
JAPAN.
We have prepared a variety of bismuth oxides by hydrothermal
reaction using NaBiO3 1nH2 O as a starting material. On the course of
this investigation single crystals of a new vanadium bismuth oxide,
V3 Bi5 O15 were prepared by using NaVO3 solution. The new
compounds has the triclinic cell with a=7.845, b=9.376, c=7.119A,
=94.46, =112.52 and =106.15. Besides V3 Bi5 O15 , two types of
new cadmium bismuth oxides, CdBi2 O4 were obtained by
hydrothermal reaction in Cd(NO3 )2 solution. One has the trirutile
related structure which was prepared
under the condition of the
reaction temperature below 130C and another has the CaF2 related
structure obtained at above 130 C.
The preparation and crystal structure of these new compounds will be
described.
DD6.3
PREPARATION OF CRYSTALLIZED Ba10x Srx MoO4 FILMS BY
ELECTROCHEMICAL METHOD AT ROOM TEMPERATURE.
Daojiang Gao, Dingquan Xiao, Jian Bi, Wen Zhang, Ping Yu, Dunmin
Lin, Dept of Materials Science, Sichuan Univ, Chengdu, P.R. CHINA.
The lms of a complete series of solid-solution oxides,
Ba10x Srx MoO4 (0x1), have been prepared on molybdenum
substrates in the
highly alkaline (PH>11) electrolytic solution
containing Ba2 and Sr2 ions by electrochemical method at room
temperature. The X value could be easily controlled by the
concentrations of Ba and Sr species in the concentrations of Ba and Sr
species in the starting solutions. The higher concentration of Ba and
Sr species and higher PH value (PH=13) favored the reaction of lm
formation. XRD, XPS and AFM analyses were employed to
characterize the structure of the lms. The results showed that a
complete series of well-crystallized solution oxides was formed even at
room temperature.
DD6.4
RAPID SYNTHESIS AND CONCURRENT CONSOLIDATION OF
TERNARY COMPOUND Ti3 SiC2 FROM DIFFERENT POWDER
MIXTURES. ZhengMing Sun, Hitoshi Hashimoto, Toshihiko Abe,
647
National Institute of Advanced Industrial Science and Technology
(AIST Tohoku), Sendai, JAPAN.
Ternary compound Ti3 SiC2 shows a unique property combination of
metals and ceramics, which has been synthesized, as a bulk material,
in the last a few years with powder metallurgy processes, where
usually high-temperature, long-time sintering was performed and the
secondary phase, mainly TiC, in the nal products remained. A novel
synthesis process, the pulse discharge sintering (PDS), (or spark
plasma sintering-SPS), was employed for the synthesis of Ti3 SiC2 . In
this process pulse electric current was applied to the powder to
generate necessary heat for sintering and concurrently a pressure was
applied to the powder for consolidation. Three powder mixtures of
(Ti,Si,C), (Ti,SiC,C) and (Ti,Si,TiC) with various compositions as
starting materials were respectively sintered with a PDS system. The
phase identities and microstructures were investigated with XRD,
SEM, EDS and optical metallography. The results demonstrated that
when the starting powder mixture of (Ti,Si,C) or (Ti,SiC,C) was used
the sintered Ti3 SiC2 contains high content of secondary phase TiC.
However, when TiC was used in the starting powder, i.e. in
(Ti,Si,TiC), the content of TiC, as a secondary phase, in the nal
sintered materials was substantially reduced. The Ti3 SiC2 phase
content was further increased to over 99% by adjusting the
composition from the stoichiometric (Ti:Si:C=50:17:33) to the
o-stoichiometric one (Ti:Si:C=50:20:30). An optimum sintering
temperature for the
material sintered from (Ti,Si,TiC) powders was
found to be 1300C, at which fully-dense single-phase Ti3 SiC2 was
obtained. Ti3 SiC2 content was found to receive limited eect of
sintering time when sintered at the optimum temperature in the
sintering time range of 8 minutes to 4 hours. In either of the materials
synthesized from dierent starting powders the immediate reactants
for the formation of Ti3 SiC2 were found to be TiC and Ti5 Si3 , by
examining the intermediate phases during the sintering process.
DD6.5
SYNTHETIC PATHWAYS TO NEW ION-EXCHANGEABLE
MIXED-ANION LAYERED COMPOUNDS. Gabriel Caruntu, Nasser
Naura, Jason W. Baisch, Leonard Spinu and John B. Wiley, Advanced
Materials Research Institute and Chemistry Department, University
of New Orleans, New Orleans, LA.
The goal of obtaining materials with novel electrical or magnetic
properties by the manipulation of layered compounds under mild
synthetic conditions has spurred extensive research over the past
decade. Although interest in known host structures has greatly
increased, new layered phases amenable to ion exchange and/or
intercalation reactions are still needed to allow for greater exibility
in this chemistry. A signicant step towards the extension of the
Dion-Jacobson family of hosts was recently made by the synthesis of
new oxyuorides (Choy et al., 2001). We have sought to build on this
chemistry and herein report on some advances in the synthesis and
characterization of a number of new ion-exchangeable layered hosts.
These compounds are mixed-anion phases (e.g., oxyhalides) that are
structurally related to Sillen or Dion-Jacobson structure types. In
addition to the amenability of these new host systems to topotactic
reactions, structural and physical properties have been explored.
Further, the incorporation of the halide anions into perovskite-like
blocks allows for the stabilization of non-d0 transition-metal cations,
giving rise to interesting electric and magnetic properties in these
materials.
DD6.6
Abstract Withdrawn.
DD6.7
SYNTHESIS AND CHARACTERIZATION OF
BaFe11:602x Mx Tix O19 . G. Mendoza-Suarez, A.F. Fernandez,
Cinvestav-Saltillo, Saltillo, MEXICO; O.E. Ayala-Valenzuela, CIMAV,
Chiahuahua, Chi., MEXICO.
Ba-ferrite (BaM) particles are attractive materials for their potential
use as high density magnetic recording media. Substitutions in BaM
are carried out aiming to obtain materials with improved properties
and more suitable characteristics for specic applications. This work
reports on the synthesis, room temperature magnetic properties, and
microstructure of some substituted BaM with formula
BaFe11:602x Mx Tix O19 , where x varied
from 0.2 to 0.8 at%. The
substituted barium ferrites with M2+ -Ti4+ (M = Co, Zn, Sn) cationic
mixtures were prepared by a sol-gel route. The materials were
heat-treated in the range 925-1000 C and characterized by x-ray
diraction (XRD), electron microscopy (EM) and vibrating sample
magnetometry (VSM). The results showed that the eect of the
substitution x was to lower the coercivity (Hc), owing to the decrease
of the magnetocrystalline anisotropy of the magnetoplumbite
structure of the BaM. In this regard Sn-Ti substitutions tended to
decrease Hc more rapidly than the Zn-Ti and Ti-Co substitutions, in
that order. Regarding the saturation magnetization (Ms), Ti-co
mixtures showed slightly better Ms than Zn-Ti substitutions; however,
the Sn-Ti showed a more marked decrease of Ms as a function of x.
The eect of the heat-treatment temperature was to decrease Hc due
to grain coarsening and consequently the appearance of an increased
volume of multi-domain particles. Contrarily, Ms improved as a result
of the increased crystallinity of the samples as observed from the
XRD peaks. Regarding the microstructure of the samples, it can be
said that crystallite size decreased below 100 nm as x increased and
this was a function of the cationic mixture. XRD studies showed that
phase constitution and crystallinity varied with heat-treatment
temperature and level of substitutions. In this respect Sn-Ti
substitutions needed higher treatment temperatures to yield materials
with adequate crystallinity and phase constitution.
DD6.8
HYDROTHERMAL SYNTHESIS OF A MICROPOROUS
ORGANIC-INORGANIC HYBRID FRAMEWORK
NH4FeO(C8 H4 O4 ) x[C8 H4 O4 (NH4)2 ]. Tabatha Whiteld, Xiqu
Wang, Allan J. Jacobson, Department of Chemistry, University of
Houston, Houston, TX.
Single crystals of a novel organic-inorganic framework,
NH4FeO(C8 H4 O4 ) x[C8 H4 O4 (NH4)2 ] 1 have been prepared by
hydrothermal synthesis in the presence of an oxidizing agent. The
structure was solved by single crystal X-ray diraction: space group
Pnma, a=17.696(2)A, b= 6.8745(7)A, c=11.930(1)A. The three
dimensional framework is constructed from chains of FeO units that
are cross-linked by 1,4-benzene dicarboxylate groups forming large
one dimensional channels. As synthesized, the compound contains
additional dicarboxylate groups that occupy disordered positions in
the channels and that can be removed by heating. The chemical
reactivity of 1 and its magnetic properties will be reported. The new
phase is closely related to the Cr(III) and V(III) analogs recently
reported by Ferey.
DD6.9
VARIANT OF THE FLUX SYNTHESIS METHOD AND CRYSTAL
STRUCTURE OF THE NEW COMPOUND Sm-Mn-Ge-O BY
SEM-TEM. Erick Juarez-Arellano, Ivonne Rosales, Gabriel
Gamboa-Espinosa, Armando Lara, Lauro Bucio, Eligio Orozco,
UNAM, Instituto de Fisica, Departamento de Estado Solido,
MEXICO.
One of the most common problems in solid state chemistry is to
dispose with the suitable synthesis method to generate novel
materials. In our case we are interested in synthesising single-crystals
of new materials with potential optical, electric or magnetic
applications. For this reason, we were in the necessity to design and
build a reective furnace, making a variation of the ux synthesis
method reported by Taviot-Guehe et al. In our reective furnace we
had synthetized the laminar monoclinic compound EuMnGe2 O7 and
recently the new compound with stoichiometric formula SmMnGe2 O7 .
We are interested in the last one due to the possible strong magnetic
spin couplings between the structure layers of the new compound. For
the synthesis, MnO2 , GeO2 and SmCl2 were mixed in stoichiometric
proportions, dried and the mixture was placed in an evacuated quartz
tube. The quartz tube was put inside the reective furnace and
treated at 750 Celsius degree for 10 days. After the thermal
treatment, many micro-crystals grew up on the quartz tube wall with
perfect crystalline appearance. The structural characterization of
those crystals was carried out using scanning electron microscopy
(SEM) and transmission electron microscopy (TEM). The
crystallographic study began with the analysis of the crystal shape
observed in SEM images. That crystal shape is in perfect agreement
with the crystal morphology that point group symmetry 4/mmm (D4h
according to Shoenies) has, belonging to the tetragonal system in
which there are two pairs of mutually perpendicular 2-fold axes
and/or symmetry planes. Analysing the electron diraction patterns
we conrmed the tetragonal symmetry in the new compound
SmMnGe2 O7 . Crystal structure characterization by TEM and SEM
result to be very a powerful tool when it is impossible to do it by
means of X-ray diraction measurements.
DD6.10
ANION INTERCALATION AND ANION EXCHANGE IN
BISMUTH COMPOUNDS. Masamichi Tsuji, Tokyo Institute of
Technology, Research Center for Carbon Recycling and Energy,
Tokyo, JAPAN; Makoto Yamaguchi, Institute of Research and
Innovation, Chiba, JAPAN; Satoshi Murao, National Institute of
Advanced Industrial Science and Technology, Institute for
Geo-resources and Environment, Tsukuba, JAPAN.
Divalent-cation-substituted bismuth(III) oxide
carbonates(Bi10x ,Mx )2 (O10x ,(OH)x )2 CO3 nH2 O where M denotes
alkaline earth and divalent transition metals, bismuth oxide Bi2 O3
and bismuth(III) nitrate basic 4BiNO3 (OH)2 BiO(OH) were studied
for anion intercalation and anion exchange. These bismuth
648
compounds have been discovered to show interesting anion
intercalation and anion exchange. These results are clearly dierent
from those of layered double hydroxides that have been extensively
studied for their potential use in catalysts, liquid waste treatment,
pharmaceuticals and other applications. These compounds may nd
new elds of application for anion separations and materials synthesis.
Relations between their structure and these chemical reactivities are
to be well investigated. The objective of this study was to gure out
the extent of anion interaction and/or exchange on these materials.
DD6.11
CONVERSION OF CALCIUM PHOSPHATES TO
HYDROXYLAPATITE. Alexander Veresov, Olga Sinitsina, Yuri
Kolenko, Moscow State University, Dept of Materials Science,
Moscow, RUSSIA; Valery Putlayev, Yuri Tretyakov, Moscow State
University, Dept of Chemistry, Moscow, RUSSIA.
-Tricalcium phosphate Ca3(PO4 )2 (alpha-TCP), dicalcium
phosphate CaHPO4 (DCP) are widely used as important components
of cement mixtures. The individual role of the calcium phosphates in
the cementing reactions is not absolutely clear. Moreover, reports on
the conversion of calcium phosphates to hydroxylapatite Ca10
(PO4 )6 (OH) 2 are controversial. For instance, some authors reported
rather fast degradation of TCP in the aqueous media while some
researches observed a very slow kinetics [1,2]. In the present study wet
methods of synthesis of hydroxylapatite have been used can be divided
into two groups: hydrolysis and hydrothermal technique. Depending
upon the technique, HAp materials with various morphology,
stoichiometry and level of crystallinity were obtained. Nanocrystalline
(size < 100 nm) powders of HAp with crystals shapes of blades
(similar to natural bone apatite), needles or equaxed particles were
synthesised. The inuence of temperature (20 - 200 C), ultrasound
treatment (for accelerating the reaction), starting precursors and pH
on the kinetics of hydrolysis of calcium phosphates were studied.
Support for this work from the Russian Foundation of Basic Research
(grant 02-03-33271) and the program \University of Russia" (grant
UR 06.03.006) are gratefully acknowledged. [1] K.S. TenHuisen, P.W.
Brown. Formation of calcium-decient hydroxyapatite from
-tricalcium phosphate. Biomaterials, 19 (1989), 2209-2217. [2] L.
Yubao, Zh. Xingdong, K. de Groot. Hydrolysis and phase transition of
alpha-tricalcium phosphate. Biomaterials, 18 (1997), 737-741.
DD6.12
TOWARDS AN ARSENIC ANALOG OF HITTORF'S
PHOSPHORUS: MIXED PNICTOGEN CHAINS IN Cu2 P10x Asx I2
X < 0.5. Buddhimathie Jayasekera, Jennifer A. Aitken, Mary Jane
Heeg, and Stephanie L. Brock, Department of Chemistry, Wayne
State University, Detroit, MI.
Transition metal pnictogen halides (pnictogen = Group 15 element)
are a small class of relatively unexplored materials in solid-state
chemistry. To date, compounds are limited to Cu-P-X (X = I, Br, Cl)
phases, and these can be classied as having neutral or anionic
phosphorus networks. The compound Cu2 P3 I2 contains neutral,
innite phosphorus chains, similar to those found in Hittorf's
modication of phosphorus. The phosphorus chains consist of fused
four- and ve-membered rings and between the chains are columns of
CuI in which Cu ions are distributed over multiple sites. We are
interested in exploring the eects of pnictogen substitution on the
structure and physical properties of these materials. We have
successfully synthesized several mixed Cu2 P10x Asx I2 phases in which
x < 0.5. These materials have been characterized by a combination of
single crystal and powder diraction techniques. The stability and
physical properties of these materials will be discussed in light of the
preferential ordering of As within the chains, and the increased
disorder in the Cu lattice.
DD6.13
SYNTHESIS OF SEVERAL
TUNGSTEN (VI) COMPLEX
PEROVSKITES, Ba(BIII 0:67 BV I 0:33 )O3 , BY THE POLYMERIC
PRECURSORS METHOD. Antonio F. Fuentes, Guillermo
Mendoza-Suarez, J.I. Escalante-Garcia, CINVESTAV-IPN Unidad
Saltillo, Saltillo, Coahuila, MEXICO; Ulises Amador, Dept. de
Quimica Inorganica y Materiales, Facultad de Ciencias
Experimentales y Tecnicas, Universidad San Pablo CEU, Boadilla del
Monte, Madrid, SPAIN.
Complex perovskites which combine ions in dierent oxidation states
sharing the octahedral positions available in this type of structures,
usually present interesting electrical and magnetic properties. In this
work we present a study of the synthesis of several hexavalent
tungsten containing perovskites, by the polymeric precursor method.
We selected a group of trivalent ions of interest (In, Y, Dy, Gd, and
Sm) to carry out this study. For the synthesis by the so-called Pechini
method, hydrated metal nitrates, barium carbonate and ammonium
paratungstate were weighed in the appropriate stoichiometric ratio
and dissolved in an aqueous citric acid solution. To promote
polymerization of the metal citrates by a polyesterication reaction,
ethylene glycol was added and the solutions heated to 80-100C. The
clear gels obtained were later dried at 150 C yielding solid resins of
high porosity. These precursors were then subjected to dierent
thermal treatments in high alumina crucibles to promote the
formation of the desired compounds. XRD, TGA, DTA and SEM were
used to follow transformation taking place in these precursors. Barium
carbonate and several tungstates of dierent stoichiometry were
identied as intermediates in the formation of the titled compounds.
Chemical reactions involving the trivalent ion seem to take place only
at high temperature, after barium carbonate decomposition. Structure
determination was carried out by using XRD data nding out that all
the compounds prepared, present a cubic symmetry. It is the rst
time that some of these compounds are prepared and their structures
studied.
DD6.14
CUBIC MESOSTRUCTURED SEMICONDUCTORS IN
SINGLE-CRYSTAL FORM. Pantelis N. Trikalitis and Mercouri G.
Kanatzidis, Department of Chemistry, Michigan State University,
East Lansing, MI.
The next important step in the development of mesostructured
materials is to discover synthetic routes and compositions that give
samples with large continuous domains in the form of single crystals
or lms. We will present a reliable and facile system for making
relatively large (2 m) single crystal particles of platinum selenido
mesostructured materials with highly organized cubic structure,
accessible pores and semiconducting properties. We have observed
that2+ building blocks40with square planar bonding topology such as
Pt and [Sn2 Se6 ] , in combination with the long chain pyridinium
surfactants (Cn PyBr, n=18, 20) favor faceted single crystal particles
with the highest possible space group symmetry, Ia 0 3d. The
precisely dened nature of these and highly symmetric particle
morphology imply that the \walls" in these materials might be
crystalline. To address this important issue, high resolution X-ray
experiments using synchrotron radiation as well as detailed
Transmission Electron Microscopy (TEM) studies are currently in
progress and will be presented. The optical, infrared, Raman
spectroscopic characterization of these materials along with their
reversible ion-exchange properties will be presented.
DD6.15
STRUCTURE OF Na-4-MICA AS AFFECTED BY EXCHANGE
WITH VARIOUS CATIONS. Man Park, Jin-Ho Choy, School of
Chemistry and Molecular Engineering, Seoul National University,
KOREA; Dong Hoon Lee, Sang Su Kim, Choi Jyung, Department of
Agricultural Chemistry, Kyungpook National University, KOREA;
Sridhar Komarneni, Materials Research Laboratory, The Pennsylvania
State University, PA.
Recent novel solid-state synthesis of phase-pure Na-4-mica enables us
to elucidate the fundamental characteristics of this swelling mica such
as structural characteristics by powder X-ray diraction (XRD)
analysis, reversible dehydration-hydration behavior up to 800C, and
cation exchange and selectivity behavior. This study deals with the
structural aspects of Na-4-mica as aected by exchange with various
kinds of cations. Exchangeable sodium cations in the interlayers of
Na-4-mica could be exchanged by alkali cations, alkali-earth cations,
and divalent transition metal cations. Stability of layer structure was
signicantly aected by the size and valency of exchangeable cations.
Large divalent cations like Ba and Pb ions led to a signicant
deterioration of layer structure. Furthermore, swelling property also
exclusively depended on the size and valency of the incoming cation.
Na-4-mica accommodates many numbers of exchangeable cations
within its interlayer space due to its extraordinarily high layer charge
density. The spatial arrangement of exchangeable cations exclusively
depends on their size and valency, which is clearly reected in the
XRD patterns. This study enables one to understand and explain
cation exchange behavior of Na-4-mica such as xation of radioactive
cations through layer collapse and preferential uptake of divalent
cations.
DD6.16
PHOTOCHEMICAL REACTIVITY OF Sr2 (Tax Nb10x )2 O7 (0.8 < x
< 1) AS A FUNCTION OF COMPOSITION. Jennifer L. Giocondi,
Ariana M. Zimbouski, Shahrzad Samadzadeh, Gregory S. Rohrer,
Carnegie Mellon University, Dept of Materials Science and
Engineering, Pittsburgh, PA.
Recent observations of photochemical reactions on BaTiO3 surfaces
suggest that internal dipolar elds can drive photogenerated electrons
and holes to dierent locations of the surface and this leads to a
spatial separation of the reduction and oxidation products. If this
spatial separation of charge carriers and reaction products reduces
both the rate of electron-hole recombination and the rate of the back
reaction of the reduced and oxidized species, then it is a potentially
649
important mechanism for increasing the eciency of photocatalysts.
To investigate the role of static dipolar elds in materials that are
active water photolysis catalysts, we have examined the
photochemical activity of compositions in the system Sr2
(Tax Nb10x )2 O7 with 0.8 < x < 1. Both Sr2 Nb2 O7 and Sr2 Ta2O7
have a layered perovskite structure but, while Sr2 Nb2 O7 is
ferroelectric at room temperature, Sr2 Ta2 O7 is not. The two end
members form a complete solid solution with constantly varying Curie
temperature (x = 0.91 has Tc = RT) and dielectric constant. Using
microscopic analysis of photochemically deposited reaction products,
systematic changes are observed in the reactivity of this system and
will be discussed in terms of the changing band gap (which alters light
absorption) and the changes in the internal polarization as the
material transforms from a ferroelectric to a paraelectric.
DD6.17
SYNTHESIS OF SILYLATED -ZIRCONIUM PHOSPHATE AND
ITS THERMAL BEHAVIOR. Takahiro Takei, Emi Aaraya, Nobuhiro
Kumada, Nobukazu Kinomura, Yamanashi Univ, Center for Crystal
Science and Technology, Faculty of Engineering, Yamanashi, JAPAN;
Hirokazu Nakayama, Mitsutomo Tsuhako, Kobe Pharmaceutical Univ,
Kobe, JAPAN.
Silylated -zirconium phosphate was synthesized and its thermal
behavior was examined. Silylated -zirconium phosphate
(-Zr(HPO4 )2 1H2 O) was synthesized to form inorganic-organic hybrid
material via two steps as followings; intercalation of alkylmonoamine
and silylation of some kinds of chlorosilane. The amine intercalation
for layered -zirconium phosphate was carried out in order to form
the expanded interlayer space sucient for approach of chlorosilane
molecules. Silylation reaction was actually advanced only in the
intercalated zirconium phosphate. From powder XRD patterns, the
d-spacing of 001 diraction line for -ZrP as starting material,
intercalated and silylated compounds were estimated at around 0.75,
2.76 and 1.60 nm, respectively. From this result, amine molecules in
the intercalated compound were found to be formed bilayer texture,
though those in silylated compound monolayer. The synthesized
compound of silylated -zirconium phosphate was regarded as
inorganic-organic hybrid material, and it was considered to become
porous by decomposition of intercalated amine and inxed silane 2
molecules. Heating at 400 C, specic surface area of around 70 m /g
was obtained as a result. Since the decomposition of organic species is
aectable for its porous and adsorption properties, thermal behavior
of silylated -zirconium phosphate was examined via high
temperature XRD, NMR and TEM. The thermal behavior was
concluded
as followings. In the silylated compound red at 100 1000C, the d-spacing decrease
with ring temperature via three
stages. Up to around 300C, silane coexists amine. At the range of
300 - 600 C, interlayerspace pillared via decomposition of amine.
Further higher the 600 C, silane decomposition occurred and silica
formed by polymerization and oxidation of silane.
DD6.18
HETEROGENEOUS DESIGN: CONCENTRATION FIELDS
DETERMINATION WITH THE UNIQUE CRYSTALLIZATION
SCHEMES AND MICROSTRUCTURES. Vasily Lutsyk, Vera
Vorob'eva, Anna Zelenaya, Buryat Scientic Center, Physical
Problems Dept, Ulan-Ude, RUSSIA; Julia Arzhitova, Buryat Univ,
Dept of Physics, Ulan-Ude, RUSSIA.
A special language of the applied four-dimensional geometry has been
elaborated to simulate and analyze the isobaric phase diagrams of
four-component systems with the experimental data on binary,
ternary and quaternary invariant points. Ruled hypersurfaces with the
horizontal generating simplexes may be approximated as the skewed
hyperplanes with the linear one-dimensional boundaries or by the set
of equations for their directing and generating elements. Two types of
ruled hypersurfaces exist in T-x-y-z diagram: with one-dimensional
generating segment and with two-dimensional generating plane. As a
result of their projection and the phase regions projection a
tetrahedron of concentration has been divided into the elds with the
dierent crystallization schemes of the initial melt. At any
temperature the quantity of every type of crystals (primary,
secondary, ternary, quaternary, peritectic (produced in bi-, mono- and
invariant reactions)) have being calculated. In two-phase regions of
ternary and quaternary systems the tie-lines are determined as a
result of curvature analyses for the bordering lines and surfaces.
Special algorithms for three-phase region analysis permit to x the
temperature at which an eutectical reaction is being changed for the
peritectical one, and vice versa. Concentration elds are three-, two-,
one- and zero-dimensional. Few of them may be additionaly divided
for domains where the reagent of peritectic reaction interact with the
melt preliminary in one type of dispersion. The concentration elds
and domains are characterized by the structural diagrams in which
the quantity of every microstructural element is calculated and shown.
DD6.19
A SERIES OF NEW LOW-DIMENSIONAL TIN OXALATES AND
PHOSPHATES: BING-1,2,3,4,7,8. Tolulope O.Salami, Peter Y.
Zavalij and Scott R.J. Oliver, State University of New York at
Binghamton, Dept of Chemistry, Binghamton, NY.
Our ongoing research involves the study of solvothermal systems for
the isolation of new tin (II) and tin (IV) based extended materials.
Anionic structural directing agents (A-SDAs), such as
tetraouroborate, were investigated in an attempt to isolate cationic
materials with tunable pore/channel size and shape. These materials
have potential application in anion exchange, anion trapping, or as
solid-state precursors for other compounds. We have discovered
several new extended structures, such as BING-2 [KSn(C2 O4 )F6 ] (tin
oxalate potassium uoride). This layered structure was isolated from
a reaction mixture of pyridine, H2 O, HF, SnC2 O4 and KBF4 , The
structure was resolved using single-crystal X-ray diraction. This
structure, and others discovered from related systems, will be
discussed, along with their materials characterization.
DD6.20
CLATHRATED STATE OF OXYGENIC RADICALS O0 AND O02
IN NANO-POROUS CRYSTAL 12CaOa;b
CW
17Al2O3 STUDIED BY
b,
AND PULSED EPR.
Satoru
Matsuishi
,
Katsuro
Hayashi
Masahiro Hiranob and Hideo Hosonoa;b; a Materials and
Structures
Laboratory, Tokyo Institute of Technology, JAPAN; b Hosono
Transparent Electro-Active Materials Project, ERATO, JST, JAPAN.
We found that active oxygen species O0 and O02 were generated in
polycrystalline 12CaO17Al2O3 (C12 A7 ) by heating in dry-oxygen
atmosphere. The crystal structure of C12 A7 is characterized
by a
positively charged lattice framework [Ca24 Al28 O64 ]4+ having 12
crystallographic cages per unit cell (I43d with a = 1.199 2nm)
with a
free space of 0.4 nm in diameter. The remaining two O 0 , referred
to as \free oxygen", are clathrated in the cages to maintain charge
neutrality. The oxygenic radicals are likely to substitute for free 0
oxygen. EPR analysis of the C12 A7 powder indicates that the O2
tumbles in the cage at 300 K and is adsorbed on Ca2+ ion below
100 K. However, no more information about clathrated state of the
radicals has been obtained. Recently, we obtained the single crystals
of C12 A7 grown by FZ method, and
found the generation of a large
amount of radicals in these (821020 cm03 , [O0 ]/[O02 ] =1). The
angular-dependence of cw-EPR spectrum at 20 K for the single
crystal was analyzed to determine orientation of the radicals with
respect
to the crystal axis. The cage in C12 A7 consists of 6 Ca2+ , 8
Al3+ and 16 O20 . One 2-fold axis (C2 ) parallel
to crystal axis crosses
center of the cage. On the assumption that O02 is clathrated in the
cage, the analysis of EPR spectra revealed that O02 is adsorbed on
either 2 Ca2+ ions on the C2 axis, and then O-O bond of O02 is
perpendicular to the C2 . Pulsed EPR measurements of C12 A7
powders were performed
to obtain ESEEM pattern reecting a
distance between O02 and neighboring magnetic Al nuclei. The
separation between O02 and Ca2+ obtained through simulation of
ESEEM pattern, which agreed well with the conclusion obtained from
the cw-EPR on the single crystal.
DD6.21
SYNTHESIS OF Ru-Sr-Zr OXIDE ELECTRICAL CONDUCTOR
FROM PRECURSOR SOLUTION. Tadashi Ishigaki, Keishi Nishio,
Takashi Nakajima, and Toshio Tsuchiya, Department of Materials
Science and Technology, Tokyo University of Science, Chiba, JAPAN.
Some metal oxide electrical conductors can be applied to an electrode
for many applications. It has been reported that ruthenium oxide
shows electronic conduction and electronic-protonic mix conduction,
and ruthenium-strontium oxides have some unique characteristics
such as supper conduction (Sr2 RuO4 ), and ferromagnetic (SrRuO3 ).
Yttria stabilized zirconia (YSZ) is used for the electrolyte of a solid
oxide fuel cell (SOFC) because it has chemical stability and high
oxide ion conduction at a high temperature. Some studies have been
reported about SrZrO3 , too. From these facts, three elements
Ru-Sr-Zr oxides are expected to show new properties. There is few
reports structural analyses of Ru-Sr-Zr oxide and Ru-Zr oxide and
their properties. Generally, a sol-gel process uses metal alkoxides as
raw materials for preparing precursor solution. However some kinds of
alkoxides are very expensive. This process has received much
attention due to the potentials not only precise control of chemical
stoichiometry, but also homogeneity, low-temperature processing. On
the other hand, on this process, it is dicult to control hydrolysis
speeds of alkoxides in the solution. In this study, Ru-Sr-Zr oxides were
prepared from precursor solution consisted with metal salts, chelate
agent and organic solvents. New diractions could be observed around
45 and 56 degree in the diraction pattern of the oxide
(Ru:Sr:Zr=1:2:1). This material showed that high electric
conductivity. It is expected to nd new materials.
650
materials exhibit long-range along the b axis, as indicated by
transmission electron microscopy data. High-resolution scanning
electron microscopy studies show that morphologies of the products
are nanorods or nanobers, depending on the cross-linking reagents
used in the preparation. Thermogravimetric analyses
indicate that
these nanomaterials are thermally stable to 700C.
DD6.22
THE TERNARY SYSTEM Li2 O { Sb2 O5 { CuO.
Mara A. Castellanos R., M. Sonia Trujillo T., Depto de Q. Analtica,
Facultad de Qumica, UNAM, Mexico D.F., MEXICO.
In the search for more Cu-containing complex oxides, this work gives
some additional information about the ternary diagram. The phase
formation in this system has been studied by the ceramic method at
temperatures below 1200 C. Powder X-ray diraction data was
recorded using a SIEMENS D5000 diractometer. This data was used
both for phase identication and as an indication of the purity of the
synthesized compounds. Previously, we had studied the formations of
new phases on the binary joins: a) Li3 SbO4 - CuO(1), the crystal
structure of the phases in this join has been fully determined
now(2,3,4) and b) LiSbO3 - CuO(5), the structural powder
characterization of the solid solution and a new phase found in this
system is in progress. Details of the phase diagram results will be
presented.
(1) M.A. Castellanos R. et al, Mat. Res. Soc. Symp. Proc., (MRS),
453, 159-164, 1997
(2) Sylvain Bernes et al., Acta Cryst., C57, 883-884, 2001
(3) Sonia Trujillo T. et al., J. Solid State Chemistry, 156, 321-324,
2001
(4) J.M.S. Skakle et al., J. Solid State Chemistry, 131, 115-120, 1997
(5) M.A. Castellanos R. et al, International Materials Research
Congress, 1998
This work was supported by CONACyT whose sponsorship is
acknowledged
DD6.25
DD6.23
NEW METHOD OF PREPARATION OF SUPERIONIC BaSnF4 .
Georges Denes, A. Muntasar and Tony Retrif, Concordia University,
Dept of Chemistry and Biochemistry, Laboratory of Solid State
Chemistry and Mossbauer Spectroscopy, Laboratories for Inorganic
Materials, Montreal, Quebec, CANADA.
BaSnF4 is a high performance uoride-ion conductor, and it is
isostructural with -PbSnF4 , the latter being the highest performance
uoride-ion conductor known to date. The exceptionally high mobility
of the uoride ions in the -PbSnF4 structure has been ascribed to
the2+the disturbance brought about by the replacement of half the
Pb ions in the uorite-type structure of -PbF2 by covalently
bonded Sn(II), and to the presence of a vacant uoride-ion layer
between two adjacent tin layers. BaSnF4 was prepared rst by one of
us (GD) by direct reaction between SnF2 and BaF2 at 500 C, under
dry conditions, in inert
atmosphere. For the synthesis of -PbSnF4 in
dry conditions, 250C should be used since phase transitions take
place at higher temperatures. In addition, -PbSnF4 can also be
prepared by two wet methods: (i) -PbSnF4 (aq1) precipitates when a
solution of Pb(NO3 )2 is added to a solution of SnF2 , however, BaSnF4
cannot be prepared by the same method, using Ba(NO3 )2 , and (ii)
-PbSnF4 (aq2) is obtained by reaction of solid -PbF2 with an
aqueous solution of SnF2 , however, BaSnF4 cannot be prepared by the
same method, using BaF2 . Recently, a new method of preparation was
discovered in our laboratory, by leaching in water of barium tin(II)
chloride uorides, also newly discovered in our laboratory. These new
barium tin(II) chloride uorides are prepared by precipitation either
by adding a solution of SnF2 to a solution BaCl2 (Sn ! Ba) or
vice-versa (Ba ! Sn), for a X molar ratio of BaCl2 in the reaction
mixture. For the barium tin(II) chloride uorides prepared at high X
values, and only if Ba ! Sn, the precipitate contains, in some cases,
some BaSnF4 , together with either stoichiometric BaSnClF3 .0.8H2 O,
or with the non-stoichiometric Ba10x Snx Cl1+y F10y solid solution.
Pure BaSnF4 is obtained on stirring the precipitate in water for 24
hours, only for (0.735<X<0.870) and if Ba ! Sn. Some of the
properties of BaSnF4 prepared by the two methods have been
investigated and compared to one another.
DD6.24
SYNTHESIS OF METAL-DOPED CRYPTOMELANE
NANOMATERIALS
USING CROSS-LINKING REAGENTS.
Jia Liuaa;d
, Juna Caib, Xiongfei Shena , Steven L.
Suiba;b;c , Mark
Aindow , c Institute of Materials Science, b Department
of
Chemistry, Department of Chemical Engineering, d Department of
Metallurgy and Materials Engineering, University of Connecticut,
Storrs, CT.
Three cross-linking reagents (PVA, glycerol and glucose) have
successfully been used to synthesize non-doped and metal-doped
nanosized cryptomelane materials via a solid-state preparation
method.
The 2x2 tunnel structure of cryptomelane was formed at
500C. FT-IR data show that no cross-linking reagents residue were
found in the products after the reactions were complete at 800 C. The
metal dopants used were Fe, Ag, Co, Cu, Ni, and Zn. XRD data show
that Fe and Co cations can be doped into the materials without the
formation of additional phases. The tunnel structures of the nanosized
PREPARATION AND PROPERTIES OF Li-Mn-O-F COMPOUNDS.
Hanxing Liu,Yale University, Department of Electrical Engineering,
Wuhan University of Technology, State Key Laboratory of Advanced
Technology for Materials Synthesis and Processing, Wuhan, P.R.
CHINA; Junlei Xia, Shixi Zhao, Chen Hua, Shixi Ouyang, Wuhan
University of Technology, State Key Laboratory of Advanced
Technology for Materials Synthesis and Processing, Wuhan, Hubei,
P.R. CHINA.
Li-Mn-O-F prepared by the sol-gel method has perfect crystal
formation.The crystal particle size of the material was medium and
distributed uniformly. The substitution of F for O increased the
specic capacity of the material at the cost of the recycle. Our
explanation of the results is that the F decreased the valence of Mn,
that is, more Mn3+ and less Mn4+ existed in the material. As we all
known, the increase of Mn3+ will elevate the initial special capacity
and Mn3+ is the original reason of Jahn-Teller eect which caused
the poor recycle of the cathode material by the micro-deformation of
the crystal structure. In addition, the applied measurement of the
crystal lattice is also the reason of the poor recycle. Therefore, Simple
F-substitution can't improve the initial specic capacity and the
recycle but if the method was combined with cation substitution, the
satised results maybe be obtained.
DD6.26
Na+/H+ TOPOTACTIC EXCHANGE ON Na6 Nb6 W4 O30 WITH
TTB-LIKE STRUCTURE: THE SERIES Hx Na60x Nb6 W4 O30 .
Flaviano Garca-Alvarado, Alois Kuhn and Carlos Reparaz,
Universidad San Pablo-CEU, Departamento de Qumicas, Boadilla del
Monte, Madrid, SPAIN.
In the NaNbWO3 -WO3 -Nb2 O5 system there is an extended region
where structures of the existing phases are related to the tetragonal
tungsten bronze (TTB) structure [1]. On the NaNbO3-WO3 join, a
single TTB structure has been observed [1,2]. The composition of this
phase is Na6Nb6 W4 O30 , implying a TTB structure where all
tetragonal and pentagonal cavities are lled by sodium atoms, while
niobium and +tungsten
atoms are disordered over the same octahedral
site. Easy Na /H+ ion exchange occurs in acidic aqueous solutions,
yielding well crystallised powder samples of a series that can be
formulated as Hx Na60x Nb6 W4 O30 . A TTB-related superstructure is
produced upon the incorporation of H+ , as conrmed by X-ray and
electron diraction patterns. Thermal decomposition of the ion
exchanged materials has been studied by both TG and DTA analysis
which conrm the presence of protonic species in the exchanged
samples. Other features found at high temperature have been
investigated by means of high temperature X-ray diraction
experiments. On the other hand high
ionic conductivity has been
found at temperatures close to 90C under a water saturated
atmosphere. References [1] B.-O. Marinder, Chemica Script, 26,
547-560 (1986). [2] T. Horlin, B.O. Marinder and M. Nygren, Rev.
Chim. Miner., 19, 231-238 (1986).
DD6.27
DESIGN OF NEW OXIDE CERAMIC MATERIALS AND
NANOCOMPOSITES WITH MIXED CONDUCTIVITY BY USING
MECHANICAL ACTIVATION ROUTE. Vladimir V. Zyrianov, N.F.
Uvarov, V.G. Kostrovskii, Inst. of Solid State Chem. and
Mechanochemistry, Novosibirsk, RUSSIA; Vladislav A. Sadykov, T.G.
Kuznetsova, V.A. Rogov, E.B. Burgina, V.I. Zaikovskii, V.V.
Kriventsov, D.I. Kochubei, G.S. Litvak, Boreskov Inst. Catalysis,
Novosibirsk, RUSSIA; Stylianos Neophytides, Inst. of Chem. Eng. &
High Temperature Proc., Patras, GREECE.
Mechanical activation (MA) of solid reagents is known to be a
promising approach to design of new ceramic materials and
nanocomposites including synthesis of new metastable compounds
with unusual structural features which could not be obtained by
another routes. The phase diagrams of systems obtained via this route
strongly dier from the equilibrium ones. Thus, around 40 new
metastable compounds in binary oxides of heavy metals are obtained
via this route. Densication of those powdered samples by sintering in
the 600-1100 K temperature range is accompanied by annealing of
metastable phases generating \core-shell" nanocomposites with
oxygen transport properties dierent from those of traditional
materials. This work presents results for solid solutions in the
Sr(Ba)-Fe(Co)-O and Sr(Ba, Ca)-Bi(Sb)-O systems obtained via MA
route now considered as promising materials for high oxygen ux
membranes. Structural/microstructural features of those systems
651
characterized by TEM, XRD, EXAFS and Raman spectroscopy are
compared with the data on the mixed conductivity of compacted
(density > 95%) materials in the 600-1100 K range as well as the
oxygen mobility estimated by thermogravimetry, H2 TPR and
isothermal reduction by CO. High-temperature interaction of those
materials with methane is also studied by using pulse/ow
microcatalytic experiments. Properties of those materials
nanocomposites with such oxides as Fe2O3, BaTiO3, BaBiO3 are
elucidated as well. Prospects of those materials application as
oxygen-separating membranes in reactors of methane selective
oxidation into syngas by the oxygen of air are considered. This work is
in part supported by INTAS-01-2162 and RFBR-02-03-33330 projects.
DD6.28
ULTRATHIN, PROTECTIVE COATINGS OF
POLY(O-PHENYLENEDIAMINE) AT NANOSTRUCTURED
METAL OXIDE ELECTRODES: MAKING MnO2 STABLE IN ACID
ELECTROLYTES. Jerey Long, Christopher Rhodes, Amanda
Young, Debra Rolison, Naval Research Laboratory, Washington, DC.
Manganese oxides (MnO2 ) have been extensively investigated for
energy storage devices including Zn/MnO2 alkaline cells and lithium
and lithium-ion batteries. Charge storage at MnO2 is accomplished
by
a cation-electron
insertion mechanism, where cations, such as H+ or
+
Li , are supplied to the metal oxide surface from the supporting
electrolyte. Electrochemical properties such as charge/discharge rate
and reversibility are optimized when MnO2 is rendered in
nanostructured, mesoporous forms, such as aerogels and ambigels.
Manganese oxides have more recently been investigated as
ultracapacitor electrodes in aqueous electrolytes. Metal oxides
typically exhibit maximum ultracapacitance
in acidic electrolytes,
where high concentrations of H+ are available to the electrode. The
performance of MnO2 as an ultracapacitor, therefore, is limited, as
MnO2 undergoes an electrochemical dissolution process with even
mildly acidic electrolytes, forming soluble Mn (II). Dissolution is
exacerbated for high-surface-area forms of MnO2 . We+ are exploring
electrochemical strategies for depositing ultrathin
H -conducting
polymer lms onto high-surface-area (> 200 m2 g01 ) MnO2
electrodes. The oxidative electropolymerization of o-phenylenediamine
(OPD) results in ultrathin (7-9 nm), self-limited polymer coatings
when deposited from basic aqueous electrolytes. When cycled in acidic
electrolyte poly(OPD)-coated MnO2 exhibits no electrochemical
features that are indicative of reductive dissolution. Well-dened
faradaic features are observed that correspond with the
electrochemical-protonation reactions observed for more conductive
forms of poly(OPD). Based on preliminary spectroelectrochemical
characterization
we propose an electrochemical gating mechanism,
where H+ -insertion at the underlying MnO2 electrode is coupled to
and restricted by the electrochemical protonation reaction of the
overlying poly(OPD) coating. This strategy will be expanded to
include other acid-unstable oxides, such as V2 O5 and Fe2 O3 , as well
as other H+ -conducting polymer coatings.
DD6.29
SUPERPROTONIC PHASE TRANSITION OF CsHSO4 : A
MOLECULAR DYNAMICS SIMULATION STUDY WITH NEW
MSXX FORCE FIELD. Calum Chisholm, Lan Yang, Sossina M.
Haile, Dept of Materials Science, California Institute of Technology,
Pasadena, CA; Yun Hee Jang, William A. Goddard III, Materials and
Process Simulation Center, California Institute of Technology,
Pasadena, CA.
The superprotonic phase transition (monoclinic ! tetragonal; 414 K)
of cesium hydrogensulfate has been simulated by molecular dynamics
as a function of temperature over the range 298 K to 723 K. The
simulations employed a \Drieding" based force eld, constant NPT
conditions, and a 2 x 2 x 2 supercell comprising 32 CsHSO4 units.
The initial Drieding default values for the force eld parameters of Cs,
S, O, and H were adjusted to reproduce quantum mechanically
derived properties including structure, bonding energy, and
frequencies of a CsHSO4 monomer. Each hydrogen atom was treated
as bonded exclusively to a single oxygen atom (proton donor), with
hydrogen bonds extending to other nearby oxygen atoms (proton
acceptors). Proton diusion (i.e. proton jumps) between oxygen
atoms, as normally occurs in superprotonic CsHSO4 , was not
permitted. Nevertheless, this series of simulations showed a clear
phase transition at 598 K, as evidenced by signicant changes in
lattice parameters, unit cell volume, X-ray powder diraction
patterns, and molar enthalpy,
as well as the degree of reorientation of
the hydrogensulfate (HSO04 ) groups. Independently, the importance of
the hydrogen torsional barrier height, hydrogen bond strength, and
oxygen charge distribution to the phase transition was probed. These
results show (1) that proton diusion is not essential to the existence
of a superprotonic phase transition (2) that the transition behavior is
nevertheless sensitive to the details of the hydrogen bonding and (3)
suggest that new superprotonic conductors can be \discovered" by
computational approaches.
DD6.30
PREPARATION AND CHARACTERIZATION OF Pb2 SnF6 , THE
FIRST LEAD(II)-TIN(II) FLUORIDE THAT IS A SUPERSTRUCTURE OF -PbF2 . Raimondo Calandrino, Anthony Collin,
Georges Denes, Morgane Logiou, and M. Cecilia Madamba, Concordia
University, Department of Chemistry and Biochemistry, Laboratory of
Solid State Chemistry and Mossbauer Spectroscopy, Laboratories for
Inorganic Materials, Montreal, Quebec, CANADA.
Both -PbF2 and all phases of SnF2 are good uoride-ion conductors,
however, the highest performance materials are mixedlead(II)-tin(II)
uorides. The PbF2 /SnF2 system has been studied extensively in our
laboratory. It contains four kinds of materials: (i) a -PbF2 -type
cubic Pb10x Snx F2 solid solution for x = 0 - 0.30, (ii) a
-PbSnF4 -type tetragonal Pb10x Snx F2 solid solution for x = 0.31 0.50, stoichiometric PbSnF4 at x = 0.50, and metastable PbSn4 -F10
at x = 0.80. In addition, PbSn4 undergoes a large number of phase
transitions when temperature is varied, upon ball-milling, and
depending on the reaction medium by wet methods. All the above
phases have crystal structures related to that of uorite-type -PbF2 ,
with either cubic disordered structures or lower symmetry unit-cells
for ordered structures. It should also be noted that all the above
phases are the highest performance uoride-ion conductors known up
to date. In the present work, a new phase, Pb2 SnF6 , has been
prepared and characterized. It is prepared by the reaction of solid
-PbF2 with a solution of SnF2 upon stirring for a long time (one day
or more). Surprisingly, X-ray diraction shows that its unit-cell is a
supercell of -PbF2 , in contrast with all the other known phases in
the PbF2 /SnF2 system.
SESSION DD7: FILMS AND CATALYTIC
MATERIALS
Chairs: Allan J. Jacobson and Terrell A. Vanderah
Wednesday Morning, December 4, 2002
Back Bay C (Sheraton)
8:30 AM *DD7.1
EPITAXIAL STABILISATION IN THIN FILMS OF OXIDES.
Andrey R. Kaul, Oleg Yu. Gorbenko, Igor E. Graboy, Mikhail A.
Novojilov, Alexei A. Bosak, Anton A. Kamenev and Sergey V.
Samoilenkov, Moscow State University, Department of Chemistry,
Moscow, RUSSIA.
In the growth of thin epitaxial lms of oxides, such as high Tc
superconductors, CMR manganites, ferroelectrics and other new
electronic materials, the formation of some phases (primary or
secondary ones) occurs often at the thermodynamic conditions (T,
total pressure, Po2 , composition) which are far beyond the stability
range of corresponding phase in the bulk form (polycrystalline or
single crystal). These phenomena, reviewed in the paper, are
explained by epitaxial stabilization (ES) of the growing phase due to
its structural coherency to the substrate or to the surrounding lm
matrix. A thermodynamic model of ES based on the Dankov { Van
der Merwe principle is discussed and it is shown that the lattice
coherence at the lm/substrate interface as well as free energy
dierence of unstable and equilibrium phases are the main factors
determining the phenomenon. While earlier work could only interpret
a posteriory the occasional formation of unstable phases as
manifestation of the ES, now the later becames ecient tool to obtain
thin lms of otherwise unstable compounds what opens new facilities
for materials chemistry. This is illustrated by recent author's results
obtained using XRD and HREM of MOCVD derived thin lms and by
literature data. In particular, the ES-expansion of morphotropic
perovskite and hexagonal series of rare earth compounds REBO3
(B=Mn, Fe, Ga, In), the ES of high oxidation states of 3d metals in
REBO3 (B=Ni, Co, Cu) as well as the epitaxial synthesis of the
compounds unknown in bulk is regarded. The use of ES for selective
epitaxy in the preparation of heterostructures is also described.
9:00 AM DD7.2
THIN FILM SYNTHESIS OF HEXAGONAL RARE-EARTH
MANGANESE OXIDES. Balasubramanian Kavaipatti, Antoine
Berret, and Paul A. Salvador, Carnegie Mellon University,
Department of Materials Science and Engineering, Pittsburgh, PA.
The hexagonal rare-earth (RE) manganese oxides are an interesting
class of ferroic materials in which both magnetic and electrical
long-range interactions can coexist. The prototype structure for these
ferroelectric compounds is the non-close-packed, two-dimensional
LuMnO3 structure, which is a distorted derivative of the
centrosymmetric hexagonal YAlO3 structure. In the REMnO3 system,
the hexagonal ferroelectrics are only stable for RE cations smaller
than Dy. In this work, various strategies for attaining the metastable
ferroelectrics for the larger rare-earth containing compounds are
652
investigated. The fundamental motivation is to develop a general
synthetic procedure for attaining new compounds in this structural
family of inorganic materials. The principle strategy is to use epitaxial
stabilization during thin lm growth to synthesize the metastable
materials. Because of the two-dimensional character of this crystal
structure, certain challenges arise in stabilizing new materials, and
these will be discussed. In this work, we describe how metastable
materials can be synthesized. Thin lms of REMnO3 were deposited
by pulsed laser deposition upon single crystals of (111) MgO,
thin-lms of (111) Pt and (001) or (110) hexagonal-YMnO3 , and
polycrystalline YMnO3 . It is demonstrated that the chemical nature
of the substrate surface plays the preeminent role in stabilizing the
metastable phases, and that new materials can be grown through
rational synthetic routes. Structural characterizations were carried out
by X-ray and electron diraction techniques, and these will be
discussed in relation to the new metastable phases that were grown.
The applicability of this synthetic approach to developing other new
compounds in this family of hexagonal structures will also be
discussed.
9:15 AM DD7.3
HIGH QUALITY ERBIUM-DOPED BISMUTH-BASED OXIDE
FILM FOR PLANER WAVEGUIDE AMPLIFIER PREPARED BY
SPUTTERING. Susumu Suzuki, Yuki Kondo, Tatsuo Nagashima,
Setsuro Ito, Research Center, Asahi Glass Co., Ltd., Yokohama,
JAPAN.
In optical telecommunication, Er-doped amplier is one of key
components for wavelength division multiplexing(WDM). We have
already reported that Bi2 O3 based Er-doped ber and waveguide are
advantageous in higher amplication eciency due to higher Er
concentration and in broader amplication bandwidth[1,2]. In the
present work, we have deposited high quality Bi2 O3 based Er-doped
lms for planer waveguide amplier by sputtering. It was found that
both the amount of residual water and the Er concentration in lms
mainly aected the life time of the uorescent light at 1530 nm. We
have obtained the lm with the life time over 3 msec, the same as that
of bulk glass prepared by the melting method. Bi2 O3 based Er-doped
lms were deposited on soda lime silicate glass at 200 C by RF
sputtering from sintered targets of Bi2 O3 -SiO2 -Ga2 O3 -Er2 O3 -Yb2 O3 ,
where Bi2 O3 , SiO2 , Ga2O3 composed a glass matrix and Er2 O3 ,
doped with 0.5-3.0 mol%, yielded
uorescence. Ar/O2 was introduced.
The input power was 3W/cm2 . The life time of the uorescent light at
1530 nm was measured using pulsed laser at 980 nm by a
semiconductor laser diode. The life time increased with decreasing
amount of residual water in lms. The decrease in life time was
ascribed to the nonradiative decay of the excited photons via
multiphonon relaxation due to OH stretching vibration. It was found
that the residual water was reduced by heat treatment of lms at over
400 C in vacuum, in addition to using higher ultimate vacuum before
deposition. The life time also showed compositional dependence, i.e.,
the life time showed a maximum in the lm from a 1 mol%Er2 O3
target. This implied that the composition quenching might occur in
the lms as in bulk glass. [1] N. Sugimoto, et al., 11th OAA2000, OSA
Technical Digest (Optical Society of America, 2000), PDP3, pp1-3. [2]
Y. Kondo, et al., 11th OFC2002, OSA Technical Digest (2002), TuB4.
9:30 AM DD7.4
THIN FILMS OF TITANIUM DIOXIDE PREPARED BY
CHEMICAL ROUTES USING NOVEL PRECURSORS. K. Shalini,
Materials Research Centre; S. Chandrasekaran, Department of
Organic Chemistry; S.A. Shivashankar, Materials Research Centre,
Indian Institute of Science, Bangalore, INDIA.
Titanium dioxide thin lms have been investigated extensively in
recent years for application in photovoltaics and as catalytic surfaces.
These applications call for large area lms of the anatase phase with
uniform thickness, for which chemical vapor deposition (CVD) is most
suitable. The CVD of thin lms of TiO2 has most often been carried
out using its tetrachloride or alkoxide as the precursor. The chloride
precursor requires high deposition temperatures and can lead to
chlorine contamination of the lms. The alkoxide precursors, though
yielding lms at lower substrate temperature, are very reactive to air
and moisture. In the present work, novel oxo-ketoesterate complexes
of Ti, whose synthesis needs only an inert atmosphere (as opposed to
a glove box), have been developed to overcome these diculties. The
thermal properties of these complexes show that they are suciently
volatile, and stable to air and moisture under ambient conditions.
Using one of these complexes as the precursor, thin lms of TiO2 have
been deposited
glass substrates at temperatures ranging from
C. Theon
400-525
lms
are crystalline at growth temperatures above
480C, and consist of the anatase phase. The lms are very smooth,
and consist of nearly monodisperse, nanocrystals of the anatase phase.
Optical studies show the band gaps in the range 3.1-3.5 eV for lms
grown at dierent temperatures. Another ketoesterate complex, when
used as the precursor in spin-coating, also yields thin lms of titania
of the anatase phase, demonstrating that the newly developed
complexes can be successfully used for thin lm growth by various
chemical routes. The molecular structure of the complexes and the
connection to their volatility will be discussed, substantiated by
thermal analysis data. The microstructure of the lms as examined by
SEM, TEM, and AFM will be presented.
10:15 AM *DD7.5
DESIGNING NEW PHOTOCATALYSTS AND TRANSPARENT
CONDUCTORS: ELECTRONIC STRUCTURE STUDIES OF
COMPLEX SEMICONDUCTING METAL OXIDES.
Patrick M. Woodward, Hiroshi Mizoguchi, and Hank W. Eng, Ohio
State University, Dept. of Chemistry, Columbus, OH.
Designing materials which can be successfully used as photocatalysts
or transparent conductors represents a signicant materials design
challenge. Both the optical and the electrical transport properties
must meet rather strict criteria. In addition, these applications
generally reuqire materials to be stable in the presence of both water
and air. Due to the stability requirements most photocatalysts and
transparent conductors are semiconducting metal oxides. However,
due to the exacting requirements on the electronic structure only a
handful of materials have been shown to be eective photocatalysts
(i.e. TiO2 ) or transparent conductors (doped In2 O3 , ZnO and SnO2 ).
As part of our eort to nd new photocatalysts and transparent
conductors, we have systematically investigated the relationships
between bonding, crystal structure and valence/conduction band
properties in ternary, quaternary and more complex metal oxides. The
conduction band position and width depend upon the
electronegativity and coordination environment of the electronically
active cation(s), as well as the connectivity of the metal centered
polyhedra. In order to develop a semiquantitative understanding of
these eects, we have studied
a large family of compounds
containing
4+
5+
octahedrally
coordinated
d0 transition
metal 4+
ions (Ti
, Nb
, Ta5+ ,
6+
6+
0
5+
5+
Mo and W ) and main group s ions (Sn , Sb , Bi ). We
have also investigated a number of avenues for modication of valence
band properties, including: (a)2 changes in 2+the oxygen
coordination
2+
3+
environment,
(b)
the
use
of
s
cations
(Sn
,
Pb
,
Bi
), (c) the use
of d10 cations (Ag+ and Cu+ ), and (d) partial replacement of oxide
ions with nitride ions to form oxynitrides. A variety of experimental
characterization techniques have been utilized in combination with
DFT band structure calculations.
10:45 AM DD7.6
ORIENTATION DEPENDENCE OF THE PHOTOCHEMICAL
REACTIVITY OF Sr2 Nb2 O7 AND BaTi4 O7 . Jennifer L. Giocondi,
Ariana M. Zimbouski, Shahrzad Samadzadeh, Gregory S. Rohrer,
Carnegie Mellon University, Dept of Materials Science and
Engineering, Pittsburgh, PA.
The photochemical properties of some transition metal oxides are
known to be surface structure sensitive. In other words, their
reactivity depends not only on the chemical composition, but also on
the orientation of the surface and the defect structure. Sr2 Nb2 O7
(SNO) and BaTi4 O7 (BTO), both reported to have high water
photolysis eciencies, have highly ansiotropic structures comprised of
layers and tunnels, respectively. The objective of this work was to
measure the anisotropy of the photochemical activity of ternary
oxides with complex (110) layered perovskite (SNO) and
pentagonal-prism tunnel (BTO) structures. By identifying the most
reactive orientations, it is also possible to infer the structural
components that promote the reaction. Surfaces were prepared for
analysis by thermally etching polished polycrystals. The surface
orientations of selected grains in the sample were then determined
from backscattered electron diraction patterns recorded in a
scanning electron microscope. To make a local measurement of the
photochemical activity of each grain, we used a well established probe
reaction (the reduction of aqueous Ag(I) to Ag(0)) that deposits
metallic silver on the surface as a reaction product. The amount of
silver deposited on each grain's surface during a given reaction, which
is determined from atomic force microscopy images, is taken to be a
quantitative indicator of that grain's relative photochemical reactivity.
In both cases, we have found that the reactivity is anisotropic and
that the reactivity can be expressed as a function of the impingement
angle between the layers or tunnels and the free surface.
11:00 AM DD7.7
THE CATALYTIC AND REACTIVE ACTIVITY OF
SILICON/SILICA NANOSTRUCTURES PREPARED FROM
METAL/METAL OXIDES AT HIGH TEMPERATURES. James Gole
and Amanda Jacob, School of Physics, and Brian D. Shinall, Alexei V.
Iretskii, and Mark G. White, School of Chemical Engineering, Georgia
Institute of Technology, Atlanta, GA; Ann S. Erickson, Department of
Chemistry, Department of Physics, Reed College, Portland, OR.
Preparations of non-porous nanoparticles from the
reaction-interaction of metals (metalloids)/metal (metalloid) oxides at
high temperature are used to produce new sites of enhanced catalytic
653
and reactive activity. Dispersed silica nanospheres have been
synthesized from a mixture of Si metal and SiO2 at 1300C to
produce non-porous structures virtually absent of dangling bonds and
defect sites. These products are nearly monodisperse having a
diameter close to 30 nm. These solids have bulk and some surface1
properties similar to silica produced by ame hydrolysis of SiCl4 ,
albeit in the absence of HCl. Indeed
1R patterns for the nanospheres
are quite similar to Cab-O-Sil.1 While the present technology requires
that we operate at elevated temperature, we produce an adsorbent,
support, or catalyst by a two-step process that does not require
solvents. The eectiveness of this approach has been demonstrated for
the synthesis of catalyst supports and conversion agents as the silica
nanospheres have been used as a supporting substrate for a
well-dispersed copper oxide
catalyst and for the selective conversion of
ethanol to acetaldehyde.1 We examine further the surface chemistry of
these silicon nanostructures using the phenol hydroxylation reaction
in excess hydrogen peroxide as this reaction is particularly useful for
identifying acid sites on solids and for describing the role of surface
oxidation state(s) in catalysis. The results obtained in the study of
this reaction cause us to examine the oxidation state distribution SiOx
for both the nanospheres and Cab-O-Sil using XPS and to examine
the photoelectron spectrum and reactivity of the corresponding
oxynitride SiO20x Nx . We further report the BET surface area and
electron microscopy of these novel silicas and compare with the same
properties for Cab-O-Sil. We extend the study of single metal oxides
to multiple metal oxide/metal combinations using the silica
nanospheres to synthesize a silica-alumina nanostructure (interaction
with Al(acac)3) and compare its properties (surface area, surface
acidity) against a commercial, cracking analyst (Nalco Chem. Co.).
The nanosphere-based catalyst is characterized using the cumene
cracking reaction as it is often employed as a probe reaction for acid
catalysis. 1. J. L. Gole and M. G. White, J. Catal. 204, 249-52 (2001).
TeMoV and TeMo(V/Nb) bronze type phases have been obtained
during the calcination
of the corresponding catalysts precursor
mixture at 600C in N2 (6). Both mixed metal oxides are structurally
related to the M1 phase reported in ref. (5) for multicomponent
catalysts. However, they are catalytically related to the M2 phase
proposed in ref. (4). The new crystalline phases have been isolated
and carefully characterized. Microstructural characterization has been
performed by means of X-ray diraction (XRD), electron diraction
(ED) and high resolution electron microscopy (HREM), and the
chemical analysis of the crystals have been carried out by means of
EDS X-ray microanalysis. Diuse reectance (DR) UV-VIS and XPS
spectra have also been used to determine the oxidation state of each
element. Although the basic average structure of both phases can be
considered as deriving from a bronze type HTB unit cell, the
microstructural study reveals the formation of an orthorhombically
distorted cell derived from the HTB structure, which does not behave
as a bronze type structure in the chemical sense. The xed
composition of the structural skeleton with 3:1 Mo:V or Mo:(V/Nb)
ratios and 1:3 Te:M (M= Mo,V/Nb) ratio, lead to the stoichiometries
Te0.33Mo0.75V0.25O3.33 and Te0.33Mo0.75(V,Nb)0.25O3.33, with
full occupancy of the hexagonal tunnels of the HTB structure.
Microstructural details responsible for the new unit cell, are discussed
in terms of tellurium location inside these hexagonal tunnels and
based on the structural model proposed. The catalytic behaviour of
these bronzes strongly depends on the phase composition and, in this
way, the results obtained here constitute the rst step to elucidate the
role of this new orthorhombic phase in the eectiveness of the
catalysts. (1). T. Ushikubo et al., US Patent 5 380 933 (1995) (2). M.
Lin and M.W. Linsen, EP 962 253 (1999). (3). T. Ushikubo et al., EP
0 529 853 A2 (1992). (4). T. Ushikubo et al., Stud. Surf. Sci. Catal.
112, 473 (1997). (5). M. Aouine et al. Chem. Comm., 1180 (2001). (6).
P. Botella et al., Catal. Lett. 78, 383 (2002).
11:15 AM DD7.8
MIXED-ANIONS (O, S, F) RARE EARTH-BASED COMPOUNDS:
DESIGN AND OPTICAL PROPERTIES. Damien Pauwels, Alain
Demourgues, Alain Tressaud, Institut de Chimie de la Matiere
Condensee de Bordeaux (ICMCB-CNRS), Pessac, FRANCE.
The mixed-anions rare earth-based compounds containing sulfur
atoms have been studied for3+their specic absorption (LnSF) and
luminescence (Ln2 O2 S: Ln ) properties. In -LnSF and Ln2 O2 S
type structures which can be considered
as a 2D network, the rare
earth and2xthe
smallest anions (O20 , F0 ) form blocks which alternate
0
with [Sx ] sulfur layers along the c-axis. Recently, new uorosulde
series Ln2 AF4 S2 (A = Ca, Sr) have been synthesized. In these
structures the size of the rare earth-based uorite block increases
without any modication of its charge. In order to follow the networks
and sheets arrangement in these compounds a new series of rare earth
oxyuorosuldes, Ln3 OF3 S2 , Ln2 O1:5 FS and Ln4 O2 F2 S3 have been
prepared by solid state route. The building of the mixed anions rare
earth-based compounds networks and their modulation by various
charges, sizes, geometries and compositions of the rare earth blocks as
well as the number and the arrangement of sulfur layers will be
presented. The absorption in UV-visible range of mixed-anions rare
earth-based compounds will be correlate to these structural features.
11:30 AM DD7.9
OPTICAL AND TRANSPORT PROPERTIES OF P-TYPE BaCuXF
(X=S, Se). H. Yanagi, J. Tate, Department of Physics, Oregon State
University, Corvallis, OR; S-M. Park, C-H. Park and D.A. Keszler
Department Chemistry, Oregon State University, Corvallis, OR.
Motivated by the search for p-type transparent conductors, we have
prepared powders of BaCuXF (X=S, Se), and measured the properties
as a function of K dopant in the doping concentration range of a few
percent. Diuse reectance spectra of the BaCuSeF powders indicate
a bandgap of approximately 3 eV. The conductivity of the powders is
p-type, with Seebeck coecients in the range of a few tens of V/K.
The conductivity increases with K doping and is as high as 80 S/cm
BaCu0:9K0:1 SF and 45 S/cm in BaCu0:9 K0:1 SeF.
11:45 AM DD7.10
ON THE NATURE AND STRUCTURE OF NEW MoVTeO AND
MoVTeNbO CRYSTALLINE PHASES. E. Garcia-Gonzalez, J.M.
Gonzalez-Calbet, Dpto Quimica Inorgsnica, Facultad de Quimicas,
Universidad Complutense de Madrid, SPAIN; J.M. Lopez-Nieto, P.
Botella, B. Solsona, Inst Tecnologia Quimica, UPV-CSIC, Valencia,
SPAIN.
MoVTeNbO multicomponent catalysts have been recently proposed as
active and selective catalysts for the selective oxidation (1, 2) and
ammoxidation (3) of propane. These have been proposed as serious
alternatives to conventional catalysts used in the oxidation and
ammoxidation of propene. These catalysts present at least two
dierent phases, the so called M1 and M2 (4, 5), although their
catalytic performances are still under discussion. Recently, new
SESSION DD8: CMR MATERIALS
Chairs: Daniel I. Khomskii and Kevin E. Smith
Wednesday Afternoon, December 4, 2002
Back Bay C (Sheraton)
1:30 PM *DD8.1
NON-STOICHIOMETRY, STRUCTURE AND MAGNETIC
PROPERTIES OF LAYERED MANGANESE OXIDES. Lisa Gillie,
Helen Palmer, Colin Greaves, School of Chemical Sciences, University
of Birmingham, Birmingham, UNITED KINGDOM; Joke Hadermann,
Gustaaf Van Tendeloo, EMAT, RUCA, Antwerp, BELGIUM.
The structures and magnetic properties of oxygen-decient
Ruddlesden-Popper phases in the Sr-Mn(III)-O system will be
described. A new type of oxygen vacancy order in the reduced Mn-O
layers has been found in both n=1 and n=2 members of this family,
which diers from that reported in layers of similar composition in the
oxygen-decient Sr-Mn(III)-O perovskite. Whereas the n=1
compound has monoclinic symmetry, interlayer disorder in the n=2
compound results in tetragonal symmetry. The proposed structure
allows prediction of magnetic order based on Goodenough-Kanamori
rules, and the this order is consistent with low temperature NPD
data. Brownmillerite phases (Sr-Mn-Ga-O and Ca-Mn-Al-O)
containing layers of octahedrally coordinated Mn will also be
described, with emphasis placed on the inuence of cation order on
magnetic properties. An unusual observation of staged oxygen
insertion in anion excess materials will be reported.
2:00 PM DD8.2
INVESTIGATION OF ORDERED SINGLE PHASE Sr2 FeMoO6
AND ITS SOLID SOLUTION WITH LaFeO3 . M.R. Suchomel, P.K.
Davies, Department of Materials Science and Engineering, University
of Pennsylvania, Philadelphia, PA.
Ordered doubled perovskites such as Sr2 FeMoO6 (SFMO) have long
been known to possess interesting magnetic and electronic properties.
However, only recently has it been shown that SFMO and some
related ordered doubled perovskites also exhibit outstanding
magnetoresistive (MR) properties at higher temperatures and lower
magnetic elds than many of the celebrated doped-manganite
systems. Although it is accepted that SFMO is a half-metallic
ferromagnet, other important aspects of the material, such as the true
nature of the magnetic exchange and the origin of the MR eect, are
still the subject of some controversy. The varied reports concerning
the magnitude and nature of the MR response in the SFMO literature
are likely due to the various sample impurities often present in these
studies. In this investigation, single-phase SFMO samples were
synthesized by careful control of temperature, oxygen partial pressure,
and previously unreported volatilization of Mo that leads to the
formation of Sr2 FeO40d impurities. The preparation of samples that
were single-phase allowed the eect of other synthesis-related
variables, such as grain size and B site ordering, on the magnetic and
MR properties to be more clearly investigated. In addition, solid
654
solution formation in the SFMO-LaFeO3 system was studied. It has
been shown that partial A and/or B site substitution may improve
the MR response of SFMO. However, all previous investigations have
maintained 1:1 stoichiometric order on the B site. In this study we
examined how the incorporation of additional Fe on the B site aects
the chemical order and magnetic interactions in the sample and leads
to the possible formation of a spin glass. Magnetic, MR, and x-ray
structural data for both single phase and LaFeO3 substituted SFMO
will be presented and discussed.
3:45 PM DD8.6
2:15 PM DD8.3
LARGE EFFECTS OF A-SITE AVERAGE CATION SIZE ON THE
PROPERTIES OF THE5 DOUBLE
PEROVSKITES,
Ba20x Srx MnReO6 : A d -d1 SYSTEM. Guerman Popov, Martha
Greenblatt, Department of Chemistry and Chemical Biology; Mark
Croft, Department of Physics and Astronomy, Rutgers, the State
University of New Jersey, Piscataway, NJ.
Ba20x Srx MnReO6 (x= 0, 0.5, 1, 2) double perovskites were
synthesized
by solid state techniques in evacuated sealed silica tubes.
Mn2+ and Re6+ , whose formal oxidation states were determined by
X-ray absorption spectroscopy, virtually completely order
on the B
site of the double perovskite structure. Their spins (d5 and d1 ) order
in an anti-parallel arrangement resulting in ferrimagnetic ordering
below 120 K. The saturation magnetic moments are between 3.3B
and 3.8B , which are lower than the expected 4B , with the largest
value observed for Ba1:5 Sr0:5 MnReO6 , whose tolerance factor is
closest to 1, and lowest for Sr2 MnReO6 . Sr2 MnReO6 exhibits a
nonequilibrium magnetization state when zero-eld cooled in 5T. All
the compounds have variable-range-hopping-type conduction with low
negative magnetoresistance above 120K. Ba2 MnReO6 exhibits an
unusually high (14% in 5T) positive MR at 80K while the MR's of the
other compounds remain negative in the temperature range measured.
2:30 PM DD8.4
DISORDERLY CONDUCT IN Bi2 Ln2 Ti3 O12 AURIVILLIUS
PHASES (Ln = La, Pr, Nd, Sm). N.C. Hyatt, Department of
Engineering Materials, The University of Sheeld, Sheeld, UNITED
KINGDOM; J.A. Hriljac, School of Chemical Sciences, The University
of Birmingham, Birmingham, UNITED KINGDOM.
The synthesis and structure of triple layered Bi2 Ln2 Ti3 O12
Aurivillius phases (Ln = La, Pr, Nd, Sm), prepared from
K2 Ln2 Ti3 O10 Ruddlesden - Popper precursors, has been investigated.
These materials adopt a body centred structure (space group I4 /
mmm, with unit-cell parameters a 3.8 A and c 33 A comprising a
regular intergrowth of [Bi2 O2 ]2+ uorite and [Ln2 Ti3 O10 ]20
perovskite-type layers. A signicant degree of cation disorder is
present in the Bi2 Ln2 Ti3 O12 system, involving the cross substitution
of Ln / Bi cations onto the Bi / Ln sites in the uorite and
perovskite-type layers, respectively. As the size of the lanthanide
cation is reduced, Bi / Ln disorder is signicantly suppressed due to
the eects of bond length mismatch at the interface between the
uorite and perovskite-type layers in the crystal structure of
Bi2 Ln2 Ti3 O12 . This oers a potential strategy for the chemical
control of cation disorder in the Bi2 Ln2 Ti3 O12 system.
3:15 PM *DD8.5
TOWARDS AN UNDERSTANDING OF THE COLLOSAL
MAGNETORESISTANCE BEHAVIOR IN A14 MnPn11
COMPOUNDS. Susan M. Kauzlarich, Department of Chemistry,
University of California, Davis, Davis, CA.
This research group has been working on Mn analogs of the
Ca14AlSb11 structure type. These compounds show long range
ferromagnetic and antiferromagnetic ordering even though there is no
obvious path for superexchange and the Mn are about 10 A apart.
The magnetic properties can be best explained by a RKKY
(Rudderman, Kittel, Kasuya, and Yosida) mechanism based on spin
exchange mediated by conduction electrons. Most recently, we have
been exploring the Eu and Yb analogs of the Mn compound and have
discovered colossal magnetoresistance (CMR) in these compounds.
The rare earth-substituted series, Eu14 MnPn11 (Pn = Bi, Sb), adds a
second magnetic ion, complicating the magnetism. These compounds
are similar to the alkaline earth analogs in that they appear to be
valence precise according to their saturation moments. However, an
increase in the magnetic complexity is evidenced by the presence of
more than one magnetic transition in the magnetic susceptibility data
of all compounds in the Eu14 MnPn11 series. The CMR behavior of
these compounds is distinct from the perovskite manganites in that
the Mn ions are isovalent. The properties of the series, Eu14 MnPn11
will be presented along with recent Eu Mossbauer results. Recent
X-ray Magnetic circular dichroism measurements (XMCD) of
Yb14 MnSb11 will be presented, giving element specic information.
New compounds composed of Eu-Mn-Pn will also be presented and
their magnetism discussed in terms of the recent Mossbauer and
XMCD results.
DESIGNING CRYSTAL STRUCTURES FROM ATOMS UP. Enkhe
Dashjav, Holger Kleinke, Dept. of Chemistry, University of Waterloo,
Waterloo, Ontario, CANADA.
A novel structure map was recently presented for metal-rich pnictides
and chalcogenides M2 Q (M = valence-electron poor transition metal,
Q = pnicogen or chalcogen). This map separates the today known 12
M2 Q structure types into dierent domains by plotting a newly
dened power product against the averaged coordination number of
the Q atoms. The power product consists only of atomic factors, a
fact which allows its calculation of all still hypothetical compounds
[1]. We discuss the ternary arsenides ZrTiAs [2] and ZrVAs [3], which
both crystallize - in perfect agreement with our structure map - in the
La2Sb type. While Zr2 As apparently forms the Zr2 P type, the (to
date) hypothetical \Ti2 As" and \V2As" could not have been prepared
yet. This contribution poster deals with the structure map and its
usability. In addition, we present the crystal structures of ZrTiAs and
ZrVAs, and discuss their band structures and physical properties. We
also make further predictions (e.g. \HfTiAs" and \HfVAs" should
both form the Co2Si type). Time will tell how correct they are. [1] H.
Kleinke, B. Harbrecht, Z. Anorg. Allg. Chem. 626, 1851 (2000). [2]
C.-S. Lee, E. Dashjav, H. Kleinke, Chem. Mater. 13, 4053 (2001). [3]
E. Dashjav, H. Kleinke, J. Solid State Chem., in press.
4:00 PM DD8.7
Abstract Withdrawn.
4:15 PM DD8.8
NEUTRON DIFFRACTION STUDY OF ALaMnMoO6 (A=Ba, Sr)
DOUBLE PEROVSKITES. M.V. Lobanov, M. Greenblatt, Rutgers
University, Piscataway, NJ; E.N. Caspi, J.D. Jorgensen, Argonne
National Laboratory, Argonne, IL.
Ferrimagnetic BaLaMnMoO6 double perovskite has been found to
exhibit large magnetoresistance (MR), and the onset of MR
surprisingly coincident with a spin glass-like transition at Tf 25K.
Detailed neutron diraction study showed that the crystal structure
of BaLaMnMoO6 is a double perovskite with the rened B-site mixing
of 3.5%. The remarkable feature is that although the lattice is
metrically cubic, strong incoherent
distortions are present, which can
be best tted in a monoclinic I1 space group. This eect
has been
attributed to the large dierence in ionic radii for Ba2+ and La3+
species. Pair Distribution Function (PDF) analysis has been
undertaken to analyze the local symmetry. Ferrimagnetic ordering has
been observed below 80K with strongly reduced ordered moment,
indicative of signicant magnetic frustration. Surprisingly, the ordered
component does not disappear at Tf , suggestive of a more complex
magnetic state. The complementary SrLaMnMoO6 compound has
been also studied. Smaller tolerance factor value results in a true
monoclinic (P21 /n) symmetry and absence of long-range magnetic
order. Spin-glass transition with Tf 25K has been observed by dc
magnetization measurements.
4:30 PM DD8.9
VACANCY-DOPED Nd10x TiO3 . MAGNETIC AND TRANSPORT
PROPERTIES AT THE METAL-INSULATOR TRANSITIONS.
Athena Safa-Sefat, John E. Greedan, McMaster Univ, Chemistry
Dept, Hamilton, Ontario, CANADA.
The parent NdTiO3 compound is a Mott antiferromagnetic insulator
with an orthorhombic Perovskite structure. By introducing cation
vacancies(x) on the Nd site, Nd10x TiO3 undergoes two metal to
insulating transitions (MITs) at the compositions x=0.20 and x0.08.
Disorder and Anderson localization play a signicant role in the MIT
at x=0.20. The composition range 0.08<x<0.20 are metals. A
Kondo-like electronic ground state bridges the insulator and
correlated metals near x=0.08. Compounds with x<0.08 order
antiferromagnetically and are semiconductors. Results from electrical
resistivity, magnetic susceptibility, thermopower and Hall eect
measurements are investigated.
4:45 PM DD8.10
STRUCTURAL AND PHYSICAL PROPERTY TRENDS OF THE
HYPERSTOICHIOMETRIC RUDDLESDEN-POPPER SYSTEM,
La2Ni(10x) CoxO4+d (0 x 1). Gisele Amow, Pamela Whiteld,
Isobel Davidson, Institute for Chemical Process and Environmental
Technology, National Research Council, Ottawa, Ontario, CANADA;
Stephen Skinner, Centre for Ion Conducting Membranes, Department
of Materials, Imperial College of Science, Technology & Medicine,
London, UNITED KINGDOM.
Members of the Ruddlesden-Popper system, La2 Ni(10x) Cox O4+d (0
x 1), were synthesized and studied for their potential use as
cathodes for solid-oxide fuel cells. An unusual structural trend has
been noted across the series, which appears to correlate with the
655
oxygen hyperstoichiometry observed. Details of the structural
variance by x-ray and neutron diraction, as well as selected physical
properties for this system will be presented.
SESSION DD9: NANOMATERIALS
Chairs: Martha Greenblatt and Angus Paul Wilkinson
Thursday Morning, December 5, 2002
Back Bay C (Sheraton)
8:30 AM *DD9.1
INORGANIC NANORODS: SYNTHESIS, PROPERTIES,
APPLICATIONS. Paul Alivisatos, Univ of California-Berkeley, Dept
of Chemistry and Lawrence Berkeley National Lab, Berkeley, CA.
Inorganic nanocrystals with well dened shapes are important for
understanding basic size-dependent scaling laws, and may be useful in
a wide range of applications. Methods for controlling the shapes of
inorganic nanocrystals are evolving rapidly. This talk will focus on a
strategy that involves pyrolysis of organometallic precursors in
mixtures of hot organic surfactants. The surfactant mixtures can be
used to control the growth rates of dierent facets of the nanocrystals,
allowing for wide tunability of shape. This will be illustrated with
CdSe and Co nanocrystals, as well as more recent work involving
transition metal oxides. These materials show pronounced variation of
fundamental properties with aspect ratio. The nanorods can be
aligned in a variety of ways. For instance, liquid crystalline phases of
the nanorods can be formed spontaneously at high density in a liquid
solution, and these liquid crystalline phases can be aligned with
external elds. These aligned nanorods can be used for example in
spin-cast photovoltaics.
9:00 AM DD9.2
SOLUTION-PHASE APPROACHES TO CHALCOGEN AND
CHALCOGENIDE NANOWIRES. Byron Gates, Brian Mayers and
Younan Xia, University of Washington, Department of Chemistry,
Seattle, WA.
We have demonstrated a templateless solution-phase synthesis for the
generation of 1-dimensional nanostructures of a variety of chalcogens
(Se, Te, and Se/Te alloys). These structures include monodispersed
nanowires, nanorods, and nanotubes with well-dened lateral (10 1000 nm) and longitudinal (0.25 - >20 um) dimensions. We have also
demonstrated topotactic conversion of these reactive chalcogens into
other functional materials such as Ag2Se. In this presentation, we will
discuss mechanisms for formation of these 1D nanostructures (as
revealed by electron microscopy and x-ray diraction), as well as some
measurements on their properties. We believe that these techniques
are adaptable for the formation a host of new functional 1D
nanostructures. Such materials will be useful in microelectronics and
as systems for probing the eects of 1D size connement.
9:15 AM DD9.3
ELECTRONIC ORIGIN OF SINGLE WALL CARBON NANOTUBE
ACTUATION. Miklos Kertesz, Guangyu Sun, Jeno Kurti,
Georgetown University, Department of Chemistry, Washington, DC;
Ray H. Baughman, Department of Chemistry and NanoTech Institute,
University of Texas at Dallas, Richardson, TX.
Motivated by the central importance of charge-induced dimensional
changes for carbon nanotube electromechanical actuators, we
calculated changes in nanotube length and diameter as a function of
charge injection for several armchair and zigzag single wall carbon
nanotubes. Density functional theory with periodic boundary
conditions (Vienna ab initio Simulation Package, VASP) is used,
which we show provides results consistent with experimental
observations for intercalated graphites. Strain-versus-charge
relationships are predicted from dimensional changes calculated using
a uniform background charge for representing the counterions. These
\jellium" calculations are consistent with calculations that include
specic counter ions for intercalated graphite, showing that
hybridization between the ions and the graphite sheets is unimportant.
The charge-strain relationships calculated using the jellium
approximation for graphite and SWNTs are asymmetric with respect
to the sign of charge transfer. This reects both the dependence of the
frontier orbitals for the semiconducting nanotubes on the nanotube
type and s-p hybridization when the nanotube diameter is small.
9:30 AM DD9.4
NUCLEATION AND GROWTH OF GALLIUM OXIDE TUBES,
NANOPAINTBRUSHES AND NANOWIRES FROM MOLTEN
GALLIUM. Shashank Sharma, Mahendra K. Sunkara, University of
Louisville, Department of Chemical Engineering, Louisville, KY.
We demonstrate bulk synthesis of highly crystalline beta-gallium
oxide tubes, nanowires, and unique brush-like one-dimensional
structures using molten gallium and microwave plasma containing a
mixture of monoatomic oxygen and hydrogen. Results showed that
multiple nucleation and growth of gallium oxide nanostructures could
easily occur directly out of molten gallium upon exposure to
appropriate composition of hydrogen and oxygen in the gas phase.
The gas phase chemistry alone controls the size and morphology of
these nanostructures. The oxide phase segregation out of molten
gallium occurs by creation of multiple nuclei on the surface. In the
absence of hydrogen in the plasma, these nuclei would aggregate to
form a polycrystalline crust on the molten gallium surface. However
hydrogen/oxygen chemistry enables nuclei segregation on the gallium
surface, preventing the complete crust formation. These nuclei grow in
one dimension upon basal attachment of the bulk growth species. The
surface dynamics of nuclei on molten gallium, i.e., pattern formation
and the time of coalescence determines the morphology of the
resulting structure. Individual nanowires were characterized for
crystallinity, composition, and contamination using high-resolution
transmission electron microscopy (HRTEM) and energy dispersive
x-ray spectroscopy (EDX) respectively. Demonstration of this
technique with gallium oxide certainly presents a new route for
synthesis of nanostructures of other important metal oxides such as
indium oxide, tin oxide, and zinc oxide.
10:15 AM *DD9.5
FUNCTIONAL NANOWIRES. Peidong Yang, Department of
Chemistry, University of California, Berkeley, CA.
Nanowires are of both fundamental and technological interest. They
represent the critical components in the potential nanoscale electronic
and photonic device applications. In this talk, I will introduce the
vapor-liquid-solid crystal growth mechanism for the general synthesis
of nanowires of dierent compositions, sizes, orientation and doping
prole. Particularly, synthesis and organization of dierent types of
heterostructured nanowires will be discussed. I will also discuss some
of the unique linear and nonlinear optical properties of the nanowires
and their potential applications including nanolaser, nanosensor and
optical switch. Ref: 1. \Block-by-block growth of Si/SiGe superlattice
nanowires", Y. Wu, R. Fan, P. Yang, Nanolett, 2, 83, 2002. 2.
\Room-temperature ultraviolet nanowire nanolasers", M. Huang, S.
Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, P. Yang,
Science, 292, 1897, 2001.
10:45 AM DD9.6
ENERGETICS OF ZIRCONIA NANOCRYSTALS. Michael Pitcher
and Alexandra Navrotsky, University of California, Davis, CA.
The study of zirconia has attracted considerable attention over the
last two decades because of its important applications. Besides being
a ceramic, it has also found use as a catalyst and in oxygen sensors.
Zirconia exists in three distinct polymorphs. The room-temperature
stable form is monoclinic which undergoes phase transformation to
the tetragonal form at around 1443 K and the cubic phase at about
2643 K. However, syntheses of ne grained powders of zirconia by
precipitation from aqueous solution often yields the tetragonal
polymorph. In this present work we have synthesized the cubic,
tetragonal and monoclinic polymorphs of zirconia with a range of
dierent particle sizes and surface areas. The energetics of these
materials has been studied using high temperature drop solution
calorimetry in a molten oxide solvent at 973 K. By comparing these
data to values obtained from bulk monoclinic zirconia, we are able to
obtain values for the surface enthalpies of the dierent polymorphs.
The closely balanced energetics directly conrms the crossover in
stability of the nanophase polymorphs.
11:00 AM DD9.7
USING THREE DIMENSIONS IN NANOSTRUCTURED,
MESOPOROUSa Au-TiO2 FOR SMALL-MOLECULE
OXIDATION.
Jeremy Pietron , Rhonda M.a Stroudb , and Debra R. Rolisona ;
Surface Chemistry
Branch, Code 6170 and Surface Modication
Branch, b Code 6370 Naval Research Laboratory, Washington, DC.
Aerogels are low density, high surface area (100-1000 m2 /g),
bicontinuous mesoporous nanostructured architectures. The
interconnected porosity facilitates rapid diusion of molecules
throughout the gel. High surface area translates into high specic
activity of the nanostructured material, as demonstrated in the
application of electrically conductive oxide aerogels as
lithium-insertion cathodes, Pt/C-silica composite aerogels as fuel-cell
electrocatalysts, and (Ru-Ti) oxide aerogels as mixed conductors. We
synthesized Au-MPC-titania aerogel composites using
monolayer-protected gold clusters (Au-MPCs), which are
nanometer-scale gold particles protected with an organothiolate
monolayer, as the source of the included gold. Appropriately designed
MPCs are soluble in the solvents compatible with the sol-gel synthesis
of oxide supports, allowing three-dimensional assembly of
nanostructured composites and formation of multiple oxide-gold
junctions around individual nanoparticles. The MPCs, originally with
656
Au-core diameters of 2-3 nm, aggregate to particles of about 6 nm in
the nal, calcined, highly catalytic composite. Multiple junctions
enhance eciency of catalytic spillover from metal particle to active
support, allowing the larger Au particles to remain catalytically
active. Several new avenues are now open to design new composites
comprising metal-oxide-supported metal nanoparticles.
results are at odds with those from previous neutron scattering
experiments on Sr8 Ga16Ge30 , but in agreement with theoretical
predictions. The implications of our measurements for the
optimization of thermoelectric properties will be discussed. Resonant
scattering is a very powerful tool for enhancing or varying scattering
contrast. Due to the availability of tunable synchrotron x-ray sources,
it is now a practical proposition for all elements beyond the early
transition metals and it can oer signicant advantages over the use
of neutron diraction. Recent developments in high-energy x-ray
optics are likely to further enhance the power of this approach for
high Z elements.
11:15 AM DD9.8
LYOTROPIC LIQUID CRYSTAL MEDIATED SYNTHESIS OF
BISMUTH AND BISMUTH ALLOY NANOPARTICLES THAT
EXHIBIT QUANTUM CONFINEMENT. T.M. Dellinger and P.V.
Braun, Dept. of Materials Science and Engineering, University of
Illinois at Urbana-Champaign, Urbana, IL.
A novel liquid crystal shear mixing methodology for nanoparticle
synthesis is demonstrated. Modulating liquid crystalline phase gives
control over aqueous nanoreactor dimensionality, and thus allows
control of particle size. In addition, precursor concentration has a
dramatic eect on particle size. Bismuth nanoparticles are of interest
due to quantum connement eects, which are expected to produce a
metal to semiconductor transition at the unusually large particle
diameters of 50 nm, producing particles of interest for
thermoelectric applications. Quantum connement eects and the
semimetal to semiconductor transition are being investigated using
SQUID and spectroscopic techniques. The nanoparticle synthetic
methodology is being extended to allow study of the eect of doping
and alloying on electronic properties.
11:30 AM DD9.9
2:00 PM DD10.2
CHALCOGENIDE-BASED AEROGELS: A NEW CLASS OF
NANOSTRUCTURED SEMICONDUCTORS DEMONSTRATING
HIGH POROSITY. Jaya L. Mohanan, Shimanti Dasgupta, Heather
Perrone, Janusz Brniak, Stephanie L. Brock, Wayne State Univ, Dept
of Chemistry, Detroit, MI.
Aerogels are inorganic polymers composed of primary nanoparticle
\building blocks" that are condensed together to form open, porous
structures. They have inherently high surface areas, and as such, great
promise as catalysts, catalyst supports, and sensors. Conventional
oxide materials, principally based on silica, are relatively well
explored, but tend to be insulators or large-bandgap semiconductors,
therefore limiting potential applications. In contrast, non-oxide forms,
with the exception of carbon aerogels, are virtually non-existent. We
have initiated a sustained eort towards developing chemical routes to
aerogel materials with the chalcogenides S and Se. The preparation of
monolithic aerogels of CdS from controlled aggregation of discrete
nanoparticles, followed by supercritical extraction of solvent, will be
described. The eect of synthetic parameters on surface area and
optical/electronic properties will be discussed along with preliminary
results for other transition metals (Mo) and chalcogens (Se).
SESSION DD10: THERMOELECTRIC MATERIALS
Chairs: Mercouri G. Kanatzidis and C. Austen Angell
Thursday Afternoon, December 5, 2002
Back Bay C (Sheraton)
1:30 PM *DD10.1
SOLVING NEIGHBORING ELEMENT PROBLEMS IN TYPE-I
CLATHRATES AND OTHER COMPLEX MATERIALS USING
RESONANT DIFFRACTION. Angus P. Wilkinson, Georgia Institute
of Technology, School of Chemistry and Biochemistry, Atlanta, GA;
Yuegang Zhang, Peter L. Lee, SRI CAT, Advanced Photon Source,
Argonne National Laboratory, IL; George S. Nolas, University of
South Florida, Department of Physics, Tampa, FL.
Many technologically and scientically interesting materials contain
two or more elements with very similar atomic numbers. To fully
understand their physical properties, the distribution of these
elements over the available sites must be known. Type-I clathrates,
such as those that have attracted much recent interest from the
perspective of thermoelectric cooling applications, provide good
examples of this problem type. In these materials, the framework
compositions of interest are constrained by the need to minimize
charge scattering due to mass uctuations and the requirement that
the electron count is compatible with a type-I framework structure.
This has led to a lot of interest in compounds such as Sr8 Ga16 Ge30
and Eu8 Ga16 Ge30. The distribution of the gallium and germanium in
their frameworks has been predicted to strongly inuence their
Seebeck coecients. However, diraction using laboratory x-ray
sources oers insucient scattering contrast to determine this
distribution and neutron scattering does not provide good contrast in
this case. The use of resonant diraction to enhance the scattering
contrast between pairs of elements and to determine the distribution
of these elements over the available crystallographic sites in complex
materials will be discussed. Recent work on Sr8 Ga16Ge30 ,
Eu4 Sr4 Ga16 Ge30 and Cs8 Cd4 Sn42 will be used as examples. Our
MAGNETIC STRUCTURE AND EXCHANGE INTERACTIONS IN
THE Eu4 Ga8 Ge16 . Henrik Birkedal, J. Daniel Bryan, Galen D.
Stucky, Department of Chemistry and Biochemistry, University of
California, Santa Barbara, CA; Mogens Christensen, Bo B. Iversen,
Department of Chemistry, University of Aarhus, Aarhus, DENMARK.
Inorganic clathrate compounds have attracted great interest due to
their possible use as thermoelectric energy conversion materials.
Clathrates incorporating rare earth guest atoms promise to show
interesting magnetic and transport properties: those of magnetically
ordered semiconductor host-guest structures. Eu4 Ga8Ge16 is a
non-oxide analogue of the CAS zeolite framework. It could be
synthesized and isolated using a Ga-ux method. We present
transport, specic heat, magnetic susceptibility, and Eu Mossbauer
data which show that the Eu magnetic moments order
antiferromagnetically at 8 K and lie along the [100] direction.
Magnetic neutron and synchrotron powder diraction are used to
obtain an atomic model of the magnetic and nuclear structure and its
temperature dependence. The background of the magnetic neutron
data and the anisotropy of the magnetic susceptibility show that
short-range ordering persits up to 150 K. While Eu4 Ga8Ge16 is not a
semiconductor, it is a suenciently poor metal that it is reasonable to
expect that a magnetic semiconductor could obtained by further
developing this system. It has become clear that the electronic
properties of inorganic clathrates, such as Ba8 Ga16Ge30 , depend
heavily on the exact composition. This behavior likely extends to rare
earth clathrates and opens a window for property engineering.
2:15 PM DD10.3
IMPROVEMENT OF THERMOELECTRIC PROPERTY OF OXIDE
CERAMICS BY NANO-STRUCTURAL CONTROL.
Masanobu Awano, Yoshinobu Fujishiro, Synergy Materials Research
Center, AIST, Nagoya, JAPAN; Osamu Shiono, Shingo Katayama,
Synergy Ceramics Lab, FCRA, Nagoya, JAPAN.
Improvement of electrical conductivity of titania ceramics was
attempted to apply it for a thermoelectric device. Chemical synthesis
enabled uniform doping of a small amount of Nb, Ta and Sb to
increase carrier concentration. Enhancement of electrical conductivity
over two order at a small doping amount less than 1mol% was
revealed. Additional Zr doping as suppressor of diusion of dopants
through heating resulted in enhanced thermal stability of dopants.
In-situ observation of the microstructure development during heating
and the microstructure dependence of electrical properties was
executed in TEM and SEM respectively. Micro four-prove
measurement method in SEM eld was developed to clarify the
relation between microstructure and electrical conductivity intra- and
inter-grain. Nanoparticle dispersion in matrix was eective for
improving thermoelectric porperties. Power factor of titania
ceramics
at optimum doping and sintering condition exceeded 2x04 Wm01 K02
at 1073K. Research supported by METI, Japan, under the Synergy
Ceramics Project, part of the work supported by NEDO.
2:30 PM DD10.4
ENHANCED THERMOELECTRIC PROPERTIES OF
(Ca2CoO30 )0:62 CoO2 POLYCRYSTALLINE BULK BY CONTROL
OF MICROSTRUCTURE AND OXYGEN CONTENT. M. Sano, S.
Horii, K. Otzschi, J. Shimoyama and K. Kishio, Univ. of Tokyo, Dept.
of Superconductivity, Tokyo, JAPAN; I. Matsubara, M. Shikano, R.
Funahashi, National Institute of Advanced Industrial Science and
Technology, Kansai, Osaka, JAPAN.
Recently, (Ca2 CoO30 )0:62 CoO2 [Ca349] has been attracted as a
good candidate material for thermoelectric application. This
compound is consisted of mist layer stacking of single CdI2 -type
CoO2 and rock salt-type Ca2 CoO30 along the c-axis. Reecting the
layered structure, its thermoelectric properties are anisotropic, in
which the CoO2 layers mainly contribute to electric conduction. In
addition, the Ca2CoO30 layer was found to have large oxygen
nonstoichiometry from = 0 to 0.14 in our preliminary study, which
may aect transport properties. In the present study, we have
investigated thermoelectric properties of highly oriented and dense
Ca349 polycrystalline bulk as a function of oxygen composition. The
c-axis oriented sample was obtained by soaking the Ca349 calcined
657
powder into the organic solvent under magnetic elds up to 3T.
The
dried powder was pressed into pellets and then heated at 500C for 2
h and at 900 C for 16 h in air. After the spark plasma sintering (SPS)
performed under a pressure of 50 MPa at 900 C for 5 min in air,
strongly grain aligned and dense Ca349 bulk samples were obtained.
Oxygen content
of the sample was controlled by annealing at 500, 600,
700 and 800C in air for 100 h and quenching. Each equilibrium state
corresponds to = 0.006, 0.033, 0.060 and 0.083, respectively.
Electrical resistivity, , along the pellet surface ( ab-plane) is
apparently decreased by grain alignment and densication2 and
consequently both
dimensionless gure of merit ZT (= S /) and
power factor S 2 / were enhanced. Furthermore,
the sample with
larger02 showed
larger
power
factors
S 2 / up to 3.4921006
WK cm01 for = 0.083 at room temperature due to enhancement
of S . This result indicates that the control of the oxygen content is
eective for optimization of the thermoelectric properties of the
present system.
3:15 PM DD10.5
SYNTHESIS OF [Ca2(Co10x Cux )2 O4 ]y CoO2 SINGLE CRYSTALS
AND THEIR INTRINSIC PROPERTIES. M. Suzuki, M. Sano, K.
Fujie, K. Otzschi, S. Horii, J. Shimoyama and K. Kishio, Dept. of
Superconductivity, Univ. of Tokyo, Tokyo, JAPAN.
In these several years, the cobalt-based layered oxides have been
eagerly studied from viewpoints of new thermoelectric devices, exotic
strongly correlated electron system and new oxide series. These
interests are originated from their characteristic alternative stacking
structure of CdI2 -type CoO2 and blocking layers. Among the
cobalt-based layered oxides, Ca3Co4 Oy (=[Ca2 CoO3]0:62 CoO) is one
of the promising candidate materials for thermoelectric application
showing large thermoelectric power and high electric conductivity.
This compound has mist layer stacking of rock-salt type
(CaO)-(CoO)-(CaO) and CoO2 . Very recently, a new related
compound showing excellent thermoelectric performance,
[Ca2 (Co0:67Cu0:33 )2 O4 ]0:624 CoO2 , was found[1] . This new compound
has a (CaO)-(Co0:67Cu0:33 O)-(Co0:67 Cu0:33 O)-(CaO) stacking in its
blocking layer. In the present study, we have attempted to synthesize
large single crystals of [Ca2(Co0:67 Cu0:33 )2 O4 ]0:624 CoO2 in order to
clarify the intrinsic and anisotropic physical properties, such as
thermoelectric power, electric conductivity, thermal conductivity and
magnetization behaviors. Sintered bulk samples of
[Ca2 (Co0:67Cu0:33 )2 O4 ]0:624 CoO2 were also prepared by2solid-state
reaction. Large plate-like single crystals with several mm in size were
successfully grown by the ux method starting from
[Ca2 (Co0:67Cu0:33 )2 O4 ]0:624 CoO2 calcined powder and SrCl2 . X-ray
diraction analysis revealed that the wide surface of the crystal
corresponds to the ab-plane and csin was calculated to be 12.76A.
Since this value is almost identical to that in the
Ca2(Co0:67Cu0:33 )2 O4 ]0:624 CoO2 sintered bulk specimen, the
obtained crystals are concluded to be of [Ca2 (Co10x Cux )2 O4 ]y CoO2
phase. In addition, relatively large oxygen nonstoichiometry was
found in thermogravimetric measurement using a
Ca2(Co0:67Cu0:33 )2 O4 ]0:624 CoO2 sintered bulk. Various intrinsic
physical properties of the present material measured as a function of
oxygen content will be reported.
[1] M. Miyazaki et al., private communications.
3:30 PM *DD10.6
NEGATIVE THERMAL EXPANSION IN OXIDES. Arthur Sleight,
Oregon State University, Dept of Chemistry, Corvallis, OR.
Negative thermal expansion in oxides is facilitated by oxygen anions
coordinated to just two cations. We have been systematically
investigating the thermal expansion of oxides of the types AO3 ,
AM2O7 , AMO5 , A2 M3 O12 , and MO2 where the A and M cations 2are
coordinated octahedrally and tetrahedrally, respectively. All the O 0
anions in these structures are coordinated to only two cations.
Signicant negative thermal expansion behavior has been found in all
families. Neutron diraction studies over a wide temperature range
conrm that the degree of negative thermal expansion is correlated
with the degree of transverse thermal motion of oxygen in N-O-N
linkages, where N is A or M. Strong A-O and M-O bonds are essential
so that the intrinsic thermal expansion of these bonds is negligible.
When negative thermal expansion is found, it frequently disappears
below a phase transition. The strong negative thermal expansion in
cubic ZrW2 O8 is likewise related to the transverse thermal motion of
oxygen in Zr-O-W linkages. Several theoretical approaches to
prediction of negative thermal have been explored and found to
provide only qualitative indications.
4:00 PM DD10.7
SELECTIVE PREPARATION OF NICKEL SILICIDES AND
NICKEL GERMANIDES FROM MULTILAYER REACTANTS.
Jacob M. Jensen, Sochetra Ly, David C. Johnson, University of
Oregon, Dept of Chemistry and Materials Science Institute, Eugene,
OR.
Controlling solid state reactions between transition metals and
semiconductors is of critical importance to the preparation of reliable
low-resistivity contact materials for microelectronic technologies. The
resistivity of a device contact can be signicantly compromised by the
presence of unwanted phases, yet the desired low-resistivity phase is
rarely, if ever, the rst nucleated phase. We have prepared a wide
array of polycrystalline nickel-(Si,Ge) compounds directly from
compositionally modulated elemental multilayers, circumventing the
so-called \rst phase rule". For multilayers with suciently small
modulation wavelength moderate annealing eects interdiusion and
mixing of the constituent layers forming a homogeneous amorphous
reaction intermediate. The products of the solid state reaction are
largely determined by the composition of this amorphous phase,
which in turn is determined by the overall composition of the initial
multilayer reactant. The nature of the solid state reaction has been
investigated using x-ray reectivity, grazing angle x-ray diraction,
and dierential scanning calorimetry.
SESSION DD11: POSTER SESSION
DIELECTRICS, CATALYSTS, PHOSPHORS, FILMS,
PROPERTIES
Chair: Miguel A. Alario-Franco
Thursday Evening, December 5, 2002
8:00 PM
Exhibition Hall D (Hynes)
DD11.1
NOVEL STRUCTURAL BEHAVIOR OF THE STRONTIUM
ALUMINATE DOPED WITH EUROPIUM. W.S. Shi, K. Nishikubo,
C.N. Xu, National Institute of Advanced Industrial Science and
Technology (AIST), Kyushu, Tosu, Saga, JAPAN; H. Yamada, C.N.
Xu, PRESTO, Japan Science and Technology Corporation (JST),
Kawaguchi, JAPAN.
Strontium aluminate doped with rare earth is well known as a
high-eciency phosphor. Usually, europium is employed to replace
strontium as an activator in this material in order to obtain strong
and long-lasting phosphor. In this paper, the eect of the europium
on the structure of the strontium aluminate synthesized by spray
pyrolysis was studied. It was found that the europium strongly
inuenced the phase structures of the strontium aluminate, which
completely diered from previous report in literatures. Results
revealed that all of the as-sprayed samples were a normal monoclinic
phase structure. However, the structural behavior of the samples
calcinated again at 1300 degree Centigrade in reducing ambient for
2hrs strongly depended on europium concentrations at room
temperature. The calcinated samples with zero or one percent
europium is still an ordinary monoclinic phase structure. As increase
of the replacement of europium, a hexagonal phase could be observed
in the calcinated samples. Up to 12 percent of strontium was replaced
by the europium, the structure of the calcinated sample achieved a
single hexagonal phase. The mechanism of the phase dependence on
europium concentration was discussed.
DD11.2
PREPARATION OF STRONTIUM TITANATE THIN FILMS BY
ELECTROCHEMICAL METHOD AT LOW TEMPERATURE. Jian
Bi, Dingquan Xiao, Daojiang Gao, Ping Yu, Wen Zhang, Dunmin Lin,
Sichuan Univ, Dept of Materials Science, Chengdu, P.R. CHINA.
Strontium titanate thin lms have been prepared on Ti-substrates
using strontium chloride solutions by electrochemical method at low
temperature (<100C). Formation of SrTiO3 is found to be favored
only in highly alkaline solutions; the thickness of SrTiO3 lm is
governed by the current density. Lower temperature (about 60 C)
favors the formation of thick, well-crystallized SrTiO3 lms. This
processing route may serve as an inexpensive and environmentally
friendly way of fabricating of ABO3 peroskite-type thin lms.
DD11.3
BaNi2 V2O8 : A TWO-DIMENSIONAL HONEYCOMB
ANTIFERROMAGNET. N. Rogado, R.J. Cava, Princeton Univ, Dept
of Chemistry and Princeton Materials Institute, Princeton, NJ; Q.
Huang, J.W. Lynn, National Institute of Science and Technology,
NIST Center for Neutron Research, Gaithersburg, MD; A.P. Ramirez,
Los Alamos National Lab, Dept of Thermal Physics, Los Alamos, NM;
D. Huse, Princeton Univ, Dept of Physics, Princeton, NJ.
The characterization of the magnetic properties of BaNi2 V2 O8 is
reported. The magnetic Ni ions are arranged5+in a two-dimensional
honeycomb
net separated by nonmagnetic V O4 tetrahedra and
Ba2+ ions. Susceptibility, and specic heat measurements reveal very
subtle features at around 50 K indicative of magnetic ordering.
Antiferromagnetic long-range ordering (LRO) is conrmed by neutron
658
diraction to occur at that temperature. Diuse scattering that is
characteristic of strong 2D magnetic correlations are observed up to
100 K. Substituting nonmagnetic Mg into the magnetic Ni sites shows
the gradual disappearance of LRO with doping.
DD11.4
STEP MOTIONS AT NaCl(001) SURFACE AT ELEVATED
TEMPERATURES STUDIED WITH ATOMIC FORCE
MICROSCOPY. Hitoshi Shindo, Takashi Hiyama, Chuo Univ, Dept of
Applied Chemistry, Tokyo, JAPAN.
Changes in morphology of crystals occur through step motions at the
surfaces, which can be clearly observed with atomic force
microscopy(AFM). In this study, changes in the step structures at
NaCl(001) surface due to thermal energy were followed by comparing
the structures before and after heat treatments. By giving appropriate
surface markings, we were able to observe the same position
repeatedly. Step motion was rst recognized at 723K, well below the
melting point of 1074K. At this temperature, the ions moved only
horizontally at the same terraces. The terraces with monatomic height
at highest levels began to decrease in area. At the lowest part, on the
other hand, the steps began to run closer to the electrostatically more
stable directions along the crystal axes (enthalpy control), although
the step lengths were increased. At 873K, vertical ionic motion
occurred and multiatomic steps split into monatomic ones, indicating
marked decrease in the monatomic step energy. Overall thermal
roughening occurred at 973K (entropy control).
DD11.5
FRICTIONAL FORCE MICROSCOPIC DETECTION
OF
ANISOTROPY AND ASYMMETRY AT (1014) SURFACE OF
CALCITE(CaCO3). Musun Kwak, Hitoshi Shindo, Chuo Univ, Dept
of Science and Engineering, Tokyo, JAPAN.
Frictional force microscopy (FFM) has shown its ability in
determining tilt directions of tetrahedral sulfate ions at crystal faces
of sulfate minerals. This time, FFM was applied to the detection of
tilt of planar carbonate ions at calcite (10-14) surface. In order to
create frictional asymmetry, two crystals were placed side by side in
opposite directions. By scanning the probe across the border in [2-21]
direction, tilt of the ions were clearly detected as a gap in frictional
loop. The intensity of the asymmetry signal relative to total friction
was large compared to the cases of sulfate ions, probably due to
smaller inclination of C-O bonds from the surface. The asymmetry
signal showed azimuthal dependence just as expected. The total
friction also depended upon scan direction of the probe. Scanning in
the most densely populated [010] direction gave smallest friction. The
anisotropy was explained by the modulation in the interaction
potential between the probe and the surface, just like in the cases of
alkali halide surfaces.
DD11.6
well as barium molecular complex with one 18-crown-6 ligand and two
hexauoroacetylacetonate ligands were obtained from water - alcohol
mediums. These compounds were used as strontium- and
barium-bearing precursors. Also the thermochemistry of the
vaporization of these complexes was examined. The possibility of the
synthesis of binuclear titanium-barium (strontium)-containing volatile
molecular compounds was discussed. References: 1. D. Sevastyanov,
V. Sevastyanov, E. Simonenko, T. Kemmitt, G.J. Gainsford, N.
Kuznetsov, Thermochimica Acta, 2002, V. 381, N2, P. 173.
DD11.7
HIGH FREQUENCY MOLECULAR REORIENTATION AND ION
MOBILITY IN POROUS FAU TYPE ALUMINOSILICATE HOSTS.
David C. Doetschman, Randy C. Mehlenbacher, Binghamton
University, Dept. of Chemistry, Binghamton, NY; David W. Dwyer,
Science Applications International Corporation, P.A.& E., Arlington,
VA.
Aluminosilicate hosts of the porous FAU type loaded at low levels
with representative polar organic molecules were studied with
transmission and resonant Q measurements in the 8-12 GHz region.
The results in NaX point to a Na ion loss mechanism inherent to NaX
that is quenched by as few as one molecule per supercage. Water
molecules are an exception to the quenching. In low Al HY, molecules
exhibit various degrees of lossiness in this frequency range at levels of
one per supercage. Aliphatic molecules with larger electronegative
elements, e.g. Br and I, exhibit comparatively higher lossiness than
other molecules in this host. Possible dynamic mechanisms for these
phenomena and the role of molecule-host interactions will be
discussed.
DD11.8
CONTROLLED SYNTHESIS OF BARIUM, STRONTIUM AND
TITANIUM PRECURSORS FOR THE PRODUCTION OF BARIUM
AND STRONTIUM TITANATE THIN FILMS BY MOCVD {
TECHNIQUE. Denis V. Sevastyanov, Vladimir G. Sevastyanov,
Nikolai T. Kuznetsov, Institute of General and Inorganic Chemistry,
Moscow, RUSSIA; Elizaveta P. Simonenko, Moscow State Academy of
Fine Chemical Technology, Moscow, RUSSIA; Tim Kemmitt,
Industrial Research Ltd, Lower Hutt, NEW ZEALAND; Boris I.
Petrov, Institute of Metalloorganic Chemistry, Nizhnii Novgorod,
RUSSIA.
The selection of coordination - saturated molecular volatile titanium,
strontium and barium compounds with similar vaporization
parameters has been grounded for the production of barium and
strontium titanates thin lms by the MOCVD - technique. For this
purpose the evaporation enthalpies of molecular titanium, strontium
and barium coordination compounds were estimated preliminarily
within the structural-thermochemical approach. Examination of
intramolecular steric shielding of individual atoms, and analysis of
intermolecular close contacts, identied which groups of atoms in the
molecules were important. Evaporation enthalpies were calculated by
summing the contributions from the individual groups. The selected
compounds were investigated by experimental and theoretical
methods, the conditions of their transfer into the gas phase were
determined. Thin lms of titanium dioxide, barium and strontium
titanates were obtained using MOCVD - technique and studied by
transmission electron microscopy, scanning probe microscopy, laser
mass spectrometry and X-ray phase analysis. As titanium - containing
precursors (and model compounds) the recently prepared titanium
complexes bis[(-N-methyldiethoxoamine)bis(2,3-dimethyl-2,3butanediolate)titanium] and
bis[(-N-ethyldiethoxoamine)bis(3,4-diethyl-3,4-hexanediolate)
titanium] were chosen. The results of their study can be found in [1].
The strontium molecular complex with one 15-crown-5 ligand and two
hexauoroacetylacetonate ligands (synthesized for the rst time), as
VIBRATIONAL
SPECTROSCOPY AND MASNMR OF A MIXED
(7 Li+ ,2 H+ ) FORM CRYPTOMELANE-TYPE MANGANIC ACID.
Masamichi Tsuji, Tokyo Institute of Technology, Research Center for
Carbon Recycling and Energy, Tokyo, JAPAN; Younkee Paik, Clare
P. Grey, State University of New York at Stony Brook, Stony Brook,
NY; Satoshi Murao, National Institute of Advanced Industrial Science
and Technology, Institute for Geo-resources and Environment,
Tsukuba, JAPAN.
Dierent claims are found on the mechanism on alkali cation insertion
into synthetic manganese oxides: ion exchange and electrochemical
reaction. This may partially come from their non-stoichiometry and
dierence of preparation route. Exactly, manganese oxides prepared
by the soft-chemical process could be properly represented by
chemical formula+ of (A,H)
z MnO20x instead of MnO2 , where the
proportion of A and H+ depends on synthetic conditions, because
manganese oxides are weakly acidic compounds. Hence, although
\manganese oxide" is a misleading name, it is also used in this paper.
A cryptomelane-type manganic acid (CMA) and other type of
manganic acid prepared via the soft-chemical route have been studied
for two decades for ion exchanges of alkali, alkaline earth, and
transition metals. These cations are found to ion exchange with
proton in the crystal lattice of manganese oxides. -MnO2 belonging
to the same group, prepared by other authors, has been reported to
show alkali cation uptake by redox process. The mutual selectivity
among the alkali cations is greatly dierent from the above CMA. Its
reason is still not known. The
objective of the present work is to
study CMA in the mixed (7 Li+ ,2 H+ ) form using FTIR and 7 Li and
2
H MASNMR for better understanding chemical reactivity of this
material at local-level. Chemical shifts of MASNMR and of
wavenumber in the FTIR spectra suggest a close relation with the
unusual alkali cation selectivity of this compound.
DD11.9
STRUCTURE AND PROPERTIES OF NEW Li-BASED ORDERED
PEROVSKITES. Albina Y. Borisevich and Peter K. Davies,
Department of Materials Science and Engineering, University of
Pennsylvania, Philadelphia, PA.
The families of perovskites with the general formulae ALix Ti10x O3 ,
ALix Nb10x O3 , and ALix Ta10x O3 (where x= 1/2, 1/3, or 1/4, and
A=Ca2+, Sr2+, La3+, Ba2+, or their mixture with appropriate
valence) have been investigated. These compounds exhibit various
types of B-site cation order, depending on the composition and degree
of lattice distortion. Compounds with 1:2 B-site stoichiometry form
ordered phases with a 1/3[111]* ordering vector. The high stability of
the order, good dielectric response, and excellent sintering properties
of some of the ALi1=3 Nb2=3 O3 compounds suggest they will be useful
additives for more refractory 1:2 ordered microwave ceramics such as
Barium Zinc Niobate. Most of the compounds with 1:3 B-site
stoichiometry form ordered phases with a 1/4[111]* ordering vector.
For SrLi1=4 Nb3=4 O3 two polymorphs with a dierent type of 1:3 order
were identied and structural investigations suggest these contain
ordered but mixed Li/Nb cation layers perpendicular to the [111]*
direction. CaLi1=4 Nb3=4 O3 was found to adopt structures with both
659
1:2 and 1:3 types of order. The variation in the ordering with
temperature and composition, and their relationship to the dielectric
properties will be discussed.
DD11.10
THERMODYNAMICS OF SOLID SOLUTION FORMATION IN
CoO-MgO. Lan Wang and Alexandra Navrotsky, University of
California-Davis, Davis, CA.
Enthalpies of mixing of Cox Mg10x O solid solutions have been
determined using high temperature drop solution calorimetry in
molten sodium molybdate (3Na2O14MoO3 ) solvent at 973 K. Slightly
positive enthalpies of mixing were observed, and conform to a regular
solution model with interaction parameter W=5,0716337 J mol01 .
This is similar to the interaction parameter calculated from the
previously measured activity-composition relations. The positive
enthalpies of mixing suggest a tendency toward clustering of like
atoms with potential immiscibility near 300 K, probably nevery
observable for kinetic reasons. Dierential scanning calorimetry
measurements show that the magnetic transition temperature (TN )
decreases as x decreases in Cox Mg10x O, thus supporting the model of
increase in magnetic disorder with dilution.
The heat capacity (Cp of CoO, MgO and Co0:50O was measured from
liquid helium temperature up to 980 K by combination of adiabatic
and dierential scanning calorimetry. The standard entropy that was
calculated from subambient
Cp data is 28.160.2 (MgO), and 40.360.2
(Co0:50Mg0:50O) J1K01 1mol01 .
DD11.11
LOCAL STRUCTURE AND PROPERTIES OF THE
(1 0 x)Pb(Sc2=3 W1=3 )O3 { (x)Pb(Ti/Zr)O3 RELAXOR
PEROVSKITES. Pavol Juhas, Wojciech Dmowski, Takeshi Egami,
Peter K. Davies, Dept. of Materials Science, Univ. of Pennsylvania,
Philadelphia, PA.
The eect of Ti and Zr on the structure and ordering in the
(1 0 x)Pb(Sc2=3 W1=3 )O3 { (x) PbMO3 , (M=Ti, Zr) systems was
studied using synchrotron X-rays and neutron diraction. Rietveld
renement was carried out to determine the average long-range
crystallographic structure and pair distribution function (PDF)
analysis to probe the local displacements of the atoms. For x < 0:25
the B-cations form a 1:1 ordered doubled perovskite structure. The
rened occupancies were consistent with a \random site model" for
the order, with one site occupied by Sc and the other by a random
mixture of the remaining cations. The B-site order is reduced by the
incorporation of Zr, but highly stabilized by Ti with the degree of
order in excess of 95%. Local atomic structure has been modelled by
tting the experimental PDF curves using the Monte Carlo method.
This analysis revealed that on the local scale the Pb and O atoms are
signicantly displaced from their average lattice positions. The
relationships between the local displacements, the cation order and
the dielectric properties will be discussed.
DD11.12
A VARIABLE-EMITTANCE RADIATOR BASED ON A
METAL-INSULATOR TRANSITION OF (La,Sr)MnO3 .
Y. Shimakawa, T. Yoshitake, and Y. Kubo, Fund. Res. Labs., NEC
DD11.14
USING A NOVEL METHOD COMBINING SOL-GEL AND
COMBUSTION SYNTHESIS TECHNIQUES FOR PREPARATION
OF Y-Ba-Cu-O SUPERCONDUCTOR. Chyi-Ching Hwang,
Ching-Kai Hong, Department of Applied Chemistry, Chung Cheng
Institute of Technology, National Defense University, Ta-Hsi,
Tao-Yuan, TAIWAN, ROC; Cheng-Hsiung Peng, San-Yuan Chen,
Department of Materials Science and Engineering, National Chao
Tung University, Hsin-Chu, TAIWAN, ROC.
A novel and simple method, which combines the sol-gel and the
combustion synthesis techniques, has been developed to prepare
Y-Ba-Cu-O high-temperature superconductor. In this study,
Y(NO3 )3 6H2O, Ba(NO3 )2 , Cu(NO3 )2 3H2O, citric acid and
ammonia are used as starting materials to form a precursor xerogel.
And then, the dried gel undergoes a self-propagating combustion
process when being ignited in air and yields voluminous ashes. These
ashes are sub-micron in size and
require low temperatures of
calcination and sintering (450C/2h and 900C/6h, respectively) to
obtain the product of Y-Ba-Cu-O superconductor with orthorhombic
phase. The redox behavior and crystallization process of the dried gel
were examined by thermal analyses (TGA-DTA) and infrared (IR)
spectra. The samples at dierent stages of the experimental process
were characterized in terms of X-ray diraction (XRD) and scanning
electron microscope (SEM). The sintered body shows diamagnetism at
liquid nitrogen temperature.
DD11.15
OPTICAL PROPERTIES OF RUTILE AND ANATASE PHASES OF
TiO2 THIN FILMS GROWN AT ROOM TEMPERATURE BY RF
MAGNETRON SPUTTERING. V.M. Naik, Department of Natural
Sciences, University of Michigan-Dearborn, Dearborn, MI; D.B.
Haddad and R. Naik, Department of Physics and Astronomy, Wayne
State University, Detroit, MI; J. Benci and G.W. Auner, Department
of Electrical and Computer Engineering, Wayne State University,
Detroit, MI.
There has been a great interest in preparing both rutile (R) and
anatase (A) forms of TiO2 lms for various optical, electrical,
photocatalysis, photovoltaics, and biosensor applications. The RTiO2 is superior in optical properties and thermodynamically more
stable than A-TiO2 . However, the latter has attracted much attention
recently as the most promising photocatalytic material. In general,
the formation of R-phase
of TiO2 lms requires a higher substrate
temperature (> 300C), whereas a lower substrate temperature
results in either A-phase or an amorphous structure. In the present
work, both Anatase and Rutile phase TiO2 lms (1 m thickness)
have been prepared on unheated glass substrates by RF magnetron
sputtering by controlling the total pressure of sputtering gases (Ar +
O2 ). The crystal structures of the lms were conrmed by x-ray
diraction and Raman scattering. The analysis of optical transmission
data measured in the UV-Visible region (175 nm - 3000 nm) show a
high optical absorption energy bandgap (Eg ) of 3.8 eV (direct) for
R-phase TiO2 . However, an indirect bandgap extrapolation yields two
values of Eg 2.8 and 3.0 eV. On the other hand, A-phase TiO2 lm
show Eg 3.1 eV (indirect) and 3.5 eV (direct).
DD11.13
Corporation, Tsukuba, JAPAN; T. Machida and K. Shinagawa, Dep.
of Phys. Toho Univ., Funabashi, JAPAN; A. Okamoto and Y.
Nakamura, NEC TOSHIBA Space Systems, Ltd., Yokohama, JAPAN;
A. Ochi, Func. Mat. Res. Labs., NEC Corporation, Kawasaki,
JAPAN; S. Tachikawa and A. Ohnishi, ISAS, Sagamihara, JAPAN.
We have developed a variable-emittance radiator based on the
metal-insulator transition that occurs through the double-exchange
interaction of (La,Sr)MnO3 . The (La,Sr)MnO3 material shows low
emittance at low temperature, but high emittance at high
temperature. Moreover, the emittance property signicantly changes
at the metal-insulator transition temperature, where the material
changes from a highly reective (i.e., low emissive) metal to a less
reective (i.e., high emissive) insulator. Therefore, (La,Sr)MnO3 lms
tted on a spacecraft surface can be used to automatically control the
emissive heat transfer from the spacecraft without the need for
electrical power. The developed radiator will also greatly reduce the
weight and production cost of thermal control devices. The emittance
property of the material was evaluated from infrared reectance
spectra, and the obtained results were understood within a framework
of a free-electron model of metals. The dependence of the emittance
property on lm thickness showed that 1500-nm-thick lms can be
used for variable-emittance radiators.
STRUCTURAL, DIELECTRIC AND PIEZOELECTRIC
PROPERTIES OF THE CdTiO3 -PbTiO3 -PbZrO3 AND
CdTiO3 -PbTiO3 -(Na0:5Bi0:5 )TiO0:5 SYSTEMS.
D.Y. Suarez-Sandoval, P.K. Davies, Dept. of Materials Science and
Engineering, University of Pennsylvania, Philadelphia, PA.
In search for new piezoelectric materials with good electromechanical
properties, recent density functional calculations (Halilov and Singh)
have suggested that cadmium titanate may be a useful additive in
inducing large responses in the (Pb10x Cdx )TiO3 system. In this
study we conducted an experimental investigation of the
(Pb10x Cdx )TiO3 system and examined the eect of CdTiO3 on the
structure and properties of PbTiO3 -PbZrO3 and
PbTiO3 -(Na0:5Bi0:5 )TiO3 solid solutions. In contrast to the behavior
of almost all other divalent A-site additives, Cd exhibits extremely
limited solubility in tetragonal PbTiO3 , and at T = 1170C Pb-rich
single phase solid solutions were only formed for x 0.15. Another
unusual feature of this system is that within this limited range the
c/a ratio of the tetragonal (Pb10x Cdx )TiO3 solid solutions increase
for increasing x. This observation is also quite dierent to the
behavior of almost all other additives, which reduce the tetragonality
of PbTiO3 , but agrees with the theoretical predictions of Halilov and
Singh. Because the range of solubility was so limited it was not
possible to access a morphotropic phase boundary (MPB) in the
(Pb10x Cdx )TiO3 system, therefore a series of Cd-containing ternary
systems were examined with a view to identifying a
CdTiO3 -containing MPB. For the CdTiO3 -PbTiO3 -(Na0:5Bi0:5 )TiO3
system the limits of the rhombohedral and tetragonal solid solutions
and the evolution of their lattice parameters as a function of
composition were determined and the phase stabilities will be
summarized. For the CdTiO3 -PbTiO3 -PbZrO3 system, small
additions of CdTiO3 modify the symmetry of binary PZT (52:48)
MPB composition. For example the replacement of 5% Pb by Cd
induces a transition from rhombohedral to tetragonal symmetry. The
eect of Cd on the MPB and the resultant values of the d33
660
piezoelectric coecient will be presented together with data for the
change in the Curie temperature.
DD11.16
CRYSTAL CHEMISTRY AND ENERGETICS OF PEROVSKITES
ALONG THE NaNbO3 {SrTiO3 JOIN. Hongwu Xu, Alexandra
Navrotsky, Univ of California at Davis, Dept of Chemical Engineering
and Material Sciences, Davis, CA; Yali Su, M. Lou Balmer, Pacic
Northwest National Lab, Richland, WA.
Perovskites in the NaNbO3 {SrTiO3 system are of interest because of
their unique combination of superior electrical and mechanical
properties. In this study, we synthesized a series of perovskite phases
with the compositions (NaNb)10x (SrTi)x O3 (0 x 1) using sol-gel
and solid-state sintering methods. Rietveld analysis of XRD data
reveals that as Sr+Ti content increases, the perovskite structure
changes rst from orthorhombic to tetragonal and then to cubic. The
enthalpies of formation from the oxides and from the elements were
determined by drop solution calorimetry in molten 3Na2O 4MoO3
at 974 K. The formation enthalpies become less exothermic with
increasing Sr+Ti content. This variation is nearly linear, suggesting
that the enthalpies of the phase transitions across the series and of
cation mixing are rather small.
DD11.17
ELECTROMAGNETIC AND THERMOELECTRIC
CHARACTERISTICS OF Nax CoO2 OF PRECISELY
CONTROLLED Na-NONSTOICHIOMETRY. Teruki Motohashi,
Maarit Karppinen, and Hisao Yamauchi, Tokyo Inst. Tech., Materials
& Structures Lab., Yokohama, JAPAN.
Electromagnetic and thermoelectric characteristics of a thermoelectric
cobalt oxide, NaxCoO2 , were investigated. Precise control of
Na-nonstoichiometry was successfully realized by a \rapid heat-up
technique". With increasing x, the absolute value of resistivity ()
monotonically decreased, while the value of thermoelectric power (S )
increased, giving rise2 to a drastic enhancement in the thermoelectric
power factor, i.e. S =. Simultaneously enhanced thermoelectric
power and reduced resistivity of the present compound are dicult to
be understood within the framework of a conventional band picture.
Moreover, for the samples with the solubility-limit Na content, i.e. x
= 0.75, an unconventional electronic transition was discovered at Tc
= 22 K, which may be induced by the strong-correlation eect of the
3d electrons.
simultaneously ferroelectricity and magnetism, thus exhibiting
magnetoelectric output under the inuence of an external magnetic
eld. Such materials have many applications. This paper reports the
synthesis and characterization of Bi6 Ti3 Mn2 O18 (BTM), which is
isomorphous with Bi6 Ti3 Fe2 O18 (BTF). The material was prepared
both by solid state and microwave sintering routes. The
characterization includes X-ray, SEM, conductivity, dielectric constant
and impedance spectroscopy. The results of BTM and BTF are
compared. Interestingly, the material also shows magneto-impedance.
The physical properties are analyzed in terms of structure.
DD11.20
OXIDATION-PROTECTION METHODOLOGY FOR LONG-TERM
USE OF CARBON-CARBON FIBER-MATRIX COMPOSITES IN
OXIDIZING AMBIENTS. Ilan Golecki, Honeywell International
(formerly AlliedSignal) Inc., Morristown, NJ; Karen Fuentes,
Honeywell International Inc., Torrance, CA; Terence Walker,
Honeywell International Inc., South Bend, IN.
A methodology is described for protecting Carbon-Carbon
ber-matrix components from oxidation for extended use in oxidizing
atmospheres for total lifetimes of the order of 10,000 hours in the
temperature range from room temperature to 650 degrees C. This
time-temperature prole is relevant to applications such as airborne
heat exchangers. Weight changes of oxidation-protected, pitch-ber
based Carbon-Carbon ber-matrix composite coupons in owing dry
air at 650 degrees C will be presented. Two types of external
protective approaches will be compared: (a) multi-phase
particulate-lled uidizing overseal coatings applied directly to C-C,
and (b) the same overseal coatings applied to CVD SiOxCy coated
C-C. The latter, dual-coating approach provides an eective
engineering solution for the above temperature-time prole and is
particularly applicable to thin-gauge (0.1-3 mm thick),
complex-shaped articles. The behavior of inert substrates (oxidized
silicon) with the same overseal coatings will be compared to the
behavior of the C-C substrates. This approach can be applied with
optional modications to suit other temperatures and times, as well
as other carbon-containing materials systems, such as carbon foams
and Carbon-SiC composites.
This work was funded by the U.S. Air Force under contract
#F33615-99-C-5009 (Roland Watts, contract monitor), as well as by
internal Honeywell R&D programs.
DD11.21
THEORETICAL STUDY OF THE ELECTRONIC STRUCTURE OF
TIN COMPOUNDS. Pierre-Emmanuel Lippens, Laboratoire des
Agregats Moleculaires et Materiaux Inorganiques, CNRS UMR 5072,
Universite Montpellier II, Montpellier, FRANCE.
X-ray absorption spectroscopy (XAS) and Mossbauer spectroscopy are
widely used experimental tools in solid state chemistry. However, the
interpretation of the experimental data is not often related to rst
principle calculations. I will present simulation of XAS and Mossbauer
spectra of tin compounds obtained from the linearized augmented
plane wave (LAPW) method. The theoretical XAS spectra of tin
oxides and tin suldes at the Sn L1 , Sn L2;3, O K and S K edges are
found to be in good agreement with the experimental spectra by
considering the core hole eects in the LAPW calculations and the
broadening of the spectra due to the nite lifetimes of both the core
hole and the photoexcited electron. From this comparison it is
possible to determine the atomic origin of the observed main peaks
and to analyse the chemical bonding. For example, it is shown that
the rst XAS peak at the Sn L2;3 edge can be related to the Sn
oxidation state. The Mossbauer spectra can be obtained from the
calculated electron density and electric eld gradients at the nucleus.
The calculated values for tin compounds have been correlated to the
experimental values of the Mossbauer isomer shift and the quadrupole
splitting, respectively. It is also shown that rst principle calculations
can be used instead of the usual analysis of the experimental data for
the interpretation of unresolved spectra. Finally, the electronic
structures of tin oxides, including both the occupied and empty
states, are interpreted from the combined use of experiments and
calculations.
STRUCTURE AND DIELECTRIC PROPERTIES OF Ba8 ZnTa6 O24 .
Meganathan Thirumal, Peter K. Davies, University of Pennsylvania,
Dept of Materials Science and Engineering, Philadelphia, PA.
Dielectric ceramic materials having perovskite and perovskite-like
structures have been widely examined for their use in microwave
dielectric resonators and lters. In particular Zn-based systems such
as Ba(Zn1=3 Ta2=3 )O3 and Ba(Zn1=3 Nb2=3 )O3 have exceptionally low
dielectric losses and are used extensively in commercial applications.
However, the performance and processing of these systems is
complicated
by the volatilization of ZnO at the high temperatures
(1550C) required to achieve full density. Currently there is no
consensus on how the loss of ZnO aects the microstructure and
dielectric performance or on the identity of the resultant impurity
phases. In this study we have investigated the phase stability of
ZnO-decient compositions in the BaO-ZnO-Ta(Nb)2 O5 systems. In
both systems we determined that the ternary compound,
Ba8 ZnTa(Nb)6 O24 , is the primary impurity phase. Single phase
samples of Ba8 ZnTa(Nb)6 O24 were prepared and found to be
isostructural with the hexagonal perovskite, Ba8 NiTa6 O24 , which has
an 8H (..cchccchc..) close packed sequence
of BaO3 layers. Although
the sintering temperature (1400C) of Ba8 ZnTa6 O24 is signicantly
lower than that of Ba(Zn1=3 Ta2=3 )O3 , initial attempts to achieve
densication were inhibited by the formation of large elongated
platelets. By modifying the sintering times and using a new double
stage sintering technique materials with densities >92% could be
obtained. The dielectric properties of Ba8 ZnTa6 O24 were measured at
microwave frequencies and found to be comparable to those of several
other perovskite niobates and tantalates. These results and data for
the compatibility of Ba8 ZnTa(Nb)6 O24 with Ba(Zn1=3 Ta(Nb)2=3)O3
will also be presented. This work is funded by Ericsson Radio Access.
DD11.19
DD11.22
DD11.18
ELECTRICAL AND DIELECTRIC PROPERTIES OF
Bi6 Ti3 Mn2 O18 . S.V. Suryanarayana, M.B. Suresh, K. Srinivas, E.V.
Ramanamurthy, Materials Research Laboratory, Physics Department,
Osmania University, Hyderabad, INDIA; G. Swaminathan, BHEL
R&D, Hyderabad, INDIA.
Bismuth layer structure ferroelectrics show interesting physical
property variations as a function of external parameters viz.,
temperature, frequency and magnetic eld. In some of these materials,
if magnetic ion is incorporated in the lattice, they show
THERMOCHEMISTRY OF PEROVSKITE OXIDES LaMO3 (M =
Al, Ga, In AND Sc). Jihong Cheng, Alexandra Navrotsky, University
of California at Davis, Thermochemistry Facility, Dept of Chemical
Engineering and Materials Science, Davis, CA.
LaMO3 (M = Al, Ga, In and Sc) with the perovskite structure
represents a group of excellent candidate parent materials of
electrolytes and cathodes in solid oxide fuel cells (SOFCs). Yet little
has been done with the thermodynamic properties. High temperature
solution calorimetry is used to measure the enthalpies of formation
661
from constituent oxides. Enthalpy and entropy of phase transitions of
these perovskites are also determined, as well as the transition
temperatures. All these thermodynamic properties are correlated with
the structural parameter, tolerance factor.
DD11.23
GENERATION0 OF A LARGE
AMOUNT OF ACTIVE OXYGENIC
RADICALS O AND O20 IN AN ANION-ENCAGING CRYSTAL
12CaO17Al2O3 . Satoru Matsuishia;b , Katsuro Hayashib , Masahiro
Hiranob and Hideo Hosonoa;b; a Materialsb and Structures Laboratory,
Tokyo Institute of Technology, JAPAN; Hosono Transparent
Electro-Active Materials Project, ERATO, JST, JAPAN.
Active oxygen species such as O0 and O20 are key chemical species in
the oxidation of hydrocarbons. In particular, O0 attracts much
attention because of its high oxidation
power and high reactivity. In
this paper, we show that a pair of O0 and O20 can be generated in a
wide concentration range up to 121021 cm03 in
12CaO17Al2O3 (C12 A7). Polycrystalline C12 A7 was prepared by the
solid-state reaction of a mixture of CaCO3 and -Al2 O3 at 1350C
for 6 h in an oxygen atmosphere and subsequently quenching. To
identify the active oxygen species, EPR spectra 0of the ceramics
were
measured. An EPR signal attributable to the O2 (421019 cm03 ) was
detected in as-prepared C12 A7 ceramics. The ceramics was reheated
in oxygen atmosphere at 550 C for 12 h. Then the EPR signal
intensity21was 0increased,
corresponding to the total spin concentration
of01210 cm 3 . Further, a signal of O0 appeared superposed on the
O2 signal. This oxygen-activated C12 A7 shows outstanding reactivity
represented by oxidation of Pt metal at high temperature (1350C).
The crystal structure of C12 A7 is characterized
by a positively
charged lattice framework [Ca24 Al28 O64 ]4+ having 12 crystallographic
cages per unit cell (I43d with a= 1.199 nm, Z=2) with a free space of
0.4 nm in diameter. The remaining two O20 , referred to as \free
oxygen", are clathrated in the cages to maintain charge neutrality.
Thus, we anticipate that a large quantity of active oxygen can be
trapped in place of the free oxygen.
This can be accomplished as a
result of electron transfer
from O020 in the
cage to O2 coming in from
20
the atmosphere (O + O2 ! O + O20 ), if oxygen molecules are
introduced into the lattice framework. The generation process
of the
oxygenic radicals is supported by an experiment using 17 O.
DD11.24
MODIFIED MATERIAL PROPERTY IN THE Ta/Nb
PEROVSKITES BY ALLOVALENT ANIONIC SUBSTITUTION.
Young-il Kim, Patrick M. Woodward, Dept of Chemistry, The Ohio
State Univ, Columbus, OH.
Perovskite type oxynitrides, ABO2 N (A = Ba, Sr, and Ca; B = Ta
and Nb) were prepared by ammonolysis reaction at 730-1000C.
Thermogravimetry and combustion analysis indicated that all the six
samples have nearly stoichiometric compositions. Rietveld renement
using the powder X-ray diraction patterns showed that the size of A
cation dictates the crystal structure of each oxynitride, where Ba, Sr,
and Ca compounds are stabilized in Pm3m, I4/mcm, and Pnma
symmetries, respectively. As evidenced by the visible absorption
spectroscopy, partial nitrogen substitution for oxygen led to
signicant decrease in the band gap (1.8 - 2.4 eV) with respect to
oxide perovskites containing Ta or Nb. Computational studies were
performed using LMTO and DFT methods to comprehensively
understand how the electronegativity of anion, structural distortion,
and induction of A cation inuence on the electronic structure of
oxynitride compounds. Dielectric properties will also0be
reported.
Initial measurements indicate that replacement of N 3 for O02 leads
to a dramatic increase in the dielectric constant.
DD11.25
HIGH-PRESSURE VOLUME EXPANSION
IN THE DEFECT
PYROCHLORES ANbWO6 (A=NH+4 , H+ , Rb+ , K+ ).
DD11.27
MICROSTRUCTURAL STUDIES OF HIGH DIELECTRIC
CONSTANT COPPER TITANATE BULK MATERIALS.
D.X. Huang, C.Y. Park, L. Chen, and A.J. Jacobson, Materials
Research Science and Engineering Center, University of Houston,
Houston, TX.
CaCu3Ti4 O12 (CCTO) is an unusual oxide that has5a very high
dielectric constant at room temperature of about 10 with minimal
temperature dependence between 100 and 600 K. The detailed
properties of this material and the origin of the high dielectric
constant have been the subject of several recent studies. For example,
the dielectric constant displays a 1000-fold reduction below 100 K at a
frequency of 20 `Hz without any detectable change of the long-range
crystallographic structure, which is contrast to known ferroelectrics.
Recently, we found that quenching could signicantly increase the
dielectric constant of CCTO. Even though the dielectric constant
changes, the temperature at which the drop in dielectric constant
occurs remains the same for the quenched and non-quenched samples
over a large range of frequency. In this study, we have systematically
investigated the microstructure dierences for quenched and
non-quenched specimens by using electron microscopy. The results
obtained were compared with impedance spectroscopy measurements
and the measurement for the temperature dependence of the real part
of the complex dielectric function and the dissipation factor. A
bricklayer model was developed to better understand both the
physical and structural properties of the materials.
DD11.28
EVALUATION OF THE THERMODYNAMIC PROPERTIES AND
PHASE EQUILIBRIA OF THE Ni-Al-Ta SYSTEM FOR Ni-BASED
SUPERALLOYS. Sihuai Zhou, Longqing Chen, Zi-Kui Liu,
Department of Materials Science and Engineering, The Pennsylvania
State University, University Park, PA.
The phase equilibria and thermodynamic properties of the Ni-Al-Ta
system are analyzed and a complete thermodynamic description of the
ternary system is obtained with the CALPHAD technique using a
computerized optimization procedure. The thermodynamic modeling
of ternary compounds Laves, Ni2AlTa and PI-Ni6AlTa phases with
two or three sublattices is discussed in terms of the eects of a large
number of interaction parameters in the phases. The solubility of a
third element in several binary compounds is determined with
available experimental data. The calculated phase diagrams show a
good agreement with experimental data.
DD11.26
Paris W. Barnes, Patrick M. Woodward, The Ohio State University,
Dept. of Chemistry, Columbus, OH; Yongjae Lee, Thomas Vogt,
Brookhaven National Laboratory, Physics Dept., Upton, NY.
The behavior of ANbWO6 (A= NH+4 , H+ , Rb+ , K+ ) defect
pyrochlores was examined using X-ray powder diraction as a
function of pressure (up to 6 GPa). Under hydrostatic conditions,
NH4NbWO6 and RbNbWO6 exhibit signicant unit cell volume
increases of 5.8 and 7.5%, respectively upon increasing the pressure.
The volume swelling observed in NH4 NbWO6 was previously reported
[Phys. Rev. Letters, 78(15), 2991-2994 (1997)] and attributed to
forceful insertion of water molecules present in the hydrostatic
medium into the compound's crystal structure. Details of the high
pressure water insertion observed in NH4NbWO6 were not determined
previously due to the limited resolution of the energy dispersive
diraction technique used. Behavior of the four defect pyrochlores
studied reveal that the occurrence of the phase transition responsible
for the expansion is dependent upon the size of the monovalent ion.
Our renements show that the expansion is driven by a shift of the
monovalent cation from the 8b Wycko site to a position near the
smaller 16d Wycko site for space group Fd3m. This shift presumably
occurs to allow further insertion of water into the channels, which
interpenetrate the (Nb,W)O6 -octahedral corner sharing framework.
Such a shift can only occur if the A-cation has the appropriate size.
Rietveld renements of the collected diraction data address
important fundamental questions regarding the selective water uptake
by the defect pyrochlore structure.
EDGE-DEFINED FILM-FED GROWTH (EFG) AND
CHARACTERIZATION OF SINGLE CRYSTAL PIEZOELECTRIC
FIBERS. Jian Shen, Benjamin P. Nunes, Andrey N. Soukhojak,
Yet-Ming Chiang, Massachusetts Institute of Technology, Department
of Materials Science and Engineering, Cambridge, MA.
EFG growth of <001> and <111> oriented single crystal bers has
been conducted for a range of (Bi1=2 Na1=2)10x Bax Zry Ti10y O3
perovskite compositions. Fibers are seeded with SrTiO3 single
crystals, and grown at 300-500 mm diameter and 1-meter lengths, at
pull rates ranging from 70-480 mm/hr in air and oxygen.
Electromechanical testing has been preformed on 1-3 composites
fabricated from the EFG bers. ICP chemical analysis shows that the
overall composition of EFG bers is indistinguishable from that of the
starting powders. The presence of a minor fraction of second phase
inclusions suggests that the congruently melting composition in
BNBZT is slightly o-stoichiometry. The distribution of second phase
inclusions is observed to be a function of growth rate and has a strong
inuence on electromechanical actuation. Results on bers of
compositions within the rhombohedral phase eld, near the MPB, and
in the tetragonal phase eld will be presented, demonstrating a broad
range of actuation characteristics. Research supported by ONR Grant
No. N00014-97-0989 and AFOSR/DARPA Grant No.
F49620-99-2-0332.
DD11.29
BAND GAPS OF D0 OXIDES: FROM Ti TO W. H.W. Eng, P.M.
Woodward, The Ohio State Univ, Dept of Chemistry, Columbus, OH.
Photocatalytic properties of a material are highly dependent upon the
662
energy levels of the valence and conduction bands relative to the
reactant's HOMO and LUMO. Band edge positions control not only
the wavelength of light that can be absorbed, but also the energetics
of permissible surface redox reactions. Band edge positions are
aected by (a) the charge transfer energy from the oxygen to metal,
(b) local coordination and symmetry about the metal, (c) the
connectivity of the MOn polyhedra, and (d) inductive
eects. We
have6+systematically
examined
band4+gaps of d0 transition metal oxides
6+
5+
5+
(W , Mo , Ta , Nb , and Ti ) in a variety of structures, using
UV-Vis reectance spectroscopy, x-ray powder diraction, and LMTO
band structure calculations. The prospects for tuning band edge
positions of oxide materials, by modifying the polyhedral connectivity
and the identities of the transition metal and spectator cations, will
be discussed. The feasibility of using calculations for predicting band
gaps will also be presented.
DD11.32
STRUCTURAL AND MAGNETIC PROPERTIES OF
NdBaCo2O5+ . Jonathan Burley, John Mitchell, Materials Science
Division, Argonne National Laboratory, IL.
The structural and magnetic properties of the oxygen-decient
perovskite series NdBaCo2O5+ have been studied using neutron
powder diraction, electron microscopy and magnetic measurements.
We nd evidence of: i) long-range spin-crossover behavior as a
function of but not temperature; ii) no long-range
charge order for
2+
any composition, notably at = 0 where Co
=
1;
iii) short-range
3+
Co
magnetic order in the structurally well-ordered
sample having = 0.5,
in contrast to the G-type long-range magnetic order shown by the
structurally disordered materials with 6= 0.5.
DD11.30
THERMOELECTRIC PROPERTIES OF MAGNETICALLY c-AXIS
ALIGNED POLYCRYSTALS IN (Ca2Com Om+20 )0:62 CoO2 (m=1
and 2). Shigeru Horii, M. Sano, M. Suzuki, K. Otzschi, J. Shimoyama,
and K. Kishio, Univ. of Tokyo, Dept. of Superconductivity, JAPAN; I.
Matsubara, M. Shikano, and R. Funahashi, National Institute of
Advanced Industrial Science and Technology, Osaka, JAPAN.
Recent development of thermoelectric (TE) materials in cobalt oxides
has been triggered by the discovery of high TE properties in
NaxCoO2 [1]. Up to now, high TE performance was reported also in a
homologous series of (Ax By Ox+y )0:62 CoO2 consisting of (A, B, x,
y) = (Bi, Sr, 2, 2), (Ca, Co, 2, 1) and (Ca, [Co, Cu], 2, 2), in which
the blocking layer (Ax By Ox+y ) of the rocksalt-type and the CoO2
layer of CdI2 -type were alternately stacking along the c-axis direction.
Therefore, their electronic properties are anisotropic and it is
expected that the c-axis alignment brings
development of TE
performance, especially power factor (S 2 /), along ab plane due to
decrease of resistivity compared with a non-oriented polycrystal. In
the present study, for the materials in (Ax By Ox+y ) = (Ca, Co, 2, 1)
and (Ca, [Co, Cu], 2, 2), we prepared highly c-axis-oriented and
densied polycrystalline bulks by means of magnetic alignment
process (MA) and the spark plasma sintering process (SPS).
Resistivity of the MA+SPS sample along ab-plane at 300K was found
to be approximately 6 m
cm, which is two times smaller than that of
the SPS sample. We report TE properties of the MA, SPS and
MA+SPS samples, and discuss close relationship between the power
factor and microstructure. [1] I. Terasaki, Y. Sasago, and K.
Uchinokura, Phys. Rev. B, R12685 (1997).
DD11.31
SYNTHESIS AND CHARACTERIZATION OF RARE-EARTH
SUBSTITUTED BISMUTH IRON TITANATE CERAMIC SYSTEM
(R-BIT). Srinivas Adiraj, Dong-Wan Kim, Kug Sun Hong, Seoul
National University, School of Materials Science & Engineering, Seoul,
SOUTH KOREA.
Bismuth Layer Structured Ferroelectric materials (BLSF) have been
studied widely, because of their stability in structure, high curie
temperatures, anisotropic characteristics and possible properties for
memory2+devices with general2formula
of
(Bi2 O2 ) (Am01 Bm O3m+1 ) 0 . Bismuth titanate (BT) is ferroelectric with a high transition temperature around 675 C and
Bismuth ferrite with a transition temperature around 850 C. When
one mole of Bismuth ferrite is added to Bismuth titanate, the material
Bi5 FeTi3 O15 , showed high
order of resistivity with two dielectric
transitions around 580C and 750C. To reduce the high transition
temperatures, large coercive eld and hence large switching eld, it is
necessary to reduce transition temperature, which can be attempted
by substituting dierent ions at A or B site respectively. In this study,
Rare-earth ions are substituted (R= Nd, Sm, Gd, Dy) at A-site to
study the structural changes, electrical properties and dielectric
behaviour. The system can be written as RBi3 Ti3 O12 + BiFeO3 ( R =
Nd, Sm, Gd, Dy) giving rise to these compounds, viz.,
NdBi4 FeTi3 O15 , SmBi4 FeTi3 O15 , GdBi4 FeTi3 O15 , DyBi4 FeTi3 O15 .
The compounds are synthesized by solid-state double sintering
method. X-ray analysis indicate that the materials are formed in
single phase with an Orthorhombic distortion. The order of resistivity
is around 1012 1cm at room temperature. The dielectric
measurements were carried out from 80-300K and 30-800 C. Low
temperature transitions were observed in these compounds at an
elevated temperatures. With the change of frequency there is a
gradual change in the peak positions. A similar behavior is observed
at high temperature dielectric measurements. A gradual decrease of
transition temperature is observed
in high temperature dielectric
measurements ie., from 680C to 250C. The change in dielectric
peaks with frequency indicates a relaxor type of behavior. Hence, with
the addition of Rare earth ions at the A-site with an attempt to
reduce the transition temperature have been acheived and the results
are to be discussed.
SESSION DD12: SYNTHESIS, CRYSTAL GROWTH
Chairs: Arthur W. Sleight and Paul Alivisatos
Friday Morning, December 6, 2002
Back Bay C (Sheraton)
8:30 AM *DD12.1
CRYSTAL GROWTH OF QUATERNARY RUTHENIUM AND
OSMIUM CONTAINING PEROVSKITES FROM REACTIVE
HYDROXIDE FLUXES. H.-C. zur Loye, K.E. Stitzer, M.D. Smith,
University of South Carolina, Department of Chemistry and
Biochemistry, Columbia, SC.
The utilization of high temperature solutions has been very eective
for the growth of oxide single crystals containing virtually all elements
in the periodic table with a wide range of oxidation states. Oxide
crystals have been grown from many dierent high temperature
solutions, including alkali and alkaline earth carbonates, halides,
peroxides, super oxides, and hydroxides. Of these diverse solvent
systems, the hydroxide melts have proven to be the most
advantageous for obtaining crystals containing elements in unusually
high oxidation states. Our group has been concentrating on the use of
such melts to incorporate members of the platinum group metals into
oxide structures. To that end, we have synthesized new ternary
osmium and ruthenium containing perovskite oxides from reactive
hydroxide uxes. Specically, the crystal growth, structural
characterization, and magnetic properties of Ba2 MOsO6 (M = Li, Na)
and Ba3 MRu2 O9 (M = Li, Na) will be discussed. Of particular
interest is the coupled structural and magnetic transition that
Ba3 NaRu2 O9 undergoes at low temperatures.
9:00 AM DD12.2
BOND VALENCE SUMMATIONS FOR PARTIALLY-DISORDERED
PYROCHLORE
SOLID SOLUTIONS A2(B0 y B10y )2 O7 AND
(A0 z A10z )2 B2 O7 . David J. Davis and Bernhardt J. Wuensch,
Massachusetts Institute of Technology, Department of Materials
Science and Engineering, Cambridge, MA; and Kevin W. Eberman,
3M Center, St. Paul, MN.
Oxides with the pyrochlore structure type, A2 B2 O7 , are
superstructures based upon a parent uorite-type oxide,3+M4 O8 . The
pyrochlores4+ that we have examined combine a larger A ion with a
smaller B . Ordering of the A and B species among the available
tetrahedral sites within the oxygen array results in doubling of the
lattice constants of the M4 O8 parent structure. Electroneutrality is
achieved through omission of one-eighth of the anions per formula
unit. The arrangement of the vacant anion sites is also ordered.
Dierence in cation size is believed to be responsible for the ordering
because a disordered non-stoichiometric uorite phase forms in
preference to pyrochlore for radius ratios RA/RB below0 a critical
value. The substitution of a0 larger tetravalent cation, B , for B or of a
smaller trivalent species, A , for A results in a reduction in the
average size dierence of the cations and should thus drive the system
toward disorder. Neutron or X-ray Rietveld analyses were performed
on four series0 of solid solutions in which B was progressively replaced
by a larger B . Two systems were driven to complete disorder before
full replacement of B. The other two systems remained steadfastly
ordered despite overlap of the range of radius ratios with the former
systems. Solid solution extended only to z<0.4 in a recently-examined
series of A-site solid solutions but partial disorder was induced over
this range of compositions. Remarkably, disorder (in the systems in
which it occurred) evolved at independent rates in the anion and
cation arrays in spite of the Coulombic coupling that one would
anticipate. Bond-valence summations were evaluated to successfully
explain this behavior. An increase in occupancy of the interstitial
oxygen site is necessary to compensate the change in bond valence
that results from the shift in atomic positions caused by solid solution.
9:15 AM DD12.3
NEW MATERIALS FROM POLYCHALCOARSENATE FLUXES.
Ratnasabapathy G. Iyer and Mercouri G. Kanatzidis, Department of
663
Chemistry, Michigan State University, East Lansing, MI.
In view of the considerable body of information now available on
polychalcophosphate uxes (Kanatzidis M. G. Curr. Opin. Solid State
Mater. Sci. 1997, 2, 139), it is timely to ask how the corresponding
polychalcoarsenate uxes perform as synthetic tools and what type of
phases are likely to form. Since P and As are members of the same
group in the periodic table one might expect simple analogs both in
composition and structure. However, there seems to be a signicant
partition at the P-As boundary in terms of chemical and electronic
behavior in these two elements mainly because of the dierence in
their ionization energies. For example, whereas the most stable
oxidation states of P s are +4 and +5, this is not likely to be the case
for As because of the greater stability of the +3 state and the extreme
rarity of the +4 state. The corresponding ethane-like unit [As2Q6]4(ubiquitous in P chemistry) does not exist, however other anions such
as [As2Q5]4-, [AsQ3]3-, are known and might form in the melt.
Conversely, in P chemistry these species are unknown or are
extremely rare. The only species common in both elements are the
classical tetrahedral [PQ4]3- and [AsQ4]3-, anions. Arguably, we
anticipate a sharp contrast between [AsxQy]z- and [PxQy]zchemistry. We will present recent results in this area of inorganic solid
state chemistry along with new materials in the A-Sn-As-Q (A=alkali
metal) system and their corresponding properties.
9:30 AM DD12.4
SYNTHESIS OF A NEW CLASS OF HYBRID SOLIDS VIA SALT
INCLUSION. Qun Huang, Mutlu Kartin, Xunhua Mo,
Shiou-Jyh Hwu, Clemson University, Dept of Chemistry, Clemson, SC.
Traditional synthesis of inorganic/organic hybrid materials employing
organic molecules as a structural directing agent has resulted in many
solids with special frameworks. We have recently discovered a new
class of transition-metal-oxide based composite solids via the inclusion
of alkali and alkaline-earth metal halides. These new solids were
synthesized by conventional high-temperature, solid-state methods
employing reactive molten salt. Single crystal structure studies
revealed a new type of composite frameworks made of mixed covalent
and ionic lattices. The incorporated salt exhibits promising structural
directing eects giving rise to a number of fascinating hybrid lattices
containing nano-structured transition-metal-oxide frameworks.
Depending upon the composition and, subsequently, the coordination
environment of halide anions, the resulting covalent lattice varies from
clusters, sheets, to porous structures. Due to the weak interaction
between the two chemically dissimilar lattices, in some cases, the salt
lattice is removable showing the de-intercalation and re-intercalation
reactions of technological importance. In this seminar, we will present
three families of composite solids that exhibit novel host/guest
structure relationships. The discussion will include the synthesis and
characterization of the following new phases: Na5ACu4 (AsO4 )4 Cl2 (A
= Rb, Cs), Cs2 Mo4P2 O16 CsBr, ANbAsO5 Cl (A = Rb, Cs), and
(salt)A2Cu2n01 (P2 O7 )n (A = Cs; n = 14). We will also present
some highlights on the recent synthesis of chiral solids via newly
discovered salt-inclusion methods.
10:15 AM DD12.5
GAS ABSORPTION IN RIGID NANOPOROUS GLASSY
NETWORKS PRODUCED BY ORGANIC-INORGANIC
SYNTHESIS AND COMPUTER SIMULATION. C.A. Angell, X.-G.
Sun, W. Xu, A. Chizmeshya, and A. Kahn, Depts. of Chemistry and
Materials Science, Arizona State University, Tempe, AZ.
We describe the synthesis of \microporous" glassy materials based on
J. C. Maxwell's original 1864 framework rigidity analyses in which he
determined how many freely-jointed slats must be randomly
connected before a rigid structure results. This is related to the
rigidity percolation problem in covalent glasses studied by Thorpe and
Phillips. With both bond lengths and bond angles xed, rigidity set in
at a bond density of 2.4 per atom. We study the intermediate case
using molecular slats in place of atoms, to produce microporous
glasses. This resolves one of the major problems of Yaghi et al. which
has been to promote rapid crystallization of their microporous
compounds. We suggest that, for slats longer than some minimum
value (to be determined) the amorphous state will become the
thermodynamically stable state. By changing the bond density,
porosity becomes a variable of the composition. The ability to tune
porosity would be a great advantage for applications e.g. (i)
optimizing gas surface interactions to maximize storage capacity for a
given gas, or alternatively (ii) optimizing average porosity to promote
gas separations We conrm nanoporous amorphous character in
materials produced from the reactions of rigid slat precursors like 1,9
dihydroxy naphthalene, and bis-phenol A, with \4-linkers" such as
TiCl4, and Ti(OEt)4 and 3-linkers like B(OEt)3. The void-void
correlation length, estimated from the position of the \rst sharp
diraction peak" in the x-ray powder pattern, is 12-14 A. To explore
the parameters of importance to gas storage in such materials we
perform MD simulations on a constant pressure model system in
which the slats are end-charged \stick" ions whose interaction with
the gas molecules (here argon) can be varied. Network centres are
Si4+ ions. The net lls rapidly with gas at low pressure and 25 C
from empty starting conguration. Structural and dynamic
correlations are described.
10:30 AM DD12.6
MODULATED STRUCTURES IN VANADIUM OXIDE
INTERCALATES. Peter Y. Zavalij, M. Stanley Whittingham,
Institute for Materials Research and Chemistry Department, State
University of New York at Binghamton, Binghamton, NY.
There has been much interest recently in vanadium oxides and their
intercalates because of their potential use as secondary cathode
materials for lithium batteries and their application in oxidative
catalysis. The vanadium oxide frameworks have rich crystal-chemistry
[1] and intercalation chemistry because of the variety of vanadium
coordination polyhedra as well as oxidation states varying from +5 to
+3 or even to +2. The latter denes red-ox properties, which readily
allow the insertion or removal of ions such as lithium. The formation
of the vanadium oxide frameworks is dictated to a great extent by the
intercalating/templating species usually such as ammonium,
tetramethyl ammonium (tma), lithium and other metals or their
complexes. The size, shape and other properties (e.g. charge) of these
particles play key roles in the framework organization. For instance,
intercalation of two dierent ions results in more complex framework
as it was found in layered V3O7 intercalated with tetramethyl
ammonium and cobalt(II) tetrahydrate [2]. However, sometimes ions
cannot t perfectly into the framework they form which yields
dierent kinds of structure disorder. This work presents disordered
structure of two layered vanadium oxides and eect of temperature on
disorder. In (NH4 )2 V3O8 , it was found that at room temperature
orientation of the ammonium is statistically disordered. Amazingly,
when this structure is cooled to 100 K, it does not become ordered; in
contrary it turns into an incommensurate structure with
two-dimensional modulation. Another compound, tmaV4O10 , has
one-dimensional modulated structure at room temperature. This
incommensurate structure, when cooled, turns into commensurate
structure except with two-dimensional modulation. This work was
supported by NSF under grant DMR9810198. 1. P.Y. Zavalij and M.S.
Whittingham Acta Cryst., B55, 627-663 (1999) 2. X. Wang, L. Liu,
A.J. Jacobson, and K. Ross. J. Mater. Chem., 9, 859-861 (1999).
10:45 AM DD12.7
UNDERSTANDING OF Li ORDER-DISORDER
TRANSITIONS IN
Lix V2 (PO4 )3 PHASES (x=3.00.0) by 7 Li SOLID STATE NMR
AND NEUTRON DIFFRACTION. Shih-Chieh Yin, Linda F. Nazar,
Department of Chemistry, University of Waterloo, CANADA; Hiltrud
Grondey, Department of Chemistry, University of Toronto, CANADA;
Robert Hammond, Chalk River Laboratories, CANADA; Pierre
Strobel, ILL, Grenoble, FRANCE.
Open framework structures composed of polyanions (XO4 )n0
tetrahedra (X=P, As) and MO6 octahedra (M=Fe, V, Mn) were rst
introduced by Goodenough and Delmas as alternatives to lithium
transition metal oxides as Li hosts for reversible Li insertion reactions.
These form the basis for Li-ion electrodes. Typical open circuit
voltages (up to 2V higher than their oxide analogues) provide high
energy densities along with good stability features. -Li3 V2(PO4 )3
has a theoretical capacity of 200mAh/g at an average potential of
3.7V - this, coupled with a fast kinetic response make it a very
appealing cathode material. The material exhibits a series of
interesting steps in its voltage-composition curve at 3.55V, 4.1V and
4.6V upon Li extraction, that correspond to distinct Li compositions
(single phases). We have prepared these four delithiated phases,
Lix V2 (PO4 )3 , (x = 2.5, 2, 1, 0) by controlled chemical oxidation of
-Li3 V2(PO4 )3 . Chemical lithiation was used to prepare re-inserted
phases up to the7 starting composition Li3 V2(PO4 )3 . We have used a
combination of Li NMR and neutron diraction to precisely locate
the Li siting, and obtain an understanding of Li migration and lattice
thermodynamics in this system. These studies show that the excellent
electrochemical behavior is related to the fact that the basic
V2 (PO4 )3 framework changes little throughout Li extraction and
deinsertion; and that the series of phase transitions observed
electrochemically are solely due to Li reordering within specic lattice
sites. Only small distortions of the framework occur that are
completely reversible on Li re-insertion. On re-insertion of Li, solid
solution
behavior is exhibited up to x= 2.0, which results from subtle
Li+ - Vn+ interactions
that aect the potential of the Li sites. Charge
ordering of the Vn+ sites contributes to this phenomenon. Complete
reversibility of the system on Li extraction/re-insertion is
demonstrated by both diraction and NMR data.
11:00 AM DD12.8
REINVESTIGATION OF THE INCOMMENSURATE STRUCTURE
OF LITHARGE. Gianguido Baldinozzi, Jean-Marc Raulot,
Structures, proprietes et modelisation des solides, CNRS-Ecole
664
Centrale Paris, Ch^atenay-Malabry, FRANCE; Vaclav Petricek, Dept
of Physics, Czech Academy of Sciences, Praha, CZECH REPUBLIC;
Georgette Petot, Structures, proprietes et modelisation des solides,
CNRS-Ecole Centrale Paris, Ch^atenay-Malabry, FRANCE.
Lead monoxide exists in two crystal modications, namely {PbO,
litharge (red, tetragonal) and {PbO massicot (yellow, orthorhombic)
and both nd widespread applications (storage battery plates,
ceramics, paint, rubber products, piezoelectric devices, glass, : : :).
Both forms are photoactive semiconductors with band gap energies
lying in the visible region of the solar spectrum, 1.92 () and 2.7 eV
(). {PbO crystallizes below 765 K in a P4/nmm (Z=2) tetragonal
phase (a=3.970 A, c=5.022 A). A second order phase transition occurs
at 224 K. The low temperature phase is incommensurately modulated
and no lock{in transition occurs down to 2 K. The average structure
is orthorhombic Cmma and the spontaneous strain 12 is only
0.000437 at 2K. The satellite reections are quite weak both by X-ray
and neutron diraction. The weak bonds along the c axis and the
ferroelastic nature of the incommensurate phase prevent the growth of
single crystal suitable for high quality diraction techniques (very
small ferroelastic domains and frequent stacking faults). Accurate
measurements on powder samples? have shown unambiguously that the
modulation vector is along the b axis. A structural determination of
the incommensurate structure was proposed in the superspace group
C2mb(00) using the integrated intensities extracted from the powder
diraction patterns. More recently an electron microscopy study
suggests the existence of systematic extinctions aecting the satellite
reections and it supports the more symmetric space group
Cmma(00)s00. In this work, high resolution powder diraction
patterns (synchrotron and neutron) were rened in the
incommensurate phase using the Rietveld method. Various superspace
groups and forms for the modulated displacements were tested. A
structural model is proposed for this phase, and the domain
microstructure observed by electron microscopy is discussed. The
consequences of this structural model on the electronic structure are
analysed by ab-initio calculations (LMTO and Abinit).
Much attention to perovskite-type and related oxides containing Bi3+
such as Bi1=2 Na1=2TiO3 [1] have been recently paid owing to their
ferroelectricity(FE) and antiferroelectricity(AFE).
Because Bi3+ ion
has the same electronic conguration (6s)2 as Pb2+ ion has, FE and
AFE in Bi compounds
is thought to be induced by the hybridization
between the (6s)2 and 2p orbitals of oxygens as Pb compounds[1].
However, due to the lower structural stability of Bi-containg
perovskite under ambient condition than Pb-containig
perovskite
originated from the smaller ionic radius of Bi3+ than Pb2+ [2], there
are fewer studies with respect to Bi-containing perovskites compared
with those with respect to Pb-containing, and in order to discuss
about FE and AFE more extensively it is important to synthesize
novel bismuth perovskites and investigate the structures and dielectric
properties. The stabilization of Bi-containing perovskite phase has
been demonstrated using high pressure. It has been reported that
BiMO3 (M=Mn, Cr [3], Sc, Ni, Co, Y[4]) was successfully synthesized
under a pressure as high as 4-7 GPa. In this study, a ferroelectric
perovskite Bi1=2 Ag1=2 TiO3 [5] and antiferroelectric perovskites
Bi(M1=2 Ti1=2 )O3 (M=Ni and so on) under oxygen pressure or high
pressure of 5-6 GPa were synthesized and their crystal structures were
examined. The lattice distortion of ferroelectric/antiferroelectric
bismuth perovskites including them will be discussed. 1. G.A.
Smolenskii, V.A. Isupov, A.I. Agaranovskaya and N.N. Krainik,
Soviet Physics-Solid State, 2, 2651 (1961) [translated from Fizika
Tverdogo Tela, 2(11), 2982 (1960)]. 2. R.D. Shannon, Acta Cryst.,
A32, 751(1976). 3. F. Sugawara and S. Iida, J. Phys. Soc. Jpn., 20,
1529(1965). 4. Y.Y. Tomashpo'lski and Y. N. Venettsev, Translation
of Izv. Akad. Nauk SSSR, Neorg. Mat., 5, 1279(1969). 5. Y.
Inaguma, T. Katsumata, R. Wang, K. Kobashi, M. Itoh, Y.-J. Shan
and T. Nakamura, Ferroelectrics, 264, 127 (2001).
SESSION DD13: SYNTHESIS AND PROPERTIES
Chairs: Hans-Conrad zur Loye and
Bernhardt J. Wuensch
Friday Afternoon, December 6, 2002
Back Bay C (Sheraton)
11:15 AM DD12.9
READY REACTIVITY AND UNEXPECTED PHASE
TRANSFORMATION AT THE NANOMETER SCALE.
James L. Gole and John Stout, School of Physics, and Zurong Dai
and Z.L. Wang, School of Materials Science and Engineering, Georgia
Institute of Technology, Atlanta, GA; Clemens Burda and Frank
Ernst, Case Western Reserve University, Cleveland, OH.
Signicant changes in reactivity and phase transformation are found
to accompany the transition to the nanometer scale for both SnO2
and TiO2 structures. Two unique snytheses have been used to
generate SnO20x nanowires, nanoribbons, and nanotubes. Crystalline
nanowires which display both a rutile and orthohombic structure are
formed from high temperature synthesis with SnO/SnO and Sn/SnO
mixtures. Several of the wires display phase transformations between
the rutile and orthohombic crystal structures normally observed at
pressures in excess of 150 kbar in the bulk. Similarly, under somewhat
dierent experimental conditions nanoribbons and nanotubular
structures can be formed which display combined rutile and
orthohombic structures. These tin oxide nanostructures have now
been used to provide a considerably improved hydroxylation of phenol
by hydrogen peroxide, and may play a future role in advanced acid
catalysis. Unique reactivity and ready phase transformation is found
to accompany the nitriding of TiO2 nanoparticles, eciently
producing TiO20x N2 nanoparticles which represent photocatalytically1
active quantum dots absorbing light well into the visible. Asahi et al.
have prepared TiO20x N2 lms and powders by sputtering TiO
2
targets in N2/Ar gas and anealing for 4 hours in N2 at 550C or by
treating TiO2 powder in an NH3 (67%)/Ar atmosphere at 600 C for 3
hours. Taking advantage of the fact that nanoparticles may have a
signicantly enhanced interaction-reaction probability, we have
successfully accomplished the conversion of TiO2 to TiO2 0 xNx at
room temperature on a time frame less than two minutes. Here, TiO2
nanoparticles are treated with triethylamine to provide the source of
nitrogen in forming TiO20x Nx . This solution phase conversion process
represents a much
simpler, faster, and higher yield process than that
of Asahi et al.1 in the gas phase to produce an eective photocatalyst
absorbing in the visible. In distinct contrast, the similar treatment of
either rutile or anatase TiO2 powders does not produce the conversion
to the oxynitride at room temperature. A ready reactivity for TiO2
operative only at the nanoscale regime, is accompanied also by the
palladium induced phase transformation of TiO20x Nx .
1
R. Asahi et al., Science 293, 269 (2001).
11:30 AM DD12.10
SYNTHESIS AND LATTICE DISTORTION OF FERROELECRIC/
ANTIFERROELECTRIC BISMUTH(III)-CONTAINING
PEROVSKITES. Yoshiyuki Inaguma, Atsushi Miyaguchi, and
Tetsuhiro Katsumata, Dept. of Chemistry, Gakushuin Univ., Tokyo,
JAPAN.
1:30 PM *DD13.1
DIRECT FABRICATION OF PATTERNED FILMS OF
FUNCTIONAL CERAMICS BY ADVANCED SOFT SOLUTION
PROCESSING WITHOUT FIRING. Masahiro Yoshimura, Tomoaki
Watanabe, Takeshi Fujiwara, and Ryo Teranishi, Materials and
Structures Laboratory, Tokyo Institute of Technology, Yokohama,
JAPAN.
Soft chemical synthesis for inorganic \substance" have been developed
signicantly, but not for inorganic \materials". In order to consider
certain purpose(s) and/or application(s), \material" must have a
particular (1) shape, (2) size, (3) location, and (4) orientation, etc., in
addition to the denition of a \substance": a xed (5) chemical
composition and (6) physical state including structure, which can give
(7) characteristic properties. For inorganic \materials", shape forming
and shape xing are generally more dicult than synthesis of
\substance" due to their brittle and refractory natures. Thus we must
consider \soft processing for inorganic materials" rather than \soft
chemistry for inorganic substances." Considering those problems, we
are proposing \soft solution processing (SSP)", which can fabricate
crystallized double oxide lms in aqueous solutions at RT-200 C
without post-ring. In SSP, interfacial reactions between a
substrate/reactant (mostly of a metal) and species in a solution have
been activated electrochemically, hydrothermally,
hydrothermal-electrochemically, etc., to fabricate the lms of double
oxides. We have already succeeded to fabricate well-crystallized lms
of LiCoO2 and LiNiO2 which are electrochemically active, in addition
to BaTiO3 , SrTiO3 , SrWO4 , BaMoO4 , etc. Double
layer lm of
BaTiO3 /SrTiO3 has also been fabricated at 150C using a ow-cell
apparatus. LiCoO2 lms could be deposited on Pt, Ni, and graphite
substrates. Direct patterning of ceramic lms such as LiCoO2 ,
BaTiO3 , YVO4 , CdS and PbS, etc., in solutions has been developed.
Detailed of preparation and properties of them and feature and future
of SSP will be presented.
[References]
1) J. Mater. Res., 13 [4] 796-802 & 875-879 (1998)
2) Rev. Sci. Instr., 70 [5] 4232-2437 (1999)
3) J. Solid State Chem., 162, 364-370 (2001)
4) Adv. Mater., 14 (No., Feb. 19), 268-271 (2002)
5) MRS Bulletin, Special Issue of SSP, 25 [9] 12-16 & 17-25 (2000),
Proc. of Int. Symp. on SSP will be published in Solid State Ionics
(2002)
2:00 PM DD13.2
SYNTHESIS AND PROPERTIES OF ANATASE AND RUTILE
Ti10x Cox NF. Robert Butterick, Chris Lanci, Samuel Loand, and
K.V. Ramanujachary, Rowan University, Dept of Chemistry and
Physics, Glassboro, NJ.
665
We have synthesized both the anatase and rutile phases of TiNF via a
new chemie deuce, low-temperature method. We have completed
high-temperature x-ray diraction, magnetic susceptibility, dierential
scanning calorimetry, and thermogravimetric analysis studies. These
compounds are isostructural
to TiO2 and behave rather similarly.
Between 600 and 700C, the anatase phase changes into the rutile
one, which appears to be the thermodynamically stable phase. The
magnetic susceptibility of the parent compound appears to be very
weakly paramagnetic and temperature independent. Doping with a
few percent Co changes the color of the material from pea green to
black and gives rise to a sizable ferromagnetic moment, similar to
what has been found in Ti10x Cox O2 . The doped compound may serve
a potential magnetic semiconductor so desired for use in spintronics.
2:15 PM DD13.3
SYNTHESES OF DENSE, NEAR NET-SHAPED, ULTRAHIGH-MELTING CARBIDE/METAL
AND BORIDE/METAL
COMPOSITES AT 1300C BY THE DISPLACIVE
COMPENSATION OF POROSITY PROCESS. Matthew Dickerson,
Zbigniew Grzesik, Robert Snyder, Ken Sandhage, Dept of Materials
Science and Engineering, Ohio State Univ, Columbus, OH.
Ultra-high-melting composites of carbides or borides with refractory
metals can be more resistant to high-temperature creep and wear,
exhibit higher hardness values, and possess lower weights than
monolithic refractory metals. The fracture strengths and toughness
values of such composites can also exceed those of monolithic carbides
or borides. Consequently, such composites can be attractive for
aerospace (leading edges, rocket nozzles, heat shields) and other
applications (extrusion dies, x-ray targets, grinding tools, electrical
heaters and contacts, etc.). The fabrication of dense carbide/refractory
metal or boride/refractory
metal composites usually involves the use
of temperatures 2000C during reaction forming and/or sintering.
Such composites
can be synthesized at much lower temperatures
(1300C) via the Displacive Compensation of Porosity (DCP)
process. In this process, a rigid, porous carbide-bearing or
boride-bearing preform is inltrated with a metallic alloy liquid at
ambient pressure. A reactive element in the liquid undergoes a
displacement reaction with the preform to yield new ceramic and
metal products. By choosing a displacement reaction that generates
solid products of larger net volume than the ceramic reactant, the
pores within the rigid preform can be lled with little change in the
external shape and dimensions (\displacive compensation of
porosity"). For example, dense,
near net-shaped ZrC/W-bearing
composites (Tsolidus=2800C) have been produced by the reactive
inltration of Zr-Cu liquid into rigid, porous WC-bearing preforms at
1300C. The Zr in the liquid underwent a displacement reaction
with WC to yield W + ZrC. These solid products lled the pores
without altering the preform shape or dimensions (to within 1%). As
the pores became lled with ZrC and W, the residual Cu-rich liquid
was extruded from the preform. HfC/W, TiC/W,
and ZrB2 /W
composites have also been produced at 1300C. The rate-limiting
step(s) of such DCP reactions will be discussed, along with
microstructural tailoring and composite properties.
2:30 PM DD13.4
INTERFACING SOLID STATE AND SOFT MATERIALS.
Ulrich Wiesner, Cornell Univ, Dept of Materials Science and
Engineering, Ithaca, NY.
The study of amphiphilic polymer based functional polymer-ceramic
hybrid materials is an exciting emerging research area interfacing
solid state and soft materials and oering enormous scientic and
technological promise. By choice of the appropriate functional
polymers as well as ceramic precursors unprecedented morphology
control on the nanoscale is obtained. It is based on a unique
polymerceramic interface. The hydrophilic parts of the polymer are
completely integrated into the ceramic phase analogous to what is
found in biological hybrid materials. Through this unique interface
the ceramic phase is plasticized by the polymers thus leading to a
novel class of materials referred to as exible ceramics. The structures
generated on the nanoscale are a result of a ne balance of competing
interactions, another feature of complex biological systems. A
particularly fascinating structure discovered is a bicontinuous cubic
morphology referred to as the Plumbers Nightmare. This structure
was known from surfactant studies but was not known to exist for
polymers. The potential for new functional materials lies in the
versatility of the sol-gel chemistry as well as that of the polymer
chemistry that can be exploited in the materials synthesis. In the
present contribution the synthesis and characterization of
nanostructued materials will be presented with potential applications
ranging from microelectronics to nanobiotechnology. References: 1.)
P.F.W. Simon, R. Ulrich, H.W. Spiess, U. Wiesner, Review: Block
copolymer - ceramic hybrid materials from organically modied silicon
precursors, Chem. Mater. 13, 3464-3486, (2001). 2.) A.C. Finnefrock,
R. Ulrich, A. Du Chesne, C.C. Honeker, K. Schumacher, K.K. Unger,
S.M. Gruner, U. Wiesner, Metal-Oxide-Containing Mesoporous Silica
with Bicontinuous Plumber's Nightmare Morphology from a Block
Copolymer-Hybrid Mesophase, Angew. Chem. Int. Ed. 40, 1208-1211,
(2001); Angew. Chem. 113, 1248-1251, (2001).
3:15 PM DD13.5
RATIONAL DESIGN AND SYNTHESIS OF NEW OXY-HALIDES
AND OXIDES THROUGH LOW TEMPERATURE SYNTHETIC
STRATEGIES. Thomas A. Kodenkandath, Liliana Viciu, Andrew
Bankston and John B. Wiley, Department of Chemistry & Advanced
Materials Research Institute, University of New Orleans, New
Orleans, LA.
The search for novel materials with interesting structures and
properties continues to be an active area of solid-state chemistry. The
challenge, however, has been to develop methodologies by which one
can rationally design and synthesize new materials with specic
structural and chemical motifs so that it will be possible to predict
and control their properties. Here we demonstrate low temperature
topotactic routes to assemble metal-halide networks within oxide
hosts to from new oxy-halides and further extraction to from new
oxides. Ion exchange between RbLaNb2O7 and MCl2 (M = Mn, Fe,
Cu) results in (MCl)LaNb2O7 . In the case of (CuCl)LaNb2 O7 , the
extraction of CuCl2 results in Cu0:5 LaNb2O7 . For the other metals,
M0:5 LaNb2O7 compounds can be formed directly by ion exchange
reactions. All of these conversions were achieved below 500C and the
materials retain the original perovskite lattice of the host. Details of
the synthesis, structure and properties of these novel phases with
emphasis on (CuCl)LaNb2O7 and Cu0:5LaNb2O7 will be presented.
3:30 PM DD13.6
EXPLORATION OF CATION SUBSTITUTION IN THE LAYERED
COMPOUND CHROMIUM TUNGSTEN DINITRIDE. K. Scott Weil,
Pacic Northwest National Laboratory, Department of Materials
Science, Richland, WA; Prashant Kumta, Carnegie Mellon University,
Department of Materials Science, Pittsburgh, PA; Jekabs Grins,
Stockholm University, Department of Inorganic Chemistry,
Stockholm, SWEDEN.
A series of substituted compounds, based on the layered parent phase
chromium tungsten dinitride, have been synthesized using a
complexed precursor synthesis route. As determined by powder x-ray
diraction data, Rietveld analysis, and crystal structural modeling,
the layer in which the substituted cation sits depends on its size and
charge. In some cases, cation substitution does not occur directly, but
instead causes a step-wise displacement of cations within the parent
structure. The magnetic properties of these compounds display trends
with composition that appear to conrm the results from the crystal
structure analyses. The methodology for compound synthesis and the
results from the structure and property characterization studies will
be discussed.
3:45 PM DD13.7
SYNTHESIS AND CHARACTERIZATION OF HETEROPOLYNIOBATES. May Nyman, Francois Bonhomme, Brian R.
Cherry, Todd M. Alam, Mark A. Rodriguez, Louise J. Criscenti,
Randall T. Cygan, Sandia National Laboratories, Albuquerque, NM.
The chemistry of heteropolyanions has been known for hundreds of
years, rst being dominated by heteropolytungstates and
heteropolymolybdates, and more recently heteropolyvanadates. The
related isopolyanions include not only isopoly -molybdates,
-tungstates and -vanadates, but also a few -niobates and -tantalates.
Yet, heteropolyniobates and heteropolytungstates have been relatively
unexplored compared to their close periodic neighbors. We present
here a general synthetic procedure from which we have obtained the
rst examples of heteropolyniobates. This procedure involves
hydrothermal dissolution of metal oxide precursors in basic solution,
rather than room temperature precipitation from an acidic solution, as
heteropolymetalates are more commonly formed. Structures featuring
both isolated, soluble heteropolyniobate clusters, and extended solids
of linked heteropolyniobates will be presented. Cluster types include
the well-known Keggin geometry, as well as unprecedented cluster
geometries. We will discuss the dierences in synthetic procedures and
chemical characteristics of the heteropolyniobates compared to the
heteropoly -vanadates, -molybdates and -tungstates. Molecular
modeling of stability of heteroatoms within a niobate cluster will also
be presented. Sandia is a multiprogram laboratory operated by Sandia
Corporation, a Lockheed Martin Company, for the United States
Department of Energy under Contract DE-AC04-94AL85000.
4:00 PM DD13.8
TEMPLATED GROWTH OF COMPLEX NITRIDE ISLAND
DISPERSIONS BY CONTROLLED INTERNAL REACTIONS.
Michael Brady, Peter Tortorelli, Joseph Horton, Sarah Wrobel, David
Hoelzer, Andrew Payzant, Ian Anderson, Larry Walker, Oak Ridge
National Laboratory, Oak Ridge, TN.
666
A new synthesis route for the controlled production of near-surface,
complex (ternary and higher order) ceramic island dispersions is
proposed. This approach is based on internal reaction phenomena
(oxidation, nitridation, carburization, etc.) in two-phase metallic alloy
precursors and can be used to synthesize structures on the micro,
meso, and, potentially, nano scales. Proof of principle is shown by
synthesis of a micro-dispersion of a complex nitride perovskite,
Cr3PtN, in Cr2N or Cr(Pt) by internal nitridation of a two-phase
Cr(Pt) + Cr3Pt precursor alloy. We are attempting to further develop
and extend this approach to the synthesis of magnetic nano/meso
scale dispersions of Fe17RE2Nx (RE = rare earth) type phases in Fe
or FexNy by internal nitridation in Fe17RE2-precipitated Fe. A
framework for the proposed synthesis concept, details of nitridation
behavior in the model Cr3Pt/Cr system, and preliminary results of
nitridation reactions in Fe17Nd2-dispersed Fe will be presented.
4:15 PM DD13.9
NOVEL URANYL MOLYBDATE TRIAZOLATES AND THEIR
RELATIONSHIP TO MINERAL STRUCTURES.
Christopher L. Cahill, Nils Schnor, Jacquelynn Danek and Lauren
Borkowski, George Washington University, Dept. of Chemistry,
Washington, DC.
Several novel uranyl molybdate compounds have been synthesized
under hydrothermal conditions using 1,2,4-trazole or related
compounds as organic structure directing agents. In particular,
hydrothermal treatment of MoO3 , UO2 (NO3 )2 and 1,2-4 triazole has
lead to the formation of (C2 H3 N2)UO2 Mo2 O7 (GW2-1). This
material contains U(VI)-O pentagonal bipyramids and Mo(VI)-X (X
= O, N) octahedra as structural building units. These polyhedra link
at their vertices to form neutral layers with a topology identical to
that of the mineral iriginite. The neutral triazole molecules in GW2-1
are coordinated to the molybdenum sites at a distance of approx. 2.4
; an unprecedented interaction in the organic-U-Mo system. This
A
coordination suggests the potential to tether or stitch the layers
together through difunctionalized N-containing ligands.
4:30 PM DD13.10
Abstract Withdrawn.
4:45 PM DD13.11
PREPARATION OF IRON(III) OXIDE AND ITS HYDRATES
FROM IRON(III) VERSUS THE REACTION PARAMETERS.
Meriadeg Charlou, Georges Denes and Andre L. Yonkeu, Concordia
University, Department of Chemistry and Biochemistry, Laboratory of
Solid State Chemistry and Mossbauer Spectroscopy, Laboratories for
Inorganic Materials, Montreal, Quebec, CANADA.
Many hydrated iron oxides, natural and synthetic, have been
reported. They are major constituents of soils and sediments, and are
important corrosion at iron surfaces. They are usually prepared in the
laboratory by hydrolysis of a ferric solution in highly basic conditions.
This results in a gel that can take a very long time to dry. It was
shown by one of us (GD) that the resulting dark brown powder is
antiferromagnetically ordered. It is amorphous and has
superparamagnetic properties down to 77K. At 4.2K, hyperne
magnetic eld distribution is observed by Mossbauer Spectroscopy. In
the present study, the preparation conditions were varied as follows:
pH = 2.30 - 9.30, temperature
of reaction mixture: ambient to 85 C,
annealing temperature: 150C to 1000C. In acidic medium, no
precipitation occurs at ambient temperature, however, at high
temperature, a precipitate is formed
after standing 24 hours. In basic
conditions, synthesis up to 45C result in amorphous iron(III)
hydroxide being produced. However, at 65 C, a minor amount of
crystalline FeOOH is also obtained. At 85 C, the amount of FeOOH
obtained is much higher. Annealing results in dehydration and
recrystallization of hematite. The average particle size of hematite
increases
linearly with increasing temperature, from ca. 13nm at
150C to 700C at 1000C. On the other hand, the particle dimension
of FeOOH
decreases from 27nm (not annealed) to 11nm (annealed at
250C.
667