NEW ASPECTS OF THE STRUCTURE AND DYNAMICS IN NANOCRYSTALLINE OXIDES
I. OVERVIEW OF THE PROJECT
Properties of materials can be drastically changed when one or more dimensions are in the nanometre regime. The
resulting changes in chemical, physical and biological behaviour, with exciting technological applications, has been of
intense and growing interest over the last decade and a new research area, that of nanostructured materials, has emerged.
Applications of these materials, nanotechnology, features in the forward science planning of most developed countries
(e.g. in Foresight plans of the UK, Japan and US) and the US government regards it as “the next industrial revolution”.
This application is focused on one particular class of these novel materials, namely nanocrystalline oxides, which are
attracting special attention as advanced ceramics, catalysts, sensors and adsorbents. These applications rely on the unique,
but very poorly understood, structures and atomic transport mechanisms in nanocrystals. The aim of the project is to
define the microstructure and measure atomic transport in selected materials, and hence better understand the fundamental
parameters and mechanisms, which govern these properties. The planned work will build on the expertise of the
applicants, their successful EPSRC project (grant GR/K74876) in this area, and recent developments in the synthesis of
such materials. Key features of the proposal are the use of nanocrystals from different preparative routes and novel
methods of restricting the grain growth.
II. TRACK RECORD OF THE APPLICANTS
The applicants firmly believe that it is the synergy of understanding the underlying chemistry and physics that underpins
strong materials technology in this country. They have specialised expertise in the various sophisticated methods and
techniques involved in this proposal, and have well established reputations in the area of solid-state science. However,
key to the success of this project will be the very strong research links that exist between the applicants (joint grants,
postdoctoral fellows, postgraduate students and publications) that give the combined team a unique position in the study
of defective materials. The investigators have closely collaborated on combined studies of glasses [1,2] and, particularly
relevant to the current project, sol-gel synthesis of nanocrystalline oxides [3,4]. The applicants were the investigators on
project GR/K74876 (rated 4), an investigation of O2- ion diffusion in technologically important nanocrystalline oxides.
That project was extremely fruitful [4-7] and provided some of the foundations on which the current proposal is based.
Alan V. Chadwick (Professor of Physical Chemistry, University of Kent, AVC). Since the 1970's his group has specialised
in experimental studies of point defects and diffusion in solids, including ionic crystals, inert gas crystals and amorphous
solids, with over 190 research papers. The major experimental techniques have been radiotracer diffusion and electrical
conductivity, with a strong emphasis on carefully prepared and characterised samples. The opening of the Daresbury SRS
led to the inclusion of X-ray absorption spectroscopy (XAFS) in the armoury of techniques available to the group, and
they have been amongst the pioneers in XAFS studies of defect structures in ionic materials [8-10]. Recently, a theme of
the XAFS work of the group has been the nature of nanocrystalline oxides [e.g. 11-16] and played a significant part in the
formulation of the present proposal. Currently the group is involved in a variety of materials-based projects of both
academic and technological importance supported by government and industrial sources. In all cases the underlying goal
is a detailed understanding of the defects and/or mechanisms of atomic migration and their role in chemical and physical
processes. Examples include gas-sensing materials (EU-Interreg and Teaching Company projects), preparation of acoustooptic ionic crystals (CASE studentship with Hilger Crystals), ionic transport in polymer electrolytes (EPSRC studentship)
and proton-conducting ceramics (EPSRC grant GR/L66212). The group has long-standing collaborations with other
materials groups in the UK and abroad, was a member of the ESF Nano Project and is part of a current EU Network of
Excellence proposal for the development of lithium batteries.
Mark E. Smith (Professor of Physics, University of Warwick, MES). Mark Smith’s research programme over the last
decade has been centred on the development and application of solid-state NMR techniques to tackle questions from
materials science and technology, condensed matter physics and solid-state chemistry. The research is centred on using
NMR to improve the fundamental understanding of the local structure in a wide range of materials with an emphasis
on disordered inorganic materials. This has included developing 17O, being the first to use this approach to detect
nanoscale phase separation in sol-gel systems [17] (funded through GR/J23938). Work has also examined
nanocrystalline oxides, detecting the presence of bulk, surface and defect oxygen sites in nanocrystalline MgO [4]
(GR/K74876). Currently a central theme of the research programme is to develop a comprehensive experimental
methodology (with Prof. Newport, Kent) for disordered solids by combining NMR with neutron and X-ray diffraction,
vibrational spectroscopies and computer modelling of structure [20-24] (GR/L28647, GR/N64151 and GR/R59298).
The standing of this work can be gauged by the number of on-going international collaborations that exist resulting in
numerous publications in leading journals, and the group has recently been designated a Marie Curie training site in
“Solid State NMR of Inorganic Materials”. One of these collaborations (with Prof. K.J.D. MacKenzie FRSNZ, IRL
New Zealand) is of direct relevance to this proposal having looked at mechanochemical activation of a range of
materials with NMR. NMR provides important information on how the structure develops as amorphisation progresses
1
as the material is crushed [21-23]. All of these projects directly impact on the work of this current proposal, leading to
better materials characterisation and provide a route to understanding their composition-structure-properties relations.
A research monograph examining applications of solid state NMR to inorganic materials was recently completed [24].
A new strand to the NMR work at Warwick is to look at applications to biomolecular problems (GR/N24549). In
particular 17O NMR is proving very sensitive to structural details such as changes in hydrogen-bonding. To help this
work Smith was awarded a Royal Society Leverhulme Trust Senior Research Fellowship for the academic year
2001/2. The NMR group at Warwick is ideally equipped with internationally leading-edge hardware including 4
dedicated solid-state NMR spectrometers, as well as being one of 3 partners in the only wide-bore 800 MHz
spectrometer in the world. The group also has a very wide range of probes that include the fastest MAS rates available
(up to 50 kHz). Variable temperature experiments can be carried out over the range 4-1250 K.
TRACK RECORD REFERENCES (including titles to illustrate areas of work)
[1] Ali, F., Chadwick, A.V., Greaves, G.N., Jermy, M.C., Ngai, M.C. and Smith, M.E., ‘Examination of the mixed-alkali effect in
(Li,Na) disilicate glasses by NMR and conductivity measurements’, Solid State Nucl. Magn. Reson., 1996, 5, 133.
[2] Greaves, G.N., Chadwick, A.V., Jermy, M.C., Smith, M.E. and Zhu, R., ‘Changing Debye-Waller factors in mixed alkali KxCs(1x)Si2O5 glasses’, J. Non-Cryst. Solids, 1998, 235, 766.
[3] Ali, F., Chadwick, A.V. and Smith, M.E., ‘EXAFS analysis of the structural evolution of gel-formed La2O3’, J. Mater. Chem.,
1997, 7, 285.
[4] Chadwick, A.V., Poplett, I.J.F., Maitland, D.T.S. and Smith, M.E., ‘Oxygen speciation in nanophase MgO from solid-state O-17
NMR’, Chem. Mat., 1998¸10, 864.
[5] Chadwick, A.V., Mountjoy, G., Nield, V.M., Poplett, I.J.F., Smith, M.E., Strange, J.H. and Tucker, M.G., ‘Solid state NMR and
X-ray studies of the structural evolution of nanocrystalline zirconia’, Chem. Mater., 2001, 13, 1219.
[6] Tucker, M.G., Ph.D. thesis, 1999 (University of Kent, Canterbury, U.K.)
[7] Poplett, I.J.F., Smith, M.E. and Strange, J.H., ’A novel high temperature NMR probe design: application to O-17 studies of
gel formation of zirconia’. Meas. Sci. Technol., 2000, 11, 1703.
[8] Catlow, C.R.A., Chadwick, A.V., Greaves, G.N. and Moroney, L.M., Nature, ‘EXAFS study of defects in fluorites’, 1984, 312,
601.
[9] Catlow, C.R.A., Chadwick, A.V., Moroney, L.M. and Greaves, G.N., ‘An EXAFS study of disorder in stabilized zirconia’,
J. Amer. Ceram. Soc., 1986, 69, 272.
[10] Bush, T.S., Catlow, C.R.A., Chadwick, A.V., Cole, M., Geatches, R.M., Greaves, G.N. and Tomlinson, S.M., ‘Studies of cation
dopant sites in metal oxides by EXAFS and computer-simulation techniques’, J. Mater. Chem., 1992, 2, 309.
[11] Davis, S.R., Chadwick, A.V. and Wright, J.D., ‘A combined EXAFS and diffraction study of pure and doped nanocrystalline tin
oxide’, J. Phys. Chem. B, 1997, 101, 9901.
[12] Rush, G.E., Chadwick, A.V., Kosacki, I. and Anderson, H.U. ‘An EXAFS study of nanocrystalline yttrium stabilized cubic
zirconia films and pure zirconia powders’, J. Phys. Chem. B., 2000, 104, 9597.
[13] Rush, G.E., Chadwick, A.V., Kosacki, I. and Anderson, H.U. ‘An EXAFS study of nanocrystalline thin films’, Rad. Eff. and
Latt. Def. Solids, 2001, 156, 117.
[14] Chadwick, A.V. and Rush, G.E., ‘Characterisation of nanocrystalline metal oxides by XAS’ in Nanocrystalline Materials, eds. P.
Knauth and J. Schoonman, Kluwer, 2002, chapter 5.
[15] Chadwick, A.V., Pooley, M.J., Rammutla, K.E., Savin, S.L.P. and Rougier, A., ‘A comparison of the EXAFS of nanocrystalline
ZrO2 prepared by high-energy ball milling and other methods’, J. Phys: Condensed Matter, 2003, 15, 431.
[16] Al-Angry, Y., Savin, S.L.P., Rammutla, K.E., Pooley, M.J., van Eck, E.R.H. and Chadwick, A.V., ‘The stabilisation of metal
oxide nanocrystals by the addition of alumina’, Rad. Eff. and Latt. Def. Solids, 2003, in press.
[17] Gervais, C., Babonneau, F. and Smith, M.E., ‘Detection, quantification, and magnetic field dependence of solid-state O-17 NMR
of X-O-Y (X,Y = Si,Ti) linkages: Implications for characterizing amorphous titania-silica-based materials’, J. Phys. Chem. B,
2001, 105, 1971.
[18] Pickup, D.M., Mountjoy, G., Wallidge, G.W., Newport, R.J. and Smith, M.E., ‘Structure of (ZrO2)(x)(SiO2)(1-x) xerogels (x=0.1,
0.2, 0.3 and 0.4) from FTIR, Si-29 and O-17 MAS NMR and EXAFS’, Phys. Chem. Chem. Phys., 1999, 1, 2527.
[19] Holland, M.A., Pickup, D.M., Mountjoy, G., Tsang, E.S.C., Wallidge, G.W., Newport, R.J. and Smith, M.E., ‘Synthesis,
characterisation and performance of (TiO2)0.18(SiO2)0.82 xerogel catalysts’, J. Mater. Chem., 2000, 10, 2495.
[20] Pickup, D.M., Mountjoy, G., Holland, M.A., Wallidge, G.W., Newport, R.J. and Smith, M.E., ‘In situ EXAFS and XANES
measurements of the change in Ti co-ordination during the calcination of a (TiO2)0.18(SiO2)0.82 aerogel’, J. Phys.-Condens. Matter,
2000, 12, 9751.
[21] Temuujin, J., MacKenzie, K.J.D., Jadambaa, T., Namjildorj, B., Orziiburen, B., Smith, M.E. and Angerer, P., ‘Effect of
mechanochemical treatment on the synthesis of calcium dialuminate’, J.Mater.Chem., 2000, 20, 1019.
[22] Temuujin, J., MacKenzie, K.J.D., Jadambaa, T., Namjildorj, B., Orziiburen, B., Smith, M.E. and Angerer, P., ‘Effect of
mechanochemical activation on the thermal reactions of boehmite (-AlOOH) and -Al2O3’, Thermochimica Acta, 2000, 359,
87.
[23] MacKenzie, K.J.D., Temuujin, J., Jadambaa, T., Smith, M.E. and Angerer, P., ‘Mechanochemical synthesis and sintering
behaviour of magnesium aluminate spinel’, J.Mater.Sci. 2000, 35, 5529.
[24] MacKenzie, K.J.D. and Smith, M.E., ‘Multinuclear solid state NMR of inorganic materials’, 2002, Pergamon Press, Oxford.
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CASE FOR SUPPORT
III. SCIENTIFIC BACKGROUND
III.1 Introduction
Nanostructured materials and nanophase systems are terms used to describe materials with structure on the scale of 1 to
100nm. In comparison to their bulk counterparts they often have unique physical and chemical properties [25-31] and are
currently the focus of intense academic and technological interest. Exploiting their technological potential is a key target
in the scientific strategies of the developed countries and is highlighted in the UK Foresight programme in the areas of
both chemistry and materials [32]. In general terms the origins of the unusual behaviour are (i) that the particles have
dimensions comparable to the length scale of basic quanta in solids (e.g. the de Broglie wavelength of electrons, phonon
wavelengths, mean-free path of excitons, etc.) and/or (ii) surface effects dominate the thermodynamics and energetics of
the particles (e.g. crystal structure, surface morphology, reactivity, etc.). In nanostructured semiconductors it is the first of
these, which leads to special electrical, magnetic and optical properties and the possibility of quantum dot devices. The
second factor can lead to nanocrystals adopting different morphologies to bulk crystals with different exposed lattice
planes leading to an extraordinary surface chemistry [33,34] and catalytic activity [35]. In purely ionic nanocrystals the
particles can be smaller than the width of the space-charge region [36-40] with the prospect of novel point defect
possibilities, particularly when the crystals are doped with aliovalent impurities. The recent demonstration of unusually
high ionic conductivity in nanocrystalline heterostructures by Maier and co-workers [40] shows the potential for exciting
applications of nanocrystals in effects and devices which are dependent on ionic motion, for example in catalysis, in
chemical sensors and solid electrolytes [41]. However, the understanding of nanocrystalline ionic solids is poor and the
experimental data are both confusing and conflicting [39,42]. Maier succinctly concludes his recent review [39] with the
phrase 'even though a few conceptual points can be stated, the field of nano-ionics is largely terra incognita'. The
objectives of this project are to gain a detailed understanding of the point defects in a series of ionic nanocrystalline
oxides and explore their potential for technological applications. This will involve a programme of materials synthesis
and processing, specifically aimed at producing novel nanocrystals with high temperature stability, and their
characterisation with a range of modern techniques.
III.2 Current Knowledge
At this point it is necessary to discuss in some detail the available information on nanocrystalline solids, particularly metal
oxides. Two properties that appear generic to nanocrystalline materials are unusually high diffusion coefficients of the
atoms and very high solubilities for impurities [25]. These features have been reproduced in many experiments and have
been explained in terms of the unusual nature of the grain boundaries in nanocrystals. The early models proposed that the
high proportion of surface atoms in a nanocrystalline solid (which can approach 50% in very small crystallites) led to
highly disordered grain boundaries where the atoms would have 'gas-like' behaviour [25]. However, recent work, at Kent
and elsewhere, has shown that the method of sample preparation can play an important role in determining the
microstructure of nanocrystalline solids. The highly disordered grain boundary model is appropriate to samples prepared
by high-energy ball milling, as this commonly used preparative approach [43] has recently been shown by XRD [44] and
XAFS [15] to produce materials with a very high amorphous content. In contrast, there is mounting evidence, particularly
from XAS, that the grain boundaries in nanocrystalline metals [45] and oxides [11,12,14] are not different to those in bulk
materials. Therefore more sophisticated explanations of the experimental observations are required, which in turn must be
based on better experimental data than is currently available.
The more sophisticated explanations of the origins of the high diffusion coefficients and impurity solubilities in ionic
nanocrystals are based on the fact that the sizes of nanocrystals approach the size of the space-charge layer, which
typically extends some 100nm in a simple ionic solid like sodium chloride [38,42,46]. In the space-charge layer at the
surface of a crystal the concentrations of positively and negatively charged point defects could be vastly different due to
their different free energies of formation. Hence, if the more mobile defect is in excess, there can be enhanced diffusion in
the surface regions of the crystal. This effect has been invoked [38] to explain the unusually high conductivity in the class
of materials termed ionic-insulator composites (finely ground and compacted mixtures of a simple ionic crystal, such as
lithium iodide, and an insulator, such as alumina) and should be important in compacts of nanocrystals. A defect excess in
the space charge layer would also lead to a surface segregation of aliovalent impurities, which would be reflected in an
apparently high solubility of the impurity. When the nanocrystallite size becomes less than the thickness of the spacecharge layer the models suggest [37-40] the whole crystallite has a defect excess leading to a further diffusion
enhancement, and presumably even greater impurity solubility.
III.3 Transport Measurements in Ionic Nanocrystals
Conductivity measurements have been the major means of studying ionic transport in nanocrystals and have limitations in
3
that they monitor the total charge transport and it is can be difficult to extract diffusion coefficients for component ions.
Data for compacts of CaF2 with mean particle size ~9nm show a conductivity enhancement of some five orders of
magnitude that was explained in terms of the effect of the space-charge layer contribution [47]. No enhancement was seen
in the conductivity of nanocrystalline compacts of yttrium stabilised cubic zirconia (YSZ) with particle sizes of 35nm [48]
and <200nm [49]. In contrast, thin films of YSZ with crystallite sizes of 10, 20 and 200nm exhibited a conductivity
enhancement of two orders of magnitude over bulk samples [50]. This discrepancy has still to be resolved [18]. Several
groups have reported an enhanced conductivity in nanocrystalline ceria [42], however in this case this has been shown to
be due to a greatly increased electronic conductivity, which totally masks the ionic conductivity. Similar, but less dramatic
effects have been found in titania [42]. It is noteworthy that NMR measurements of nanocrystalline CaF2 [51] and LiNbO3
(prepared by high-energy ball milling) [52] differentiated between slow moving ions in the bulk and fast moving ions in
the grain boundaries. The most convincing evidence for enhanced transport in nanocrystals is the conductivity study of
alternating nanometre thick layers of CaF2 and BaF2 by Maier’s group [40]. Studies of impurity solubility in ionic oxides
are few, although work on SnO2 does suggest there is an increased solubility of several cations in nanocrystals [53].
III.4 Criteria for New Experimental Work
A detailed understanding of diffusion and impurity solubility is vital to both fundamental and technological development
of nanocrystals and this is the aim of the experimental work in this project. However, the experiments must satisfy
stringent criteria to avoid the controversies outlined in the preceding paragraphs. The first criterion is that samples with a
range of crystallite sizes down to 10nm must be available to observe all the effects that have been proposed from the
theoretical models [38]. In addition, the particle size of a given sample must be invariant up to temperatures of ~1000oC if
the energetics of the processes are to be revealed. This is not a trivial requirement as nanocrystalline oxides begin to sinter
at ~400oC [11], and in systems like zirconia temperatures of ~700oC are required to produce single-phase oxides [5]. A
second criterion is that the effect of the synthetic route to the nanocrystals must be explored, and samples prepared by
both sol-gel and high-energy ball milling will be investigated. The third criterion is that ionic conductivity measurements
alone cannot be used to monitor ionic motion and direct diffusion measurements (e.g. from NMR or tracers) are required.
The fourth criterion is the use of modern local structural probes, such as NMR spectroscopy and XAFS, to identify the
chemical nature of the impurities and their precise location in the microstructure of the sample. Finally, it is important that
the samples are thoroughly chemically (e.g. composition, etc.) and physically (e.g. particle size, phase, microstructure,
etc.) characterised. This project methodology (see below) will meet these criteria thereby providing crucial information
required to understand the defects and ionic transport in nanocrystalline oxides.
IV. AIMS AND OBJECTIVES
The project will focus on three key metal oxides of fundamental and technological importance; magnesium oxide (MgO),
zirconia (ZrO2) and ceria (CeO2). MgO is the most thoroughly studied binary oxide and is an ideal model system due to
the wealth of available experimental and theoretical information. ZrO2 is a very important ceramic and the addition of
aliovalent dopants will stabilise the cubic phase (CSZ) which has a high oxygen ion conductivity and is the currently the
preferred electrolyte membrane in oxygen sensors [54,55] and solid electrolyte fuel cells (SOFC) [56,57]. It is also an
important catalyst [58] and catalyst support [59]. CeO2 is cubic and is a mixed oxygen ion and electronic conductor. It can
be doped with trivalent rare earth cations to provide oxygen ion conductivities higher than in CSZ. CeO2 is also used as a
catalyst [60] and has potential as a SOFC electrolyte for lower temperature cell operation [61].
The aims of the project can be summarised as follows:(a)
The understanding of the nature of ionic transport in nanocrystalline oxides.
(b)
The understanding of the nature of impurity solubility in nanocrystalline oxides.
(c)
The role of preparative route on the transport and impurity solubility properties of nanocrystalline
oxides.
The specific objectives of the project will be experiments on the target materials that will yield:(i)
Nanocrystalline samples with a range of particle sizes from 10 to 100nm, which are stable to grain
growth up to 1000oC.
(ii)
Nanocrystalline samples from both sol-gel and high-energy ball milling routes.
(iii) Ionic conductivity results for the above samples over a wide temperature range.
(iv)
Oxide ion diffusion coefficients for the above samples over a wide temperature range.
(v)
The location of impurity ions in the microstructures of the above samples.
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V. PROGRAMME OF WORK AND DETAILED METHODOLOGY
The programme of work will begin with the preparation and general characterisation of samples. This will be followed by
detailed studies of ionic transport and structural investigations - the major part of the project. Of the three target materials
MgO will be studied first as our benchmark material. We note that evidence for cation and anion motion in bulk
polycrystalline MgO has been reported from 17O and 25Mg NMR studies [62]. For dopant studies in MgO we will focus
on the alkali and alkaline earth elements. ZrO2 and CeO2 will then be studied in parallel and we expect fast oxide ion
motion in these materials [63-67]. The target dopants in these systems will be rare earth atoms. Sample preparation,
characterisation, ionic conductivity, XAFS and NMR cryoporometry will be undertaken at Kent. Warwick will undertake
the 17O NMR relaxation and general multinuclear magnetic resonance spectroscopy studies. The methodology is
summarised below and in the diagrammatic project plan.
Transport Measurements
Sample Preparation
(AVC, MES, PDRA, PhD)
 AC impedance (AVC, PDRA)
 17O VT NMR relaxation times
(MES, PhD)
 Nanocrystalline MgO, ZrO2 and
CeO2 – pure and doped
o Sol-gel
o Mechanochemical
Local Structure
 Confinement by
o Sol-gel co-precipitation in
silica/alumina matrix
o Alkoxide reaction within a
mesoporous framework
 Procedure for O enrichment
17
 XAFS (AVC, PDRA, PhD)
 NMR Spectroscopy
(MES, PhD)
Improved understanding of the
modification of structure,
impurity distribution and ionic
motion in nanocrystalline oxides
Other Characterisation




XRPD (AVC, PDRA)
BET (AVC, PDRA)
TEM (MES, PhD)
NMR cryoporometry
(AVC, PDRA)
V.1 Sample preparation
We will employ two major techniques to prepare the nanocrystalline samples, namely sol-gel methods and
mechanochemical high-energy ball milling. A key to the success of the project is the restriction of grain growth of the
nanocrystals at high temperature, an area in which we have devoted considerable effort in recent years and in which we
have been successful [16,66]. We propose two strategies to restrict the grain growth in the target oxides, namely (1)
pinning the grain boundaries by surface treatment, and (2) confining in a pre-formed inert matrix. The methods will be
used to produce bulk samples of pure and doped nanocrystals and they can be adapted to allow for 17O isotopic
enrichment. In addition thin film nanocrystalline samples prepared by spin coating from polymer precursors will be
available from Professor I. Kosacki (University of Missouri, Rolla), with whom we have a successful collaboration
[12,13].
Method 1 involves an approach that has been proven in the literature, the hydrolysis and calcination of the metal alkoxide
with aluminium [67] or silicon alkoxide [68]. When relatively low levels of metal alkoxide are used the resulting metal
oxide nanoparticle is 'trapped' in a silica or alumina network. With relatively high levels of the metal alkoxide small
particles of alumina or silica form on the surface of the metal oxide and pin the grain boundaries [69]. We have repeated
the work on the preparation of 10nm ZrO2 nanocrystals from zirconium and aluminium alkoxides (in the ratio 9 to 1) and
confirmed that the particle growth is not significant until 1000oC [16,66]. An intriguing feature of this method is that
Al2O3 crystallites are only discernible in the X-ray diffraction patterns after annealing above 1200oC. We have also shown
that the method is also effective in the preparation of thermally stable MgO 10nm nanocrystals [66]. A variation on this
approach has recently been reported [70] and involves reacting the surface hydroxyl groups of a hydrous gel with
hexamethyldisilazane and calcining. The treatment produces small particles of silica on the surface of the oxide that pin
the boundaries. The method has been shown to be effective in restricting the growth of SnO2, ZrO2 and TiO2 nanocrystals,
and almost certainly can be used with a very wide range of metal oxides.
It is samples prepared by this route that will be used in the conductivity measurements as the pinning particles (Al2O3 or
SiO2) do not prevent contact between the grains of the host nanocrystals.
Method 2 has a long history; early work by Barrer [71,73] showed that nanocrystalline silver halide could be formed by
5
melting the salt into the pores of zeolites. Many groups have deposited compounds into porous and microporous silica and
converted them to oxides (see, for example reference [73]). Recently this approach has been used to deposit metal oxides
into the new mesoporous silica MCM-41 [74] that can be prepared with well-defined pore sizes. The advantage of this
approach is that the combination of zeolites, mesoporous silicas and commercially available porous silicas (e.g. from
Reatec GmbH) gives a wide range of pore sizes, and hence crystallite sizes, from 1 to 100nm. In preliminary work we
have shown that incorporation of the metal alkoxide into the pores followed by calcination is very effective in producing
nanocrystalline oxides, which are stable to 1000oC [66]. At higher temperatures reaction to form the silicate was a
problem for confined MgO.
V.2 Transport Measurements
A.C. impedance spectroscopy will be used to determine the ionic conductivity of samples and to separate the
contributions to the overall charge transport from the bulk and grain boundaries [75]. This has been the major technique
used in previous studies of atomic transport in nanocrystalline ionic materials, however we have already noted that it has
limitations. A unique feature of this project will be the use of variable temperature NMR relaxation methods to determine
oxide ion motion using 17O as the probe nucleus. Previous relaxation time studies have included study bulk CeO2 [76],
and relaxation can readily differentiate between fast and slow moving ions in the same sample, as in nanocrystalline 19F
NMR of CaF2 [51]. Since the target materials all have a cubic structure the calculation of diffusion coefficients from the
relaxation times will be relatively straightforward. The work will employ the novel high temperature probe recently
developed by the applicants under grant GR/K74876 [77].
V.3 Local Structure Measurements
Studies of the local structure of dopants in the oxide and the investigation of surface segregation in nanocrystals will use
XAFS and, where suitable isotopes are available, NMR spectroscopy. Our work has shown that 17O NMR is a very
sensitive probe of the local structure of these materials and multifield (4.7-18.8T) high-resolution measurements will be
carried out. XAFS will be very powerful in this work as it can be used over a very wide range of dopant concentration.
The use of Station 9.3 at the Daresbury SRS will be vital in the work as it offers combined XRD and XAFS, and a high
temperature stage. When the nanocrystalline oxides are confined in silica/alumina matrices 27Al and 29Si MAS NMR
spectroscopy will be used to monitor interactions between the oxide and the matrices/pinning agents used to restrict
particle growth.
V.4 Sample Characterisation
It is of key importance to know as much as possible about the characteristics of the samples and extensive background
characterisation will be carried in addition to the core measurements. All samples will be monitored by extensive powder
X-ray diffraction to determine the crystallite size. For samples in which the oxides are confined in porous matrices we
will use BET areas and the expertise in NMR cryoporometry at Kent [78] to monitor the degree of pore filling.
Understanding the microstructure is of key importance so that the PhD student will undertake detailed TEM studies at
Warwick. This will provide key information about the nature of the grains, and in the confined oxides the interaction
between the nanocrystalline oxide and the matrix. As the interface in confined systems is important high-resolution
electron microscopy will be undertaken at the Midlands centre FEG-TEM in Birmingham.
VI. PROJECT MANAGEMENT
The project will be coordinated by AVC with the PIs taking responsibility for their designated parts of the project. Both
applicants have a hands-on approach to such projects and will get involved on a day-to-day basis. The initial sample
manufacture will be based at Kent. The applications for central facilities for the XFAS measurements will be the
responsibility of the PDRA. The PDRA will be responsible for maintaining a web site that keep a record of progress of
the project and an up to date list of the literature relevant to the project. The whole team will get together quarterly
alternating between Warwick and Kent. The applicants have a good record of both collaborating together and running
successful projects involving multiple sites.
VII. RELEVANCE TO BENEFICIARIES
The major beneficiaries will initially be the academic community working on ionic materials, electrolytes and fuel cells.
This is a particularly strong community in the UK with large experimental groups at Aberdeen (Ingram), St. Andrews
(Bruce, Irvine and Vincent), Imperial (Kilner, Atkinson and Steele), Sheffield (West and Sinclair) and Surrey (Slater), and
computer modelling expertise at the RI/UCL (Catlow/Gillan, Harding, Stoneham and Shluger), Bath (Parker), Keele
(Jackson), St. Andrews (Mackrodt), Surrey (Islam) and Kent (Lindan). The work is relevant to the applications of ionic
solids, particularly in the fields of catalysis and sensors and could have an impact on the medium term development of
such materials industrially. In this respect, we note the letters of support from Dr Couves (BP) and Dr Bahra (Dstl).
6
There is also the training aspect of the project as well, giving both the PDRA and the PhD student experience in a leadingedge materials-based project. Both will get exposure to a wide range of important techniques that will make them very
attractive for the materials technology industry. As well as scientific skills other wider transferable skills will be
inculcated such as the PDRA being given some project management responsibilities The project will also offer good
opportunities for publications and conference presentations, and the quarterly meetings will sharpen presentation skills.
VIII. DISSEMINATION OF RESULTS
The applicants have a demonstrably vigorous record of publishing in a range of journals. Results of this research will be
published in internationally-leading high impact journals, that make contact with both the physical chemistry and
materials sciences communities. Presentations at conferences, involving both the direct peer community, and also more
generally to the solid-state science community (both academic and industrial), will make the beneficiaries aware of the
unique possibilities afforded by such nanocrystalline materials and the improved understanding this work develops. The
work would be regularly updated on the Kent and Warwick groups websites. Any materials or processes developed that
have commercial value will be discussed with the relevant University offices that can advise on patent protection and
commercial exploitation.
IX. RESOURCE REQUIREMENTS
The programme of work is ambitious and our major requirement is for skilled manpower, with a PDRA based at Kent and
a PhD project student based at Warwick. The work at Kent (sample characterisation, ionic conductivity, XAFS and some
NMR) will require a broad experience in materials studies and hence a higher level of training is expected for this post. In
addition, the PDRA will be expected to take charge of the day-to-day coordination of the project, e.g. arranging sample
exchanges, team meetings, timetabling and applying for XAFS runs, etc. We have identified Miss Shelley Savin, currently
a student of Dr. J.D. Wright at Kent, who will have graduated with her PhD by the proposed start of this grant. We will
appoint her to this post as she is an outstanding experimental worker with has some experience with the materials in the
project. NMR work at Warwick is more specific and will form ideal training for a PhD student, hence the request for a
project studentship for this work. The student would also gain training in electron microscopy. During the later stages of
the project we expect the student to gain some additional broader experience by involvement in the XAFS work. A
defined programme of work for the student is attached in the Diagrammatic Project Plan. We believe this training along
with the departmental postgraduate training programme will lead to a highly skilled research scientist ideally equipped to
work in materials-related research projects.
At Kent technical support is requested for the Centre for Materials experimental officer (Dr. J.B.W. Webber) to assist
with the project. The laboratories at Kent have recently been re-equipped through SRIF funds and we have a new A.C.
impedance spectrometer, X-ray powder diffractometer and X-ray fluorescence spectrometer, which will be used in the
project. Our only equipment request is for a high-energy ball mill as we are currently relying on collaborators to provide
mechanochemically activated samples. At Kent we are also requesting support for consumables (e.g. high purity reagents,
liquid nitrogen, rf components). Beamtime at the Daresbury SRS will be requested for the XAFS studies (~10 days per
annum) through the new mechanisms. As the project will involve work at two centres we are requesting a budget for UK
travel for the quarterly meetings, and for subsistence for the team to carry out some combined work at high magnetic field
at Warwick, in addition to travel to conferences, especially for the PDRA to assist in their career development.
At Warwick support is required for the NMR group experimental officer (Dr A.P. Howes) to assist with the project, in
particular maintenance of the high temperature probe, which also requires consumables. There is the need for cryogens
for the superconducting magnets that will be used, and access payments for the University contributions to the new
spectrometers is requested on a pro rata basis. There is also the need for MAS NMR consumables (e.g. rotors, caps etc.)
and some technical support for spectrometer maintenance (e.g. magnet filling). The range of NMR experiments will need
some 17O-enriched precursor water for sample manufacture; 5g of 20 at% for routine spectroscopic observation at room
temperature and 3g of 75 at% for high temperature spectroscopy and relaxation time measurements is requested. We are
also requesting support for consumables to allow the student to carry out TEM measurements both at Warwick and the
Midlands FEG-TEM facility. Some technical support is requested to help with these measurements, including the initial
training. Travel is requested for the quarterly meetings, and also for some experiments at the 18.8 T spectrometer at the
Rutherford Appleton Laboratory and to Birmingham to the FEG-TEM facility. Travel to conferences to present the work
is also requested.
REFERENCES TO CASE FOR SUPPORT
[25] Gleiter, H. Adv. Mater., 1992, 4, 474.
[26] Henglein, A., Chem. Rev., 1989, 89, 1061.
[27] Weller, H., Angew. Chem., Int. Ed. Engl. 1993, 32, 41.
7
[28]
[29]
[30]
[31]
Seigel, R.W. and Fougere, G.E., Nanostructured Mater. 1995, 6, 205.
Moriarty, P., Rep. Prog. Phys., 2001, 64, 297.
see, for example, papers in the special issue of Chem. Mat., 1996, 8, no. 8.
see, for example, papers in the journals Nanotechnology (Kluwer), Nanostructured Materials (Elsevier), Journal of
Nanoparticle Technology (IoP), Nano Letters (ACS).
[32] Foresight Programme, URL; http://www.foresight.gov.uk
[33] Koper, O.B., Lagodic, I., Volodin, A. and Klabunde, K.J., Chem. Mat., 1997, 9, 2468.
[34] Khaleel, A., Kapoor, P.N. and Klabunde, K.J., Nanostruct. Mat., 1999, 11, 459.
[35] Koper, O.B. and Klabunde, K.J., Chem. Mat., 1997, 9, 2481.
[36] Maier, J., Solid State Ionics, 1987, 23, 59.
[37] Jamnik, J., Maier, J. and Pejovnik, S., Solid State Ionics, 1995, 75, 51.
[38] Maier, J., Prog. Solid State Chem., 1995, 23, 171.
[39] Maier, J., Solid State Ionics, 2000, 131, 13.
[40] Sata, N., Eberman, K., Eberl, K. and Maier, J., Nature, 2000, 408, 946.
[41] Chadwick, A.V., Nature, 2000, 408, 925.
[42] Tuller, H.L., Solid State Ionics, 2000, 131, 143.
[43] Indris, S., Bork, D. and Heitjans, P., J. Mat. Synthesis and Processing, 2000, 8, 245.
[44] Scholz, G., Stosser, R., Klein, J., Silly, G., Buzaré, J.Y., Laligant, Y. and Ziemer, B., J. Phys.: Condens. Matter, 2002, 14,
2101.
[45] Stern, E.A., Siegel, R.W., Newville, M., Sanders, P.G.. and Haskel, D., Phys. Rev. Lett., 1995, 75, 3874.
[46] Allnatt, A.R., J. Phys. Chem., 1964, 68, 1763.
[47] Puin, W., Rodewald, S., Ramlau, R., Heitjans, P. and Maier, J., Solid State Ionics, 2000, 131, 159.
[48] Mondal, P. and Hahn, H., Ber. Bunsenges. Phys. Chem., 1997, 101, 1765.
[49] Jiang, S.S., Schulze, W.A., Amarakoon, V.R.W. and Stangle, G.C., J. Mater. Res., 1997, 12, 2374.
[50] Kosacki, I., Gorman, H.U., and Anderson, H.L., in Ionic and Mixed Conductors, Volume III, eds. T.A. Ramanarayanan et al.;
Electrochemical Society; Pennington, N.J., 1998, p. 631.
[51] Puin, W., Heitjans, P., Dickenscheid, W. and Gleiter, H., in 'Defects in Insulating Materials', eds. O. Kanert and J.M. Spaeth;
World Scientiific; Singapore, 1993, p. 137.
[52] Bork, D. and Heitjans, P., J. Phys. Chem. B., 1998, 102, 7303.
[53] Kanai, H., Mizutani, H., Tanaka, T,, Funabiki, T., Yoshida, S. and Takano, M., J. Mater. Chem., 1992, 2¸703.
[54] Maskell W.C., Solid State Ionics, 2000, 134, 43.
[55] Fouletier, J., Mantel, E. And Kleitz, M., Solid State Ionics, 1982, 6, .1.
[56] Steele, B.C.H., Phil. Trans. Roy. Soc., A., 1996¸ 354, 1695.
[57] Minh, N.Q., J. Am. Ceram. Soc., 1993, 76, 563.
[58] Arata, K. and Hino, M., Mat. Chem. Phys., 1990, 26, 213.
[59] Mercera, P.D.L., Van Ommen, J.G., Doesburg, E.B.M., Burggraaf, A.J. and Ross, J.R.H., App. Catal., 1990, 57, 127.
[60] Trovarelli, A., Catal. Rev., 1996, 38, 439.
[61] Huijsmans, J.P.P., van Berkel, F.P.F. and Christie G.M., J. Power Source, 1998, 71, 107.; Steele, B.C.H., Solid State Ionics,
2000, 134, 3.
[62] Fiske, P.S., Stebbins, J.F. and Farnan, I., Phys. Chem. Miner., 1994, 20, 587.
[63] Kosacki, I., Suzuki, T., Petrovsky, V. and Anderson, H.U., Solid State Ionics, 2000, 136, 1225.
[64] Tschöpe, A., Sommer, E. And Birringer, R., Solid State Ionics, 2001, 139, 255.
[65] Tschöpe, A., Solid State Ionics, 2001, 139, 267.
[66] Al-Angry, Y., Ph.D. thesis, University of Kent, 2002.
[67] Viswanath, R.N. and Ramasamy, S., Nanostruct. Mater., 1999, 12, 1085.; J. Mater. Sci., 1999, 34 2879.
[68] Aguilar, D.H., Torres-Gonzalez, L.C., Torres-Martinez, L.M., Lopez, T. and Quintana, P., J. Solid State Chem., 2001, 158, 349.
[69] Betz, U., Sturm, A., Loeffler, J.F., Wagner, W., Wiedenmann, A. and Hahn, H., Nanostruct. Mater., 1999, 12, 689.
[70] Wu, N.L., Wang, S.Y. and Rusakova, I.A., Science, 1999, 285, 1375.
[71] Barrer, R.M. and Meier, W.M., J. Chem. Soc., 1958, 299.
[72] Barrer, R.M., Inclusion Phenom., 1983, 1, 105.
[73] Anderson, P.A., Bell, R.G., Catlow, C.R.A., Chang, F.L., Dent, A.J., Edwards, P.P., Gameson, I., Hussain, I., Porch, A. and
Thomas, J.M., Chem. Mater., 1996, 8, 2114.
[74] Zhang, W.H., Shi, J.L., Wang, L.Z. and Yan, D.S., Chem. Mater., 2000, 12, 1408.
[75] Puin, W., Rodewald, S., Ramlau, R., Heitjans, P. and Maier, Solid State Ionics, 2000, 131, 159.
[76] Fuda, K., Kishio, K., Yamachi, S., and Fueki, K., J. Phys. Chem. Solids, 1984, 45, 1253; J. Phys. Chem. Solids, 1985, 46, 1141.
[77] Poplett, I.J.F., Smith, M.E. and Strange, J.H., Meas. Sci. Technol., 2000, 11, 1703.
[78] Allen, S.G., Stephenson, P.C.L. and Strange, J.H., J. Chem. Phys., 1998, 108, 8195.
8
DIAGRAMMATIC PROJECT PLAN - NEW ASPECTS OF THE STRUCTURE AND DYNAMICS IN NANOCRYSTALLINE OXIDES
PDRA Programme of Work based at Kent
Task
Sample preparation
Basic characterisation (XRPD, BET)
A.C. impedance studies
XAFS studies and analysis
NMR cryoporometry
Project management meetings
Report preparation
Q1
X
X
X
Q2
X
X
Year 1
Q3
X
X
X
X
X
Year 2
Q4
Q1
X
X
X
X
X
X
X
X
X
Q2
X
X
X
Year 3
Q3
X
X
X
X
X
X
Q4
X
X
Q1
X
X
X
X
X
X
Q2
X
X
X
X
X
X
Q3
Q4
X
X
X
Student Programme of Work based at Warwick
Task
Sample preparation
NMR relaxation
NMR spectroscopy
TEM analysis
XAFS studies and analysis
Project management meetings
Skills training
Literature review/coursework
Report preparation
Year 1
Q1
†
X
X
Year 2
Q2
†
X
X
Q3
Q4
X
X
X
X
X
X
X
X
X
X
X
X
Q1
†
X
X
X
X
X
Q2
†
X
X
X
X
Year 3
Q3
Q4
X
X
X
X
X
X
X
X
X
X
Q1
†
X
X
X
X
X
Q2
Q3
Q4
X
X
X
X
X
X
X
† - Student spends some time at UKC for initial sample preparation and 17O-enrichment.
9
PhD writing