AN ABSTRACT OF THE THESIS OF
for the degree of Doctor of Philosophy
Yaobo Yin
in
Chemistry
Title:
presented on
June 8. 1993
New Solid-State Fluorides: Synthesis. Crystal Chemistry.
and Optical Properties
Redacted for Privacy
Abstract approved:
youglas A. Keszl
The synthesis, structural characterization, crystal chemistry, and optical
study of new solid-state fluorides are presented. The work encompasses
results on colquiriite related materials, the compound Sr2ScF7, and new fluoride
phases containing rubidium, a lanthanide, and scandium atoms.
Through single crystal and powder X-ray diffraction methods, a
systematic study has been made on the crystal structures of the colquiriite
derivatives LiMM'Fe (M = Ca, Sr; M' = Ga, Cr, Al) and the solid solution series
(M' = Ga, Al).
The systematic distortions of the dopant M'
octahedral sites have been analyzed. These distortions introduce an odd-parity
component to the energy levels, and critically affect the electronic-transition
probabilities and the lasing properties of Cr3+-doped crystals. The maximum
solubility of Ba atoms in a colquiriite derivative has been achieved with the Ga
phase to give the formula LiSr08BaGaFe. The Ga site in this compound also
exhibits the largest distortion of all the colquiriite derivatives.
exhibits the largest distortion of all the colquiriite derivatives.
The structure of the compound Sr2ScF7 has been determined to be
isostructural to K2NbF7. The structural relationship between this type and that
of Pb2RhF7 is examined in detail.
A study of the fluorescent properties of
Cr3+:Sr2ScF7 is also described.
From a systematic study of the ternary systems RbF-ScF3-LnF3 (Ln = Y,
Yb), several new fluorides RbYb2F7, RbSc3F10, Rb2YbSc2F,,, RbY2.19Sc0.81F10, and
RbYb2.32Sc0.68F10 have been synthesized and structurally characterized. Each
compound exhibits an orthorhombic structure derived from the Re03 type that
is built by stacking layers of Sc-centered and Ln-centered polyhedra. The
resulting frameworks contain tunnels that are filled by the Rb atoms. Structural
interrelationships among these frameworks are discussed in detail.
New Solid-State Fluorides:
Synthesis, Crystal Chemistry, and Optical Properties
by
Yaobo Yin
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirement for the
degree of
Doctor of Philosophy
Completed June 8, 1993
Commencement June 1994
APPROVED:
Redacted for Privacy
Professa of Chemistry in ofiarge of major
Redacted for Privacy
Head of Department of Chemistry
Redacted for Privacy
Dean of Grad late School
Date thesis is presented
June 8, 1993
Prepared and presented by
Yaobo Yin
ACKNOWLEDGMENT
At first, I like to thank my major professor, Douglas A. Keszler, for all his
help and guidance in my graduate study here at Oregon State University.
Without his expertise, guidance and patience, the completion of this thesis will
not come true. Indeed, I must acknowledge that I owe a great debt to Doug.
Also, I like to thank for the help from all my friends and my colleagues,
with whom I have been through my good time and bad for years. Especially
to these colleagues: Kathleen Schaffers, James Cox, Ted Alekel, Dr. Thomas
Reynolds, George Pon, Juming Tu, Chris Orf, Annapoorna Ake Ila, Dr. Robert
Smith, Dr. Hongxing Sun, and Dr. Paul Thompson.
I want to express my gratitude to the faculties and staffs of Chemistry
Department,
my graduate committee members for their help and
encouragement. Additionally, I want to thank John Archibald of Mechanical
Shop for his willingness to repair my research apparatus at any time.
Without all the people I mentioned above, my time here would not be so
enjoyable and memorable.
TABLE OF CONTENTS
Page
CHAPTER 1: INTRODUCTION
Optical Properties of Solid Inorganic Fluorides
1
2
Cr + Ion Lasers
3
Nd3+ Ion Lasers
8
Cr3+, Nd3+ Codoped Lasers
10
Laser Hosts of Inorganic Fluorides
11
Structural Aspects of Fluorides
13
Structure of Colquiriite Fluoride
14
Structure of ANF3+. (A = Alkali Ions;
15
M = Trivalent Transition Metal and
Rare-Earth Ions)
Preparative Chemistry of Solid Inorganic Fluorides
15
References
19
CHAPTER 2: CRYSTAL CHEMISTRY OF COLQUIRIITE-TYPE
22
FLUORIDES
Abstract
23
Introduction
24
Experimental
25
Discussion
30
Acknowledgment
41
References
42
CHAPTER 3: SOLID SOLUTIONS IN COLQUIRIITE-TYPE FLUORIDES
43
LiSrl,Ba.MF6 (M = Al, Ga)
Abstract
44
Introduction
45
Experimental
46
Results and Discussion
51
Acknowledgment
58
References
59
TABLE OF CONTENTS (Continued)
CHAPTER 4: STRUCTURE OF DISTRONTIUM SCANDIUM
60
HEPTAFLUORIDE AND CHROMIUM(III) LUMINESCENCE
Abstract
61
Introduction
62
Experimental
63
Results and Discussion
67
Conclusion
75
Acknowledgment
76
References
77
CHAPTER 5: CRYSTAL CHEMISTRY OF NEW FLUORIDES IN THE
79
TERNARY SYSTEMS RbF-ScF3-LnF3 (Ln = Y, Yb)
Abstract
80
Introduction
81
Experimental
83
Results and Discussion
90
Structural Description
90
Structural Relationships
114
Acknowledgment
121
References
122
BIBLIOGRAPHY
123
APPENDICES
Appendix A. THE BORATE Na3Sc2(B03)3
127
Appendix B. THE FLUORIDES Sr2AIF7
128
Appendix C. ANISOTROPIC DISPLACEMENT COEFFICIENTS
129
OF THE CRYSTALS
LIST OF FIGURES
Figure
Page
1.1
Simplied Tanabe-Sugano diagram of a d3 ion.
4
1.2
Operation scheme of Nd3+:crystal lasers.
9
1.3
Hydrofluorinating line.
18
2.1
Drawing of the colquiriite structure.
31
2.2
Relative rotation of two trigonal F planes about the M' site.
38
2.3
Comparison of F closest packing with F packing in the
39
structure of LiSrGaF6 by projection onto (001).
3.1
Cell volume vs x for the series LiSr1.,(13a.MF6 (M = Al, Ga).
52
3.2
Drawing of the unit cell for LiAEMF6.
53
3.3
Rings of edge-shared Li- and M-centered polyhedra
54
around AE atom.
3.4
Relative rotation of two trigonal F planes about the M site.
56
4.1
Drawing of the contents of the unit cell of Sr2ScF7.
68
4.2
Structural relationship between (a) Pb2RhF7 and (b) Sr2ScF7.
73
4.3
Emission spectrum of Cr3+:Sr2ScF7 at room temperature.
74
5.1a
The c-axis projection of framework for RbYb2F7.
91
5.1b
Coordination environments of atoms in RbYb2F7.
92
5.2a
The a-axis projection of framework for RbSc3F10.
96
5.2b
Coordination environments of atoms in RbSc3F10.
97
5.3a
The b-axis projection of framework for RbY2.16Sc0.81F10.
102
5.3b
Coordination environments of atoms in RbY2.16Sc0.81F10.
103
5.4a
The c-axis projection of framework for Rb2YbSc2F11.
110
5.4b
Coordination environments of atoms in Rb2YbSc2F11.
111
5.5
Frameworks of (a) (Yb2F7)-, and (b) (Sc3F10)-,
116
(c) (Ln2+,Sc1,F10), and (d) (YbSc2F11).
5.6
Structural relationship between (a) Re03 and (d) RbSc3F10.
117
LIST OF FIGURES (Continued)
7
Figures
5.7
Structural relationship between (a) RbSc3Flo and
Page
118
(b) RbY219Sco.81Flo.
5.8
Structural relationship between (a) Re03 and (b) RbYb2F7.
119
5.9
Structural relationship between (a) RbYb2F7 and (d) Rb2YbSc2Fil.
120
LIST OF TABLES
Page
Tables
2.1
Crystal data and experimental conditions for
27
colquiriite-type fluorides.
2.2
Atomic parameters of colquiriite-type fluorides LiMM'F6.
29
2.3
Interatomic distances for colquiriite derivatives.
32
2.4
Interatomic angles for colquiriite derivatives.
33
2.5
Twist angles of colquiriite-type fluorides.
40
3.1
Crystal data and experimental conditions.
48
3.2
Atomic parametersa.
49
3.3
Interatomic distances (A) and selected angles ( °).
50
3.4
Twist angles of D3, M-centered octahedra.
57
4.1
Crystal data for Sr2ScF7.
65
4.2
Positional parameters for Sr2ScF7.
66
4.3
Selected bond distances (A) and bond angles (A) of Sr2ScF7.
69
4.4
Bond valence calculation for Sr(1) atom.
71
5.1
Crystal data and experimental conditions for data collections.
85
5.2a
Atomic parameters for RbYb2F7.
86
5.2b
Atomic parameters for RbSc3F10.
87
5.2c
Atomic parameters for RbY2.19(3)Sc0.81F10
88
and RbYb2.32(3)Sc0.68Fl0.
5.2d
Atomic parameters for Rb2Y131.04Sc1.98F11.
89
5.3a
Selected bond distances (A) for RbYb2F7.
93
LIST OF TABLES (Continued)
Page
Tables
5.3b
Selected bond angles (°) for RbYb2F7.
94
5.4a
Selected bond distances (A) for RbSc3F10.
98
5.4b
Selected bond angles (°) for RbSc3F10.
99
5.5a
Selected bond distances (A) for RbY2.19Sco.81Flo.
104
5.5b
Selected bond distances (A) for RbYbanScomFlo.
105
5.5c
Selected bond angles (°) for RbY2.19Sc0.81F10.
106
5.5d
Selected bond angles (°) for RbYb2.68Sc0.32F10.
107
5.6a
Bond distances (A) for Rb2YbSc2F11.
112
5.6b
Selected bond angles (°) for Rb2YbSc2F11.
113
LIST OF APPENDICES TABLES
Tables
Page
C1. Anisotropic displacement coefficients for LiCaAlFe.
130
C2. Anisotropic displacement coefficients for LiCaGaFe.
131
C3. Anisotropic displacement coefficients for LiCaCrFe.
132
C4. Anisotropic displacement coefficients for LiSrA10.6CroAFe.
133
C5. Anisotropic displacement coefficients for LiSrGaFe.
134
C6. Anisotropic displacement coefficients for LiSrCrFe.
135
C7. Anisotropic displacement coefficients
136
for LiSr0.94Ba0.06A1Fe.
C8. Anisotropic displacement coefficients
137
for LiSropao2GaFe.
C9. Anisotropic displacement coefficients for Sr2ScF7.
138
C10. Anisotropic displacement coefficients for RbYb2F7.
139
C11. Anisotropic displacement coefficients for RbSc3Flo.
140
C12. Anisotropic displacement coefficients
141
for RbY2.19Scom F10.
C13. Anisotropic displacement coefficients
142
for RbYb2.32ScaseFlo.
C14. Anisotropic displacement coefficients
for Rb2YbSc2F, 1.
143
1
NEW SOLID-STATE FLUORIDES:
SYNTHESIS, CRYSTAL CHEMISTRY, AND OPTICAL PROPERTIES
CHAPTER 1
INTRODUCTION
Fluorine exists widely in nature, especially in minerals such as fluorspar
(CaF2), cryolite (Na3AIF6), and fluorapatite (Ca5(PO4)3(F,CI)). It has the highest
electronegativity, 4.10, of any element in the periodic table. As a consequence,
a small polarizability is encountered, and limited n back bonding is observed in
interactions with cations. It exhibits an exceptional tendency to adopt the octet
configuration of its neighbor Ne (1s22s22p6) by obtaining an extra electron in its
electron cloud. In elemental form, this reactivity is so high that compounds can
readily be formed with all elements except for the lighter noble gases.
In comparison with most oxides, fluorides have lower melting points.
This results from the lower, uninegative charge of the F- anion and attendant
smaller Made lung energies (U = (ZardonZeas.)/r + B /r ").
These energies,
however, are sufficient for many phases to afford ready crystallization and
sturdy materials for industrial applications and spectroscopic studies.
In recent years, researchers have studied numerous physical properties
of solid inorganic fluorides, but applications of the materials have remained
2
relatively undeveloped, at least, in comparison with oxides. Some unique
characteristics of solid inorganic fluorides, i.e., their low refractive indices, high
ionic conductivities, and low melting points have led to selected applications in
the fields of optics, electronics, and energy storage.
In the remaining portion of this introduction, I will briefly review those
aspects of solid-state fluorides that have provided the motivation for my work.
State-of-the-art laser materials doped with the ions Cr + or Nd3+, or both, and
the advantages of fluorides as optical hosts are described.
A section is
devoted to a review of Colquiriite, and another to the family of kInF3+,
structures that are related to some of the fluorides synthesized in this work. In
the final section the preparative chemistry of solid inorganic fluorides, a
traditional bottleneck in developing high-purity fluorides, will be addressed.
Optical Properties of Solid Inorganic Fluorides
Stimulated by the development of room-temperature, near infrared
tunable lasers based on transition-metal ions such as Cr, + the discovery of new
nonradiative energy transfer schemes for the efficient sensitization of flashlamp-
pumped materials, and the potential of highly efficient diode pumping,
considerable effort has been directed to the development of new solid-state
laser materials. Most researchers, however, have concentrated their efforts on
spectroscopic and laser studies of doped crystals having known structures.
Very few attempts have been made to synthesize new materials for the purpose
of creating new laser hosts.
3
Among the elements in the periodic table that lase, the ions CO+ and
Nd3+ as doped constituents in solids have been used most widely; examples
include alexandrite (Cr3+:BeA1204)(1, 2, 3) and Nd:YAG (Nd3+:Y3A15012)(4).
Cr3+ Ion Lasers
The CO+ ion has been reported to lase in more than 15 materials (5).
The stability of the trivalent state, fluorescence at room temperature in most
hosts, a strong preference to occupy an octahedral site, efficient absorption of
flashlamp pump light, and a broad emission band, make it a favored transitionmetal ion for tunable solid-state lasers.
Because of a large octahedral crystal field stablization energy, the Cr +
ion occupies an octahedral or distorted octahedral site in most crystals. Its
luminescent properties in such a site are well explained by consideration of the
simplified Tanabe-Sugano energy diagram shown in Figure 1.1 (6).
The
octahedral crystal field and interelectronic repulsion factors are described by the
parameters D and B, respectively. The splitting of the electronic energy levels
by an octahedral crystal field are classified according to the irreducible
representations of the point group Oh. The free ion ground state 4F splits into
4A2, 4T2,
1
and 4T, states that correspond to the electron configurations t23, t22e,
and t2e2, respectively. In weak-field sites the 4A2 is the ground state and 4T2 is
the lowest excited state. The lowest-lying spin doublet term, 2G splits into 2E,
2T,
and 2T2 corresponding to the electronic configuration t23 and 2A1
corresponding to the configuration t22e. The 2E level lies lowest in energy, and
is also the lowest excited state in strong-field sites. The lowest excited energy
4
E/B
2F
2G
4P
4F
Dq/B
Figure 1.1 Simplified Tanabe-Sugano diagram of a d3 ion
5
levels 412 and 2E are important since the luminescence originates from one or
both of these states. Absorption transitions from 4A2 to the low-lying doublet
states 2E, 21-1, and 2T2 are spin-forbidden and relatively
weak. These doublet states as well as the 4A2 ground state are formed from the
t23 set of transition-metal orbitals, and for D/B values greater than around 1.5,
the energy separations between the 4A2 ground state and the doublet levels do
not vary greatly with Dq.
As a consequence, these transitions have small
Huang-Rhys parameters and their spectra are dominated by sharp zero-phonon
lines.
The luminescence is also characterized by sharp zero-phonon lines,
usually accompanied by one-phonon vibrational sidebands. If the Cr3+ ion
occupies a weak-field site where the 412 state is the lowest excited state, the 412
level is highly coupled to the environment and a broad luminescence band is
observed.
As mentioned above, the emission associated with the transition 2E -4 4A2
occurs in a strong crystal field. The characteristic sharp emission of the
transition allows no significant wavelength tuning.
Examples of materials
exhibiting this type of emission are Cr3+:A1203 (7) and Cr3+:Y3Ga5012 (8).
The nature of the 2E -4 4A2 transition has been analyzed by using a
simple perturbation approach (9). In Cr3+:Mg0, Cr + ions replace the Mg2+
ions, leaving cation vacancies for charge balance.
The Cr' ions occupy
strong-field octahedral sites, and the 2E -0 4A2 luminescence is characterized by
zero-phonon lines (the R lines) and associated sidebands. Since the sites have
inversion symmetry, the transition 2E -4 4A2 is electric-dipole forbidden.
6
Consequently, the transition is induced by a magnetic-dipole process. This can
be proven by Zeeman patterns of the R-line luminescence for a-, sr-, and apolarizations (10). The sideband is clearly a one-phonon process.
In the strong-field host ruby, Cr3+:A1203 , the Cr + ions substitute directly
onto the trigonally distorted Al3+ sites (11, 12). An even-parity term arising from
a large separation of the trigonal planes and the spin-orbit coupling result in
removal of the degeneracies observed for the CO+ levels in an octahedral
environment. Odd-parity terms arising from the displacement of the AP+ ion
(and CO+ ion) along the trigonal axis, the reducton in size of one trigonal face
relative to the other, and the rotation of one face relative to the other by the
angle 0 = 4.3., are important for establishing an electric-dipole component to
the transitions. The 2E 13 4A2 transitions (R-lines) have been studied by using
both absorption and luminescence spectra. The 2E and 4A2 levels are split by
29 cm-1 and 0.38 cm-1, respectively, by a combination of the even-parity trigonal
crystal field and splin-orbit coupling (11).
A second type of Cr3+ laser is based on the weak-field, broad-band
transition 412
4A2.
Therefore, systems having the lowest excited state 41-2
provide a broad tunability where the wavelength can range from 600 to 1100
nm.
One of the more promising solid-state lasers of this type is the recently
discovered host Cr3+:LiCaAlF6 (5). In this material, the lowest excited state is
41-2, and a broad luminescence band is observed.
Because of the lack of
inversion symmetry at the AP+ sites, the transition 41-2 -> 4A2 contains an electric-
7
dipole component.
The third type of material is encountered at intermediate fields.
Relaxation between the 4T2 and 2E levels is exceedingly rapid in all Cr + systems
so that excited ion populations in these levels thermally equilibrate in a much
shorter time than the decay time to the ground state. In these intermediate
fields, Cr + has a certain equilibrium population on 2E level at low temperatures
and luminescence only originates from this energy level. Upon raising the
temperature, the 4T2 level is increasingly populated according to the Boltzman
distribution, and a broad luminescence band from 4T2 -o 4A2 is observed in the
spectrum. An example of this type of host is Cr + :BeA1204.
At 77 K, the
luminescence spectrum of Cr3+:BeA1204 shows only sharp R-lines and one-
phonon sideband with a decay time near 1.5 ms. At ambient temperature,
however, where about 6% of the excited ions are in the 4T2 state, it is not
surprising to observe that the dominant emission is from 4T2 since the
probability of transition 4T2 -> 4A2 is about two orders of magnitude higher than
that of the 2E -o 4A2 transition. The decay time of the luminescence at room
temperature (220As) is consistent with population of the 4T2 level (1, 2).
Excited state absorption (ESA) from 4T2 -0 4T1a, which tends to overlap
the 4T -, 4A2 emission in some crystals (e.g., Cr3+: Na3Ga2Li3F12), or from the 2E
level to higher lying doublets (e.g., Cr3+: A1203)(13), provides the most
deleterious effect on Cr + laser efficiency. To achieve high Cr + lasing efficiency,
the following characteristics have been proposed. The 4T2 state should be the
lowest excited state so that the broad-band luminescence of the transition 4T2
8
4A2 dominates. Also, it is preferable that the 4T2 -, 4A2 emission be at the
highest possible energy without populating the 2E state to avoid an energetic
overlap of the transitions 4T2 -, 4A2 and 4T2 -> 4 T la , thereby, reducing the effects
of ESA.
To satisfy these conditions, the 4T2 should be several hundred
wavenumbers below the 2E state.
Also it is hoped that the emission is
anisotropic, preferably such that n polarization dominates for the case of a
unaxial crystal (14).
Under these conditions, the maximum possible cross
section is observed for a given lifetime, therefore a low lasing threshold. An
ideal host would also be inexpensive,
easily grown, and have good
thermomechanical properties.
Nc13+ Ion Lasers
Effective nonradiative energy transfer processes between optically active
ions and the application of diode laser pumping have led to significant
improvements in the efficiencies of solid-state lasers. The diode pumped solid-
state laser (Nd3+: W04)(15), for example, has a slope efficiency of 50%.
The visible absorption and luminescence spectra of trivalent rare-earth
ions consist of electric-dipole forbidden f - f transitions which can become
more strongly allowed with an admixture of the nearest opposite parity
configurations (such as 4f1115d1) into the e states. The ion Nd3+ is well known
for its favorable 4F3,2 .- 4111/2 (Figure 1.2) luminescence transition at 1.06 gm in
laser applications. Because the energy levels derived from the 4fn configuration
are well shielded from the crystal field, the luminescence spectra normally
consist of sharp zero-phonon lines, and the positions of the luminescent peaks
9
E
A
4F3/2
V
v
v
V
4115/2
411312
4111/2
41912
Figure 1.2 Operation scheme of Nd3+:crystal lasers.
10
differ only slightly from one host material to another. Because of the shielding
and the large energy gap between 4F3,2 and 4111/2 the quantum efficiency of the
transition is generally high. Relaxation from 4111/2 to the ground state 419,2 is
generally by multiphonon nonradiative decay (16).
With these favorable
characteristics, the Nd3+ ion can be stimulated to laser action at room
temperature in almost any ionic solid-state host. Also, the 4F3,2 upper laser level
of the Nd3+ ion can be excited by pumping the sharp absorption features in the
wavelength range from 725 to 900 nm with the output from GaAs, GaAIAs, or
GaAsP diode lasers. This feature, combined with the lack of thermal population
in the 4111/2, which lowers the threshold of the laser, makes Nd3+ doped crystals
excellent candidates as diode-pumped solid state lasers.
Two of the more widely used Nd3+ lasers currently available on the
commercial market are Nd3+:YAG and Nd3+:glass. Nd3+:YAG is normally used
in a quasi-continuous mode with the output power around one kilowatt.
Nd3+:glass lasers, which have a larger spectral bandwidth, are often used to
produce very high powers. One example is the NOVA laser used for fusion and
X-ray experiments at Lawrence Livermore National Laboratory (LLNL) (17)
where peak powers of 30 TW are produced in 101° s pulses. It is much easier
to manufacture large, uniform glass lasers in comparison with crystalline
materials.
Cr3+, Nd3+ Codoped Lasers
One of the more important developments in the technology of solid-state
lasers in the last decade has been the realization of efficient sensitization of
11
Nd3+ emission by nonradiative energy transfer from CO+. For efficient energy
transfer, the CO+ ions should occupy sites having weak crystal fields. Long
wavelength CO+ emission of the transition 4T2
4A2 provides a strong resonant
overlap with Nd3+ absorption, allowing nonradiative energy transfer to occur.
The host materials that are currently available for Cr' + and Nd3+
cosubstitution are all oxide crystals, such as Cr, + Nd3+ codoped Gd3Sc2Ga30,2.
This garnet has been shown to have a slope efficiency nearly twice that of
Nd3+:YAG (18).
No fluoride hosts, however, have been reported in which
isovalent, ordered cosubstitutions of CO+ and Nd3+ ions are possible.
Laser Hosts of Solid Inorganic Fluorides
Fluorides are attractive host materials not only for the investigation of the
spectroscopic properties of transition elements and rare-earth ions, but also for
laser hosts. The unique optical characteristics of fluorides are derived from the
specific features of the fluoride anion: high electronegativity, small polarizability
and weak covalency of the M-F bonds. These features provide in fluorides low
refractive indices and optical transparency in the visible region.
Compared with oxides, fluorides have certain advantages for use as laser
materials.
(1) According to the Fuchtbar-Landenburg relation (14)
or cc 1/n2
the product of emission cross section (a) and lifetime (r)
is inversely
proportional to the square of the refractive index (n). The typically refractive
indices of fluorides, 1.44, are smaller than those of oxides, 1.85. Therefore,
12
given a fixed decay time (v) for both fluoride and oxide, a larger emission cross
section is expected for the fluorides. Fundamentally, it should be possible to
extract greater powers from fluorides.
(2) The unique charge and small polarizability of the fluoride anion
provides a weaker crystal field and little covalent mixing in M-F bonding. In the
case of Cr + systems, the broad emission band of transition 4T2 - 4A2 is more
likely to be observed, which increases the tunability of the laser wavelength.
Also, the 4f-4f transitions in the Nd3+ ion can exhibit weak concentration
quenching even at elevated temperatures, especially when the cross-relaxation
processes are quenched in weak-field environments.
(3) The weak M-F bond in comparison with M-0 bond, affords small
phonon energies. As a result, nonradiative decay rates are reduced and
radiative emission is favored.
(4) Theoretically, in Cr + systems, an appropriate weak crystal field
reduces the probability of excited state absorption (ESA) if we assume that only
spin allowed transitions carry significant oscillator strength. In the energy level
diagram, the ESA transitions can occur from either the 1-2 state or the 2E state
depending on crystal field strength. If 4T2 is the lowest excited state, two ESA
transitions can be observed (19).
A corresponding treatment of the ESA
spectrum expected for a 2E initial state immediately shows that the spin allowed
ESA transitions from 2E lead to a more congested spectrum throughout the
visible region, and in particular, the 2E2g(a) -0 2Aig band lies in the fluorescence
region of the 2E -o 4A2 transition. Clearly, the implication is that there may be
13
a significant advantage to a 4T2 lowest excited state Cr3+ laser requiring that the
host crystal have an appropriate weak crystal field, as in most fluorides.
To date, many fluorides have been reported to be active laser materials,
both in transition-metal and rare-earth systems, e.g., the fluoride garnet
Cr3+:Na3Ga2Li3F12 (13), the fluoride pervoskite Cr3+:1<ZnF3 (20, 21), SrAIF5
(22,23), the family of Cr3+:LiCaAlFe derivatives (5), rare-earth doped KY3F10 (24),
and LiYF4 (25). Among these materials are the highest intrinsic slope efficiency
of any solid-state laser (Cr3+:LiCaAlF6) and one of the higher optical damage
thresholds of any Nd3+ laser (Nd3+:LiYF4).
Structural Aspects of Fluorides
Because of its high electronegativity, fluorine functions as the most ionic
ligand available. Its solid-state compounds can be treated by an ionic model,
so that the structures of fluorides can generally be described in terms of anionic
packing and occupation of interstitial positions by cations.
In most oxidation states of d transition-metal ions (M), the radius ratio
rarF falls in the range of 0.41-0.73, which is the stability region of octahedral
coordination in crystal chemistry. In fact, this coordination is observed in many
transition-metal fluorides.
There are few examples of fluorides where the
transition-metal ions exhibit a coordination number (CN) smaller than 6. Also,
as the result of the smaller covalency, the coordination number of the cations
in fluorides is sometimes higher than in oxides. As with oxides, the structures
of fluorides are not only determined by the relative ionic size and charge, but
also by a variety of factors, such as covalency, back bonding, spin state, ligand-
14
field splitting, and Jahn-Teller distortions.
In the following, the known structures of fluorides relating to my research
will briefly be reviewed. At first, the structures of the LiCaAIFe family are
discussed. Then, a section will be devoted to the Re03-related structures of
AXMFX +3
(A = alkali metal ions; M = transition metal or rare-earth ions).
Structure of Colquirilte Fluoride
The structures of colquiriite-type fluorides represented by the laser
material Cr3+1iCaAlFe are derived from Li2ZrFe (26). In U2ZrF6, space group
P31m, all cations occupy octahedral sites. Each corner of the ZrF62- polyhedron
is shared by two U +- centered octahedra that share edges with one another.
In colquiriite derivatives, such as UCaAIF6 and LiSrAlFe, formed by subsitituting
half of the Li+ ions with divalent ions and the Zr4+ ions with trivalent cations (28,
28), the c lattice parameter doubles and the structures form in space group
P31c. The absence of readily available tetrahedral substitutional sites in this
material is important, because the absorption cross section of Cr3+ on
tetrahedral sites is quite large, introducing a serious passive loss. Also, since
the Li+, M2+, and M' 3+ ions are generally very different from each other in terms
of charge and radius, the Cr3+ ion occupies only M' 3+ sites.
The most
important factor determining the luminescent properties of Cr3+ doped colquiriite
lasers is the relative twist angle between the trigonal F planes of the D3, M' site
(28). The effect of this twist angle on the luminescence is similar to that in ruby
Cr3+:A1203, as discussed earlier.
In Chapters 2 & 3, the structures of the
derivatives UMM Fe (M = Sr, Ca; M = Al, Cr, Ga ) and the twist angles at the
15
dopant sites are discussed.
Structure of AxMF3+x (A = Alkali Ions; M = Trivalent Transition Metal a n d
Rare-Earth Ions)
My interests in the structures of fluorides of the type RID,LnFx+3 (Ln =
trivalent transition metal or rare-earth ion) as potential Cr + or Nd3+ laser hosts
arose in connection with the known structures of rubidium indium fluorides:
Rb3InF5, RbInF4, Rb5In4F14, Rb4ln3F13, Rb2InF5, Rb21n3F11, RbIn2F7, and RbIn3F10
(29).
The structure of each of these compounds is related to that of Re03.
While the In3+ ion has octahedral coordination in most of these fluorides, it does
occupy both pentagonal bipyramidal and octahedral sites in Rbln3F10 and
Rb21n3F1 1.
Because the typical In-F distance in an octahedral site is 2.06 A and
that in a pentagon-bipyramidal site is 2.13 A, I attempted to selectively substitute
a smaller Sc + ions on the octahedrally coordinated site and a larger lanthanide
ion on the pentagonal bipyramidal site. The results of these synthetic studies
are summarized in Chapter 5.
Preparative Chemistry of Solid Inorganic Fluorides
Solid inorganic fluorides can be prepared by a variety of synthetic
methods, such as gas-phase reactions (30, 31, 32), reactions in aqueous or
nonaqueous solutions under either atmospheric or high-pressure conditions
(33), gas-solid reactions (34), or solid-state reactions.
The selection of a
synthetic method is dependent primarily on the equipment available and the
nature of the product desired.
At room or moderate temperature, reactions with HF (aq) can be done
16
in vessels of Teflon (polytetrafluorethylene), K 'elf (monochlorotrifluoroethylene),
or FEP (fluorinated ethylene-propylene copolymer). At elevated pressures or
temperatures, Monel, Nickel or Platinum containers can be used.
A simple method for synthesizing solid inorganic fluorides, where
applicable, is by precipitation from aqueous solutions. The samples obtained
from this method often are hydrated, or amorphous, and contain hydroxides or
oxygen, since F- and 02- have similar ionic radii and are sometimes
Therefore, a post treatment in flowing HF (g) is usually
interchangeable.
required to remove 0 species. A method to prepare anhydrous Sr2ScF7 is
described in Chapter 4. A precursor powder of Sr2ScF7 was obtained by drying
a precipitate that was made at room temperature by adding HF (aq) into a
saturated aqueous solution of strontium and scandium nitrates. The precipitate
was then treated in a stream of 99.99% HF (g) at an elevated temperature to
remove 0-containing impurities and to improve the crystallinity. The precursor
powder from the precipitation method is highly reactive because of the small
particle size and large surface area.
Many solid inorganic fluorides are prepared at high temperatures. Gas-
solid reactions are executed by passing HF (g) over powder mixtures of
reactants, e.g., oxides, haildes, or even commercial fluorides. A diagram of the
apparatus that
I
have used primarily for hydrofluorination at atmospheric
pressure up to 1100 °C is shown in Figure 1.3. All tubing, fittings, and valves
employed in the apparatus are made of Monel or Ni. Samples were heated in
17
graphite or platinum crucibles, and separate towers containing NaOH (aq) and
MgO were used to destroy residual HF (g).
sample
nickel tube
00
valve
eating wire
N2 gas
aOH
HF (9)
N2(9)
Figure 1.3 Hydrofluorinating line
(11
90 tower
19
References
1.
Lai, S. T., and Shand, M. L., J. Appl. Phys., 54, 5642 (1983).
2.
Walling, J. C., Heller, D. F., Samelson, H., Harter, D. J., Pete, J. A., and
O'Dell, W. E., IEEE J. Quantum Electron., QE-16, 1302 (1980).
3.
Walling, J. C., Heller, D. F., Samelson, H., Harter, D. J., Pete, J. A., and
Morris, R. C., IEEE J. Quantum Electron., QE-21, 1568 (1985).
4.
Kaminskii, A. A., Laser Crystals, Springer Series in Optical Sci., Vol. 14,
(1981)
5.
Payne, S. A., Chase, L L, Newkirk, H. W., Smith, L. K., and Krupke, W.
F., IEEE J. Quantum Electron., 24, 2243 (1988).
6.
Tanabe, Y., and Sugano, S., J. Phys. Soc. Japan, 9, 753 (1954).
7.
McClure, D. S., Electronic Spectra of Molecules and Ions in Crystals,
Academic Press, New York, 1959.
8.
Huber, G., and Petermann, K., Tunable Sold State Lasers, Hammerling,
P., Budgor, A. B., and Pinto, A., Ed, Berlin, Sprinjger-Verlag, 11 (1985).
9.
Sugano, S., Schawlow, A. L., and Varsanyi, F., Phys. Rev., 120, 2045
(1960).
10.
Henry, C. E., Schnatterly, S. E., and Slichter, C. P., Phys. Rev., Sect. A,
137, 583 (1965).
11.
Schultz du Bois, E. 0., Bell Syst. Tech. J., 38, 271 (1959).
12.
Bukin, G. V., Volkov, S. Yu., Matrosov, V. N., Sevactyanov, B. K.,
Timoshechkin, M. I., Soy. J. Quantum Electron., 8, 671 (1978).
20
13.
Caird, J. A., Payne, S. A., Stayer, P. R., Ramponi, A. J., Chase, L. L., and
Krupke, W. F., IEEE J. Quantum Electron.
14.
,
24, 1077 (1988).
Caird, J. A., Tunable Solid State Lasers II, Budgor, A., Esterowitz, L, and
Deshazer, L. G. Eds. Berlin: Springer-Verlag, 20 (1986).
15.
Fields, R. A., Birnbaum, M., and Fincher, C. L, Appl. Phys. Lett., 51, 1885
(1987).
16.
Henderson, B., and Imbusch, G. F., Optical Spectroscopy of Inorganic
Solids, Oxforf Science Publications, 515 (1989).
17.
Schulz, H., Solid State Chemistry 1982, Metselaar R., Heiligers, H. J. M.
and Schoonman, J., Ed. Elsevier Sci. Pub. Comp., 133 (1982).
18.
Pruss, D., Huber, G., Beimowski. A., Appl. Phys., Sect B, 28, 355 (1982).
19.
Andrews, L J. and Hitelman, S. M., Ettore Majorana Int. Sci. Ser., Phys.
Sci., 30, 515 (1987).
20.
Brauch, U. and Durr, U., Opt. Commun., 49, 61 (1984).
21.
Caird, J. A., Shinn, M.D., Newkirk, H. W., and Guggenheim, H. J., The
Laser Program Annual Report, 1984. Livermore, CA: LLNL. 1985, UCRL50021-84.
22.
Caird, J. A., Stayer, P. R., Shinn, M. D., Guggenheim, H. J. and Bahnck,
D., Tunable Solid State Lasers II, Bugdor, A. B., Esterowitz, L., and
Deshazer, L. G., Ed. Berlin: Springer-Verlag. 159 (1986).
23.
Jennsen, H. P. and Lai, S. T., Opt. Soc. Amer., Sect. B, 3, 115 (1986).
24.
Abdulsabirov, R. Yu., Dubinskii, M. A., Kazakov, B. N., Silkin, N. I., and
Yaqudin, Sh. I., Soy. Phys. Crystallogr., 32, 559 (1987).
21
25.
Birnbaum, H. and Deshazer, L., Engineering Design of Repetitively QSwitched Solid State Lasers for Presicion Range in Applications. Contract
NASA-23698.
26.
Brunton, G., Acta Crystallogr., Sect. B, 29, 2294 (1973).
27.
Viebahn, V. W., Z Anorg. Al lg. Chem., 386, 335 (1971).
28.
Schaffers, K I. and Keszler, D. A., Acta Crystallogr., Sect. C, 47, 18
(1991).
29.
Grannec, J., Champarnaud-Mesjard, J. C., Costy, J. P., Cousseins, J. C.,
and Gaudreau, B., Rev. Chim. Miner., 9, 569 (1972).
30.
Barttett, N. and Lohmann, D. H., Proc. Chem. Soc., London, 115 (1962).
31.
Barttett, N. and Lohmann, D. H., Proc. Chem. Soc., London, 5253 (1962).
32.
Falconer, W. B. and Sunder, W. A., J. lnorg. Nucl. Chem., 29, 1380
(1967).
33.
Tedenace, J. C., Granier, W., Norbert, A. and Cot, L., C. R. Hebd.
Seances Acad., Sci., 268, 1368 (1969).
22
CHAPTER 2
CRYSTAL CHEMISTRY of COLQUIRIITE-TYPE FLUORIDES
Yaobo Yin and Douglas A. Keszler
Published in Chem. Mater. 1992, 4
23
Abstract
Crystal structures of six fluorides in the family LiMM 'F6 ( M = Sr or Ca;
M' = Al, Ga, or Cr) have been refined with single-crystal X-ray diffraction data.
Each compound crystallizes in trigonal space group Fq1c (Z = 2) as an
ordered derivative of the Li2ZrF6 structure type. Cell parameters: LiCaAlF6, a =
5.007(1), c = 9.641(1) A; LiCaGaF6, a = 5.079(3), c = 9.752(2) A; LiCaCrF6, a
= 5.098(2), c = 9.775(1) A; LiSrAia.(1)Cro.4,(1)F., a = 5.117(3), c = 10.275(1) A;
LiSrGaF6, a = 5.154(1), c = 10.321(2) A; LiSrCrF6, a = 5.174(5), c = 10.369(1)
A. Each cation occupies a deformed octahedral site in a distorted hexagonally
closest-packed F- arrangement; the distortions of the D3 M' site are examined
in detail.
24
Introduction
Because of their long operational lifetimes, reliable and efficient flash lamp
or diode pumping, and high beam quality at high average power levels, tunable
solid-state lasers can offer considerable advantages over conventional dye
lasers.
Recently, two new tunable laser materials Cr3+:LiCaAlF6 and
Cr3+:LiSrAlF6 were reported.1'2 These materials exhibit high intrinsic lasing
efficiency, low thermal lensing, and excellent resistance to UV solarization. Each
host, however, exhibits unique lasing and optical characteristics. For example,
the Ca derivative exhibits a higher intrinsic efficiency of 67% vs. 53% for the Sr
derivative, a smaller r emission cross section of 1.3 x 10-2° cm2 vs. 4.8 x 102°
cm2, and a longer emission lifetime of 170 gs vs. 67 gs. These characteristics
are determined by the static and dynamic characteristics of the hosts and, in
particular, the characteristics of the Al dopant site. In a recent account we
described the static distortions of the AIF6 site in the host LiSrAlF6 that
contribute to the heightened cross section and shorter lifetime of the Cr +
optical emission.3
In this report we present crystal data on colquiriite (LiCaAlF6),4 and its
derivatives LiCaCrF6, LiCaGaF6, LiSrA10.66(1)Cr0.41(1)F6, LiSrCrF6, and LiSrGaF6,
some of which are being developed as new laser materials.
25
Experimental
The single crystals of LiCaCrF6, LiSrGaFe, LiCaAIF6, and LiSrAlemCro.41Fe
were grown at Lawrence Livermore National Laboratory, and the single crystals
of LiCaGaFe and LiSrCrFe were prepared at Oregon State University. Reagents
used for crystal growth at OSU were the following: LiF (AESAR, 99.99%), CaO
(AESAR, 99.95%), Ga2O3 (AESAR, 99.999%), SrF2 (Cerac, 99%), and Cr2O3
(Johnson Matthey,99%). A powder of LiCaGaFe was prepared by passing
HF(g) (Matheson, 99.9%) over a stoichiometric mixture of the starting reagents
at 700°C for 1 h followed by annealing at the same temperature for 12 h. The
single crystal was grown by maintaining the melt at 850°C for 20 min then
rapidly cooling to and annealing at 700°C for 24 h. A colorless single crystal of
dimensions 0.1 x 0.1 x 0.1 mm was physically separated from the solidified melt.
The single crystal of LiSrCrFe having dimensions 0.1 x 0.08 x 0.1 mm was
obtained by passing HF(g) over the mixture SrF2: 1.5 LiF : 0.75 Cr2O3 at 650°C
for 2 hrs, then heating to 810°C and cooling to 700°C at a rate of 12°C /h.
The single crystals were mounted on glass fibers and analyzed on a Rigaku
AFC6R diffractometer.
Cell parameters were obtained from least-squares
refinement of the setting angles of 10-19 centered reflections in the range 30
20 5_ 36°. On the basis of the systematic absence hhl, I = 2n +1, and successful
refinement, each crystal was found to crystallize in space group P1c (#163).
All calculations were performed on a microVAX II computer with programs
from the TEXSAN crystallographic software package.5 The atoms Li, M ( M =
Sr or Ca ), and M' (M' = Al, Ga, or Cr) were placed by comparison to the
26
isostructural compounds LiCaAlFe and LiSrAlFe. The position of the F atom in
each derivative was determined by examining difference electron density maps.
Following refinement of each structure with isotropic thermal parameters, the
data were corrected for absorption with the program DIFABS.6
Final least-
squares refinement included anisotropic thermal parameters on each atom. In
the mixed crystal LiSr(A1,Cr)Fe the occupancy of the M' site was refined as two
atoms disordered on one site with the total occupancy constrained to 1. Final
difference electron density maps were featureless with maximum peaks
corresponding to <0.5% of a Ca or Sr atom.
Crystal data and final atomic parameters are listed in Tables 2.1 and 2.2,
respectively, and anisotropic thermal parameters arranged in Appendices C1 C6.
Table 2.1. Crystal Data and Experimental Conditions for Colquiriite-type Fluorides
Formula
LiCaAlFe
LiCaGaFe
LiCaCrFe
FW, amu
187.99
230.73
213.01
LiSrA10.6Cro.4F6
LiSrGaFe
LiSrCrFe
278.27
260.55
ra1c
Space Group
a, A
5.007(1)
5.079(1)
5.098(1)
5.117(2)
5.154(1)
5.174(1)
c, A
9.641(2)
9.752(2)
9.775(4)
10.275(2)
10.320(1)
10.369(1)
c/a
1.926
1.920
1.917
2.008
2.002
2.004
V, A3
209.3(1)
217.9(1)
220.0(1)
233.0(1)
237.43(8)
240.34(6)
3.892
3.600
Z
2
T of data
collection, K
Peak. 9 /cm-3
radiation
296
2.983
3.517
3.215
graphite monochromated MoKa (A.(Ka) = 0.71069 A)
Table 2.1 (continued)
g, CM-1
LiCaAlF6
LiCaCrF6
LiCaGaF6
LiSrA10.6Cro.4F6
LiSrGaF6
LiSrCrF6
17.13
74.84
37.19
124.33
165.92
130.11
h, ±k, ±I
data collected
sin Com,ch
0.7035
0.7035
0.8759
0.7035
0.8566
0.7035
transmission factors
0.86-1.20
0.96-1.08
0.85-1.12
0.83-1.21
0.84-1.34
0.65-1.00
Rini
0.051
0.046
0.050
0.055
0.086
0.064
Rv(F.)
0.024
0.025
0.056
0.034
0.034
0.024
0.021
0.025
0.041
0.033
0.026
0.018
R(F,,) for
F02 > 3a(F02)
Table 2.2. Atomic Parameters of Colquiriite-type Fluorides LiMM'Fa"
M = Ca, M" = Al M = Ca, M" = Ga M = Ca, M' = Cr
M = Sr, M" = Ga M = Sr, M" = Cr
M = Sr, M" = AI,Cr
Li
Beg
1.2(1)
1.5(2)
1.6(3)
1.3(2)
1.0(2)
1.3(4)
M
13,1
0.69(2)
0.65(2)
0.89(2)
0.99(1)
0.88(2)
0.78(2)
M'
Beg
0.50(2)
0.51(1)
0.75(2)
0.81(1)
0.70(2)
0.56(4)
F
x
0.0306(1)
0.0201(3)
0.0185(3)
0.0211(4)
0.0202(3)
0.0277(4)
Y
0.3768(1)
0.3688(2)
0.3653(3)
0.3795(4)
0.3653(3)
0.3835(5)
z
-0.1434(2)
-0.1407(1)
-0.1403(1)
-0.1459(1)
-0.1458(1)
-0.1469(2)
B,
0.99(2)
1.01(4)
1.24(4)
1.51(5)
1.43(5)
1.40(7)
' Li is located in Wyckoff position 2c (1/3,3,1/4), M' in 2b (34,1/3,1/4), and M in 2a (0,0,0)
30
Discussion
Each of the materials is isostructural to the mineral colquiriite, LiCaAlFe,
which is a derivative of the Li2ZrFe structure type. In this trigonal structure,
Figure 2.1, the cations occupy distorted octahedral environments between
planes of approximately closest-packed fluoride anions that extend in the ab
plane. Considering the general formula LiMM 'F6 where M = Ca or Sr and M'
= Al, Ga, or Cr, the atoms stack in the sequence
F (Li,M ') F M F
i.e., the Li and M' atoms are sandwiched together between the same anionic
layers, and the M atoms stand alone in aciacent layers. The Li- and M 'centered octahedra share edges with one another and vertices with the Srcentered octahedra.
Interatomic distances and angles for the structures are listed in Tables 2.3
and 2.4, respectively. M '-F distances increase in the order Al-F < Ga-F < Cr-F
for both the Ca and Sr derivatives. Ca-F and Sr-F distances are constant with
changes in the M' atom, while a trend of larger Li-F distances with longer M '-F
distances is evident in both the Ca and Sr series; this trend is consistent with
the height of the (Li,M ')-centered sandwich which expands as the size of the
M' atom increases.
The D3 sites of the atoms M' exhibit small, but important, distortions from
Oh symmetry. In Table 2.4, the first F-M '-F angle corresponds to two F atoms
in the same trigonal plane while the second and third correspond to interactions
in opposite planes. The deviations from orthogonality for the latter two
31
Figure 2.1
Drawing of the colquiriite structure. Large open circles represent F atoms.
Small filled circles represent Al atoms, small open circles U atoms, and small
shaded circles Sr atoms, here, and in Figure 2.
32
Table 2.3. Interatomic Distances for Colquiriite Derivatives
Distance (A)
Compound
LiCaAlFe
LiCaGaFe
LiCaCrFe
LiSrAlFes
LiSrGaFe
LiSrCrFe
LiSrAlezeCreA,F6
Ca - F
2.281(4)
Al - F
1.805(6)
Ca - F
2.283(1)
Ga - F
1.884(1)
Ca - F
2.277(2)
Cr - F
1.903(1)
Sr - F
2.424(1)
Al - F
1.795(5)
Sr - F
2.428(2)
Ga - F
1.885(1)
Sr - F
2.425(2)
Cr - F
1.902(1)
Sr - F
2.423(3)
Al(Cr)
'ref. 3
F
1.845(2)
Li - F
2.006(7)
Li - F
2.017(1)
U-F
2.025(2)
Li - F
2.018(6)
Li - F
2.028(2)
Li - F
2.039(1)
Li - F
2.032(2)
33
Table 2.4. Interatomic Angles for Colquiriite Derivatives
Compound
LiCaAlFe
Li CaG a Fe
Angles (°)
F - Al - F
90.81(3)
F - Al - F
91.76(4)
F - Al - F
86.72(4)
F - Ca - F
92.93(3)
F - Li - F
96.13(3)
F - Li - F
92.34(4)
F-U-F
76.31(3)
Ca - F - Al
133.78(3)
Ca - F - U
122.60(3)
Al - F - Li
98.48(3)
F - Ga - F
91.14(6)
F - Ga - F
91.87(7)
F - Ga - F
85.99(8)
F - Ca - F
92.41(5)
F-U-F
94.65(5)
F - Li - F
92.19(7)
F-U-F
79.14(7)
Ca - F - Li
124.87(6)
Ca - F - Ga 132.25(6)
LiCaCrFe
Ga - F - U
97.43(5)
F - Cr - F
91.34(5)
F - Cr - F
91.29(7)
F - Cr - F
86.14(7)
F - Ca - F
92.53(5)
F-U-F
94.54(5)
F - Li - F
91.60(8)
F - Li - F
79.83(6)
Ca - F - Cr
132.30(9)
Ca - F - U
125.48(5)
Cr - F - U
97.01(6)
34
Table 2.4. (continued)
LiSrAlFea
LiSrGaFe
LiSrCrFe
F - Al - F
90.32(7)
F - Al - F
94.18(7)
F - Al - F
85.48(6)
F - Sr - F
95.00(1)
F - Li - F
96.25(4)
F - Li - F
94.69(5)
F-U-F
74.27(1)
Sr - F - Al
133.22(2)
Sr - F - Li
121.47(8)
Al - F - Li
100.12(2)
F - Ga - F
90.9(1)
F - Ga - F
94.2(2)
F - Ga - F
84.3(2)
F - Sr - F
94.42(6)
F- U- F
94.5(1)
F- U- F
94.5(1)
F - Li - F
77.6(1)
Sr - F - Ga
131.3(2)
Sr - F - Li
124.2(1)
Ga - F - Li
99.0(1)
F - Cr - F
90.89(6)
F - Cr - F
93.6(1)
F - Cr - F
84.93(8)
F - Sr - F
94.76(6)
F - Li - F
94.50(5)
F-U-F
93.9(1)
F - Li - F
78.06(7)
Sr - F - Cr
131.80(7)
Sr - F - U
124.54(6)
Cr - F - U
98.50(6)
35
Table 2.4. (continued)
LiSr(AI,Cr)F6 F - AI,Cr - F
aref. 3
90.3(1)
F - (AI,Cr) - F
85.5(1)
F - Sr - F
94.71(8)
F - Li - F
95.29(8)
F - Li - F
76.1(1)
Sr - F - (AI,Cr)
132.6(1)
(AI,Cr) - F - Li
99.2(1)
F - (AI,Cr) - F
94.2(1)
F - Li - F
94.6(1)
Sr - F - Li
122.79(9)
36
interactions are associated with the relative orientations of the trigonal F planes
perpendicular to the C3 c axis. These planes are twisted to afford angles, 0,
that deviate from the ideal 60° (Figure 2.2), Table 2.5. The greatest change in
the magnitude of the angle occurs between the Ca and Sr derivatives where
larger angles are associated with the larger Sr atom. In the series Al, Ga, and
Cr, the Ga derivatives exhibit the larger distortions while the sites in the Al and
Cr derivatives are comparable.
As noted in the report on the compound
LiSrAIF6,3 the distortion results from displacements of the F atoms from an ideal
closest packing (Figure 2.3).
Trigonal hollows of F atoms expand in the
presence of the large Ca or Sr atoms. Since each F atom interacts with one Li
atom, one M atom, and one M" atom, this expansion is coupled with an
electrostatic relaxation toward the more highly charged M"3+ cations. Because
the M atoms about an M 'F6 site define a trigonal prism, the two trigonal F
planes rotate in opposite directions. The primary effect of this distortion is the
introduction of an odd-parity component to the crystal field at the Cr + dopant
site. The sensitivity of the optical properties to this distortion is noted by the
(A0)2 [A0 = 0 60°] dependence of the radiative rates.'
The stoichiometry of the mixed crystal LiSrA10.59Cr0.41 Fe compares well to
that of the melt, LiSrA10.6Cr0.4F6. The results are consistent with congruency of
the sample and a segregation coefficient = 1. Also, significant doping levels of
CO+ ions can be achieved in the Al system while maintaining high crystal
quality. In this regard, the solution series LiSrl.Ba.AIF6 should be examined for
crystal quality as a function of the level of Ba substitution, and to determine the
37
maximum value of x consistent with formation of the colquiriite structure type
since LiBaAlF6 crystallizes in a different structure.° The presence of Ba atoms
should afford larger twist angles and higher cross sections for Cr + optical
emission.
38
Figure 2.2
Relative rotation of two trigonal F planes about the M' site
39
00 00
0 o00o0
000000
0
0
0
0
0 00000
Figure 2.3
Comparison of F closest packing with F packing in the structure of LiSrGaF6 by
projection onto (001). Ideal F closest packing is represented by large shaded
circles.
40
Table 2.5. Twist Angles of Colquiriite-type Fluorides
Compound
AO°
LiCaAIF6
4.3
LiCaGaF6
5.0
LiCaCrF6
4.3
LiSrAlF6b
7.2
LiSrGaF6
8.2
LiSrCrF6
7.4
LiSrA10.59Cr0m Fe
7.5
bref. 3
41
Acknowledgments
We thank Dr. Stephen A. Payne of Lawrence Livermore Laboratory for
supplying crystals.
This work was supported by the US National Science
Foundation, DMR-88144332. DAK is grateful to the Alfred P. Sloan Foundation
for a fellowship, 1989 - 1991.
42
References
1.
Payne, S. A.; Chase, L. L.; Newkirk, H. W.; Smith, L. K.; Krupke, W. F.
IEEE J. Quantum Electron. 1988, 24, 2243.
2.
Payne, S. A.; Chase, L. L.; Smith, L. K.; Kway, W. L.; Newkirk, H. W. J.
Appl. Phys. 1989, 66, 1051.
3.
Schaffers, K. I.; Keszler, D. A. Acta Crystallogr., Sect. C 1991, 47, 18.
4.
Viebahn, V. W. Z Anorg.
5.
Molecular Structure Corporation. TEXSAN. TEXRAY Structure Analysis
lg. Chem. 1971, 386, 335.
Package. MSC, 3200A Research Forest Drive, The Woodlands, TX
77381, USA.
6.
Walker, N.; Stuart D. Acta Crystallogr., Sect. A 1983, 39, 158.
7.
Payne, S. A., Lawrence Livermore Laboratory, private communication.
8.
Babel, von D. Z Anorg.
g. Chem. 1976, 406, 23.
43
CHAPTER 3
SOLID SOLUTIONS IN COLQUIRIITE-TYPE FLUORIDES
LiSrl.,.Ba,MF6 (M = Al. Ga)
Yaobo Yin and Douglas A. Keszler
Materials Research Bulletin, 1993
44
Abstract
The systems LiSrl.BaMFe (M = Al, Ga) have been studied by powder
and single-crystal X-ray diffraction methods. Solubility limits of x = 0.06 for the
Al compound and x = 0.20 for the Ba compound have been established. The
structures of LiSr0.94(1)BaaceAlF6 and LiSratc(,)Bao.20GaFe corresponding to these
limits are isotypic to the mineral Colquiriite. Each crystallizes in space group
P*3-1c: LiSrumBacceAlFa: a = 5.096(1) A, c = 10.269(2) A, R = 0.034, R., = 0.041;
and LiSr0.80Bao.20GaFe: a = 5.173(1) A, c = 10.415(1) A, R = 0.028, 1:1, = 0.033.
The trigonal F planes about the Al and Ga atoms are rotated, one relative to the
other, by 68.0 and 69.0°, respectively.
MATERIALS INDEX: lithium, strontium, barium, aluminum, gallium, fluoride
45
Introduction
Several crystals in the family of Colquiriite fluorides LiAEMF6 (AE = Ca,
Sr; M = Al, Ga, Cr) have been reported to function as efficient, broadly tunable
laser materials when doped with the ion Cr + (1-4). The optical characteristics
of the CO+ ion are considerably affected by the specific AE atom in the crystal.
For example, the emission lifetime decreases by more than a factor of two and
the emission cross section increases by more than a factor of three on
changing the AE atom from Ca to Sr in the Al derivatives LiAEAIF6 (1, 2). From
recent structural work (5), we found these results to be consistent with the
degree of distortion of the F environment about the M dopant site. As reflected
by the optical properties, the distortion was found to become more severe with
increasing size of the AE atom.
To determine the maximum distortion about the M site that can be
achieved in this family, we have examined the solid solution series LiSrl,Ba,MF6
(M = Al, Ga). Limited solubilities are expected for these systems since the
compounds LiBaAIF6 and LiBaGaF6 do not crystallize as Colquiriite derivatives
(6). The solubility limits and structures of the compounds LiSr0.86Ba0.06A1F6 and
LiSr0.60Ba0.20GaF6 are described herein. These Ba crystals may provide shorter
lifetimes and higher cross sections for CO+ emission - desirable characteristics
for Q-switched laser operation.
46
Experimental
All powder samples of LiSr1_,BaNFe (M = Al, Ga) were prepared by a
method described previously (5). A stoichiometric mixture of suitable reagents LiF (AESAR, 99.99%), Sr(NO3)2 (AESAR, 99.9965%), Ba(NO3)2 (Alfa, 99.95%),
A1203 (Cerac, 99.99%), Ga203 (AESAR, 99.999%) - was heated to 700 °C for 1
h under flowing HF (g) (Matheson, 99.9%), followed by annealing at the same
temperature for 12 h. Single crystals were obtained by heating the fluorides to
800 °C and then cooling to 650 °C at a rate of 12 °C/h.
The cell parameters of the compounds LiSr1_,Ba.MF6 (M = Al, Ga) were
determined by powder X-ray diffraction methods with data collected on an
automated Philips diffractometer. Peak positions were corrected with an internal
Si standard (NIST Standard Reference Material 640b), and cell parameters were
refined with a local version of the program POLSQ.
Single crystal
X-ray data were collected on a Rigaku AFC6R
diffractometer. Cell parameters were obtained from a least-square refinement
of the setting angles of 16 centered reflections for LiSr0.94Ba0.08A1F6 and 17 for
LiSr0.30Ba0.20GaFe in the range 30° 5 20
40°.
Each crystal forms in same
space group Rai c, the same as that of LiSrMF3 (M = Al, Ga).
All calculations were performed on a microVAX
II
computer with
programs from the TEXSAN crystallographic software package (7). The cations
were placed by comparison to the isostructural compounds LiSrMFe (M = Al,
Cr, Ga). The F position was determined by examining a difference electron
density map. Following refinement of each structure with isotropic displacement
47
coefficients, the data were corrected for absorption with the program DIFABS
(8). Final least-square refinement included anistropic displacement coefficients
on each atom and the occupancy of the AE site which was refined as two
disordered atoms (Sr and Ba) with the total occupancy constrained to unity.
The final difference electron density maps revealed no features greater than 0.4
% of the AE site in LiSr0.8Ba0.2GaFe and 0.71 % of the AE site in LiSr0.94Ba0.08A1Fe.
Crystal data and atomic parameters are listed in Tables 3.1 and 3.2,
respectively; interatomic distances and angles are summarized in Table 3.3.
48
TABLE 3.1
Crystal Data and Experimental Conditions
LiSr0.94BaneAlFe
FW, u
LiSr0.80Bao.20GaFe
238.51
space group
288.21
P-3-1c
a, A
5.096(1)
5.173(1)
c, A
10.269(2)
10.415(1)
V, A3
231.0(1)
241.3(1)
Z
ti, cm-1
2
115.48
163.23
data collected
h, ±k, ±I
sin 0,JA,
0.8071
transmission factors
0.83 - 1.29
0.8 - 1.26
R(FO> for FQ2 > 3sr(F02)
0.034
0.028
Rw
0.041
0.033
49
TABLE 3.2
Atomic Parameters a
LiSr0.94(1)Bao.06A1F6
LiSra6emBee20GeF6
Li
B,,q
1.8(3)
1.9(3)
(Sr, Ba)
13,,
0.89(1)
0.93(2)
M
Beg
0.72(3)
1.13(1)
F
x
0.0321(3)
0.0226(3)
Y
0.3568(3)
0.3829(3)
z
-0.1490(1)
-0.1468(1)
Beg
1.61(5)
1.84(5)
aLi is located in Wyckoff position 2c (1/3, 2/3, 1/4), Sr and Ba in
2a (0, 0, 0), M in 2b (2/3, 1/3, 1/4)
50
TABLE 3.3
Interatomic Distances (A) and Selected Angles ( °)
LiSr0.94Ba0.05A1F6
LiSraeoBao.20GaFe
Sr(Ba)-F
2.444(1)
Al-F
1.807(1)
F-Al-F
90.32(6)
F-Al-F
85.22(8)
F-(Sr,Ba)-F
95.05(5)
F-Li-F
96.09(5)
F-Li-F
74.35(7)
(Sr,Ba)-F-Al
132.93(7)
(Sr,Ba)-F-Li
121.57(6)
Al-F-Li
100.21(6)
Sr(Ba)-F
2.458(2)
Ga-F
1.880(1)
F-Ga-F
90.54(6)
F-Ga-F
84.47(8)
F-(Sr,Ba)-F
94.59(5)
F-Li-F
94.64(5)
F-Li-F
76.81(7)
(Sr,Ba)-F-Ga
131.47(7)
(Sr,Ba)-F-Li
123.49(6)
Ga-F-Li
99.36(6)
Li-F
2.024(1)
F-Al-F
94.52(9)
F-Li-F
94.99(8)
Li-F
2.035(1)
F-Ga-F
94.9(1)
F-Li-F 95.17(9)
51
Results and Discussion
Results of the powder X-ray diffraction studies are summarized in Figure
3.1. For each series LiSrl.,Ba,A1Fe and LiSrl.,BaxGaFe, the unit cell volume is
observed to increase linearly with increasing concentration of the larger Ba
atom. The cell volumes plateau at the solubility limits of x = 0.06 for the Al
derivative and x = 0.20 for the Ga compound. These results are consistent with
the single-crystal analyses. To ensure that the stoichiometry of each crystal
would be representative of the solubility limit, each was grown from a melt
having a 5 mol% excess of BaF2. The refined occupancies of the AE sites are
in complete agreement with the solubility limits determined from the powder Xray data. The AE-F distances (Table 3.3) are longer than the values of 2.424(2)
and 2.428(2) A for the Al and Ga derivatives, respectively, and this lengthening
is in agreement with the substitution of Ba at the Sr site. The Al-F and Ga-F are
statistically comparable to the same interactions in the stoichiometric Sr
derivatives (5).
The single-crystal studies also provide verification for retention of the
Colquiriite structure. This structure is an ordered derivative of the Li2ZrFe type,
wherein each of the metal atoms occupies a distorted octahedral site between
hexagonally close-packed layers of F atoms (Figure 3.2). The Li- and Mcentered octahedra are bound by the same F sheets, while the Sr(Ba) atoms
are alone between aciacent sheets.
The larger dissolution of Ba in the Ga derivative arises from the greater
ease in enlarging the AE site. And this is best reflected by the longer cell axes
52
242
0
240-
Ga derivative
238-
tn.-,
04C
236-
0
E
m 234
0
t 232-
0
230-
1,41 derivative
o.b..5
0:1
13:15
62
chis
x
FIG. 3.1
Cell volume vs x for the series LiSrl.BaMF6 (M = Al, Ga)
0.3
53
FIG. 3.2
Drawing of the unit cell for LIAEMFe. (Filled octahedron: M-centered site;
stippled octahedron: Li-centered site; here, and in Fig. 3.3)
54
1
1
0
L.,,,-0"##.7.
FIG. 3.3
Ring of edge-shared Li- and M-centered polyhedra around AE atom
(open circle: AE atom)
55
a in the Ga compounds. The size of this site is primarily constrained by the ring
of edge-shared Li- and M-centered polyhedra (Figure 3.3). Because the Ga3+
ion (r = 0.620 A) is larger than the Al3+ ion (r = 0.535 A) (9), the rings, that lie
above and below the AE atom and define the octahedral site, more readily
expand to accomodate a greater concentration of Ba atoms.
As mentioned earlier, the environment of the M dopant site has a
profound effect on the Cr + emission characteristics. The symmetry at this site
is D3. As a result, the principal distortion of the octahedron about the M atom
is associated with the relative rotations of the two opposite trigonal F faces. For
an octahedron with Oh symmetry, the angle between these faces is 60° (Figure
3.4). Because the AE atoms are placed at the vertices of a distorted trigonal
prism about the M atom, longer AE-F distances produce greater deviations of
the twist angle 0 from 60° (Table 3.4). Substituting Ba for Sr to the limit in the
Al and Ga derivatives results in an increase of the twist angles by 0.8° for each
M environment. For each material, this larger distortion is likely to afford a
higher emission cross section and a shorter excited-state lifetime for Cr3+
emission.
56
FIG. 3.4
Relative rotation of two trigonal F planes about the M site
57
TABLE 3.4
Twist Angles of D3 , M-centered Octahedra
Compound
LiSrAlFeb
7.2
LiSras4BaomeAlFe
8.0
LiSrGaFec
8.2
LiSr0.80843.20GaFes
9.0
aA0 = 0 - 60°. b (10), c (5)
58
Acknowledgment
This work was supported by the US National Science Foundation, DMR8814332.
fellowship.
D. A. K achnowledges the Alfred P. Sloan Foundation for a
59
References
1.
S. A. PAYNE, L. L Chase, L K Smith, W. L. Kway and H. W. Newkirk,
J. Appl. Phys., 66, 1051 (1989) .
2.
S. A. Payne, L. L. Chase, H. W. Newkirk, L. K. Smith and W. F. Krupke,
J. Quantum Electron., 24, 2243 (1988).
3.
L. K. Smith, S. A. Payne, W. F. Krupke and L D. Deloach,
Optics
Letters, 18, 200 (1993).
4.
S. A. Payne, L. L Chase, L. K Smith, W. L Kway and B. H. T. Chai,
Advanced Solid-State Lasers Conference, Hilton Head, S. Carolina
(1991).
5.
Y. Yin and D. A. Keszler, Chem. Mater., 4, 645 (1992).
6.
Von. D. Babel, Z Anorg. Al g. Chem., 406, 23 (1976).
7.
Molecular Structure Corporation. TEXSAN: TEXRAY Structure Analysis
Package; MSC, 3200A Research Forest Drive, The Woodlands, TX
77388.
8.
N. Walker and D. Stuart, Acta Crystallogr., Section A, 39, 158 (1983).
9.
R. D. Shannon, Acta Crystallogr., Section A, 32, 751 (1976).
10.
K. I. Schaffers and D. A. Keszler, Acta Crystallogr., Section C, 47, 18
(1991).
60
CHAPTER 4
STRUCTURE OF DISTRONTIUM SCANDIUM HEPTAFLUORIDE
AND CHROMIUM(III) LUMINESCENCE
Yaobo Yin and Douglas A. Keszler
Materials Research Bulletin, 1993
61
Abstract
The crystal structure of the compound Sr2ScF7 has been established by
single-crystal X-ray diffraction methods to determine the local F arrangements
about the Sr and Sc atoms.
The monoclinic three-dimensional framework
contains 7-coordinate Sc atoms and [9 + 1]- and 9-coordinate Sr atoms. The
luminescence spectrum of Cr-3+:Sr2ScF7 exhibits a broad emission band
extending from 740 nm to 940 nm with a maximum at 844 nm.
MATERIALS INDEX: strontium, scandium, chromium, fluorides
62
Introduction
Small phonon energies and refractive indices make fluorides attractive
hosts for a variety of luminescent processes. As part of our interests in
studying the optical and structural characteristics of compounds containing the
ion Sc3+, we have determined the structure
of the material
Sr2ScF7.
Establishment of the structure and the point symmetries of the metal sites is
important, for example, in an initial assessment and precognition of the optical
properties of doped laser-active ions. This phase was first reported by Ravez
and Hagenmuller (1) and subsequently identified by Domes le and Hoppe on the
basis of powder X-ray diffraction data (2) as a derivative of the Pb2RhF7 or
K2NbF7 structure types. In this report, we establish the structure of Sr2ScF7 to
be similar to that of K2NbF7 and present the photoluminesce spectrum of a Cr3+-
doped sample.
63
Experimental
The reagents for synthesis of Sr2ScF7 were commercially available SrF2
(Cerac, Inc., 99%), Sr(NO3)2 (AESAR/Johnson Matthey, 99.99%), Sc203 (Boulder
Scientific Co., 99.99%), Cr203 ( AESAR/Johnson Matthey, 99.997%), HF (g)
(Matheson, 99.9%), HF (aq) (EM Science, 48 wt%), and HNO3(aq)(Mallinckrodt,
70.4 wt%). One sample was prepared by first heating a stoichiometric mixture
of SrF2 and Sc203 in a graphite crucible under flowing HF (g) at 700 °C for 2
hrs, and then under flowing N2 (g) at the same temperature for 10 hrs. Another
was made by dissolving Sc203 and Sr(NO3)2 in hot HNO3 (aq) and precipitating
the cations by addition of HF (aq). The precipitate was then heated under
flowing HF (g) at 700 °C for 20 mins and under N2 for 10 h. The powder from
the precipitation method is more homogeneous as shown by the narrow and
intense peaks in the powder X-ray diffraction patterns. All products were
determined to be single phase on the basis of the X-ray results.
The single crystal was grown by heating the melt of the initial sample at
1050°C for 30 mins, then cooling by turning the furnace power off. A single
crystal was physically separated from the solidified melt, mounted on a glass
fiber, and analyzed on a Rigaku AFC6R X-ray diffractometer.
Reflections were measured in the w -20 mode with a scan width = 1.20
+ 0.30 tan° and a scan speed = 16.0° min-1 in CO. The structure was solved and
refined on a microVAX II computer by using programs from the TEXSAN
crystallographic software package (3). Heavy-atom positions were determined
with direct methods.
The positions of the F atoms were subsequently
64
determined from examination of difference electron density maps. Following
refinement with isotropic displacement coefficients on each atom, the data were
corrected for absorption empirically with the program DIFABS (4) (transmission
= 0.75-1.48) and averaged (R1 = 0.051). Final refinement with anisotropic
displacement coefficients on each atom affords the residual R = 0.048. The
maximum peak in the final difference electron density map corresponds to 1.05
% of a Sr atom. Relevant crystal data are listed in Table 4.1, and final positional
and equivalent isotropic displacement coefficients are summarized in Table 4.2.
The
powder
sample
for
the
luminescence
measurement
Sr2ScaosCro.02F7 was prepared by the first method described above.
of
The
emission spectrum was measured by exciting the sample with the 514.5-nm line
from a Spectra-Physics Ar+ ion laser operated at 12 mW. Fluorescence was
passed through a yellow filter to eliminate any scattered green light from the
laser and collected at 90° to the excitation beam with a 0.5-m Jarrell-Ash
monochromator containing a holographic grating. Monochromated light was
detected with an RCA 7102 (type S-1) photomultipier tube by using a lock-in
amplifier. Output data were acquired and stored with an IBM PC.
65
TABLE 4.1
Crystal Data for Sr2ScF7
FW, amu
353.18
crystal system
monoclinic
space group
P21/c (#14)
a, A
5.450(3)
b, A
12.190(3)
c, A
8.236(3)
13, °
89.53(4)
V, A3
547.1(6)
Z Value
4
Pcalc, 9 criT3
4.287
I.L(Molta), cm-1
201.32
data collected
±h, ±k, ±I
sin email
0.8071
transimission factors
0.75 - 1.48
R1
0.051
Rw(Fo)
0.048
R(F0) for F02 > 3a(F02)
0.045
66
TABLE 4.2
Positional Parameters for Sr2ScF7
atom
x
y
z
Beg
Sr(1)
0.2364(1)
0.27981(5)
0.05359(7)
0.60(2)
Sr(2)
0.2365(1)
0.93817(4)
0.17668(7)
0.60(2)
Sc
0.7203(2)
0.37428(9)
0.7852(1)
0.52(4)
F(1)
0.5120(7)
0.1058(3)
0.0756(5)
0.9(1)
F(2)
0.5118(7)
0.2307(3)
0.7956(5)
0.9(1)
F(3)
0.3824(7)
0.4256(3)
0.8713(5)
1.0(1)
F(4)
0.9838(7)
0.1048(3)
0.0925(5)
0.9(1)
F(5)
0.2046(8)
0.4624(3)
0.2116(5)
1.3(2)
F(6)
0.9850(7)
0.2463(3)
0.8052(5)
0.8(1)
F(7)
0.7932(9)
0.3620(3)
0.0267(5)
1.4(2)
67
Results and Discussion
A drawing of the contents of the unit cell of Sr2ScF7 is given in Figure 4.1.
The structure is similar to that of K2NbF7 (5). This structure type contains two
inequivalent larger cations. The cation Sr(1) occupies a [9+1]-coordination
environment, and other Sr(2) occupies a 9-coordinate site; the smaller cation
se+ occupies a 7-coordinate site. The [9+1]-type polyhedra join by sharing
edges, and the 9-fold polyhedra also join by sharing edges; these two types
then join by sharing both edges and faces. The smaller Sc atom is isolated in
this matrix by sharing edges and vertices with the [9+1]- and 9-fold
environments, respectively.
Selected interatomic distances and angles are listed in Table 4.3. Sc-F
lengths range from 2.032(4) to 2.132(4) A, and the average distance 2.08(4) A
is similar to that observed in the compound ScF3, 2.01 A (6). The average
lengths Sr(1)-F = 2.6(2) A and Sr(2)-F = 2.56(7) A compare favorably to the
distance 2.61 A computed from crystal radii (7). Results of a valence-bond
calculation for the Sr(1) atom are listed in Table 4.4. Each of nine nearestneighbor F atoms individually makes approximately a 10% contribution to the
valency of atom Sr(1), while the tenth atom F(7) contributes less than half this
value. From this result, we derive the [9+1] description for the F environment.
The structure of Sr2ScF7 is also similar to that of Pb2RhF7. The significant
difference between these structures is the 6-coordination of the Rh atom in
comparison with the 7-coordination of the Sc atom. This discriminating feature
68
FIG. 4.1
Drawing of the contents of the unit cell of Sr2ScF7. (filled circles: Sc;
lightly shaded circles: Sr(1); heavily shaded circles: Sr(2); open circles: F)
69
TABLE 4.3
Selected Bond Distances (A) and Bond Angles ( °) of Sr2ScF7
Sr(1)-F(3)
2.455(4)
Sr(2)-F(3)
2.446(4)
Sc-F(3)
2.065(4)
Sr(1)-F(6)
2.495(4)
Sr(2)-F(6)
2.556(4)
Sc-F(6)
2.132(4)
Sr(1)-F(6)
2.505(4)
Sr(2)-F(2)
2.486(4)
Sc-F(5)
2.032(4)
Sr(1)-F(2)
2.508(4)
Sr(2)-F(1)
2.537(4)
Sc-F(7)
2.037(4)
Sr(1)-F(4)
2.558(4)
Sr(2)-F(4)
2.553(4)
Sc-F (2)
2.088(4)
Sr(1)-F(5)
2.584(4)
Sr(2)-F(4)
2.583(4)
Sc-F(1)
2.088(4)
Sr(1)-F(1)
2.606(4)
Sr(2)-F (5)
2.584(4)
Sc-F (4)
2.147(4)
Sr(1)-F(7)
2.626(5)
Sr(2)-F(7)
2.618(4)
Sr(1)-F(2)
2.659(4)
Sr(2)-F(1)
2.665(4)
Sr(1)-F(7)
3.203(1)
<Sc-F>
2.08(4)
average bond distances
<Sr(1)-F>
2.6(2)
<Sr(2)-F>
2.56(7)
F(3)-Sr(1)-F(6)
78.2(1)
F(3)-Sr(2)-F(2)
108.6(1)
F(3)-Sr(1)-F(2)
109.3(1)
F(3)-Sr(2)-F(4)
79.4(1)
F(3)-Sr(1)-F(5)
72.8(1)
F(1)-Sr(2)-F(2)
66.7(1)
F(6)-Sr(1)-F(6)
110.9(1)
F(1)-Sr(2)-F(3)
59.9(1)
70
Table 4.3 (continued)
F(7)-Sr(1)-F(6)
67.6(1)
F(4)-Sr(2)-F(7)
134.7(1)
F(1)-Sr(1)-F(4)
67.8(1)
F(5)-Sr(2)-F(1)
122.9(1)
F(4)-Sr(1)-F(5)
128.4(1)
F(6)-Sr(2)-F(1)
163.2(1)
F (5)-Sc-F (7)
91.1(2)
F(7)-Sc-F(1)
158.1(1)
F (6)-Sc-F (4)
72.3(2)
F (3)-Sc-F (6)
142.9(2)
F (7)-Sc-F (3)
82.4(2)
F(5)-Sc-F(6)
125.4(2)
71
TABLE 4.4
Bond Valence Calculation for Sr(1) Atom
Atom
Ra
Sb
% Contribution
F(1)
2.606
0.195
9.69
F(2)
2.508
0.232
11.53
F(3)
2.455
0.255
12.67
F(4)
2.558
0.212
10.53
F(5)
2.584
0.203
10.08
F(6)
2.495
0.237
11.77
F(6)
2.505
0.233
11.57
F(7)
2.626
0.189
9.39
F(7)
3.203
0.078
3.87
2.013
100.00
total
a
interatomic distance;
b bond valence S = (R/R0)-N (8)
72
may be discerned by considering Figure 4.2. The higher coordination number
of Sc vs Rh occurs from movements of atoms F(1) and F(4). A significant shift
of atom F(4), in particular, leads to the additional interaction with the Sc atom.
Because of the larger crystal radius of Sc3+ (0.885 A) in comparison with that
of Rh3+ (0.805 A), considerable displacements of the remaining F atoms are
observed between the two structures.
The photoluminescence spectrum of a powder sample of Sr2ScF7 doped
to 2 mol% with the ion CO+ is reproduced in Figure 4.3. The broad band
extends from 740 to 940 nm and maximizes at 844 nm - typical characteristics
for a 6-coordinate Cr3+ ion. The emission peak is blue shifted by nearly 20 nm
relative to that of Cr3+:ScF3 (9) and red shifted by approximately 65 nm relative
to the peak of Cr3+:LiCaAlF6 (10). It is well known that the Cr + ion tends to
occupy 6-coordinate sites in crystals; this preference has commonly been
modeled on the basis of the strong octahedral site preference energy of the d3
ion.
The charge and similar radius (0.755 A) of the CO+ ion indicate that it
substitutes for the 7-coordinate se+ ion in the title compound.
Upon
substitution, atoms F(1) and F(4) may locally relax about the Cr + ion to
produce a 6-coordinate environment that is similar to the Rh environment of
Pb2RhF7. Similar relaxations have been proposed on the basis of optical and
ESR data for fluoride fluorites (Cr3+:SrF2, Cr3+:BaF2) (11, 12) and other
fluorides (13). Experiments are ongoing to characterize the emission properties
of ions in this host.
73
a
b
FIG. 4.2
Structural relationship between (a) Pb2RhF7 and (b) Sr2ScF7
74
0
680
720
760
800
840
880
920
Wavelength (nm)
FIG. 4.3
Emission spectrum of Cr3+:Sr2ScF7 at room temperature
75
Conclusion
The single crystal structure of Sr2ScF7 has been established by singlecrystal X-ray methods to be a derivative of the K2NbF7 type. When doped into
this host, the Cr + ion gives rise to a broad-band luminescence that is typical
for a weak-field dopant site. The structural results presented here should be
useful in the potential development of the title compound as a laser material
wherein high cross sections and short lifetimes are to be expected for the laseractive ions.
76
Acknowledgment
This work was supported by the US National Science Foudation, DMR8814332. DAK is grateful to the Alfred P. Sloan Foundation for a fellowship. We
also thank Drs. Paul Thompson and Thomas Reynolds for their assistance in the
measurement of the luminescence spectrum.
77
References
1.
J. Ravez and P. Hagenmuller, Bull. Soc. Chim. Fr., 3452 (1971).
2.
R. Domes le and R. Hoppe, Z Anorg. Aug.
l Chem., 501, 102
(1983).
3.
Molecular Structure Corporation. TEXSAN. TEXRAY Structure
Analysis
Package. MSC, 3200A Research Forest Drive, The
Woodlands, TX 77381, USA.
4.
N. Walker and D. Stuart,
Acta Crystallogr., Sect. A, 39, 158
(1983).
5.
G. M. Brown and L A. Walker, Acta Crystallogr., 20, 220-29
(1966).
6.
W. Nowacki, Z Kristallogr., A101, 273-283 (1939).
7.
R. D. Shannon, Acta Crystallogr., Sect. A, 32, 751 (1976).
8.
I. D. Brown, Structure and Bonding in Crystals, Vo1.11, Academic
Press, New York (1981), P.1.
9.
G. Huber, S. A. Payne, L. L Chase and W. F. Krupke,
J.
Luminescence, 33, 259 (1988).
10.
S. A. Payne, L. L. Chase, H. W. Newkirk, L. K. Smith, and W. F.
Krupke, IEEE J. Quantum Electron., 24, 2243 (1988).
11.
S. A. Payne, L L. Chase, and W. F. Krupke, J. Chem. Phys., 86,
3455 (1988).
12.
W. Gehlhoff and W. VIrici, Phys. Stat. Sot, 8102, 11 (1980).
78
13.
S. A. Payne, L L. Chase, and W. F. Krupke, J. Luminescence,
40&41, 305 (1988).
79
CHAPTER 5
CRYSTAL CHEMISTRY OF NEW FLUORIDES IN THE TERNARY SYSTEMS
RbF - ScF3 - LnF3 (Ln = Y. Yb)
Yaobo Yin and Douglas A. Keszler*
in preparation for submission to J. Solid-State Chem.
80
Abstract
The ternary systems RbF-ScF3-LnF3
systematically studied.
(Ln = Y, Yb) have been
A number of new fluorides RbSc3F10, RbYb2F7,
Rb2YbSc2Fil, and RbLn2.Sci Flo (Ln = Yb, Y) have been synthesized and their
structures determined by single crystal X-ray diffraction methods. All crystallize
in the orthorhombic system. The structures are built by stacking layers of Sc3+-
and lanthanide-centered polyhedra into frameworks that are similar to that of
Re03. The large, monovalent Rb+ ion nestles into sites within tunnels extending
through the framework. Structural relationships among these new fluorides and
Re03 are discussed.
81
Introduction
During the last decade, one of the more important developments in the
technology of solid-state lasers has been the realization of efficient sensitization
of Nd" emission by nonradiative energy transfer from Cr". As demonstrated
with Nd", Cr" codoped Gd3Sc2Ga3012 (GSGG) in 1982, the long wavelength
Cr" emission of the transition 1-2 -0 4A2 provides a strong, resonant overlap
with the Nd" absorption that allows a rapid and efficient nonradiative energy
transfer. Because of the larger Cr" absorption cross section and the efficient
energy transfer, Cr", Nd3+:GSGG exhibits a slope efficiency nearly twice that
of Nd3 +:Y3A15012 (YAG)(1). All of the hosts studied to date for Cr" and Nd"
cosubstitution are oxides. No fluoride has been reported in which isovalent,
ordered cosubstitutions of Cr" and Nd" ions are possible.
Fluorides have served as attractive host materials not only for
spectroscopic studies of transition-metal and lanthanide ions, but also as laser
materials.
In comparison with oxides, fluorides generally have smaller
polarizabilities and, when doped with an ion, may exhibit both larger cross
sections and longer excited-state lifetimes. Low phonon energies also reduce
the likelihood of nonradiative decay.
In an attempt to synthesize host crystals for Cr", Nd" cosubstitutions,
the systems RbF-ScF3-LnF3 (Ln = lanthanide ions) have been examined. We
became interested in new compounds in these systems because of the
structures of RbIn3Flo (2) and Rb21n3F, (3) that contain In atoms in both
1
octahedral and pentagonal bipyramidal sites. We assumed that we might be
82
able to substitute a larger cation such as r+ or Yb3+ on the 7-coordinate site
and a smaller Sc3+ ion on the octahedral site to mimic the selective substitution
of the luminescent dopants CO+ and Nd3+ on the octahedral and pentagonal
bipyramidal sites, repectively.
In this paper, we will describe the structural
features of the new fluorides resulting from these studies.
83
Experimental
All compounds were prepared by grinding stoichiometric mixtures of
Rb2CO3 (Johnson Matthey, 99%), Yb203 (AESAR, 99.9%), Y203 (AESAR,
99.99%), and Sc203 (Boulder Scientific Company, 99.99%) and heating in
graphite boats under flowing HF (g) (Matheson, 99%) at 700 - 800°C for 12 - 50
h. A single crystal of RbSc3Flo was grown from a stoichiometric melt by cooling
from 1000 to 800°C at rate of 6°C/h. A colorless crystal of Rb2YbSc2Fil with
dimensions 0.1 x 0.1 x 0.05 mm was obtained by cooling the melt from 950 to
700°C at rate of 8 °C/h. The single crystals of RbLn2.xSci+flo (Ln = Y, Yb) were
grown from the melts with stoichiometries of RbLn2ScFlo by cooling from 1000
to 800°C at rate of 6°C/h. The single crystal of RbYb2F7 was obtained by
cooling the samples from 900 to 700°C at rate of 6°C/h.
All crystals were physically separated from the solidified boules and
mounted on glass fibers for data collection on a Rigaku AFC6R diffractometer.
The cell parameters were obtained from least-square refinement of the setting
angles of 10-20 reflections that were centered in the range 30
20
40°. The
space group of each crystal was assigned on the basis of the Laue symmetry,
systematic absences, and successful solution and refinement of the structure.
All calculations were performed on a microVAX
II
computer with
programs from the TEXSAN crystallographic software package (4).
All
structures were solved by direct methods. After refinement of each structure
with isotropic displacement coefficients, the data were corrected for absorption
by using the program DIFABS (5) and averaged. The occupancies of the Yb,
84
Y, and Sc sites in the compounds RbYb2.32ScomF1o, RbY2.19Sc0.81F10, and
Rb2YbSc2F, I
were refined as two atoms disordered on a single
site.
Occupancies for each site were constrained to unity and an isotropic
displacement coefficient was applied. All atoms, except those having variable
occupancies, were refined with anistropic displacement coefficients during the
final cycles of least-squares refinement.
Crystal data and final atomic parameters are listed in Tables 5.1 & 5.2,
respectively, and anisotropic displacement coefficients are arranged in Tables
C10 - C14 (see Appendix C).
Table 5.1. Crystal Data and Experimental Conditions for Data Collections
RbYb2F7
RbSc3Fia
RbY2.10Sc0.01F10
RbYb2.32Sc0.00F,0
Rb2YbSC2Fil
FW, u
564.54
410.32
506.57
707.47
770.95
Space Group
C222
Pmma
Pmma
Pmma
C222
a, A
6.798(3)
7.790(3)
16.055
15.889(6)
6.712(4)
b, A
11.086(2)
7.581(3)
4.193(2)
4.174(2)
18.793(4)
c, A
4.227(2)
6.648(1)
6.614(3)
6.550(3)
4.076(3)
V, A3
318.6(2)
401.6(4)
445.2(3)
434.4(8)
514.1(4)
Z
2
2
2
2
2
Pc.,., gicm3
5.884
3.392
3.778
5.408
4.980
g, cm-1
365.55
84.60
191.59
276.01
279.26
data collected
h, k, I
h, k, I
h, ±k, I
h, ±k, I
h, k, ±I
sin 0,,JA.
0.7035
0.7035
0.7035
0.7035
0.7035
transimission factors
0.87-1.20
0.87-1.10
0.84-1.28
0.89-1.17
0.80-1.30
0.063
0.066
0.052
0.035
Flint
Rw (F0)
0.051
0.040
0.054
0.042
0.041
R (F0) for F02 > 3a(F02)
0.038
0.036
0.047
0.035
0.034
86
Table 5.2a. Atomic parameters for RbYb2F7
atom
x
y
z
BEI
Yb
0
0.3082(2)
1/2
0.58(1)
Rb
0
0
0
1.43(6)
F(1)
0.1891(7) 0.1458(5)
0.51(1)
1.1(2)
F(2)
0
0.295(1)
0
1.8(4)
F(3)
1/2
0
1/2
2.7(6)
87
Table 5.2b. Atomic Parameters for RbSc3Flo
atom
x
y
z
Bel
Rb
1/4
0
0.4899(3)
2.56(5)
Sc(1)
0
1/2
1/2
0.67(5)
Sc (2)
0
0.2303(1)
0
0.61(3)
F(1)
1/4
0.2205(6)
0.0457(6)
1.4(2)
F(2)
1/4
1/2
0.442(1)
1.9(3)
F(3)
0.0352(4) 0.3051(4)
0.6978(4)
1.6(1)
F(4)
0.0165(6) 0
0.8248(6)
1.3(1)
F(5)
0
0
2.1(2)
1/2
Table 5.2c. Atomic Parameters
of RbY2.19(3)Sco.e1F10 and RbYb2.32(3)Sco.seFlo
RbY21eSC0 ei F10
atom
x
Rb
1/2
RbYb2.32ScaseFlo
y
z
Beg
x
y
z
Big
0
0
3.49(8)
1/2
0
0
2.39(6)
0.6141(3)
1/2
0.4626(1)
1.34(4)
0.6136(4)
1/2
0.4596(4)
0.66(1)
Ln, Sc(2)b
3/4
1/2
-.0019(2)
1.10(6)
3/4
1/2
-.0009(1)
0.69(2)
F(1)
3/4
0
0.016(2)
4.9(6)
3/4
0
0.012(2)
6.7(9)
0.6110(6)
0
0.447(1)
5.0(4)
0.6074(6)
0
0.439(2)
4.1(4)
0.6298(4)
1/2
0.1309(9)
3.6(4)
0.6279(4)
1/2
0.1306(9)
2.2(3)
0.6709(4)
1/2
0.747(1)
6.3(6)
0.6724(4)
1/2
0.742(1)
6.1(6)
1/4
1/2
0.633(1)
2.1(4)
1/4
1/2
0.634(1)
1.4(3)
1/2
0.3179(9)
2.5(3)
0.4874(3)
1/2
0.3178(8)
1.5(2)
Ln, Sc(1)1
F(2)
F(3)
F(4)
F(5)
F(6)
0.0106(4)
RbY2.19SCae1 Flo:
b
occupancy Y = 0.82(1), Sc(1) = 0.18; RbYb222Sco.68F10: occupancy Yb
= 0.83(1), Sc(1) = 0.17
RbY2.19Sc0mF10: occupancy Y = 0.55(1), Sc(2) = 0.45; RbYb2.32Sc0.68F10:
occupancy Yb = 0.66(1), Sc(2) = 0.34
89
Table 5.2d. Atomic Parameters
for Rb2Y131.04Sc1.96Fil
x
y
z
Bp
(Yb, Sc)a
0
0.21721(3)
0
0.69(2)
Sc(1)
0
0
0
0.62(6)
Rb(1)
0
0.40498(6)
1/2
2.69(5)
F(1)
0
0.1067(3)
0
5.3(6)
F(2)
0.1895(6)
0.3113(2)
0.017(8)
2.3(3)
F(3)
0.2063(8)
1/2
0
3.0(3)
F(4)
0
0.2250(7)
1/2
5.7(6)
F(5)
0
0
1/2
8(1)
a
occupancy Yb = 0.52(1), Sc = 0.48
90
Results and Discussion
Structural Description
The
structures
of
RbYb2F7,
RbY2.19(3)Sco.31 Flo, and Rb2Yb1.04(2)Sc1.96F1i
RbSc3F10,
(-=
RbYb2.32(3)Sc0.63Flo
and
Rb2YbSc-2Fi1) form from the
condensation of lanthanide- or Sc-centered octahedra or pentagonal bipyramids
and exhibit a great similarity to each other and to the structures of Re03 and the
tungsten bronzes. The structure of Re03 can be described as a framework
constructed by joining only vertices of Real, octahedra to fill three-dimensional
space. Addition of other metal atoms at the centers of the unit cells gives the
symmetrical perovskite structure. By altering the stoichiometry in other ways,
a variety of structures from the bronze family are produced.
RbYb2F7 Among the fluorides synthesized in this work, RbYb2F7 has
perhaps the simplest structural features. As shown in the c-axis projection of
Figure 5.1a, the structure is formed from sheets of edge- and vertex-sharing
pentagonal bipyramids, and each unit cell contains one such layer. These
layers fuse along the c axis by sharing vertices.
As listed in Table 5.3a, the average interatomic distances for Yb-F and
Rb-F are 2.16(4) A and 3.06(1) A, respectively, and these values compare well
to the Yb-F distance of 2.15 A calculated from crystal radii (7) and 3.172 A for
Rb-F in RbF (8). The coordination environments for the Yb and Rb atoms are
shown in Figure 5.1b. The Yb atom together with five F atoms (F(1), F(3)) lie
in the same plane with one F(2) atom above and another below, forming a
pentagonal bipyramid with C2 symmetry. The bipyramid is slightly distorted with
91
tikK. Ari
'OP
iikl
lkik AV-
1444
b.
kr Igo
tr/ A)
ktr 1174
if46, 1
'P.
Wig
'A,
Wbi At
r niff
tAhk.
411'44'
,NIN'
140#1.
TA:
if
kr VI
4
AL At
Alp-
-4
C& Ai il
4
t*
V
rif
ff
A
Irti..
CO
kr 70 kr 170
Figure 5.1a
The c-axis projection of framework for RbYb2F7.
(rectangle: unit cell; open circles: Rb atoms)
92
a
b
Fig. 5.1b
Coordination environments of atoms in RbYb2F7.
(a) Yb atom and (b) Rb atom
93
Table 5.3a
Selected Bond Distances (A) for RbYb2F7
Yb-F(1) x 2
2.212(6)
Yb-F(1) x 2
2.174(5)
Yb-F(2) x 2
2.119(1)
Yb-F(3)
2.126(1)
<Yb-F> = 2.16(4)
Rb-F(1) x 4
2.98(3)
Rb-F(2) x 4
3.27(1)
Rb-F(1) x 4
<Rb-F> = 3.06(15)
2.93(3)
94
Table 5.3b
Selected Bond Angles for RbYb2F7
F(1)-Yb-F(1)
68.0(2)
F(1)-Yb-F(1)
71.1(3)
F(1)-Yb-F(2)
90(1)
F(1)-Yb-F(2)
92(1)
F(1)-Yb-F(2)
86(1)
F(1)-Yb-F(3)
76.5(1)
F(2)-Yb-F(2)
172.3(6)
F(2)-Yb-F(3)
93.9(3)
F(1)-Rb-F(1)
88(1)
F(1)-Rb-F(1)
51.6(2)
F(1)-Rb-F(1)
66.3(2)
F(1)-Rb-F(2)
57.1(4)
F(1)-Rb-F(2)
122.9(4)
F(1)-Rb-F(2)
56.5(4)
F(2)-Rb-F(2)
180
Yb-F(3)-Yb
180
Yb-F(1)-Yb
112.0(2)
Yb-F(1)-Rb
101.8(9)
Yb-F(1)-Rb
122(1)
Yb-F(2)-Rb
93.9(3)
95
an F(2)-Yb-F(2) interatomic angle at 172.3(6)° and F-Yb-F angles in the
approximate C5 plane that differ from 72° by no more than 5° (Table 5.3b). The
Rb atom lies in the center of the tunnels and is sandwiched between two
rectangular F(1) planes; two longer Rb-F(2) distances complete the 10
coordinate environment. The eight Rb-F(1) distances are split into two lengths -
2.98(3) and 2.93(3) A. The two F(2) atoms are displaced from the Rb atom by
3.27(1) A, and the bond angle F(2)-Rb-F(2) is 180°. One F(2) and two F(1)
atoms on triangular faces are shared between the Rb and Yb atoms.
The structure of RbYb2F7 is similar to that of KIn2F7 (space group =
P21/m) (6). The structural differences between the two crystals is evident from
the different crystal systems, cell parameters, and coordination environments of
the Rb and K atoms. Because of the differences in the crystal radii of Rb and
K, the framework of (In2F7). deforms to give an unit cell containing two layers of
polyhedra; two coordination environments for the K atom also result. While Rb
in RbYb2F7 has only 10 coordination, the K atoms in KIn2F7 have both 9- and 10-
coordinations.
The K(2) atom in KIn2F7 presents a similar coordination
environment as the Rb atom in RbYb2F7.
RbSc3Fic, The Sc atoms in RbScflo present two different kinds of
coordination environments: 1/3 of the Sc atoms occupy distorted F octahedra
and 2/3 occupy pentagonal bipyramids. An a-axis projection of the framework
is shown in Figure 5.2a. The structure is formed by the insertion of octahedral
chains between parallel sheets of pentagonal bipyramids. The bipyramids
share edges and vertices in the c direction and vertices only along the a
96
.11
0
0
tog&
It* or -10
Ph
4) tlk
4*
fflonoMon
0
o
0
Figure 5.2a
The a-axis projection of framework for RbSc3Flo-
(rectangle: unit cell; open circles: Rb atoms)
97
b
a
C
Figure 5.2b
Coordination environments of atoms in RbSc3Flo.
(a) Sc(1) atom; (b) Sc(2) atom; and (c) Rb atom.
98
Table 5.4a Selected Bond Distances (A) for RbSclio
Sc(1)-F(2) x 2
2.030(1)
Sc(1)-F(3) x 4
1.998(3)
<Sc(1)-F> = 2.01(1)
Sc(2)-F(1) x 2
2.017(1)
Sc(2)-F(3) x 2
2.106(3)
Sc(2)-F(4) x 2
2.103(2)
Sc(2)-F(5)
2.044(1)
<Sc(2)-F> = 2.07(1)
Rb-F(1) x 2
3.393(5)
Rb-F(3) x 4
3.192(3)
Rb-F(4) x 2
2.902(4)
Rb-F(4) x 2
2.981(4)
<Rb-F> = 3.13(18)
99
Table 5.4b Selected Bond Angles ( °) for RbSc3Flo
F(2)-Sc(1)-F(2)
180
F(2)-Sc(1)-F(3)
89.3(2)
F(3)-Sc(1)-F(3)
180
F(3)-Sc(1)-F(3)
84.6(2)
F(1)-Sc(2)-F(1)
175.7(3)
F(1)-Sc(2)-F(3)
91.3(1)
F(1)-Sc(2)-F(3)
89.9(1)
F(1)-Sc(2)-F(4)
89.5(2)
F(1)-Sc(2)-F(4)
87.0(2)
F(1)-Sc(2)-F(5)
92.1(1)
F (3)-Sc (2)-F (3)
148.8(2)
F (4)-Sc(2)-F (4)
67.7(2)
F (3)-Sc(2)-F (4)
71.7(2)
F (3)-Sc(2)-F (5)
74.40(8)
Sc(1)-F(2)-Sc(1)
158.0(4)
Sc(1)-F(3)-Sc(2)
143.9(2)
Sc(2)-F(1)-Sc(2)
162.1(2)
Sc(2)-F(4)-Sc (2)
112.3(2)
Sc (2)-F (5)-Sc(2)
180
Rb-F(3)-Sc(1)
109.0(1)
Rb-F(3)-Sc(2)
106.8(1)
Rb-F(4)-Sc(2)
117.7(1)
Rb-F(4)-Sc(2)
110.1(1)
100
direction. The tunnels in the three dimensional framework (M3F10)- are occupied
by 14-coordinate Rb atoms. The smaller radius of the Sc3+ ion (0.885 A), in
comparison with the radius of the Yb3+ ion (1.008 A), leads to the existence of
Sc-centered octahedra. The average Sc-F distance in the octahedron is 2.01(1)
A, which is equivalent to 2.01 A in ScF3. The average Sc-F distance in the
pentagonal bipyramid is a longer 2.07(1) A, and the average Rb-F distance is
3.13(18) A (Table 5.4a).
The coordination environments of the metal atoms are shown in Figure
5.2b. The C2, coordination environment about the Sc(1) atom exhibits the bond
angle F(2)-Sc-F(2) of 180° and the largest deviation from orthogonality with the
angle F(3)-Sc(1)-F(3) = 84.6(2)°. The Sc(2) atom occupies the center of a
distorted pentagonal bipyramid with F(1)-Sc(2)-F(1) at 175.7(3)°.
The two
distinct Sc-centered polyhedra are joined together by sharing a F(3) atom. The
connections of the Sc-centered polyhedra between different layers are indicated
by the bond angles, 158.0(4)° and 162.1(2)°, of Sc(1)-F(2)-Sc(1) and Sc(2) -F(1)-
Sc(2), respectively (Table 5.4b). The Rb atom is sandwiched by two distorted
hexagonal F planes with bond distances ranging from 2.902(4) A to 3.192(3) A.
Two additional F(1) atoms from the vertices of the pentagonal bipyramids are
bonded to the Rb atom at a longer distance - 3.393(5) A. The connection
between Rb-centered polyhedra and the octahedra is through edge-sharing.
Both face- and edge-sharing exist among the pentagonal bipyramids and the
Rb-centered polyhedra.
101
RbSc3Flo has a structure similar to that of RbIn3Flo (3), although the In
compound has been reported to crystallize in the space group P2221, rather
than Pmma. This deformation of the framework leads to different coordination
environments for the alkali atoms. In comparison with the 14-coordinated Rb
atom in RbSc3F,0, the Rb atom in RbIn3Fio has an [8 + 2J-coordination
environment.
RbYbzuScatieFlo and RbY2.1,SccunFlo
These crystals resulted from
attempts to selectively substitute the bipyramidal site in RbScflo with a larger
lanthanide - r+ or Yb3+. Rather than forming a compound having the desired
substitution pattern, a new three-dimensional framework (M3Floy is formed in
which each of the M atoms occupies a pentagonal bipyramid (Figure 5.3a).
Tunnels extending parallel to the b axis are occupied by 10-coordinated Rb
atoms.
In contrast to the unit cell containing two layers of polyhedra in
RbScflo, the unit cell contains only one layer of M-centered polyhedra (M =
Sc, Yb, Y). The framework, in fact, is quite similar to that in RbScflo. A small
displacment of the F atom serving as the common vertex within the sheets of
pentagonal bipyramids is slightly displaced to convert the octahedral site into
a highly distorted bipyramid.
The crystallographic inequivalence of the
polyhedra is maintained in the structures. Each polyhedron (Yb, Sc)(2)Fe and
(Y, Sc)(2)Fes contains six interatomic M-F distances near 2.10 A and a longer
distance at greater than 2.40 A (Tables 5.5a & b). The interatomic distances in
the other pentagonal bipyramid are more regular. The average interatomic
distances of Rb-F are 3.09(15) A and 3.11(18) A, in the Yb and Y phases,
102
Figure 5.3a
The b-axis projection of framework for RbY2.19ScomFlo
(rectangle: unit cell; open circle: Rb atoms)
103
b
a
C
Figure 5.3b Coordination environments of atoms in RbYa19Sc.481F10.
(a) (Y, Sc) (1) atom; (b) (Y, Sc) (2) atom; and (c) Rb atom.
104
Table 5.5a. Selected Bond Distances (A) for RbY2.19Sc0.81F10
Y,Sc(1)-F(2) x 2
2.0995(7)
Y,Sc(1)-F(3)
2.208(6)
Y,Sc(1)-F(4)
2.092(6)
Y,Sc(1)-F (5)
2.272(3)
Y,Sc(1)-F(6)
2.220(6)
Y,Sc(1)-F (6)
2.207(6)
<Y,Sc(1)-F> = 2.17(7)
Y,Sc(2)-F(1) x 2
2.0999(7)
Y,Sc(2)-F(3) x 2
2.120(6)
Y,Sc(2)-F(4) x 2
2.090(6)
Y,Sc(2)-F(5)
2.438(8)
<Y,Sc(2)-F> = 2.15(12)
Rb-F(2) x 2
3.45(1)
Rb-F(6) x 4
2.974(4)
Rb-F(3) x 4
<Rb-F> = 3.11(18)
3.081(5)
105
Table 5.5b Selected Bond Distances (A) for RbYb232Sc0.68Flo
Yb,Sc(1)-F(2) x 2
2.094(1)
Yb,Sc(1)-F(3)
2.167(6)
Yb,Sc(1)-F(4)
2.075(7)
Yb,Sc(1)-F (5)
2.253(2)
Yb,Sc(1)-F(6)
2.209(5)
Yb,Sc(1)-F (6)
2.168(5)
<Yb,Sc(1)-F> = 2.15(7)
Yb,Sc(2)-F(1) x 2
2.089(1)
Yb,Sc(2)-F(3) x 2
2.123(6)
Yb,Sc(2)-F(4) x 2
2.085(7)
Yb,Sc(2)-F(5)
2.403(9)
<Yb,Sc(2)-F> = 2.14(11)
Rb-F(2) x 2
3.34(1)
Rb-F(6) x 2
2.955(4)
Rb-F(3) x 4
<Rb-F> = 3.09(15)
3.036(4)
106
Table 5.5c Selected Bond Angles (°) for RbY2.19Sco.81F10
F(2)-Y,Sc(1)-F(2)
173.8(6)
F(2)-Y,Sc(1)-F (4)
93.1(3)
F (3)-Y,Sc(1)-F (6)
71.0(2)
F(4)-Y,Sc(1)-F (5)
80.4(3)
F (1)-Y,Sc(2)-F (3)
88.6(1)
F(3)-Y,Sc(2)-F (5)
65.5(2)
F(4)-Y,Sc(2)-F(5)
142.6(2)
F(4)-Y,Sc(2)-F (4)
74.8(3)
F(1)-Y,Sc(2)-F(4)
92.6(2)
F(1)-Y,Sc(2)-F (5)
86.7(3)
F(2)-Rb-F(2)
180
F (2)-Rb-F (3)
53.9(1)
F (3)-Rb-F (3)
180
F (6)-Rb-F (6)
180
Y,Sc (1)-F (2)-Rb
93.1(3)
Y,Sc(1)-F(3)-Rb
101.6(2)
Y,Sc(1)-F(3)-Y,Sc(2)
121.0(3)
107
Table 5.5d
Selected bond Angles (°) for RbYbaseSco.32Flo
F (2)-Yb,Sc(1)-F (2)
170.8(6)
F (2)-Yb,Sc(1)-F (4)
94.5(3)
F (3)-Yb,Sc(1)-F (6)
71.2(2)
F (4)-Yb,Sc(1)-F (4)
79.0(3)
F(1)-Yb,Sc(2)-F(3)
89.0(1)
F (3)-Yb,Sc(2)-F (5)
66.1(2)
F (5)-Yb,Sc(2)-F (4)
143.7(2)
F (4)-Yb,Sc (2)-F (4)
72.5(4)
F(1)-Yb,Sc(2)-F(4)
91.9(3)
F(1)-Yb,Sc(2)-F(5)
87.6(3)
F (2)-Rb-F (2)
180
F(2)-Rb-F(3)
54.3(1)
F(3)-Rb-F(3)
180
F (6)-Rb-F (6)
180
Yb,Sc(1)-F(2)-Rb
94.6(3)
Yb,Sc (1)-F (3)-Rb
102.1(2)
Yb,Sc(1)-F(3)-Yb,Sc(2)
120.0(3)
108
respectively. As seen from the refined occupancies (Table 5.2c), the Sc atom
prefers occupation of the irregular [6 + 1 ] bipyramid.
The two types of
pentagonal bipyramids are joined together by both face- and edge-sharing.
The layers are joined along the b axis by vertex-sharing.
The M-centered polyhedra are illustrated in Figure 5.3b. In the M(1)centered polyhedra having C, symmetry, the F(3), F(4), F(5), and F(6) atoms lie
in the mirror plane. Both bipyramids are distorted as shown by the interatomic
angles in Tables 5.5c & d.
The Rb atom is sandwiched between two
rectangular F planes and bonded to two F(2) atoms at longer distances (Tables
5.5a & b). The bond angle for F(2)-Rb-F(2) is 180°. The smaller coordination
number of the Rb atom in this structure results from the deformation of the
RbSc3Flo framework, in comparison to the 14-coordinate Rb atom in RbScflo.
The M(1)- and Rb-centered polyhedra are joined by both face- and edgesharing, and the M(2)- and Rb-centered polyhedra are joined by edge-sharing.
Rb2YbSc2Fil A projection of the structure of Rb2YbSc2Fil is shown in
Figure 5.4a. Again, this structure is built from the condensation of distorted
octahedra and pentagonal bipyramids with only one layer of polyhedra in the
unit cell. Only the Sc atom occupies the octahedra while the Yb and Sc atoms
are disordered over the bipyramidal sites. Tunnels extending along the c axis
are occupied by 9-coordinate Rb atoms.
The average Sc-F distance in the octahedron, the (Sc, Yb)-F distance in
the pentagonal bipyramid, and the Rb-F distance
in
the 9-coordinate
109
environment are 2.00(2) , 2.12(6) and 3.02(5) A, respectively (Table 5.6a). The
octahedron has Da symmetry, and all angles F-Sc-F are 90 or 180° (Figure
5.4b). The (Yb, Sc) atoms in the pentagonal-bipyramidal site together with five
F atoms (F(1), F(2)) lie in the same plane with one F(4) atom above and another
below. The bipyramid is distorted with an interatomic angle F(4)-(Yb, Sc)-F(4)
at 171.8(7)* (Table 5.6b). The Rb atom is sandwiched between two rectangular
F planes with Rb-F distances ranging from 2.93(2) to 3.30(2) A; a ninth atom
F(4) is positioned at 3.38(1) A. The Rb-centered polyhedra are joined together
by sharing four F(2) atoms and to the octahedra and pentagonal bipyramids by
vertex- and face-sharing, respectively.
The structure of Rb2YbSc.2Fil is similar to that of monoclinic Rb21n3F, i (2).
The distortions of the pentagonal bipyramidal-octahedral framework result from
the atomic displacements associated with the different sizes of the atoms in the
two crystals. The deformations result in different coordination environments for
the Rb atoms and a change in the unit-cell parameters between the two
crystals. Rb2In3Fil has an unit cell containing two layers of polyhedra. While
the Rb atom in Rb2YbSc2F1, occupies only one site, the Rb atoms in Rb2In3Fil
occupy four types of crystallographic sites with coordination numbers of 8, 9,
and 12. Rb2YbSc2Fil is the first fluoride structure that contains a six-coordinate
transition-metal site in conjunction with a lanthanide site having a higher
coordination number.
110
Figure 5.4a
The o-axis projection of framework for Rb2YbSc2Fil.
111
a
b
C
Figure 5.4b Coordination environments of atoms in Rb2YbSc2Fil.
(a) Sc atom; (b) (Yb, Sc) atom; and (c) Rb atom.
112
Table 5.6a
Bond Distances (A) for Rb2YbSc2Fil
Yb,Sc-F(1)
2.078(6)
Yb,Sc-F(2) x 2
2.179(4)
Yb,Sc-F(4) x 2
2.043(2)
Yb,Sc-F(2) x 2
2.153(4)
<Yb,Sc-F> 2.12(6)
Sc(1)-F(1) x 2
2.005(6)
Sc(1)-F(5) x 2
2.038(1)
<Sc(1)-F>
Rb-F(2) x 2
2.93(2)
Rb-F(3) x 4
3.043(3)
<Rb-F>
Sc(1)-F(3) x 2
1.971(6)
2.00(2)
Rb-F(3) x 4
3.02(5)
3.03(2)
113
Table 5.6b
Selected Bond Angles (0) for Fib2YbSc2Fil
F(1)-Yb,Sc-F(2)
144.2(1)
F(1)-Yb,Sc-F(2)
75.6(1)
F (1)-Yb,Sc-F (4)
94.1(4)
F (2)-Yb,Sc-F (2)
71.5(2)
F (2)-Yb,Sc-F (2)
68.6(2)
F (2)-Yb,Sc-F (4)
88.5(9)
F(4)-Yb,Sc-F(4)
171.8(7)
F(1)-Sc(1)-F(1)
180
F(1)-Sc(1)-F(3)
90
F(1)-Sc(1)-F(5)
90
F(3)-Sc(1)-F(5)
90
F(3)-Sc(1)-F(3)
180
F(5)-Sc(1)-F (5)
180
F (2)-Rb-F (2)
50.6(2)
F (2)-Rb-F (2)
86.3(1)
F (2)-Rb-F (3)
177.5(4)
F (2)-Rb-F (4)
54.4(3)
F (3)-Rb-F (3)
54.1(2)
F (3)-Rb-F (3)
84.1(1)
F (3)-Rb-F (4)
125.93(4)
Rb-F(3)-Rb
71.87(8)
Rb-F(3)-Rb
84.1(1)
Yb-F(4)-Yb
171.8(7)
Yb-F(4)-Rb
94.1(4)
Sc(1)-F(5)-Sc(1)
180
Sc(1)-F(1)-Yb,Sc
180
Yb,Sc-F(2)-Rb
101.8(8)
114
Structural Relationships
The three-dimensional frameworks of (Yb2F7)-, (Sc3F10Y, (1-n2+Ac1.xFio)-
and (YbSc2F11)2. observed in this work are pictorially represented in Figure 5.5.
Each can be related to the framework of the Re03 structure type. By gliding
ac§acent octahedral arrays from Re03 in opposite directions along [110] by 1/2
of the unit-cell face diagonal, a new three-dimensional framework is obtained
(Figure 5.6a -- 5.6b). By inserting F atoms (Figure 5.6c) into the centers of the
square vacancies and bonding these F atoms to two neighboring metal atoms
in the plane, the framework for RbSc3Fl0 is produced (Figure 5.6d). The
structure of RbSc3F10 is established by inserting Rb atoms into the larger
rectangular voids and allowing the framework to relax. Replacing the small Sc
atoms in the octahedra with larger Yb or Y atoms distorts the sheets of
pentagonal bipyramids and leads to displacement of a F atom along the
direction shown in Figure 5.7a.
The framework for RbYb2.32Sc0.88Flo and
RbY2.19Sco.81Flo is established when a new set of pentagonal bipyramids is
formed (Figure 5.7b). By locating Rb atoms into the distorted hexagonal voids,
the structures of RbYb2.32Sc0.68Flo and RbY2.19Sc0m Flo are formed.
Again, by gliding alternative octahedral arrays from Re03 along [110] by
1/2 of the unit-cell face diagonal, a new framework containing sheets of
octahedra is created (Figure 5.8a - 5.8b). Inserting F atoms (Figure 5.8c) into
the vacancies between the sheets and bonding them to the two nearest metal
atoms affords the framework of RbYb2F7 (Figure 5.8d).
Separating vertex-
sharing sheets along the direction shown in Figure 5.9a, a two-dimensional
115
network is formed (Figure 5.9b). Inserting F atoms and metal atoms into the
vacancies between the bipyramidal sheets (Figure 5.9c), the framework of
Rb2YbSc.2Fli containing chains of octahedra is obtained.
The structure of
Rb2YbSc2Fil is obtained by inserting Rb atoms into the voids within the
framework.
116
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b
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Figure 5.5
Frameworks of (a) (Yb2F7)", (b) (Sc3F10)..
(c) (Ln2+,Sc1.xF10).. and (d) (YbSc2F11)..
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0
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b
Figure 5.7
Structural relationship between (a) RbSc3F10
and (b) RbYzieScoaFlo.
119
vl
Po
tP3
Do
co
co
co
co
pal
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b
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Figure 5.8
Structural relationship between (a) Re03 and (d) RbYb2F7.
Open circles are F atoms.
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Figure 5.9
Structural relationship between (a) RbYb2F7 and (d) Rb2YbSc2Fi1.
121
Acknowledgment
This work was supported by the US National Science Foundation, DMR8814432. DAK thanks the Alfred P. Sloan Foundation for a fellowship.
122
References
1.
Pruss, D., Huber, G., Beimowski, A., Appl. Phys., B28, 355(1982).
2.
Champarnaud-Mesjard, J. C. & Frit, B., Acta Crystallogr., Sect. B, 34, 736
(1978).
3.
Champardaud-Mesjard, J. C., Mercurio. D. & Frit, B., J. lnorg. Nucl.
Chem., 39, 947 (1977).
3.
Magneli, A., Acta Chem. Scand., Z 315 (1953).
4.
Molecular Structure Corporation. TEXSAN. TEXRAY Structure Analysis
Package. MSC, 3200A Research Forest Drive, The Woodlands, TX77381,
USA. 1989.
5.
Walker, N. & Stuart, D., Acta Crystallogr., Sect. A, 39, 158 (1983).
6.
Champarnaud-Mesjard, J., & Frit, B., Acta Crystallogr., Sect. B, 32, 3722
(1977).
7.
Shannon, R. D., Acta Crystallogr., Sect. A, 32, 751 (1976).
8.
Davey, W. P., Phys. Rev., 21, 143 (1923).
123
BIBLIOGRAPHY
Abdulsabirov, R. Yu., Dubinskii, M. A., Kazakov, B. N., Silkin, N. I., and
Yagudin, Sh. I., Soy. Phys. Crystallogr., 32, 559 (1987).
Andrews, L. J. and Hitelman, S. M., Ettore Majorana Int. Sci. Ser., Phys.
Sci., 30, 515 (1987).
Babel, Von. D., Z Anorg. Aug. Chem., 406, 23 (1976).
Barttett, N. and Lohmann, D. H., Proc. Chem. Soc., London, 115 (1962).
Barttett, N. and Lohmann, D. H., Proc. Chem. Soc., London, 5253 (1962).
Birnbaum, H. and Deshazer, L, Engineering Design of Repetitively QSwitched Solid State Lasers for Presicion Range in Applications. Contract
NASA-23698.
Brauch, U. and Durr, U., Opt. Commun., 49, 61 (1984).
Brown, I. D., Structure and Bonding in Crystals, Vol. II, Academic Press,
New York (1981).
Brunton, G., Acta Crystallogr., Sect. B, 29, 2294 (1973).
Bukin, G. V., Volkov, S. Yu., Matrosov, V. N., Sevactyanov, B. K.,
Timoshechkin, M. 1, Soy. J. Quantum Electron., 8, 671 (1978).
Caird, J. A., Tunable Solid State Lasers II, Budgor, A., Esterowitz, L., and
Deshazer, L. G. Eds. Berlin: Springer-Verlag, 20 (1986).
Caird, J. A., Payne, S. A., Stayer, P. R., Ramponi, A. J., Chase, L. L., and
Krupke, W. F., IEEE J. Quantum Electron. , 24, 1077 (1988).
Caird, J. A., Shinn, M.D., Newkirk, H. W., and Guggenheim, H. J., The
Laser Program Annual Report, 1984. Livermore, CA: LLNL. 1985, UCRL50021-84.
124
Caird, J. A., Stayer, P. R., Shinn, M. D., Guggenheim, H. J. and Bahnck,
D., Tunable Solid State Lasers II, Bugdor, A. B., Esterowitz, L., and
Deshazer L. G., Ed. Berlin: Springer-Verlag. 159 (1986).
Domes le, R. and Hoppe, R., Z Anorg.
g. Chem., 501, 102(1983).
Falconer, W. B. and Sunder, W. A., J. Inorg. Nucl. Chem., 29, 1380
(1967).
Fields, R. A., Birnbaum, M., and Fincher, C. L., Appl. Phys. Lett., 51, 1885
(1987).
Gehihoff, W. and Vlrici, W., Phys. Stat. Sol., Sect. B, 102, 11 (1980).
Grannec, J., Champarnaud-Mesjard, J. C., Costy, J. P., Cousseins, J. C.
and Gaudreau, B., Rev. Chim. Minerale, 9, 569 (1972).
Hagenmuller, P., et. al., Inorganic Solid Fluorides-Chemistry and Physics,
Eds. Hagenmuller, P., Academic Press, Inc., (1985).
Henderson, B., and Imbusch, G. F., Optical Spectroscopy of Inorganic
solids, Oxforf Science Publications, 515 (1989).
Henry, C. E., Schnatterly, S. E., and Slichter, C.
137, 583 (1965).
Huber, G., Payne, S. A., Chase,
L.
L.
P., Phys.
Rev., Sect. A,
and Krupke, W.
F., J.
Luminescence, 33, 258 (1988).
Huber, G., and Petermann, K, Tunable Sold State Lasers, Hammerling,
P., Budgor, A. B., and Pinto, A., Ed, Berlin, Sprinjger-Verlag, 11 (1985).
Jennsen, H. P. and Lai, S. T., Opt. Soc. Amer., Sect. B, 3, 115 (1986).
Kaminskii, A. A., Laser Crystals, Springer Series in Optical Sci., Vol. 14,
(1981)
Lai, S. T., and Shand, M. L., J. Appl.
Phys., 54,
5642 (1983).
125
McClure, D. S., Electronic Spectra of Molecules and Ions in Crystals,
Academic Press, New York, 1959.
Molecular Structure Corporation. TEXSAN: TEXRAY Structure Analysis
Package; MSC, 3200A Research Forest Drive, The Woodlands, TX 77381,
USA (1985).
Nowacki, W., Z Kristallogr., Sect. A, 101, 273 (1939).
Payne, S. A., Chase, L. L., Krupke, W. F., J. Chem. Phys., 86, 3455
(1988).
Payne, S. A., Chase, L. L. and Krupke, W. F., J. Luminescence, 40&41,
305 (1988).
Payne, S. A., Chase, L. L., Newkirk, H. W., Smith, L. K., and Krupke, W.
F., IEEE J. Quantum Electron., 24, 2243 (1988).
Payne, S. A., Chase, L. L., Smith, L. K., Kway, W. L. and Chai, B. H. T.,
Advanced Solid-State Lasers Conference, Hilton Head, S. Carolina
(1991).
Pruss, D., Huber, G., and Beimowski. A., Appl. Phys., Sect. B, 28, 355
(1982).
Ravez, J., and Hagenmuller, P., Bull. Soc. Chim. Fr., 3452 (1971).
Ravez, J., and Hagenmuller, P., Bull. Soc. Chim. Fr., 2545 (1967).
Schaffers, K. I. and Keszler, D. A., Acta Crystallogr., Sect. C, 47, 18
(1991).
Schulz, H., Solid State Chemistry 1982, Metselaar R., Heijligers, H. J. M.
and Schoonman, J., Ed. Elsevier Sci. Pub. Comp., 133 (1982).
Schultz du Bois, E. 0., Bell Syst. Tech. J., 38, 271 (1959).
Shannon, R. D., Acta Crystallogr., Sect. A, 32, 751 (1976).
126
Smith, L K., Payne, S. A., Krupke, W. F. and Deloach, L. D., Optics
Letters, 18, 200(1993).
Sugano, S., Schawlow, A. L, and Varsanyi, F., Phys. Rev., 120, 2045
(1960).
Sun, Hongxing, Ph.D. Dissertation, Oregon State University, (1989).
Tanabe, Y., and Sugano, S., J. Phys. Soc. Japan, 9, 753 (1954).
Tedenace, J. C., Granier, W., Norbert, A. and Cot, L, C. R. Hebd.
Seances Acad., Sci., 268, 1368 (1969).
Viebahn, V. W., Z Anorg. Aug.
l Chem., 386, 335 (1971).
Walker, N. and Stuart, D., Acta Crystallogr., Sect. A, 39, 158 (1983).
Walling, J. C., Heller, D. F., Samelson, H., Harter, D. J., Pete, J. A., and
O'Dell, W. E., IEEE J. Quantum Electron., QE-16, 1302 (1980).
Walling, J. C., Heller, D. F., Samelson, H., Harter, D. J., Pete, J. A., and
Morris, R. C., IEEE J. Quantum Electron., QE-21, 1568 (1985).
APPENDICES
127
Appendix A
THE BORATE Na3Sc2(B03)3
The borate Na3Sc2(B03)3 was first synthesized by Dr. Hongxing Sun of
this laboratory while studying phase equilibria in the system Na20-Sc203-B203
(1).
A single crystal of Na3Sc2(B03)3, which melts incongruently, has been
physically removed from a solidified melt that was cooled from 850 °C to 600
°C at a rate of 6 °C/h. The chemical composition of the melt was Na3Sc2(B03)3
+ 0.25 Na3BO3.
X-ray data of the single crystal were collected on a Rigaku AFC6R
diffractometer.
The crystal has been determined to be hexagonal and to
crystallize in one of the following space groups: P63/mcm, P63cm or P6cm. The
cell parameters are a = 8.604 A, c = 19.903 A, and V = 1275.90 A3.
References
1.
Hunxing Sun, Ph.D dissertation, Oregon State University, 1989
Appendix B
128
THE FLUORIDES Sr2AIF7
The fluoride Sr2AIF7 was synthesized by passing HF (g) over a
stoichiometric mixture of SrF2 and AIF3 at 700 °C for 1/2 h, then annealing the
sample at the same temperature for 12 h under flowing N2. A single crystal of
Sr2AIF7 with dimensions 0.1 x 0.1 x 0.1 mm was obtained from a sample that
was annealed at 700 °C for 72 hrs. X-ray data were collected on a Rigaku
AFC6R diffractometer. The compound was found to crystallize in the tetragonal
space group P42/n (86#). The cell parameters a = 14.160 A, c = 6.329 A, and
V = 1269.05 A3 differ from those obtained by the powder X-ray diffraction
method (1).
References
1.
J. Ravez, and P. Hagenmuller, Bull. Soc. Chim. Fr., 2545 (1967).
Appendix C
C1. Anisotropic displacement coefficients for LiCaAlFe.
C2. Anisotropic displacement coefficients for LiCaGaF6.
C3. Anisotropic displacement coefficients for LiCaCrFe.
C4. Anisotropic displacement coefficients for LiSrAl06Cr0.4Fe
C5. Anisotropic displacement coefficients for LiSrGaFe.
C6. Anisotropic displacement coefficients for LiSrCrFe.
C7. Anisotropic displacement coefficients
for LiSr0.94Ba0.06A1Fe.
C8. Anisotropic displacement coefficients
for LiSr0.8F3a0.2GaF6.
C9. Anisotropic displacement coefficients for Sr2ScF7.
C10. Anisotropic displacement coefficients for RbYb2F7.
C11. Anisotropic displacement coefficients for RbSc3F10.
C12. Anisotropic displacement coefficients
for RbY2.19Sc0.e1 F10.
C13. Anisotropic displacement coefficients
for RbYb2.328c0.68F 10.
C14. Anisotropic displacement coefficients
for Rb2YbSc2F, 1.
129
Appendix C1. Anistropic displacement coefficients for LiCaAIF6
U11
U22
U33
U12
U13
U23
U
0.013(1)
0.013
0.021(2)
0.006
0
0
Ca
0.095(2)
0.095
0.0073(3)
0.0047
0
0
Al
0.0059(2)
0.0059
0.0073(3)
0.0030
0
0
F
0.0139(3)
0.0103(3)
0.0135(4)
0.0062(2)
0.0032(2)
-.0016(2)
Table C2.
Anistropic displacement coefficients for LiCaGaFe
U11
U22
U33
U12
U13
U23
Li
0.016(3)
0.016
0.024(5)
0.008
0
0
Ca
0.0095(3)
0.0095
0.0056(4)
0.0048
0
0
Ga
0.0065(2)
0.0065
0.0063(3)
0.0032
0
0
F
0.0112(5)
0.0142(6)
0.0128(6)
0.0064(5)
0.0019(4)
-.0035(4)
CJ3
Table C3.
Anistropic displacement coefficients for LiCaCrFe
U11
U22
U33
U12
U13
U23
U
0.021(4)
0.021
0.029(5)
0.010
0
0
Ca
0.0109(4)
0.0109
0.0100(3)
0.0055
0
0
Cr
0.0095(4)
0.0095
0.0102(3)
0.0048
0
0
F
0.0136(5)
0.0151(5)
0.0160(5)
0.0054(4)
0.0021(4)
0.0054(4)
rJ
IV
Table C4. Anistropic displacement coefficients for LiSrA10.6Cro.4Fe
U11
U22
U33
U12
U13
U23
Li
0.014(6)
0.014
0.015(6)
0.007
0
0
Sr
0.0096(4)
0.0096
0.0086(4)
0.0048
0
0
(Al, Cr)
0.0065(7)
0.0065
0.0106(7)
0.0032
0
0
F
0.0014(1)
0.015(1)
0.0022(1)
0.0054(7)
0.002(4)
0.0071(8)
-s.
8
Table C5.
Anisotropic displacement coefficients for LiSrGare
U11
U22
U33
U12
U13
U23
U
0.016(3)
0.016
0.017(4)
0.008
0
0
Sr
0.0136(2)
0.0136
0.0103(2)
0.0068
0
0
Ga
0.0092(2)
0.0092
0.0124
0.0046
0
0
F
0.0145(7)
0.0190(7)
0.0206(6)
0.0059(5)
0.0026(5)
0.0091(6)
.a
W
Table C6.
Anisotropic displacement coefficients for LiSrCrFe
U11
U22
U33
U12
U13
U23
U
0.011(4)
0.011
0.014(4)
0.006
0
0
Sr
0.0123(3)
0.0123
0.0097(3)
0.0054
0
0
Cr
0.0090(4)
0.0090
0.0011(3)
0.0045
0
0
F
0.0145(4)
0.0169(2)
0.0212(3)
0.0061(5)
0.0023(4)
0.0086(6)
Table C7.
Anistropic displacement coefficients for LiSr0.34Ba0.09A1F8
U11
U22
U33
U12
U13
U23
Li
0.020(3)
0.020
0.028(5)
0.010
0
0
(Sr, Ba)
0.0117(1)
0.0117
0.0103(2)
0.0058
0
0
Al
0.0079(3)
0.0079
0.0142(7)
0.0040
0
0
F
0.0223(7)
0.0142(8)
0.0242(7)
0.0088(6)
0.0065(5)
-.0026(5)
Table C8.
Anistropic displacement coefficients for LiSr0.813a0.2GaFs
U11
U22
U33
U12
U13
U23
U
0.018(4)
0.018
0.033(7)
0.009
0
0
(Sr, Ba)
0.0182(2)
0.0182
0.0099(3)
0.0091
0
0
Ga
0.0117(3)
0.0117
0.0142(3)
0.0058
0
0
F
0.023(1)
0.0017(1)
0.0261(8)
0.0066(8)
0.0107(8)
0.0033(7)
Table C9.
Anisotropic displacement coefficients for Sr2ScF7
U11
U22
U33
U12
U13
U23
Sr(1)
0.0070(3)
0.0088(2)
0.0069(2)
0.0006(2)
0.0003(2)
0.0001(2)
Sr (2)
0.0085(3)
0.0065(2)
0.0078(2)
-.0001(2)
-.0004(2)
-.0006(2)
Sc
0.0074(5)
0.0068(4)
0.0057(4)
0.0005(4)
-.0001(4)
-.0003(4)
F(1)
0.009(2)
0.013(2)
0.013(2)
-.002(1)
0.002(1)
-.002(1)
F(2)
0.016(2)
0.010(2)
0.006(2)
0.002(1)
0.000(1)
-.001(1)
F(3)
0.012(2)
0.012(2)
0.013(2)
0.001(1)
-.003(2)
-.003(1)
F(4)
0.011(2)
0.011(2)
0.011(2)
0.000(1)
-.003(1)
-.001(1)
F(5)
0.020(2)
0.010(2)
0.020(2)
-.004(1)
-.008(2)
0.004(2)
F(6)
0.012(2)
0.010(2)
0.009(2)
-.004(1)
-.000(2)
0.000(1)
F(7)
0.008(2)
0.021(2)
0.025(2)
-.002(1)
0.004(2)
-.013(2)
Table C10.
Anisotropic displacement coefficients for RbYb2F7
U11
U22
U33
U12
U13
U23
Yb
0.0072(2)
0.0074(2)
0.0075(2)
0
-.0032(5)
0
Rb
0.034(1)
0.0096(6)
0.0106(6)
0
0
0
F(1)
0.004(1)
0.006(2)
0.031(4)
-.001(1)
0.001(8)
-.002(8)
F(2)
0.022(5)
0.040(6)
0.005(3)
0
0.003(7)
0
F(3)
0.006(4)
0.011(4)
0.09(1)
0
0
0
Table C11.
Anisotropic displacement coefficients for RbSclio
U11
U22
U33
U12
U13
U23
Rb
0.0232(5)
0.0518(8)
0.0222(6)
0
0
0
Sc(1)
0.0119(6)
0.0047(6)
0.0090(6)
0
-.002(1)
0
Sc(2)
0.0081(4)
0.0053(4)
0.0098(4)
0
-.0002(6)
0
F(1)
0.009(2)
0.017(2)
0.029(2)
0
0
0.003(2)
F(2)
0.013(3)
0.034(4)
0.025(3)
0
0
0
F(3)
0.035(2)
0.013(1)
0.015(1)
0.003(1)
0.003(1)
0.004(1)
F(4)
0.030(3)
0.007(1)
0.014(2)
0
0.004(2)
0
F(5)
0.048(4)
0.007(2)
0.026(3)
0
0.003(4)
0
Table C12. Anisotropic displacement coefficients for RbY2.19Sc0.81F10
U11
U22
U33
U12
U,3
U23
(Y, Sc) (1)
0.0198(5)
0.0167(5)
0.0145(5)
0
0.0006(4)
0
(Y, Sc) (2)
0.0145(6)
0.0156(9)
0.0118(7)
0
0
0
Rb
0.077(1)
0.0238(9)
0.032(1)
0
-.0208(8)
0
F(1)
0.12(1)
0.021(6)
0.044(6)
0
0
0
F(2)
0.069(6)
0.023(4)
0.100(7)
0
0.029(5)
0
F(3)
0.038(4)
0.081(7)
0.018(3)
0
0.004(3)
0
F(4)
0.023(3)
0.19(1)
0.025(4)
0
-.006(3)
0
F(5)
0.015
0.038(6)
0.028(4)
0
0
0
F(6)
0.027(3)
0.056(5)
0.013(3)
0
-.002(2)
0
Table C13.
Anisotropic displacement coefficients for RbYb2.32Sc0.68F10
U11
U22
U33
U12
U13
U23
(Yb, Sc) (1)
0.0059(1)
0.0108(1)
0.0085(1)
0
-.0004(1)
0
(Yb, Sc) (2)
0.0052(2)
0.0124(3)
0.0086(2)
0
0
0
Rb
0.044(1)
0.0194(6)
0.0272(7)
0
-.0143(7)
0
F(1)
0.22(2)
0.013(4)
0.019(5)
0
0
0
F(2)
0.038(4)
0.012(3)
0.106(8)
0
0.023(5)
0
F(3)
0.013(2)
0.060(5)
0.011(2)
0
0.002(2)
0
F(4)
0.010(3)
0.21(2)
0.017(3)
0
-.001(2)
0
F(5)
0.007(3)
0.028(4)
0.020(4)
0
0
0
F (6)
0.008(2)
0.042(40
0.008(2)
0
0.000(2)
0
Table C14.
Anisotropic displacement coefficients for Rb2YbSc2F,
U11
U22
U33
U12
U13
U23
Sc
0.0045(7)
0.0103(8)
0.0086(8)
0
0
0
(Yb, Sc)
0.0077(2)
0.0095(2)
0.0091(2)
0
0.001(1)
0
Rb
0.0533(9)
0.0221(5)
0.0247(6)
0
0.012(3)
0
F(1)
0.028(4)
0.011(3)
0.16(1)
0
0.01(2)
0
F(2)
0.013(2)
0.012(2)
0.064(7)
-.002(1)
0.000(6)
-.013(6)
F(3)
0.008(2)
0.034(3)
0.072(7)
0
0
0.02(1)
F(4)
0.057(6)
0.15(1)
0.015(4)
0
0.027(9)
0
F(5)
0.14(2)
0.15(2)
0.007(5)
0
0
0