NASICON phases of variable composition K1-x A1-x R1+x (MoO4)3 (0 ≤ x ≤ 0.2-0.6), where A = Ni, Mg, Co, or Mn and R = Yb, Lu, or Sc

Article abstract of DOI:10.1134/S0036023608050215

Phases of variable composition K_1-x A_1-x R _1+x (MoO₄)₃) (0 ≤ x ≤ 0.2-0.6), where A = Ni, Mg, Co, or Mn and R = Yb, Lu, or Sc, which crystallize in a NASICON-type structure (space group R 3?c) were synthesized by solid-phase reactions. Their crystal parameters were calculated, and IR and Raman spectra described.

Full text of DOI:10.1134/S0036023608050215

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2008, Vol. 53, No. 5, pp. 800–804. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © N.M. Kozhevnikova, T.N. Khamaganova, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 5, pp. 864–865.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
NASICON Phases of Variable Composition
K A R (MoO ) (0 ≤ x ≤ 0.2–0.6),
1
– x 1 – x 1 + x
4 3
where A = Ni, Mg, Co, or Mn and R = Yb, Lu, or Sc
N. M. Kozhevnikova and T. N. Khamaganova
Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences
ul. Sakh’anova 8, Ulan-Ude, Buryat Republic, 67004 Russia
Received March 1, 2007
Abstract—Phases of variable composition K1 – xA1 – xR1+ x(MoO ) (0 ≤ x ≤ 0.2–0.6), where A = Ni, Mg, Co,
4 3
or Mn and R =Yb, Lu, or Sc, which crystallize in a NASICON-type structure (space group R3 c) were synthe-
sized by solid-phase reactions. Their crystal parameters were calculated, and IR and Raman spectra described.
DOI: 10.1134/S0036023608050215
Structural analogues of NASICON are known
One goal in this work is to study the possibility of
among complex oxides in sulfate, phosphate, arsenate, Yb, Lu, Sc, Mg, Mn, Co, and Ni octahedral cations
and molybdate systems [1]. The considerable interest in entering the NASICON structure. Another goal is to
the preparation and characterization of NASICON determine the crystallization regions for triple molyb-
phases is due to their nonlinear optical, ferroelectric, dates KAR(MoO ) and their atom-vacancy solid solu-
4
3
and superionic properties and high thermal stability. tions K1 – xA1 – xR1 + x(MoO ) . Still another goal is to
4 3
Laser and luminescent materials have been prepared on
the basis of these phases. The base of the crystal struc-
study crystal characteristics and discuss the effect of
cation substitutions on the distortion of coordination
polyhedra and cation distributions in some phases of
ture of the representatives of this family is a rhombohe-
p–
dral framework {[M (XO ) ] } , which is built of cor- variable composition.
2
4 3
3∞
ner-sharing MO octahedra and XO tetrahedra. Low-
6
4
charge alkali cations reside in interstices, which are
connected into a system of channels with large and
variable cross sections. This endows some NASICON
phases, namely those having partially vacant alkali cat-
ion positions, with superionic conductivity [2].
EXPERIMENTAL
Interactions in systems K MoO –AMoO −R (MoO )
4 3
2
4
4
2
was studied in the subsolidus region at 450–800°ë.
The starting components (K MoO , NiMoO ,
2
4
4
NASICON structures have the following character-
istic features: a high isomorphic capacity for
extraframework cations and the possibility of isomor-
phic substitutions in the octahedra and tetrahedra of the
framework. NASICON phases have a potential for use
as solid electrolytes, catalysts, and matrices for immo-
bilization of long-lived isotopes and toxins.
MgMoO , CoMoO , MnMoO , Yb (MoO ) , Lu (MoO ) ,
4
4
4
2
4 3
2
4 3
and Sc (MoO ) ) were presynthesized by ceramic tech-
2
4 3
nology from K CO , di- and tervalent metal oxides, and
2
3
MoO . The study was carried out in two stages. First,
3
the phase composition of the samples whose chemical
composition corresponded to the meeting points of all
sections in systems K MoO –AMoO –R (MoO ) was
2
4
4
2
4 3
In a study of M MoO –AMoO –R (MoO ) systems
2
4
4
2
4 3
studied by X-ray diffraction.As a result, the system was
triangulated. Second, the quasi-binary joins determined
at the first stage were studied.
where M = Na or K; A = Mg, Mn, Co, or Ni; and R =
Al, Cr, or Fe, we synthesized triple molybdates
MAR(MoO ) and phases of variable composition
4
3
Triple molybdates KAR(MoO ) were found to
4
3
M1 − xA1 – xR1 + x(MoO ) (0 ≤ x ≤ 0.3–0.5), which are
4 3
form along sections KR(MoO ) –AMoO
and
K A (MoO ) –R (MoO ) at 600–650°ë (figure).
4
2
4
MAR(MoO ) -based subtraction solid solutions [2].
4
3
2
2
4 3
2
4 3
The possibility of varying the cationic composition
within one structure type offers a means for the targeted
synthesis of NASICON phases; the necessary condi-
tions for the appearance of this structure are the size of AMoO
Phases of variable composition K1 – xA1 – xR1 + x(MoO4)3
are formed in the plane of the triangle K MoO –
2
4
–R
(MoO
)
and
along
the
section
4
2
4
3
octahedral cations equal to 0.6–0.9 Å (R = Yb, Lu, or KAR(MoO ) –R (MoO ) . Samples with compositions
4
3
2
4 3
Sc; and A = Mg, Mn, Co, or Ni meet this condition) and lying along quasi-binary joins were prepared in 25–5 mol %
+
the size of the extraframework cation K .
steps; for refining the composition of the triple molyb-
8
00

NASICON PHASES OF VARIABLE COMPOSITION
K MoO
4
801
date KAR(MoO ) and the homogeneity regions of the
4
3
2
phases of variable composition K1 – xA1 – xR1 + x(MoO4)3,
the steps were 1 mol %. Samples were annealed at 450,
5
50, 600, 650, and 700°ë. Nickel and cobalt samples
were in addition annealed at 750 and 800°ë with inter-
mediate grinding every 20–30 h. The annealing time at
each temperature was 80–100 h. Once annealed, sam-
ples were slowly cooled with the furnace. Nonequili-
brated samples were annealed additionally. Equilib-
rium was considered acquired if the phase composition
of a sample remained unchanged after two sequential
anneals. Synthesis products were identified by X-ray
powder diffraction (FR-552 monochromator camera,
1
:1
1:2
T
CuK radiation, Ge internal standard). Powder patterns
α
were digitized on an IZA-2 comparator. The standard
program package Rentgen was used to process X-ray
diffraction patterns (Table 1).
MgMoO4
Sc (MoO )
2 4 3
Vibration spectra were recorded from polycrystal-
line M1 – xA1 – xR1 + x(MoO ) samples (Bruker FT-IR and
4 3
Phase relations in the system K MoO –MgMoO –Sc (MoO )
at 750°ë.
0 ≤ x ≤ 0.6).
2
=
4
4
2
4 3
Specord M80 spectrometers, excitation with near-IR
Notation: T
K1 – xMg1 – xSc1 + x(MoO4)3
–1
laser (1.06 nm), reflection geometry, 3–5 cm resolu-
tion). Test samples were Nujol mulls on polyethylene
substrates or KBr disks. Molybdenum-isotope-substi-
(
92
tuted samples were prepared from MoO3 and
three-fold axis, and MoO groups on twofold axes.
4
1
00
MoO . Vibration frequencies are compiled in Vacant octahedral and tetrahedral voids merge into a
3
Tables 2 and 3.
three-dimensional system of channels, which are filled
by potassium cations.
As x increases, the octahedral positions in the
K1 − xA1 – xR1 + x(MoO ) structure, which are randomly
Differential thermal analysis (DTA) was performed
on an MOM OD-103 derivatograph (temperature eleva-
tion rate, 10 K/min; sample sizes, 0.3–0.4 g).
4 3
occupied by di- and tervalent atoms, acquire an excess
of the tervalent element and a deficit of the divalent one.
Potassium, which resides in interstices, is also in a def-
RESULTS AND DISCUSSION
The interactions in systems K MoO –AMoO – icit. This cation distribution increases the contribution
2
4
4
of R–O to the overall electrostatic balance of the struc-
ture. In order for the balance to be conserved, K–O
bonds should weaken, which is provided by the deficit
of extraframework potassium atoms and the increase in
the framework size; the unit cell volume increases with
R (MoO ) at 600–650°C are slow and do not go to
2
4 3
completion. The annealing temperature was progressively
elevated to 700–800°ë. Annealing at 750–800°ë for
150−200 h yielded single-phase K1 – xA1 – xR1 + x(MoO4)3
samples, whose homogeneity ranges de-pended on the
two- and three-charged cations. Scandium phases with
A = Mg or Mn have the greatest extent: 0 ≤ x ≤ 0.6. For
increasing the K1 – xA1 – xR1 + x(MoO ) extent (Table 1).
4 3
The
phases
of
variable
composition
R = Yb or Lu and A = Mg or Mn, 0 ≤ x ≤ 0.3. Phases K1 – xA1 – xR1 + x(MoO4)3 contain isolated distorted
K1 − xCo(Ni)1 – xR1 + x(MoO ) were obtained for R = Sc
2–
4 3
anionic tetrahedral groups MoO , in their structure;
4
with 0 ≤ x ≤ 0.3 and for R = Yb or Lu with 0 ≤ x ≤ 0.2.
therefore, we can comparatively analyze the internal
Single-phase K1 – xCo(Ni)1 – xR1 + x (MoO ) samples were
4 3
vibrations in these groups and the external vibrations of
prepared at 800°ë after 180–200 h of annealing. The fig-
cationic sublattices and tetrahedra MoO as a whole. The
4
ure illustrates phase relations in the system K MoO –
2
4
2
4
–
MgMoO –Sc (MoO ) ; in the other systems, they are bands associated with the vibrations of groups MoO
4
2
4 3
92
100
alike.
can experience an isotopic shift upon Mo– Mo substi-
tutions (Tables 2, 3).
X-ray diffraction showed that the compounds
K1 − xA1 – xR1 + x(MoO ) are isostructural to each other
X-ray crystallography shows that molybdenum
4 3
and the compound Na0.625Zn0.625Sc1.375(MoO ) [3]; atoms lay on twofold axes (c2) and atoms A and R on
4 3
threefold axes (c3). The potassium site symmetry is c3i.
they crystallize in trigonal space group R3 c, Z = 6.
The comparatively low symmetry of tetrahedra MoO4
The
structural
base
of
compounds
implies that degeneracy is released from their doubly
and triply degenerate vibrations and that the compo-
K1− xA1 − xR1 + x(MoO ) is the framework assembly of
4 3
octahedra A(R)O and tetrahedra MoO . This structure nents of the full-symmetry stretching vibrations are
6
4
is an analogue of corundum: atoms A(R) reside on active in IR spectra.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

8
02
KOZHEVNIKOVA, KHAMAGANOVA
Table 1. Crystal and thermal parameters for K1 – xA1 – xR1 + x(MoO4)3
Composition
a, Å
c, Å
V/Z, Å3
Tm, °C
A
R
x
Ni
Sc
0
9.422(2)
24.145(2)
309.4
1170
Ni
Sc
0.3
0
9.437(3)
9.428(1)
9.439(4)
9.430(2)
9.441(3)
9.421(2)
9.440(6)
9.451(2)
9.491(1)
9.498(2)
9.505(4)
9.512(2)
9.530(2)
9.542(4)
9.557(2)
9.586(3)
9.594(4)
9.601(2)
9.608(3)
9.611(1)
9.627(4)
9.634(5)
9.641(4)
9.674(1)
9.692(5)
24.153(5)
24.437(5)
24.441(2)
24.439(3)
24.445(1)
24.414(5)
24.453(3)
24.488(7)
24.262(4)
24.285(3)
24.312(6)
24.346(1)
24.345(5)
24.354(2)
24.361(1)
24.373(2)
24.382(3)
24.399(5)
24.417(6)
24.435(5)
24.452(1)
24.462(2)
24.485(3)
24.503(4)
24.526(3)
310.5
313.5
314.3
313.6
314.4
312.8
314.5
315.7
315.5
316.3
317.1
317.9
319.2
320.1
321.1
323.3
323.9
324.6
325.3
325.8
327.1
327.7
328.5
330.9
332.5
–
1150
–
Ni
Lu
Lu
Yb
Yb
Sc
Ni
0.2
0
Ni
1130
–
Ni
0.2
0
Mg
Mg
Mg
Mg
Mg
Mg
Mg
Co
Co
Co
Co
Co
Co
Mn
Mn
Mn
Mn
Mn
Mn
Mn
1100
–
Sc
0.3
0.6
0
Sc
–
Lu
Lu
Yb
Yb
Sc
1055
–
0.3
0
1030
–
0.3
0
1120
–
Sc
0.3
0
Lu
Lu
Yb
Yb
Sc
1090
–
0.2
0
1070
–
0.2
0
1060
–
Sc
0.3
0.6
0
Sc
–
Lu
Lu
Yb
Yb
1005
–
0.3
0
990
–
0.3
2
+
3+
The group theory analysis implies the following dis-
Three lines of the vibrations of cations A and R
tribution over irreducible representations for the factor should be observed in the Raman spectrum; in the IR
+
group of space group D3d:
É = A (inact.) + A (IR) + E (IR),
spectrum, there are two bands due to cations K and
three due to A + R . Six lines associated with the
vibrations of MoO groups should be observed in the
2+
3+
k
1u
2u
u
4
Raman spectrum and nines bands in the IR spectrum.
ÉA + R = A + A (inact.) +2E (Raman) + A (inact.)
1g
2g
g
1u
–
1
The bands with frequencies of 980–760 cm
+
A (IR) + 2E (IR),
2u
u
–
1
(
stretching vibrations) and 410–300 cm (bending
ÉMo = 3A (inact.) + 3E (Raman) + 3A (IR) + 3E (IR). vibrations) were assigned to the internal vibrations in
2g
g
2u
u
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

NASICON PHASES OF VARIABLE COMPOSITION
Table 2. Raman vibration frequencies, cm–1
803
Assignment
9
8
8
8
46
67
28
12
948
869
830
813
945
864
826
810
954
870
830
810
957
872
828
812
952
865
826
808
956
870
828
810
960
872
827
810
962
874
829
812
965
877
832
814
Stretching vibrations
of MoO groups
4
3
72
372
352
340
368
348
337
371
350
339
370
350
336
370
350
338
372
352
340
3
3
48
35
348
338
348
336
350
338
Bending vibrations
of MoO groups
4
2
72
272
270
272
272
261
212
261
212
261
214
Joint vibrations
of M cations
2
12
212
1
1
1
1
96
80
58
40
196
180
158
140
196
180
158
140
197
182
160
140
197
182
160
140
190
158
190
158
185
155
Vibrations of A2+ cat-
ions and translation
vibrations
of various sublattices
1
24
124
82
123
84
8
2
groups MoO ; these bands, as a rule, experience shifts rising x (Tables 2, 3). This is likely due to the Mo–O
4
upon isotope substitution and lie in the spectral region bond energy increasing because of generation of extra
characteristic of the vibrations in molybdenum–oxygen cationic vacancies.
tetrahedra [4].
The vibrations of potassium cations are inactive in
–1
the Raman spectrum; the lines below 300 cm are
assigned to the vibrations of two- and three-charged
cations, experience a shift upon cation substitutions
Three components correspond to the degenerate
vibration in agreement with the low anion symmetry.
The full-symmetry stretching vibrations of molybdate
groups, which are distributed over two sets of crystal-
lographic positions, are degenerate, probably because
Mn
Co
Mg and Yb
Lu
Sc, and are
sensitive to molybdenum isotope substitutions (282–
–1
of the similar geometry and dynamics of these polyhe- 277 cm ). Bands in the IR spectra behave in a similar
–1
dra. The stretching frequencies along the series manner. The band at 190 cm is due to the dominant
K1 − xA1 – xR1 + x(MoO ) are less strongly affected by vibration of scandium cations. The low-frequency
4 3
–
1
the nature of the cation but increase considerably with Raman bands at 124–82 cm experience a shift upon
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008

8
04
KOZHEVNIKOVA, KHAMAGANOVA
Table 3. IR vibration frequencies, cm–1
Assignment
Stretching vibrations
9
8
8
8
52
83
35
12
954
885
833
810
950
881
836
811
955
885
837
813
957
890
837
813
954
887
835
810
958
880
838
812
965
878
833
800
974
875
834
805
980
877
836
820
of MoO groups
4
4
3
3
08
50
05
403
352
305
405
352
305
412
358
309
407
356
309
405
360
309
403
362
308
412
365
312
407
360
312
407
362
312
Bending vibrations
of MoO groups
4
2
2
2
80
22
13
282
224
213
279
224
213
279
228
213
280
229
213
282
230
215
282
232
215
277
277
277
Joint vibrations
of M cations
2
+
1
90
190
158
145
123
190
158
145
123
Vibrations of A
3
+
and R cations
1
1
1
47
38
09
150
138
109
150
138
109
152
140
114
152
140
114
154
142
118
156
142
118
158
145
123
Vibrations of cations
+
K and librations
of MoO groups
4
substitution Mn
Co
Mg and are assigned to
REFERENCES
2
+
the vibrations of A . In the IR spectra, the bands below
1
2
. V. B. Kalinin, Izv. Akad. Nauk SSSR, Neorg. Mater. 26
(11), 2229 (1990).
–1
1
60 cm are assigned to the vibrations of potassium
cations; the bands associated with the librations of
molybdate groups appear in the same region [4].
. N. M. Kozhevnikova and M. V. Mokhosoev, Triple
Molybdates (Buryat State Univ., Ulan-Ude, 2000) [in
Russian].
The above-described study implies that excess
3
4
. B. I. Lazoryak and V. A. Efremov, Zh. Neorg. Khim. 32
2
+
three-charged cations are accommodated at A sites
(3), 652 (1987).
upon aliovalent substitution K + A2
+
R
3+
+ ꢀ,
. K. I. Petrov, M. E. Poloznikova, Kh. T. Sharipov, and V.
V. Fomichev, Vibration Spectra of Molybdates and Tung-
states (FAN, Tashkent, 1990) [in Russian].
whereas the newly generated vacancies are located in
the potassium sublattice.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 5 2008