Synthesis, structure and vibration spectra of the triple molybdates Tl5A0.5Hf1.5(MoO4)6, A = Ca, Sr, Ba, Pb

Article abstract of DOI:10.1016/j.jallcom.2006.11.086

The systems Tl₂MoO₄-AMoO₄-Hf(MoO₄)₂ (A = Ca, Sr, Ba, Pb) have been studied in their subsolidus regions using X-ray powder diffraction and differential thermal analysis. Intermediate phases of composition 5:1:3 are formed in these systems. The crystallographic and thermal characteristics of these phases have been determined. The vibration spectra of Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Sr, Ba, Pb) have been considered and analysed for each new compound. In the Raman spectra, the influence of the divalent cation on the bands of the ν₁ vibrational mode and deformation fluctuations has been demonstrated. The bands of the ν₃(F₂) vibrational mode are split in the IR spectra of the given triple molybdates. This splitting increases with the radius of the divalent cation.

Full text of DOI:10.1016/j.jallcom.2006.11.086

Journal of Alloys and Compounds 448 (2008) 325–330
Synthesis, structure and vibration spectra of the triple molybdates
Tl A Hf (MoO ) , A = Ca, Sr, Ba, Pb
5
0.5
1.5
4 6
a
a,∗
b
b
B.G. Bazarov , A.E. Sarapulova , R.F. Klevtsova , L.A. Glinskaya ,
a
a
K.N. Fedorov , Zh.G. Bazarova
a
Baikal Institute of Nature Management, Siberian Division, Russian Academy of Sciences, Sakhyanova Street 6, Ulan-Ude 670047, Buryat Republic, Russia
b
Nikolaev Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences, Akad. Lavrentyev Av. 3, Novosibirsk 630090, Russia
Received 31 July 2006; received in revised form 10 November 2006; accepted 16 November 2006
Available online 27 December 2006
Abstract
The systems Tl
2
4 4 4 2
MoO –AMoO –Hf(MoO ) (A = Ca, Sr, Ba, Pb) have been studied in their subsolidus regions using X-ray powder diffraction and
differential thermal analysis. Intermediate phases of composition 5:1:3 are formed in these systems. The crystallographic and thermal characteristics
of these phases have been determined. The vibration spectra of Tl (A = Ca, Sr, Ba, Pb) have been considered and analysed for
each new compound. In the Raman spectra, the influence of the divalent cation on the bands of the ν vibrational mode and deformation fluctuations
) vibrational mode are split in the IR spectra of the given triple molybdates. This splitting increases
5
4 6
A0.5Hf1.5(MoO )
1
3 2
has been demonstrated. The bands of the ν (F
with the radius of the divalent cation.
©
2006 Published by Elsevier B.V.
Keywords: Triple molybdate; Vibration spectra; Vibrational mode; Frequency; Band; Factor-group splitting; Space group
1
. Introduction
of the divalent element is, the more the ionic conductivity of
the corresponding compound increases. Thus we are engaged
in studying the structure and properties of triple molybdates
Complex oxides may be useful materials due to their vari-
˚
ety of physical–chemical, electrophysical and optical properties.
Investigations in the field of molybdenum and tungsten chem-
istry have led to a significantly enlarged number of materials
with useful properties.
with divalent elements having large ion radii (r > 1 A).
The purpose of this work is to investigate the phase formation
in the systems Tl2MoO4–AMoO4–Hf (MoO4)2 (A = Ca, Sr, Ba,
Pb) and the properties of the phases obtained.
Earlier, the triple molybdates K (A0.5Zr1.5)(MoO4)6
5
(
A = Mg, Mn) were observed in the K2MoO4–AMoO4–
2
. Experimental details
Zr(MoO4)2 systems [1]. The structures of these compounds
have been described elsewhere [2,3]. More recently, similar
triple molybdates have been obtained in the systems with
A = Co, Ni, Cu, Zn, Cd [4,5]. All the above-mentioned phases
are isostructural and crystallize in the R3c trigonal space group.
We then obtained thallium analogues of potassium triple molyb-
The starting reactants used were MoO3 (analytical grade), BaMoO4 (pure
grade), PbMoO (high-purity grade 5-3), SrCO (high-purity grade 7-2), CaCO
3
and Tl2CO3 (pure grade), HfO2 (analytical grade). Hafnium molybdate was syn-
thesized by sintering a mixture of hafnium and molybdenum oxide at 750 C for
4
3
◦
50–70 h. Strontium, calcium and thallium molybdates were prepared by anneal-
ing stoichiometric amounts of the corresponding carbonate and molybdenum
trioxide at 600–650 C for 50–70 h. To avoid the loss of MoO3 by sublimation,
we started sintering at 400 C.
dates (Tl Cd0.5Zr1.5(MoO4) [6] and Tl Mg0.5Zr1.5(MoO4)6
[
◦
5
6
5
◦
7]). An investigation of the electrophysical properties of the
obtained triple molybdates has shown that they may be used as
solid electrolytes [6,8]. It is found that the larger the ion radius
Phase formation in the systems Tl2MoO4–AMoO4–Hf(MoO4)2 (A = Ca,
Sr, Ba, Pb) was investigated in air by the intersecting sections method in the
subsolidus region at 500–550 C. The essence of this method is to study the
◦
crossing-point phase composition of all possible sections connecting the double
and initial molybdates on the isothermal projections of the triple-system dia-
grams. X-ray analysis of these points allows quasi-binary sections, which split
the primary Tl2MoO4–AMoO4–Hf(MoO4)2 system on the secondary simple
∗
Corresponding author. Tel.: +7 8 301 2 433362
E-mail address: sarapulova80@mail.ru (A.E. Sarapulova).
0
925-8388/$ – see front matter © 2006 Published by Elsevier B.V.
doi:10.1016/j.jallcom.2006.11.086

3
26
B.G. Bazarov et al. / Journal of Alloys and Compounds 448 (2008) 325–330
eutectic systems, to be revealed. The revealed quasi-binary sections were inves-
tigated with stepsof5–10 mol%. The samples for the investigationwereprepared
3.3. Tl2MoO4–AMoO4 systems
◦
◦
by solid-phase synthesis. They were annealed from 350 C up to 500–550 C
for 100–150 h. Equilibration was controlled by X-ray diffraction.
The X-ray powder diffraction (XPD) analysis was carried out using an
Advance D8 diffractometer (Cu K␣ radiation). The unit-cell parameters were
refined using uniquely indexed lines of X-ray powder diffraction patterns (Poly-
crystal software [9]).
There are no compounds in the Tl2МоO4–CaМоO4 and
Tl2МоO4–SrМоO4 systems [11]. In the Tl2МоO4–BaМоO4
and Tl2МоO4–PbМоO4 systems, double molybdates of com-
positions Tl2Ba(MoO4)2 and Tl2Pb(MoO4)2 were found. These
compounds crystallize in the trigonal crystal system and are thus
isostructural to their potassium analogues.
A Tl5Pb0.5Hf1.5(MoO4)6 single crystal was grown by flux crystallization
with spontaneous nucleation and characterized by X-ray structural analysis
◦
(
XSA). The flux used for this purpose was Tl2Mo4O13 (tm = 616 C). Single
crystals were grown from a melt containing 33.3 wt.% Tl5Pb0.5Hf1.5(MoO4)6
3.4. Tl MoO –Hf(MoO ) system
2
4
4 2
◦
and 66.7 wt.% Tl2Mo4O13. The melt obtained was annealed at 700 C for
◦
◦
homogenization, and then cooled down to 500 C at a rate of 1.5 C/h.
In other to conduct the XSA, a colourless single crystal was investigated
According to previous results [12], there are two
compounds, Tl8Zr(MoO4)6 and Tl2Zr(MoO4)3, in the
Tl2MoO4–Hf(MoO4)2 binary system. These compounds are
isostructural to their rubidium analogues and crystallize in the
monoclinic crystal system.
◦
using a X8 APEX (Mo K␣ radiation, graphite monochromator, max. 2θ = 65 )
autodiffractometer. The structure-refinement calculations were performed using
the SHELX-97 program complex [10].
The differential thermal analysis (DTA) was carried out using a thermoan-
alytical set-up that allowed us to record heating (cooling) curves and to reveal
◦
DTA peaks up to 1000 C. The temperature was measured using a Pt–Pt/10%
Rh thermocouple, whose hot junction was placed into the thermowell of a quartz
crucible with a sample, while the cold junctions were thermostatted at 0 C. The
3.5. New Tl5A0.5Hf1.5(MoO4)6 compounds
◦
sample size was 0.1–0.3 g. Heating was carried out from room temperature to
As shown in Fig. 1, new triple molybdates of composition
5:1:3 were obtained in the given systems. The stoichiomet-
ric correlation of the initial components for the synthesis of
these new compounds was taken from existing data [1–8].
The compounds obtained are isostructural and belong to
the trigonal crystal system. Isostructural phases of the same
composition were also observed in the zirconium systems
◦
◦
1
±
000 C at a rate of 10 C/min. The temperature measurement was accurate to
10 C.
◦
Infrared (IR) spectra of the polycrystalline samples were measured in a field
−1
of 1000–400 cm with a Scimitar FTS 2000 spectrometer. The samples were
pressed into tablets with KBr. Raman spectra were registered on a Triplemate
Spex spectrometer. The wavelength of the excitation was 488 nm.
The density of the samples was measured pycnometrically in carbon tetra-
chloridebythestandardprocedure. Thepycnometervolumewas5 ml, thesample
◦
Tl MoO –AMoO –Zr(MoO ) (A = Ca, Sr, Pb).
weight was 0.5 g, and the temperature was maintained at 26 C.
2
4
4
4 2
As
a
result of XSA, the composition of the
compound is confirmed.
Tl Pb0.5Hf1.5(MoO4)6
5
3
. Results and discussion
¯
Tl Pb0.5Hf1.5(MoO4)6 crystallizes in the R3 trigonal space
5
group with the unit-cell parameters a = b = 10.6830(3),
3
.1. Subsolidus phase relations
3
3
˚
˚
c = 38.599(2)A, V = 3815.0(2)A , Z = 6andρ = 6.145 g/cm .
calc
According to the results of the XPD analysis, the subsolidus
The melting point of this compound was determined to be
570 C by DTA.
◦
phase relations in the Tl2MoO4–AMoO4–Hf(MoO4)2 (A = Ca,
Sr, Ba, Pb) systems are as shown in Fig. 1. Triple molybdates
with a 5:1:3 (S) mole ratio of starting reactants are formed in
these systems. The amount of three-phase regions in these sys-
tems depends on the number of double and triple molybdates
obtained, and varies within the range 5–6.
The crystal structure of the Tl5Pb0.5Hf1.5(MoO4)6 (I) molyb-
date consists of two kinds of consecutively alternating Mo
tetrahedrons and Pb and Hf octahedrons, connecting through
shared O-tops. Three kinds of thallium cations are situated in the
large cavities of the framework. A projection of this structure on
the plane (1 1 0) is shown in Fig. 2.
In the crystal structure of Tl Pb0.5Hf (MoO4) , both kinds
3
.2. AMoO4–Hf(MoO4)2 systems
5
1.5
6
of the somewhat distorted MoO4 tetrahedra are characterized by
˚
We investigated these systems by XPD analysis. They are
Mo–O distances within the ranges 1.74–1.83 and 1.71–1.81 A,
eutectic systems, and no double molybdates are formed at
respectively. The significant scatter of Mo–O distances is
accounted for by the different coordinations of oxygen atoms
◦
5
50–600 C.
Fig. 1. The subsolidus phase relations in the Tl2MoO4–AMoO4–Hf(MoO4)2 (A = Ca, Sr, Ba, Pb) systems.

B.G. Bazarov et al. / Journal of Alloys and Compounds 448 (2008) 325–330
327
Table 1
Selected interatomic distances (d, A˚ ) in the structure Tl5Pb0.5 Hf1.5(MoO4)6
Bond
d ( A˚ )
Mo(1)-tetrahedron
Mo(1)-O(3)
Mo(1)-O(2)
Mo(1)-O(1)
Mo(1)-O(4)
1.74(1)
1.75(1)
1.76(1)
1.83(1)
1.77
ꢀMo(1)-Oꢁ
Mo(2)-tetrahedron
Mo(2)-O(5)
Mo(2)-O(6)
Mo(2)-O(7)
Mo(2)-O(8)
1.71(1)
1.72(1)
1.80(1)
1.81(1)
1.76
ꢀMo(2)-Oꢁ
Angle
ω (grad)
Mo(1)-tetrahedron
O(1)-Mo(1)-O(2)
O(1)-Mo(1)-O(3)
O(2)-Mo(1)-O(3)
O(1)-Mo(1)-O(4)
O(2)-Mo(1)-O(4)
O(3)-Mo(1)-O(4)
110.4(5)
109.2(6)
109.2(6)
105.6(5)
112.4(4)
109.9(5)
109.45
107.3(6)
108.3(4)
111.3(5)
109.1(5)
108.8(5)
111.9(5)
109.45
ꢀ
O-Mo(1)-Oꢁ
O(5)-Mo(2)-O(6)
O(5)-Mo(2)-O(7)
O(6)-Mo(2)-O(7)
O(5)-Mo(2)-O(8)
O(6)-Mo(2)-O(8)
O(7)-Mo(2)-O(8)
ꢀO-Mo(2)-Oꢁ
Fig. 2. A projection of Tl5Pb0.5Hf1.5(MoO4)6 crystal structure on the plane
1 1 0).
˚
Bond
d (A)
(
Pb(1)-octahedron
Pb(1)-O(3)
Hf-octahedron
Hf(1)-O(7)
Hf(2)-O(4)
Hf(2)-O(8)
2.35(1) × 6
by Tl, Pb, and Hf. So, the O(5) and O(6) atoms coordinate to
the Mo atoms and two Tl atoms, and the distances from such
O atoms to the Mo atoms are the shortest. The O(4), O(7) and
O(8) atoms in addition coordinate with more highly charged Hf
cations and, therefore, are situated at the farthest distances from
the Mo atoms.
2.091(9) × 6
2.067(8) × 3
2.077(8) × 3
Bond
d ( A˚ )
The Pb(1) atoms and one of the Hf(1) atoms are located on the
Tl(1)-nine-top polyhedron
Tl(1)-O(2)
Tl(1)-O(1)
¯
2.803(9) × 3
2.97(2) × 3
3.268(9) × 3
inversion 3 axis, inside somewhat deformed octahedrons with
˚
six equal Pb–O and Hf–O distances, 2.35(1) and 2.091(9) A,
Tl(1)-O(4)
respectively. The second hafnium Hf(2) atom is on the rotational
˚
Tl(3)-polyhedron
Tl(3)-O(1)
Tl(3)-O(5)
Tl(3)-O(2)
Tl(3)-O(6)
3
axis (Hf–O = 3 × 2.067(8) + 3 × 2.077(8) A), also inside an
2.85(1)
2.98(1)
2.990(9)
3.13(1)
octahedron.
Three kinds of low-charge thallium cations are located in
the large polyhedrons. The Tl(1) atoms are located on the 3
axis inside nine-top polyhedrons with three different Tl–O dis-
tances: 2.803(9), 2.97(2) and 3.268(9) A. The polyhedron, at
Bond
d ( A˚ )
˚
the top of which 11 O atoms are located at different Tl–O dis-
tances in the range 2.85(1)–3.47(1) A, is more isometric for the
Tl(2a)-polyhedron
Tl(2a)-O(5)
Tl(2a)-O(6)
Tl(2a)-O(8)
Tl(3)-O(8)
˚
2.85(1) × 3
2.93(1) × 3
3.36(1) × 3
3.13(1)
3.155(8)
3.25(1)
Tl(3) atom in the general position. The Tl(2) atoms are situ-
ated on the 3 axis in the large plane extending along the c-axis.
After refinement of the structure, it is found that this kind of
thallium atom occupies two closely located statistical positions
Tl(3)-O(4)
Tl(3)-O(3)
Tl(3)-O(2)
ꢂ
˚
3.28(1)
(
Tl(2a)–Tl(2b) = 0.75 A), each with a space factor equal to 0.5.
In this case 9 O atoms are included in the coordination sphere
of each thallium atom. The O atoms form nine-top polyhedrons,

3
28
B.G. Bazarov et al. / Journal of Alloys and Compounds 448 (2008) 325–330
Table 1 (Continued )
Bond
Table 2
4
Coordinates of basis atoms (×10 ) and equivalent isotopic heat parameters
d ( A˚ )
A˚ × 10 ) in the structure Tl5Pb0.5Hf1.5(MoO4)6
2
3
(
Tl(2b)-polyhedron
Atom
x
y
z
Ueq
ꢂ
Tl(2b)-O(6)
2.73(1) × 3
3.07(1) × 3
3.70(2) × 3
3.32(2)
3.37(1)
3.47(1)
Tl(2b)-O(5)
Tl(2b)-O(3)
Mo(1)
Mo(2)
Pb(1)
Hf(1)
Hf(2)
Tl(1)
Tl(2a)
Tl(2b)
Tl(3)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
9832(1)
3546(1)
6156(1)
2835(1)
0
1317(1)
319(1)
5000
20(1)
22(1)
23(1)
13(1)
11(1)
37(1)
39(1)
62(4)
50(1)
52(3)
31(2)
65(4)
23(2)
50(4)
46(3)
31(2)
29(2)
ꢂ
ꢂ
Tl(3)-O(3)
Tl(3)-O(7)
Tl(3)-O(6)
Tl(3)-O(7)
0
0
0
0
0
0
0
0
0
0
0
ꢂ
ꢂ
7502(1)
8528(1)
6434(2)
6240(5)
853(1)
1760(3)
1121(2)
1267(4)
1139(2)
−102(3)
526(3)
323(2)
521(2)
3.65(1)
Bond
d ( A˚ )
0
2761(1)
9429(15)
9756(11)
−562(1)
6074(13)
7591(10)
6407(13)
4404(11)
3332(13)
4278(12)
1282(11)
2457(13)
Shortest non-bonded contacts
ꢂ
Mo(1)-Mo(1)
4.420(3)
3.930(5)
4.258(3)
3.752(2)
3.712(3)
3.840(3)
3.785(3)
3.683(2)
3.688(3)
3.917(3)
3.764(5)
3.881(3)
4.041(3)
3.958(6)
4.068(3)
0.75(2)
Mo(1)-Mo(2)
Mo(2)-Mo(2)
11565(12)
8500(9)
ꢂ
Mo(1)-Pb(1)
Mo(1)-Hf(2)
Mo(1)-Tl(1)
Mo(1)-Tl(3)
Mo(2)-Hf(1)
Mo(2)-Hf(2)
4041(10)
3588(13)
1755(9)
4845(9)
ꢂ
Mo(1)-Tl(3)
characteristics of the Tl A0.5Hf1.5(MoO4)6 compounds are
listed in Table 3.
5
Mo(2)-Tl(2a)
Mo(2)-Tl(3)
ꢂ
Mo(2)-Tl(3)
Tl(1)-Hf(2)
Tl(1)-Tl(3)
Tl(2a)-Tl(2b)
Tl(2b)-Tl(3)
Tl(2a)-Tl(3)
Tl(3)-Hf(2)
Tl(2a)-Hf(2)
3.6. Vibration spectra of new triple molybdates
We have studied the vibration spectra of Tl A0.5Hf1.5
5
3.695(9)
4.084(5)
4.167(1)
4.123(9)
(MoO4) compounds. The vibration spectra of triple molybdates
6
basically contain the bands of the MoO4 group.
The free MoO42 ion is well known to pertain to the point
−
group T and has normal fluctuations with the following fre-
d
−
1
quencies (cm ): ν1(A1) = 936, ν2(E) = 220, ν3(F2) = 895, and
ν4(F2) = 365 [13]. Moreover, all four fluctuations are active in
the Raman spectra; but only the valence and deformation fluc-
tuations F2 are active in the IR spectra.
which are the same as the Tl(1) polyhedrons (Table 1). It should
be noted that in the nearest Tl(2b) atom coordination sphere,
˚
6
oxygen atoms at Tl(2b)–O distances of 2.73–3.07 A form an
¯
octahedron, in which the Tl(2b) atom is located at a distance
In the internal field of the crystal with space group R3, the
−
˚
of 0.38 A from one of the edges of the octahedron. So, in order
local symmetry of the complex MoO42 ion decreases to C1
[14]. If a molecule or ion is situated in the general position, i.e.,
it does not lie on any symmetry element of the crystal (C1), then
under the action of the crystalline field all confluent fluctuations
must be split into non-confluent ones. Thereby, ν3 and ν4 are
split into three bands: 3A, ν2 and into two: 2A, respectively, and
the ν1(A) band becomes active in the IR spectra.
to make the polyhedron more isometric, we have included in
the Tl(2b) coordination sphere three O atoms at a more remote
˚
distance of 3.70 A.
In the structure of the triple molybdate of composition 5:1:3
with divalent and tetravalent (Zr and Hf) cations studied earlier,
2
+
4+
A
and R are statistically distributed among two crystallo-
graphic positions with different space factors for these cations.
The typical particularity of the studied structure of triple molyb-
date (I) is the distribution of lead and hafnium atoms among
different crystallographic positions due to their vastly differing
ion radii. This, in turn, has brought about a change of space
group of compound (I). But, as a whole, the crystalline struc-
tures of these two groups of compounds are similar and in both
types of structure it is possible to pick out the continuous chan-
nels of large cross section in which the large thallium cations
are located.
From six to eight bands were observed in the experi-
−1
mental IR spectra in the range 1000–400 cm
and 9–13
bands were observed in the Raman spectra in the range
−
1
−1
1000–90 cm (Figs. 3 and 4). The main bands at 980–700 cm
−
1
(valence fluctuations) and 410–300 cm (deformation fluctua-
tions) were related to internal fluctuations of the MoO4 groups
(Tables 4 and 5) [15].
Because the total number of observed IR and Raman bands
does not coincide with the predicted number, and since the Mo
sites have a low symmetry and the unit-cell volume is large,
the spectra were analysed using the site-group approach. The
vibrational spectra are consistent to a first approximation with
the results of the site-group analysis. However, the ν1 vibrational
mode is split into two components. The splitting ranges from 29
Indexing of the X-ray diffraction patterns for other thallium
compounds was based on the result of the XSA (Table 2) of
the Tl Pb0.5Hf1.5(MoO4) compound. The unit-cell parameters
5
6
of these compounds were refined by indexed X-ray diffraction
patterns using Polycrystal software. The crystal and thermal
−
1
to 38 cm
.

B.G. Bazarov et al. / Journal of Alloys and Compounds 448 (2008) 325–330
329
Table 3
The crystal and thermal characteristics of the Tl5A0.5Hf1.5(MoO4)6 compounds, space group R3
¯
Vel.cell ( A˚ 3)
˚
˚
dcalc (g/cm3)
dexp (g/cm3)
◦
Compounds
a (A)
c (A)
Tm ( C)
Tl5Ba0.5Hf1.5(MoO4)6
Tl5Pb0.5Hf1.5(MoO4)6a
Tl5Sr0.5Hf1.5(MoO4)6
Tl5Ca0.5Hf1.5(MoO4)6
3849
3815
3813
3804
10.691(1)
10.6830(3)
10.679(1)
10.675(1)
38.89(1)
38.599(2)
38.61(1)
38.55(1)
6.00
6.145
5.99
5.94
6.02
5.99
5.95
5.92
560
570
570
600
a
Single crystal data (in bold).
Fig. 3. The IR spectra of the Tl5Ca0.5Hf1.5(MoO4)6 (1), Tl5Sr0.5Hf1.5(MoO4)6
2), Tl5Pb0.5Hf1.5(MoO4)6 (3), Tl5Ba0.5Hf1.5(MoO4)6 and (4) triple molyb-
dates.
(
Fig. 4. The Raman spectra of the Tl5Ca0.5Hf1.5(MoO4)6 (1),
Tl5Sr0.5Hf1.5(MoO4)6 (2), Tl5Pb0.5Hf1.5(MoO4)6 (3), Tl5Ba0.5Hf1.5(MoO4)6
and (4) triple molybdates.
As they are located between molybdenum–oxygen tetrahe-
dra, the divalent cations have a perturbating influence on the
vibrationalmodes, whichisespeciallypronouncedforthemodes
that are similar in energy to the proper vibrational modes, i.e.
on the deformation fluctuation. When considering the Raman
Table 5
The fluctuations in the Raman spectra of the Tl5A0.5Hf1.5(MoO4)6 triple molyb-
−
1
dates, cm
Cation composition
TlCaHf TlSrHf
32
Vibrational mode
TlPbHf
TlBaHf
Table 4
9
902
934
905
935
900
940
903
ν1(MoO4)
ν3(MoO4)
The fluctuations in the IR spectra of the Tl5A0.5Hf1.5(MoO4)6 triple molybdates,
−
1
cm
Cation composition
TlCaHf TlSrHf
939
8
8
93
77
884
Vibrational mode
877
836
810
TlPbHf
TlBaHf
832
836
808
809
9
34
945
907
941
909
ν1(MoO4)
ν3(MoO4)
906
354
352
339
338
ν4(MoO4)
ν2(MoO4)
884
849
829
800
886
845
828
792
887
847
886
843
826
791
741
723
320
292
317
289
314
288
323
288
158
154
155
155
113
Libration MoO4
805
737
110
112
96
113
96
Translation MoO4
7
31
727
727

3
30
B.G. Bazarov et al. / Journal of Alloys and Compounds 448 (2008) 325–330
spectra of our compounds, the frequencies of the ν4 vibrational
References
−
1
mode decrease from Ca to Ba (∼16 cm ). The frequencies of
[
[
[
[
[
[
[
[
[
1] Zh.G. Bazarova, B.G. Bazarov, R.F. Klevtsova, et al., Zhurnal Neorganich-
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48 (2003) 1410.
the ν1 vibrational mode are also sensitive to a change of diva-
−
1
lent cation and increase from Ca to Ba (∼8 cm ). The bands
corresponding to external fluctuations of the MoO4 tetrahedron
−1
(
<300 cm ) are observed in the Raman spectra apart from the
specified bands. The frequencies of these fluctuations do not
change within a sequence of compounds.
It should be noted that fluctuations of the thallium framework
are not active in the Raman spectra [16].
The range of experimental IR spectra has included only
valence fluctuations. The low symmetry of the MoO4 tetra-
hedron local position (C1) has brought about splitting of the
−
1
ν3(F2) (∼890–720 cm ) mode into three components. The
factor-group splitting of each confluent fluctuation grows with
an increase in the radius of the divalent cation (Fig. 3).
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[
[
[
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materials, Khabarovsk, Russia, November 4–6, 2002.
4
. Conclusions
To summarize, phase formation in the Tl2MoO4–AMoO4–
Hf(MoO4)2 (A = Ca, Sr, Ba, Pb) systems has been investigated.
New triple molybdates of composition 5:1:3 have been found
to form, and their thermal and crystallographic characteristics
have been determined. The frequencies of their vibration spectra
have been studied and analysed for each new compound.
[13] K. Nakamoto, Infrared and Raman spectra of Inorganic and Coordination
Compounds, Moscow, Russia, 1966, p. 151.
[14] A.I. Grigoriev, Introduction to Vibration spectroscopy of Inorganic Com-
pounds, Moscow, Russia, 1997, p. 87.
Acknowledgement
[15] Z.I. Hazheeva, B.G. Bazarov, Zh.G. Bazarova, Russ. J. Inorg. Chem. 47
2002) 407.
(
[
16] M.V. Mohosoev, I.I. Murzahanova, N.M. Kozhevnikova, et al., Zhurnal
Neorganicheskoi Khimii 36 (1991) 1273.
This work was supported by the Russian Foundation for Basic
Researches (RFBR Grant 04-03-32714).