SYNTHESIS AND STUDY OF Li3BaSrR3(MoO4)8 COMPOUNDS
1501
to libration vibrations of MoO4 groups, and those at
103–102 and 92–90 cm–1, to vibrations of atoms in
the strontium and barium sublattices, respectively.
Translation vibrations of molybdenum are mixed with
vibrations of atoms in the REE sublattice and have
frequencies of 265 and 186 cm–1. In the long-wavelength
part of the spectra of the compounds under study, we
recorded two bands at 232–227 and 263–258 cm–1,
attributed to vibrations of lithium cations [5].
for lithium, barium, strontium, and REE cations in
common positions (position M2 in octavertices).
ΓM2 = 3Ag + 3Bg + 3Au + 3Bu;
These vibrations, active in IR absorption spectra,
must have frequencies below 500 cm–1. In addition,
44 bands associated with deformation, libration, and
translation vibrations of MoO4 groups must be observed
in the same spectral range.
CONCLUSIONS
The spectra recorded for the compounds under study
have no noticeable differences in the high-frequen-
cy part (990–660 cm–1). The absorption bands in this
spectral range, associated with stretching vibrations of
MoO4 groups, are poorly resolved. This results from
the above-described way of cation arrangement over
crystallographic positions and the related statistics in
distortions of tetrahedral anionic groups. In the region
of deformation vibrations of MoO4 groups and vibra-
tions of cation sublattices (<500 cm–1), the spectrum of
Li3BaSrR3(MoO4)8 shows up to 14 absorption bands.
This number is substantially smaller than the expected
number of vibrations. These differences between the
results of the theoretical group analysis and the experi-
mentally recorded number of vibrations are presumably
due to the insignificant factor-group splitting of internal
(deformation) and external vibrations of MoO4 groups.
At the same time, the spectra of the compounds under
consideration are very close in this spectral range to the
spectra of Li3Ba2R3(MoO4)8. This indicates that vibra-
tions of the cationic sublattices are closely similar to
each other and to deformation vibrations of MoO4 tet-
rahedra.
(1) The method of solid-phase reactions in a mixture
3Li2MoO4 + 2SrMoO4 +2BaMoO4 + 3R2(MoO4)3 was
used to synthesize new molybdates of composition
Li3BaSrR3(MoO4)8 (R = REE, Y).
(2) An X-ray diffraction analysis demonstrated
that the molybdates Li3BaSrR3(MoO4)8 belong to the
structuraltypeofmonoclinicallydistortedsheelite, sp. gr.
C2/c, Z = 2. The compounds are isostructural with each
other and with ternary molybdates Li3Ba2R3(MoO4)8.
REFERENCES
1. Kozhevnikova, N.M., Korsun, V.P., Mokhosoev, M.V.,
and Alekseev, F.P., Zh. Neorg. Khim., 1990, vol. 35, no. 4,
pp. 835–838.
2. Kozhevnikova, N.M., Korsun, V.P., Mursakhanova, I.I.,
and Mokhosoev, M.V., J. Rare Earth., 1991, vol. 2,
pp. 845–849.
3. Klevtsova, R.F., Vasil’ev, A.D., Glinskaya, L.A., et al., Zh.
Strukt. Khim., 1992, vol. 33, no. 3, pp. 126–130.
4. Trunov, V.K., Efremov, V.A., and Velikodnyi, Yu.A.,
Kristallokhimiya
i svoistva dvoinykh molibdatov i
vol’framatov (Crystal Chemistry and Properties of Double
Molybdates and Tungstates), Leningrad: Nauka, 1986.
The frequencies of the external vibrations of MoO4
groups and of vibrations of heavy-cation sublattices
have approximately the same values as those in the case
of Li3Ba2R3(MoO4)8.
5. Petrov, K.I., Poloznikova, M.E., Sharipov, Kh.T., and
Fomichev, V.V., Kolebatel’nye spektry molibdatov i
vol’framatov (Vibration Spectra of Molybdates and
Tungstates), Tashkent: FAN, 1990.
We attribute bands with frequencies of 164–156 cm–1
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 9 2011