ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2016, Vol. 61, No. 12, pp. 1518–1521. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © N.M. Kozhevnikova, 2016, published in Zhurnal Neorganicheskoi Khimii, 2016, Vol. 61, No. 12, pp. 1579–1582.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Synthesis and Study of Ternary Molybdates RbCaR(MoO4)3
with a Scheelite-Like Structure in Rb2MoO4–CaMoO4–R2(MoO4)3
Systems (R = Nd, Sm, Eu, Gd)
N. M. Kozhevnikova
Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences,
ul. Sakh’yanovoi 8, Ulan-Ude, Republic of Buryatia, 670047 Russia
e-mail: nicas@binm.bscnet.ru
Received September 3, 2015
Abstract—Phase ratios in the subsolidus regions of Rb2MoO4–CaMoO4–R2(MoO4)3 systems (R = Nd, Sm,
Eu, or Gd) were studied by vibrational spectroscopy, X-ray diffraction, and differential thermal analysis. Ter-
nary molybdates RbCaR(MoO4)3 (R = Nd, Sm, Eu, Gd) with scheelite derivative structures (monoclinic
symmetry system, space group P21/n) were synthesized. Unit cell parameters were determined, and IR and
Raman spectra were characterized.
DOI: 10.1134/S0036023616120081
Molybdates and tungstates with scheelite derivative
structures are of interest as sources of materials for
solid electrolytes, luminophors, lasers, and ferroelec-
trics [1, 2]. They have low thermal expansion coeffi-
cients and heat conductivities and high chemical and
thermal stabilities. The wide crystallization fields of
EXPERIMENTAL
The initial compounds for studying the formation
of phases in Rb2MoO4–CaMoO4–R2(MoO4)3 sys-
tems were Rb2MoO4, CaMoO4, and R2(MoO4)3,
which had been preliminary synthesized by the solid-
phase method from Rb2CO3, CaCO3, molybdenum
individual compounds and solid solutions with a trioxide MoO3 (all of pure for analysis grade), and
rare-earth oxides R2O3 (≥99.99% pure). The Rb2CO3,
CaCO3, and MoO3 were calcined for 10 h at 400°C,
and R2O3 was calcined within a temperature range of
400–700°C. RbCaR(MoO4)3 was synthesized from a
mixture of rubidium, calcium, and rare-earth molyb-
dates Rb2MoO4 + 2CaMoO4 + R2(MoO4)3, which was
calcined within a temperature range of 400–650°C
with intermediate grinding every 20–30 h. The calci-
nation time at each temperature was 100–110 h. After
calcination, the samples were slowly cooled together
with the furnace. Nonequilibrium samples were addi-
tionally annealed, and equilibrium was considered as
attained when the phase composition of the samples
remained unchanged during two sequential anneal-
ings.
The synthesis products were identified by X-ray
diffraction analysis in an FR-552 monochromator
chamber (CuKα radiation, Ge internal standard).
X-ray diffraction patterns were calculated using the
Rentgen software.
The vibrational spectra of polycrystalline
RbCaR(MoO4)3 samples were recorded on Bruker
FT-IR and Specord М-80 spectrometers using a laser
with 1.06-nm near-infrared radiation for excitation
scheelite-like structure are due to the possibility of
iso- and heterovalent substitutions of alkaline-earth
elements by cations of various characters and sizes that
populate crystallographic positions in the framework
and out of framework. The extensive isomorphism of
cations leads to charge disbalance the scheelite struc-
ture due to some geometric features in the arrange-
ment of neighboring polyhedra. The appearance of
local and cooperative distortions is just the factor that
enables the properties of phases to be controlled. Due
to these structural features, scheelite-like molybdates
are promising for use as luminescent and laser materi-
als, chemical sensors, and ion-exchange materials,
and this stimulates intensive theoretical and experi-
mental studies of this group of inorganic compounds
[2–4].
The objective of this work is to study the formation
of phases in the subsolidus region of Rb2MoO4–
CaMoO4–R2(MoO4)3 systems (R = Pr, Nd, Sm, Eu,
or Gd), prepare ternary molybdates, and to study them
by differential thermal and X-ray diffraction analyses
and vibrational spectroscopy.
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