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A ternary salt system Rb 2 MoO 4 -Ce 2 (MoO 4 ) 3 -Zr(MoO 4 ) 2 is studied by powder XRD. Single crystals of 5:1:2 ternary rubidium-cerium-zirconium molybdate Rb 5 CeZr(MoO 4 ) 6 are obtained by solution melt crystallization under spontaneous nucleation conditions. The crystal structure is solved by X-ray crystallography (X8 APEX automated diffractometer, ɆɨK D radiation, 1274 F(hkl), R = 0.0456). The parameters of a trigonal unit cell are: a = b = 10.7248(2) Å, c = 38.796(1) Å, V = 3864.52(14) Å 3 , Z = 6, R 3 c space group. The three-dimensional complex framework comprises Ɇɨ tetrahedra linked to two independent (Ce,Zr)O 6 octahedra. Two types of rubidium atoms occupy large cavities of the framework.The quest for novel functional materials involves the preparation of composite oxide compounds, with complex molybdates being of interest. Many of them are known as multifunctional materials with many properties useful for modern applications (luminescence, electrical, adsorption, etc).Ternary Ɇ 2 MoO 4 -Ln 2 (MoO 4 ) 3 -Hf(MoO 4 ) 2 salt systems (Ɇ = K, Rb, Tl; Ln = rare earth elements) have received significant attention, while the systems with zirconium have not been studied.The purpose of this study was the synthesis of Rb 5 CeZr(MoO 4 ) 6 single crystals and the examination of their crystal structure.Starting rubidium and zirconium molybdates were prepared from the corresponding carbonates, zirconium oxide, and molybdenum trioxide at 450-700qC; the annealing time was 50-100 h.The development of phases in the Rb 2 MoO 4 -Ce 2 (MoO 4 ) 3 -Zr(MoO 4 ) 2 system was investigated with the approach of "crossing sections" in the subsolidus field (550-600qC). The achievement of the equilibrium was controlled by X-ray diffraction (Advance D8 Bruker AXS diffractometer with a graphite monochromator). The formation of ternary molybdates with compositions 5:1:2, 1:1:1 has been established for the system (Fig. 1). Solution-melt crystallization with spontaneous nucleation afforded 5:1:2 single crystals of Rb 5 CeZr(MoO 4 ) 6 (I). Rubidium dimolybdate was used as the solvent. The prepared crystals were identified by powder XRD and DTA applied † Deceased.