A series of isostructural trigonal molybdates CsMZr 0.5 (MoO 4 ) 3 with M = Al, Ga, In, Sc, Cr, V, Fe, and CsCrTi 0.5 (MoO 4 ) 3 was synthesized by solid state reactions and characterized by synchrotron powder diffraction, differential scanning calorimetry, thermal conductivity measurements, and magnetization measurements for compounds with a magnetic 3d transition metal cation. The NASICON-type structure of these compounds represents a three-dimensional framework of corner-sharing trigonal MoO 4 -pyramids and MO 6 -octahedra, in which M and Zr (Ti) ions are randomly distributed. The Cs ions occupy large channels along the c-axis. A combination of phenomena like a drastic increase of thermal conductivity, endothermic signals in the DSC curve and anomalies in the thermal expansion coefficients, observed for the compounds with M = Cr, V, Fe, and CsCrTi 0.5 (MoO 4 ) 3 above 700 K, allows one to propose a structural phase transition. The crystal structure of the hightemperature phase is very close to the low-temperature one. A significant hysteresis in high-temperature electronic and thermal conductivity was observed. A possible transition from the piezoelectric to the paraelectric state is discussed.
Phase equilibria in the Rb 2 MoO 4-Na 2 MoO 4-Zr(MoO 4) 2 system were studied for the first time, quasi-binary cuts in the concentration triangle were determined, and triangulation was performed. The formation of a new phase of molybdate Rb 5 Na 1 / 3 Zr 5 / 3 (MoO 4) 6 was established in the system. New triple molybdates Rb 5 M I 1 / 3 Zr 5 / 3 (MoO 4) 6 (M I-Na,K) were synthesized by the solid-phase reaction in the temperature interval 400-510°C. The physicochemical characteristics of the prepared materials were carried out by Х-ray diffraction, differential scanning calorimetry, IR-spectroscopy, and scanning electron microscopy. It was established that synthesized molybdates crystallized in the trigonal space group R-3С, Z = 6. The crystal structure consists of MoO 4-tetrahedra and octahedrally coordinated MO 6-polyhedra. Rubidium cations are located in the cavities of the framework. Cation (sodium, potassium) and zirconium atoms are statistically distributed in M positions. The curves of differential-scanning calorimetry are characterized by endothermic effects corresponding to phase transitions and melting of the samples. The phase transitions found in the high-temperature region as a result of multiple measurements in the heating and cooling modes without melting the samples belong to the first-order phase transitions due to the temperature hysteresis. The IR spectra contain intense absorption bands associated with stretching vibrations of MoO bonds in MoO 4-tetrahedra. In the final annealing product, the particle size is 80-400 nm, as measured at electron micrographs. The identified compounds of the composition Rb 5 M I 1 / 3 Zr 5 / 3 (MoO 4) 6 (M I-Na, K) have a framework structure with channels appropriate for ion transport, which is a prerequisite for ion-conducting properties and use of the compounds as promising solid electrolytes.
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