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Abstract:
A series of isostructural trigonal molybdates CsMZr0.5(MoO4)(3) with M = Al, Ga, In, Sc, Cr, V, Fe, and CsCrTi0.5(MoO4)(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 MoO4-pyramids and MO6-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 CsCrTi0.3(MoO4)(3) above 700 K, allows one to propose a structural phase transition. The crystal structure of the high-temperature 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.
