Possible Piezoelectric Materials Cs<i>M</i>Zr_0.5(MoO₄)₃ (<i>M</i> = Al, Sc, V, Cr, Fe, Ga, In) and CsCrTi_0.5(MoO₄)₃: Structure and Physical Properties

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 CsCrTi0.5(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.