High temperature properties of rare-earth tungstates RE2W2O9

Abstract

RE2W2O9 (RE=Ce, Nd, Pr, Sm, Eu, Gd and Tb) compounds have been prepared by a freeze-drying precursor method in order to explore their high temperature thermal properties by different techniques. Samples with Nd, Pr, Sm, Eu and Gd crystallize in the same monoclinic structure with space group P21/c. The thermal, X-ray diffraction, and electrical analysis reveal the existence of a reversible first order phase transition, which is accompanied by a sudden decrease of the unit cell volume and conductivity. A large thermal hysteresis of about 250°C is also observed during the heating and cooling processes. These materials exhibit low electrical conductivity of the order of 10−5Scm−1 at 800°C.