Low frequency dielectric relaxation in oxidic pyrochlores Cd2Nb2O7and Cd2Ta2O7

Abstract

Electric permittivity of Cd₂Nb₂O₇ and Cd₂Ta₂O₇ single crystals was investigated in the frequency region of 1 kHz-1 MHz. A low-frequency dielectric relaxation in these isostructural pyrochlores is observed over the whole temperature region from 90 to 300 K, but only below phase transitions. The relaxation results from thermal displacements of the “seventh” oxygens with respect to Cd²⁺ ions of the (CdO₈)^n- polyhedra. In Cd₂Nb₂O₇, the dielectric relaxation is also determined by thermal vibrations of domain walls in ferroelectric phase.