Some physical properties of calcia and yttria stabilized ThO2 ceramics

Abstract

In this paper the density, electrical conductivity, and dielectric permittivity of vacant ceramics of Ca x Th1−x O2−x and Y x Th1−x O2−x /2 type, respectivelly, were investigated as functions of temperature, frequency, and composition of these systems. The densityϱ drops with increasing calcium or yttrium amount, respectively. In the ThO2-CaO system this is in agreement with the mechanism of formation of vacant phase Ca x Th1−x O2x . The decrease of porosity in the ThO2-Y2O3 system with increasing yttrium content can be due various factors which influence the mobility of Y3+ ions and, thus, also the formation of pores. The investigation of transport numbers has shown that whilst the Ca x Th1−x O2−x phase under our experimental conditions is essentially p-type conductor, the Y x Th1−x O2−x/2 phase is essentially ionic conductor. The transport of ion carriers is a diffusion-like process which has activation energy 1·28 to 1·16eV in the Ca x Th1−x O2−x phase and 1·28 to 1·06 in the Y x Th1−x O2−x /2 phase, respectively. The association of impurity ions with anion vacancies provides the maxima in conductivity isotherms. The relative dielectric permittivity ɛ′ of the vacant phase Ca x Th1−x O2−x ranges from 19·2 to 36·2, in the phase Y x Th1−x O2−x /2 from 19·2 to 103, depending on temperature, frequency, and composition of these systems.