Lattice Disorder in Some CaF2-Type Crystals

Abstract

The ionic conductivity of BaF2, SrF2, and SrCl2 single crystals doped with monovalent and trivalent cations has been investigated from 300°C to within 100°C of the melting temperature. These measurements correct the intrinsic conductivity of SrF2 and show a consistent trend in the slopes of the Arrenhius plots of the conductivity for these and other fluorides: both the activation energy for conduction and the resistivity decreases with a decrease in the melting temperature of the materials. A Koch—Wagner-type analysis of conductivity isotherms confirms an anion Frenkel thermal-disorder model for the fluorides. The type of disorder for SrCl2 could not be determined unambiguously, however. Values for the energy of formation of the intrinsic defects and their motion energies have been deduced from the slopes of the conductivity curves. Estimates of concentration of the thermal defects were made in each case.