High-Temperature Dielectric Constant of Potassium Chloride

A dispersion of the dielectric constant of zone-purified potassium chloride has been observed at temperatures above 650°C and in the frequency range between one and ten megacycles/sec. The data are interpreted in terms of the Debye equations and the assumption that the dipoles are vacancy pairs. The activation energy for reorientation of a vacancy pair is found to be ${1.04}^{\pm 0.05}$ eV and the heat of formation of a vacancy pair is found to be ${1.34}^{\pm 0.07}$ eV. These quantities have been calculated by Tharmalingam and Lidiard as 1.15 and 1.28 eV, respectively. The dielectric data yield, however, an absolute number of vacancy pairs that is at least a factor of ten larger than is acceptable. Interfacial or Maxwell-Wagner types of polarization are excluded as explanations of the data.