Theory of dielectric properties of ionic crystals under hydrostatic pressure

Abstract

The dielectric behavior of typical ionic crystals, viz. alkali halides under hydrostatic pressure has been studied employing the shell model and the exchange-charge-polarization model originally formulated by Dick and Overhauser. It is observed that the simple shell model is not capable of explaining the dielectric properties of alkali halides. The effect of the exchange-charge polarization has been incorporated into the shell model, and the exchange-charge shell model thus developed is employed to evaluate the strain derivatives of dielectric constants. The volume dependence of the effective-charge parameter has been discussed within the framework of various dielectric models. The calculations presented in this paper reveal the necessity of considering the effect of exchange-charge polarization. A comparison of theoretical and experimental values of the strain derivatives of the Szigeti effective-charge parameters has been presented.