The first- and second-order strain derivatives of electronic dielectric constants in alkali halides

Abstract

An analysis of the first- and second-order strain derivatives of the electronic dielectric constants of alkali halide crystals is performed in terms of a bond-polarizability approach and Penns' model. The derivatives V( dϵ ∞ dV ) and V 2( d 2ϵ ∞ dV 2 ) are related to the second- and third-order nonlinear polarizabilities of crystal bonds. V 2( d 2ϵ ∞ dV 2 ) is considered in connection with the quadratic electro-optic effect. Results obtained suggest small changes in the third-order polarizability of the crystal bonds in different crystals. The assumption of the approximate constancy of the third-order polarizability provides a simple link of nonlinear phenomena with the crystal structure.