THE 1ST-ORDER AND 2ND-ORDER STRAIN DERIVATIVES OF ELECTRONIC DIELECTRIC-CONSTANTS IN ALKALI-HALIDES

An analysis of the first- and second-order strain derivatives of the e lectronic dielectric constants of alkali halide crystals is performed in terms of a bond-polarizability approach and Penns' model. The deriv atives V(depsilon(infinity)/dV) and V2(d2epsilon(infinity)/dV2) are re lated to the second- and third-order nonlinear polarizabilities of cry stal bonds. V2(d2epsilon(infinity)/dV2) is considered in connection wi th the quadratic electro-optic effect. Results obtained suggest small changes in the third-order polarizability of the crystal bonds in diff erent crystals. The assumption of the approximate constancy of the thi rd-order polarizability provides a simple link of nonlinear phenomena with the crystal structure.