Strain derivatives of the static and high-frequency dielectric constants of rubidium and cesium halides

Abstract

The strain derivatives of the static and high-frequency dielectric constants of rubidium and cesium halides have been calculated using the two ion polarizable shell model and the theoretical expressions of Srinivasan. The details of the model used and the relevant theoretical expressions are given. The relative magnitudes of the different elements of the strain derivative tensor is clearly seen to depend on the arrangement of the nearest neighbours. In the rubidum halides the calculated pressure derivatives of the static dielectric constant are in reasonable agreement with experiment while in cesium halides the calculated values are larger than the experimental ones. The strain optical constants calculated for the rubidium and cesium halides are in reasonable agreement with available experimental data. It is pointed out that the large contribution from overlap forces to the anisotropy in the polarizability arising from strain is fairly well represented by this simple shell model.