Theory of strain derivatives of electronic and static dielectric constants of alkali halides and alkaline-earth fluorides

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Abstract
An analysis of the first-, second-, and third-order strain derivatives of electronic and static dielectric constants of alkali halides and alkaline-earth fluorides has been performed within the framework of the Clausius-Mossotti theory. The strain derivatives of the electronic dielectric constant are evaluated using Ruffa's theory of electronic polarizabilities. The lattice contribution to the strain derivatives of the static dielectric constant has been calculated using two potential forms for the short-range repulsive energy showing the inverse power dependence and the exponential dependence upon the interionic separation. The contribution arising from the Van der Waals dipole-dipole and dipole-quadrupole interactions has also been considered. The calculated values of the strain derivatives of the dielectric constants are compared with the available experimental data. It is found that the inverse power law for the short-range repulsive potential is more consistent with experimental facts. This prediction is consistent with recent investigations on the elastic properties of ionic solids.