The relation between the electrostriction and elastic and dielectric properties of the alkali halides

Abstract

Relations between the electrostriction and elastic and dielectric properties of the alkali halides have been derived. A linear relation is found between the electrostrictive coefficients on the one hand, and the elastic compliance tensor and third derivatives of the lattice energy on the other. To calculate the lattice energy the authors have considered the crystal in a polarized state. The polarizations alter the distances between the ions and induce dipoles, both of which influence the lattice energy. The energy of the crystal is split into the Coulomb energy and the repulsive potential. The Coulomb energy of one molecule is considered relative to all the other molecules in the crystal. The repulsive potential is assumed to extend only over nearest-neighbour ions. By splitting up the lattice energy, the influence of the Coulomb energy and the repulsive potential on the electrostriction can be calculated separately. The derived equations show that there is a relationship between the electrostriction coefficients and other elastic and dielectric properties, such as the dielectric constant, the refractive index, the elastic compliance tensor, the thermal expansion coefficient and the lattice constant. Results of the calculations show fair agreement with new measured values of the electrostriction coefficients. The theory could lead to a better understanding of the origin of electrostriction and be a support in the development of new materials suitable for practical applications.