Orientation polarization of defect pairs in crystals

Abstract

The orientation polarization of pairs of defects in crystals is usually treated with a simple model of non-interacting pairs subject only to the applied field, without internal field corrections, and with the defects confined to nearest or at the most next-nearest neighbour positions. In the present paper, an expression for the orientation polarization is developed for a more general model. Interactions among the pairs are treated in the Onsager approximation. Internal field corrections arising from the fact that the polariza-bilities at the defect sites differ from those of the normal ions are included. Extended configurations for the pair are allowed. Sastry and Srinivasan (1963) have observed dielectric relaxation in pure KCl near the melting point which they attribute to vacancy pairs. The simple theory requires too many pairs to account for the data. The present theory also fails in this respect, and it is concluded that the problem of vacancy pairs cannot be treated on the basis of discrete pairs interacting only through an averaged internal field. For impurity vacancy pairs, the several refinements to the simple theory tend to cancel one another, thus accounting for the success of the simple theory in fitting experimental data.