Study of Defect Reactions in Crystals by Means of Anelastic and Dielectric Relaxation

Abstract

A general theory of anelastic and dielectric relaxation processes has previously been developed for a single defect species which can exist in several crystallographically equivalent orientations. In the present paper, the occurrence of a reaction between different defect species is considered. It is shown that the existence of such a reaction introduces a mode of relaxation, called the “reaction mode”, which involves a net change in the concentration of each species, but no reorientations. This mode gives rise to relaxation of those compliance (or susceptibility) constants associated with stress- (or electric-) field components which are invariant under the symmetry operations of the crystal. A table of these components and the corresponding material constants is presented. The thermodynamic and kinetic theory for such relaxation processes is developed in general, and then considered for important special cases. The few examples in which the reaction mode has been studied are reviewed. Finally, an example (the Al–Na defect in α quartz) is given to demonstrate the value of studying the reaction mode.