Lattice dynamics of alkali halide crystals in relation to specific heat data

Abstract

An analysis of the dynamics of the alkali halides which allows for the polarizability of the ions and their ‘deformation’ by the overlap repulsion is presented. This represents a refinement of earlier work by other authors in which the ions are treated as rigid point charges. The analysis has been applied to KCl and used to calculate ‘effective’ Debye temperatures and the moments of the lattice vibrational spectrum. This analysis enables us to decide that, although the anion and cation polarizabilities are comparable, the ‘deformation’ takes place almost entirely on the anion. The results obtained from this last assumption also represent a considerable improvement on those derived from the ‘rigid ion’ theory, and indicate that short-range anion-anion interactions are significant in KCl.