Lattice-Dynamics Approach to the Theory of Elastic Dielectrics with Polarization Gradient

Abstract

A continuum theory of elastic dielectrics including polarization gradient is obtained as the long-wave approximation of a theory of lattice dynamics for the shell model of cubic ionic crystals. The additional energy associated with the formation and relaxation of a free surface is obtained by considering the unbalanced charges and dipole moments on the surface. The material coefficients of the continuum theory are related to the lattice properties, and their numerical values are calculated for NaI, NaCl, KI, and KCl. The surface energy density of a free half-space predicted by the continuum theory is compared with experimental results as well as other theoretical results based on discrete models.