Microscopic model for a ferroelectric glass

Abstract

This paper explores the concept of a ferroelectric glass and finds no fundamental objection to the concept. The essential ingredient is a dielectrically soft local atomic configuration which remains identifiable, though possibly badly distorted, in the glassy matrix. A specific model of such a glassy phase is constructed and a simple statistical theory developed to determine the necessary conditions favoring a dielectric instability. Since the essential "destabilizing" forces are of long range (the electric dipolar forces) the required averages can be performed explicitly even in ignorance of the local microscopic details of the structure. We conclude that a dielectric instability in a dielectrically soft glass can certainly not be excluded by these arguments, particularly for systems in which the basic soft unit has a high degree of symmetry in its "prototype" or undistorted form (such as the $B{\mathrm{O}}_6$ unit in the $\mathrm{AB}{\mathrm{O}}_3$ crystalline ferroelectrics). The concept of a ferroelectric glass is in no way related to that of a ferroelectric ceramic, the properties of which are very closely related to those of the parent single crystal.