Mean field theories of sublattice melting in ionic crystals.

A number of materials with essentially ionic binding exhibit a transition in the solid state to a high conductivity state which has been identified with positional disorder of one of the ionic species. In this paper the contrasting roles of the disorder dependence of energy and entropy in determining the nature of the transition are examined within the mean field approximation at high point defect concentration. A generalization of the Mott-Littleton defect theory is used to illustrate the role of various physical characteristics such as polarizability, elastic properties, etc., and two types of phenomenological description of the transition are discussed. [ABSTRACT FROM AUTHOR]