Phase Transitions in Ionic Conductors

Abstract

Upon melting, the ionic conductivity σ of a salt generally shows a sharp increase, typically several orders of magnitude, to a liquid value of σ ~ 102 Ω−1. Crystals with superionic [7.1] or solid electrolyte phases, however, pass, either gradually or through a series of phase transitions, from normal ionic conductivity (σ < 0.1 Ω−1m−1) to liquidlike values while still solid. The purpose of this chapter is to examine the nature of the phase transitions between low- and high-conductivity phases in the light of modern understanding of critical phenomena. We show that analysis of the critical behavior near the transitions between the high and low ionic conductivity phases of these materials contributes to our understanding of the nature of ion-ion interactions, the role of lattice strain, the importance of phonon coupling to the ionic motion, and the degree of collectiveness involved in superionic conduction.KeywordsIonic ConductivityCritical BehaviorLandau TheoryLandau ModelSuperionic PhaseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.