Multiple phase transitions in perovskite structure ceramics: Structural transitions

Abstract

A Ginzburg-Landau theory for the multiple structural phase transition observed in the cuprate perovskite structure ceramics is developed. The order parameters Ai for each phase are defined in terms of the deformations which occur in each phase. In terms of the deformation, the expansion of the free energies is to the twelfth order. The theory can account for a second-order tetragonal to orthorhombic-I transition at high temperatures and a first-order orthorhombic-I to orthorhombic-II transition at lower temperatures. The criterion for the existence of a tricritical line is established. © World Scientific Publishing Company.