Thermodynamical Models for Phase Changes between Tetragonal and Cubic Phases in ZrO2-CeO2 Solid Solution

The Gibbs energies of cubic (c-) and tetragonal (t-) phases in pseudobinary solid solutions of Zr1-X Ce X O2 were assessed by two models. A regular solution model in which the Gibbs energy differences between c- and t-phases of end members were assumed to be linear functions of temperature, could not explain simultaneously the stable and metastable phase diagrams. A mathematical expression on the basis of Landau's theory for the second-order phase transition explained both of them.