The microscopic model of the displacive phase transition in solid solutions is considered. In the virtual crystal approximation the number of predictions for the concentrational dependence of the transition temperature is obtained. The solid solutions of improper ferroelastics are discussed.

Structural phase transitions in solid solutions.

The self-consistent phonon theory and the coherent potential approximation method are applied to investigate the displacive ferroelectric phase transitions occurring in the ternary solid solution. Especially, the substitutional disordered phonon system with both random diagonal and off-diagonal interactions has been dealt with and numerical computation has been made under different strengths of the atomic coupling. The results show that the interactions between different atoms greatly influence the properties of phase transitions in solid solutions and the anomalous relation between dielectric constant versus temperature can be explained. The new approach is shown to be able to offer a much more detailed description for the various solid solution systems.

Yumei Zhang

Papers

Off-diagonal coherent potential approximation and their application to PSZT systems