Phase transitions in mixed Jahn-Teller systems with competitive interactions

Phase diagrams of mixed crystal systems exhibiting the cooperative Jahn-Teller effect are investigated. The competition of Jahn-Teller interaction with a) the preference energy of cation distribution over nonequivalent sublattices or b) stabilization energy of 3d-ion valence configuration is considered. The developed model enables to explain the nature of equilibrium and metastable states, the variety of phase diagrams and its special features in crystals with the competing interactions.