Pretransitional Effects at Structural Phase Transitions

Heterogeneous coexistence of high- and low-temperature phases has been observed around structural phase transitions. We find that such intermediate states result from a cubic coupling term of the form e 1 ψ 2 in the free energy, with which the dilation strain e 1 can modify the effective temperature for the order parameter (tetragonal strain) ψ. We show that e 1 is asymmetrically induced in the high- and low-temperature phases, leading to elastic stabilization of tetragonally strained domains coherently embedded in the disordered matrix.