Mechanisms of the ferroelectric and structural phase transitions. structural distortions in perovskites

Abstract

The symmetry aspects of probable distortions in perovskite-like crystals are discussed. Four soft modes of the lattice which are condensed at different conditions lead to the distortions. The superpositions of the independent distortions (tilts and polar displacements) are considered and the symmetry of the phases is derived. The sequences of phase transitions in the ABX3-crystals are analysed.