The Microscopic Theory of Photoferroelectric Phenomena

Abstract

It is well known that the mechanism of phase transitions in crystals is associated with instability of atomic vibrations. In particular, the mechanism of ferroelectric phase transitions in contemporary dynamic theory is conditioned by the instability of one of the transverse optical vibrations at the center of the Brillouin zone, and the anharmonicity of the corresponding vibration branch is considered to be responsible for the instability. This mechanism was first suggested by GINSBURG [29] and COCHRAN [3.1], who demonstrated the agreement between this microscopic approach and the thermodynamic theory of ferroelectrics. Before proceeding to the specific features of the dynamic theory of ferroelectric semiconductors we shall consider briefly the pecularities of optical vibrations in a ferroelectric at k = 0 and their relationship with the ferroelectric phase transition.