Displacive Ferroelectric Phase Transitions with the Order-Disorder Component in Oxide Perovskites and Photo-Induced Ferroelectricity

Abstract

A microscopic electron-lattice theory of displacive ferroelectric phase transitions with an order-disorder component in the ABO3 type (A is alkaline, an earth alkaline ion, B is a transition metal ion) oxide perovskites has been developed further. The short-range electron-phonon interaction in BO 6 n −(n = 6,8) clusters and the long-range electron-lattice coupling in oxide perovskites are considered. The short-range electron-lattice coupling between electronic oxygen 2p and titanium 3d states leads to the static off-center displacements of the Ti ions in [111] directions (local ferroelectricity) above and below the ferroelectric phase transition temperature, which results in the order-disorder component of the phase transition. The displacive components of the ferroelectric phase transitions in BaTiO3 and SrTi18O3 are caused by the long-range electron-lattice p-d hybridization. The coupling of the displacive and order-disorder components is considered. The theory is supported by recent experimental data.