ORIGIN OF FERROELECTRICITY IN PEROVSKITES: THE PRINCIPAL PROBLEMS FROM A THEORETICAL PERSPECTIVE

Much progress has been made in understanding perovskite ferroelectrics and ferroelectric phase transitions, and the number of theoretical and experimental studies continues to mushroom. We now know that the origin of ferroelectric phase transitions in oxides is due to the underlying anharmonic potential surfaces which are caused by softening of the short-range repulsions by covalent hybridization so that the atoms can move off-center and towards each other. Nevertheless, we are still far from our goals of usefully predicting ferroelectric behavior. There is also now much experimental and theoretical support for the eight-site model in perovskite oxides. An understanding of the fundamental origins of ferroelectric behavior should lead us more rapidly towards the ability to predict and tune ferroelectrics from first-principles.