Electronic states of perovskite-type oxides and ferroelectricity

A relation between B-site transition metal and ferroelectricity is investig ated in ABO(3) perovskite-type oxides. We focus on intensity of the covalen t bonds between the B-site atom and the oxygen octahedron and evaluate Harr ison's covalency parameter alpha. The density functional theory within the local density approximation is adopted to obtain the valence electron energ y levels of free atoms from which the covalency alpha is calculated. Strong correlation between the covalency alpha and the Curie temperature (T-C) is found. As the covalency alpha increases, T-C of ferroelectricity arises. I t is also noted that the hybridization between Pb 6p and O 2p is crucial fo r the high ferroelectricity of PbTiO3.