Electronic and Structural Properties of ABO(3): Role of the B-O Coulomb Repulsions for Ferroelectricity

We have investigated the role of the Ti–O Coulomb repulsions in the appearance of the ferroelectric state in BaTiO [Formula: see text] as well as the role of the Zn–O Coulomb repulsions in BiZn [Formula: see text] Ti [Formula: see text] O [Formula: see text] , using a first-principles calculation with optimized structures. In tetragonal BaTiO [Formula: see text] , it is found that the Coulomb repulsions between Ti 3s and 3p states and O 2s and 2p states have an important role for the appearance of Ti ion displacement. In BiZn [Formula: see text] Ti [Formula: see text] O [Formula: see text] , on the other hand, the stronger Zn–O Coulomb repulsions, which are due to the 3s, 3p, and 3d (d [Formula: see text]) states of the Zn ion, have more important role than the Ti–O Coulomb repulsions for the appearance of the tetragonal structure. Our suggestion is consistent with the other ferroelectric perovskite oxides [Formula: see text] O [Formula: see text] in the appearance of tetragonal structures as well as rhombohedral structures.