First-principles predictions of giant electric polarization

Giant electric polarization of more than 150 mu C/cm(2) is predicted for PbVO3 and BiCoO3 on the basis of the first-principles Berry-phase method. The stable crystal structure is tetragonally distorted with a large c/a ratio and significant ionic displacements breaking centrosymmetry. In PbVO3, the key factor that stabilizes such a highly distorted structure and realizes an insulating electronic structure, leading to giant polarization, is the coexistence of ferro-orbital and antiferro-spin orderings in the V4+ d(1) configuration. It is shown that the same electronic mechanism works also for BiCoO3 with Co3+ d(6) configuration.