Perovskite

Oxides with a perovskite structure yield many commercial ferroelectrics (materials that possess a net macroscopic polarization switchable under external electric field). The structure of these oxides, having a general formula ABO3, can be represented as a network of corner-sharing oxygen octahedra with higher-charge cations B located inside these octahedra and lower-charge cations A occupying the cavities between the octahedra. Typically the spontaneous polarization originates from the concerted off-centering of cations B, which generates an electric dipole. This polarizing behavior occurs in a classical ferroelectric material BaTiO3. However, some perovskite materials, such as PbTiO3 exhibit off-centering of both A (Pb) and B (Ti) cations, which then results in even larger values of electric polarization. The theoretical calculations performed in this paper demonstrate that a ferroelectric behavior in BaTiO3 and PbTiO3 results from hybridization between the electrons on the titanium and oxygen atoms, which overcomes the repulsive interatomic forces and stabilizes large off-centering of Ti. In PbTiO3, the effect is enhanced by the additional Pb-O hybridization.

Reference:
R. E. Cohen, “Origin of Ferroelectricity in Perovskite Oxide,” Nature, 358, 136 (1992)

Oxides with a perovskite structure yield many commercial ferroelectrics (materials that possess a net macroscopic polarization switchable under external electric field). The structure of these oxides, having a general formula ABO3, can be represented as a network of corner-sharing oxygen octahedra with higher-charge cations B located inside these octahedra and lower-charge cations A occupying the cavities between the octahedra. Typically the spontaneous polarization originates from the concerted off-centering of cations B, which generates an electric dipole. This polarizing behavior occurs in a classical ferroelectric material BaTiO3. However, some perovskite materials, such as PbTiO3