Electronic and structural properties of : A proposal about the role of Ti 3s and 3p states for ferroelectricity

We have investigated the role of the Coulomb repulsions between Ti 3s and 3p states and O 2s and 2p states in ferroelectric BaTiO3, using a first-principles calculation with optimized structures. It has been found that the Coulomb repulsions between Ti 3s and 3p x ( y ) states and O x ( y ) 2s and 2p x ( y ) states are closely related to the appearance of Ti ion displacement in tetragonal BaTiO3. The mechanism of the Ti–O Coulomb repulsions also seems to be consistent with the appearance of Ti ion displacement in rhombohedral BaTiO3. Our investigation suggests that the Coulomb repulsions between Ti 3s and 3p x ( y ) states and O x ( y ) 2s and 2p x ( y ) states have an important role in the appearance of the ferroelectric state in tetragonal BaTiO3.