Electrostatics of the ferroelectric phases of BaTiO3

Extensive theoretical calculations are reported here on the electrostatics of the three ferroelectric phases of BaTiO₃ using the static polarizable point-ion model. For each structure the following quantities have been calculated: monopole and dipole fields at ionic sites, field gradients, spontaneous polarization, high frequency dielectric constant and the Coulomb energy terms. The parameters of the model have been fitted on the basis of the experimental information on the tetragonal structure and then treated as constants for all the studied structures. The use of the experimental positional parameters of the orthorhombic structure gives such exceptional behaviour for all the calculated quantities that a redetermination of the structural parameters for this phase is suggested. Numerical study of the changes in the Coulomb energy as a function of the macroscopic depolarization potential demonstrated that the most stable state is achieved with the value zero for the potential.