THEORY OF FERROELECTRICITY IN THE TETRAGONAL PHASE OF PURE AND CO-DOPED BATIO3 DUE TO THE LATTICE DEFORMATION

The ferroelectricity in the tetragonal phase of pure and Go-doped BaTi O3, BaTiO3:Co, is discussed quantitatively from the dipole-dipole inte raction caused by the strong local field acting on the constituent ion s. In this microscopic model, only the Ti ions situated at the center of the lattice are assumed to have the spontaneous shift. The ferroelc tric-paraelectric phase transition in BaTiO3 is also analyzed. It is f ound that the ferroelectricity and the order of the phase transition i n BaTi03 are in good agreement with the experimental data.