Theory of anisotropic oxygen polarizability in the tetragonal phase of PbTiO3

The optical anisotropy of the tetragonal phase of PbTiO3 is discussed accor ding to the point-dipole approach. In this microscopic model, we have takin g into account of the electronic polarization and the lattice deformation a nd it is shown that anisotropic electronic polarizabilities are the dominan t source of the optical properties of PbTiO3. This anisotropy is attributed to the O-z oxygen ion and it is due to the Ti-Oz and Pb-Oz overlap in the tetragonal phase. By analyzing the optical refractive index data of PbTiO3 at 0.589 mu m, we have determined the temperature dependence of the oxygen polarizabilities. Based on the dispersion data of the refractive index of PbTiO3, the dispers ion of the oxygen polarizabilities are similarly calculated at room tempera ture.