Band structure and optical properties of tetragonal BaTiO₃

The electronic band structure of ferroelectric BaTiO3 is determined according to the Slater and Koster interpolation scheme (1954) with nonorthogonal orbitals. The effects of a phase transition on the energy levels are studied. Some integrated functions, such as the density of states, the joint density of states and the imaginary part of the dielectric constant epsilon 2( omega ), are deduced from the band scheme. The moments of the optical spectrum related to epsilon 2( omega ) are computed and the results related to the empirical relations concerning the behaviour of the dielectric constant, with a constant optical frequency conductivity model. For T<Tc (Curie temperature), the transverse absorption coefficient alpha perpendicular to is higher than the longitudinal one alpha /sub /// and alpha perpendicular to / alpha /sub /// approximately=1.9.