Surface effect on the electrical and optical properties of barium titanate at room temperature

The surface effect on the electrical and optical properties of tetragonal barium titanate at room temperature is investigated theoretically by using a microscopic model based on the orbital approximation in correlation with the dipole--dipole interaction. Both the first-, second-, and third-order electronic polarizabilities were considered in this calculation in order to obtain accurate results for both the spontaneous polarization and refractive indices. All types of surfaces were studied, either being a- or c^±-surfaces (both BaO- and TiO₂-terminated). The spontaneous polarization is drastically reduced near the c-surfaces while it remains almost unchanged near the a-surfaces. Furthermore, both the a- and c^±-surfaces show the tendency to deeply reduce the refractive index for light polarized perpendicular to the surface.