Electric and optical properties of the 90° ferroelectric domain wall in tetragonal barium titanate

The electric and optical properties within 90degrees ferroelectric domain walls of tetragonal barium titanate (BaTiO3) are theoretically examined at room temperature using a microscopic model which is based on the orbital approximation in correlation with the dipole-dipole interaction. We find that when perpendicularly crossing the domain wall, the variation of the spontaneous polarization and refractive indices does not depend on the thickness of the domain wall which varies between 1.5 and 2.5 nm. Moreover, within the domain wall, the refractive indices n(2) and n(3), corresponding to light polarized parallel to the principal axes y(p) and z(p), respectively, exhibit an important transition in which n(2) transforms from the ordinary to the extraordinary state, while n(3) behaves oppositely to n(2).