The microscopic mechanism of spontaneous polarization and refractive indices in 180 ferroelectric domain walls of tetragonal Barium titanate (BaTiO 3 ) is discussed by using a microscopic model. This model bases on the orbital approximation in correlation with the dipole-dipole interaction due to the local field acting on all constituent ions within the domain wall. It is found that the behavior of both the spontaneous polarization and the refractive indices depends on the thickness of the domain wall which was varied between 5 and 20 A. Moreover, the spontaneous polarization shows a hyperbolic tangent shape for domain walls of a larger thickness which then vanishes at the center of the domain wall. The refractive indices suggest the domain wall to act like a biaxial crystal resulting in refractive index profiles of a Gaussian shape for domain walls of $20 A. This dramatically affects optical transmission through the domain wall especially for light being polarized parallel to the domain wall.
The microscopic mechanism of refractive indices, birefringence and spontaneous polarization of BaTiO 3 and KNbO 3 in the tetragonal phase is discussed by using a microscopic model. In this model, we have taken account of a quantum method based upon the orbital approximation and the dipole±dipole interaction due to the local field acting on the constituent ions. It is found that the electronic polarizabilities play a major role in these calculations and that the obtained results of the refractive indices, birefringence dn and spontaneous polarization are in good agreement with the experimental data.
We present an approach to inspecting the electro-optical properties of a ferroelectric crystal on the nanometer scale by applying a confined electric field E between a pointed optical fiber and the sample under investigation. Monitoring the optical transmission of barium titanate (BaTiO3) provides a complete image of the ferroelectric domain distribution in a single scan, including also antiparallel domains. The spatial resolution of ∼250 nm in this experiment is determined by the confinement of the electric field.
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