Optical properties of Na0.5Bi0.5TiO3 crystals

Abstract

We report some peculiarities of behavior of domain structure and birefringence ∆n of Na_0.5Bi_0.5TiO₃ crystals. Polarization-optical methods are used to study the domain structure and the birefringence ∆n in temperature interval 25°C÷520°C and axial pressure interval 2.5÷60 bar. Single domain state is achieved by application of axial pressure along [100] and [110] directions at temperature near 500°C. Application of axial pressure ~50 bar along [100] direction leads to switching of the samples into anisotropic single domain state. While application of axial pressure ~0.5 bar along [110] direction results in exposition of visually isotropic state and the state is preserved during a cooling process in temperature interval ~500°C÷240°C. In both cases the anisotropic single domain state is observed at room temperature. It is shown that f axial pressure (2.5÷25 bar) application along [110] direction at room temperature leads to a significant increase of the birefringence. It is supposed that both the peculiarities of Δn behavior and the linear behavior of Δn = f(p) are associated with presence of the nanoregions with various orientations of optical indicatrices and their involvement into the orientation process under the action of axial pressure.