The piezo-optical effect in Na0.5Bi0.5TiO3 crystals

The work reports some aspects of the effect of applied axial pressure on birefringence in Na0.5Bi0.5TiO3 crystals, which have peculiarities of the macroscopic properties in a large extent due to the coexistence of nanoregions of different phases in a wide temperature range. The birefringence ∆n is investigated by the polarization-optical method in temperature range 25–500 °C. The temperature behavior of spontaneous birefringence in single domain crystals is associated with the structure phase transitions and the “isotropization point” and depend on the way used to switch the sample into the single domain state. Also, the influence of axial pressure on ∆n of samples preliminary switched to the single domain state is studied. It is discovered that application of the axial pressure (6.25–16.6 bar) along [100] direction does not show significant changes of birefringence in temperature range 25–500 °C. While the application of axial pressure (2.5–25 bar) along [110] direction leads to exhibition of significant piezo-optical effect. It is supposed that both the presence of polar nanoregions and changes of their orientation make contribution to the piezo-optical effect.