Inherent optical behavior and structural variation in Na _0.5Bi_0.5TiO₃-6%BaTiO₃ revealed by temperature dependent Raman scattering and ultraviolet-visible transmittance

Optical properties of Na_0.5Bi_0.5TiO ₃-6%BaTiO₃ (NBT-6%BT) single crystal have been studied by temperature dependent Raman and ultraviolet-visible spectra from 25 to 180 C. With increasing the temperature, the absorption edge approximately decreases from 3.13 to 3.04 eV. Moreover, abnormal changes of phonon mode and spectral transmission are observed at 83, 106, and 150 C, which can be unambiguously correlated with thermal evolutions of polar nano-regions and phase transition. It indicates that there is an inherent relationship between optical behavior and structural variation of NBT-6%BT, which provides a valid methodology to explore the phase transition of relaxor ferroelectric oxides.