Optical dispersion and interband transition in Na_(0.5)Bi_(0.5)TiO_3-x%BaTiO_3 lead-free relaxor ferroelectric single crystals

摘要

Optical properties of A-site disordered Na_(0.5)Bi_(0.5)TiO_3-x%BaTiO_3 (NBT-xBT) single crystals with three typical compositions were studied systematically. Refractive index as a function of wavelength was measured by Spectroscopic ellipsometry, and modified Sellmeier dispersion equations were obtained by the least square fitting. High optical transmittance (65%) over a wide transparent region (from 400 to 6000 nm) has been found in NBT-7.5BT, much higher than that of NBT and NBT-5BT. Optical band gap energies were calculated using the absorption coefficient through Tauc equation. With increasing BT content, refractive index and absorption coefficient decrease, while transmission and band gap energy increase.