First-principles study on the electronic and optical properties of Na0.5Bi0.5TiO3 lead-free piezoelectric crystal

First-principles calculation is used to study the structural, electronic, and optical properties of Na0.5Bi0.5TiO3 (NBT) lead-free piezoelectric crystal. The band structure calculation reveals that NBT has a direct band gap of 2.1 eV. The calculated imaginary part of dielectric function indicates interband transition mainly from O 2p valence bands to Ti 3d and Bi 6p conduction bands in the low-energy region. The calculated absorption spectrum is in agreement with the available experimental data. Based on the fit of the result of optical abruption spectrum, the optical band gap is estimated to be 3.03 eV. Other optical constants, such as refractive index, extinction coefficient, energy-loss spectrum, and reflectivity are discussed in details. Those found show that NBT has the potential applications in optoelectrics.