Ab initio study of structural, electronic and optical properties of the Bi12TiO20 sillenite crystal

It is presented an analysis of some important structural, electronic and optical characteristics of the pure Bi12TiO20 sillenite crystal, based on the ab initio calculations of its electronic structure and complex dielectric tensor. The band gap is calculated to be 2.3 eV and found to be direct. The contributions to the valence band top and conduction band bottom come predominantly from O 2p- and Bi 6p-states, respectively. The optical absorption spectrum is calculated and interpreted in terms of electronic band structure for incident radiation energy up to 40 eV. The principal absorption occurs within the energy range from 2.5 to 10 eV, originating manly from the electronic transitions from the O 2p- to the Bi 6p-states.