Investigation of electronic band structure and optical properties of AgNbO3 and AgTaO3 crystals

In this dissertation, the electronic energy band structure, density of states (DOS) and optical properties of AgNbO3 and AgTaO3 crystals in the paraelectric cubic and tetragonal phase were investigated by using density functional theory within the local density approximation for exchange-correlation for the first time. The band structure shows an indirect band gap of 1.533 eV (AgNbO3 in cubic phase), 1.621 eV (AgNbO3 in tetragonal phase) and 1.537 eV (AgTaO3 in cubic phase) at (M-?) point in the Brillouin zone. The linear photon-energy dependent dielectric functions and some optical properties such as the absorption coefficient, extinction coeffcient, refractivity index, energy-loss function and reflectivity are calculated under the scissor approximation for both AgNbO3 and AgTaO3. The effective number of valence electrons and the effective optical dielectric constant are calculated for both crystals. We have also made some comparisons with related experimental and theoretical data which is available.