Electronic and optical properties of double perovskites Ba2-xSrxBiSbO6 (x=0,1)

The electronic and optical properties of ordered double perovskites Ba2BiSbO6 and BaSrBiSbO6 have been studied using density functional theory within the generalized gradient approximation. The electronic structure calculation shows these materials to be semiconducting with an indirect band gap of 1.68 eV for Ba2BiSbO6 and 1.67 eV for BaSrBiSbO6 with spin-orbit coupling taken into account. With hybrid-functionals, the band gap rises to an insulating domain for both materials. In the density of states and band structure around the valence band maximum and conduction band minimum, the main contributions are from O-2p, Bi-6s, Bi-6p, and Sb-5s states. From optical calculations, the optical band gap obtained from the imaginary part of dielectric constants agrees fairly with the electronic band gap. Both Ba2BiSbO6 and BaSrBiSbO6 are found to be optically active in ultraviolet as well as visible regions of the incident photon energies. The noted optical response indicates these materials as possible candidates for opto-electronic devices.