Optical and Electronic Properties of Double Perovskite Ba2ScSbO6

Ba2ScSbO6 (BSS) has been synthesized in polycrystalline form by solid state reaction. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Riedvelt analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No. 225. Optical band-gap of the present system has been calculated using the UV-Vis Spectroscopy to be 4.2eV. A detailed study of the electronic properties has also been carried out using the Full-Potential Linear Augmented Plane Wave (FPLAPW) as implemented in WIEN2k. BSS is found to be a large band-gap insulator with potential technological applications, such as dielectric resonators and filers in microwave applications

Effects of octahedral tilting on the electronic structure and optical properties of $d^0$ double perovskites $mathbf{rm A_2ScSbO_6}$ ($mathbf{rm A=Sr, Ca}$)

With increasing temperature, ${rm Sr}_2{rm ScSbO}_6$ undergoes three structural phase transitions at approximately ${rm 400K}$, ${rm 560K}$ and ${rm 650K}$, leading to the following sequence of phases: $P2_1/n rightarrow I2/m rightarrow I4/m rightarrow Fmbar{3}m$, making it an ideal candidate to study the effects of octahedral tilting keeping other parameters fixed. To ascertain the isolated effects of octahedral distortions, the electronic and optical properties of the monoclinic $P2_1/n$ (at room temperature), monoclinic $I2/m$ (at ${rm 430K}$), tetragonal $I4/m$ (at ${rm 613K}$) and the cubic $Fmbar{3}m$ (at ${rm 660K}$) phases have been studied in terms of the electronic structure, dielectric constant, optical conductivity and electron energy loss spectroscopy using density functional theory. ${rm Ca}_2{rm ScSbO}_6$, on the other hand, shows only a $P2_1/n$ phase at room temperature and its properties have been been compared with the corresponding ${rm Sr}$ compound. UV-Vis spectroscopic studies of the optical properties of the room-temperature phase of these $d^0$ double perovskite have been performed and presence of large direct bandgap for both the compounds have been reported. The electronic bandgaps for the room temperature phases is found to be in good agreement with the corresponding experimental values obtained using the Kubelka-Munk function. Interestingly, in contrast to other Sc-based $d^0$ double perovskites, with increasing octahedral distortions, the effective $t_{rm 2g}$ bandwidth remains unaffected while the states forming the band change due to changes in unit cell orientation, leading to small effects on the electronic and optical properties.

Electronic Structure of Ordered Double Perovskite Ba2CoWO6

Ba2CoWO6 (BCoW) has been synthesized in polycrystalline form by solid state reaction at 1200C. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No 225) with the lattice parameter, a=8.210A. Optical band-gap of the present system has been calculated using the UV-Vis Spectroscopy and Kubelka-Munk function, its value being 2.45 eV. A detailed study of the electronic properties has also been carried out using the density functional theory (DFT) techniques implemented on WIEN2k. Importance of electron-electron interaction between the Co ions leading to half-metallic behavior, crystal and exchange splitting together with the hybridization between O and Co, W has been investigated using the total and partial density of states.