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Double perovskite type compounds of the formula BaA'LaTeO6 (A' = Na, K, Rb) were synthesized by solid state route and their crystal structures were determined by Rietveld analysis using powder X-ray diffraction and neutron diffraction data. Na compound crystallizes in the monoclinic system with P21/n space group whereas, K and Rb compounds crystallize in Fm3m space group. All the three compounds show rock salt type ordering at B site. Crystal structure analysis shows that La ion occupies A site in Na compound whereas, it occupies B site in K and Rb compounds according to the general formula of AA'BB'O6 for a double perovskite type compound. Effect of this crystallographic site swapping of the La ion was also observed in the photoluminescence study by doping Eu3+ in La3+ site. The large decrease in the intensity of the electric dipole (5D0-7F2) transition in the Rb compound compared to the Na compound indicates that Eu3+ ion resides in the centrosymmetric octahedral environment in the Rb compound. [ABSTRACT FROM AUTHOR]

The ground state structural, electronic, optical, elastic and thermal properties of the copper thallium chalcogenides (CuTlX2: X=S, Se, Te) in the body centered tetragonal (BCT) phase have been studied using the accurate full potential linearized augmented plane wave (FP-LAPW) method. We have reported the electronic and optical properties with the recently developed density functional theory of Tran and Blaha and this theory are used along with the Wu-Cohen generalized gradient approximation (WC-GGA) for the exchange-correlation potential. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, were calculated for photon energies up to 40 eV. The elastic constants at equilibrium in BCT structure are also determined. The thermodynamical properties such as thermal expansion, heat capacity, Debye temperature, entropy, Gruneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures and pressures and the silent results were interpreted. Hardness of the materials was calculated for the first time at different temperatures and pressures. [ABSTRACT FROM AUTHOR]