Crystallographic site swapping of La3+ ion in BaA′LaTeO6 (A′ = Na, K, Rb) double perovskite type compounds: diffraction and photoluminescence evidence for the site swapping

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 P2(1)/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'O-6 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 (D-5(0)-F-7(2)) transition in the Rb compound compared to the Na compound indicates that Eu3+ ion resides in the centrosymmetric octahedral environment in the Rb compound.