Sr3TeO6 and Ba3TeO6: double perovskites with pronounced superstructures

Abstract

Abstract The orthotellurates (VI) of strontium and barium were synthesized at 1373 K in air by oxidation of TeO2 in a melt of SrBr2 and BaBr2, respectively. Their unprecedented structures were determined from room temperature single crystal X-ray diffraction data. Sr3TeO6, [F-1, Z = 32, a = 16.5338(2) Å, b = 16.6308(2) Å, c = 16.7112(3) Å, α = 90.031(2)°, β = 90.035(2)°, γ = 90.1370(10)°, R[F 2 > 2σ(F 2)] = 0.035, 19195 F 2 data, 375 variable parameters] and Ba3TeO6 [I41/a, Z = 80, a = 19.3878(10) Å, c = 34.909(2) Å, R[F 2 > 2σ(F 2)] = 0.034, 19576 F 2 data, 453 variable parameters] are eight- and 40-fold superstructures which can be described as a pseudo-cubic close-packing of [TeO6]6– octahedra with M 2+ (M = Ba, Sr) atoms located in the tetrahedral and octahedral voids. Sr3TeO6 and Ba3TeO6 are hettotypes of the cubic aristotype with the double perovskite structure crystallizing in space group Fm-3m. A comparative discussion of the crystal structures and their group-subgroup relations are given, including different approaches for the structure descriptions.