Abstract
The perovskites Sr3CoSb2O9, Sr2CoSbO6, and Sr2CoSbO5.63 have been synthesized in polycrystalline form by solid state reactions from acetate precursors as obtained by freeze-drying. The crystal structure of insulating Sr3CoSb2O9 has been refined from X-ray data by the Rietveld method and was found to be orthorhombic (Immm) with a=5.6411(1) Å, b=5.6610(1) Å, c=7.9829(2) Å. From the molar susceptibility curves an effective magnetic moment μeff=5.39μB and a spin-glass transition at ca. 6 K are deduced. The semiconducting perovskite Sr2CoSbO6 was synthesized by applying an elevated O2 pressure (3 kbar), and Co exclusively in the oxidation state +3 was attained. The Rietveld refinement of this compound has revealed a rhombohedral cell (R3m) with a=5.5992(2) Å and c=13.6609(2) Å and partial order (77%) of the B cations. An effective magnetic moment per formula unit of μeff=3.83μB and a spin-glass transition at ca. 47 K were observed. A semiconducting and oxygen-deficient perovskite, Sr2CoSbO5.63, was obtained by annealing Sr2CoSbO6 at 950°C in Ar. The Rietveld refinement proved it to be a double-cubic perovskite (Fm3m) with a=7.9658(1) Å, and a higher order of Co and Sb at the B sites (84%) was found, due to the formation of Co2+. From the magnetic susceptibility data an effective moment of 4.85μB and a spin-glass transition at ca.17 K were deduced.
Published Version
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