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Synthesis, Structure, and Physical Properties of Cobalt Perovskites: Sr3CoSb2O9 and Sr2CoSbO6−δ

✍ Scribed by Vicent Primo-Martı́n; Martin Jansen

Publisher
Elsevier Science
Year
2001
Tongue
English
Weight
226 KB
Volume
157
Category
Article
ISSN
0022-4596

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✦ Synopsis

The perovskites Sr 3 CoSb 2 O 9 , Sr 2 CoSbO 6 , and Sr 2 CoSbO 5.63 have been synthesized in polycrystalline form by solid state reactions from acetate precursors as obtained by freeze-drying. The crystal structure of insulating Sr 3 CoSb 2 O 9 has been re5ned from X-ray data by the Rietveld method and was found to be orthorhombic (Immm) with a ‫؍‬ 5.6411(1) A > , b ‫؍‬ 5.6610(1) A > , c ‫؍‬ 7.9829(2) A > . From the molar susceptibility curves an e4ective magnetic moment eff ‫؍‬ 5.39 B and a spin-glass transition at ca. 6 K are deduced. The semiconducting perovskite Sr 2 CoSbO 6 was synthesized by applying an elevated O 2 pressure (3 kbar), and Co exclusively in the oxidation state ؉3 was attained. The Rietveld re5nement of this compound has revealed a rhombohedral cell (R3 m) with a ‫؍‬ 5.5992(2) A > and c ‫؍‬ 13.6609(2) A > and partial order (77%) of the B cations. An e4ective magnetic moment per formula unit of eff ‫؍‬ 3.83 B and a spin-glass transition at ca. 47 K were observed. A semiconducting and oxygen-de5cient perovskite, Sr 2 CoSbO 5.63 , was obtained by annealing Sr 2 CoSbO 6 at 9503C in Ar. The Rietveld re5nement proved it to be a double-cubic perovskite (Fm3 m) with a ‫؍‬ 7.9658(1) A > , and a higher order of Co and Sb at the B sites (84%) was found, due to the formation of Co 2؉ . From the magnetic susceptibility data an e4ective moment of 4.85 B and a spin-glass transition at ca.17 K were deduced.

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