Cobaltite-related phases

The cobaltite phases show a similar complexity to the manganites and ferrites described previously. Sr COjO is a brownmillerite with Co in both octahedral and tetrahedral coordination. Careful oxidation of the brownmillerite allows a series Sr Co Oj j to form analogous to those in the SrjFePj j system. Brownmillerite represents the n=2 phase and SrCoOj the n=°° form. Series members with n=4,5, 6,7 and 8 have been reported. 

The cobaltites LnBaCOjOjjQ, with Ln being Y, La, Pr, Nd, Sm, Eu, Gd, Tb and Dy, have been widely studied. The phases have stmctures similar to that of orthorhombic PrBaCo Oj space group Pmmm (47), a=0.39049 run, b=0.78737 nm, c=0.76084 nm, with idealised unit cell of dimensions a a, b 2a, c 2a. In common with the majority of perovskite-related phases, most show structural changes at higher temperatures or with changing oxygen stoichiometry. 

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The formula, structure, and chemical bonding of tetradymite, Bii4Tei3S8 and the phase Bii4Tei5S6. American Mineralogist 60 (1975) 994—997. Covalent chemical bonding of transition metals in pyrite, cobaltite, skutterudite, millerite, and related minerals. Can. Mineral. 16 (1978), 447-452. 

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