Members of the series Ba2M2-x, Cux O4+δ, M = In, Sc (0 ≤ x ≤ 1), have been synthesised by solid-state reaction methods and products characterized by powder X-ray diffraction (PXD). Selected compounds have been annealed under oxygen at 1 atm and oxygen stoichiometries for unannealed and oxygen annealed samples have been calculated following thermogravimetric analysis (TGA). Structures for M = In, x = 0, 0.5, 1 and M = Sc, x = 1 were determined by Rietveld analysis of PXD data. Ba2In2O5 has been shown to crystallize in the orthorhombic space group Ibm2 (Brownmillerite structure) with a = 6.0956(1) Å, b = 16.7112(3) Å c = 5.9601(1) Å. The copper-containing phases adopt a tetragonal “doubled perovskite” structure built up of copper-substituted BaInO2.5 cubes. The copper coordination and oxidation state can be controlled by varying the oxygen level of the structure.
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