The electronic and structural properties of most of the high temperature superconducting copper oxides are highly dependent upon the oxidation conditions used to prepare the cuprate compounds. Until recently superconductivity had only been observed in highly oxidized compounds, however recent work has shown that under certain circumstances superconducting transitions can also occur in n-doped, reduced cuprates. In an effort to understand some of the chemical factors that lead to the stabilization of both oxidized and reduced cuprates, we have investigated the stability of several cuprates. In this paper we report our results on the metallic, non-superconducting BaLa4Cu5O13±δ (“145”) system.At high temperature most of the highly oxidized cuprates are reduced as oxygen is reversibly removed from the perovskite lattice and the Cu valence is lowered to ≤ 2. However, for compounds with the 145 stoichiometry there is no significant oxygen loss in “non-reactive” gases such as air, O2 or He, and even at 1000°C Cu is apparently stable in a valence state greater than 2.3+.
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