Oxygen nonstoichiometry and thermo-chemical stability of La _0.6Sr _0.4CoO _3-δ

The oxygen nonstoichiometry of La _0.6Sr _0.4CoO _3-δ has been the topic of various reports in the literature, but has been exclusively measured at high oxygen partial pressures, pO ₂, and/or elevated temperatures. For applications of La _0.6Sr _0.4CoO _3-δ, such as solid oxide fuel cell cathodes or oxygen permeation membranes, knowledge of the oxygen nonstoichiometry and thermo-chemical stability over a wide range of pO ₂ is crucial, as localized low pO ₂ could trigger failure of the material and device. By employing coulometric titration combined with thermogravimetry, the oxygen nonstoichiometry of La _0.6Sr _0.4CoO _3-δ was measured at high and intermediate pO ₂ until the material decomposed (at log(pO ₂/bar)≈-4.5 at 1073 K). For a gradually reduced sample, an offset in oxygen content suggests that La _0.6Sr _0.4CoO _3-δ forms a super-reduced solid solution before decomposing. When the sample underwent alternate reduction-oxidation, a hysteresis-like pO ₂ dependence of the oxygen content in the decomposition pO ₂ range was attributed to the reversible formation of ABO ₃ and A ₂BO ₄ phases. Reduction enthalpy and entropy were determined for the single-phase region and confirmed interpolated values from the literature.