La2CuO4+δ having various δ values was prepared by the KMnO4 oxidation method in aqueous solutions at 333 K. Some samples oxidized in concentrated KMnO4 solutions underwent spinodal decomposition resulting in products having δ∼0.01 and δ∼0.22. The former showed a superconducting transition at ∼ 14 K, the latter at 40 K. The partial molar enthalpy of excess oxygen up to ∼ -57 kJ/mol O was obtained for La2CuO4+δ by high-temperature drop calorimetry. This value suggests that La2CuO4+δ is, disregarding the spinodal decomposition, thermodynamically stable in oxygen fugacities less than 1 atm at room temperature.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering