Oxidation thermodynamics of ErBa2Cu3O6 + x

Abstract The oxygen content, x in ErBa 2 Cu 3 O 6 + x was measured at oxygen pressures between 0.1 and 2000 mbar and at temperatures between 450 and 750°C. From the experimental data, the chemical potential, Δμ O ( x ), the partial molar enthalpy, Δ H O ( x ), and entropy, Δ S O ( x ) of oxygen in ErBa 2 Cu 3 O 6 + x were derived. The Er-substituted material qualitatively behaves like YBa 2 Cu 3 O 6 + x . The thermodynamic data are therefore discussed on the basis of two-dimensional lattice gas models proposed for YBa 2 Cu 3 O 6 + x which are able to describe the location of the orthorhombic-to-tetragonal phase transition. Since the comparison between model predictions and experimental data is extended to the chemical potential, as well as to the partial molar enthalpy and entropy, weaknesses of the model used become clearly visible.