Thermodynamic Evaluation for the Y ₂ O ₃ –BaO–CuO x System

The thermodynamic data for the Y 2 O 3 –BaO–Cu 2 O–CuO quaternary system were optimized from measured thermodynamic data. A two‐sublattice model for ionic solution was used to express the Gibbs free energy of the liquid phase, and a two‐sublattice regular solution model was used for the nonstoichiometric YBa 2 Cu 3 O 6+δ superconducting compound. The optimized thermodynamic data were used to calculate the phase diagrams of the Cu 2 O–CuO binary system and the CuO x –Y 2 Cu 2 O 5 and CuO x –BaCuO 2 quasi‐binary systems. The results were in good agreement with reported measured data. The liquidus projection and isothermal and vertical sections of the Y 2 O 3 –BaO‐CuO x quasi‐ternary system were calculated. The effect of oxygen pressure on some reaction temperatures was predicted by calculating them at various oxygen pressures, and the oxygen contents (6 +δ) in YBa 2 Cu 3 O 6+δ were calculated at various temperatures and oxygen pressures. The results were compared with experimental data.