Thermodynamic reassessment of the Cu-O phase diagram

Parts of the copper-oxygen equilibrium phase diagram were reassessed using the calculation of phase diagram technique (CALPHAD). The model parameters were optimized to yield the best fit between calculated and experimentally determined phase equilibria at elevated oxygen pressures up to 11 MPa. The Cu-O liquid phase is represented by the two-sublattice model for ionic liquids containing copper on the cation sublattice with formal valences of Cu+1, Cu+2, and Cu+3. The presence of Cu+3 ions in the liquid phase, corresponding to a formation of Cu2O3 species, was the key assumption of this model. Congruent melting of CuO at 1551 K under an oxygen pressure of ∼126.8 MPa is predicted, which is considerably below previous theoretical values.