Compatible phases of the Y₂O₃–CuO–Cu₂O system in air

The phase diagram of the Y₂O₃–CuO–Cu₂O system was constructed as a function of temperature in air by means of thermal analysis and x-ray diffraction. The phase Y₂Cu₂O₅ was found to be stoichiometric and melted peritectically at about 1110 °C. A new intermediate phase with the composition YCu₂O_2.5 was discovered. It exists between 990 and 1105 °C in air and quenching did not preserve it to room temperature. High temperature x-ray diffraction established its pattern and confirmed its peritectic decomposition. Above 1110 °C YCu₂O_2.5 consists of Y₂O₃ and liquid. The results of this system are shown on a ternary system as well as on a pseudo-binary phase diagram. The solid state reactions were established. Melting occurs with isothermal oxygen loss or gain, depending on the initial composition.