Abstract:Mathematical principle and method for the calculation of subsolidus phase relation diagrams of the quasi-ternary system YO_1.5-BaO-CuO were developed, and the corresponding mathematical model was established. Subsolidus phase relation diagrams of this system at different temperatures were calculated from thermodynamic data. The calculated results showed that in Y-Ba-Cu-O system BaCuO₂ and Y₂BaCuO₅ are thermodynamically stable at room-temperature, and Y₂Cu₂O₅ and YBa₂Cu₃O_6.5 also become stable at temperatures higher than 300 ℃ and 750 ℃ respectively. The calculated results are in good agreement with those from experiments.

Key words: superconductor,  yttrium-barium-copper-oxygen system,  phase diagrams