PHASE-EQUILIBRIA AND STABILITY OF SUPERCONDUCTORS IN THE Y-BA-CU-O SYSTEM

The thermodynamic properties of nonsuperconducting phases in the Y-Ba-Cu-O system are critically reviewed and those of YBa4Cu3O8.5 are estimated. With the aid of these data, subsolidus phase equilibria are calculated for a wide range of oxygen pressures and temperatures, and stability fields of the 123, 124, and 247 superconductors are constructed. It is shown that the orthorhombic 123 phase is thermodynamically unstable at all temperatures and compositions. The stability diagrams obtained in this study, can be readily used for optimization of synthesis conditions of the superconducting phases in the Y-Ba-Cu-O system.