STUDIES OF THE P-T-X PHASE-DIAGRAM OF THE YBA2CU3O7+/-X SYSTEM UP TO 2800 BAR O2

Thermodynamic investigations (P-T-x phase diagram) of the YBa2Cu3O7±x-O2 system are performed for the first time up to high oxygen pressures. The P-T diagram is measured up to 2800 bar with parameter the composition (x). The Van't Hoff curves are not linear, indicating an appreciable dependence of the enthalpy of formation from oxygen pressure, particularly at the high contents of oxygen. Measurements of the P-x diagram with parameter the temperature are presented up to 100 bar. They show that under 100 bar oxygen, it is possible to avoid the orthorhombic to tetragonal phase transition up to the temperature of 1000°C.