High-pressure phase diagrams (1–3000 bar oxygen) of the (Y-Ba-Cu-O)-O 2 systems

Abstract

New data on the P- T- x phase diagram of the pseudobinary (Y-Ba-Cu-O)-O 2 system are presented. These data led to the discovery of two new bulk phase superconductors, YBa 2Cu 3.5O 7 − x ( T c ≈ 40 K) and YBa 2Cu 4O 8 ( T c ≈ 80 K). The region of thermodynamic stability of YBa 2Cu 3O 7 − x and of these new phases has been roughly determined, from the change of slope of the decomposition curve in the Van't Hoff diagram and from X-ray, energy dispersive X-ray analysis, susceptibility and high-accuracy chemical characterization. The T- x diagram shows for the first time the position of the oxygen-rich phase boundary, as well as its strong dependence on oxygen pressure. From this the shift of the orthorhombic-tetragonal phase transition up to 1100 °C can be deduced.