Phase equilibria in the YBCuO system and melt processing of Ag clad Y₁Ba₂Cu₃O_7-x tapes at reduced oxygen partial pressures

Abstract

We have undertaken phase-stability studies of Y1Ba2Cu3O7-x(+Ag) and BaCu2O2 (+Ag) over the temperature range 780°C-950°C and oxygen partial pressure range 1.0 × 10-6-2.0 × 10 -1 atm. Ag was found to have no effect on the thermodynamic stability of either phase. Partial melting of YBCO was found at temperatures as low as 800°C ± 10°C, with significant peritectic melting at temperatures as low as 900°C ± 10°C. These thermochemical studies have enabled us to determine the optimum conditions for reduced temperature and pressure (RTP) processing of Ag clad Y1Ba2Cu3O7-x pellets and tapes. The classic domain structure with strong texturing over short lengths was produced in samples melt processed by controlling oxygen partial pressure at a fixed temperature. The RTP method has the advantage that the second phase Y2BaCuO5 particle size can be controlled. Moreover, the technique offers the promise of long lengths of flexible Y1Ba2Cu3O7-x tapes with high current carrying capability. © 1995.