Phase transformations in melt-spun Y-Ba-Cu-O bulk superconductor

Powders of YBa/sub 2/Cu/sub 3/O/sub 7/ (Y123) and compositions around Y123 were heated by a containerless process and melt-spun in 21% oxygen atmosphere at temperatures of 1400/spl deg/C to 1650/spl deg/C. Homogeneous materials were obtained with micron and submicron crystalline phases uniformly dispersed in an amorphous matrix. For Y123, the crystalline phases are identified by XRD as BaCu/sub 2/O/sub 2/ and Y/sub 2/O/sub 3/ when the melt-spinning temperature is below 1600/spl deg/C. At 1650/spl deg/C, the crystalline phases are Y/sub 4/Ba/sub 3/O/sub 9/, BaCu/sub 2/O/sub 2/ and Y/sub 2/O/sub 3/. The phase composition of the solidified melt is directly related to the oxygen content of the melt and can be related to the equilibrium phase diagrams at lower oxygen partial pressures. Isothermal annealing in oxygen at temperatures 500/spl deg/C to 950/spl deg/C reveals that the crystallization sequence is: Y123 begins to form at 500/spl deg/C, Y123 with minor amount of Y/sub 2/BaCuO/sub 5/ at 800/spl deg/C, Y123 with very minor amount of CuO at 900/spl deg/C, and single phase Y123 at 950/spl deg/C.<>