Effect of post-annealing at extensively varied temperature on phase formation and superconductive properties in Bi-2223/Ag tapes

Abstract

The phase formation and superconductive properties of the high Tc superconductive Bi-2223/Ag tapes were studied by different post-annealing conditions. Monocore tapes were prepared for the thermo-mechanical process in air, in which a final heat treatment with isothermal post-annealing was performed. After an isotherm at 836 °C for 48 h in this process, successive isotherms were applied at extensively varied temperatures in a range of 820–400 °C at a fixed time of 12 h. Two peaks were observed in the critical current density (Jc) as well as in the critical temperature (Tc) against this temperature. The phase formation behaviour and microstructure development were identified from XRD and SEM–EDS. The results could be correlated with each other, and a qualitative understanding was obtained with the aid of the reported equilibrium phase relationships. Furthermore, a stepwise post-annealing process was developed and applied to the same tapes. Post-annealing of two sequential isotherms was designed by adopting the two peak temperatures found above. The Jc was enhanced relative to that by normal post-annealing.