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A significant enhancement of J , in a magnetic fieid for Ag-sheathed Bi-Pb-Sr-Ca-Cu-0 (BPSCCO) tapes has been achieved by post-annealing at reduced temperature after processing. This post-annealing at reduced temperature introduced extra oxygen into the oxide superconductor. Weak links were eliminated and J, has been increased in the post-annealed tapes by a factor of 1.5 to 3 at 0 T over the normally processed tapes without post-annealing. The optimized J , values for the post-annealed tapes ranged from 30000 to 57 000 A cm-2 at 77.3 K and 0 T. The irreversibility lines measured by a DC SQUID exhibited an improvement in flux pinning in the post-annealed tapes compared with that in normally processed tapes. The introduced oxygen ions are responsible for the enhanced J. and may affect two dimensionality in superconductivity for the BPSCCO system.

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A new phenomenological model for realizing the current-voltage ( I-V ) characteristics of superconducting weak links has been proposed and studied. In this model, the total bias current to the weak link is decomposed in two parts. One part obeys the usual resistively shunted junction (RSJ) type current-voltage relation, and the other obeys the flux-flow (FF) one. It has been shown that the fitting results of the I-V characteristics agree quite well to experimental data. The model and analysis method presented here is quite general, thus the model can be applied to other types of superconducting weak links for both high- and low-T c material.