Effect on critical current density and irreversibility behaviour of mechanical deformation of Bi-(Pb)-Sr-Ca-Cu-O superconducting tapes

Comparative studies on the Ag-clad 27-filamentary Bi-2223 tapes deformed under different conditions have been carried out using ac susceptibility and critical current measurements. Hot pressing improves the grain alignment and grain connectivity, resulting in a noticeable improvement in the critical current density in the low field region. However, the irreversibility line for the cold pressed Ag/Bi-2223 tape is positioned at higher temperatures than that for the rolled tape which is in turn positioned at higher temperatures than that for the hot-pressed tape. These results indicate that the hot deformation is only beneficial to the improvement of weak links whereas the cold deformation induces more defects which act as pinning centres in these tapes, responsible for the improvement in flux pinning.