Enhancement of critical current density and strain tolerance in Ag-sheathed BSCCO (2223) tapes by continuous silver reinforcement

We have used a modified powder-in-tube technique in various configurations to demonstrate significant improvement in the transport properties and strain tolerance of Ag-sheathed BSCCO superconducting tapes. In this process, the BSCCO core has been reinforced with a silver rod placed concentrically within the silver tube and then processed into approx. 250 μm thick tapes by established metal-working techniques. A noticeable improvement in critical current density, Jc, was observed as a result of this modification. This increase is attributed to increased texturing, decrease in thickness of BSCCO layers, increase in the length of the Ag/BSCCO interface, and decrease in the volume fraction of the superconducting core which is less effective in contributing towards the overall critical current of the tape. Further improvements have been made to this configuration by incorporating another ring of superconductor into the core. The improved configurations led to a significant increase in Jc over that of monolithic BSCCO tapes. Critical current densities of approx. 40 kA cm-2 at 77 K and self-field have been consistently achieved in 150 μm thick tapes after 150 h of sintering. Analysis of critical current through various sections of the tape indicates that 80% of the critical current is carried by the centre section of the core within which the Ag rod is located. The bend strain tolerance of the tapes containing a silver core was found to be significantly better than that of the monolithic tapes. At an applied surface bend strain of 1.0%, about 98% of initial Jc was retained in Ag-reinforced tapes, compared with only 54% in monolithic tapes. (author)