A superconducting joint between Bi-Pb-Sr-Ca-Cu-O multifilamentary tapes

We evaluated the effects of the joining process on the electrical properties of Bi-Pb-Sr-Ca-Cu-O (BSCCO) multifilamentary jointed tapes. In the process, a 37-filament BSCCO tape was fabricated by the powder-in-tube technique and the tapes were joined by a superconducting-joint method. To improve the filament connectivity between the tapes, the contacting surface of each tape was modified to a stepped shape, and the joined region was uniaxially pressed at 1000-2500 MPa. The critical current ratio (CCR) and n-value of the jointed tape were evaluated as a function of uniaxial pressure and number of steps in the contacting region. It was observed that those properties were dependent on the number of steps, but were almost independent of uniaxial pressure. The highest CCR and n-value for the jointed tape were 61.9% and 5.1, respectively, obtained by optimizing the number of steps and the pressure. It is believed that the highest values for the jointed tape resulted because the contacting area (the 'window') increased and more tape filaments were connected to each other in the joined region. The microstructural evolution was also evaluated and correlated to the resultant properties of the jointed tape.