AG-SHEATHED BI(PB)SRCACUO SUPERCONDUCTING TAPES

The processing and properties of Ag-sheathed Bi-based superconducting tapes prepared using the powder-in-tube technique have been reviewed. Powder processing and heat treatment, among various other factors, were found to be critical to the J(c) of Ag/Bi-based superconducting wires. Reactive, homogeneous, carbonate-free and incompletely reacted powders, produced by the solution route are desirable. Liquid phase sintering, which is essential to achieve intimate grain connectivity and high grain alignment, can be achieved using a short period of melt or by annealing at temperatures near the melting point of the composites. An Ag sheath has been proved to be sufficient for achieving the flexibility and stability of these tapes. The interfacial layer between Ag and oxides shows an improved strength and flexibility. The thermally activated flux creep determines the J(c) at high temperature. Weak links have been largely eliminated in high-quality tapes at high temperatures but the weak-link behaviour becomes pronounced at low temperatures. The dispersed 2212 phase and defects in the Ag/2223 tapes may act as potential pinning sites. Multiprobe measurements show no accumulative grain boundary resistance for long tapes. Fabrication of long tapes shows a better reproducibility than that for the short tapes.