Fabrication, current density and strain dependence of sintered, Ag-sheathed BiSrCaCuO (2212) single filament and multifilamentary tape superconductors

Bi₂Sr₂CaCu₂O_x (2212) superconductors have been fabricated into silver (Ag)-sheathed single-filament, multifilament, and wire-in-tube (WIT) tapes. Calcining, annealing and sintering conditions have been studied to improve the critical current density J_c(B, 4.2 K) at high magnetic field (B). The optimization is discussed, and resulting properties are related to the microstructure of the superconductor. Superconductor J_c~1-5×10⁴ A/cm² has been obtained in fields >20 T at 4.2 K in both single and multifilamentary tapes. The dependence of J_c upon mechanical strain (∈) has been investigated. No prestraining of the superconductor occurred in any of the samples, most likely due to yielding of the Ag sheath. Although strain resistance was good in all samples, the WIT tapes were significantly more resistant than the single-filament tapes. For the single-filament tapes, ∈_irr~0.24%, while for the WIT tapes, ∈_irr~0.36%, where ∈_irr is the irreversible strain limit