Sandwich Roiling, J_c, and pinning energy in Ag-sheathed BPSCCO superconducting tapes

Abstract

A “sandwich rolling” process was developed to prevent the formation of sausaging and cracks in the longitudinal direction. The stress-strain state of the tape in “sandwich” rolling is the same as that of uniaxial pressed tape because the deformation of steel sheets is negligible in comparison to that of Ag-clad tape. Critical current densities of 3.2 × 10⁴ A/cm² at 77K and 2.7 × 105 A/cm² at 4.2K and zero field Ag-sheathed Bi-based 2212 tapes have been achieved using a melt and atmosphere-controlled process. The comparison of pinning potential U₀(B) < U(T-0, B) for Bi-2212 tape and Bi-2223 tapes consisting of a different fraction of 2212 phase as well as Bi-2212 and Bi-2223 thin films shows that for the same fields, the U_o for good quality 2223 tapes is at least 1.3 times that for the best 2212 tape and epitaxial thin films after taking into account the difference of the T_c between 2223 tape and 2212 tape, indicating that in BSCCO compounds, in addition to anisotropy, the specific pinning centers such as dislocations, introduced during processing, affect the flux motion at lower B.