Influence of modification of annealing and sheath materials on critical current density of Bi-2223/Ag tapes

It is important to improve critical current density of silver-sheathed Bi-2223 tapes for practical applications of material. Bi-2223/Ag superconducting wires with various sheath materials were fabricated by stacking, drawing process with different pre-annealing schedules. Two kinds of powders were prepared. One was pre-annealed at 760°C and low oxygen partial pressure, and the other was only calcined state. Before rolling process, round wires were pre-annealed at 760°C and in a low oxygen partial pressure. Bi-2223/Ag conductor was needed softening annealing at low temperature during drawing process because pre-annealed precursor powder brought about decrease in workability. Pre-annealing let tetragonal structure of Bi-2212 phase of precursor transform to orthorhombic structure and reduce the fraction of second phases at superconducting wire, which could increase critical current density. However the breakages occurred at Ag-alloy sheathed long Bi-2223/Ag tapes during rolling after pre-annealing. Several pre-annealing scenarios were introduced to reduce the breakages during rolling process. We could achieve proper pre-annealing conditions for Ag-alloy clad Bi-2223 tapes by the analysis of mechanical properties. We could achieve highest Je of 8800 A/cm² at Bi-2223 tape by two-step pre-annealing.