High-Jc Reproducibility of Ag-Sheathed Bi-2212 Tapes
In the fabrication of Ag-sheathed Bi-2212 superconducting tapes, J c reproducibility is obstructed by (1) swelling of the Ag sheath, (2) the rough interface of the sheath and core, (3) cracks in the oxide core, (4) inhomogeneities in composition, particle size, and particle hardness of the raw powder. The swelling is caused by the expansion of dissociated 02 gas within the weak, pure-Ag sheath during the high-temperature melting process; it can be eliminated by using powder calcined in low, partial O2 pressure. Complex, misoriented Bi-2212 layer structures often grow from rough interfaces, which are due to improper deformation processes. Cracks in the oxide core, easily introduced by mishandling, can be significantly reduced to achieve a mechanically stronger AgCu-alloy-sheathed tape. Improvement in high-J c reproducibility and the effects of Cu addition into the sheath on increasing J c and mechanical strength are presented.
KeywordsRough Interface Cold Isostatic Pressing Oxide Core Tape Sample Partial Melting Process
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