Process Optimization for Ag-Sheathed Bi-2212 Superconductors.

The powder-in-tube (PIT) process has been widely used to fabricate long lengths of superconducting wires and tapes. However, it has been noted that the performance of long lengths of superconductor is variable and difficult to replace. To help pinpoint the possible sources of variation, a systematic study of the effect of processing variables, including deformation and heat treatment procedures, on the electrical properties of the Bi-2212 tapes at cryogenic temperatures was conducted. In addition, the effect of varying powder particle sizes was examined. For tapes fabricated by different thickness reduction schedules, significant variations in critical current density ( J_c) were observed. It is concluded that a combination of small roll diameter and small reduction-per-pass produces tapes with highest J_c. Moreover, the maximum J_c occurred in a narrow temperature range when melt processing was done in pure oxygen. Microstructural examination was used to correlate J_c and both the volume fractions of a nonsuperconducting second phase and the Bi-2212 grain orientation. [ABSTRACT FROM AUTHOR]