ROLE OF AG ADDITIONS IN THE MICROSTRUCTURAL DEVELOPMENT, STRAIN TOLERANCE, AND CRITICAL-CURRENT DENSITY OF AG-SHEATHED BSCCO SUPERCONDUCTING TAPES

Ag-sheathed tapes of Bi-Sr-Ca-Cu-O (BSCCO) and BSCCO-Ag superconducting cores were made by a powder-in-tube technique and subjected to repeated cycles of pressing and heat treatments. These thermomechanical treatments resulted in enhanced texturing and grain growth that improved the critical current density (J(c)). Additions of Ag to the BSCCO core further increased texturing and brought an additional improvement in J(c). Strain tolerance of the tapes was evaluated by measuring J(c) before and after application of a predetermined level of tensile strain in a uniaxial mode. The fraction of J(c) retained after the strain application was higher in the BSCCO-Ag composite tapes than in the monolithic BSCCO. For a 1.2% applied strain, 90% of the initial J(c) was retained in the BSCCO-Ag composite tape, compared to only 40% in the monolithic BSCCO tapes. The higher strain tolerance of the BSCCO-Ag tapes may be related to improved mechanical properties (strength, flexibility, and fracture toughness) and grain connectivity due to Ag addition.