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 superconductin g cores were made by a powder-in-tube technique and subjected to repea ted cycles of pressing and heat treatments. These thermomechanical tre atments 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) be fore and after application of a predetermined level of tensile strain in a uniaxial mode. The fraction of J(c) retained after the strain app lication was higher in the BSCCO-Ag composite tapes than in the monoli thic BSCCO. For a 1.2% applied strain, 90% of the initial J(c) was ret ained in the BSCCO-Ag composite tape, compared to only 40% in the mono lithic BSCCO tapes. The higher strain tolerance of the BSCCO-Ag tapes may be related to improved mechanical properties (strength, flexibilit y, and fracture toughness) and grain connectivity due to Ag addition.