Strain and grain connectivity in Bi2223/Ag superconducting tapes

The critical current reduction in silver-sheathed (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ superconducting tapes (Bi2223/Ag) is investigated when loaded with uni-axial strains in combination with a magnetic field perpendicular to the tape surface. The number and quality of the grain-to-grain connections and the alignment of the superconducting cores mainly determine the critical current in Bi2223/Ag tapes. It is assumed that the transport current flows simultaneously through two current carrying paths in the tape: one through the network of Josephson junctions and the other is through the well-connected grains. The model describes well the magnetic field dependence of the critical current at various strains. A detailed analysis has shown that strain deteriorates grain connectivity, induces cracking and hence changes the current carrying path. Furthermore, strain may introduce new defects inside the grains along the strong-link current path and increase intra-granular pinning strength.