ANALYSIS OF TRANSPORT CRITICAL-CURRENT DENSITY IN A BENT BI-PB-SR-CA-CU-O SILVER-SHEATHED TAPE

The experimental results on the magnetic behavior of the transport critical current density in a bent Bi based superconducting tape have shown that the irreversible strain limit epsilon(irrev) for the onset of permanent strain damage to Ag sheathed superconductors is not dependent on the magnetic field, nor does the normalized I-c(H, epsilon)/I-c(0, epsilon) current depend on the strain at least up to 0.5 T at 77 K. Such a behavior has been attributed to two reasons: (1) The intrinsic pinning properties are unchanged in a bent tape; (2) The strain effect is extrinsic and arises from superconductor cracks. Thus, based on these arguments a Josephson junction tunneling model with cracks in between the grain boundaries is proposed to explain the J(c) behavior quite well for a bent granular high-T-c superconducting tape. Our model calculation shows that the critical current density of high-T-c superconductor may be enhanced by increasing the strain tolerance epsilon(irrev) and the epsilon(irrev) is determined by the properties of Ag sheathed tape and its related material parameters, which are dependent on the connectivity of the grain boundaries.