Analysis of transport critical current density in a bent BiPbSrCaCuO silver-sheathed tape

Abstract

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 ε 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, ε) I c (0, ε) 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 ε irrev and the ε 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.