TRANSPORT CRITICAL-CURRENT IN C-AXIS-ORIENTED BI1.8PB0.4SR2CA2CU3OY/AG TAPES

The transport critical current density J(c) of c-axis-oriented Pi-based silver sheathed tapes was studied as a function of temperature T and magnetic field H in the case of the field applied parallel (H parallel to ab) and perpendicular (H parallel to c) to the tape surface. It can be concluded that the J(c) dependences of the temperature J(c)(T) at various magnetic fields are dominated by the weak-link effect at temperatures very close to T-c (above 90 K). For the temperatures well below T-c (77-90 K), J(c)(T) is primarily controlled by the conventional flux creep model of Anderson-Kim in the low-magnetic-field regime. This observation was further confirmed by the field dependence of J(c). The anisotropy in J(c) can be well described by using the effective-mass model and the overall J(c) of the tapes is determined by the small-angle grain boundaries. In the high-field range, an exponential behavior of J(c)(H) at higher temperatures and a linear J(c)(H) dependence at lower temperatures were clearly observed and can be well accounted for on the basis of collective pinning theory and a strong intrinsic pinning effect, respectively, in this anisotropic material.