Critical currents in Ag/Bi-2223 superconducting tapes: Grain connectivity and flux pinning

Critical current (I-c) was measured for a large number of different Ag/Bi-2223 tapes at 77 K, with field H perpendicular to the tape plane. I-c vs. H shows weak and strong link regimes. Critical current through strong links (for H > 100 mT) was described by: I-c(s)(H) = I(c0)(s)exp(-(H/H-0)(a+1)). It was shown that I-c0(s)/I-c0 is correlated with critical current density (J(c0)) and it can be used as a reliable parameter for determining the quality of the links between the grains. A method for obtaining accurate values of I-c0(s)/I-c0 was presented. I-c0(s)/I-c0 increases with J(c0) and attains a constant value of about 0.36 for J(c0) > 20 kA/cm(2). Similarly, normalized critical current for a parallel field of 1 T (I-c(1T)/I-c0) increases with J(c0) and reaches a constant value of about 0.2 for J(c0) > 20 kA/cm(2).