Further evidence that the critical current density of (Bi, Pb)2Sr2Ca2Cu3Ox silver-sheathed tapes is controlled by residual layers of (Bi, Pb)2Sr2CaCu2Oy at (001) twist boundaries

Abstract Field-dependent AC susceptibility measurements are correlated with the transport critical current density ( J ct ) and microstructure for some 20 Ag-clad (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x (2223) tapes having J ct (0 T, 77 K) values ranging from 0–20 000 A/cm 2 . Fields of 0.1-1 mT induced a double transition in the real component of the susceptibility of all samples. The field dependence of the lower temperature transition ( T ' ( H )) exhibited a marked kink at 80 K and was always very sensitive to the applied field above 80 K, indicating an electromagnetically granular behavior. High-resolution transmission electron microscopy often revealed (Bi, Pb) 2 Sr 2 CaCu 2 O x (2212 phase) intergrowths at the numerous (001) twist grain boundaries. Samples with a high J ct (0 T, 77 K) had only occasional half layers of 2212 at the (001) boundaries and required correspondingly higher fields to induce a kink in the T '( H ) characteristic. The universal appearance of a kink at 80 K in all samples and the strong correlation of the field required to produce the kink to the zero-field, 77 K transport critical current density strongly suggests that c -axis transport across (001) twist boundaries within grain colonies controls the critical current density, even in relatively high J c BSCCO-2223 tapes.