Using a high-resolution magneto-optical imaging technique, we study the flow of transport currents around cracks in monofilament (BiPb)2Sr2Ca2Cu2Ox composite conductors. Shunting through the Ag clad is directly observed. The current in the silver decays exponentially with distance from the crack as expected in a one dimensional distributed resistance model. At 77 K, the transfer length, λ, is approximately 0.56 mm, implying an interface resistivity of 7.5×10−8 Ω cm2. This transfer length is found to increase slightly with increasing temperature.
Effects of bend strains on monocore Bi-2223 tapes were studied by transport measurements, magneto-optical imaging and electron microscopy. The strain tolerance of tapes that were sintered for 100 (uniform and well-textured microstructure with high I c ) and 50 h (nonuniform microstructure with low I c ) was evaluated. The strain tolerance of the 100-h sintered tape was superior to that of the 50-h sintered tape. We have shown that the observed strain tolerance is largely determined by the interplay of nonuniform strains and microstructural variation across the tape cross section, leading to nonuniform I c values. An explanation that accounts for an observed concentration of the critical-current density at the Ag/BSCCO interface was presented for the measured strain dependence of the retained I c .
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