Relation between critical current and exponent n in Bi(2223)/Ag tapes

Transport critical currents I-c at 1 mu V cm(-1) and exponents n of the power law characteristics (E similar to j(n)) of single-filament Bi(2223)/Ag tapes were measured at 77 K in the self-field and in external magnetic fields up to 1.2 T. The effects of tape orientation in a transverse magnetic field from -120 degrees to +120 degrees (related to the basic state at B parallel to c-axis) were investigated as well. The values of the transport critical current I-c and exponent n as well their mutual relation reflect the quality of the Josephson-linked current network connectivity at B < B-* (B-* is the cross-over field at which the weak-link currents cease to contribute to the transport current) and the ability of pinning centres to pin flux lines in the whole magnetic field region. The weak-link connectivity and the pinning potential are directly related to the structural state of the samples resulting from their different thermomechanical treatments. The better the structural quality, the higher the I-c/n ratio. This ratio seems to reflect the effective number of intergrain connections and pinning centres.