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 th e 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 tra nsverse magnetic field from -120 degrees to +120 degrees (related to t he 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 t heir mutual relation reflect the quality of the Josephson-linked curre nt network connectivity at B < B- (B-* is the cross-over field at whi ch the weak-link currents cease to contribute to the transport current ) and the ability of pinning centres to pin flux lines in the whole ma gnetic field region. The weak-link connectivity and the pinning potent ial are directly related to the structural state of the samples result ing from their different thermomechanical treatments. The better the s tructural quality, the higher the I-c/n ratio. This ratio seems to ref lect the effective number of intergrain connections and pinning centre s.