HIGH-MAGNETIC-FIELD TRANSPORT-PROPERTIES AND IRREVERSIBILITY LINE OF SINGLE-CRYSTALS (2212) AND CERAMICS OF BPSCCO (2223)

We have measured the high-magnetic-field (up to 15 T) transport properties of (BiPb)(2)Sr2Ca1Cu2Oy (BPSCCO) single crystals and (2223) ceramics. We have extracted the melting line of BPSCCO crystals from the measurements of precise I-V curves when the field is applied parallel to the c-axis and shown that the melting line coincides with the irreversibility line measured by the magnetisation technique. This is explained for the case of weak pinning. The depinning line was found to be 10 to 12 K above the melting line. The observed hump in the magnetoresistance curve above 2 T predicts the depinning of flux from the weak pinning centres when the temperature approaches the depinning temperature. The basic behaviour of ceramic BPSCCO, although having a higher T-c, is similar to its single crystal analogue with (2212) phase except for the enhanced depinning line.