INFLUENCE OF LEAD SUBSTITUTION ON THE MAGNETIC IRREVERSIBILITY LINE OF 2212 SUPERCONDUCTING SINGLE-CRYSTALS

An experimental study of the magnetic irreversibility lines has been c arried out on superconducting single crystals of Bi2-xPbxSr2CaCuO2O8, with and without lead. The irreversibility field values B(irr)(T) are almost identical for x=0 and x=0.4. However, the power-law fits of B(i rr)(T) approximately 1/T(alpha) at low temperatures provide different exponents alpha in both cases, alpha = 6 in the lead-free sample and a lpha = 4 in the lead-substituted sample. At high temperatures a regime change is observed in both samples and B(irr) vanishes as (T(c) - T)b eta with beta = 1 for x = 0 and beta = 0. 3 7 for x = 0.4. A discussio n of these results is achieved within the TAFF and vortex solid meltin g models taking into account a possible ''dimensional crossover, of th e vortex system behavior.