Superconductivity and flux pinning in Y and heavily Pb codoped Bi-2212 single crystals

Studies of superconductivity and flux pinning were carried out on (Bi1.64Pb 0.36)Sr2Ca1 - xYxCu2O8 + y (x = 0, 0.05, 0.11, 0.33) single crystals grown by the self-flux method. X-ray diffraction, transport, and magnetic measure ments were performed for purposes of characterization. X-ray analysis revea led that the c lattice parameter systemically decreases as the Y doping lev el increases. The superconducting transition temperature T-c decreases from 80 to 30 K as x increases. A strong annealing effect on T-c and supercondu cting volume has been observed. Resistance measurements show that x = 0.33 samples are semiconductive over a wide temperature range between 4.2 and 30 0 K for the as-grown state, but become metallic with T-c of 65-70 K after a ir or oxygen annealing. Flux pinning was studied by measuring the hysteresi s loop at different temperatures and different fields. A peak effect was ob served in all the codoped samples. Results show that at low temperatures, t he peak field is smaller than in solely Pb doped crystals and decreases as x increases (x > 0.1). However, the peak field at high temperature for the x = 0.05 sample is higher than in heavily Pb doped Bi2212 crystals, indicat ive of a strong pinning due to the codoping. (C) 2001 American Institute of Physics.