Flux creep in heavily lead doped Bi2212 single crystal

A comparative study of normalised flux creep rate S(T,H) for heavily lead d oped Bi2212 single crystal and pure Bi2212 single crystal has been performe d. A sharp anomaly in S(T) was observed at a temperature T = T-CR, a cross over temperature below which collective pinning theory is valid for Bi2212 pure single crystal. Observed S(T) over a wide temperature range for the le ad doped sample revealed a shift of T-CR to a higher temperature. Xray meas urements showed a decrease of c-axis parameter with lead doping for this sa mple. The reduction of c-axis parameter improved the inter-layer coupling o f the pancake vortices, enhancing the vortex pinning and causing the shift of the peak in S(T) towards a higher temperature. The critical current dens ity J(c) as a function of field also indicated strong pinning in the lead d oped sample, as compared to pure Bi2212 single crystals.