Effect of Pb substitution in bulk superconducting MgB2

The samples of Mg1-xPbxB2 (x = 0, 0.01, 0.03, 0.05, and 0.06) were successfully synthesized. The temperature dependence of resistance was measured at variant external magnetic field ranged from 0 to 6.15 T. The effects of Pb-doping on the critical temperatures in zero magnetic field, the upper critical fields and the coherence lengths of the samples are discussed. The experiment results show that the critical temperature of Mg1-xPbxB2 decreases with increasing the content of Pb. Contrarily, the absolute value of derivative of Hc2, namely |dHc2/dT|, increases as the content of Pb is increasing. The results imply that the impurities and defects due to Pb-doping play an important role in the system of Mg1-xPbxB2. Finally, according to the relationship between Hc2 and T, the value of coherence lengths at zero temperature of the samples was estimated.