Charge transport of Bi_{2-x}Pb_xSr_2ErCu_2O_8 single crystals near the   insulator-superconductor transition
  We prepared a set of Pb-substituted Bi_{2-x}Pb_xSr_2ErCu_2O_8 single crystals. The resistivity and the in-plane thermopower decrease with increasing x from 0 to 0.8, which indicates that the Pb substitution supplies holes in the CuO_2 plane. For x=0.8, a tiny resistivity drop (a trace of superconductivity) is seen near 70 K, suggesting that the doping level is close to the critical concentration. The c-axis dielectric constant also systematically changes with x, and suggests that the charge inhomogeneity is suppressed by the Pb substitution. 
I. Terasaki, T. Mizuno, K. Inagaki, and Y. Yoshino