Hole doping in Pb-free and Pb-substituted _{(Bi, Pb)2}Sr₂Ca₂Cu₃O_10+δ superconductors

Using single-phase samples of the _{(Bi, Pb)2}Sr₂Ca₂Cu₃O_10+δ [(Bi, Pb)-2223] high-T_c superconductor and utilizing two complementary analysis techniques, i.e., coulometric redox titration and x-ray-absorption near-edge structure spectroscopy at both O K and Cu L edges, the individual charges of the _{(Bi, Pb)2}O_2+δ charge reservoir and the superconductive block that contains the three CuO₂ planes are consistently determined. Lead is found to enter the (Bi, Pb)-2223 phase with a valence close to III on average. As the oxygen content concomitantly decreases, the average CuO₂-plane hole concentration decreases upon substituting bismuth in the pristine Bi-2223 phase with lead.