Distinguish Different Factors Dominating Superconductivity in Y-Doped Bi₂Sr₂CaCu₂O_y

We observed in Y-doped Bi₂Sr₂CaCu₂O_y superconductors an interesting phenomenon, the T_c(onset) of the Y-doped samples is higher, but the T_c (end) is lower than that of Y-free samples. After annealing in N₂ atmosphere, the T_c (end) is increased, but the T_c (onset) is hardly changed. After careful studying, by structure analysis, x-ray photoelectron spectroscopy, R - T relationship measurement, and Hall effect, we successfully distinguish the different factors that dominate the superconductivity. of which one is carrier concentration, others may possibly be structure change and charges redistribution.