Effect of Pb-doping and annealing on the structure and Tc of Bi-2212 phase superconductor

A systematic study of Pb-doping and annealing effects in vacuum (2×10 −3 Pa) on Tc and microstructure of Bi 2−xPb xSr 2CaCu 2O δ compounds has been carried out. It is found that the structure belongs to Bi-2212 phase. The c and b axes almost keep unchanged while Bi is replaced by Pb. With annealing temperature increasing, c and b axes parameters monotonously increase while the a-axis parameter is unchanged. There is an optimum Tc with annealing temperature increasing which reveals that the carrier concentration p changes from overdoped to underdoped. It is suggested that a charge-transfer between carrier group (BiOSrO) and conducting CuO 2 plane is induced by Pb-doping and annealing in vacuum. The change of the microstructure and superconductivity of Pb-doped Bi-2212 phase is related to the charge transfer.