Phase diagram and flux pinning in Bi-doping BaPbO3 compounds

BaPb1−xBixO3-δ with x = 0.1-0.3 were prepared by a solid-state reaction method. X-ray diffraction patterns show that the cell parameters increase with the increasing x. From the result of transport measurement, we have drawn a BaPb1−xBixO3-δ phase diagram, which is divided into three regions: metal, semiconducting and superconducting. In the superconducting region, the doping x dependence of critical temperature can be fitted well by a parabolic equation, 1-Tc/Tcmax = A(x-xc)2 with A = 120.68 and xc = 0.223. Compared with the phase diagram of high-Tc cuprates, we think that x > 0.223 should be underdoped region and x < 0.223 is overdoped region. The field dependence of critical temperature for all samples displays a power law, Hc = Hc(0) (1-T/Tc)n and the n-value depends on the doping level. The effective pinning energy is enhanced by Bi-doping. In low field, a possible strong collective flux pinning of 2D defects may be produced by stripe-like nanoscale structure and/or Bi3+ and Bi5+ ions induced dislocations. Above crossover field, a weak pinning of linear-like defects and/or point defects dominated in higher field. The magnetization measurement confirms the flux pinning mechanism.