Pb Content and Oxygen Content Dependences of Tc and Jc for Bi2.20-zPbzSr1.86Ca2.03Y0.05Cu2.86Oy Superconducting Oxide

The purpose of this paper is to interpret the enhancement of Tc and Jc by the replacement of cations and changing the excess oxygen content for Bi-2223 system by the replacement of Bi and Ca by Pb and Y, respectively, that is Bi2.20-zPbzSr1.86Ca2.03Y0.05Cu2.86Oy. The relations between lattice constant, average valences of Bi+Pb and Cu, excess oxygen content and superconducting characteristics have been studied by changing Pb substitution content, and annealing treatment. Bulk samples were prepared by the coprecipitation method. Furthermore, in order to elucidate the effect of metal substitution and oxygen content on Jc of the Bi-2223 system, films which have the same metal composition of the bulk, were prepared on MgO (100) single crystal substrate by the spin coating-pyrolysis method. Measurements of Jc and Tc were carried out on highly oriented films of Bi-2223 phase with changing Pb content and oxygen content: Tc (zero) experienced a maximum at Pb content, z=0.50 (nominal composition), and Tc (zero) decreased with increasing z in the region z>0.50. On the other hand, Jc also showed a maximum at z=0.50, but it was constant with increasing z in the region z>0.50. Oxygen underdoped and overdoped regions, and the highest Tc (zero) and Jc were obtained upon adjusting the optimum excess oxygen content, by changing Pb content and annealing treatment.