Influence of Pb doping on properties of BSCCO superconductor

Abstract

Summary. --We report here about measurements of resistance vs. temperature, alternating current (a.c.) susceptibility and X-ray diffraction performed on Bae Sr 2 Cae Cu30x superconductor doped with various amounts of Pb. The results could be explained in terms of Pb contribution in increasing both the amount of the highest To0 phase and connectivity between superconductive regions. The Pb substitution on Bi sites is also discussed.PACS 74.70 -Superconducting materials.Recently large interest has been devoted to the influence of Pb doping on BSCCOtype superconductors. This because the addition of Pb on BSCCO sintered sample has the effect of raising both zero-resistance transition temperature Tco and critical current density [l, 2, 3]. The reason why Pb produces these variations and the knowledge of the stoichiometry of the BSCCO are not yet established. Some authors [4] think that the Pb substitution of Bi sites on the Bi2 Sr2 Ca2 Cu30~ phase is the reason of Tco variation. Other authors [5] think that Pb acts like a flux favouring both the growth of higher-Tc0 superconductor phase and the improving of superconductor grain coupling.In order to better understand the role of Pb doping on BSCCO superconductor, we have detected, in the sintered bulk samples, resistive transition and alternating current (a.c.) susceptibility. X-ray diffraction pattern on powder has been obtained in dependence of various amounts of Pb referred to undoped sample. The undoped sample was obtained by a standard solid-state reaction [6]. The material was then pressed into a disk of 25 mm diameter, about 1 mm thick, and sintered in air at 865~ for a period of 120 h followed by an annealing period of 50 h at 450 ~ and final quench in air at room temperature. The doping procedure was performed by adding a fraction of PbO, ranging from 0.05 to 0.75 mole, plus a CuO mole, to the prereacted powder of BSCCO. The powdered mixture, for the lowering of melting point, was calcinated at 820 ~ for 88 -Il Nuovo Cimento D 1315