Abstract
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 a Bi-2223 system by the replacement of Bi and Ca by Pb and Y, respectively, to form Bi1.76Pb0.44Sr1.86Ca2.08-xYxCu2.86Oy. The relation between lattice constant, average valences of Bi+Pb and Cu, excess oxygen content and superconducting characteristics has been studied as a function of Y substitution content, and anneal treatment. The highest Tc was obtained at x=0.05. Oxygen doped and overdoped regions and highest Tc(zero), which were obtained upon adjusting the optimum excess oxygen content, existed at each Y content, x=0-0.30. Furthermore, in order to elucidate the effect of metal substitution and oxygen content on Jc of a Bi-2223 system, films were prepared, which have the same metal composition of bulk, on a MgO(100) single crystal substrate by the spin coating-pyrolysis method. The measurements of Jc and Tc were carried out on highly oriented films of Bi-2223 phase with changing Y content. The highest Tc(zero) was obtained at Y content, x=0.05. Tc(zero) decreased with increasing x in the region of x>0.05. On the other hand, the highest Jc was obtained at x=0.10. The Y content for optimum Jc was different from that for optimum Tc. Jc increased with increasing excess oxygen content, Δy, and after that increase or constant in the oxygen overdoped region. Consequently, the metal and oxygen contents were very important for obtaining the highest Tc and Jc.
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