Composition Dependence on the Superconducting Properties of Bi-Pb-Sr-Ca-Cu-O

Abstract

Superconductors with a nominal composition close to the ideal high- T c phase, (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O y , were prepared to study the effect of composition variation on the superconducting properties. It was found that the deviation from the ideal composition delicately affects the T c (0), and that even a small surplus of Ca and Cu is enough to make it lower to around 95 K. In order to obtain a pure 110 K phase which allows a large current flow to yield a T c (0) above 100 K, the composition must be strictly controlled around Sr:Ca:Cu=2:2:3 with the smallest excess of Ca and Cu. Lead was revealed to occupy Bi sites supplying positive holes to the system along with Sr defects.