Abstract
Pure compounds of Bi2(Bi, Sr, Ca)3Cu2O y (y=8.65–8.86) were prepared in air and studied in order to elucidate the close relationships among T c, Bi content, quenching temperature and lattice constants. It was found that formation of the pure superconductor strongly depended on the Bi content and Ca/Sr ratio. A considerable change of T c took place with a slight change in oxygen number y which was below 0.04. To achieve the highest T c, the oxygen number y should be controlled to an appropriate value which depends on the Bi content.