On the composition of 110 K superconductor in a (Bi,Pb)-Sr-Ca-Cu-O system

The 110 K superconductor of the (Bi,Pb)-Sr-Ca-Cu-O system is prepared in single-phase form at the composition Bi1.6Pb0.4Sr2.01Ca2.71Cu3.93Oy. Disks of the material with favorable texture can be obtained in relatively short durations in an O2 poor atmosphere. The literature on the compositions of the 110 K superconductor is reviewed to reveal that the material can be synthesized in single-phase form in a range of compositions, which is poorer simultaneously in Bi and Sr with respect to the nominal composition (Bi,Pb)2Sr2Ca2Cu3Oy, (2:2:2:3). At compositions close to 2:2:2:3, intermediate cold pressing steps between heat treatments are necessary to promote the formation of single-phase material. We find that at compositions which are considerably poorer in Bi and Sr with respect to 2:2:2:3, no such steps are necessary. In this paper, the microstructural reasons for this difference in behavior are also investigated