ChemInform Abstract: Solid-Solution Ranges of the n = 2 and n = 3 Superconducting Phases in Bi2(SrxCa1-x)n+1CunOy and the Effect on Tc

Abstract

The cation solubility limits of the n= 2 and n= 3 superconducting phases in the Bi2(SrxCa1 −x)n+1CunOy system were established along tie lines with compatible phases via electron probe microanalysis on bi- (or poly-) phasic samples prepared at 860°C. Pb additions (15 mol% of the Bi content) were used to facilitate formation of the n= 3 phase. In each case football-shaped volumes in composition space were established as the solubility limits which bordered on the nominal compositions 2212 or 2223 (Bi:Sr:Ca:Cu) with the long axis parallel to the Sr-Ca side of the quaternary (i.e., Sr-to-Ca intersolubility) but also extending toward Bi and Cu. This means that, for the most part, the superconducting phases are alkaline-earth deficient relative to the ideal 2212 and 2223 compositions. The Pb content in the 2223 phase is typically 10% of the Bi content. Tc variations could be correlated with variations in Sr or (Sr + Bi) content and the length of the c-axis parameter.