Phase Equilibria in BiO1.5-SrO-CaO-CuO

BSCCO melting relations under pure oxygen are dominated by the primary phase volumes of (Sr,Ca)O and, to a lesser extent, of CuO. Between these volumes are those of alkaline earth cuprates. Liquids that crystallize Bi-bearing phases are confined to a small region along the Bi-Ca-Sr face. In Bi-Ca-Cu oxides, there is a single eutectic and melting relations are dominated by slopes down to that eutectic. Bi-Sr-Cu oxides include multiple eutectics as Bi-2201 generates a thermal divide, thus separating more Bi-rich thermal minima from more Bi-poor ones. The latter phase relations dominate inside the quaternary with Bi-2201 and other phases creating thermal divides that considerably restrict those liquid compositions that may evolve to ones in equilibrium with Bi-2212 and Bi-2223. Further, melting relations of these phases change with p(O₂). Bi-2212 melts invariantly in pure oxygen (to 50% liquid) but univariantly at 10% oxygen (to 80% liquid). Further decrease in oxygen content returns Bi-2212 to invariant melting but at a different point. Gradual decrease in incongruent melting temperature of Bi-2212 reflects increasing amounts of univalent copper in the coexisting liquids.