Phase composition and compatibilities in the Bi-Sr-Ca-Cu quaternary oxide system at 800°C in air

Subsolidus phase relations in the system (Bi-Sr-Ca-Cu)-O at 800°C were investigated via powder X-ray diffraction and electron probe microanalysis of solid-state reaction products. Two recently reported (Bi-Sr-Ca)-O phases were detected in quaternary assemblages and had the approximate cation stoichiometries of 9115 and 825. The only truly quaternary compound detected is the superconducting phase with the cation stoichiometry 2212. Tie lines, tie triangles, and compatibility tetrahedra involving this phase and the 2201 superconducting phase were determined. Both superconducting compounds exhibit small but detectable Sr-to-Ca solubility and are Sr-deficient with respect to the 'ideal' formulas.