Equilibrium phase relations in the Bi-Ca-Sr-Cu-O system at 850 and 900°C

The phase relations of equilibrium compounds in the pseudoternary system Bi{sub 2}O{sub 3}-(Ca,Sr)O-CuO at 850 and 900 {degree}C were studied. The ratio of Ca:Sr was fixed at 1:2. Starting materials of Bi{sub 2}O{sub 3}, CaCO{sub 3}, SrCo{sub 3} and CuO with various ratios were mixed, pressed into pellets, and heated at or above and then brought back to 850 or 900 {degree}C for different durations to ensure that equilibrium had been reached. The products were cooled in air or quenched in liquid nitrogen and then identified by x-ray powder diffraction. At 850 {degree}C, only the superconducting phase, Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub {ital x}}(2122), was observed inside the triangle. The other stable phases were all positioned on the boundary lines, and included CuO{center dot}3/5MO, CuO{center dot}MO, CuO{center dot}2MO, 1.1/2Bi{sub 2}O{sub 3}{center dot}0.9MO, Bi{sub 2}O{sub 3}{center dot}4MO, Bi{sub 2}O{sub 3}{center dot}9MO, and a solid solution, Bi{sub 2}O{sub 3}{center dot}xMO, where 0.16 {le} x {le} 0.82 and MO represents 1/3(CaO{center dot}2SrO). At 900 {degree}C, the above boundary line phases remained stable but the 2122 phase was not observed. The tie lines among the stable phases in the two isotherms were established.

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