The Single Phase Regions and the Phase Stability of the High-Tc Superconducting Compounds Bi2+x(Sr,Ca)3Cu2O8+d (2212) and Bi2−x(Sr,Ca)4Cu3O10+d (2223)

Abstract

ABSTRACTThe 2212 phase exhibits an extended single phase region having a variable Sr/Ca ratio and Bi-content of 2.1 < Bi < 2.3. At T = 820°C the single phase region extends between 2.05/0.95 > Sr/Ca > 1.2/1.8, whereas, at T = 870° C the single phase region extends between 2.2/0.8 > Sr/Ca > 1.6/1.4. The 2223 phase exhibits a significant higher Bi-content of Bi ∼ 2.5 compared to the formal composition Bi2Sr2Ca2Cu3O10. The Sr/Ca ratio varies between 2/2 > Sr/Ca > 1.9/2.1 reffering to Cu-content of Cu = 3. Samples with the nominal composition Bi2.5Sr2Ca2Cu3Ox and Bi2.5Sr1.9Ca2.1Cu3Ox have been sintered at 880 – 885°C for 90 h in air and consist of 90 – 95 volume percent 2223 phase. Tc depends on the chemical composition of the phases. With decreasing Ca- and Bi-content of the phases Tc increases. Both phases are metastable at roomtemperature. 2212 and 2223 rapidly decompose at 600 °C and 800 °C in air, respectively. At 300°c two new Bi-Sr-Cuprates have been found.