Structural Study on Fluorine Doped Bi (Pb)-Sr-Ca-Cu-O Superconductors

A F-doped Bi (Pb)-Sr-Ca-Cu-O superconductor shows a higher Tc value than that without F doping in AC susceptibility measurement. Specimens were sintered in two stages. The doping of CaF2 in starting powders caused a considerable amount of Ca2PbO4 as an intermediate phase on the first sintering, which eventually resulted in the formation of Pb-enriched Ca2CuO3 and then the enhancement of the 2223 phase during the second sintering. The EPMA results revealed that Pb is mostly trapped in Ca2PbO4 after the first sintering and incorporated in the grains of the 2223 phase after the second sintering. F exists in finely distributed SrF2 among the grains. It is made clear according to DTA that the temperature range for socalled partial melting is lowered and widened, i.e. the optimum synthesizing temperature for the 2223 phase is lower than 840°C.