Minoru Ishihara

Variation of Composition in a Bi(Pb)-Sr-Ca-Cu-O Grain and the Influence of Mg and Ba Doping on Its Superconductivity

The 110 K phase (2223) and (Sr, Ca)-Cu-O phase exist in the Bi(Pb)-Sr-Ca-Cu-O ceramics. The Cu content varies in the perpendicular direction of platelike 2223 grains, but little variation is observed on the planer surface of the grains along their length. Only the 110 K phase was found in the X-ray diffraction pattern of Bi(Pb)-Sr(Ba, Mg)-Ca-Cu-O. Its electrical resistivity became zero at 110 K. By the partial substitution of Mg and Ba for Sr, the range of sintering temperatures in which we obtained a higher Tczero was much larger than that for Bi(Pb)-Sr-Ca-Cu-O.

Formation of 2223 Phase and Variation in Composition of Bi(Pb)-Sr-Ca-Cu-O Superconductors

Sintering of Bi1.6Pb0.4Sr2Ca2Cu3.6Ox for long time resulted in an increase of the volume fraction of the 2223 phase to 53%. The 2223 phase appears to take the form of flaky grains. The chemical composition of the constituents of the flaky grains are not exact stoichiometric proportions. Substances in the calcined powder start to react around 832°C, then change to (Sr,Ca)-Cu-O and an unknown phase at 862°C. Growth of the 2223 phase is enhanced between these two temperatures.