HIGH Tc SUPERCONDUCTIVITY AND SUBSTRUCTURE OF Bi-Sr-Ca-Cu-O SYSTEM

BixSr1Ca1CuyOz(x, y=1, 2 or 3) high Tc superconductors were synthesized by solid state reaction method. There are two superconducting phases in Bi-Sr-Ca-Cu-O system: 110 K phase and 80 K phase. The relative portion of the two phases and the state of superconducting connection are closely related to chemical compositions and the conditions of processing. X-ray powder diffraction shows that there exists a main phase with orthorhombic symmetry in the samples of different compositions and conditions of processing. According to X-ray diffraction data, the lattice constants of the main phase in the sample of nominal composition Bi1Sr1Ca1Cu2Oz have been determined as aο=5.44A, bο=5.35A and co=30.66A. Electron diffraction shows complicated modulation structure along b− and c− axes. High resolution image along [001] zone axis indicates the modulation structure along b− axis.