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

Bi x Sr 1 Ca 1 Cu y O z(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 Bi 1 Sr 1 Ca 1 Cu 2 O z have been determined as aο=5.44Å, bο=5.35Å and co=30.66Å. 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.