THE CRYSTAL-STRUCTURE OF A NEW 84-K SUPERCONDUCTOR, BI4SR4CACU3O14+X

The crystal structure of a new superconductor in the Bi-Sr-Ca-Cu oxide system of nominal composition BiSr4CaCu3O14 has been studied by singl e crystal X-ray diffraction. A modulation was observed along the b-axi s. The structure of the fundamental unit cell has been determined in o rthorhombic space group Pbmm, a=5.411(2), b=5.417(3), c=27.75(1) angst rom, Z=2. The final R-factor is 0.067 for 167 unique reflections colle cted up to 2theta=60-degrees with Ag Kalpha radiation. The essential f eature of the structure is the existence of two kinds of copper-oxygen layers with square-pyramidal (CuO3-layer) and square-dipyramidal (CuO 4-layer) oxygen coordinations of the Cu atoms. Two perovskite-like blo cks [Sr-CuO3-Ca-CuO3-Sr] and [Sr-CuO4-Sr] are alternated by double [Bi O]2 layers. The bonds in the BiO planes form chains Bi-O-Bi extending along the b-axis.