CAUSES OF MODULATION AND HOLE CONDUCTIVITY OF THE HIGH-T(C) SUPERCONDUCTOR BI2SR2CACU2O8-RAY SINGLE-CRYSTAL DATA(X ACCORDING TO X)

The one-dimensionally modulated structure of the high-T(c) superconduc tor Bi2Sr2CaCu2O8+x with a0 = 5.407(2), b0 = 5.412(3), c0 = 30.771(8) angstrom, q = 0.210(2)b0 has been analysed in the commensurate approx imation using the conventional three-dimensional space group Pnnn and utilizing single-crystal x-ray diffraction data. A reliable model (R = 0.07, R(w) = 0.079 for 1011 unique reflections) has been obtained. Th e extra oxygen atoms have been found inside and between the Bi-O-Bi ch ains of the BiO layer. The modulation displacement functions of the at oms have been obtained by means of harmonic analysis of the modulation displacements. It has been shown that the topology of Bi-O-Bi chains, the modulation of the structure and the form of the modulation displa cement functions can be explained by the shifts of the oxygen atoms in the BiO layer correlated according to the antiferroelectrical law. Th e cationic vacancies in the Sr sites provide the hole conductivity in the copper-oxygen plane and lead to the formation of the percolation p icture in this plane.