LONG-RANGE PAIRING OF BISMUTH ATOMS AND THE MODULATIONS IN BI2SR2CACU2O8-TEMPERATURE SUPERCONDUCTOR(X HIGH)

Modulations and ''pairing'' of Bi atoms in the B2Sr2CaCu2O8+x high-tem perature superconductor are simultaneously observed on tile high-resol ution electron micrographs, viewed along: the [101] crystal direction. We analyze the obtained images by laser diffraction and photodensitom etric technique applied to the negatives. The ''pairing'' of Bi atoms is assumed to be connected with tile regular Bi 6sp lone-pair ordering . The shift of tile Bi atoms in the ''pairing'' is estimated to be 0.3 Angstrom. By the Fourier transform of the optical modulation we estim ate tile period of the structure modulation in the direction perpendic ular to the ''pairing'' to be 9.76 times the period of the average cry stal-plane spacing. The analysis of the structure is supported by ''ha rd-sphere'' simulations, We set up a model for the extra oxygen arrang ement, on the basis of which we estimate the extra oxygen content to b e x approximate to 0.33 per molecule.