ANGULAR-DEPENDENCE OF THE OXYGEN K-EDGE FINE-STRUCTURE IN ELECTRON-ENERGY-LOSS SPECTRA OF BI2-XPBXSR2CACU2O8

By using a transmission-electron microscope, we have performed electron-energy loss measurements above the 0 K-edge at almost-equal-to 528 eV on very thin layers cut from good-quality single crystals of Bi2-xPbxSr2CaCu2O8. We have selected a surface region of the superconductor of known chemical composition free from microprecipitates of Ca. For different directions of the transfer momentum q with respect to the c-axis we observe for the first time the strong orientational dependence of the 0 K-edge transitions in the extended energy loss fine structure. The momentum-transfer-resolved radial distribution functions allow one to identify several characteristic bond lengths of O-Cu and O-Bi parallel and perpendicular to the c-axis.