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 electro n-energy loss measurements above the 0 K-edge at almost-equal-to 528 e V on very thin layers cut from good-quality single crystals of Bi2-xPb xSr2CaCu2O8. We have selected a surface region of the superconductor o f known chemical composition free from microprecipitates of Ca. For di fferent directions of the transfer momentum q with respect to the c-ax is we observe for the first time the strong orientational dependence o f the 0 K-edge transitions in the extended energy loss fine structure. The momentum-transfer-resolved radial distribution functions allow on e to identify several characteristic bond lengths of O-Cu and O-Bi par allel and perpendicular to the c-axis.