X -Ray Emission and X -Ray Self-Absorption in the High - Tc Superconductor YBa2Cu3O6.9 and other Copper Oxides

Abstract

O-Kα X-ray emission spectra of La2CuO4 and YBa2Cu3O6.9 are compared with calculated spectra. It is shown from O-Kα emission spectra of YBa2Cu3Ox with varying oxygen content (6.0 < X < 6.9) that with heating the superconducting compound (x = 6.9) oxygen atoms are removed from the Cu-O chains. A method for comparing X-ray self-absorption spectra from compounds with different concentrations of the element under consideration is presented. Cu-L selfabsorption spectra of YBa2Cu3Ox (6.0 < x < 6.9) are compared with those of Cu, Cu2O, CuO, and NaCuOn. By this comparison and from O-K., emission spectra, oxygen 2p holes are found to be present in the superconducting compound. The ionic character of the Cu-O bonds in the nonsuperconducting green phase Y2BaCuO5 is shown with O-Kα emission and Cu-L3 self-absorption spectroscopy. The energy gap of Y2BaCuO5 is found to be about 5 e V.