Abstract
Synchrotron-radiation photoemission was used to compare the electronic structure of YBa/sub 2/Cu/sub 3/O/sub x/ (x = 6.8) which has a superconducting transition at 93 K, and semiconducting YBa/sub 2/Cu/sub 3/O/sub x/ (x = 6.2) which was prepared by vacuum annealing the x = 6.8 material. The decrease in oxygen stoichiometry not only affects the intensity of two-oxygen-related valence-band features, but also shifts the Fermi level upward and alters the shape of the Cu 3d satellite peak. The latter effect indicates a partial reduction to the Cu/sup 1+/ valence state in the vacuum-annealed sample. The superconducting sample could also be modified in situ by an intense soft x-ray beam, leading to oxygen desorption and to photoemission spectra much like the annealed sample.
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