High energy spectroscopies of cu compounds, including the new superconductors

High energy spectroscopies are well suited to address the controversial issue of Cu valence in the new high Tc superconductors, as they can discriminate between various possible Cu configurations (d8, d9 or d10). XAS, XPS and AES spectra of CuI, CuII and CuIII compounds show that, as a results of hybridization, the actual Cu d-count can be quite different from what is expected from simple considerations based on the formal valence. A value of ~ 9.3. is inferred electrons for the superconducters. Discrepancies in the published results are attributed to insufficient sample characterization : we propose to adopt the O is XPS signal as a standard probe of surface condition in these materials.