DEPENDENCE OF THE ELECTRONIC STRUCTURE OF YBa2Cu3O7-∂ CERAMICS ON OXYGEN STOICHIOMETRY : A PHOTOEMISSION AND PHOTOABSORPTION STUDY

X-ray photoemission (XPS) and X-ray absorption (XAS) have been performed on YBa2Cu3O7-∂ ceramics as a function of ∂ (0.1 < ∂ < 0.7). The results show the modifications of the Cu electronic structure around the superconducting-semiconducting transition. XPS and XAS experiments give complementary informations allowing the identification of Cu+, Cu2+ and the so-called Cu3+ configurations as a function of ∂