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 YBa2Cu307-8 ceramics as a function of a(0.1 < 8 < 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 a.