Electronic structure and chemical bonding of superconductor YBa sub 2 Cu sub 3 O sub 7-x

X-ray photoelectron spectra of high-temperature superconductor YBa sub 2 Cu sub 3 O sub 7-x is investigated at the temperatures both above and below the temperature of transition to superconductive state T sub c . It is shown that in this material the copper atoms are in three different states characterized by different number of oxygen atoms in their surroundings. At the temperature below T sub c the changes in the valence band structure of YBa sub 2 Cu sub 3 O sub 7-x are found which are associated with the hybridization of Cu3d- and O2p-states (without any charge transfer). Copyright (c) 1996 Elsevier Science B.V. All rights reserved.