Electronic structure of YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta by x-ray photoemission and Auger spectroscopies

X-ray photoemission and Auger spectra of the Cu 2p core level in YBCO and of the O 1s level in YBCO and BiSCCO are measured as a function of the oxygen concentration and of temperature. A molecular cluster description of the Cu states is introduced which includes the contribution of trivalent copper. Correlation energies for copper and oxygen valence holes are estimated. An oxygen excess is likely to modify the surface stoichiometry of both materials.