OXYGEN DIFFUSION AT THE SURFACE OF THE HIGH-TC SUPERCONDUCTOR YBA2CU3O7-DELTA

The electronic structure of the superconductor is analyzed as a function of the oxygen content adjusted by reducing and oxidizing anneals. The modifications of the Cu2p, O1s, Ba4d core level lines are found to be reversible and directly related to the presence of oxygen vacancies in the crystallographic structure. Two O-lines and two Ba-doublets specific to the cuprate are detected with variable intensities and extrinsic high binding energy O- and Ba-components are attributed to an oxygen adsorption at the surface of the samples. The texture of the samples varies the relative weight of the extrinsic lines and modifies the kinetic of the oxygen diffusion.