EXAMINATION OF THE TIME-DEPENDENCE OF CONCENTRATION OF DEFECTS AND SURFACE-STATES DURING INTRINSIC REDOX PROCESSES IN OXIDE-FILMS

Intrinsic redox reactions of oxides are closely related to the electro nic properties of the examined systems. Information about the electron ic structure can be achieved by examining the potential dependence of the electrode capacity at various polarisation times and potentials. - Redox processes within passive layers on Ni (d < 10 nm) and within La NiO3 (d > 1 mum) are shown as example of intrinsic reactions. Oxidatio n as well as reduction starts with the charging of surface states and defects during 100 mus. The redox process of the Ni-O-matrix needs 10 ms to start. During oxidation, formation of Ni3+ and O2-evolution take s place. Surface states, formed by Ni3+, covers nearly the whole surfa ce. They will be compensated during O2-evolution. During reduction, th e amount of surface states decreases down to 30% of the surface and th e defect number decreases as well. The redox process within LaNiO3 is governed by the reaction of Ni-ions. It depends strongly on the mobili ty of vacancies. - The doping of oxides by protons is demonstrated for passive layers on Ti. During polarisation near U(fb) (reduction), pro tons penetrate into the layer and the donor number increases. Polarisa tion at anodic potentials (oxidation) forces the protons out of the la yer. During the redox process, no change of the oxide takes place and surface states can be neglected.