Characterization of the Mixed Oxide Layer Structure of the Ti/SnO 2 -Sb 2 O 5 Anode by Photoelectron Spectroscopy and Impedance Spectroscopy

Abstract

The in-depth chemistry of a Ti/SnO2-Sb2O5 anode was investigated by X-ray photoelectron spectroscopy combined with ion etching. The coating was found to be composed of multiple layers of tin and titanium oxides and composition gradients at both the oxide-air and oxide-metal interfaces. The existence of such an extensive titanium oxide layer may be related to the fabrication of the Ti/SnO2-Sb2O5 anode and subsequent inter-diffusion of species. Also, the surface tin oxide layer was found to be non-stoichiometric, which, in relation to the extensive titanium oxide structure, could be explained by a migration of oxygen toward the Ti substrate. Electrochemical tests showed that the film was unstable and continued to grow under anodic polarization. Impedance spectroscopy displayed a continuum in the dielectric relaxation time constants with depth. This variation in relaxation time constants was proposed to be caused by the continuous variation of the composition in the film.