Ionic Mobilities in Amorphous Anodic Titania

Abstract

The mobilities of various electrolyte-derived species in amorphous anodic titania have been determined, with stabilization of the oxide structure by incorporation of silicon species from a sputter-deposited Ti-6 atom % Si alloy. From comparison of the distributions of silicon marker species and electrolyte-derived species in films formed at high current efficiency, boron, chromium, molybdenum, and tungsten species migrate outward more slowly than do Ti4+Ti4+ ions. Their migration rates, relative to that of Ti4+Ti4+ ions, correlate well with the energies of the respective metal-oxygen bonds. Further, chromium species incorporated into the film from chromate electrolyte are mainly present in the trivalent state, indicating reduction of Cr6+Cr6+ ions to Cr3+Cr3+ ions in the growing anodic oxide. This reduction of chromium species can be explained by considering the influences of Cr3+Cr3+ and Cr6+Cr6+ ions on the band structure of titania. © 2002 The Electrochemical Society. All rights reserved.