Ionic Mobilities in Amorphous Anodic Titania

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 ions. Their migration rates, relative to that of 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 ions to ions in the growing anodic oxide. This reduction of chromium species can be explained by considering the influences of and ions on the band structure of titania. © 2002 The Electrochemical Society. All rights reserved.