The nature of electronic states in anodic zirconium oxide films .2. Photoelectrochemical characterization

Coupling between the electronic and crystallographic defect structures of anodic ZrO2 films has been explored using the recently developed photoelectrochemical impedance technique. With this technique, the dynamic photocurrent response for ultra-violet excitation was analyzed. Additionally, photo-stimulated capacitance transients were also examined. Our studies indicate that, upon UV irradiation, photo-generated holes are transported to the oxide/solution interface by a diffusion/migration mechanism. Coincidentally with this electronic response, oxygen ion vacancies also migrate through anodic zirconia films upon UV irradiation. This leads to photo-stimulated formation of ZrO2. The rate-limiting step in this film formation process is the transport of oxygen ion vacancies in the film by a diffusion/migration mechanism. Both the photo-electric response and the ''photo-ionic'' response of anodic zirconia films can be explained by the point defect model for anodic films.