It was found that reduced rutile exhibited anomalous electrical properties under a direct-current electric field of several tens of V/cm. When a direct-current electric field was applied to a sample of reduced TiO2, a single pulse of electric current was observed together with a constant background current. This pulsed electric current occurred only once when the polarity of the electric field was kept unchanged. However, when the polarity of the electric field was changed, a pulsed electric current was again observed. This pulsed current was attributed to the migration of O vacancies in reduced TiO2. It was also found that the migration of O vacancies was visually observable under a direct-current electric field. That is, when a direct-current electric field was applied to the sample after repeated changes in polarity, the color of the sample around the negative electrode changed to dark blue; due to a higher density of O vacancies. The region around the positive electrode lost color.

Anomalous Electromigration of Oxygen Vacancies in Reduced TiO2. Miyaoka, H., Mizutani, G., Sano, H., Omote, M., Nakatsuji, K., Komori, F.: Solid State Communications, 2002, 123[9], 399-404