Small polaron characteristics of an OD center in TiO2 studied by infrared spectroscopy

The fundamental OD center in TiO2 has been studied by IR absorption spectroscopy and by theory. Our experiments reveal a single sharp OD line in oxygenated samples that we attribute to a positively charged center. In TiO2 samples reduced by a treatment in a D-2 ambient at 500 degrees C, a neutral OD center with two additional IR lines is produced. Similar results reported recently by Herklotz et al. [F. Herklotz, E. V. Lavrov, and J. Weber, Phys. Rev. B 83, 235202 (2011)] led them to suggest that the neutral OD center is a shallow donor with IR lines arising from its two charge states. Our analysis suggests instead that the properties of the neutral OD center are explained by a small polaron model, which involves several configurations corresponding to the localization of the electron on different nearby Ti sites.