Structure, Energetics, and Spectra for the Oxygen Vacancy in Rutile: Prominence of the Ti-H O -Ti Bond.

Under reducing conditions, rutile TiO ₂ develops O vacancies (V _O ) coupled to Ti ³⁺ centers. It is favorable for H atoms to enter this system, either forming OH groups or occupying vacancy sites (denoted H _O ) that bond to two Ti atoms next to the vacancy. OH defects are well documented by the presence of infrared modes at ∼3300 cm ^-1 , while H _O is relatively underinvestigated. We report the energies, geometries, and vibrational frequencies of hydrogen defects in rutile predicted from quantum mechanics calculations, focusing on the coexistence of OH and H _O . We find that H _O is more stable than OH by 1.42 eV, leading to an infrared mode at ∼1200 cm ^-1 . Introducing a second H forms an OH bond with an infrared mode at ∼3300 cm ^-1 . These results suggest that assessments of hydrogen storage in mantle phases of rutile and similar minerals based on OH bands may significantly underestimate H concentrations.