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Published October 21, 2021 | Supplemental Material
Journal Article Open

Structure, Energetics, and Spectra for the Oxygen Vacancy in Rutile: Prominence of the Ti–Hₒ–Ti Bond

Abstract

Under reducing conditions, rutile TiO₂ develops O vacancies (VO) coupled to Ti³⁺ centers. It is favorable for H atoms to enter this system, either forming OH groups or occupying vacancy sites (denoted HO) 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 HO 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.

Additional Information

© 2021 American Chemical Society. Received: August 30, 2021; Accepted: October 5, 2021; Published: October 13, 2021. W.A.G. was supported by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub, under Grant DE-SC0021266. G.R.R. is thankful for National Science Foundation Grant EAR-1322082. The authors thank Dr. Ted Yu and Charles Musgrave for helpful discussions. Author Contributions: All authors conceived and designed the project. W.R.P. carried out the calculations and data analysis. All authors wrote the manuscript. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.

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Created:
August 20, 2023
Modified:
October 23, 2023