“…[10][11][12] Upon H 2 exposure at high temperatures (600-1000 °C), TiO 2 can be bulk-reduced to the Magneli phases down to Ti 2 O 3 . 13,14 At lower temperatures, theory 15,16 and experiments [17][18][19] indicate that traces of hydrogen can form deep donor levels in rutile TiO 2 forming O-H + complexes, while hydrogen in O vacancies can be stabilized as hydride H − species.…”