Theoretical Study of the Interstitial Oxygen Atom in Anatase and Rutile TiO2: Electron Trapping and Elongation of the r(O−O) Bond

Abstract

Interstitial oxygen atoms (Oi) in TiO2 were investigated using the density functional theory-based first-principle band structure method. Two polymorphs of TiO2, anatase and rutile structures, were considered. A symmetric O−O structure was obtained in rutile and is quite similar to the reported structure in anatase. In both polymorphs, Oi traps electrons from the conduction band to the σ* orbital of the O−O structure. The bond length r(O−O) is elongated in this process. The interactions between Oi and Nb or Ta impurities were also surveyed. There was weak attraction for both impurities. A simple statistical analysis was conducted to evaluate the Oi formation in anatase. Two conclusions were drawn from the present results. 1) Oi forms in n-type TiO2 in either the anatase or rutile structure under an O-rich condition. 2) The entropy factor, which originates from the distribution of Oi and from the electrons in the conduction band, makes a small contribution to the free energy at room temperature. The discre...