Calculation of point defects in rutile TiO2 by the Screened Exchange Hybrid Functional

TL;DR

This study uses the screened exchange hybrid functional to accurately calculate defect formation energies in rutile TiO2, clarifying the roles of oxygen vacancies and titanium interstitials in oxygen deficiency.

Contribution

It applies the sX hybrid functional to compute defect energies in TiO2, providing more accurate insights into defect states and their prevalence under different conditions.

Findings

O vacancy creates a gap state 0.7 eV below conduction band

Ti interstitial generates four defect states in the gap

O vacancy dominates under O-rich conditions

Abstract

The formation energies of the oxygen vacancy and titanium interstitial in rutile TiO2 were calculated by the screened exchange (sX) hybrid density functional method, which gives a band gap of 3.1 eV, close to the experimental value. The O vacancy gives rise to a gap state lying 0.7 eV below the conduction band edge, whose charge density is localised around the two of three Ti atoms next to the vacancy. The Ti interstitial generates four defect states in the gap, whose unpaired electrons lie on the interstitial and the adjacent Ti 3d orbitals. The formation energy for the neutral O vacancy is 1.9 eV for the O-poor chemical potential, and similar to that of the neutral Ti interstitial, and has a lower formation energy for Ti interstitial under O-rich conditions. This indicates that both the O vacancy and Ti interstitial are relevant for oxygen deficiency in rutile TiO2 but the O vacancy will dominate under O-rich conditions. This resolves the questions about defect localisation and defect predominance in the literature.