Migrations of oxygen vacancy in tungsten oxide (WO3): A density functional theory study

In this paper, we present a theoretical study of oxygen vacancy (VO) diffusions in tungsten oxide (WO3) using density functional theory approaches. By employing PBE calculations, we investigate the energy profiles of VO migrations in three different WOx models: WO2.984 (2 × 2 × 2 supercell), WO2.938 (1 × 2 × 1 supercell), and WO2.875 (one primary unit cell). It is found that the lowest energy barrier is 0.14 eV when VO migrates from the –W–(O)–W– chain in the z axis to that in the y axis in WO2.938, while the VO migrations between the –W–(O)–W– linkage in x and y axis in the same structure are found to have a larger barrier (0.867 and 1.074 eV for the forward and backward reactions, respectively). We suggest that VO migrations are most likely to occur in WO2.984 (lowest oxygen-defect concentration), while the VO migrations do not preferentially occur in WO2.938. Additional PW91 calculations are executed for the VO migrations in WO2.875 to compare with PBE results. Overall, we have found that PBE and PW91 establish very good agreement in predicting relative energies of different VO structures and VO migration barriers with an average percent difference of 10.6%.