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

In this paper, we present a theoretical study of oxygen vacancy (V-O) diffusions in tungsten oxide (WO3) using density functional theory approaches. By employing PBE calculations, we investigate the energy profiles of V-O migrations in three different WOx models: WO2.984 (2 x 2 x 2 supercell), WO2.938 (1 x 2 x 1 supercell), and WO2.875 (one primary unit cell). It is found that the lowest energy barrier is 0.14 eV when V-O migrates from the -W-(O)-W- chain in the z axis to that in the y axis in WO2.938, while the V-O 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 V-O migrations are most likely to occur in WO2.984 (lowest oxygen-defect concentration), while the V-O migrations do not preferentially occur in WO2.938. Additional PW91 calculations are executed for the V-O 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 V-O structures and V-O migration barriers with an average percent difference of 10.6%. (C) 2014 Elsevier B. V. All rights reserved.