First-principles study of oxygen atom adsorption on γ-TiAl(111) surface

Oxygen atom adsorption on γ-TiAl(111) surface is studied using first-principles approach. The adsorption site with more Ti atoms as its nearest neighbors on the surface layer is found to be preferred. Adsorption energy differences between different adsorption sites become smaller with increasing of oxygen coverage. Electron structure analysis shows the chemisorption is characterized mainly by ionic bonds. The stability of γ-TiAl(111) surfaces are investigated in a range of oxygen chemical potential, which indicated that the clean surface can be energetically stable only when the oxygen chemical potential is very low. For higher oxygen chemical potential the clean surface becomes unstable, therefore, the oxygen atoms start to adsorb on it, and soon come up to high coverage.