Initial oxidation of Cr₂Nb (1 1 1) surface: A density functional study

Surface properties of the clean and O adsorption Cr₂Nb (1 1 1) are investigated using a density functional theory. The result shows that the Cr₂Nb (1 1 1) with Cr-Nb mixed termination is more stable than the Cr-terminated surface in both Cr-rich condition and Nb-rich condition for clean (1 1 1) surface. The O atoms strongly interact with both Cr and Nb atoms on the Cr₂Nb (1 1 1) with Cr-Nb mixed surface. And the O atoms strongly interact with the Cr atom on Cr-terminated surface. The binding energy increases with increasing O atom coverage due to the repulsive interaction between O atoms. It is found the Cr₂Nb (1 1 1) with Cr-Nb mixed surface is more stable than the Cr-terminated Cr₂Nb (1 1 1) under O-rich or O-poor conditions. And a Cr-Nb oxide layer may be produced at the initial stage of oxidation on Cr₂Nb (1 1 1) surface.