A first-principles study of HfB2 anisotropic surface stability and its oxygen adsorption behavior

Abstract In this work, the HfB 2 anisotropic surface stability, and the adsorption behavior of oxygen molecule on the most likely exposed HfB 2 surface were investigated based on density functional theory. The study found that the HfB 2 (0001) surface terminated by Hf (labeled as: Hf-(0001)) is more stable, and more likely interact with oxygen. By rotating the oxygen molecule orientation and changing the adsorption site, all possible high and low-symmetry adsorption configurations are considered. The results show that the low symmetry structure is unstable, and eventually turn into the high symmetry ones. For the highly symmetric structures, oxygen molecule tends to be adsorbed in parallel, and the dissociated oxygen molecule tends to be located at the bridge and hollow site of the Hf-(0001) surface, and there is no energy barrier to this process. Charge density difference and partial density of states proved that oxygen absorbed structures present similar electronic interaction characteristics, and oxygen adsorption process mainly affects the Hf atom at the outmost layer of the Hf-(0001) plane. Oxygen atoms bind to the Hf-(0001) surface mainly in the form of ionic bonds and covalent bonds, originating from the orbital hybridization of O- p and Hf- d . The oxidation of HfB 2 starts from the interaction between oxygen and Hf.