Ab initio calculations for the H-decorated neutral and charged oxygen vacancy in erbium oxide
Point defects created by neutron/electron irradiation often determine the performance and the chemical stability and activity of oxide materials. Oxygen vacancies constitute a common point defect in metal oxides, such as erbium oxide (Er 2 O 3 ), one of the candidate materials for tritium permeation barriers in fusion blanket systems. However, a systematic study of the oxygen vacancy properties in Er 2 O 3 has been lacking. Here, the properties of isolated neutral and charged oxygen vacancies in Er 2 O 3 are investigated by means of supercell total-energy calculations using a first-principles method based on density-functional theory. Vacancy formation energies, hydrogen-vacancy interactions, and geometry rearrangements around these point defects are investigated in detail. The characterization of the electronic structure of these point defects is established by the analysis of the spin-orbital density of states. It is found that the energetic and electronic properties of the oxygen vacancies depend on the chemical potentials of the O and Er atoms in Er 2 O 3 . The defect formation energy decreases when one hydrogen atom is trapped into the vacancy in both charged oxidizing and reduced environments. Also, the interstitial hydrogen 1s orbital forms multicenter bonds with the 5d orbital of the neighboring Er atoms, and the net charge transfer from the defected Er 2 O 3 is 1.04e, 1.02e, and 0.80e for the defect charge states of 1−, 0 and 1+, respectively. We suggest that the H-decorated vacancy defect may be responsible for the increase of the self-healing properties of Er 2 O 3 .