First-principles study on surface and internal hydrogen diffusion of Y₂O₃

Y₂O₃ is widely utilized as a coating material to prevent hydrogen permeation in alloys. However, there is limited research on the performance of this coating under hydrogen exposure. The adsorption of hydrogen on the surface and hydrogen diffusion within Y₂O₃ are investigated, with a particular focus on the role of surface oxygen vacancies. The results show that O-layer termination of Y₂O₃ is more stable. The unsaturated O atom promotes the adsorption of the H atom, which tends to occupy the sites above O atoms. Surface vacancies act as intermediate sites, reducing the migration energy barrier between the surface and subsurface, thereby facilitating the diffusion of the H atom into the bulk of Y₂O₃. Additionally, the H atom diffuses through channels formed by octahedral and tetrahedral interstitial sites. The calculated diffusion coefficient and permeability align closely with the experimental value. These results offer a theoretical foundation for enhancing hydrogen resistance of the Y₂O₃ coating.