Hydrogen isotope in erbium oxide: Adsorption, penetration, diffusion, and vacancy trapping

• H adsorption on cubic Er2O3 surface results in electron transfer from H to the surface.
• The H penetration energy of at least 1.6 eV is required for cubic Er2O3 surface.
• The dominated mechanisms of H diffusion in bulk Er2O3 are elucidated.
• H diffusion near or at vacancies in Er2O3 is an exothermic reaction.

In this study, we report results using first-principles density functional theory calculations for four critical aspects of the interaction: H adsorption on Er2O3 surface, surface-to-subsurface penetration of H into Er2O3, bulk diffusion of H in Er2O3, and trapping of H at vacancies. We identify surface stable adsorption positions and find that H prefers to transfer electrons to the surfaces and form covalent bonds with the nearest neighboring four oxygen atoms. For low surface coverage of H as in our case (0.89 × 1014 H/cm2), a penetration energy of at least 1.60 eV is required for cubic Er2O3 surfaces. Further, the H diffusion barrier between the planes defined by Er2O3 units along the favorable 〈1 1 1〉 direction is found to be very small – 0.16 eV – whereas higher barriers of 0.41 eV and 1.64 eV are required for diffusion across the planes, somewhat higher than the diffusion energy barrier of 0.20 eV observed experimentally at 873 K. In addition, we predict that interstitial H is exothermically trapped when it approaches a vacancy with the vacancy defect behaving as an electron trap since the H-vacancy defect is found to be more stable than the intrinsic defect.