First-principles study of the incorporation and diffusion of helium in cubic zirconia

The incorporation and the diffusion of helium (He) with and without the intrinsic vacancy defects in the cubic ZrO2 are investigated through the first-principles total-energy calculations, in which the projector-augmented-wave (PAW) method with the generalized gradient approximation (GGA) is adopted. Ab initio calculations are carried out to identify the dominant defects and understand their electronic properties as well. Both the intrinsic oxygen interstitials and the oxygen vacancies in the cubic ZrO2 show the negative-U behavior. The incorporation energy of He impurity indicates that it is preferable to occupy the Zr vacancy at first, whereas the solution energy suggests that He would be accommodated in the interstitial site at the thermodynamic equilibrium concentration. By calculating the He migration energies corresponding to both the interstitial diffusion and the vacancy assisted diffusion, we suggest that it is most likely to diffuse by hopping through a single vacancy. Remarkably, our calculated vacancy-assisted diffusion energy barrier of He is consistent well with the experimental measurement.