Stability and migration of charged oxygen interstitials in ThO2 and CeO2

Density functional theory calculations have been carried out to study the stability and migration of charged oxygen interstitials in ThO2 and CeO2. The calculations demonstrate that the oxygen interstitial is likely to lose electrons under p-type conditions and gain electrons under n-type conditions. Neutral image and singly positive image O–O〈1 1 0〉 split interstitials, and doubly negative octahedral (image) oxygen interstitial are found to be the lowest-energy configurations within a certain Fermi energy range. In both oxides, the image is the most mobile, and the migration energies of the split oxygen interstitials in ThO2 are lower than in CeO2, indicating higher oxygen interstitial mobility in ThO2 than in CeO2.