Molecular dynamics simulations of oxygen Frenkel pairs in cerium dioxide

Molecular dynamics simulations of oxygen Frenkel pairs (FPs) in cerium dioxide (CeO₂) were carried out in order to understand their kinetic behavior. The results show that an oxygen FP recombine with the vacancy and the interstitial after the vacancy jump preferentially along the 〈1 0 0〉 direction. When multiple oxygen FPs are introduced, the interstitials aggregate into a (1 1 1) plate-like cluster at relatively lower temperature lower than 600 K, while they recombine with vacancies at elevated temperatures higher than 900 K within 10 ps. Molecular mechanics calculations of oxygen FPs on a (1 1 1) plane show that the formation energy per a FP decreases with increase of the number of FPs. The theoretical results are consistent with the transmission electron microscopy observations of formation of 1/9〈1 1 1〉{1 1 1} oxygen interstitial platelets in CeO₂ under electron irradiation.