First-principles DFT+Uinvestigation of charged states of defects and fission gas atoms inCeO2

Abstract

Cerium dioxide $({\mathrm{CeO}}_{2})$ is considered as a model material for the experimental study of radiation damage in the standard nuclear fuel uranium dioxide $({\mathrm{UO}}_{2})$. In this paper, we present a first-principles study in the framework of the DFT+$U$ approach to investigate the charged point defects and the incorporation of the fission gases Xe and Kr in ${\mathrm{CeO}}_{2}$ and compare it with published data in ${\mathrm{UO}}_{2}$. All intrinsic charge states are considered for point defects in contrast to previous published studies. Our calculations prove that ${\mathrm{CeO}}_{2}$ shows similar behavior to ${\mathrm{UO}}_{2}$ in the formation of point defects with the same charge states under stoichiometric and nonstoichiometric conditions. The charge states of vacancies have an important effect on the incorporation of fission gas atoms in ${\mathrm{CeO}}_{2}$. The bound Schottky defect with the two oxygen vacancies along the (100) direction is found to be energetically preferable to trap Xe and Kr atoms both in ${\mathrm{CeO}}_{2}$ and ${\mathrm{UO}}_{2}$. Xe and Kr atoms in the cation vacancy sites under nonformal charge states (different from $4\ensuremath{-}$) in ${\mathrm{CeO}}_{2}$, unlike in ${\mathrm{UO}}_{2}$, lose electrons to their neighboring atoms, which is traced back to the absence of the +5 valence state for Ce in contrast to its existence for U.