The native surface oxide of plutonium plays a critical role in ensuring the stability and safe storage of the underlying metal; consequently, understanding the role of defects and impurities in determining the properties of the oxide layer is critical. Here, we use hybrid density-functional theory calculations to evaluate the electronic structure and defect chemistry of ${\mathrm{PuO}}_2$, the most stable of the native oxide phases, including both native and extrinsic defects. We find that oxygen vacancies ($V_{\mathrm{O}}$) form readily in ${\mathrm{PuO}}_2$, as do polarons. Electron polarons (${\eta }^{-}$) are the lowest-energy acceptor species in ${\mathrm{PuO}}_2$, while the charge compensating donor species will shift from $V_{\mathrm{O}}$ under O-poor conditions to hole polarons (${\eta }^{+}$) under O-rich conditions. Nitrogen and fluorine can substitute readily for oxygen atoms under O-poor conditions, while fluorine can also incorporate in an interstitial configuration (${\mathrm{F}}_i^{-}$) under more O-rich conditions. Carbon and chlorine incorporation in ${\mathrm{PuO}}_2$ will be very limited. We also evaluate the kinetic barriers for oxygen-related defects, which we find to diffuse readily when present. Our results provide valuable insights into the critical role and variable chemistry of point defects and impurities in ${\mathrm{PuO}}_2$, which in turn have important implications for the safe storage of the underlying metal layer. In short, exposure of freshly prepared plutonium to reactive nitrogen- and fluorine-containing contaminants should be avoided, while carbon- or chlorine-containing contaminants are less likely to incorporate readily into the oxide.

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• Impurities in superconductors
• Point defects
• Actinides
• Oxides
• Density functional theory
• Hybrid functionals