New insights into the process of intrinsic point defects in PuO₂

Intrinsic point defects are known to play a crucial role in determining the physical properties of solid-state materials. In this study, we systematically investigate the intrinsic point defects, including vacancies (V_Pu and V_O), interstitials (Pu_i and O_i), and antisite atoms (Pu_O and O_Pu) in PuO₂ using the first-principles plane wave pseudopotential method. Our calculations consider the whole charge state of these point defects, as well as the effect of oxygen partial pressure. This leads to a new perspective on the process of intrinsic point defects in PuO₂. We find that the antisite atoms O_Pu and Pu_O are more likely to appear in O-rich and O-deficient environments, respectively. Interestingly, the most energetically favorable type of Schottky defect is {2V_Pu^3-: 3V_O²⁺} in an O-rich environment, while {4V_O¹⁺: V_Pu^4-} is preferred in an O-deficient environment. These results differ from the commonly known {V_Pu^4-: 2V_O²⁺} type of Schottky defect. Moreover, under O-deficient conditions, we predict that the stable cation Frenkel defect is {V_Pu⁴⁺: Pu_i⁴⁺}, while the most stable anion Frenkel defect is {V_O²⁺: O_i^2-} under O-rich conditions. Lastly, we find that the only two types of antisite pairs that can appear are {O_Pu^5-: Pu_O⁵⁺} and {O_Pu^6-: Pu_O⁶⁺}, with the latter being the more stable configuration. These unconventional defect configurations provide a new viewpoint on the process of intrinsic point defects in PuO₂ and lay theoretical foundations for future experiments.