New insights into the process of intrinsic point defects in PuO(2)

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 PuO(2) 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 PuO(2). 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(O)(2+)} in an O-rich environment, while {4V(O)(1+): V(Pu)(4−)} is preferred in an O-deficient environment. These results differ from the commonly known {V(Pu)(4−): 2V(O)(2+)} type of Schottky defect. Moreover, under O-deficient conditions, we predict that the stable cation Frenkel defect is {V(Pu)(4+): Pu(i)(4+)}, while the most stable anion Frenkel defect is {V(O)(2+): 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(O)(5+)} and {O(Pu)(6−): Pu(O)(6+)}, with the latter being the more stable configuration. These unconventional defect configurations provide a new viewpoint on the process of intrinsic point defects in PuO(2) and lay theoretical foundations for future experiments.