Title: Thermodynamical Stability of Plutonium Monoxide with Carbon Substitution
Abstract: The existence of condensed plutonium monoxide (PuO) has long been controversial, in which carbon element plays a vital role. In this work, we modeled PuO with carbon substitution of oxygen as the special quasirandom structures of NaCl-type plutonium monoxycarbide (PuOxC1–x) and performed first-principles calculations on these models. It is found that PuO could indeed be stabilized by carbon substitution. The amount of carbon element to stabilize PuO is very small if the source of carbon is CO or CO2. If the carbon is contributed by plutonium monocarbide, the range of stable PuOxC1–x agrees well with the experimental result. By analyzing the electronic structures and chemical bonds, we ascribe the stabilization of PuO by carbon substitution to the newly established Pu 5f/6d–C 2p hybridization around the Fermi level, i.e., stronger Pu–C bonds.