Thermodynamical Stability of Substoichiometric Plutonium Monocarbide from First-principles Calculation

Plutonium monocarbide, which contains a considerable amount of vacancies in the carbon sublattice, has never been synthesized in a stoichiometric form. The intriguing substoichiometric behavior of plutonium monocarbide is investigated here using first-principles calculation combined with the special quasirandom structure. It is found that the NaCl-type substoichiometric plutonium monocarbide is stable for PuC$_{0.741-0.923}$, which is in good agreement with the experiment. From the electronic structure calculations and chemical bond analyses, the stabilization of PuC$_{1-x}$ in this range is attributed to strengthened Pu-C bonds opposite to the carbon vacancies.