Insights into the thermal decomposition of plutonium(IV) oxalate-a DFT study of the intermediate structures

The thermal decomposition of plutonium oxalate to oxide is one of the most studied reactions in actinide chemistry but the intermediates have been the subject of debate for decades. Recent experimental data suggest that the decomposition of Pu(IV) oxalate in air undergoes dehydration first, then reduction to Pu(III) oxalate. The precise structural modifications that take place are unknown as experiments have not been able to fully characterize the intermediates at the microscopic level. To rectify this, we employed solid state density functional theory calculations at the PBE-D3 level with a Hubbard U correction to model the structures and energetics of potential dehydrated Pu(IV) and Pu(III) oxalate intermediate compounds. Based on the theoretical study presented here, the anhydrous analogues of the known hydrated Pu(IV) and Pu(III) oxalates are the preferred crystal structures formed through an overall exothermic reaction process. However, decomposition could proceed through the formation of a higher energy, more complicated 3D lattice structure with frustrated oxalate binding. It is expected that the intermediates presented here could be identified using spectroscopic techniques to enable further insight into the reaction mechanism.& nbsp; (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The thermal decomposition of plutonium oxalate to oxide and the intermediates involved have been studied using solid state density functional theory calculations. The results suggest that anhydrous analogues of the hydrated Pu(IV) and Pu(III) oxalates are preferred crystal structures formed through an overall exothermic reaction process, with a possibility of more complex structures with higher energy formation as well.