A first-principles study on Ga stabilized 6-Pu phase stability based on structural and electronic properties

The high temperature face-centered-cubic delta phase of plutonium (FCC 6-Pu) is metallurgically important in industrial applications and can be stabilized at room temperature by alloying with small amounts of gallium (Ga). Therefore, it is of fundamental interest to elucidate the factors that govern the 6-Pu-Ga interactions via the electronic structure to understand the stabilization mechanism of the FCC phase. We employed density functional theory to systematically model the change in the structural and electronic properties with increasing Ga concentrations of 6-Pu-Ga alloys. The results indicate that structural optimizations with an applied cubic symmetry constraint are sufficient to describe the alloy properties. The variations in Pu-Pu and Pu-Ga bond lengths and the lattice disorder induced by the Ga substitution at Pu sites are in qualitative agreement with previously published experimental EXAFS data. Additionally, in accordance with the experimental results, the atomic volume decreases as the Ga concentration increases. The alloy formation energy decreases as the Ga concentration increases, indicating an increase in stability and an exothermic alloying reaction. The Pu-Ga electronic interaction is governed principally by hybridization between the Pu 6d and Ga 4p states, with decreasing Pu 5f states at the Fermi energy with increasing Ga content due to the increase of Ga-Pu-Ga bonds within the lattice.