Ab initio study of gallium stabilized δ-plutonium alloys and hydrogen–vacancy complexes

Abstract

All-electron density functional theory was used to investigate δ-plutonium (δ-Pu) alloyed with gallium (Ga) impurities at 3.125, 6.25, 9.375 atomic (at)% Ga concentrations. The results indicated that the lowest energy structure is anti-ferromagnetic, independent of the Ga concentration. At higher Ga concentrations (>3.125 at%), the position of the Ga atoms are separated by four nearest neighbor Pu–Pu shells. The results also showed that the lattice constant contracts with increasing Ga concentration, which is in agreement with experimental data. Furthermore with increasing Ga concentration, the face-centered-cubic structure becomes more stably coupled with increasing short-range disorder. The formation energies show that the alloying process is exothermic, with an energy range of −0.028 to −0.099 eV/atom. The analyses of the partial density of states indicated that the Pu–Ga interactions are dominated by Pu 6d and Ga 4p hybridizations, as well as Ga 4s–4p hybridizations. Finally, the computed formation energies for vacancy and hydrogen–vacancy complexes within the 3.125 at% Ga cell were 1.12 eV (endothermic) and −3.88 eV (exothermic), respectively. In addition, the hydrogen atom prefers to interact much more strongly to the Pu atom than the Ga atom in the hydrogen–vacancy complex.