A first-principles study on Ga stabilized δ-Pu alloys

The puzzling behavior of the 5f electrons makes plutonium metal one of most complex materials in the periodic table. It has six solid phases that go through five solid-state phase transformations in a relatively short temperature range, and these solid phases have interestingly crystal symmetries coupled with different mechanical properties. The room temperature low-symmetry monoclinic α-phase is brittle and the high-temperature high symmetry face-centered-cubic δ-phase is ductile. Essentially, ductility makes the δ-phase metallurgically easier to manipulate. Stabilizing the δ-phase to room temperature requires alloying with an element from Group IIIA (Al, Ga, In, and Tl) where the stability zones is dependent on alloying solute concentrations and temperature. For Ga stabilized δ-Pu, upon cooling the alloy undergoes a decomposition into other pure solid phases of Pu and Pu-Ga alloys according to the Russian phase diagram contrary to the US phase diagram which indicates metastability. In this work, we employ density functional theory to investigate the thermodynamics and electronic structures of Ga-δ-Pu alloys from 0 to 9at% of Ga to further understand the metastability of δ-Pu from a first-principles perspective.