Anomalous thermodynamic properties and phase stability of δ-Pu_(1-x)M_x (M=Ga and Al)alloys from first-principles calculations

摘要

The composition-dependent crystal structure, volume, elastic constants, and electronic structure of δ-Pu_(1-x)M_x (M = Ga and Al, 0 ≤ x ≤ 0.1) alloys are systematically studied by using first-principles EMTO-CPA calculations. It is shown that the fcc and Ll_2 structures co-exist in the alloys with x ≤ 0.04 whereas for x > 0.04, the L1_2 structure is more and more preferable and around x = 0.1, it tends to be stabilized alone. The evaluated V ～ x of the Ll_2 structure, being negative deviation from Vegard's law, turns out to be in good agreement with the experimental result. For x ≤ 0.04, the estimated E, G, v, and Θ of both the fcc and L1_2 structures are in line with the measured data, whereas when x > 0.04, only those of the L1_2 structure are close to the experimental results. The electronic hybridization between Pu and M atoms is dominated by Pu for the s, d, and f states but M for the p state. The strong interactions between Pu and M atoms in the same site of the L1_2 structure should be responsible for its relative stability in the alloys with x > 0.04. The electron-phonon coupling further decreases the phase stability of δ-Pu_(1-x)M_x with increasing x.