Ab Initio Study of He Migrations in Fcc Au-Ag Alloys

Ab initio calculations based on the density functional theory have been performed to investigate the migrations of interstitial helium (He) atoms in Au-Ag alloys with two different mass ratios (Au₃Ag₂ and AuAg). The results show that the migration mechanisms of He atoms mainly depend on the crystal structures of alloys, and their migration energy barriers are affected by the migration paths in Au-Ag alloys. He interstitials preferentially occupied the most stable sites, but it is difficult for He interstitials to migrate to nearest most stable sites via second stable positions at room temperature. When He atom is at the tetrahedral position which has higher formation energy, it possibly migrates to nearest tetrahedral positions directly for AuAg alloy. In addition, comparing the migration of He defects in the two alloys, we found that the properties of migration energy and relative stability of He atoms probably slightly depend on the mass-density of Au-Ag alloys.