Ab initio study of He point defects in fcc Au–Ag alloys

► Stability of He in Au–Ag alloys depends on atomic arrangements of nearest metals. ► Substitutional He is the most stable in Au–Ag alloys. ► Octahedral He interstitials are energetically more favorable than the tetrahedral. ► The properties of He defects slightly depend on the mass–density of Au–Ag alloys. ► Relative stability of He is due to hybridization between metal d and He p states. The relative stabilities of He defects in two fcc Au–Ag alloys (Au3Ag2 and AuAg) are investigated using ab initio method based on density functional theory. The results show that the stabilities of He defects in the two alloys mainly depend on the atomic arrangements of the nearest neighboring host metals. A He interstitial prefers to stay at a site with more Ag neighboring atoms, while the favorable substitutional site has more Au neighboring atoms in Au–Ag alloys. Moreover, the substitutional He defects are the most stable configurations in both the alloys, and the octahedral He interstitials are energetically more favorable than the tetrahedral interstitials. It is of interest to note that the properties of He defects slightly depend on the mass–density of Au–Ag alloys. The results also demonstrate that the relative stabilities of He defects are primarily attributed to the hybridization between metals d states and He p states.