First-principles study of helium behavior in nickel with noble gas incorporation

The behavior of helium in nickel with noble gas atom (helium, neon, argon, krypton, and xenon) incorporations is systematically studied by using the first-principles method. The formation energies of noble gas atoms in nickel increase with atomic size increase from helium to xenon. All noble gas atoms considered in this work energetically prefer to stay at the substitutional sites when compared to the interstitial ones. The variations in formation energies among noble gas atoms can be mainly attributed to the steric effects caused by their incorporation. The chemical binding between nickel and noble gas atoms are further identified by their projected density of states. The substitutional noble gas shows a trapping effect on interstitial helium, and their binding energies also exhibit an approximately linear relation with their size. In addition, the effect of noble gas incorporation on helium clustering in nickel is studied. It shows that noble gas atoms attract small helium clusters and further repel the relatively larger ones. The results help to understand the influence of noble gas atoms on the fundamental helium behavior such as helium stability, trapping, and clustering in nickel and are also technologically important for further study on helium bubble nucleation under similar irradiation conditions.