Diffusion coefficients and thermal stability of small helium–vacancy clusters in iron

Recent studies of helium clustering kinetics in bcc iron have revealed noticeable mobility of small He–vacancy complexes, which are commonly thought of as immobile. Here, the lifetimes and diffusion coefficients of small He–vacancy clusters were quantified. These kinetic parameters were estimated for clusters of different sizes and compositions by lattice kinetic Monte-Carlo using ab initio data for helium and vacancy interactions energies. It is shown that nanosized He–vacancy clusters have high thermal stability. It is also found that the diffusion coefficients of some small clusters are indeed very high, being at 573 K only 1–2 orders of magnitude lower than the diffusion coefficient of a monovacancy. Finally, it is demonstrated how the coupling of Monte-Carlo numeric experiments with the rate theory approach can be used for the estimation of the rate theory parameters, such as the defect and cluster agglomeration rates.