He diffusion in irradiated α-Fe: An ab-initio-based rate theory model

The diffusion of He in irradiated α-Fe is studied using a rate theory model addressing the effect of impurities. Ab initio values for the migration and binding energies of He, He-vacancy complexes, vacancy, and self-interstitial clusters are used to model desorption experiments of He-implanted α-Fe. Using the brute ab initio data yields a significant discrepancy with experimental measurements. On the other hand, good agreement is obtained when the vacancy migration energy is increased from the original ab initio value while the binding energies of vacancies with substitutional and interstitial helium are lowered. The presence of impurities, with carbon being the most likely candidate, is proposed as a justification for these effective energies. Our simulations also provide a detailed description of the diffusion mechanisms of He active under these particular experimental conditions.