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

Evidence of a temperature transition for denuded zone formation in nanocrystalline Fe under He irradiation

“…However, the rapid formation of helium-vacancy complexes can affect the migration of the vacancies. It was reported [31] that migration of helium-vacancy complexes can occur at temperatures higher than 573 K (the low temperature case in this study). Moreover, vacancies are predicted to be unstable at temperatures below 573 K and can only be stabilized through helium-vacancy complex formation [31].…”

“…It was reported [31] that migration of helium-vacancy complexes can occur at temperatures higher than 573 K (the low temperature case in this study). Moreover, vacancies are predicted to be unstable at temperatures below 573 K and can only be stabilized through helium-vacancy complex formation [31]. Therefore, one might expect a change in the efficiency in the migration of small helium-vacancy complexes in the 700 K irradiation case.…”

Helium and point defect accumulation: (ii) kinetic modelling

“…According to some calculations [34,35] the migration through the vacancy mechanism for conditions with low ratios of FP per He atom is negligible. Other authors, however, consider this as the only mechanism responsible for He migration [36,37].…”

“…The lifetimes and migration energies of He n V m clusters have also been studied by Borodin and co-workers using, in this case, input from ab initio calculations [36,37]. These authors show that vacancy clusters (without He) are mobile but at temperatures relevant for fusion conditions are unstable and dissociate, and, therefore, are not expected to contribute significantly to self-diffusion.…”

“…There is a smaller number of calculations devoted to study long term evolution of He in α-Fe based on ab initio or empirical potential calculations [15,[33][34][35][36][37]. Simulations are compared, in most cases, with thermal helium desorption spectroscopy experiments, one among the few experiments from which information on He behaviour in iron can be obtained indirectly.…”