Small interstitial-type defects in iron with complex structures and very low mobilities were revealed by molecular dynamics simulations. The stability of these defect clusters formed by non-parallel {110} dumb-bells was confirmed by density functional theory calculations, and it was shown to increase with increasing temperature due to large vibrational formation entropies. This new family of defects provided an explanation for the low mobility of clusters needed to account for experimental observations of microstructure evolution under irradiation at variance with the fast migration obtained from previous atomistic simulations for conventional self-interstitial clusters.

Self-Trapped Interstitial-Type Defects in Iron. D.A.Terentyev, T.P.Klaver, P.Olsson, M.C.Marinica, F.Willaime, C.Domain, L.Malerba: Physical Review Letters, 2008, 100[14], 145503