Sessile ⟨100⟩ self-interstitial clusters with non-parallel edge dumbbells in irradiated bcc Fe and other metals

Density Functional Theory calculations of self-interstitial atom clusters in bcc Fe unexpectedly show that from ∼9–14 self-interstitial atoms, an intriguing new family of sessile ⟨100⟩ clusters, surrounded by ⟨110⟩ dumbbells, are more stable than highly mobile clusters of parallel ⟨111⟩ dumbbells. The ⟨110⟩ edge dumbbells find a favorable location in terms of strain energy on the tensile side around the edges of the ⟨100⟩ center, thus stabilizing the clusters. These sessile clusters might explain resistivity recovery results that suggested an absence of glissile self-interstitial clusters up to large cluster sizes in irradiated Fe, while smaller self-interstitial atom clusters likely would have been present. The mechanism of non-parallel edge interstitials stabilizing an otherwise higher energy interstitial loop is also found in some fcc metals.