The migration mechanisms and the corresponding activation energies of Cr-vacancy (Cr-V) clusters and Cr interstitials in α-Fe were investigated using the dimer and the nudged elastic-band methods. Dimer searches were employed to find the possible transition states of these defects and the lowest-energy paths were used to determine the energy barriers for migration. A substitutional Cr atom could migrate to a nearest-neighbour vacancy through an energy barrier of 0.56 eV but this simple mechanism alone was unlikely to lead to the long-distance migration of Cr unless there was a supersaturated concentration of vacancies in the system. The Cr-vacancy clusters could lead to long-distance migration of a Cr atom that was accomplished by Fe and Cr atoms successively jumping to nearest-neighbour vacancy positions, defined as a self-vacancy-assisted migration mechanism, with the migration energies ranging from 0.64 to 0.89 eV. In addition, a mixed Cr-Fe dumbbell interstitial could easily migrate through Fe lattices, with the migration energy barrier of 0.17, which was lower than that of the Fe-Fe interstitial. The on-site rotation of the Cr-Fe interstitial and Cr atom hopping from one site to another were believed to comprise the dominant migration mechanism. The calculated binding energies of Cr-V clusters were strongly dependent on the size of clusters and the concentration of Cr atoms in clusters.

Migration of Cr-Vacancy Clusters and Interstitial Cr in α-Fe using the Dimer Method. D.Chen, F.Gao, W.Y.Hu, S.Y.Hu, D.Terentyev, X.Sun, H.L.Heinisch, C.H.Henager, M.A.Khaleel: Physical Review B, 2010, 81[6], 064101