Thermally activated migration of defects drives microstructural evolution of materials under irradiation. In the case of vacancies, the activation energy for migration was many times the absolute temperature, and the dependence of the diffusion coefficient on temperature was well approximated by the Arrhenius law. On the other hand the activation energy for the migration of self-interstitial defects, and particularly self-interstitial atom clusters, was very low. In this case a trajectory of a defect performing Brownian motion at or above room temperature did not follow the Arrhenius-like pattern of migration involving infrequent hops separated by the relatively long intervals of time during which a defect resides at a certain point in the crystal lattice. A review was given of recent atomistic simulations of migration of individual interstitial defects, as well as clusters of interstitial defects, and rationalizes the results of simulations on the basis of solutions of the multi-string Frenkel–Kontorova model. The treatment developed here shows that the origin of the non-Arrhenius migration of interstitial defects and interstitial defect clusters was associated with the interaction between a defect and the classical field of thermal phonons.

The Non-Arrhenius Migration of Interstitial Defects in BCC Transition Metals. S.L.Dudarev: Comptes Rendus Physique, 2008, 9[3-4], 409-17