Self-interstitial transport in vanadium

We study the diffusion of self-interstitial atoms (SIAs) and SIA clusters in vanadium via molecular dynamics simulations with an improved Finnis-Sinclair potential (fit to first-principles results for SIA structure and energetics). The present results demonstrate that single SIAs exist in a 〈1 1 1〉-dumbbell configuration and migrate easily along 〈1 1 1〉 directions. Changes of direction through rotations into other 〈1 1 1〉 directions are infrequent at low temperatures, but become prominent at higher temperatures, thereby changing the migration path from predominantly one-dimensional to almost isotropically three-dimensional. SIA clusters (i.e., clusters of 〈1 1 1〉-dumbbells) can be described as perfect prismatic dislocation loops with Burgers vector and habit planes of 1/2〈1 1 1〉{2 2 0} that migrate only along their glide cylinder. SIA clusters also migrate along 〈1 1 1〉-directions, but do not rotate. Both single SIAs and their clusters exhibit a highly non-Arrhenius diffusivity, which originates from a combination of a temperature dependent correlation factor and the presence of very low migration barriers. At low temperature, the diffusion is approximately Arrhenius, while above room temperature, the diffusivity is a linear function of temperature. A simple model is proposed to describe these diffusion regimes and the transition between them.