It was noted that self-interstitial atoms in body-centered cubic Fe displayed unusual migration behaviors; a strong anisotropy in a <111> direction with occasional rotation to an equivalent direction, as well as retracing the same path it had come along, and also a ultra-high mobility when they clustered. These singularities could not be explained by simple interstitial or interstitialcy diffusion mechanisms. However, some of them could be explained if the self-interstitial atom behaved as a soliton, which apparently made 3-dimensional movements, but really involved a combination of 1-dimensional migrations. Thus, a crowdion (an isomeric configuration of the self-interstitial atom) had an atomic arrangement which was very similar to the 1-dimensional dislocation core structure, whose migration kinetics were well modelled by a 1-dimensional soliton equation. Here, the decisive molecular dynamics simulation observation was made that both single and colliding 2 crowdions behaved as solitons in Fe crystals. It was deduced that the present results were due to the intrinsic nature of the crowdion, where the overall potential felt by atoms therein was very shallow, and periodic along the migration direction.

Solitonic Migration and Collisions of Self-Interstitial Defects in BCC Iron. K.Kusunoki: Materials Transactions, 2006, 47[11], 2658-62