It was pointed out that the thermally activated mobility of clusters of interstitial atoms was an important factor driving the microstructural evolution of materials under irradiation. Molecular dynamics simulations showed that the statistics of 1-dimensional Brownian motion of clusters was characterized by unusual correlated jumps which spanned many interatomic distances. The Frenkel-Kontorova model was used to investigate the dynamics of 1-dimensional Brownian motion of a spatially delocalized interstitial defect which interacted with acoustic phonon excitations. By using a quantum-mechanical approach, the coefficient of dissipative friction which characterized the stochastic motion of the defect was evaluated. It was shown that the origin of the unusual features observed in atomistic simulations was associated with the low friction experienced by an interstitial defect that propagated through the crystal lattice in the presence of thermal fluctuations. It was also found that the coefficient of dissipative friction was highly sensitive to the character of the interatomic bonding in the material.

Thermal Mobility of Interstitial Defects in Irradiated Materials. S.L.Dudarev: Physical Review B, 2002, 65[22], 224105 (8pp)