An investigation was made of the structure and mobility of single self-interstitial atom and vacancy defects in body-centred-cubic transition metals from groups 5B (V, Nb, Ta) and 6B (Cr, Mo, W). Density-functional calculations showed that, in all of these metals, the axially symmetrical <111> self-interstitial atom configuration had the lowest formation energy. In Cr, the difference between the energies of the <111> and the <110> self-interstitial configurations was very small; making the 2 structures almost degenerate. The local densities of states for the atoms which formed the core of crowdion configurations exhibited systematic widening of the so-called local d-band and an upward shift of the anti-bonding peak. Using the information provided by electronic structure calculations, a family of Finnis-Sinclair-type interatomic potentials was derived for V, Nb, Ta, Mo and W. Using these potentials, an investigation was made of the thermally activated migration of self-interstitial atom defects in W. The results of simulations, using analytical solutions of the multi-string Frenkel-Kontorova model which described non-linear elastic interactions between a defect and phonon excitations, were rationalized. It was found that the discreteness of the crystal lattice played a dominant part in the mobility of defects. It was found to be possible to explain the origin of the non-Arrhenius diffusion of crowdions, and to show that - at high temperatures - the diffusion coefficient varied linearly as a function of absolute temperature.

Multiscale Modeling of Crowdion and Vacancy Defects in Body-Centered-Cubic Transition Metals. P.M.Derlet, D.Nguyen-Manh, S.L.Dudarev: Physical Review B, 2007, 76[5], 054107 (22pp)