Inclination of self-interstitial dumbbells in molybdenum and tungsten; A First-principles study

Suzudo, Tomoaki   ; Tsuru, Tomohito   

In the current study, we analyzed the self-interstitial atoms (SIAs) in BCC molybdenum (Mo) and tungsten (W) in comparison with other BCC transition metals utilizing first-principles method; particularly, we focused on uncommon dumbbells, whose direction are inclined from 111 toward 110 on the {110} plane. Such a direction is not stable neither in the group 5 BCC metals (i.e., vanadium, niobium, and tantalum) nor in -iron. Our first-principles relaxation simulations indicated that inclined dumbbells were more energetically-favored than common 111 dumbbells in Mo, while this is not necessarily the case for W. However, under a certain degree of lattice strain, such as shear or expansive strain, could make inclined dumbbells more favored also in W, suggesting that the lattice strain can substantially influence the migration barrier of SIAs in these metals because inclined dumbbells generally have a larger migration barrier than 111 dumbbells.