Theoretical investigations of interstitial atoms in bcc metals: Local lattice distortion and diffusion barrier

In this paper, the local asymmetrical distortion (measured as the dipole shape factor) induced by interstitial atoms (IAs: C, N, and O) in bcc-metals (V, Nb, and Ta) and the diffusion barriers of the IAs in the matrix are calculated by the use of a first-principles pseudopotential method. The obtained dipole shape factor and diffusion barrier are in reasonable agreement with the experimental values. The trend of the dipole shape factor and diffusion barrier with respect to the IAs and host metals are discussed in terms of the size difference between the IA and the interstice, the chemical and elastic interaction between the IA and the host metals. It is shown that both the size difference and the chemical interaction affect significantly the dipole shape factor, whereas the diffusion barrier is dominated by the chemical interaction.

► For the same matrix, dipole shape factor increases in sequence of C, N, O.
► For the same IA, dipole shape factor decreases in sequence of V, Nb, Ta.
► Both size effect and chemical interaction affect the component λ1 of λ-tensor.
► The diffusion barrier of IAs is dominated by chemical interaction.