First-principles study of the effect of lanthanum on the niobium diffusion in fcc Fe

The effect of La on the diffusion of Nb in fcc Fe has been investigated using the first-principles calculations based on the density functional theory. The binding energies of Nbvacancy, Lavacancy and LaNb pairs have been calculated. The interactions of Nbvacancy and LaNb are attractive in 1nn and 2nn configurations (nn: nearestneighbor). La atom attracts strongly with the 1nn vacancy, but has a weakly repulsive interaction with the 2nn vacancy. We consider four different Nb jumps in the presence of La atom to investigate the Nb diffusion in terms of vacancy formation and migration energy. The results suggest that La increases the diffusion activation energy of Nb in fcc Fe matrix, and is helpful to decelerate the Nb-diffusion-involved phase transformation process.