Diffusion of oxygen in bcc Fe under the influence of other foreign atoms

Density Functional Theory (DFT) and Atomistic Kinetic Monte Carlo (AKMC) simulations are applied to investigate the diffusion of oxygen in bcc Fe under the influence of substitutional foreign atoms, such as Al, Si, P, S, Ti, Cr, Mn, Ni, Y, Mo, and W. These atoms are assumed to be immobile since their diffusion coefficient is much smaller than that of oxygen.
In the first part of the work jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites are investigated by DFT. It is found that the first-neighbor jump is most relevant with the tetrahedral site as the saddle point. The second-neighbor jump consists of two consecutive first-neighbor jumps whereas the barrier of the third-neighbor jump is too high to be significant for the diffusion process. In the second part DFT is applied to determine the modified migration barriers, i.e. for the oxygen jump between the first and the second neighbor of the substitutional foreign atom, etc. Si, P, Ni, Mo and W influence the migration barriers of oxygen and their interaction energy with O is mainly repulsive. While Al, Cr and Mn have also a significant influence on the barriers they show strong attractive interactions. The strongest modification of the barriers is found for S, Ti, and Y where deep attractive states exist. At large distance from the solutes the O migration barriers converge to the value for pure Fe. The most relevant migration paths are first-neighbor jumps between (modified) octahedral sites with (modified) tetrahedral sites as saddle points. Finally, the diffusion coefficient of oxygen is determined by AKMC simulations on a rigid lattice, considering a dilute iron alloy and using the migration barriers calculated by DFT. Si, P, Ni, Mo, and W have almost no influence on the diffusivity of O, i.e. it is nearly identical to that in pure bcc Fe. The presence of Al, Cr, Mn, S, Ti, and Y causes a reduction of the mobility of oxygen. The strongest decrease of the diffusion coefficient is obtained for the foreign atoms S, Ti, and Y.