The dimer method with the Ackland EAM potential was used to determine the diffusion mechanisms of isolated defects in the bulk of α-Fe. Three defect systems were studied, an isolated vacancy, a P-vacancy complex and a P interstitial defect. Using an event table consisting of the transitions found using the dimer method, the kinetic Monte Carlo method was used to simulate the diffusion of these defects. Periodic boundary conditions were used to simulate Fe crystals with finite concentrations of P atoms between 0.006 and 0.038at%. At around 350K, substitutional P atoms in Fe acted as centers of attraction for vacancy defects, such that the defect moves as a P-vacancy complex for most of the time. However, as the temperature was increased, the P atom and the vacancy spend greater amounts of time dissociated. It was found that P interstitial defects could also diffuse through the lattice. Diffusion constants were calculated for these systems at various temperatures and P concentrations. These showed that an Fe-P dumbbell was the most mobile of these defect systems and a P-vacancy complex the least mobile. For the isolated vacancy and P interstitial defect systems, the diffusion constant was found to satisfy the Arrhenius relation; the P-vacancy complex, however, showed a deviation from this relation.

Diffusion Dynamics of Defects in Fe and Fe-P Systems. S.M.J.Gordon, S.D.Kenny, R.Smith: Physical Review B, 2005, 72[21], 214104 (10pp)