Kink model for extended defect migration in the presence of diffusing impurities: theory and simulation Original Research Article

The mobility of extended defects in solids (e.g., grain boundaries, anti-phase boundaries, dislocations, ferroelectric and magnetic domain walls) is often controlled by their interactions with impurities that can move diffusively. In this paper, we develop a theoretical model for extended defect migration in the presence of diffusing impurities which is valid in cases where impurity drag is significant. Model predictions of boundary velocity versus driving force, bulk impurity concentration, impurity diffusivity and temperature were shown to be in good agreement with kinetic Monte Carlo simulations based on an Ising model. At low temperatures and/or sufficiently large bulk concentrations, the kink model predicts that the boundary mobility is independent of the bulk impurity concentration. The activation energy for boundary migration is shown to depend on the formation energy of kinks on the boundary, the heat of segregation and the activation energy for bulk diffusion. The dependence on the kink formation energy remains even in the strong impurity drag limit. The present model is compared with earlier continuum models.