Calculation of strain effects on vacancy-mediated diffusion of impurities in fcc structures: General approach and application to Ni1-x Six

Transport coefficients, the elements of the so-called Onsager matrix, are required for accurate mesoscopic simulations of kinetics or to predict macroscopic diffusion kinetic behavior. These coefficients can be significantly affected by strain. At the atomic scale, the effect of strain on atomic jump frequencies can be computed using density functional theory calculations. The present work shows how these results can be used to compute the strain-dependent Onsager matrix. Using an analytical method - the self-consistent mean field method - we compute analytical expressions of the Onsager matrix describing vacancy-mediated diffusion of impurities in face-centered cubic structures under elementary strains. Also, we compute the derivatives of the Onsager matrix with respect to strain - the elasto-diffusion tensor - to investigate strain sensitivity of transport. We show that the atomic scale symmetry breaking induced by strain changes diffusion behavior qualitatively. This phenomenon is shown for the Ni(Si) alloy under tetragonal strain. The terms of the Onsager matrix are found to be non-Arrhenian, as well as their derivative with respect to strain. In this case, nonlinear effects leading to a solute drag reduction are identified.