The Soret effect in diffusion in crystals

The Soret effect, as it occurs in the diffusion of solutes in crystals, is analyzed using the principle of microscopic reversibility whereby an approach is developed for interpreting and computing Q∗, the heat of transport. To compute the transport of energy during the diffusion jump process, and then Q∗, the processes of thermal activation to the transition state and the decay from the transition state are considered to be inverses; thus the net process is reduced to the analysis of the purely mechanical decay process. Molecular statics and dynamics are then suggested as the means to simulate the decay process and the case of carbon diffusion in body-centered cubic α-iron is so analyzed as an example. Our results show that, for the case Q∗ ≈ −Qm, where Qm is the activation energy for carbon diffusion, this is in agreement with experimental evidence reported in the literature. Thus both the sign and magnitude of Q∗ are correctly predicted. Various cases, such as the diffusion of substitutional solutes and vacancies, are also considered within our approach along with implications for future study.