Diffusion of interstitial species (H and O atoms) in fcc systems (Al, Cu, Co, Ni and Pd): Contribution of first and second order transition states

We present a discussion on the influence of high-order transition states on interstitial diffusion in fcc systems using first-principles calculations. In earlier works, only first-order transition states (1TS) were used to compute the diffusivity at the atomic-scale: the direct diffusion between tetrahedral (t) and octahedral (o) sites has been proposed to describe atomic-scale diffusion mechanisms. However, we show here that if this direct diffusion makes it possible to reproduce displacements remarkably well, neglecting higher-order transition states induces an underestimation of the diffusion coefficient at high temperature. We hereinafter revisit the diffusion coefficient of interstitial species in different fcc-systems. The effect of these configurations on atom diffusion in Al, Co, Cu, Ni and Pd, whose only stable sites are the tetrahedral and octahedral positions (H and O atoms) is thus discussed here. We show that if the correction is low, taking into account higher-transition states can modify the diffusivity values at high temperature.