A phenomenological model was proposed for bulk self-diffusion and diffusion of interstitial atoms in the ranges of high (T > TD) and low (T < TD) temperatures (where TD was Debye temperature). It was shown that the mechanisms of diffusion at high and low temperatures differ significantly. In the high-temperature range, the diffusion was provided by fluctuations, which could be described in terms of local melting, i.e., the formation of a “liquid diffusion channel.” In the low-temperature range, when melting for some reasons was hindered, the diffusion was due to the fluctuation formation of a “hollow diffusion channel.” The calculation of the activation energies of these processes in the case of self-diffusion agreed well with the experiment in the temperature range T > TD and had demonstrated that the activation energy increased significantly at T < TD. The calculation of the activation energy for diffusion of interstitial atoms in body-centered cubic metals agreed well with the experiment in the entire temperature range and provided an explanation of the decrease in the activation energy of diffusion at low temperatures.

Mechanisms of Bulk Diffusion at “High” and “Low” Temperatures. V.N.Chuvildeev, E.S.Smirnova: Physics of the Solid State, 2011, 53[4], 779-85