It was demonstrated that the phenomenological concept of free volume, which had originally been introduced for the case of diffusion in supercooled liquids, could be modified in order to describe the temperature dependence of self-diffusion in crystalline metals. As a result, the Van Limpt-Bugakov relationship between the self-diffusion activation energy and melting point was confirmed.

A Free Volume Approach for Self-Diffusion in Metals. F.G.Shi, T.G.Nieh, Y.T.Chou: Scripta Materialia, 2000, 43[3], 265-7