THE ACTIVATION-ENERGY FOR LATTICE SELF-DIFFUSION AND THE ENGEL-BREWER THEORY

A phenomenological formula for the calculation of the activation energy for lattice self-diffusion is proposed. Use of the Engel-Brewer theory to determine the valence of an element provides an unambiguous means of calculating the activation energy from the formula Q = RT(m)(16 + V), where R is the gas constant, T(m) the melting temperature, and V the Engel-Brewer valence [1 for body-centered cubic (bcc) structures, 2 for close-packed hexagonal (cph) structures and 3 for face-centered cubic (fcc) structures]. The approach works well for the great majority of metals and correctly predicts the activation energy for diffusion in fcc argon and xenon. Diffusion coefficients for elements with other structures, elements with anomalous diffusion coefficients and semiconductors, are also discussed.