· A similar barrier to the diffusing atom exists for a vacancy mechanism of diffusion.
· The Gibbs function has the same minimum value in configurations (a) and (c). The saddle point location is shown in (b).
· For the atom to jump it must have a vacancy on an adjacent site. The probability of this is just the vacancy concentration, X_V.
X_V= (n_V/N) = exp(-Δ G_V/kT)
· The jump rate, R, is then the joint probability of having enough energy to jump, and a having a vacancy on an adjacent site:
R = ν exp(-Δ G_m/kT) exp(-Δ G_V/kT)