The possibility of measuring the so-called true grain boundary diffusivity in the type-C kinetic regime was illustrated for Ag self-diffusion. It was noted that there existed a transitional regime in which a classical analysis of grain-boundary diffusion profiles (assuming B-type or C-type conditions) was inapplicable. An alternative method for treating this regime was tested. It permitted the determination of both the true grain-boundary double products, and the true grain-boundary diffusion coefficients, from the experimental profiles. The ratio of these values furnished the thickness of the grain boundary. This value was consistent with the usually assumed value of 0.5nm. At temperatures of between 423 and 803K, the true grain-boundary diffusivity of Ag could be described by:

D (m2/s) = 1.26 x 10-5exp[-0.87(eV)/kT]

P.Gas, D.L.Beke, J.Bernardini. Philosophical Magazine Letters, 1992, 65[3], 133-9