The diffusion coefficients of chloride ions were measured between 300 and 700C using an isotopic exchange method (table 120). In the extrinsic region, the coefficients did not decrease with increasing amounts of cation impurity to the extent required for diffusion by single vacancies.

Anion Diffusion in Crystals of NaCl. L.W.Barr, J.A.Morrison, P.A.Schroeder: Journal of Applied Physics, 1965, 36[2], 624