The diffusion coefficient of Na was determined by using a radiotracer technique. For Te-rich undoped material (p-type), the diffusion coefficient could be represented by,

D(cm2/s) = 0·17 exp[-1.91(eV)/kT]

The diffusion coefficient was found to increase with increasing sodium concentration.

A.J.Crocker, B.F.Dorning: Journal of Physics and Chemistry of Solids, 1968, 29[1], 155-61