A thin-layer method was used to study the diffusion, and final-concentration versus distance profiles were measured by using an optical absorption method. The Arrhenius plot exhibited 2 straight segments. The results for low temperatures (table 204) could be described by:

D (cm2/s) = 10.0 exp[-1.00(eV)/kT]

The results for high temperatures could be described by:

D (cm2/s) = 0.026 exp[-0.652(eV)/kT]

The diffusion coefficient for Cu exceeded the self-diffusion coefficient for Na by factors of 1000 to 10000. The data strongly suggested that, above 415C, most of the Cu impurity was interstitial.

Copper Impurity Diffusion in Sodium Iodide. N.H.Chan, W.J.Van Scriver: Physical Review B, 1975, 12[8], 3438-48