Diffusivity in single crystals was measured by using secondary ion mass spectrometry at 2195 to 2461K. The results could be described by:

D (cm2/s) = 4.0 x 100 exp[-137(kcal/mol)/RT]

The results were explained in terms of the Lazarus-LeClaire vacancy mechanism.

S.M.Klotsman, G.N.Tatarinova, A.N.Timofeev: Materials Science Forum, 1987, 15-18, 457-62