It was found that the data for polycrystalline samples, at 650 to 900C, were described by:

D (cm2/s) = 1.08 x 100 exp[-44.80(kcal/mol)/RT]

S.D.Gertsriken, D.D.Tsitsiliano: Fizika Metallov i Metallovedenie, 1958, 6, 89