It was found that the data for polycrystalline samples, at 750 to 925C, were described by:

D (cm2/s) = 5.8 x 10-1 exp[-45.0(kcal/mol)/RT]

A.A.Zhukhovitskii, A.E.Geodakhyan: Doklady Akademii Nauk SSSR, 1955, 102, 301