The diffusive behavior of D in 5N-purity single crystals was studied at 720 to 1200C. The results could be described by:

D (cm2/s) = 7.3 x 10-3 exp[-8.79(kcal/mol)/RT]

L.Katz, M.Guinan, R.J.Borg: Physical Review B, 1971, 4[2], 330-41