The diffusion of 55Fe in nickel oxide was studied in air at 1000 to 1400C, using a decrease in surface activity method. The measured diffusion coefficients were expressed as:

D(cm2/s) = 1.81 x 10-3 exp[-44.5(kcal/mol)/RT]

K.J.Richards, F.E.Wagstaff: Journal of Physical Chemistry, 1966, 70[5], 1553-7