A statistical analysis of previous data indicated that only those results which had been obtained by using electrochemical and H-gas equilibration methods involving ultra-high vacuum and Pd-coated membranes were reliable. It was concluded that, at -40 to  80C, the most trustworthy expression for D was:

D (m2/s) = 7.23 x 10-8 exp[-5.69(kJ/mol)/RT]

At between 50 and 550C, the best expression was suggested to be based upon a pre-exponential factor of between 10-7 and 2.52 x 10-7m2/s and an activation energy of between 6.70 and 7.12kJ/mol. It was proposed that the differing diffusivities were the result of an increase, with increasing temperature, of the fraction of H atoms which hopped from octahedral, rather than from tetrahedral, sites.

K.Kiuchi, R.B.McLellan: Acta Metallurgica, 1983, 31[7], 961-84