The ion-driven permeation technique was used to determine the diffusivity. The steady-state permeation rate and the diffusion coefficient tended to decrease with increasing fluence, because of changes in the surface or sub-surface regions. It was found that the results could be described by:

D (cm2/s) = 3.9 x 10-3 exp[-9.2(kcal/mol)/RT]

at 500 to 1100K.

Y.Furuyama, T.Tanabe, S.Imoto: Journal of the Japan Institute of Metals, 1986, 50[8], 688-94