The diffusivity was measured along, and at right-angles to, the c-axis of monocrystals of the -phase at 773 to 1124K by using tracer and secondary ion mass spectrometric techniques. The results revealed a temperature dependence which could be explained by invoking 2 regions of diffusion behavior. At temperatures above 1035K, the diffusivity could be described by:

D (cm2/s) = 1.7 x 101 exp[-2.93(eV)/kT]

At temperatures below 1035K, the diffusivities appeared to be higher than the values which were predicted by extrapolation from higher temperatures.

G.M.Hood, H.Zou, R.J.Schultz, E.H.Bromley, J.A.Jackman: Journal of Nuclear Materials, 1994, 217[3], 229-32