The diffusivity of Nb was measured in α- and γ-phase material by using serial sectioning techniques. The diffusivity in both phases was greater, by a factor of 6 to 10, as compared with the value for self-diffusion. For the γ-phase, the results could be described by:

D (cm2/s) = 8.3 x 10-1 exp[-63.5(kcal/mol)/RT]

and were attributed to normal vacancy diffusion. The diffusivity in the α-phase was much lower, below the Curie temperature, due to magnetic ordering effects. In the paramagnetic state, the results could be described by:

D (cm2/s) = 5.02 x 101 exp[-60(kcal/mol)/RT]

It was suggested that magnetic ordering had some effect upon diffusion, even above the Curie temperature.

J.Geise, C.Herzig: Zeitschrift für Metallkunde, 1985, 76[9], 622-6