
It's easy in principle: You produce
and measure a diffusion profile. 




Put whatever is supposed to diffuse on the
crystal surface (make sure you cope properly with the "dirt" or oxide
on the surface). 



Let it diffuse at a defined T for a
defined time t. 



Measure the diffusion profile
"somehow". 



Fit to a solution of Fick's law = one data point
for D(T). 



Repeat at different temperatures until you gave
enough data points for an (Arrhenius) D(T) plot. 







Use isotopes of the material in
question for selfdiffusion measurements. 







While the intrinsic point defect
serving as diffusion vehicle will do a perfectly random walk, the diffusing
atom may not. 




There is a correlation coefficient
f linking measured and theoretical diffusion coefficients. 







D_{SD}(T) 
= 
f_{1V} · D_{SD}(Theo) 









The correlation coefficient f is
= 0 for 1dim. diffusion, around 1/2  2/3 for 2dim.
diffusion (e.g. in the base plane of hexagonal lattices) and around 2/3 
3/4 for 3dim. diffusion. 






There are many other ways to obtain
diffusion data, none foolproof and all money and/or time expensive. 





