Is there an isotope effect for diffusion of an ion through a crystal lattice? Consider the diffusion of natural abundance $\ce{Li^{+}}$ and $\ce{{}^{6}Li^{+}}$ through a crystalline matrix, say a spinel such as $\ce{LiMn2O4}$.  The two lithium ions will have the same ionic radius and electric charge.  They will differ only in atomic weight.  Is there any reason to believe that the lighter isotope, $\ce{{}^{6}Li^{+}}$, will diffuse through the crystal any faster than the natural abundance isotope?  When I consider the forces acting upon the ions in the crystal, I come up with coloumbic, dispersion and hard shell repulsive forces.  I cannot see how any of those would change by simply changing the mass of the ion.  Am I missing anything?
$F = ma$, so a less massive isotope should move faster, depending on the forces moving it.