The effect of various contaminants (Al, Ga, Co, Fe, Mg, Zn, Zr, Ca, Sr, Ba) upon TiO2 ceramics was studied. Color boundary migration, caused by Al diffusion in Nb-doped material, was measured quantitatively. From the kinetics of the boundary migration, the Al diffusivity was deduced to be given by:

D (cm2/s) = 2.67 exp[−53.3(kcal/mol)/RT]

at 1200 to 1400C. Rapid diffusion of small cations (Al, Ga, Co, Fe, Mg) resulted from an interstitial diffusion mechanism. Other cations, with radii larger than the interstitial channel radius (~0.77Å) could not diffuse via this mechanism.

M.F.Yan, W.W.Rhodes: Journal of Applied Physics, 1982, 53[12], 8809-18