The diffusion of interstitial Li in rutile was measured at 80 to 360C, utilizing the optical absorption associated with the Li impurity as a measure of its concentration. Diffusion was found to be strongly anisotropic with diffusion coefficient D perpendicular to the c-axis smaller than Dparallel by a factor of at least 108 up to 550C. Dparallel was accurately described by:

D (cm2/s) = 2.95 x 10-1exp[-0.330(eV)/kT]

(95% confidence limits). Concentrations and solubility of Li in rutile were measured approximately using chemical analysis; a solubility limit of 2.5 x 1019/cm3 at room temperature was obtained. Lattice distortion and other impurities strongly inhibited Li diffusion. Possible explanations for apparent deviations from Fick's law were suggested, based upon the assumption that the optical absorption associated with Li doping was due to conduction electrons.

One-Dimensional Diffusion of Li in Rutile. Johnson, O.W.: Physical Review A, 1964, 136, 284–90