One-Dimensional Diffusion of Li in Rutile

Abstract

The diffusion of interstitial Li in rutile (Ti${\mathrm{O}}_2$) was measured over a temperature range of 80-360°C, 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 $D$ parallel by a factor of at least ${10}^8$ up to 550°C. $D$ parallel was accurately described by $D=D_0{e}^{-\frac{Q}{\mathrm{KT}}}$ with $Q=0.330\mathrm{}\pm 0.003$ eV and $D_0=0.295\mathrm{}\pm 0.028$ ${\mathrm{cm}}^2$/sec (95% confidence limits). Concentrations and solubility of Li in rutile were measured approximately using chemical analysis; a solubility limit of 2.5×${10}^{19}$/${\mathrm{cm}}^3$ at room temperature was obtained. Lattice distortion and other impurities strongly inhibit Li diffusion. Possible explanations for apparent deviations from Fick's law are suggested, based on the assumption that the optical absorption associated with Li doping is conduction electrons.