The self-diffusion of 44Ti was measured both parallel to and perpendicular to the c-axis in rutile single crystals by a serial-sectioning technique at 1000 to 1500C under oxygen partial pressures of 10−14 to 1atm. The oxygen partial-pressure dependence of DTi indicated that cation self-diffusion occurred by an interstitial-type mechanism and that both trivalent and tetravalent interstitial titanium ions may contribute to cation self-diffusion. At PO2 = 1.50 x 10−7atm where impurity-induced defects were unimportant,

D||c(cm2/s) = 6.50 x 100exp[-66.11(kcal/mol)/RT]

and

D⊥c(cm2/s) = 4.55 x 100exp[-64.08(kcal/mol)/RT]

In the intrinsic region the ratio, D⊥c/D||c, was found to increase from 1.2 to 1.6 as the temperature decreased from 1500 to 1000C. Computations based upon the defect model of Kofstad, of Marucco et al., and of Blumenthal et al. were compared with the experimental data on deviation from stoichiometry, electrical conductivity, cation self-diffusion and chemical diffusion in TiO2−x. These comparisons provided values of defect concentrations, cation-defect diffusivities, electron mobility and reasonable values of the correlation factor for cation diffusion via the interstitialcy mechanism. Only the model of Kofstad was inconsistent with the data.

Diffusion and Point Defects in TiO2-x. Hoshino, K., Peterson, N.L., Wiley, C.L.: Journal of Physics and Chemistry of Solids, 1985, 46[12], 1397-411