The self-diffusion of 44Ti was measured parallel to, and perpendicular to, the c-axis of

rutile single crystals by using a serial-sectioning technique at 1000 to 1500C under O partial pressures of 10-14 to 1atm (table 200). The O-partial-pressure dependence indicated that cation self-diffusion occurred via an interstitial-type mechanism and that both trivalent and tetravalent interstitial Ti ions could contribute to cation self-diffusion. At PO2 = 1.50 x 10-7atm, where impurity-induced defects were unimportant,

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

and,

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

In the intrinsic region, the perpendicular/parallel ratio was found to increase from 1.2 to 1.6 as the temperature decreased from 1500 to 1000C.

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