## Abstract

The diffraction contrast from isolated {101} and {1$\overline{3}$2} planar faults in rutile has been reexamined, bearing in mind that the displacement vectors R = <uvw> may not be defined by simple integers. Our analysis confirms the previously reported R = $\frac{1}{2}$$\langle $10$\overline{1}$$\rangle $ at {101} faults, but shows that, at {1$\overline{3}$2} faults, R $\doteqdot $ $\frac{1}{2}$$\langle $0, 0.90, 0.90$\rangle $ and not $\frac{1}{6}$$\langle $211$\rangle $ as has been suggested. This new value is close to R = $\frac{1}{2}$$\langle $011$\rangle $, which is also the 'ideal' displacement vector at ordered {1$\overline{2}$1} c.s. planes in the reduced rutiles Ti$_{n}$O$_{2n-1}$, 4 $\leq $ n $\leq $ 9. The modified criterion for extinction, g. R = N $\pm $ 0.02, applies only when the crystal thickness is an integral multiple of the extinction distance. For half integral values strong fringe contrast can occur for [Note: See the image of page 147 for this formatted text]|g.R - N| < 0.02.