The plastic deformation of titanium dioxide single crystals

Abstract

Compression tests have been carried out, by means of a hard beam machine at a strain rate of 3.4 x 10$^{-4}$, on single crystals of titanium dioxide in air at atmospheric pressure and in vacuo and at temperatures up to 1300 $^\circ$C. Deformation is always by slip on the systems {101} $\langle$101$\rangle$ and {110} $\langle$001$\rangle$, the former slip system being by far the more active. It is proposed that the Burgers vector of a dislocation gliding on a {101} $\langle$101$\rangle$ system is $\frac{1}{2}\langle aOc\rangle$, and that pairs of partial dislocations are separated by stacking faults. Direct electron microscope evidence is presented for such stacking faults. As the composition of titanium dioxide deviates from the stoichiometric value, an increase in yield stress is observed, which may be explained in terms of an increase in lattice friction due to the interaction of point defects with dislocations. The effect of temperature and oxygen pressure on both the yield stress and rate of work hardening has also been examined.