By combining diffraction contrast and high-resolution transmission electron microscopic imaging, a study was made of the relationship between the 2 most commonly observed features of shock-deformed sapphire. These were: 1/3<10•0> dislocations, and basal twins. It was noted that the triple partial dislocation could be identified by the fact that stacking-fault fringes appeared at the first and second partials, but disappeared after the third. High-resolution transmission electron microscopic imaging of this dislocation showed that the partial dislocation was not a co-planar partial, but was separated by one third of a unit cell along the [00•1] direction. This was the same as the height of the twin step. The twin-boundary dislocation which was associated with the twin step also had a Burgers vector of 1/3<10•0>. High-resolution transmission electron microscopy and diffraction contrast imaging suggested that the basal twin might be a mirror twin, with a glide of 1/3<10•0>. The overall conclusion drawn was that the partials were twinning dislocations for the basal twins.

S.J.Chen, D.G.Howitt: Philosophical Magazine A, 1998, 78[3], 765-76