Burgers vector determination in deformed perovskite and post-perovskite of CaIrO 3 using thickness fringes in weak-beam dark-field images

Abstract

The thickness-fringe method [Ishida et al. , Philosophical Magazine 42 (1980) 453] for complete determination of the character of a dislocation Burgers vector has been performed in CaIrO 3 perovskite and post-perovskite deformed at high pressures and high temperatures. By selecting several main zone axes and determining the number of terminating thickness fringes at the extremity of a dislocation from a wedge-shaped thin-foil specimen in weak-beam dark-field transmission electron microscope (TEM) images, the Burgers vectors were unambiguously determined. The results demonstrate that [1 0 0] screw and edge dislocations on the (0 1 0) slip plane are dominant in the post-perovskite phase. Curved [1 0 0] and [0 1 0] dislocations and straight 〈1 1 0〉 screw dislocations on a potential (0 0 1) slip plane were identified in the perovskite phase as well as a high density of {1 1 0} twins. Low-angle tilt boundaries consisting of different groups of parallel edge dislocations on the {1 1 0} and (0 0 1) planes indicate diffusion-assisted climb in perovskite at high temperatures. The differences in dislocation microstructures could be due to activations of limited numbers of slip systems for post-perovskite and of a large number of multiple slip systems for perovskite, which may result in the strong crystallographic preferred orientation (CPO) in post-perovskite and the lack of CPO in deformed perovskite.