Transmission electron microscopy, using 2-beam dynamic conditions, were used to determine the direction of the displacement vector of planar faults in specimens of pyrite (Pa3¯). The nature of the fringe contrast which was exhibited by the faults confirmed them to be antiphase domain boundaries. Experimental and computer-simulated selected-area diffraction patterns, and experimental convergent-beam electron diffraction patterns, were used to account for the relatively high intensity of the kinematically forbidden reflections which were observed experimentally. The high intensity of the forbidden reflections in the experimental selected-area diffraction patterns from faulted pyrites were successfully modelled by using a diffraction simulation of a pyrite lattice which contained an antiphase boundary. The experimental and simulated data indicated that the intensity of the kinematically forbidden reflections from pyrite arose from 3 separate mechanisms. One was double diffraction from translational symmetry elements in the pyrite lattice (which increased with specimen thickness). Another source was a small misorientation of the specimen away from the zone axis. The third source arose from the structure and configuration of the antiphase boundaries. The latter effect was expected to be predominant when boundaries in the plane of the thin-foil specimen were considered.

A.J.Strutt, K.S.Vecchio: Philosophical Magazine A, 1996, 73[3], 779-801