USE OF KIKUCHI LINE INTERSECTIONS IN CRYSTAL SYMMETRY DETERMINATION - APPLICATION TO CHALCOPYRITE STRUCTURE

The crystallographic point group 4BAR2m of chalcopyrite has been determined using Kikuchi diffraction patterns obtained in both the TEM and the SEM. Backscatter Kikuchi diffraction patterns (BKDPs) recorded in the SEM revealed evidence for the breakdown of Friedel's law, thus confirming the non-centrosymmetric structure of chalcopyrite. In addition, shifted Kikuchi line intersections were observed in BKDPs within the Ohh systematic row of reflections, indicating that the [100] axis has Laue group 2, in agreement with 4BAR2m. Diffraction patterns obtained from chalcopyrite in the TEM also revealed fine displacements at the intersections of various Kikuchi lines including 413BAR and 43BAR1, in agreement with the point group symmetry of chalcopyrite. It was observed that Kikuchi line intersections were sensitive to small differences in interplanar spacings and were unaffected by variations in specimen thickness, diffraction intensities and off-axis electron beams.