Observation of Dynamic Extinction Lines in the (420) Diffraction Disks of the MgAl2O4 Spinel <100> CBED Pattern

Abstract

Many people have observed dynamic extinction lines in the {200} diffraction disks of the <100> zone axis CBED (convergent beam electron diffraction) patterns of the MgAl2O4 spinel. These dark lines are manifestation of the space group of the material and can easily be explained with the Gjønnes-Moodie theory. However, in addition to the extinction lines in the {200} disks, We have also been able to observe dynamic extinction lines present in the {420} diffraction disks in the same CBED pattern.The CBED work in this work was carried out with a JEOL-2000FX microscope operated at 100.15 kV. One <100> zone axis CBED pattern is shown in Fig. 1. The dark lines are clearly shown in the {420} disks running through the two perpendicular non-principal axes, in exactly same way as the dark lines in {200} disks.One can easily explain the dynamic extinction lines in the {200} disks with the Gjønnes-Moodie theory by drawing dynamic scattering pairs oG-Ga and oH-Ha, oK-Ka and oL-La etc. in the diagram (Fig. 2).