An efficient approach to characterize pseudo-merohedral twins by precession electron diffraction: application to the LaGaO(3) perovskite.
Pseudo-merohedral twins are frequently observed in crystals displaying pseudo-symmetry. In these crystals, many [u v w] zone axis electron diffraction patterns are very close and can only be distinguished from intensity considerations. On conventional diffraction patterns (selected-area electron diffraction or microdiffraction), a strong dynamical behaviour averages the diffracted intensities so that only the positions of the reflections on a pattern can be considered. On precession electron diffraction patterns, the diffracted beams display an integrated intensity and a "few-beam" or "systematic row" behaviour prevails which strongly reduces the dynamical interactions. Therefore the diffracted intensity can be taken into account. A procedure based on observation of the weak extra-reflections connected with the pseudo-symmetry is given to identify without ambiguity any zone axis. It is successfully applied to the identification and characterization of {1 2 1} reflection twins present in the LaGaO(3) perovskite.
Ji
G
G
Laboratoire de Métallurgie Physique et Génie des Matériaux, UMR CNRS 8517, USTL and ENSCL, Cité Scientifique, Villeneuve d'Ascq, France. gang.ji@univ-lille1.fr
Morniroli
J-P
JP
Auchterlonie
G J
GJ
Drennan
J
J
Jacob
D
D