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Synchrotron Laue topography studies of pseudo‐hexagonal twinning
Author(s) -
Docherty R.,
ElKorashy A.,
Jennissen H.D.,
Klapper H.,
Roberts K. J.,
ScheffenLauenroth T.
Publication year - 1988
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s002188988800408x
Subject(s) - crystal twinning , synchrotron radiation , orthorhombic crystal system , synchrotron , reciprocal lattice , hexagonal crystal system , optics , lattice (music) , crystallography , physics , x ray , macle , x ray crystallography , diffraction , materials science , condensed matter physics , chemistry , microstructure , acoustics
Pseudo‐hexagonally twinned orthorhombic crystals generally exhibit three domain variants related by mirror planes or (approximately) by 120° rotations. The reciprocal lattices of the three domains coincide partially. Those reciprocal‐lattice points hkl with h + k = 2 N coincide or are split depending upon the deviation of the a : b ratio from orthohexagonality ( i.e. a : b = tan 60°). With (white‐beam) synchrotron radiation these domains are simultaneously imaged by Laue X‐ray topography for these reflections. Lattice points hkl with h + k = 2 N + 1 are `single' and only one of the three domain variants is imaged in such reflections. Two examples of these twins are presented, LiNH 4 SO 4 and (NH 4 ) 2 SO 4 . In the former case the lattice is closer to the ideal ratio a : b = tan 60° than the latter. These two cases are contrasted. Both materials are subject to some extent to radiation damage in the synchrotron beam.