The application of eigensymmetries of face forms to X-ray diffraction intensities of crystals twinned by `reticular merohedry'

Klapper, H.; Hahn, Th.

doi:10.1107/S0108767311032454

Figure 2
X-ray topographs (Mo Kα₁ radiation) of an obverse/reverse growth twin of FeBO₃ (calcite structure, space group R $[\overline 3]$ m), grown from the vapour phase by chemical transport. (0001) plate (diameter about 3.5 mm, thickness 0.2 mm), cut close to the centre of the crystal. (a) `Single' reflection { $[\overline 2]$ 202} (rhombohedron) of obverse domain I (domain II `extinct'); (b) `single' reflection {2 $[\overline 2]$ 02} (rhombohedron) of domain II (domain I `extinct'); (c) coincident reflection {2 $[{\overline 1}{\overline 1}]$ 3} (hexagonal dipyramid) with equal F moduli of domains I and II (no domain contrast, diffraction case A). Arrows: diffraction vectors. In (a) and (b) the domains appear by `black-and-white' contrast. The dark contrasts in the domains result from crystal defects. The straight contrast lines are dislocations or dislocation bundles. Note that the twin boundaries do not show diffraction contrast (except for a very faint contrast ending on the re-entrant corner marked by a small arrow in (c), indicating a good structural fit of the domains along their boundaries. The hexagonal contrast feature in the centre of (c) results from the growth-sector boundaries between the (0001) pinacoid and the {1 $[\overline 1]$ 01} rhombohedral growth faces. Courtesy of D. Götz et al. (2012

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ISSN: 2053-2733

Volume 68| Part 1| November 2012| Pages 82-109

doi:10.1107/S0108767311032454

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