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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. (2012BB16).

ISSN: 2053-2733
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