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Figure 5
Reciprocal tetragonal lattices (hk0 lattice planes) of twin domain I (start domain, lattice points small circles) and of the Σ5 twin-related domain II (small crosses). The reciprocal lattice of the (direct-space) Σ5 coincidence lattice is represented by the grid of small squares. The unit cells, their handedness and their colours correspond to those of the direct lattices in Fig. 4[link]. In the square formed by the four reciprocal coincidence points 000, 2[\overline 1]0, 310, 120 (in terms of a1*, b1*) or 000, 500, 550, 050 (in terms of aT*, bT*) there are four `single' points of twin domains I and II each, one `coincident' point 000 and, with reference to aT*, bT*, 16 `extinct' reciprocal points (cf. Table 1[link]). These strange `non-space-group extinctions' are characteristic of the Σ5 twin law.

ISSN: 2053-2733
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