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Figure 10
Reciprocal hexagonal lattices (hk0 lattice planes) of twin domain I (start domain, lattice points small circles) and of the Σ7 twin-related domain II (small crosses). The reciprocal lattice of the (direct-space) Σ7 coincidence lattice is represented by the grid of small rhombuses. The unit cells, their handedness and their colours correspond to those of the direct lattices in Fig. 9[link]. In the large cell formed by the four reciprocal coincidence points 000, 3[\overline 1]0, 410, 120 (in terms of a1*, b1*) or 000, 700, 770, 070 (in terms of aT*, bT*) there are six `single' points of twin domains I and II each, one `coincident' point 000 and, with reference to aT*, bT*, 36 `extinct' reciprocal points (cf. Table 1[link]). These strange `non-space-group extinctions' are characteristic of the Σ7 twin law.

ISSN: 2053-2733
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