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 10
Reciprocal hexagonal lattices (hk0 lattice planes) of twin domain I (start domain, lattice points small circles) and of the [Sigma]

7 twin-related domain II (small crosses). The reciprocal lattice of the (direct-space) [Sigma]

7 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

. 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 a_T*, b_T*) there are six `single' points of twin domains I and II each, one `coincident' point 000 and, with reference to a_T*, b_T*, 36 `extinct' reciprocal points (cf. Table 1

). These strange `non-space-group extinctions' are characteristic of the [Sigma]

7 twin law.