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Figure 9
Hexagonal lattices (ab planes, common c axis pointing upwards) of twin domain I (start domain, lattice points small circles, right-handed green unit cell a1, b1, c1), of the Σ7 twin-related domain II (small crosses, left-handed blue unit cell a2, b2, c2) and of the Σ7 coincidence lattice (large black points, right-handed red unit cell aT, bT, cT). The six alternative twin reflection planes m′(12[\bar 3]0), m′([\overline 3]120), m′(2[\overline 3]10), m′([\overline 5]410), m′(1[\overline 5]40) and m′(41[\overline 5]0) are indicated by dashed lines. The coordinate axes a2, b2, c2 of domain II (blue) are defined by the reflection plane m′(12[\overline 3]0). The right-handed yellow unit cell a3, b3, c3 of domain II is obtained from a1, b1, c1 by a clockwise rotation of φ = 120° + 2 arcsin [(1/2)(3/7)1/2] = 120° + 38.2° = 158.2° around the hexagonal axis (cf. Appendix C[link]). This cell is commonly used in structure determinations.

ISSN: 2053-2733
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