International
Tables for
Crystallography
Volume B
Reciprocal space
Edited by U. Shmueli

International Tables for Crystallography (2006). Vol. B. ch. 2.5, p. 293   | 1 | 2 |

Figure 2.5.3.4 

P. Goodmanb
[Figure 2.5.3.4]
Figure 2.5.3.4

(a) Zone-axis patterns from hexagonal structures β-[\hbox{Si}_{3}\hbox{N}_{4}] (left) and β-GaS (right) together with the appropriate planar figures for point symmetries 6 and 6mm, respectively. (b) [[12\bar{1}0]] zone-axis pattern from β-[\hbox{Si}_{3}\hbox{N}_{4}], showing Friedel's law breakdown in symmetry between 0002 and [000\bar{2}] reflections (Bando, 1981[link]). (c) Conjugate pair of [1\bar{1}01/\bar{1}101] patterns from β-GaS, taken near the [[110\bar{2}]] zone axis, showing a translational symmetry associated with structural centrosymmetry.