Laue class
From Online Dictionary of Crystallography
Revision as of 14:26, 22 December 2016 by MassimoNespolo (talk | contribs) (→Definition: better formulation to emphasize the difference between a class and a group)
Revision as of 14:26, 22 December 2016 by MassimoNespolo (talk | contribs) (→Definition: better formulation to emphasize the difference between a class and a group)
Classes de Laue (Fr). Laue Klassen (Ge). Clases de Laue (Sp). Classi di Laue (It)
Definition
The Laue classes are eleven geometric crystal classes containing centrosymmetric crystallographic types of point groups and their subgroups. When absorption is negligible and Friedel's law applies, it is impossible to distinguish by diffraction between a centrosymmetric point group and one of its non-centrosymmetric subgroups; only point groups belonging to different Laue classes can then be distinguished.
Laue classes | Non-centrosymmetric groups in the same Laue class |
[math]{\bar 1}[/math] | 1 |
2/m | 2, m |
mmm | 222, 2mm |
[math]{\bar 3}[/math] | 3 |
[math]{\bar 3}m[/math] | 32, 3m |
4/m | 4, [math]{\bar 4}[/math] |
4/mmm | 422, [math]{\bar 4}2m[/math], 42m |
6/m | 6, [math]{\bar 6}[/math] |
6/mmm | 622, [math]{\bar 6}2m[/math], 62m |
[math]m{\bar 3}[/math] | 23 |
[math]m{\bar 3}m[/math] | 432, [math]{\bar 4}[/math]32 |
See also
Chapter 3.1 of International Tables of Crystallography, Section A
Chapter 2.4 of International Tables of Crystallography, Section D