Difference between revisions of "Laue class"
From Online Dictionary of Crystallography
AndreAuthier (talk | contribs) |
(→Definition: better formulation to emphasize the difference between a class and a group) |
||
| Line 4: | Line 4: | ||
== Definition == | == Definition == | ||
| − | The Laue classes | + | The Laue classes are eleven [[geometric crystal class]]es 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. |
| Line 10: | Line 10: | ||
{| border cellspacing="0" cellpadding="5" align=center> | {| border cellspacing="0" cellpadding="5" align=center> | ||
| − | |Laue classes||Non-centrosymmetric groups<br> | + | |Laue classes||Non-centrosymmetric groups<br> in the same Laue class |
|- | |- | ||
| <math>{\bar 1}</math>|| 1 | | <math>{\bar 1}</math>|| 1 | ||
Revision as of 14:26, 22 December 2016
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