# Crystal

(Difference between revisions)
 Revision as of 12:36, 3 April 2009 (view source)← Older edit Revision as of 12:41, 3 April 2009 (view source)Newer edit → Line 13: Line 13: == See also == == See also == - ''Acta Cryst.'' (1992), '''A48''', 928 [http://dx.doi.org/10.1107/S0108767392008328] + ''Acta Cryst.'' (1992), '''A48''', 928. [http://dx.doi.org/10.1107/S0108767392008328 The definition is given in the '''Terms of reference''' of the IUCr commission on aperiodic crystals] [[Category:Fundamental crystallography]] [[Category:Fundamental crystallography]]

## Definition

A material is a crystal if it has essentially a sharp diffraction pattern. The word essentially means that most of the intensity of the diffraction is concentrated in relatively sharp Bragg peaks, besides the always present diffuse scattering. In all cases, the positions of the diffraction peaks can be expressed by

$\textbf{H}=\sum_{i=1}^nh_{i}\textbf{a}_{i}^{*}~~(n\ge 3)$

Here $\textbf{a}_{i}$ and hi are the reciprocal lattice vectors and integer coefficients respectively.

The conventional crystals are a special class, though very large, for which n = 3.