Crystal

(Difference between revisions)
 Revision as of 10:59, 15 February 2010 (view source) (→Definition)← Older edit Revision as of 11:51, 6 February 2012 (view source)mNewer edit → Line 14: Line 14: ''Acta Cryst.'' (1992), '''A48''', 928 where  the definition of a  [http://dx.doi.org/10.1107/S0108767392008328 crystal]  appears in the '''Terms of reference''' of the IUCr commission on aperiodic crystals ''Acta Cryst.'' (1992), '''A48''', 928 where  the definition of a  [http://dx.doi.org/10.1107/S0108767392008328 crystal]  appears 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 and the number n is the minimum for which the positions of the peaks can be described with integer coefficient hi.

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