# Difference between revisions of "Crystal"

### From Online Dictionary of Crystallography

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== See also == | == See also == | ||

− | ''Acta Cryst.'' (1992), ''' | + | *''Acta Cryst.'' (1992), A'''48''', 928 where the definition of a [https://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]] |

## Revision as of 10:58, 13 May 2017

Cristal (*Fr*). Kristall (*Ge*). Cristal (*Sp*). Кристалл (*Ru*). Cristallo (*It*). 結晶 (*Ja*)

## 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

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

Here [math]\textbf{a}_{i}^{*}[/math] and [math]h_{i}[/math] are the basis vectors of the reciprocal lattice and integer coefficients respectively and the number *n* is the minimum for which the positions of the peaks can be described with integer coefficient [math]h_{i}[/math].

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

## See also

*Acta Cryst.*(1992), A**48**, 928 where the definition of a crystal appears in the**Terms of reference**of the IUCr Commission on Aperiodic Crystals.