# Difference between revisions of "Crystal"

### From Online Dictionary of Crystallography

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+ | <font color="blue">Cristal</font> (''Fr''). <font color="red">Kristall</font> (''Ge''). <font color="green">Cristal</font> (''Sp''). <font color="brown">Кристалл</font> (''Ru''). <font color="black">Cristallo</font> (''It''). <font color="purple">結晶</font> (''Ja'') | ||

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== Definition== | == Definition== | ||

## Revision as of 05:57, 4 March 2015

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), **A48**, 928 where the definition of a crystal appears in the **Terms of reference** of the IUCr commission on aperiodic crystals