# Bragg's law

### From Online Dictionary of Crystallography

##### Revision as of 07:56, 27 March 2006 by AndreAuthier (talk | contribs)

Loi de Bragg (*Fr*). Bragg Gesetz (*Ge*). Ley de Bragg (*Sp*). Legge di Bragg (*It*)

## Definition

Bragg's law provides the condition for a plane wave to be diffracted by a family of lattice planes:

2 *d _{hkl}* sin θ =

*n*λ.

where [math] d_{hkl} [/math] is the **lattice** spacing, θ the angle between the wavevector of the incident plane wave and the reflecting planes, λ its wave length and *n* is an integer, the order of the reflection. It is equivalent to the diffraction condition in reciprocal space and to the Laue equations.

## History

Bragg (1890-1971) presented his derivation of the reflection condition at a meeting of the Cambridge Philosophical Society on 11 November 1912. His paper was published in 1913 (Bragg W.L., 1913, *The Diffraction of Short Electromagnetic Waves by a Crystal*, *Proc. Cambridge Phil. Soc.*, **17**, 43-57. For details, see P. P. Ewald, 1962, IUCr, 50 Years of X-ray Diffraction, Section 5, page 64.

## See also