X-ray diffraction

X-ray diffraction is a technique used to investigate the crystal structure of a sample. X-rays are incident on the sample at a range of angles, giving a diffraction pattern since the crystal lattice of the sample constitutues a diffraction grating.  At certain angles, the diffracted waves add constructively, so the XRD detector detects a “peak” at these angles. The angle that these peaks are found at depends on the crystallographic parameters of the material ie. the lattice spacing, so these can be extracted from the XRD results via Bragg’s law. This law describes the relationship between the diffraction angle, the wavelength of the incident beam, and the planar spacing in the lattice.

Information about the crystal structure of the sample, and the phases present may also be found, given that each crystal structure contains its own set of characteristic planes which appear in XRD analysis (these are not necessarily the only planes present – intermedicate planes may not be visible via XRD as the nature of the diffraction means that some signals may interfere destructively). For example, a body-centred cubic structure shows a trio of peaks corresponding to the 110, 200, and 211 planes, which will allow a phase of this structure to be identified.

Powder diffraction may also be used in order to provide a textured isotropic sample, therefore representing each plane in the signal due to the random orientation of each particle.