The University of Sheffield
Department of Materials Science and Engineering

The X-ray Diffraction Small Research Facility: What is XRD?

What is XRD?

One of the most fundamental questions that we can ask of a material is simply `what is it?´ X-ray diffraction provides the answer.

The properties of a material can often be linked back to the arrangement of atoms in its crystal structure. X-ray diffraction is a non-destructive analytical technique which can yield the unique fingerprint of Bragg reflections associated with a crystal structure.

One can regard a crystal structure as being built of layers, or planes, which each act as a semi-transparent mirror. X-rays with a wavelength similar to the distances between these planes can be reflected such that the angle of reflection is equal to the angle of incidence. We call this behaviour `diffraction´, and it is described by Bragg's Law:

2dsinθ = nλ

When Bragg´s Law is satisfied, constructive interference of diffracted X-ray beams occur and a `Bragg reflection´ will be picked up by a detector scanning at this angle. The positions of these reflections tell us about the inter-layer spacings of atoms in the crystal structure, thanks to Bragg´s Law. Peak intensities give information about how much X-ray scattering is contributing to that reflection – e.g. where particular atoms lie in the structure, or how much of a phase is present in a sample.

Analysis of the diffraction pattern allows the identification of phases within a given sample. With that achieved, it may be possible to quantify each phase present, the crystallinity of a sample, the crystal structures and their lattice parameters, crystallite size and strain... all information that can be vital in material characterisation and quality control.

Useful links to learn more about XRD

XRD on Wikipedia

PanAlytical website

Bruker AXS website