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