INTRODUCTION
Few techniques have contributed as much to the understanding of matter as X-Ray diffraction (XRD). XRD is a constantly-evolving analytical technique that can provide fundamental information about the structure of matter, and also provide direct support in resolving many industrial problems. X-ray diffraction has given us knowledge of the internal structure of all compounds and materials, including those in common use, such as steel and ceramics, and of the distinction between polymorphs, i.e. substances with the same ”chemistry” but a different crystal habit. For example, graphite and diamond, as well as other forms of carbon recently identified, such as graphene and nanotubes; or austenite and ferrite in steels; but also glass and quatz, which are respectively the amorphous and crystalline forms of silicon dioxide. XRD has also contributed fundamentally in the field of biology, for example in the discovery of the double helix structure of DNA, and it is now the standard technique used to understand and develop new pharmaceutical compounds, and in the study of proteins and viruses.
In parallel to this fundamental contribution on the structure of materials, X-ray diffraction is used in a variety of industrial technologies and activities. Through XRD it is possible to identify and quantify the presence of crystalline phases, the ‘components’ of various materials, or to know the form and dimension of the crystals that they consist of, as well as the type and density of defects, such as the density of dislocations caused by the plastic deformation of a metal. In the area of technology, XRD can be used to measure residual stresses in mechanical components or in electronics, and the orientation or arrangement of the crystals in coatings and thin films, fibres or various types of surface layers.
XRD is available at laboratory scale, but also at the big synchrotron facilities, for cutting edge research on materials, on the chemistry and physics of matter. XRD is used increasingly in industry, and it is estimated that over 2/3 of XRD machines are in company research and development departments.
