Powder X-ray diffraction and crystal identification

In this technique, which is the most important structure determination tool, a small single crystal of the material, of the order of a fraction of a millimetre in size, is mounted in a beam of X-rays. The diffraction pattern used to be recorded photographically, but now the task is carried out electronically. The technique has been used to solve enormously complex structures, such as that of huge proteins, or DNA. 

When the intensity and the positions of the diffraction pattern are taken into account, the pattern is unique for a single substance. The X-ray diffraction pattern of a substance can be likened to a fingerprint, and mixtures of different crystals can be analysed if a reference set of patterns is consulted. This technique is routine in metallurgical and mineralogical laboratories. The same technique is widely used in the determination of phase diagrams. 

An extension of the experiments to higher temperatures will allow the whole of the solid part of the phase diagram to be mapped. 

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