X-ray powder methods

Article By:

Jenkins, Ron International Center for Diffraction Data, Newtown Square, Pennsylvania.

Last reviewed:June 2020

DOI:https://doi.org/10.1036/1097-8542.751000

Physical techniques used for the identification of substances, and for other types of analyses, principally for crystalline materials in the solid state. In these techniques, a monochromatic beam of x-rays is directed onto a polycrystalline (powder) specimen, producing a diffraction pattern that is recorded on film or with a diffractometer. This x-ray pattern is a fundamental and unique property resulting from the atomic arrangement of the diffracting substance. Different substances have different atomic arrangements or crystal structures, and hence no two chemically distinct substances give identical diffraction patterns. Identification may be made by comparing the pattern of the unknown substance with patterns of known substances in a manner analogous to the identification of people by their fingerprints. The analytical information is different from that obtained by chemical or spectrographic analysis. X-ray identification of chemical compounds indicates the constituent elements and shows how they are combined.

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