grain (rus. зерно) — homogeneous part of a solid body that has clearly identifiable boundaries observed by means of optical or electron microscopy; single element of a polycrystalline material.


Grain size is determined by optical or electron microscopy as the average distance between opposing grain boundaries, and can range in various materials from several nanometres to several millimetres. In a range of sizes up to 100 nm when the sizes of the grain and the coherent scattering region are usually the same, the average grain size can be estimated by calculating the size of the coherent scattering region on the basis of X-ray diffraction data. This method is most accurate within the range of 20-50 nm.

Russian and international standards govern the rules for determining the size and shape of grains in metals and alloys. Automated systems designed for the analysis of images obtained by optical microscopy are widely used to determine the grain size in metallic systems. The average grain size in this case is calculated as the mean of random grain sections of the polycrystalline material.

Grains may contain crystallographic defects of twinning (twins), whose presence does not affect the grain size.


BiNbO4 ceramic grains microphotography  taken by 
Oleg A. Shlyakhtin
BiNbO4 ceramic grains microphotography  taken by  Oleg A. Shlyakhtin  at Lomonosov Moscow State University.Photograph from personal the files.


  • Zhuravleva Natalya G.
  • Shlyakhtin Oleg A.

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