crystallite

Crystallite refers to a region of a crystal that has a uniform lattice orientation. In a polycrystalline material, many crystallites are joined together; the interfaces between them are grain boundaries. Crystallite size typically ranges from a few nanometers to tens of micrometers, depending on the material and processing.

Crystallite size can be estimated from diffraction data. X-ray diffraction measures peak broadening related to finite crystallite size; the Scherrer equation relates peak width to size. Other methods include transmission electron microscopy and electron backscatter diffraction, which can image or map orientations of individual crystallites.

Formation and properties: The crystallite size is controlled by processing such as milling, annealing, and deposition conditions. Smaller crystallites increase the density of grain boundaries, which can strengthen materials through the Hall-Petch effect but may reduce electrical or thermal conductivity and increase diffusion along boundaries. At very small sizes, nanoscale effects can alter optical, magnetic, or catalytic properties.

Applications: Control of crystallite size is important in metals and alloys for mechanical properties, in ceramics and semiconductors for microstructure, and in catalytic nanoparticles where active surface area is linked to crystallite size. Crystallite size is a key parameter in materials design and performance.