policristaline

Policristaline, in English often referred to as polycrystalline, describes solids that are composed of many small crystals or grains, rather than a single continuous crystal. Each grain has a crystalline lattice, but the grains are oriented differently and meet at grain boundaries, which are regions of disrupted lattice continuity.

The microstructure of policristaline materials influences their properties. Grain boundaries can impede the movement of dislocations, which affects mechanical strength and hardness. In many cases, smaller grain sizes increase yield strength per the Hall-Petch relationship, while very small grains or certain boundary types can promote diffusion or creep along boundaries. The overall properties of a policristaline sample can be isotropic at a macroscopic scale if grain orientations are random, yet anisotropic behavior may appear locally depending on texture.

Production and processing methods for policristaline materials include casting, where crystals nucleate and grow into many grains, and powder metallurgy, where fine powders are sintered to form a consolidated body. Annealing and controlled heat treatments can modify grain size and distribution. Techniques such as hot rolling, extrusion, and sintering are commonly used to tailor the microstructure for specific applications.

Applications of policristaline materials are widespread. Most metals and many ceramics used in engineering are polycrystalline, including steel, aluminum alloys, and alumina. Polycrystalline silicon is standard in photovoltaic cells and some electronic devices, offering cost advantages over single-crystal forms. Characterization methods such as electron microscopy, X-ray diffraction, and electron backscatter diffraction are used to study grain size, orientation, and boundary characteristics.

See also: polycrystal, grain boundary, diffusion, Hall-Petch relationship.