polykrystallinsk

Polykrystallinsk, or polycrystalline, describes a solid material composed of many small crystals, or grains, each with its own crystallographic orientation. The grains are separated by grain boundaries, which are regions of mismatch where the lattice orientation changes. In a polycrystal, there is no single continuous crystal lattice spanning the entire material, as opposed to a monocrystal.

This structure arises during solidification and processing when multiple nucleation events occur or when grains grow together during annealing and deformation. Grain size can range from a few micrometers to several millimeters, depending on cooling rate, composition, and thermomechanical processing. Grain boundaries influence properties by hindering dislocation motion, affecting mechanical strength, and by altering diffusion, electrical, and thermal transport, as well as optical scattering.

Polycrystalline forms are ubiquitous in metals (such as steel, aluminum, brass), ceramics, and in many semiconductors, most notably polycrystalline silicon used in solar photovoltaic cells. Production methods include casting, hot or cold working, powder metallurgy, and directional solidification. In solar technology, large-area polysilicon ingots and ribbons are produced to form the active photovoltaic layer.

Compared with monocrystalline materials, polycrystals are typically cheaper to manufacture and can offer near-isotropic properties at macroscopic scales. However, grain boundaries can reduce fracture strength, electrical conductivity, and corrosion resistance depending on the material and environment. The properties of a polycrystal can often be described statistically via grain size distributions and texture.

Common term in materials science and solid-state physics; research focuses on controlling grain size and orientation to tailor strength, ductility, conductivity, and diffusion.