Polükristalliline

Polükristalliline refers to a solid material composed of many smaller, randomly oriented individual crystals. These individual crystals are known as grains or crystallites. The boundaries between these grains are called grain boundaries. In a polycrystalline material, the atoms are arranged in a crystalline lattice within each grain, but the orientation of this lattice differs from one grain to another. This differs from a single crystal, where the entire material possesses a continuous, unbroken crystalline lattice.

The properties of a polycrystalline material are often an average of the properties of its constituent grains and the influence of the grain boundaries. For instance, mechanical strength can be affected by grain size; smaller grains generally lead to higher strength. Electrical and thermal conductivity can also be influenced by the presence of grain boundaries, which can act as scattering sites for electrons or phonons. Many common metals, ceramics, and alloys are polycrystalline. Examples include steel, aluminum, and most types of glass (though glass is technically amorphous, it can exhibit microcrystalline structures). The process of creating or modifying polycrystalline materials often involves heat treatment, such as annealing, which can alter grain size and structure.