The so-called single crystal (monocrystal, monocrystalline, single crystal), that is, the crystalline body inside the particles in three-dimensional space is a regular, periodic arrangement, or that the whole crystal in the three-dimensional direction by the same space lattice composition, the whole crystal in the arrangement of the material points in the space for the long-range order; single crystal lattice is continuous.
Polycrystalline is a collection of single crystals with many oriented grains. Both polycrystals and single crystals are based on a periodic structure of dots, and they are essentially the same for the same type of crystal. The difference between the two is that single crystals are anisotropic and polycrystals are isotropic.
Some crystals are composed of many small grains, if the arrangement of the grains is not regular, this crystal is called polycrystalline, such as the metal copper and iron.
But there are also crystals itself is a complete large grain, this kind of crystal is called a monocrystalline body, such as crystal and diamond. Crystals in the directional order of the atoms or ions is a single crystal, and vice versa is a polycrystalline body, under certain conditions polycrystalline body can be transformed into a monocrystalline body, and similarly monocrystalline body can be transformed into a polycrystalline body. Polycrystalline and monocrystalline differences are mainly manifested in the physical propertie
