Monocrystalline
A monocrystalline, also known as a single crystal, is a crystal where the internal particles are arranged in a regular and periodic manner in three-dimensional space. In other words, the entire crystal is composed of a uniform spatial lattice in all three dimensions, and the arrangement of particles within the crystal is long-range ordered. The crystal lattice of a monocrystal is continuous throughout the structure.
Polycrystalline
A polycrystalline is a collection of single crystal grains with different orientations. Both polycrystalline and monocrystalline are based on a periodic lattice structure. Essentially, for the same type of crystal, their nature is identical. The difference lies in the fact that monocrystalline are anisotropic, while polycrystalline are isotropic.
Some crystals are made up of many small grains. When these grains are arranged without a specific order, the crystal is referred to as a polycrystalline, such as copper and iron metals.
On the other hand, some crystals are a single, large, and complete grain. These are referred to as monocrystalline, such as quartz and diamond. Crystals in which atoms or ions are aligned in an orderly and directional manner are monocrystalline, while those without this order are polycrystalline. Under certain conditions, polycrystalline can transform into monocrystalline, and similarly, monocrystalline can also transform into polycrystalline. The main difference between polycrystalline and monocrystalline is in their physical properties.
