Explanation

The smallest building unit constituting the crystal structure. Generally, it is a parallelepiped with the highest symmetry and the smallest volume in the crystal structure. The entire crystal structure can be obtained by infinitely repeating the parallelepiped along three edges in space. The space lattice of crystal (sometimes called crystal lattice) can be abstracted from the equivalent points in the crystal structure (the lattice or nodes with the same spatial environment), and the smallest building unit that constitutes the space lattice is called the unit cell. When each node of the space lattice is placed with a specific crystal structural particle (such as atoms, ions or molecules), the unit cell becomes a basic unit of crystal structure, also known as the unit unit cell of crystal of crystal structure or simply called unit cell of crystal. The principles for selecting cells in space lattice are: ① to fully reflect the symmetry of the entire space lattice; ② To have as many right angles as possible; ③ The volume should be as small as possible.

Classification