Nitrogen has high electronegativity and can form a series of nitrides with many elements with lower electronegativity, including three types of ionic nitrides, covalent nitrides and metal nitrides. Boron Nitride

The nitrides formed by alkali metals and alkaline earth metal elements belong to ionic nitrides, and their crystals are mainly ionic bonds, and the nitrogen elements exist in the form of N3-, which is also called salt-like nitrides. The chemical properties of ionic nitrides are more active, and they are easily hydrolyzed to generate corresponding hydroxides and ammonia. At present, Li3N in ionic nitrides is used. Li3N is a deep red solid and belongs to the hexagonal crystal system. It has a density of 1.27g/cm3 and a melting point of 813°C. It is easy to synthesize and has high ionic conductivity. It can be combined with solid or liquid lithium. Coexistence is one of the solid lithium electrolytes currently available.

The nitrides formed by group IIIA~VIIA elements are covalent nitrides, and their crystals are dominated by covalent bonds. Among them, the compounds formed by oxygen, group VIIA elements and nitrogen elements should be accurately called nitrogen oxides and nitrogen halides. The most widely used covalent nitrides are the nitrides of IIIA and IVA elements (such as BN, AlN, GaN, InN, C3N4 and Si3N4, etc.). The structural unit is similar to the tetrahedron of diamond, so it is also called class Diamond nitride. They have high hardness, high melting point, and good chemical stability. Most of them are edge bodies or semiconductors. They are widely used in cutting tools, high-temperature ceramics, microelectronic devices, and luminescent materials.

Nitrides formed by transition metal elements belong to metallic nitrides. Nitrogen atoms are located in cubic or hexagonal close-packed metal lattice gaps, which are also called infill nitrides. The chemical formula of this type of nitride does not follow a strict stoichiometric ratio, and its composition can vary within a range. Most metal-type nitrides have a NaCl-type structure, and the chemical formula is MN-type. Generally, it has metal-like properties, such as metallic luster, good conductivity, high hardness, high melting point, damage and corrosion resistance, etc., and has good application prospects in cutting materials, electrical materials and catalytic materials.