Hexagonal boron nitride (h-BN) is an allotrope of boron nitride (BN), with a hexagonal lattice. It is an extremely hard material, second only to diamond in terms of hardness. Hexagonal boron nitride has a wide range of applications, including as a lubricant, an electrical insulator, and a thermal conductor.
Boron nitride is a chemical compound composed of boron and nitrogen atoms. There are two main types of BN: cubic BN (c-BN) and hexagonal BN (h-BN). Both c-BN and h-BN are synthetically produced; natural BN does not exist. h-BN is also known as white graphene due to its similar appearance to the better-known carbon allotrope graphene. Both h-BN and graphene have honeycomb structures; however, the atoms in h-BN are arranged in a hexagonal pattern, while those in graphene are arranged in a triangular pattern.
The differences between c-BN and h-BN arise from the different ways that the boron and nitrogen atoms bond together. In c-BN, each atom bonds with three other atoms to form tetrahedral units; this results in a close packing of the atoms and gives rise to covalent bonding between them. In contrast, each atom in h-BD bonds with two other atoms; this leads to weaker interatomic interactions and predominately ionic bonding between the atoms. The different atomic arrangements also lead to different properties for the two allotropes: c-BN is harder than h=BD but less thermally conductive; conversely, h=BD is softer than c=BD but more thermally conductive.
There are many potential applications for h=BD due to its unique combination of properties. For example, it can be used as both a lubricant and an electrical insulator; it is also transparent over a wide range of wavelengths, making it potentially useful for optical applications such as solar cells or displays. Additionally, because it has low density yet high thermal conductivity, it could be used in lightweight heat sink materials for electronic devices such as processors or LEDSs