Diboride

Diboride is the name given to binary compounds composed of boron and a metal with the general formula MB2. Diborides are a large and chemically diverse class of borides that includes alkaline earth, transition metal, and post-transition metal members. They are of interest for their high-temperature stability and metallic conductivity.

Most extensively studied are transition metal diborides such as TiB2, VB2, ZrB2, and HfB2, as well as magnesium diboride MgB2. The compounds typically crystallize in the AlB2-type structure, a hexagonal arrangement in which hexagonal sheets of boron form a covalent network separated by layers of metal atoms.

Bonding in diborides combines strong covalent B–B bonds within the boron sheets with more metallic metal–boron interactions between the layers. This gives high hardness and high melting points, while preserving substantial electrical conductivity. MgB2 is notable for its superconducting properties, with a critical temperature around 39 kelvin.

Synthesis usually involves high-temperature reactions between the metal and boron, or deposition methods such as chemical vapor deposition used to produce thin films. Diborides are often refractory ceramics and are used as wear-resistant coatings, crucibles for high-temperature processing, and components in cutting tools. Magnesium diboride has also triggered research into superconducting materials.

Overall, diborides represent a versatile family of compounds that combine ceramic stability with metallic conduction, enabling applications that span extreme environments and, in some cases, quantum materials research.