Metal Borides
Contrary to carbon-based systems, metal borides can be easily synthesized in large quantities under ambient conditions, which is an important technological advantage. A few examples of these metal borides include RuB2, OsB2 and ReB2. The electronic density of states of these materials reveals their metallic nature, but the extensive covalent B-B and M-B bonding (M = metal) leads to high hardness. Metals such as osmium, rhenium, tungsten, etc. are desirable due to the high electron density, small atomic radius, high bulk modulus, and highly controlled directional bonding with boron. The M-B bond contributes to this due to the overlapping of the transition metal d states and boron p states.
Read more about this topic: Superhard Material
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