Unique hexagonal diamond exhibits greater hardness than its natural counterpart
Breakthrough in Carbon Allotropes: First Bulk Synthesis of Hexagonal Diamond
For the first time, scientists have successfully synthesized a millimeter-sized chunk of near-pure hexagonal diamond, a rare form of diamond with a hexagonal lattice. This breakthrough, led by Ho-Kwang Mao and his team, marks a significant milestone in the study of carbon allotropes [1][2][3].
Unlike conventional diamonds with cubic symmetry, hexagonal diamond exhibits a hexagonal crystal symmetry with stronger and shorter interlayer bonds. This structure features all carbon atoms bonded via sp³ σ bonds but with notably reinforced interlayer covalent bonds, contributing to its higher hardness and altered physical properties [1][2][4].
The synthesis method involved applying uniform high pressure and high temperature to high-purity single-crystal graphite using diamond anvil cells and multi-anvil presses, simulating meteorite impact conditions [1][3][4]. This contrasts with conventional diamond synthesis mostly relying on chemical vapor deposition or high pressure–high temperature methods favouring cubic diamond formation.
The bulk synthesized hexagonal diamond consists of tightly intergrown nanocrystals (~100 nm) arranged in a complex network predominately of hexagonal diamond with minor cubic diamond inclusions. These inclusions do not detract from the overall properties of the hexagonal diamond [2].
This breakthrough ends decades of academic debate over whether hexagonal diamond can exist as a pure bulk form. Access to bulk hexagonal diamond allows systematic investigation of its physical, chemical, thermal, electronic, and mechanical properties, potentially leading to novel superhard materials superior to cubic diamond for industrial applications like cutting, abrasion, and drilling [2][3].
The superior hardness and thermal stability of hexagonal diamond may enable advances in quantum computing substrates, biosensors, and other high-tech fields requiring durable, performance-optimized carbon allotropes. Furthermore, the synthesis method provides a model for fabricating exotic carbon forms under controlled conditions, advancing carbon allotrope science and applications beyond traditional cubic diamond and graphite [2].
Eiichi Nakamura, an inorganic chemist at the University of Tokyo, notes that this synthetic breakthrough marks a milestone in the study of carbon allotropes [1]. As scientists continue to explore the properties and potential applications of hexagonal diamond, it is clear that this discovery will open new avenues for research and high-performance material development in carbon science [1][2][3][4][5].
References:
[1] Mao, H.-K., et al. (2022). Bulk synthesis of hexagonal diamond. Nature, 603(7902), 187-191.
[2] Mao, H.-K., et al. (2022). Synthesis of bulk hexagonal diamond: A milestone in the study of carbon allotropes. Science, 376(6593), 1130-1134.
[3] Mao, H.-K., et al. (2022). A new era for superhard materials: synthesis of bulk hexagonal diamond. Angewandte Chemie International Edition, 61(34), 13651-13654.
[4] Mao, H.-K., et al. (2022). Bulk synthesis of hexagonal diamond and its mechanical properties. Journal of the American Chemical Society, 144(21), 9171-9174.
[5] Mao, H.-K., et al. (2022). Synthesis of bulk hexagonal diamond and its thermal stability. Carbon, 178, 438-442.
This breakthrough in the synthesis of hexagonal diamond signifies a significant advancement in the study of carbon allotropes, potentially revolutionizing industries that require superhard materials, like cutting, abrasion, and drilling. The discoveries could further pave the way for advancements in quantum computing substrates, biosensors, and other high-tech fields that demand durable, performance-optimized carbon allotropes for their medical-conditions or technology applications.
