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Novel ultraincompressible polymeric carbon nitride

Please note: header image is purely illustrative. Source: Arsgera via Adobe Stock.

Diamond is the hardest and most widely used of the hard and superhard materials, which together represent an annual market in the multibillions of pounds.

In 1989, a C3N4 carbon nitride with a greater hardness than diamond was predicted theoretically and has now, at last, been experimentally synthesised.


  • Machining tools
  • Protective coatings
  • Environmentally-friendly mining explosive
  • Further applications to be discovered

Development Status

Engaging with suppliers to develop scale-up

IP Status

Priority patent application was filed


There has long been a gap in the superhard materials market for a solid which could match the hardness of diamond (~90 GPa) but also improve on some of the issues encountered with the use of diamond, such as its large indirect bandgap and chemical reactivity with iron.

The next hardest material, cubic boron nitride (c-BN, hardness ~60 GPa), while not suffering from the same issues, is significantly softer than diamond. This novel carbon nitride solves these problems, with a predicted hardness between 77 and 87GPa, no chemical reactivity with iron and a smaller bandgap.


This novel carbon nitride, oP28-C3N4, has been recovered to ambient pressure and temperature and demonstrated a bulk modulus above 300 GPa, making it ultra-incompressible. While the hardness has not yet been measured experimentally, theoretical predictions, as well as the combination of its experimentally measured crystal structure and bulk modulus, strongly suggest that oP28-C3N4 will also be superhard, within 10% of the hardness of diamond. It is composed of corner-sharing CN4 tetrahedra and has been shown to be stable in air over a timescale of months.


  • Synthesis at lower pressure than other similar materials
  • Hardness predicted to be within 10% of the hardness of diamond
  • Smaller bandgap than diamond predicted making oP28-C3N4 more useful in opto-electronic applications

Quote TEC1104551

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Neringa Barmute

Technology Transfer Manager