New work from a team led by the Carnegie Institution for Science has created an extremely incompressible carbon nitride compound. The researchers believe it could be the prototype for a new family of superhard materials due to the unexpected ratio of carbon and nitrogen atoms.Chemical structures showing how elemental carbon and nitrogen under extreme pressures and temperature conditions were synthesized into the new incompressible form of carbon nitride. Image credit: Elissaios Stavrou.

Compounds comprised of carbon and nitrogen are of great interest to materials scientists because they can be both superhard and very resistant to heat. Synthesis of such carbon nitrides could have a number of practical applications, particularly in the arenas of materials machining and protective coatings. However, producing them has been elusive.

“It was long ago theorized that a certain structural form of carbon nitride composed of three carbons and four nitrogens would create the ultimate harder-than-diamond material, the Holy Grail of materials science,” says Senior Scientist Alexander Goncharov.

Goncharov and his team set out to synthesize an ultra-incompressible form of carbon nitride in very clean, pure conditions with just the component elements under high heat and intense pressure. The carbon and nitrogen atoms were heated to more than 12,000 degrees Fahrenheit under more than 550,000 times normal atmospheric pressure.

The result was a compound with a 1:1 ratio rather than the long-sought-after 3:4 ratio. The material satisfies all the conditions for superhardness, including a high number of bonds with very short distances between the component atoms. It is not metallic, meaning it isn’t capable of conducting the flow of electrons that makes up an electric current. This is important, since metallic compounds are less hard than insulating ones, which do not conduct electricity well.

“This work demonstrates that a good understanding of the laws of high-pressure chemistry is crucial to discovering new chemical structures never seen under ambient conditions,” Goncharov says.