A molecular model of a buckyball, which researchers have now crushed into a new ultrahard diamond glass

Researchers at Carnegie Science have developed an ultrahard diamond glass. Made entirely of crushed “soccerballs” of carbon, the new material also has high thermal conductivity and could find use in electronics.

Carbon is a versatile element, forming many stable structures in a variety of atomic arrangements, from graphene to diamond. They can be repeating crystalline patterns or amorphous like glass, and the atomic bonds themselves can form in either two or three dimensions, which determines the material’s hardness. However, some forms, like diamond glass, have been trickier to make than others.

“The synthesis of an amorphous carbon material with three-dimensional bonds has been a long-standing goal,” says Yingwei Fei, an author of the new study. “The trick is to find the right starting material to transform with the application of pressure.”

If you apply pressure to graphite, for example, you end up with the crystalline arrangement of diamond. Diamond itself might seem like the logical starting point to make diamond glass, but its melting point of 4,227 °C (7,640 °F) is far too high for practical use. The team needed to find a form of carbon that could become atomically disordered enough before being put under pressure.

They found their target in fullerene, widely known as buckyballs, which is composed of 60 carbon atoms arranged in a hollow soccer ball shape. The team heated them until the ball shape collapsed into a disordered arrangement, then high pressure was applied using a multi-anvil press. The end result is a diamond-like glass, which was able to be produced in millimeter-sized pieces.

A diagram demonstrating how the new ultrahard diamond glass is made

On closer inspection, the team found that the new glass boasted a hardness of around 102 GigaPascals (GPa). That’s higher than naturally occurring diamond, but not quite as hard as AM-III, a form of glass recently synthesized in China that had a hardness of up to 113 GPa.

The team also claims that the new ultrahard glass has the highest thermal conductivity of any amorphous material, with a k value of 26. Importantly, it can be synthesized at temperatures of between 900 and 1,000 °C (1,652 and 1,832 °F), which is within reach of industrial manufacturing.

“The creation of a glass with such superior properties will open the door to new applications,” says Fei. “The use of new glass materials hinges on making large pieces, which has posed a challenge in the past. The comparatively low temperature at which we were able to synthesize this new ultrahard diamond glass makes mass production more practical.”

The research was published in the journal Nature.