The new form of carbon glass synthesized by scientists from Jilin University and elsewhere consists of many randomly oriented clusters with diamond-like order and possesses the highest hardness (101.9 GPa), elastic modulus and thermal conductivity observed in any known amorphous material.
Optical photographs of the recovered amorphous carbon (AC) samples from different conditions: (a) optical photographs of AC-1 synthesized at 20 GPa and 1,000 degrees Celsius; (b) AC-2, 25 GPa and 1,000 degrees Celsius; (c) AC-3, 27 GPa and 1,000 degrees Celsius; (d) AC-4, 27 GPa and 900 degrees Celsius; (e) AC-5, 30 GPa and 870 degrees Celsius; and (f) AC-6, 37 GPa and 450 degrees Celsius. Image credit: Shang et al., doi: 10.1038/s41586-021-03882-9.
Amorphous solids lack long-range order, exhibit many excellent mechanical properties and are often easy to shape for applications.
Such materials include natural amorphous solids, artificial glasses (oxides and metallic glasses), plastics, amorphous semiconductors and so on, which are produced and used in many areas.
Many other amorphous materials have been proposed for use but remain unrealized and unexplored because of the challenging synthesis conditions.
Amorphous carbon has attracted intense research interest due to its tunable properties and importance in applications.
“The synthesis of an amorphous carbon material with 3D bonds has been a long-standing goal,” said co-author Dr. Yingwei Fei, a researcher in the Earth and Planets Laboratory at the Carnegie Institution for Science.
“The trick is to find the right starting material to transform with the application of pressure.”
Because of the very high melting point, above 4,500 K, it’s impossible to use diamond as the starting point to synthesize diamond-like glass.
However, the authors made their breakthrough by using fullerene, a form of carbon composed of 60 molecules arranged to form a hollow ball.
Informally called a buckyball, this Nobel Prize-winning material was heated just enough to collapse its soccer-ball-like structure to induce disorder before turning the carbon to crystalline diamond under pressure.
The researchers used a large-volume multi-anvil press to synthesize the diamond-like glass, which was sufficiently large for characterization.
Its properties were confirmed using a variety of advanced, high-resolution techniques for probing atomic structure. “The creation of a glass with such superior properties will open the door to new applications,” Dr. Fei said.
“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 team’s work was published in the journal Nature.
Y. Shang et al. 2021. Ultrahard bulk amorphous carbon from collapsed fullerene. Nature 599, 599-604; doi: 10.1038/s41586-021-03882-9