Using data from advanced modeling and experimental studies, researchers are trying to synthesize BC8, a carbon structure predicted to be stronger than diamond. Theoretically common in the extreme pressures of exoplanets, this material remains a scientific mystery with promising applications in materials science.

Diamond is the strongest known material. But another form of carbon is predicted to be even stronger than diamond. The question is how to create this on Earth.

Octahedral body-centered cubic crystal (BC8) is a distinct carbon phase: not diamond but very similar. BC8 is estimated to be a stronger material, exhibiting 30% greater compressive strength than diamond. It is believed to be at the center of carbon-rich exoplanets. If BC8 could be recovered under ambient conditions, it could be classified as a super diamond.

Theoretical ideas and experimental challenges

This high-pressure crystalline phase of carbon is theoretically predicted to be the most stable phase of carbon under pressures exceeding 10 million atmospheres.

“At ambient conditions, the BC8 phase of carbon will be a new superhard material, possibly stronger than diamond,” said Ivan Oliynyk, professor of physics at the University of South Florida (USF) and senior author of the newly published paper. . inside Journal of Physical Chemistry Letters.

extraterrestrial communication

“Despite numerous attempts to synthesize this elusive crystalline phase of carbon, including previous National Ignition Facility (NIF) campaigns, it has not yet been observed,” said Marius Millot, a research scientist at Lawrence Livermore National Laboratory (LLNL). study. . “But we think it might exist on carbon-rich exoplanets.”

Recent astrophysical observations indicate the possible existence of carbon-rich exoplanets. These celestial bodies, which have a significant mass, are exposed to enormous pressures reaching millions of atmospheres in their depths.

Understanding BC8’s unique features

“Therefore, the extreme conditions prevailing on these carbon-rich exoplanets may lead to the formation of structural forms of carbon such as diamond and BC8,” Olijnyk said. “Therefore, an in-depth understanding of the properties of BC8’s carbon phase becomes critical for the development of accurate internal models of these exoplanets.”

BC8 is a high-pressure phase of both silicon and germanium that can be reduced to ambient conditions, and theory suggests that BC8 carbon should also be stable at ambient conditions. LLNL scientist and co-author John Eggert said the key reason why diamond is so hard is that the tetrahedral shape of the four nearest neighbor atoms in the diamond structure matches perfectly with the optimal configuration of four valence electrons in the elements in column 14. periodic table (starts with carbon, followed by silicon and germanium).

Pathway to BC8 synthesis

“The BC8 structure retains the perfect nearest neighbor tetrahedral shape, but without the cleavage planes found in the diamond structure,” Eggert said, agreeing with Olijnyk that “the carbon phase of BC8 would likely be much stronger than diamond at ambient conditions.” “

Through multimillion-second atomic molecular dynamics simulations on Frontier, the world’s fastest exascale supercomputer, the team discovered diamond’s extraordinary metastability at very high pressures, well beyond its thermodynamic stability range. The key to success was the development of a highly accurate machine learning interatomic potential that describes interactions between individual atoms with unprecedented quantum precision across a wide range of high pressure and temperature conditions.

“By effectively realizing this potential in Frontier’s GPU (graphics processing unit), we can accurately simulate the time evolution of billions of carbon atoms under extreme conditions on experimental time and length scales,” Olijnyk said. said. “We predicted that the post-diamond BC8 stage would be experimentally accessible only in the narrow, high-pressure, high-temperature region of the carbon phase diagram.”

Future horizons in BC8 research

Its meaning is twofold. First, it clarifies the reasons for the impossibility of previous experiments to synthesize and observe the elusive BC8 carbon phase. This limitation stems from the fact that BC8 can only be synthesized within a very narrow range of pressure and temperature. Furthermore, the study suggests suitable compression pathways to access this highly restricted area where BC8 synthesis is possible. Olijnyk, Eggert, Millot, and others are now collaborating to explore these theoretical avenues using the Discovery Science staff allocation at NIF.

The team dreams of one day growing a BC8 super diamond in the laboratory; as long as they can synthesize the phase and return the BC8 seed crystal to ambient conditions.