Everyone knows that diamonds are the hardest material in the world, but that might change someday. The world's most powerful supercomputer has predicted that an even tougher material could exist. This so-called "super-diamond" material may exist in the core of certain exoplanets, and the simulation points to possible ways to create it on Earth.
Like regular diamonds, the newly modeled material is composed entirely of carbon atoms, but the crystalline arrangement is different. The eight-atom body-centered cubic (BC8) crystal doesn't technically count as a diamond but is a distinct carbon phase that requires even higher temperatures and pressure to form. The Frontier supercomputer at Lawrence Livermore National Laboratory (LLNL) determined a stable structure for BC8 carbon, predicting that the material could be 30% stronger than diamonds. This conformation maintains a "perfect" tetrahedral arrangement of atoms without the cleavage planes of a regular diamond.
Scientists have long theorized that BC8 carbon could exist—carbon has four valence electrons like other elements in the same periodic table column, and those materials have BC8 conformations. Attempts have been made at the National Ignition Facility (NIF) to create a super-diamond, but those efforts failed. The new data from Frontier, however, may show the way.
"We predicted that the post-diamond BC8 phase would be experimentally accessible only within a narrow, high-pressure, high-temperature region of the carbon phase diagram," said Ivan Oleynik, a physicist at the University of South Florida (USF) and lead author of the paper. BC8 carbon may be the most stable form of the element under pressures over 10 million atmospheres. Recent observations with instruments like the James Webb Space Telescope have revealed carbon-rich exoplanets where the interior pressure might be high enough to produce BC8 carbon crystals.
The key to this work was developing a hyper-accurate model describing interatomic potential. The exascale Frontier system was not only able to describe the structure of BC8 diamond but also determine the right mix of temperature and pressure to create it. The LLNL team hopes to one day grow BC8 super-diamonds in the lab with a process called double-shock compression, and there is reason to think this material could remain stable under less extreme conditions. The BC8 configurations of silicon and germanium form under high pressure but can be removed to ambient pressure.
The researchers say that super-diamonds could be useful in material science and may also be key to understanding the structure of carbon-rich exoplanets.
