DgcityPhysicists at a laser laboratory in Mianyang report that they have created and directly observed BC8 carbon, a denser form of the element often called superdiamond, after decades of failed attempts around the world. The evidence, posted in a preprint, comes from single-crystal X-ray diffraction of diamond shocked to pressures above one terapascal.
The BC8 structure has been known in other elements since the 1960s. When silicon or germanium is squeezed to extreme pressure and released, its atoms rearrange from the familiar diamond-like lattice into a denser, twisted configuration with eight atoms per body-centred cubic unit cell. Theory said carbon should do the same at sufficiently brutal pressure, since the tighter packing becomes energetically favourable. Diamond, however, proved stubborn, and experiment after experiment found no sign of the transformation.
The Mianyang team, led by Liang Sun at the Laser Fusion Research Center, changed tactics. Simply compressing diamond harder had already failed, including at the United States’ National Ignition Facility, where diamond survived at two terapascals. Instead, the Chinese researchers drove a shock wave through the sample that both compressed and heated it, melting the diamond into a liquid. As the shock eased and the material cooled, they say, BC8 crystals nucleated out of the fluid.
Bright X-ray pulses caught the crystals in the act, revealing a diffraction pattern the team identifies as single-crystal BC8. Their conclusion is that pressure alone is not enough; the material must also follow a specific thermal path, melting and refreezing rather than being coldly squeezed.
The claim carries real weight if confirmed. Predicted properties include hardness beyond that of ordinary diamond and possible semiconducting behaviour, materials traits that would interest engineers even though recovering the phase at everyday pressure remains unproven. The phase may also occur naturally deep inside ice giants such as Uranus and Neptune, where carbon-rich fluids experience similar pressures, and it could influence how magnetic fields form in carbon-rich exoplanets.
The work also matters to fusion research. Diamond shells encase the hydrogen fuel used in inertial confinement experiments, and understanding when that carbon changes structure helps physicists interpret their shots and refine weapons-physics models without underground testing.
Outside scientists will scrutinise the evidence. The results rest on two laser shots and a small number of diffraction spots, the measured lattice is slightly distorted, and alternative explanations have not been fully ruled out. The authors attribute the distortion to stress and pressure-temperature gradients, plausible but not yet independently confirmed.
Follow-up experiments, including attempts to recover BC8 after pressure is released, will decide whether the claim stands. Even a sceptical reading leaves one clear result: a smaller laser facility matched a much larger rival by changing the route rather than the raw power, a pattern that may define the next decade of high-pressure physics.
