Fluffy diamonds could be a completely new form of carbon

Imagine an ordinary carbon atom that's replaced with a tightly packed pyramid of four carbon atoms. Inspired by Egypt's pyramids, this elegant arrangement has never even been proposed before, but this so-called T-carbon could have tons of uses...if it exists.

The idea has been proposed by Gang Su, a researcher at Beijing's Chinese Academy of Sciences. In ordinary cubic diamonds, carbons are already tightly packed, but if a pyramid substructure was built into all the atoms of the diamond, you would have a completely new material that was lightweight, very hard, and, in its way, fluffy. This new kind of diamond, made of what the researchers have dubbed T-carbon, would be only 43 percent a regular diamond's density, but it would be at least 65 percent as hard.

Su is optimistic about the potential applications of T-carbon, and it might even solve a cosmic mystery. The researchers speculate that T-carbon is naturally found in interstellar dust, and its presence could explain certain irregularities in the dust that have been detected over the last fifty years. Back on Earth, the material could be used for storing hydrogen or in the aerospace industry.

But all this assumes T-carbon is stable enough to exist, and there's plenty of reason to be skeptical on that crucial point. Carbon is one of the most flexible of all elements, and so it's possible to arrange its atoms in any number of theoretical combinations. But the vast, vast majority of these possible arrangements can't exist for more than the tiniest fraction of a second before breaking apart. Those that can survive earn the classification "allotrope", which includes diamonds, graphite, graphene, fullerenes, and other materials.

T-carbon is unusual because its density is so low, which goes against the current trend in allotrope creation, which favors squeezing carbon together at ever higher densities. Su thinks the best way to create the material would be to blow apart a diamond. Another intriguing possibility is to create "negative pressure", which would involve actually stretching diamonds using some incredibly powerful force.

It's a fascinating idea, and it's very different from a lot of other recent proposals about new types of carbon. But the only way to settle the arguments about whether it's purely theoretical is to get into the lab and see if T-carbon can actually be synthesized. Time to start stretching those diamonds, I guess.

Via Proceedings of the National Academy of Sciences.