Dense, sparkling ultra-diamonds could be the next superconductors

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Carbon is one of the most versatile materials in the universe, forming everything from the graphite found in the pencils to hard, sparkling diamonds. But three new forms of carbon might make even the most breathtaking diamond look impossibly dull.


As you might remember from middle school science class, diamonds are the hardest minerals in the world. That's because the carbon atoms are arranged in a uniquely tough, tightly packed crystal structure known, predictably enough, as a diamond lattice. This super rigidity also means diamonds aren't easily contaminated by other substances, which gives it its clear, colorless appearance. Diamond's relatively high density means its refractive index is also high, which results in its much-prized sparkle and luster.

Researchers at Stony Brook University wanted to find out whether it was possible to make any stable configurations of carbon that were even denser than diamonds. They tried a bunch of different simulations at various different temperatures and pressures, and ultimately they came up with three new carbon forms, or allotropes, which theoretically should be able to remain stable. These have been given the downright poetic names of hP3, tI12 and tP12.

While none of these new allotropes would be harder than diamonds - which means, again for those who remember their Mohs scale, that diamonds would be able to scratch any of these new forms - they're all between 1.1 and 3.2% denser than diamonds. That may not seem like much, but even a slight increase in density would make an appreciable difference. They'd all have even higher refractive indexes, meaning they would sparkle in ways even diamonds can't, which would be a pretty incredible sight to see.

But this isn't just about creating business for the jewelry industry. There's some intriguing indications that these allotropes would be ideal candidates for superconductors. Writing for New Scientist, MacGregor Campbell explains:

The simulations also suggest that the three materials have band gaps – the amount of energy needed for electrons to jump from one energy level to another – that are very different to one another. One of them, tP12, has the largest band gap of any carbon allotrope. This variability may make the allotropes good candidates for superconductors – exotic substances that conduct electricity without resistance...According to Boris Yakobson at Rice University in Houston, Texas, a large variation in band gap implies strong interactions between electrons and packets of energy in the lattice called phonons. This in turn could lead to the formation of electron couplings called Cooper pairs, which are necessary for superconductivity.

It's all very exciting, and there's only one small problem - we don't actually know how to make any of these allotropes. They should be stable forms, but just knowing that doesn't really help us make them. Vadim Brazhkin of the Institute for High Pressure Physics explains the problem:

"It is not clear how we can fabricate them. Using standard pristine materials, such as graphite or amorphous carbon [an allotrope in which the atoms have no crystal structure], we can possibly obtain a tiny amount of new materials using extreme pressure treatment."


So then, until we figure out how to make these superconducting, super-sparkling ultra-diamonds, I guess diamonds are still sort of cool. I guess...

Physical Review B via New Scientist. Image via James Thew/Shutterstock.




So he was onto something after all?