Last month, we looked at an emerging debate amongst materials scientists over the nature of a new form of carbon that was recently discovered by compressing graphite at room temperature to pressures in excess of 10 GigaPascals.

Under these conditions, various properties of graphite change, such as its resistivity, optical transparency, reflectance and so on. That’s a good indication that something different is forming.

But the question is what? Various groups have proposed new carbon allotropes that could explain the results. These are variously called monoclinic M-carbon, cubic body center C4 carbon, orthorhombic W-carbon and most recently M10-carbon.

Today, Chaoyu He and buddies at the Institute for Quantum Engineering and Micro-Nano Energy Technology in Xiangtan, China, propose two new superhard structures, which they call S-carbon and H-carbon.

One of the problems with the previous structures is the uncertainty over their stability, which may mean they cannot form in reality. He and co say the new structures are more stable than M or W-carbon and even more stable than graphite at high pressures. What’s more, their bulk properties more or less exactly match those measured in the experimental samples

Of course, this work, like the other structural predictions, is entirely theoretical, relying on computer simulations based on first principle calculations. And until somebody actually measures the structure of this new form of carbon, we won’t know which proposal is correct.

Nevertheless, the process of predicting new carbon allotropes and calculating their properties is itself providing a clear impetus for new research in this field.

A snapshot of an interesting piece of science in action.

Ref: arxiv.org/abs/1203.5509: New Superhard Carbon Phases Between Graphite and Diamond