A new route to a superhard material?

For years, scientists have tried to synthesize beta-carbon nitride, a material predicted by theorists to be harder than diamond. Most attempts, however, have ended in frustration, and claims of success have encountered skepticism from outside observers (SN: 7/11/98, p. 28).

Now, Peter Kroll and Roald Hoffmann of Cornell University have explored the feasibility of a new way to make beta-carbon nitride. They argue, using theoretical computations, that squeezing a soft polymer containing the right ratio of carbon and nitrogen could yield the elusive material. A previously unknown form, which they call lambda-carbon nitride, should appear as well. They report these conclusions in the May 19 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

Kroll says the new calculations indicate that the polymer will compress into dense networks under high pressure. Whether the final material will be as hard as everyone expects is unclear.

Researchers at the Technical University of Darmstadt in Germany have made the soft polymer but have not yet put it under high pressure. The Darmstadt group "is still trying to synthesize [the polymer] without major impurities," says Kroll.

The Cornell theorists "propose a rather clever approach to the synthesis of hard [beta-carbon nitride] solids," says YipWah Chung of Northwestern University in Evanston, Ill. "Of course, the proof is in the pudding," he remarks.

The method will work only if beta-carbon nitride is more stable under high pressure than other carbon-nitrogen structures. He also suggests combining this technique with others. For example, synthesizing the polymers on a template could guide the atoms into the desired structure. --C. W.