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Predicted new form of carbon is a metal

The creation of carbon that can behave like a metal has been a longstanding dream, but previous attempts to synthesize metallic carbon led to materials that are not stable at room temperature and pressure. Now computer simulations predict that a form of carbon resembling interlocked versions of the carbon rings found in many organic molecules could be stably metallic under ambient conditions, report findings detailed in the Proceedings of the National Academy of Sciences.

Carbon is now known to come in a dazzling menagerie of different phases — for instance, carbon atoms can be arranged as pipes with carbon nanotubes, as sheets with graphene, as soccer-ball-shaped buckyballs, and as crystals with diamond. One carbon phase that had long tantalized scientists was metallic carbon, where the electrons in the outermost shells of atoms move in a more diffuse cloud, just as is true with conventional metals, thus making it possible to have a variety of intriguing properties — for instance, it might be an excellent catalyst, or can become magnetic, or superconducting.

However, synthesizing 3D forms of metallic carbon that are stable under ambient conditions had long eluded researchers. Now theoretical calculations from physicist Qian Wang at Peking University and Virginia Commonwealth University and her colleagues predict metallic carbon made of interlocking hexagons of carbon atoms might be stable under ambient conditions after all.

“The most surprising and exciting finding in our study is that the structure turned out to be so simple, as well as stable and metallic under ambient conditions,” Wang says. “Since the predicted structure is porous, it can have potential applications in catalysis for energy conversion and storage. Because of its light weight, it may also find applications in space.”

The researchers explored several possible carbon structures before they discovered one with interlocking hexagons that was stable as well as metallic. Past studies found one way electrons can be arranged, sp2 bonding, led to metallicity as well as 2D hexagonal structures, while another way electrons can be arranged, sp3 bonding, led to 3D structures and strength. “Having both structures through interlocking hexagons seemed to combine the best of both worlds,” Wang says.

Wang cautions that while they have theoretical calculations suggesting this metallic carbon is possible, further experiments still have to synthesize it and confirm its predicted traits. “We hope that our result is exciting enough that experimentalists will try to synthesize this material,” Wang says.

Hexagonal rings of carbon atoms are common in organic molecules — for instance, benzene is such a ring. “Since benzene molecules have been used to synthesize carbon nanotubes, and experimental techniques for forming interlocking molecular structures are well-developed, we hope that it will not be difficult to synthesize the new metallic form of 3D carbon,” Wang says.

Categories: Physics
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