Diamond, one of the hardest known materials, could have a rival. A new form of carbon that is just as hard as the gemstone but as light as pencil graphite could theoretically be used for applications including gas storage and optoelectronics.
Carbon exists in different natural forms, called allotropes, depending on how its atoms bond with each other. Among the most well-known carbon allotropes are diamond and graphite, the substance used for pencils, although many more types can be made synthetically.
Susumu Okada and his colleagues at the University of Tsukuba in Japan used a computer program that simulates molecules and their properties to uncover a new theoretical carbon allotrope, which the researchers propose can be made from readily available molecules. They named the structure pentadiamond because it consists of pentagon-shaped rings of carbon atoms that are each bonded to three or four other carbons.
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The team鈥檚 calculations showed that pentadiamond is slightly more stiff and rigid than diamond and can withstand similarly high pressures without compressing, probably due to its pentagon rings. It can also tolerate temperatures of almost 4000掳C without breaking down.
Despite this, it is as lightweight as graphite, which Okada says might make it a useful material for storing gases or for the frame of race cars. It may also have a more unusual property: whereas most materials get thinner as they are stretched, pentadiamond could do the opposite and become thicker.
Another possible application for pentadiamond is in optoelectronics since it conducts electricity and can convert currents into blue and green light. But it is debatable whether it offers an improvement on current materials used for this purpose, says Nicola Manini at the University of Milan in Italy.
Making allotropes out of a mix of carbon atoms that are bonded to three or four others is of particular interest because they can lead to varied structures with desirable characteristics, such as resistance to stretching. 鈥淭hey are the Lego blocks of carbon allotropes,鈥� says Okada. 鈥淪o, by assembling them, we can design 鈥� in principle 鈥� an infinite number of allotropes.鈥�
鈥淚t is fantastic how many materials with completely different, novel and amazing properties can be made just from carbon, and still we explore new ones as shown in this work,鈥� says Leo Gross at IBM Research in Zurich, Switzerland.
Physical Review Letters
