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Weird new 'pentadiamonds' could be ultrahard, ultralight and conduct electricity

a ball and stick model of a pentadiamond
(Image: © Susumu Okada)

What's lighter than a diamond, almost as hard and could zip with electricity? A pentadiamond — a crystalline arrangement of carbon atoms that is made up mostly of pentagons. 

These pentadiamonds don't exist yet; they've only been created in computer simulations. But if a pentadiamond can be made, it could have a number of useful properties.

Carbon is one of the most versatile elements on the periodic table. Since each carbon atom can bond with up to four others, it is able to form intricate assemblies with different properties, such as ultra-hard diamond, semiconducting graphene and rope-like nanotubes. 

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Novel arrangements, or allotropes, of carbon are being discovered all the time. As many as 1,000 different types are currently known, according to the Samara Carbon Allotrope Database.

The search for additional allotropes is like "playing [with] LEGO blocks to create materials with fascinating shapes and structures," Susumu Okada, a condensed matter physicist at the University of Tsukuba in Japan and co-author of a paper published June 30 in the journal Physical Review Letters, told Live Science. 

Using state-of-the-art computer modeling, Okada and his colleagues decided to bring together two molecules — called spiro[4.4]nona-2,7-diene and []fenestratetraene — each of which contained a pentagonal ring of carbon atoms, to see if they might generate a potentially useful material. 

The simulations produced a carbon arrangement looking a bit like a soccer ball with several smaller soccer balls glued all around its exterior. The computer model was able to show that this pentadiamond, if it were synthesized in real life, would have some interesting properties. 

Along with being about 80 percent as hard as diamond, one of the hardest substances known, pentadiamond would be slightly porous, and could conduct electricity like the semiconductors used in electronic devices if chemical impurities were added, the authors wrote. It would also have the odd ability to expand uniformly in all directions when stretched, sort of like the children's toy known as a Hoberman sphere.

Related: The biggest unsolved mysteries in physics

If you held pentadiamond in your hand, it would likely feel lighter than a similar-sized diamond, though it wouldn't be clear but rather a grayish color like graphite, Purusottam Jena, a physicist at the Virginia Commonwealth University in Richmond, told Live Science. 

Because of its porous nature, pentadiamond might be useful for storing gas, Okada said. Its lightness and hardness could make it useful for building the bodies of race cars, he added. 

Jena, who was not involved in the work but has discovered other carbon allotropes, said the material is potentially quite exciting. "However, it needs to be experimentally synthesized," he added, and until then remains strictly theoretical. 

Sometimes materials behave differently in real life than in simulations, Jena said, though he considers the work interesting enough to send the paper to a colleague who might be able to produce it in a lab. 

For his part, Okada thinks chemists will be able to create pentadiamond in the near future. And, until then, he will continue to play with "LEGO blocks of carbon atoms."

Originally published on Live Science.

Editor's Note: This story was updated to note that, like other semiconductors, pentadiamonds could theoretically conduct electricity if chemical impurities are added.