Tsukuba University researchers create Carbon-based material, harder than diamond

Tsukuba: Researchers at the University of Tsukuba, Japan have created a new form of carbon that is harder than a diamond. They have named this structure ‘pentadiamond’, which they believe may be useful for replacing current synthetic diamonds in difficult cutting manufacturing tasks.

The researchers used complex computer calculations to design this new carbon-based material, according to the sciencedaily.com report. The researchers - Yasumaru Fujii, Mina Maruyama, Nguyen Thanh Cuong, Susumu Okada - published their findings under the title - Pentadiamond: A Hard Carbon Allotrope of a Pentagonal Network of sp2 and sp3 C Atoms. 

 Diamond, which is the hardest natural substance on Earth, is made entirely of carbon atoms arranged in a dense lattice. They are famous for their unmatched hardness among known materials.

But carbon, which is a solid non-metal element, can form many other stable configurations, called allotropes. These include the familiar graphite in pencil lead, as well as nanomaterials such as carbon nanotubes. 

The mechanical properties, including hardness, of an allotrope, depend mostly on the way its atoms are arranged with each other. In conventional diamonds, each carbon atom forms a covalent bond with four neighbors. Chemists call carbon atoms like this as having sp3 hybridization. In nanotubes and some other materials, each carbon forms three bonds, called sp2 hybridization.

Keeping this mind, the researchers at the University of Tsukuba explored what would happen if carbon atoms were arranged in a more complex structure with a mixture of sp3 and sp2 hybridization.

Yasumaru Fujii, one of the researchers, said, "Carbon allotropes with both sp2 and sp3 hybridized atoms have greater morphological diversity due to the huge number of combinations and arrangements in networks.”

In order to calculate the most stable atomic configuration and its hardness, the researchers relied on a computational method called density functional theory (DFT), which is used for predicting the structure and properties of materials. 

According to scientists, the DFT theory uses an approximation that focuses on the final density of electrons in space orbiting the atoms.

This makes it easier for computers to do calculations, giving precise results. Using this theory, the team found that the Young's Modulus, a measure of hardness, of pentadiamond was predicted to be almost 1700 GPa, compared with about 1200 GPa for conventional diamond.

"Not only is pentadiamond harder than conventional diamond, its density is much lower, equal to that of graphite," Professor Mina Maruyama was quoted as saying by sciencedaily.com.