Building a harder diamond

Date:
July 1, 2020
Source:
University of Tsukuba
Summary:
Scientists create a theoretical carbon-based material that would be
even harder than diamond. This work may have industrial applications
for cutting and polishing in place of current synthetic diamond.



FULL STORY ========================================================================== Researchers at the University of Tsukuba used computer calculations
to design a new carbon-based material even harder than diamond. This
structure, dubbed "pentadiamond" by its creators, may be useful for
replacing current synthetic diamonds in difficult cutting manufacturing
tasks.


========================================================================== Diamonds, which are made entirely of carbon atoms arranged in a
dense lattice, are famous for their unmatched hardness among known
materials. However, carbon 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
bond 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.

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

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

To calculate the most stable atomic configuration, as well as estimate
its hardness, the team relied on a computational method called density functional theory (DFT). DFT has been successfully used throughout
chemistry and solid- state physics to predict the structure and properties
of materials. Keeping track of the quantum states of all of the electrons
in a sample, and especially their interactions, is usually an intractable
task. Instead, DFT uses an approximation that focuses on the final
density of electrons in space orbiting the atoms.

This simplifies the calculation to make it suitable for computers,
while still providing very precise results. The scientists 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," explains co-author Professor
Mina Maruyama.

"This work shows the power of designing materials ab initio. In addition
to industrial cutting and drilling uses, pentadiamonds might be used
in place of diamond anvil cells currently used in scientific research
to recreate the extreme pressure inside planets" said senior co-author Professor Susumu Okada.


========================================================================== Story Source: Materials provided by University_of_Tsukuba. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Yasumaru Fujii, Mina Maruyama, Nguyen Thanh Cuong, Susumu Okada.

Pentadiamond: A Hard Carbon Allotrope of a Pentagonal Network of
sp2 and sp3 C Atoms. Physical Review Letters, 2020; 125 (1) DOI:
10.1103/ PhysRevLett.125.016001 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200701100014.htm

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