1 research outputs found
Synthesis of Ultra-incompressible sp<sup>3</sup>āHybridized Carbon Nitride with 1:1 Stoichiometry
The search of compounds
with C<sub><i>x</i></sub>N<sub><i>y</i></sub> composition
holds great promise for creating
materials which would rival diamond in hardness due to the very strong
covalent CāN bond. Early theoretical and experimental works
on C<sub><i>x</i></sub>N<sub><i>y</i></sub> compounds
were based on the hypothetical structural similarity of predicted
C<sub>3</sub>N<sub>4</sub> phases with known binary A<sub>3</sub>B<sub>4</sub> structural types; however, the synthesis of C<sub>3</sub>N<sub>4</sub> other than g-C<sub>3</sub>N<sub>4</sub> remains elusive.
Here, we explore an āelemental synthesisā at high pressures
and temperatures in which the compositional limitations due to the
use of precursors in the early works are substantially lifted. Using
in situ synchrotron X-ray diffraction and Raman spectroscopy, we demonstrate
the synthesis of a highly incompressible <i>Pnnm</i> CN
compound (<i>x</i> = <i>y</i> = 1) with sp<sup>3</sup>-hybridized carbon above 55 GPa and 7000 K. This result is
supported by first-principles evolutionary search, which finds that
CN is the most stable compound above 14 GPa. On pressure release below
6 GPa, the synthesized CN compound amorphizes, maintaining its 1:1
stoichiometry as confirmed by energy-dispersive X-ray spectroscopy.
This work underscores the importance of understanding the novel high-pressure
chemistry laws that promote extended 3D C-N structures, never observed
at ambient conditions. Moreover, it opens a new route for synthesis
of superhard materials based on novel stoichiometrie