A new carbon-nitride-related C 2 N 2 (CH 2 ) nanoplatelet was synthesized by subjecting a precursor C 3 N 4 H x O y nanoparticle in a laser-heating diamond anvil cell to the pressure of 40 GPa and temperature of 1200-2000 K. The C and N composition of the quenched sample was determined to be C 3 N 2 by using an energy dispersive X-ray spectroscope attached to a transmission electron microscope. The crystal structure and atomic positions of this C 3 N 2 were obtained through Rietveld analysis of the X-ray diffraction pattern measured using synchrotron radiation. The hydrogen composition was difficult to determine experimentally because of the several-hundred-nanometer dimensions of the sample. Firstprinciples calculation was alternatively used to discover the hydrogen composition. The synthesized C 2 N 2 (CH 2 ) was accordingly found to be an orthorhombic unit cell of the space group Cmc2 1 with lattice constants a ¼ 7:625 A, b ¼ 4:490 A, and c ¼ 4:047 A. If the CH 2 atomic unit is replaced with the CN 2 atomic unit and the bonding rearranged, the C 2 N 2 (CH 2 ) becomes the expected superhard C 3 N 4 .

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