Crystal Structure of New Carbon–Nitride-Related Material C2N2(CH2)

A new carbon–nitride-related C2N2(CH2) nanoplatelet was synthesized by subjecting a precursor C3N4HxOy 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 C3N2 by using an energy dispersive X-ray spectroscope attached to a transmission electron microscope. The crystal structure and atomic positions of this C3N2 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. First-principles calculation was alternatively used to discover the hydrogen composition. The synthesized C2N2(CH2) was accordingly found to be an orthorhombic unit cell of the space group Cmc21 with lattice constants a = 7.625 A, b = 4.490 A, and c = 4.047 A. If the CH2 atomic unit is replaced with the CN2 atomic unit and the bonding rearranged, the C2N2(CH2) becomes the expected superhard C3N4.