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

Abstract

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 .

Mechanical and Electronic Properties of Carbon Nitride Methanediide under High Pressure

“…The bulk modulus is 254, 229, and 301 GPa, from the LDA, GGA, and sX-LDA calculations, respectively, compared with 258 GPa from the experiment. 1 It is worth mentioning here that the bulk modulus of the C 2 N 2 (CH 2 ) compound is approximately 45% of that of diamond.…”

“…During the optimization, the simulation cell is fully relaxed. For phonon calculations, the k-point is set to a finer mesh of 8 × 8 × 8.■ RESULTS AND DISCUSSIONFrom the experimental data, the C 2 N 2 (CH 2 ) compound has an orthorhombic Cmc2 1 structure 1. The unit cell is shown in Figure1a.…”

“…They found theoretically that the bulk modulus of β-C 3 N 4 is 427 ± 15 GPa which is close to 442 GPa of diamond. After Lin and Cohen proposed this phase of C 3 N 4 , there were many theoretical studies − of other phases of C 3 N 4 and also experimental searches for this compound. − As mentioned earlier, C 3 N 4 and C 2 N 2 (CH 2 ) are closely related . Thus, we would like to examine the possibility that C 2 N 2 (CH 2 ) could be a very hard material.…”

“…In 2011, the carbon nitride methanediide, C 2 N 2 (CH 2 ), compound was synthesized under high pressure and high temperature for the first time by Sougawa et.al. 1 They claimed that this compound could be an initial substrate for C 3 N 4 , a candidate of superhard materials. There have been a number of theoretical studies of this C 2 N 2 (CH 2 ) compound using the first principle calculations.…”

“…14−20 As mentioned earlier, C 3 N 4 and C 2 N 2 (CH 2 ) are closely related. 1 Thus, we would like to examine the possibility that C 2 N 2 (CH 2 ) could be a very hard material.…”