The phase diagram and hardness of carbon nitrides.
Novel superhard materials, especially those with superior thermal and chemical stability, are needed to replace diamond. Carbon nitrides (C-N), which are likely to possess these characteristics and have even been expected to be harder than diamond, are excellent candidates. Here we report three new superhard and thermodynamically stable carbon nitride phases. Based on a systematic evolutionary structure searches, we report a complete phase diagram of the C-N system at 0-300 GPa and analyze the hardest metastable structures. Surprisingly, we find that at zero pressure, the earlier proposed graphitic-C3N4 structure () is dynamically unstable, and we find the lowest-energy structure based on s-triazine unit and s-heptazine unit.
Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.|Center for Materials by Design, Institute for Advanced Computational Science, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.
Huafeng
H
Dong
Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.|Center for Materials by Design, Institute for Advanced Computational Science, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.|Moscow Institute of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny City, Moscow Region 141700, Russia.|School of Materials Science, Northwestern Polytechnical University, Xi'an 710072, China.
Artem R
AR
Oganov
Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.|Center for Materials by Design, Institute for Advanced Computational Science, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.
Qiang
Q
Zhu
Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.|Center for Materials by Design, Institute for Advanced Computational Science, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.
Guang-Rui
GR
Qian