The Phase Diagram and Hardness of Carbon Nitrides

Abstract

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 charac- teristics 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. Surprising- ly, we find that at zero pressure, the earlier proposed graphitic-C3N4 structure (P-6m2) is dynamically unstable and the lowest energy form of structures based on s-triazine unit and s-heptazine unit have similar topology and belong to the same space group.

5 pages, 3 figures http://www.nature.com/srep/2015/150424/srep09870/full/srep09870.html

References in corpus (1)

• Intrinsic Correlation between Hardness and Elasticity in Polycrystalline Materials and Bulk Metallic Glasses

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