A Novel Superhard Tetragonal Carbon Mononitride

Wei, Qun; Yan, Haiyan; Zhao, Ya-Ru; Wang, Hui

doi:10.1021/jp409152t

Cited by 33 publications

(26 citation statements)

References 51 publications

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“…Therefore, compared to TiN 2 and HfN 2 , the ZrN 2 exhibits the lowest moduli and hardness. Next we investigate the mechanical anisotropy of tetragonal TMN 2 by calculating the orientation dependences of the Young’s modulus E and shear modulus G which can be determined from the elastic compliance constants s ij 38. The computational details of elastic moduli-crystal orientation dependences conducted here are presented in the Supporting information section.…”

Section: Resultsmentioning

confidence: 99%

Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN2 (TM = Ti, Zr, and Hf)

Cheng

Yan

Wei

et al. 2016

Sci Rep

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Motivated by recent successful synthesis of transition metal dinitride TiN2, the electronic structure and mechanical properties of the discovered TiN2 and other two family members (ZrN2 and HfN2) have been thus fully investigated by using first-principles calculations to explore the possibilities and provide guidance for future experimental efforts. The incompressible nature of these tetragonal TMN2 (TM = Ti, Zr, and Hf) compounds has been demonstrated by the calculated elastic moduli, originating from the strong N-N covalent bonds that connect the TMN8 units. However, as compared with traditional fcc transition metal mononitride (TMN), the TMN2 possess a larger elastic anisotropy may impose certain limitations on possible applications. Further mechanical strength calculations show that tetragonal TMN2 exhibits a strong resistance against (100)[010] shear deformation prevents the indenter from making a deep imprint, whereas the peak stress values (below 12 GPa) of TMN2 along shear directions are much lower than those of TMN, showing their lower shear resistances than these known hard wear-resistant materials. The shear deformation of TMN2 at the atomic level during shear deformation can be attributed to the collapse of TMN8 units with breaking of TM-N bonds through the bonding evolution and electronic localization analyses.

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Section: Resultsmentioning

confidence: 99%

Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN2 (TM = Ti, Zr, and Hf)

Cheng

Yan

Wei

et al. 2016

Sci Rep

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“…It is noteworthy that the predicted Pnnm structure is identical with β-InS which has been proposed as the most energetically favored structure by Hart et al based on simple DFT calculations of the known structural types. In a very recent study using the same structural search method, Zhang et al [19] proposed a different tetragonal crystal structure P42/m, with very similar to β-InS structural characteristics, as the most stable one between ca. 10 and 22 GPa (inset of supplemental Fig.…”

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Synthesis of Ultra-incompressible sp³-Hybridized Carbon Nitride with 1:1 Stoichiometry

et al. 2016

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Search of materials with C-N composition hold a great promise in creating materials which would rival diamond in hardness due to the very strong and relatively low-ionic C-N bond. Early experimental and theoretical works on C-N compounds were based on structural similarity with binary A 3 B 4 structuraltypes; however, the synthesis of C 3 N 4 remains elusive. Here we explored an unbiased synthesis from the elemental materials at high pressures and temperatures. Using in situ synchrotron X-ray diffraction and Raman spectroscopy we demonstrate synthesis of highly incompressible Pnnm CN compound with sp 3 hybridized carbon is synthesized above 55 GPa and 7000 K. This result is supported by first principles evolutionary search, which finds that Pnnm CN is the most stable compound above 10.9 GPa. On pressure release below 6 GPa the synthesized CN compound amorphizes reattaining its 1:1 stoichiometry as confirmed by Energy-Dispersive X-ray Spectroscopy. This work underscores the importance of understanding of novel high-pressure chemistry rules and it opens a new route for synthesis of superhard materials.Since the pioneering work of Liu and Cohen [1] introducing a new class of highly incompressible material, search for C 3 N 4 material harder than has diamond become the Holy Grail in the field of superhard materials. The original proposal was based on realization that carbon atoms in a hypothetical C 3 N 4 compound in the β-Si 3 N 4 structure are bound to 4 nitrogen atoms by very strong C-N bonds, which are shorter in comparison to the C-C bond in diamond (1.47 vs 1.53Å at ambient pressure) and the material is of low ionicity. In the subsequent work of Teter and Hemley [2], a number of structures with similar bonding properties have been proposed. These structures, with the exception of the graphite-like g-C 3 N 4 , have the sp 3 and sp 2 bonding for C and N atoms, respectively with the formation of CN 4 corner sharing tetrahedra (see Fig. 1(c)) where C atoms are connected with 4 N atoms and N atoms with 3 C atoms. The bulk moduli of these compounds have been calculated (using a DFT method) to be very high, exceeding that of diamond for the majority of structures, and, moreover, revealing very high densities and the presence of wide optical bandgaps (> 3 eV). These early predictions were based on the structural similarity with the known A 3 B 4 structural types, but for materials with atomic substitutions, e.g. α-and β-C 3 N 4 [2] are analogues to α-and β-Si 3 N 4 , respectively; also cubic C 3 N 4 is analogous to Th 3 P 4 .

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“…Experiments face challenges related to metastability, selection of precursors, determination of the crystal structures and chemical compositions from tiny samples 5 6 7 ; theoretical calculations suffer from assumptions of certain stoichiometries, e.g., C 3 N 4 1 , CN 8 , C 2 N 9 10 , CN 2 11 , C 11 N 4 12 , C 3 N 2 13 , CN 6 .... Some of them are meaningful, while most of them are probably not.…”

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The phase diagram and hardness of carbon nitrides

Dong

Oganov

Zhu

et al. 2015

Sci Rep

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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.

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A Novel Superhard Tetragonal Carbon Mononitride

Cited by 33 publications

References 51 publications

Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN2 (TM = Ti, Zr, and Hf)

Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN2 (TM = Ti, Zr, and Hf)

Synthesis of Ultra-incompressible sp³-Hybridized Carbon Nitride with 1:1 Stoichiometry

The phase diagram and hardness of carbon nitrides

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A Novel Superhard Tetragonal Carbon Mononitride

Cited by 33 publications

References 51 publications

Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN2 (TM = Ti, Zr, and Hf)

Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN2 (TM = Ti, Zr, and Hf)

Synthesis of Ultra-incompressible sp3-Hybridized Carbon Nitride with 1:1 Stoichiometry

The phase diagram and hardness of carbon nitrides

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Synthesis of Ultra-incompressible sp³-Hybridized Carbon Nitride with 1:1 Stoichiometry