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Inorg Chem. 2017 Apr 3;56(7):3970-3975. doi: 10.1021/acs.inorgchem.6b03041. Epub 2017 Mar 22.

Synthesis and Mechanical Character of Hexagonal Phase δ-WN.

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State Key Laboratory of Superhard Materials, College of Physics, Jilin University , Changchun 130012, China.


In this work, high-quality bulk WC-structured WN (δ-WN) was synthesized via an untraditional method and the structure was accurately determined by X-ray diffraction and Rietveld refinement. In the process of synthesizing δ-WN, W2N3 and melamine were used as tungsten source and nitrogen source, respectively. The result of successfully synthesized high-quality δ-WN indicates that our method is an effective route for synthesizing high-quality bulk δ-WN and melamine is a pure nitrogen source for introducing the nitrogen to the metal precursor. The mechanical properties, bulk modulus, and Vickers hardness (HV) were first investigated by in situ high-pressure X-ray diffraction and Vickers microhardness tests, respectively. It is worth noting that the bulk modulus of δ-WN is 373 ± 8.3 GPa, which is comparable to that of c-BN. The Vickers hardness is 13.8 GPa under an applied load of 4.9 N. It is worth noting that W-W metallic bond and W-N ionic bond are mainly chemical bond in δ-WN based on the analysis of electron localization function (ELF), density of states (DOS), and Mulliken population. This result can well clarify that δ-WN is only a hard material for the lack of strong W-N covalent bonds to form 3D network structure. Our results are helpful to understand the hardness mechanism and design superhard materials in transition-metal nitrides.

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