New multifunctional tungsten nitride with energetic N 6 and extreme hardness predicted from first principles

Le résumé fourni par la source

We report a new member to the family of tungsten nitrides, WN 6 , predicted from the structure search. Ground-state convex hull calculation reveals that crystalline WN 6 is thermodynamically stable at pressures above 16 GPa, but remains dynamically stable at ambient conditions. The predicted high-pressure WN 6 structure contains chaired cyclo-N 6 6 − rings isoelectronic to cyclo-hexasulfur (S 6 ), which is unprecedented in nitrogen. In the cyclo-N 6 6 − unit all nitrogen atoms are singly bonded and therefore contain a high energy density. By means of efficiently packing the covalent-bonded species, WN 6 is estimated to have extremely high Vickers hardness greater than 40 GPa at ambient conditions, placing it as one of the hardest materials. The present results reveal that WN 6 may be used as a superhard material but simultaneously maintaining other desirable properties, which represents an interesting example of multifunctional materials.

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