A novel superhard tungsten nitride predicted by machine-learning accelerated crystal structure search

Kang Xia; Hao Gao; Cong Liu; Jianan Yuan; Jian Sun; Hui-Tian Wang; Dingyu Xing

doi:10.1016/j.scib.2018.05.027

A novel superhard tungsten nitride predicted by machine-learning accelerated crystal structure search

Sci Bull (Beijing). 2018 Jul 15;63(13):817-824. doi: 10.1016/j.scib.2018.05.027. Epub 2018 May 29.

Authors

Kang Xia¹, Hao Gao¹, Cong Liu¹, Jianan Yuan¹, Jian Sun², Hui-Tian Wang³, Dingyu Xing¹

Affiliations

¹ National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
² National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China. Electronic address: jiansun@nju.edu.cn.
³ National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China. Electronic address: htwang@nju.edu.cn.

PMID: 36658960
DOI: 10.1016/j.scib.2018.05.027

Abstract

Transition metal nitrides have been suggested to have both high hardness and good thermal stability with large potential application value, but so far stable superhard transition metal nitrides have not been synthesized. Here, with our newly developed machine-learning accelerated crystal structure searching method, we designed a superhard tungsten nitride, h-WN₆, which can be synthesized at pressure around 65 GPa and quenchable to ambient pressure. This h-WN₆ is constructed with single-bonded armchair-like N₆ rings and presents ionic-like features, which can be formulated as W^2.4+N₆^2.4-. It has a band gap of 1.6 eV at 0 GPa and exhibits an abnormal gap broadening behavior under pressure. Excitingly, this h-WN₆ is found to be the hardest among transition metal nitrides known so far (Vickers hardness around 57 GPa) and also has a very high melting temperature (around 1,900 K). Additionally, the good gravimetric (3.1 kJ/g) and volumetric (28.0 kJ/cm³) energy densities make this nitrogen-rich compound a potential high-energy-density material. These predictions support the designing rules and may stimulate future experiments to synthesize superhard and high-energy-density material.

Keywords: Machine-learning accelerated crystal structure searching method; Superhard tungsten nitride; Transition metal nitrides; Tungsten nitride.