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.

过渡金属氮化物被认为兼具高硬度和良好的热稳定性，具有较大的潜在应用价值，但迄今为止尚未合成出稳定的超硬过渡金属氮化物。在这里，利用我们新开发的机器学习加速晶体结构搜索方法，我们设计了一种超硬氮化钨h -WN ₆，它可以在 65 GPa 左右的压力下合成并可淬火至环境压力。这个h -WN ₆由单键扶手椅状 N ₆环构成，呈现出类离子特征，可以表示为 W ^2.4+ N ₆ ^2.4−. 它在 0 GPa 时的带隙为 1.6 eV，并且在压力下表现出异常的带隙展宽行为。令人兴奋的是，这种h -WN ₆被发现是迄今为止已知的过渡金属氮化物中最硬的（维氏硬度约为 57 GPa），并且还具有非常高的熔化温度（约 1,900 K）。此外，良好的重量 (3.1 kJ/g) 和体积 (28.0 kJ/cm ³ ) 能量密度使这种富含氮的化合物成为潜在的高能量密度材料。这些预测支持设计规则，并可能刺激未来合成超硬和高能量密度材料的实验。