WN6 phase discovered at 126–165 GPa after heating of W in nitrogen. XRD refinements reveal a unit cell in space group R¯3m which is consistent with the WN6 structure with armchairlike hexazine (N6) rings, while strong A1g Raman mode confirms its N─N single bonds. Density functional theory (DFT) calculations reveal balanced contributions of attractive interactions between W and covalent N6 rings, and repulsions between N6 rings that make WN6 ultrastiff and tough. The WN6 phase displays long bond lengths in the nearest N-N and pressure-enhanced electronic band gap, which pave the way for finding novel nitrides.
Salke, Nilesh P. and Xia, Kang and Fu, Suyu and Zhang, Youjun and Greenberg, Eran and Prakapenka, Vitali B. and Liu, Jin and Sun, Jian and Lin, Jung-Fu, Tungsten Hexanitride with Single-Bonded Armchairlike Hexazine Structure at High Pressure, Phys. Rev. Lett.126, (6), 2021, 065702, DOI : 10.1103/PhysRevLett.126.065702 abstract
Crystal structure of the WN6 phase with the space group R¯3m determined by high-pressure XRD refinement. (a) Le Bail refinement of the WN6 phase at 165 GPa (λ=0.3344 Å) (red vertical ticks). Blue vertical ticks represent unreacted W in the bcc phase that coexists with the WN6. Red open circles, black line and green line represents the experimental data, the fit and the residual difference respectively. (b) Crystal structure of the WN6 phase with the novel armchairlike N6 rings and W atoms in between the rings along the c axis. See a representative XRD image at 165 GPa shown in Fig. S5 in Supplemental Material