Exploring Hardness and the Distorted sp² Hybridization of B–B Bonds in WB₃

In this work, tungsten triboride (WB 3 ) was successfully synthesized at high pressure and high temperature. The structure was reconfirmed to be WB 3 ( P 6 3 mmc ), and some part has a tungsten atomic defect according to the measurement results of X-ray diffraction, high-resolution transmission electron microscopy, and Rietveld refinement. The asymptotic Vickers hardness that had eliminated influence of excess boron is 25.5 GPa for WB 3 . This value is in good agreement with the previous theoretic results. Proof of novel electron transfer between the tungsten atom and the boron atom was found. A deficient amount of transfer electron induces distorted sp 2 hybridization of B–B bonds in WB 3 . The weakly directional sp 2 hybridization of B–B bonds is an essential factor that can influence the hardness of WB 3 . Our results are helpful to design new hard and superhard materials of transition metal borides.