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

In this work, tungsten triboride (WB3) was successfully synthesized at high pressure and high temperature. The structure was reconfirmed to be WB3 (P6(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 WB3. 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 se hybridization of B-B bonds in WB3. The weakly directional sp(2) hybridization of B-B bonds is an essential factor that can influence the hardness of WB3. Our results are helpful to design new hard and superhard materials of transition metal borides.