Origin of hardness in WB4 and its implications for ReB4, TaB4, MoB4, TcB4, and OsB4

Abstract

First-principles calculations were performed on the superhard material, WB4 (Vicker hardness exceeding 46GPa), to reveal the origin of its high hardness. Our simulated lattice parameters, bulk modulus, and hardness are in excellent agreement with the experimental data. A three-dimensional B network with a peculiar B2 dimer along the z-axis and a xy planar honeycomb B sublattice is uncovered to be mainly responsible for the high hardness. We further predicted that five other transition metal B compounds (TMB4, TM=Re, Mo, Ta, Os, and Tc) within the WB4 structure are potential superhard materials.