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

First-principles calculations were performed on the superhard material, WB4 ( Vicker hardness exceeding 46 GPa), 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 B-2 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. (c) 2008 American Institute of Physics.