A New Superhard Phase and Physical Properties of ZrB(3) from First-Principles Calculations

Using the first-principles particle swarm optimization algorithm for crystal structural prediction, we have predicted a novel monoclinic C2/m structure for ZrB(3), which is more energetically favorable than the previously proposed FeB(3)-, TcP(3)-, MoB(3)-, WB(3)-, and OsB(3)-type structures in the considered pressure range. The new phase is mechanically and dynamically stable, as confirmed by the calculations of its elastic constants and phonon dispersion curve. The calculated large shear modulus (227 GPa) and high hardness (42.2 GPa) show that ZrB(3) within the monoclinic phase is a potentially superhard material. The analyses of the electronic density of states and chemical bonding reveal that the strong B–B and B–Zr covalent bonds are attributed to its high hardness. By the quasi-harmonic Debye model, the heat capacity, thermal expansion coefficient and Grüneisen parameter of ZrB(3) are also systemically investigated.