A first-principles prediction of anisotropic elasticity and thermal properties of potential superhard WB3

The first-principles calculations were used to predict the anisotropic elasticity and thermal properties of hexagonal (hP4-WB3, hP8-WB3 and hP16-WB3) and trigonal (hR24-WB3) WB3 triborides. The single-crystal and polycrystalline elastic properties were computed from the stress-strain method and Voigt-Reuss-Hill approximations, respectively. Based on the obtained elastic modulus, two theoretical models were used to theoretically calculate Vickers hardness HV of WB3. The results showed that hP16-WB3 and hR24-WB3 are potential candidates for superhard materials. The elastic anisotropies of WB3 were characterized by elastic anisotropic indexes (AU, Acomp and Ashear, and A1, A2 and A3), three-dimensional views and projections of bulk, shear and Young's moduli. The anisotropic elasticity is ordered as hP8-WB3 > hP4-WB3 > hR24-WB3 > hP16-WB3. Furthermore, the thermal properties such as Debye temperature and sound velocity were computed from the elastic constants and moduli. Finally, the directional sound velocities were also discussed.