First-principles calculation of structural, thermodynamic and mechanical properties of 5d transitional metal triborides TMB3 (TMÂ =Â Hf-Au)

Due to their useful physical and chemical characteristics, transitional metal borides have attracted much attention. In this study, the structural, thermodynamical, mechanical, dynamical and electronic properties of 5d transitional metal triborides TMB3 (TM = Hf-Au) are investigated by density functional theory. For each triboride, five structures are considered, i.e., m-AlB2 (modified AlB2), OsB3, FeB3, WB3 and TcP3 structures. The calculated lattice parameters are in good agreement with previously theoretical results. Thermodynamic stability of compounds is predicted and the formation enthalpy increases from TaB3 to AuB3. The calculated phonon dispersion curves demonstrate that each TMB3 in the most stable structure is dynamically stable. The calculated density of states shows that they are all metallic. Among the studied compounds, OsB3-ReB3 (OsB3-ReB3 represents ReB3 in OsB3 structure, the same hereinafter) has the largest shear modulus (261 GPa), bulk modulus (355 GPa) and Young modulus (630 GPa). WB3-WB3 has the second largest shear modulus (257 GPa). This suggests that OsB3-ReB3 and WB3-WB3 might be potential ultra-incompressible and superhard materials.