First-principles study of influence of transition metal doping on the physical properties of TiB3

Superhard materials possess a multitude of advantageous properties and are utilized in a plethora of fields. The calculated hardness of TiB3 is 41.6 GPa and those of all TM-doped TiB3 are higher than 40 GPa, thereby indicating that TiB3 and TM-doped TiB3 are potential superhard materials. This paper presents a comprehensive study of the electronic, elastic and thermal properties, fracture toughness and damage tolerance of TiB3 and its doped transition metals (TMs, including Sc, V, Y, Zr, Nb, Hf and Ta) through the use of first-principles calculations. These materials are thermodynamically, kinetically and mechanically stable, as evidenced by the dispersion of phonon and Debye temperature. Furthermore, calculations were performed to determine the impact of doping on the brittleness and toughness of the materials, with specific attention paid to hardness, fracture toughness and elastic modulus. The anisotropy of the doped material is analysed through the projection of the 3D surface structure and the 2D Young's modulus. The metallic nature of these materials is revealed by energy band structure and density of states analyses. Finally, the effect of doping on the thermodynamic properties of the materials is explored by means of Debye temperature and sound velocity evaluations.