Theoretical investigation on the transition metal borides with Ta3B4-type structure: a class of hard and refractory materials

摘要

Based on density functional theory, we have systematically studied thestructural stability, mechanical properties and chemical bonding of thetransition metal borides M3B4 (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) for thefirst time. All the present studied M3B4 have been demonstrated to bethermodynamically and mechanically stable. The bulk modulus, shear modulus,Young's modulus, Poisson's ratio, microhardness, Debye temperature andanisotropy have been derived for ideal polycrystalline M3B4 aggregates. Inaddition, the relationship between Debye temperature and microhardness has beendiscussed for these isostructral M3B4. Furthermore, the results of the Cauchypressure, the ratio of bulk modulus to shear modulus, and Poisson's ratiosuggest that the valence electrons of transition metals play an important rolein the ductility of M3B4. The calculated total density of states for M3B4indicates that all these borides display a metallic conductivity. By analyzingthe electron localization function, we show that the improvement of theductility in these M3B4 might attribute to the decrease of their angularbonding character.