Phase stability, elasticity, hardness and electronic structures for binary MnBm (M = Ni, Cr, Mo, W, n = 23, 5, 3, 1, m = 6, 3, 2, 1) borides: a comprehensive study using first principles

Abstract

ABSTRACTPhase stability, elasticity, hardness and relevant electronic structures of MnBm(M = Ni, Cr, Mo, W, n = 23,5,3,1, m = 6,3,2,1) binary borides have been investigated by first-principles calculations. The linear relationships between the formation enthalpies and their boron content x are found in 4 kinds of MnBm. The formation enthalpies gradually decrease with the increase of B content. The calculated elastic constants indicate that the MnBm (M = Cr, Mo and W) borides change gradually from ductility to brittleness with the increase of B content, while the NinBm borides show a ductile nature. The sequence in regard to hardness is CrnBm>MonBm (and WnBm) > NinBm. Electronic structure analysis shows that the variation trend of N(EF) is in accordance with that of formation enthalpies. Strong M–B bonds and pseudogap between the peaks at both side of the fermi energy are found to play important roles in the hardness and phase stability of these borides.