Effect of Mo concentration on structural, mechanical, electronic and magnetic properties of Fe2B: a first-principles study

First-principles calculations were performed to study the structural, mechanical, electronic and magnetic properties of Fe(8-x)MoxB4 (x = 0, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8). Results show that the Mo atoms would enter the Fe2B lattice by replacing the Fe atoms and cause a change in the crystal structure. According to the calculated formation enthalpy, all borides are thermodynamically stable; moreover, Mo would reduce the stability of Fe2B when the Mo atomic number is less than four in the unit cell. On the whole, with the increase of Mo content, the Young's moduli and shear moduli decrease firstly and then increase, while the bulk moduli get bigger. Although the hardness of Fe2B would decline with increasing Mo content, Mo is an excellent candidate for improving the ductility of Fe2B on the basis of the G/B and Poisson's ratio nu values. The charge density plots indicate that the integral strength of the linear boron chains in [002] orientation is reduced in Mo-alloyed Fe2B. The toughness improvement of Fe2B would be attributed to the evolutions of B-B bonds, Fe/Mo-B bonds and Fe/Mo-Fe bonds, which may induce the deflection of the Fe2B cleavage plane. Besides, the magnetic moments of these borides monotonically decrease with the increase in Mo content.