ABSTRACT

First-principles calculations were performed to study the structural, mechanical, electronic and magnetic properties of Fe_(8−x)Mo_xB₄ (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 ν 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.

摘要

进行第一性原理计算以研究 Fe _{(8− x )} Mo _x B ₄ ( x  = 0, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7 , 8)。结果表明，Mo原子会通过取代Fe原子进入Fe ₂ B晶格并引起晶体结构的变化。根据计算的生成焓，所有的硼化物都是热力学稳定的；此外，Mo 会降低 Fe ₂的稳定性B 当晶胞中 Mo 原子序数小于 4 时。总体上，随着Mo含量的增加，杨氏模量和剪切模量先减小后增大，体积模量变大。尽管 Fe ₂ B的硬度会随着 Mo 含量的增加而下降，但基于 G/B 和泊松比 ν 值，Mo 是改善 Fe ₂ B延展性的极好候选者。电荷密度曲线表明，在硼线性链的积分强度[002]取向减小莫合金的Fe ₂的Fe B.韧性改善₂ B将归因于B-B键，铁的演进/ Mo-B 键和 Fe/Mo-Fe 键，这可能会导致 Fe ₂的偏转B解理面。此外，这些硼化物的磁矩随着 Mo 含量的增加而单调减小。