Atomic packing and diffusion in Fe₈₅Si₂B₉P₄ amorphous alloy analyzed by ab initio molecular dynamics simulation

In the work reported in this paper, ab initio molecular dynamics simulation was performed on Fe₈₅Si₂B₉P₄ amorphous alloy. Preferred atomic environment of the elements was analyzed with Voronoi polyhedrons. It showed that B and P atoms prefer less neighbors compared with Fe and Si, making them structurally incompatible with Fe rich structure and repulsive to the formation of α-Fe. However, due to the low bonding energy of B and P caused by low coordination number, the diffusion rates of them were considerably large, resulting in the requirement of fast annealing for achieving optimum nano-crystallization for its soft magnetic property. The simulation work also indicates that diffusion rate in amorphous alloy is largely determined by bonding energy rather than atomic size.