Local atomic structure of quaternary Fe-based metallic glass studied by X-ray diffraction, Mössbauer spectroscopy and Reverse Monte Carlo modeling

The atomic structure of Fe₄₂Co₂₀Nb₈B₃₀ glassy alloy was investigated using synchrotron high-energy X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and Reverse Monte Carlo modeling (RMC). The RMC method basing on the results of XRD measurements was used for evaluating interatomic distances and coordination numbers in the local structure of quaternary alloy. The coordination numbers for Fe-Fe atomic pairs were additionally determined using Mössbauer spectroscopy investigations and Gonser et al. approach. The measured Mössbauer spectra of glassy alloy were decomposed into subspectra representing average Fe-Fe coordination numbers. A layer with thickness of 0.5 nm was extracted from the RMC configuration box containing 8000 atoms and short-range ordering in the investigated glassy alloy was analyzed within this fragment. Coordination polyhedra for Fe-Fe, Co-Fe, B-Fe and Nb-Fe atomic pairs are represented by the Bernal's tetrahedra and octahedral as well by the monocapped square antiprism with one atom missing and B-centered clusters related to the tricapped trigonal prisms. The presence of clusters with five-fold coordination for the Fe-Fe pairs is confirmed by analysis of the Mössbauer spectra using the Gonser approach.