Atomic coordinates from the 3D structure were then used for more detailed

Atomic coordinates from the 3d structure were then

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which are absent in earlier models. Atomic coordinates from the 3D structure were then used for more detailed analysis of structural features, from which basic principles underlying the short-to-med- ium-range order could be extracted. As illustrated in detail below, our results validate several of the earlier concepts regarding the SRO and efficient packing, specify the particular topologies of cluster-like entities, and suggest a fundamentally new cluster packing scheme that constitutes the MRO. For completeness, we also illustrate how the solute atoms arrange themselves in alloys with enriched solute concentrations. Metallic glass structure from XRD, EXAFS and RMC. We started by analysing a model MG, Ni 80 P 20 , using structural information acquired through synchrotron X-ray measurements. In addition to wide-angle X-ray scattering (Fig. 1a), extended X-ray absorption fine structure (EXAFS) experiments have been used as the species-specific probe to provide local coordination information (see Fig. 1 and the Methods). Unlike previous work that dealt mostly with the one- dimensional pair distribution functions, we focused on the 3D atomic configuration (atomic positions, density) reconstructed using the reverse Monte Carlo (RMC) 11,12 method, which produced the excellent fits to the experimental spectra in Fig. 1 (see Methods). The final configuration was double-checked by comparing the X-ray absorption near-edge structure (XANES) patterns calculated from the RMC structure (Fig. 1d) with that observed in the X-ray absorption experiments (shown in Supplementary Fig. S1 but not used in RMC fitting). We also confirmed that the one-dimensional partial pair distribution functions obtained from the RMC configu- ration are in satisfactory agreement with those obtained before from neutron isotope experimental measurements 13 (see the comparison in Supplementary Fig. S2). Structure from ab initio molecular dynamics simulations. We also pursued the 3D MG structure via a completely independent route: ab initio molecular dynamics simulations 14,15 . Here the atomic forces are determined on the basis of first-principles calculations without the need for any experimental data or empirical potentials (details in the Methods 16–21 ). The ab initio calculations allowed us not only to obtain and analyse the static amorphous structure, but also to monitor the structural evolution during the liquid cooling process. More importantly, the ab initio modelling enabled us to deduce a general trend by systematically comparing a number of MG systems with different chemical make-ups (such as transition metal (TM)– TM and TM–metalloid), different atomic size ratios and different levels of solute concentrations. ARTICLES 1 Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
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  • Summer '19
  • Amorphous metal

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