Packing of quasi equivalent clusters For each one of the MGs the several types

Packing of quasi equivalent clusters for each one of

This preview shows page 4 - 5 out of 7 pages.

Packing of quasi-equivalent clusters For each one of the MGs, the several types of local coordination polyhedra specified above are geometrically different, not identical in topology and CN. They can nevertheless be considered quasi- equivalent, or cluster-like units for a given glass, supporting the framework of cluster packing 9 . This is because, first, the solute- centred ‘clusters’ in Fig. 5 (dashed circles) have similar sizes, as seen from their narrow volume distribution. Second, as discussed above, the CN of the solute at centre has a relatively small variance around an average controlled by R *, and the polyhedra can be considered distortions of certain specific types of Kasper polyhedra. That the CN is not a unique integer for a given glass, as is sometimes designated in idealized hard-sphere models 9,10 , is not surprising. This moderate CN distribution (or a range of quasi-equivalent clusters) is a natural consequence of strain relaxation in an MG to allow for more comfortable packing of ‘soft’ atoms (many-body interactions rather than touching hard spheres all of the same size), in the entire solid (not just one nearest-neighbouring shell as idealized in some models 10 ). Such arrangements will permit more flexibility for efficient filling of the entire 3D space, with reduced energy (see below). We point out that the formation of the local solute-centred coordination polyhedra is a manifestation of the strong chemical SRO favouring unlike bonds. An examination of the calculated electronic structures demonstrates the strong chemical affinity between the TM and metalloid, resulting from the partially covalent nature of the bonding that is still mostly non-directional. In the TM– TM glasses, we often observed non-additive pair interaction, arising from the charge transfer and screening of d electrons. Chemical SRO is well known in these TM–metalloid and TM–TM systems, and is usually one of the prerequisites for the easy formation of MGs 35 . Owing to the bond non-additivity, the effective R * is different from that estimated from their Goldschmidt atomic radii. In the literature, the absence of the direct solute–solute contacts is termed ‘solute–solute avoidance’ 7 . In other words, in the partial RRDFs of the solutes (see TM–metalloid glasses in Fig. 2 and Supplementary Fig. S7), there is little or no solute–solute pair correlation peak at the nearest-neighbour position. The chemical SRO that is, the fact that the solute atom sits in the centre defining the quasi-equivalent clusters sets the stage for the formation of the type of MRO discussed below. The solute–solute correlations and MRO. With the ‘quasi-equivalent cluster’ defined in this way, and after illustrating the intra-cluster packing (topological and chemical SRO), the next issue we discuss is the correlation among solute atoms (and solute-centred clusters).
Image of page 4

Subscribe to view the full document.

Image of page 5
  • Summer '19
  • Amorphous metal

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes