Topological Close Packing in Structurally Complex Intermetallics (Crystalline, Quasicrystalline and Noncrystalline)

摘要

Atomic Cluster Configurations in Metallic Glasses: In connection with the model for metallic glasses proposed by D. B. Miracle (A structural model for metallic glasses. Nature Materials 3 (2004) 697-702), the structures consisting of a single solute atom surrounded by a coordination shell of solvent atoms has been examined. The possible coordination number (CN) depends, of course, on the ratio of radii of the two kinds of atom. Atomic Size Factor Criterion in Designing Bulk Metallic Glasses: In the heuristic formulations for glass forming ability by Inoue, atomic size, negative enthalpy of mixing and multicomponent criteria are used. A study of related crystalline and quasicrystalline intermetallics lends weight to the atomic size being the dominant factor. The largest size atom plays a key role in all topologically close-packed phases, even when it happens to be a minority constituent. The supertetrahedron: The various structures that can arise from supertetrahedral clusters serve to illustrate the interplay between the different approaches to visualising the geometry underlying complex material structures - sphere packing models, clusters describable as sets of nested polyhedra, network structures, and network-type configurations of polyhedra. A concise description and visualization of atomic structures is fundamental to a clear understanding of a broad range of phenomena in the expansive class of intermetallic alloys. Geometrical models based on polytetrahedral units have been adopted in order to rationalize a number of important intermetallic structures: the family of gamma- phases, the Laves phases and the so-called 'anti-Laves' phases. An icosahedral cluster consisting of a 13 equal-sized spheres is a simple polytetrahedral unit of relevance in many crystalline, quasicrystalline and amorphous structures. A more complicated polytetrahedral unit has been emphasized; the supertetrahedron, consisting of four interpenetrating icosahedra.