Quasicrystals and Complex Metallic Alloys

Abstract

With his famous discovery of quasicrystalline order in 1982–1984, Dan Shechtman, the 2011 Nobel Laureate for Chemistry, helped establish a fascinating field in materials science that has impacted also other fields in metallurgy, geology, polymer science, artificial nanostructured materials, low temperature physics, etc. The discovery forced scientists to deepen their understanding of structure and order of matter in nature and matter's properties; thereby suggesting new applications. In this article, the most salient features of this field are presented, beginning with a view of the different ways quasiperiodicity is expressed in solids, and explaining how atomic arrangements and electron transport properties may be described in aperiodic structures. Quasicrystals, as the ultimate degree of complexity in metallic compounds, are then discussed in the context of complex metallic alloys. Finally, two examples of applications—composites and catalysts—that take advantage of the specific electron transport and electron bonding in quasicrystals are mentioned.

Crystalline and Electronic Structures of the Al1+xV2Sn2–x (x = 0.19) Intermetallic Compound

“…As shown in Table 1, further difference Fourier calculations did not reveal any significant residual electron density peaks. Consequently, the composition of the investigated crystal is Al 1.19(2) V 2 Sn 1.81 (2) . The positional parameters standardized using the program Structure Tidy 27 are listed in Table 2, the anisotropic thermal factors are gathered in Table 3 and the main interatomic distances in Table 4.…”

“…Derived from the extensive works performed on quasicrystalline systems, the Push-Pull alloy (PPA) concept has emerged as one route potentially leading to the identification of new structurally complex ternary intermetallic compounds 2 . For a A x B y C z system, the PPA terminology refers to attractive interactions between constituents in A-B and A-C binary systems (Pull) and to repulsive one between B and C elements (Push), often forming no binary compound or being immiscible.…”

Solid Solubility in Cu5Gd1−xCax System: Structure, Stability, and Hydrogenation

“…Such systems are found in ternary, or multinary, alloys of generic composition A B C and are characterized by two important key facts: (i) the binary components A-B and A-C form well-defined compounds (negative formation enthalpy) and (ii) the B-C pair forms no compound nor solid solution, as B and C are immiscible due to the positive formation or mixing enthalpy. Such alloys are coined "push-pull" alloys [10]. A well-known example is the already mentioned, Al-Cu-Fe system [11], in which several binary Al-Cu and Al-Fe compounds are known, with some being rather complex.…”