ABSTRACT
We have estimated in Chapter 2, Section 2.3 how deep and wide a pseudogap at the Fermi level must be to stabilize structurally complex metallic alloys (CMAs), and concluded that the experimentally observed pseudogap in many quasicrystals and approximants is indeed deep and large enough. It is also noted in Chapter 4 that first-principles band calculations can be performed successfully even for crystals containing more than 100 atoms in the unit cell, once their atom positions are defined without any ambiguities, such as chemical disorder or fractional site occupancy.*
Both I-and P-cell gamma-brasses in binary alloy systems may be classified into three groups, as discussed in Chapter 6, Section 6.2. Among them, group (I) gamma-brasses refer to those based on the noble metals Cu, Ag, or Au alloyed with the polyvalent elements such as Al, Zn, and so on (see Table 6.1). ἀ ey are, we believe, the best suited to study the role of
the FsBz interaction and its impact on the stability of the CMAs. As will be shown below, the electronic structure of group (I) gamma-brasses is characterized by a FsBz-induced pseudogap at the Fermi level. In the present chapter, we consider Cu5Zn8 and Cu9Al4 gamma-brasses as the representative alloys of group (I), and demonstrate that a pseudogap is indeed induced by the FsBz interaction. We will also explain why the particular electron concentration e/a = 21/13 plays a predominant and key role in their stabilization.
