Semimetallic Band Structure and Cluster-Based Description of a Cubic Quasicrystalline Approximant in the Al–Cu–Ir System

Abstract

Density functional calculations were performed for a cubic quasicrystalline approximant in the Al-Cu-Ir system. A semimetallic band structure was developed and analyzed on the basis of Wannier functions constructed from the valence and a part of the conduction band manifold. The Wannier functions were s-and p-like orbitals centered on either the centers of conventional clusters or the icosahedron-like vertices of pseudo-Mackay clusters, and d-like orbitals centered on the transition metals. Grouping the orbitals according to their center, we considered a small cluster for each group of the orbitals. Most of the orbitals contribute to the density of states only within the valence bands, i.e., they are valence states. The exceptions are some of p-like orbitals centered on the icosahedron-like vertices of the pseudo-Mackay clusters, and they contribute to both valence and conduction bands. Each of these p-like orbitals forms a covalent bond with one centered on the neighboring small cluster. The resulting bonding and antibonding orbitals are valence and conduction states, respectively. The number of valence bands (173) of our Al 39 Cu 8 Ir 15 model was then decomposed in terms of the numbers of transition metals (23), clusters (16), and covalent bonds between the clusters (6) as 23 Â 5 þ 16 Â 4 À 6 ¼ 173. The description for the valence-band formation may also be applicable to some of the group 13 element-transition metal intermetallic compounds, such as RuAl 2 .

Principles of weakly ordered domains in intermetallics: the cooperative effects of atomic packing and electronics in Fe2Al5

“…We now turn to exploring the role that these features play in the stability of Fe 2 Al 5 . The composition of this compound places it within the domain of a broad electron counting rule for transition metal-main group (T-E) intermetallic phases, the 18 À n rule , 2015, which can be considered as a limiting case of the more general 5t + 4c À b scheme of Kitahara et al (2015Kitahara et al ( , 2017. In these compounds, the T atoms strive for filled 18-electron configurations, in which an electron pair is associated with each of their valence s, p and d atomic orbitals.…”

Inducing Complexity in Intermetallics through Electron–Hole Matching: The Structure of Fe14Pd17Al69

“…Of course, the two phases adopt the same structure type, and an electron precise phase can be obtained by simply alloying Pd and Fe in a pseudo‐binary CsCl‐type phase . However, less structurally trivial phases also appear in the system, including Fe 14 Pd 17 Al 69 , whose structure was previously solved, revealing features similar to the F‐centered Cu 8 Ir 15 Al 39 quasicrystal approximant model constructed and explained in terms of a variation of the 18− n rule by Kitahara et al . However, more detailed features related to potential soft vibrational modes, such as anisotropic atomic displacement parameters, were not reported.…”

“…In this sense, Fe 14 Pd 17 Al 69 is one of a number of supercell derivatives of another, more closely related compound, IrAl 2.75 (Figure b) . IrAl 2.75 is thus a useful starting point for a discussion of Fe 14 Pd 17 Al 69 ’s structure and bonding.…”

Experimental realization of a semiconducting quasicrystalline approximant in Al-Si-Ru system by band engineering

“…In contrast, the VBM consists of p-like orbitals in the inner clusters. Note that these p-like orbitals should not be considered to be the Ir-p orbitals but are the p orbitals of clusters composed of Ir and the surrounding Al, which is also confirmed in the Al-Cu-Ir C 2 phase [28]. To shift the VBM downward, it is considered effective to substitute Al, which is the main constituent element of the inner clusters, with Si, which has a lower orbital energy.…”