A cubic approximant of the icosahedral phase in the (Al - Si) - Cu - Fe system

Abstract

We present a stable simple cubic structure in the quaternary system (Al-Si)-Cu-Fe with the composition Al 55 Si 7 Cu 25.5 Fe 12.5 which corresponds to the p/q = 1/1 cubic approximant of the icosahedral Al-Cu-Fe phase. This cubic structure, with lattice parameter a = 12.330 Å and density ρ ≈ 4.773 g cm −3 , contains roughly 135 atoms per unit cell. Preliminary studies of NMR and ME spectra as well as electric conductivity properties strongly suggest that this alloy shares most of the basic structural and physical properties of the parent icosahedral phase I-(Al-Cu-Fe). † This is used to define the orientation of the 3D cut space in the standard 6D space representation of the quasicrystal.

Universal features in the electrical conductivity of icosahedral Al-transition-metal quasicrystals

“…This remarkable behavior, referred to as an inverse Matthiessen rule, 42 has been also observed in quasicrystalline approximants, 44 and even in amorphous phases prior to their thermally driven transition to the QC phase. 45 These findings indicate that the inverse Matthiessen rule may be a quite general property of structurally complex alloy phases closely related to quasicrystalline compounds.…”

Formation of α-approximant and quasicrystalline Al–Cu–Fe thin films

“…This is slightly shorter than the 1.231 nm to 1.240 nm reported for bulk samples, see e.g. [8,10,16,19].…”

“…X-ray diffraction after annealing is shown in Figure 3 (a) for Al-deficient and in (b) for Al-rich compositions. All peaks could be assigned to known phases [7,8,9,15].…”

“…From studies of multilayered Al/Cu/Fe thin films [6,7] it was shown that binary Al-Cu phases, such as θ-Al 2 Cu, η-AlCu, and γ-Al 4 Cu 9 , form initially whereafter Fe is incorporated into the ω-Al 7 Cu 2 Fe, λ-Al 13 Fe 4 , β-Al 50 (CuFe) 50 , and the icosahedral quasicrystalline ψ-Al 62.5 Cu 25 Fe 12.5 phases. There are several related approximants to this quasicrystal, among them the cubic α-Al 55 Si 7 Cu 25.5 Fe 12.5 , where a low amount of Al has been substituted for Si [8]. It has been shown in bulk that the ψ-phase can not co-exist with the approximant α-phase, as the substitution destabilizes the ψ-phase [8].…”

“…There are several related approximants to this quasicrystal, among them the cubic α-Al 55 Si 7 Cu 25.5 Fe 12.5 , where a low amount of Al has been substituted for Si [8]. It has been shown in bulk that the ψ-phase can not co-exist with the approximant α-phase, as the substitution destabilizes the ψ-phase [8]. The approximant -phase in this system has previously not been synthesized as a thin film.…”