Samples with a target composition of Al62.5Cu25Fe12.5 (at.%) have been produced from the repeated cold rolling and folding (R&F) process of Al, Cu and Fe elemental foils. Upon early increments of the R&F cycle, the mechanically-induced process led to the fragmentation of the initial foils, which resulted in the dispersion of elemental Fe layers through the refined Al and Cu layers. After 40 R&F cycles the Al2Cu phase was detected, while Fe did not contribute to the formation of compounds. Thermal analyses suggested that the formation and dissolution of the Al2Cu and Al7Cu2Fe phases are critical steps for the synthesis of the i-phase during post-R&F treatment. Annealing between 650° and 750°C enabled the formation of the stable i-phase and resulted in high values of the microhardness.

We report on a class of icosahedral aluminum-transition-metal (Al-TM) alloys with a true semiconducting behavior. The existence of a semiconducting gap is found to depend critically on a particular kind of Al-TM ordering defined by a simple rule in a 6-dimensional superspace. Any deviation from this 6D order leads to the formation of strongly localized defect states in the gap. The structure of the semiconducting quasicrystals belongs to the face-center-icosahedral structural class, the same to which also icosahedral AlPdRe belongs. The description of the structure is based on a modified Katz-Gratias-Boudard model. We have calculated the electronic structure for series of quasicrystalline approximants. In the density of states of the 1/1 approximant with 128 atoms/unit cell relaxed with Hellmann-Feynman forces we have found a real gap at or close to the Fermi level. To get a semiconductor the critical band-filling is 648 electrons per cell. It can be achieved for several different stoichiometries. We investigated semiconducting 1/1 approximants with various combinations of 3d, 4d and 5d transition-metals. The gap widens as a 3d or 4d metal is replaced by a 5d metal. Calculations for the 2/1 approximant with 544 atoms/cell show the persistence of the gap. The chemical composition for which semiconducting behavior is achieved varies in the sequence of the approximants, but the existence of the gap in the electronic spectrum persists in higher order approximants, provided the Al-TM ordering is respected. Icosahedral AlPdRe represents the quasiperiodic limit in this hierarchyof approximants. As substitutional defects which obviously exist in real samples of any quasicrystal lead to formation of localized states, a real sample of icosahedral AlPdRe seems to be a semiconductor with a band-gap filled by localized states.

First-principles structural optimization is carried out for cubic Cd6Ca crystal with 168 atoms in a unit cell. The unit cell of Cd6Ca involves two four-layered icosahedral atomic clusters and 36 glue Cd atoms. Calculations are performed to determine energy cost owing to different orientations of the Cd tetrahedron, which is the innermost shell of the icosahedral cluster. Energetically favorable ordering of central Cd tetrahedra is such that the nearest neighboring tetrahedra is oriented in an anti-parallel fashion. As a result of the structural optimization, significant changes of atomic positions are observed in the first and second shells. The optimal nearest neighbor interatomic distance between the first and second shells is found to be close to the nearest neighbor distance of pure Cd. It is found that the pseudogap in the total density of states is enhanced as a result of the structural relaxation.

The effect of Al on the crystallization behavior of (Zr0.616Ti0.087Nb0.027Cu0.15Ni0.12)100–xAlx melt-spun glassy ribbons with x = 7.5, 5, 2.5 and 0 was investigated by differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The devitrification of the ribbons is characterized by the formation of a metastable quasicrystalline phase during the first stage of the crystallization process even for the alloy with x = 0. Therefore, Al is not essential for quasicrystal formation in the present alloys. However, it affects the properties of the amorphous as well as of the quasicrystalline phase. With decreasing Al content, the temperature range of stability of the quasicrystalline phase increases whereas the thermal stability of the amorphous phase decreases together with a slight decrease of the extension of the supercooled liquid region. Thus, it is concluded that although the addition of Al improves the stability of the glassy phase, it has no beneficial effect on the formation of quasicrystals.

We investigate the high temperature decagonal quasicrystalline phase of Al72Ni20Co8 using a quasilattice gas Monte-Carlo simulation. To avoid biasing towards a specific model we use an over-dense site list with a large fraction of free sites, permitting the simulation to explore an extended region of perpendicular space. Representing the atomic surface occupancy in a basis of harmonic functions directly reveals the 5-fold symmetric component of our data. Occupancy is examined in physical and perpendicular space.