Electronic structures of hexagonal Zn-Mg-Y and Cd58Y13 compounds are studied by first-principles calculations. Both of the systems show deep pseudogap in the electronic density of states near the Fermi level and considered to be stabilized electronically. To illustrate bonding nature of electronic wavefunctions, the crystal orbital Hamilton population (COHP) is calculated for neighboring pairs of atoms in the unit cell. It is found that the bonding nature is changed from bonding to anti-bonding almost exactly at the Fermi level for Zn-Zn and Cd-Cd bonds. On the contrary, for Zn/Cd-Y bonds, both of the states below and above the pseudogap behave as bonding ones. Possible effects of the p-d hybridization are discussed.

A constitutive model describing the plasticity of icosahedral quasicrystals [1] was applied to icosahedral Al-Pd-Mn over a wide range of experimental deformation conditions. The model incorporates the evolution of two microstructural parameters: The first, as in crystals, is the dislocation density; the second is a quasicrystal-specific order parameter that accounts for deformation-induced disordering and thermally activated reordering of the quasicrystal structure. Significant strain-rate dependence was found which can be understood by the interactive evolution of these two microstructural parameters. The present work shows that the constitutive model comprehensively describes the features of quasicrystal plasticity over a wide range of experimental conditions.

We present a study of the deformation mechanism of decagonal Al73Ni10Co17 quasicrystals by means of transmission electron microscopy. We performed compression tests on single-quasicrystalline samples in three different orientations: with the compression axis parallel to, inclined by 45 ° and perpendicular to the tenfold axis of the decagonal quasicrystal. The deformed samples reveal characteristic orientation-dependent dislocation structures leading us to the conclusion that fundamentally different deformation mechanisms are involved in plastic deformation in the three deformation geometries. We explicitly identified the Burgers vectors of the dislocations as interatomic vectors in the structure of decagonal Al-Ni-Co.

We report the electrical resistivity of the ternary Ag-In-(Yb,Ca) quasicrystals (QCs) together with those of their 1/1 and 2/1 cubic approximants. The temperature coefficient of the resistivity (TCR) is negative and nearly the same for the QCs and the 2/1 approximants suggesting that the coherence length of the conduction electrons in the QCs is comparable to the lattice parameter of the 2/1 approximants, i.e., ∼2.5 nm. On the other hand, both positive and negative values of TCR are observed for the 1/1 approximants depending on the annealing temperature. Taking into consideration the occurrence of positive TCR in the binary Cd-(Yb,Ca) 1/1 approximant, the latter phenomenon suggests that the negative TCR of the ternary 1/1 approximants is due to chemical disorder between Ag and In, and the chemical disorder is possibly reduced when annealed at low temperatures.

A standard approach for structure solution of ordinary crystals begins with solving the phase problem. We show that a similar procedure can be taken even in the case of quasicrystals using single crystal X-ray diffraction by applying an ab initio structure determination method called the low density elimination method. The first picture of the occupation domains, which must be specified in a higher-dimensional structure determination of quasicrystals, is obtained from a phase-reconstructed density. We present six-dimensional densities determined by this method and give their interpretation for several different types of icosahedral quasicrystals.

Recent experiments discovered an order-disorder transition occuring at low temperatures in large unit 1/1 cell cubic approximants of the stable Cd-based binary alloy quasicrystals. The transition is related to correlations among orientational degrees of freedom whose separations are around 12 Å. We analyze the interactions between the degrees of freedom using ab-initio calculations for Cd-Ca alloys and derive an equivalent antiferromagnetic Ising model which shows a similar phase transition. However, the calculated transition temperature is higher than observed experimentally, indicating that the actual structure and its order-disorder transition are more complex than originally proposed. A side-benefit of our study is the discovery of a canonical-cell decoration model for the Cd-Ca icosahedral phase.

Specular-beam intensity profiles are measured in low-energy electron diffraction as a function of temperature for the fivefold- and threefold-symmetry surfaces of the icosahedral quasicrystal Al-Pd-Mn. The resulting shifts of the Bragg-peaks to lower energies are accounted for mainly by a lattice expansion perpendicular to the surface and allow us to determine the thermal expansion coefficient of atomic layers to be (24.5 ± 2.0) × 10−6 K−1 for both surfaces. As a result of several measurements, a surface Debye temperature of 298 ± 7 K is found for the pentagonal and 301 ± 10 K for the threefold-symmetry surface. This similarity implies comparable bonding forces for the atoms at these surfaces. Additionally, the derived thermal expansion coefficient supports a layer-based structural model for both surfaces investigated here.

Mechanical alloying of Ti45+xZr38-xNi17 (-4 ≤ x ≤ 16) elemental powder mixtures leads to the formation the amorphous phase, but subsequent annealing at 833 K causes the formation of icosahedral (i) quasicrystal and the Ti2Ni-type crystal phases. The α-Ti phase is also produced in Ti-rich powders after annealing. Both the quasilattice constant of the i-phase and the lattice parameter of the Ti2Ni-type crystal phase decrease monotonically with increasing substituted amount of Ti because of the smaller radius of the Ti atom. The maximum hydrogen concentration in the i-phase in all powder compacts, after electrochemical hydrogenation in a KOH solution, is almost the same, about 63 at% ([H] / [M] ≈ 1.7). The onset temperature of hydrogen desorption is about 570 K (at a heating rate of 5 K/min) for all powders, but the temperature for the maximum hydrogen desorption rate increases with increasing Ti concentration in the powders, suggesting that some hydrogen atoms might be more strongly bound in the quasilattice where the original Zr sites become occupied by Ti atoms.

Sn film growth on the fivefold surface of icosahedral Al63Cu24Fe13 has been investigated by employing scanning tunneling microscopy. For about monolayer coverage, the deposited Sn forms a layer of monoatomic height. A Fourier transform of the layer's structure reveals quasicrystalline long range order. At higher coverage, flat-topped clusters of uniform heights are formed. The clusters preferentially grow at the step edges.

TEM observations have been performed in AlPdMn single-grain quasicrystal deformed at low temperature. They show that dislocation motion has occurred by climb associated with vacancy diffusion. At room temperature, deformation also occurs by crack followed by re-healing.

Starting from the Zn17Sc3 cubic approximant, new icosahedral quasicrystal was searched by substituting Zn by other metals, M, at the alloy composition of Zn75M10Sc15. In the cases of M = Mn, Fe, Co, Ni, Pd, Pt, Ag and Au, new P-type quasicrystals were discovered in as-cast alloys. In the cases of M = Fe, Co, Ni, Pd and Ag, the quasicrystals are thermodynamically stable at approximately 700 °C. This result indicates that use of an approximant crystal as a starting material is very efficient way to search new quasicrystal alloy, and many kinds of metals stabilize the quasicrystal structures; i.e. noble metals and transition elements including Mn, Fe, Co and Ni in addition to Mg. Taking the variety in base metals of Tsai-type approximants into account, this variety in additional components suggests many possibilities of undiscovered quasicrystals. The equality ofthe electron concentration, ela ≈ 2.1, in Hume-Rothery rule may be a guide to these quasicrystals.

Confining pressure techniques, that superimpose a shear stress on an isostatic component, allowed us to plastically deform AlPdMn specimens at temperatures below the brittle-to-ductile transition temperature obtained using conventional uniaxial deformation tests at usual strain-rates. Microstructural observations associated with these low deformation temperatures are reported. They provide new insights on the elementary deformation mechanisms that control plasticity in this non-periodic structure.

The glassy structure and the primary precipitation phase from supercooled liquid were examined in metal-metal type Zr-, Hf- and Cu-based alloy systems by various advanced analytical techniques. The icosahedral phase precipitates as the primary phase from supercooled liquid for all the metal-metal type glassy alloys examined in the present study. The icosahedral phase has a rhombic triacontahedra type for the Zr-Al-Ni-Cu-NM (NM=Ag, Pd, Au, Pt), Zr-Cu-NM, Hf-Al-Ni-Cu-NM, Cu-Zr-Ti-Pd and Cu-Hf-Ti alloys. In addition, the short-range atomic configurations in their glassy alloys have the features of highly dense packed atomic configuration, new local atomic configurations and long-range homogeneity with attractive interaction. It is therefore concluded that the high glass-forming ability of the metal-metal type alloys is due to the self-formation of the unique glassy structure with the above-described three features which are consistent with the formation of short-range icosahedral atomic configuration.

Single grains of icosahedral Cd84Yb16 quasicrystalline phase were characterized using high resolution transmission electron microcopy (HRTEM) technique. Image reconstruction of the obtained multiple through-focal series for both the two and five-fold axes are consistent with the local cluster structure of concentric polyhedra consisting of Cd tetrahedron (1/3 occupied icosahedron), Cd dodecahedron, Yb icosahedron and a Cd icosidodecahedron. Edge-sharing of the clusters can result in complete tiling of the 2-D projections. Simple matching rules are being investigated to construct a 3-D model.

Lynntech, Inc has successfully researched and demonstrated a unique method for the manufacture of quasicrystalline (QC) coatings that utilizes the process of electrocodeposition. The purpose of this study was to optimize the physical-mechanical properties of the QC coatings. All metal substrates were aluminum alloy Al-3004 and codeposition was performed using Al65Cu23Fe12 QC powders in nickel plating solutions. X-ray diffraction spectroscopy was performed in order to verify the attachment of quasicrystals to the aluminum alloy substrate and coated samples displayed identical spectra to those of raw QC powders. The average contact angle θ was 117.2° for electrocodeposited QC coatings. Friction was monitored during pin-on-disk wear tests and QC coated samples had coefficients of friction as low as 0.01 and an average value of 0.05 with samples showing no visible wear scar. Lynntech's electrocodeposited quasicrystalline coatings withstand high temperatures and exhibit low wear and friction characteristics with a low surface energy making them ideal for cookware, as well as various other applications such as bearings, landing gear and engine parts, where thermal and mechanical conditions are prime importance.

We report the formation ω phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The ω phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of ω phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as α-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that ω phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the ω phase has been suggested.

This report continues previous studies that show melt spun Zr80Pt20 ribbons having oxygen contents ranging from <200 to approximately 5000 mass ppm form various meta-stable phases during quenching. In the presence of sufficient oxygen, a big cube Zr6Pt3O phase forms, but this structure is de-stabilized towards an icosahedral quasicrystalline structure at lower oxygen levels. Further reduction of oxygen promotes increasingly stable Zr-Pt bonds, and a meta-stable β-Zr(Pt) structure is formed.

The hydrogen diffusion constant D in the hydrogenated quasicrystalline alloy ZrCuNiAl has been determined using the technique of NMR diffusion in a static fringe field of a superconducting magnet. The diffusion constant of partially quasicrystalline Zr69.5Cu12Ni11Al7.5 exhibits a significant decrease with increasing hydrogen-to-metal ratio H/M, owing to creation of defects in the lattice during hydrogen loading, which dominates over the site-blocking effect. The actual alloy structure—the amorphous, icosahedral or approximant—appears to be less important for the hydrogen diffusivity.

We identify several new quasicrystal approximants in alloy systems in which quasicrystals have not been previously reported. Some occur in alloys with large size contrast between the constituent elements, either containing small Boron atoms, or large Ca/Eu atoms, leading to quasicrystal structures quite different from currently known systems where the size contrast is smaller. Another group of the approximants are layered Frank-Kasper structures, demonstrating competition between decagonal and dodecagonal ordering within this family of structures.

We investigate local structural variations in Al72Ni20Co8 quasicrystals using first principles density-functional total-energy calculations. We find that local chemical fluctuation can cause large structural variations on the central rings of the 2-nm clusters. Such structure variations may result in ambiguities at the central rings in high-resolution electron microscopy images of Al72Ni20Co8 decagonal quasicrystals.