Quasicrystal Samples Research Articles

Effect of rotation speed on hydrogen storage properties of Ti45Zr38Ni17 alloy ribbons produced by melt spinning

Abstract Ti/Zr-based icosahedral (i) quasicrystals are believed to have a Bergman-type cluster with a large number of tetrahedral interstitials, making them attractive as potential hydrogen storage materials. In this study, Ti45Zr38Ni17 alloy ribbons were prepared by melt spinning at different rotation speeds, and the effect of the rotation speed on the microstructures and hydrogen storage capacities was investigated. The i-phase with a small amount of Ti2Ni phase and/or some minor crystal phase was identified after melt spinning, but the amount of amorphous phase increased and the Ti2Ni and the other crystal phases decreased with increasing rotation speed. After gaseous hydrogen loading at 573 K and a pressure of 3 MPa, a hydride phase was observed in the samples with more amorphous phase, suggesting that the amorphous phase turned into the hydride phase. The maximum gaseous hydrogen capacity (H/M), 1.31, was obtained for the sample with more i-phase. After electrochemical hydrogen loading, a slightly higher maximum discharge capacity was observed in a less-quality quasicrystal sample at the first loading, that decreased drastically after the second cycle, but gradually increased with increasing cycling up to 20 cycles. The maximum hydrogen discharge capacity obtained in sample with more i-phase, reached about 10 mAh/g, while the less-amount one 4 mAh/g, suggesting the i-phase has higher hydrogen capacity than the crystal and the amorphous phases.

Eu Doping in the GdCd7.88 Quasicrystal and Its Approximant Crystal GdCd6.

The effect of Eu doping in the Tsai quasicrystal (QC) GdCd7.88 and its periodic 1/1 approximant crystal (AC) GdCd6 are investigated. This represents the first synthesis of Eu-containing stable QC samples, where three samples with the final composition Gd1-xEuxCd7.6±α at Eu doping concentrations x = 0.06, 0.13, and 0.19 are obtained (α ∼ 0.2). They are compared to two 1/1 ACs with compositions Gd1-xEuxCd6 (x = 0.12, 0.16). In addition, a new type of 1/1 AC, differing only by the inclusion of extra Cd sites unique to the Eu4Cd25 1/1 AC, has been discovered and synthesized for the concentrations Gd1-xEuxCd6+δ (x = 0.25, 0.33, 0.45, 0.69, 0.73, and 0 < δ ≤ 0.085). Due to the preferred cube morphology of its single grains, we refer to them as c-type 1/1 ACs and to the conventional standard ones as s-type. In both QCs and s-type ACs, the Eu content appears to saturate at a concentration of ∼20%. On the other hand, any Gd| Eu ratio is allowed in the c-type ACs, varying continuously between GdCd6 and Eu4Cd25. We describe and contrast the changes in composition, atomic structure, specific heat, and magnetic properties induced by Eu doping in the quasicrystalline phase and the s-type and c-type 1/1 ACs. By comparing our results to the literature data, we propose that the occupancy of the extra Cd sites can be used to predict the stability of Tsai-type quasicrystalline phases.

Influence of quasi-crystal particles and processing condition on microstructure and tensile properties of a selective laser melted high entropy alloy

Quasi-crystal (QC) Al65Cu20Fe10Cr5 powder particles were added into CoCrFeMnNi high entropy alloy (HEA) and processed by selective laser melting (SLM) under different conditions with the aim of enhancing their strengths. It is shown that increased energy density leads to increased grain size and texture in the SLMed HEA but does not cause significant influence on tensile properties. With the addition of QC particles, the microstructure and tensile properties highly depend on input energy density. Thus, HEA-10 wt% QC samples made between 55.6 J/mm3 and 92.6 J/mm3 are dominated by dispersive columnar γ grains and arc-shaped B2 phase and nano-sized Al2O3 particles while those made with high energy densities such as 133.3 J/mm3 contain mixed large vertical and horizontal columnar γ grains but no B2 phase. The B2-containing HEA-10 wt% QC samples show remarkably enhanced yield strength and ultimate tensile strength, thanks to B2 and nano-sized Al2O3 particles acting as effective dislocation motion barriers. The B2-free HEA-10 wt% QC samples show reduced strengths which is attributed to their large and complex grain structure and dendritic structure.

Effect of Li on electrochemical properties of Ti1.4V0.6Ni quasicrystal alloy produced by rapid quenching

The effect of Li on the electrochemical performance of electrodes consisting of Ti1.4V0.6Ni quasicrystal was investigated at room temperature in three-electrode cell set-up. The quasicrystal sample was initially synthesized by arc melting, followed by melt-spinning, and then infiltrated with Li atoms by electroosmosis. According to X-ray diffraction, all ribbon samples were determined to be icosahedral quasicrystal phase (I-phase), V-based solid solution phase with BCC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some Li atoms into the Ti1.4V0.6Ni quasicrystal lattice under the condition of an electroosmosis current of 0.6 A, we could observe the appearance of Li diffraction peaks. Importantly, the slight shift to the left observed in the diffraction peaks indicated that lattice expansion was caused by the infiltration of Li. The discharge capacity of Ti1.4V0.6Ni–Li material was higher than that of Ti1.4V0.6Ni.The maximum discharge capacity of 307.1 mAh/g was recorded for Ti1.4V0.6Ni–Li at a current density of 30 mAh/g. Both high-rate dischargeability and cycling stability were enhanced as a result of infiltrating Li. The lithium could get into the lattice, which resulted in the formation of microspores on surface of alloy, thus improving electrochemical activity of the alloy electrode. At the same time, the electrochemical reaction kinetics of alloy electrodes was also researched.

Hydrogen storage properties for Mg–Zn–Y quasicrystal and ternary alloys

Three Zn–Mg–Y alloys with nominal compositions of Zn50Mg42Y8 and Zn60Mg30Y10 were prepared by induction melting or gas atomisation. XRD and SEM analysis shows samples ZMY-1 and ZMY-2 consisted of multiple phases including icosahedral quasicrystal (QC) i-phase, hexagonal H-phase and Mg7Zn3, whilst ZMY-3 contained QC only. The hydrogen storage properties of the Zn–Mg–Y quasicrystal and ternary alloys were investigated for the first time. The quasicrystal sample ZMY-3 hydrogenated at 300°C had 0.3wt.% capacity and the DSC decomposition peak temperature was 503°C. Amongst the three samples, the highest hydrogen storage capacity (0.9wt.%) and the lowest decomposition peak temperature (445°C) was achieved by sample ZMY-1. The pressure–composition–isotherm (PCI) curve of ZMY-1 sample showed a flat plateau gave a plateau pressure of 3.5bar at 300°C, which indicates a lower dehydrogenation enthalpy than MgH2.

Multimode lasing from the microcavity of an octagonal quasi-crystal based on holographic polymer-dispersed liquid crystals

An eightfold photonic quasi-crystal (PQC) sample is fabricated holographically using two-beam interference with multi-exposure based on polymer-dispersed liquid crystals. The transmission spectra from the finite-difference time-domain (FDTD) simulation prove the photonic stop band of the rotational symmetry structure of the sample. The resonant mode of the circular microcavity formed in the PQC is calculated. Amplified spontaneous emission and multimode lasing action are demonstrated from the pumped laser-dye-doped PQC microcavity using a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) pulse laser.

Magnetic Properties of Hydrogen-Included TiZrNiPd Quasicrystals

Quasicrystals prepared by rapid quenching of Pd-added TiZrNi ingots were hydrogenated, and effects of hydrogen for magnetic properties were compared with the unhydrogenated ones under magnetic fields from -10000 to 10000 Oe. The magnetization values obtained from vibrating sample magnetometer (VSM) were analyzed with the combination of powder X-ray diffraction (XRD) data. While its contribution is larger than that of Pd, hydrogen decreases the magnetic moments of both Pd-doped and undoped quasicrystals. As increasing the amount of absorbed hydrogen which is represented by H/M (hydrogen to host metal atom ratio) values from 0 to 1.19, the magnetization values of Ti53Zr27Ni20 quasicrystals measured at 10000 Oe significantly decreased from 0.301 to 0.212 emu/g. A careful analysis of XRD data demonstrated that the reduced interactions of magnetic dipole moments between Ni atoms, as the product of the expansion of the quasilattice constants after hydrogenation, are responsible for the decreased magnetization values in hydrogenated TiZrNiPd quasicrystal samples.

Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding

(Al65Cu20Fe15)100−xSnx (x=0, 12, 20, 30) and Al57Si10Cu18Fe15 powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al65Cu20Fe15 sample were crystalline λ-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of θ-Al2Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al65Cu20Fe15)100−xSnx samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al57Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.

Microstructural evolutions and hardness during heat treatment of Al64Cu20Fe12Si4 quasicrystal alloy

The microhardness and microstructural characteristics and subsequent heat treatment of conventionally solidified Al64Cu20Fe12Si4 quasicrystal were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), differential thermal analysis (DTA), and Vickers microhardness tester. XRD analysis indicated that the conventionally solidified samples showed a quasicrystalline icosahedral phase (i-phase) together with cubic β-AlFe, tetragonal θ-Al2Cu, and monoclinic λ-A13Fe4 crystal phases. However, the i-phase together with cubic β-AlFe and monoclinic λ-A13Fe4 phases observed heat threaded samples. As-cast and subsequently heat-treated quasicrystal samples were measured using a microhardness test device. Vickers microindentation tests were carried out on the heat-treated quasicrystal samples with the load ranging from 1 to 500 mN at room temperature. The melting point of the i-phase was determined as 900°C by DTA examinations.

Nanostructuration of i-Al64Cu23Fe13 quasicrystals produced by arc-furnace

The Al46Cu23Fe13 quasicrystal phase, prepared by arc-melting and nanostructured using high energy ball milling technique, was studied employing X-ray diffraction, transmission electron microscopy, ferromagnetic resonance and electric transport measurements. Fe local environments were studied by Mossbauer spectroscopy. The resistivity ratio R(4.2 K)/R(300 K) is within the expected values commonly observed in an icosahedral phase. In general, the experimental results show that an appropriate heat treatment of the as-cast alloy prepared by arc-melting makes possible to obtain good quasicrystal samples. On the other hand, for milling time longer than five hours, the average grain-size of quasicrystal phase reduces, but it preserves Fe local atomic orders. It is also observed that the quasicrystalline sample decomposes in an iron rich nano-quasicrystalline phase and a e-Al2Cu3 phase. Electric transport measurements show that at low temperatures the nano-quasicrystalline samples behave strongly different to their solid counterparts, an effect attributed to a long-range order reduction and an increasing of grain boundary regions. The presence of local magnetic moments in the nanostructured sample is also discussed.

The Role of Ni for Magnetism in Ti-Zr-Ni Quasicrystals

The interesting structural property of quasicrystals is characterized by exhibition of a five-fold symmetry which is forbidden in crystal. Most of the quasicrystals are discovered in Al- and Ti-based alloys made with rapid quenching indicating that they are metastable. Ti-based quasicrystals are still interesting in terms of structural stability and magnetic state when a sample contains Ni. We prepared metastable Ti55-xZr33Ni12+x (x = 0 , 3, 5, 7, 9) metallic ribbons of quasicrystals by rapid quenching method. A pure quasicrystal phase was obtained in a range of 5 les x les 9. The magnetization and magnetic hysteresis were measured by using a vibrating sample magnetometer (VSM). Interestingly, quasicrystal samples made with x = 7 and 9 showed magnetic hysteresis at room temperature, while no evidence for the hysteresis was noted from the samples made with x = 5. This suggests that a magnetic state of quasicrystal is strongly influenced by the Ni concentration. The magnetization values measured at zero-field-cooled (ZFC) and field-cooled (FC) conditions demonstrated little hint of significant difference suggesting that no rapid change in magnetization value is expected.

Imaging property of two-dimensional quasiperiodic photonic crystals

In this paper, we investigate the propagation of electromagnetic wave in 12-fold symmetric quasiperiod structure employing finite difference time domain (FDTD) method. The quasiperiodic photonic crystal (QPC) consists of a dodecahedral lattice of air holes embedded in a dielectric background. Simulation on wave propagation through a wedge-shaped structure shows that negative refraction can occur at the interface between air and the quasicrystal sample. We further design QPC slab for performance of a high-quality flat lens. Simulation results reveal that non-near-field imaging can be achieved through the QPC slab. TM and TE modes are discussed and both the two modes exhibit the focusing effect. Since the air-hole type QPCs are more easily fabricated and integrated than the dielectric-rod type QPCs, our results might be important to the applications.

Switchable quasi-crystal structures with five-, seven-, and ninefold symmetries

We report on the design, fabrication, and characterization of switchable quasi-crystal structures in holographic polymer-dispersed liquid-crystal materials using a multibeam hololithography exposure technique. By interfering multiple coherent laser beams on a liquid crystal-polymer mixture, one can create quasi-crystal morphologies on a mesoscale. The quasi-crystal structures with five-, seven-, and ninefold symmetries are confirmed by mapping of scanning electron microscope images to the calculated isointensity profiles and comparison of their diffraction patterns to the Fourier transforms of the calculated isointensity profiles. Diffraction properties and electro-optic switching parameters of the quasi-crystal samples are presented, and their refractive index modulation is estimated to be 3×10−3 using coupled-wave theory.

Elastic and inelastic deformations of ethylene-passivated tenfold decagonalAl−Ni−Coquasicrystal surfaces

The adhesion and friction force properties between a tenfold $\mathrm{Al}\text{\penalty1000-\hskip0pt}\mathrm{Ni}\text{\penalty1000-\hskip0pt}\mathrm{Co}$ decagonal quasicrystal and a titanium nitride (TiN)-coated tip were investigated using an atomic force microscope in ultrahigh vacuum. To suppress the strong chemical adhesion found in the clean quasicrystal surfaces, the sample was exposed to ethylene that formed a protective passivating layer. We show that the deformation mechanism of the tip-substrate junction changes from elastic to inelastic at a threshold pressure of $3.8\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}4.0\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Images of the indentation marks left above the threshold pressure indicate the absence of new steps, and indicate that surface damage is not accompanied by formation of slippage planes or dislocations, as found in plastically deforming crystalline materials. This is consistent with the lack of translational periodicity of quasicrystals. The work of adhesion in the inelastic regime is five times larger than in the elastic one, plausibly as a result of the displacement of the passivating layer. In the elastic regime, the friction dependence on load is accurately described by the Derjaguin-M\uller-Toporov (DMT) model, consistent with the high hardness of both the TiN tip and the quasicrystal sample. Above the threshold pressure, the friction versus load curve deviates from the DMT model, indicating that chemical bond formation and rupture contribute to the energy dissipation.

Insulator-like electrical transport in structurally ordered Al 65Cu 20+ xRu 15− x ( x = 1.5, 1.0, 0.5, 0.0 and −0.5) icosahedral quasicrystals

Low-temperature resistivities, in zero-field and 8 T field, and magnetoresistance have been measured down to 1.4–300 K for stable icosahedral quasicrystals Al 65Cu 20+ x Ru 15− x ( x = 1.5, 1.0, 0.5, 0.0 and −0.5). The analysis of the magnetoresistance data shows an overwhelming presence of anti weak-localization effect ( τ so ∼ 10 −12 s). But the sample with x = −0.5 shows anomalous magnetoresistance and the anti weak-localization effect breaks down ( τ so to be 10 −15 s). The in-field σ– T between 5 K and 20 K, for x = 1.0, 0.5, 0.0 and −0.5 samples, and between 1.4 K and 40 K for x = 1.5 sample, follow a power-law behavior with an exponent of 0.5 and above ∼30 K the exponent ranges from 1.17 to 1.58. The observed power-laws basically characterize the presence of critical regime of the metal–insulator (MI) transition, dominated by electron–electron and electron–phonon inelastic scattering events respectively. In samples with x = 1.0, 0.5, 0.0 and −0.5 the in field σ– T has been found to follow ln σ-vs- T 1/4 below 5 K, which indicates the presence of variable range hopping. The observed transport features indicate the occurrence of proximity of metal–insulator transition in these Al–Cu–Ru quasicrystal samples.

Plasticity of single-grain icosahedral Al–Pd–Mn quasi-crystals deformed at room temperature

Transmission electron microscopy observations have been performed on icosahedral Al–Pd–Mn quasi-crystal samples deformed at 20 °C under a high confining pressure. They reveal a large density of wavy walls from which several climbing dislocations are emitted. Near-screw dislocations have been found at the wall terminations with a Burgers vector contained in the wall plane. Careful plane determinations and dislocation analyses are not consistent with a glide and cross-slip mechanism. The results can be better interpreted as a deformation by cracks in mode III followed by a re-healing process.

Path to Strong Insulating Transport Properties in Bulk AlPdRe Samples

ABSTRACTElectronic transport measurements have been made on bulk icosahedral Al70Pd22.5Re7.5 quasicrystal (QC's) samples, having increasingly larger resistance temperature ratios, rT = R(4.2 K)/R(292 K). Data were taken between 0.023 K to 292 K and in magnetic fields up to 17.9 T. Both the zero field resistivity and the magnetoresistance (MR) changed from metallic behavior to weakly insulating behavior to highly insulating behavior, as the resistance temperature ratios rT's of the samples were made larger. For the insulating samples, the resistivities ρ's followed simple inverse temperature power laws above 50 K going as ρ(T) = a0/Tz, where z = 1 ± 0.1.The insulating QC samples exhibited saturation behaviors of their resistivities below 2 K. Below 0.3 K, the strongly insulating QC's displayed activated variable-range hopping (VRH) laws in their conductivity; the hopping exponents y's in the VRH laws varied between 0.19 ≤ y ≤ 0.43. A simple model including conductivity contributions both from the primary insulating QC phase and from a secondary metallic phase yielded good fits to the resistivity and MR data.

Analysis of Gas-Phase Clusters Made from Laser-Vaporized Icosahedral Al−Pd−Mn

An icosahedral Al-Pd-Mn quasicrystal sample is laser vaporized to form metal clusters by gas aggregation. The clusters are subsequently laser ionized and mass analyzed in a time-of-flight mass spectrometer. The mass spectra show cluster compositions which are qualitatively similar to that of the sample. This is consistent with a kinetically controlled cluster growth process. Cluster thermodynamic stability is probed by multiphoton ionization/fragmentation, which induces primarily Al and Mn loss. The resulting spectra are composed of a series of Pd-rich Al-Pd clusters. The average cluster composition is 60 (′1)% Pd. This composition is close to a known eutectic in the Al-Pd system. When manganese is seen on these clusters, it is always in units of Mn 3 . These results are discussed in terms of relative binding strengths in the Al-Pd-Mn alloy system.

Resonant fluorescence emission of Mn Kβ in quasicrystals

Resonant X-ray emission spectra of Mn Kβ 1,3 (3p ⋅ 1s) were measured near the Mn K absorption edge for quasicrystalline icosahedral Al–Pd–Mn, icosahedral Al–Pd–Mn–B, icosahedral Al–Mn–Si, decagonal Al–Mn–Fe–Ge and crystalline α–Al–Mn–Si. Except for the Raman scattering energy region, the peak energy of Kβ 1,3 is independent of incident photon energy for all the samples. The shape was also unchanged. A Kβ’ subpeak, which is caused by the splitting between the density of states of the high spin and the low spin in the 3p band, appeared in all the quasicrystal samples with lower intensity than those of the Mn oxides in spite of the fact that Mn atoms in the decagonal Al–Mn–Fe–Ge and the icosahedral Al–Pd–Mn–B are in a ferromagnetic state. In the profile of the icosahedral Al–Pd–Mn, α–Al–Mn–Si and decagonal Al–Mn–Fe–Ge, a clear hump was observed at the energy between Kβ 1,3 and Kβ’. In the emission spectra of Mn Kβ 5 (3d →1s), peak positions were 1.5 eV lower for the ferromagnetic quasicrystals than those of the other quasicrystals.

Faceted etch pits and light figures of icosahedral Zn-Mg-Y quasicrystals

Faceted etch pits have been observed on chemically etched single-grain icosahedral Zn-Mg-Y quasicrystal samples with C 2, C 3 and C 5 symmetry rotation axes perpendicular to their surfaces. The anisotropic etching was produced by 2.5-5%HCl solution in ethylene. The etch pits, analysed by scanning electron microscopy (SEM), follow the icosahedral symmetry of a rhombic triacontahedron. Light figures were observed on a screen placed in between a 10mW He-Ne laser and the reflecting quasicrystal surface. Both the SEM images and the light figures can be used to determine the twofold, threefold and fivefold symmetry axes of the quasilattice as well as for investigations of intrinsic and growth defects in the quasicrystals.