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Sample records for icosahedral zn-mg-dy quasicrystal

  1. Three-Dimensional Icosahedral Phase Field Quasicrystal

    NASA Astrophysics Data System (ADS)

    Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.

    2016-08-01

    We investigate the formation and stability of icosahedral quasicrystalline structures using a dynamic phase field crystal model. Nonlinear interactions between density waves at two length scales stabilize three-dimensional quasicrystals. We determine the phase diagram and parameter values required for the quasicrystal to be the global minimum free energy state. We demonstrate that traits that promote the formation of two-dimensional quasicrystals are extant in three dimensions, and highlight the characteristics required for three-dimensional soft matter quasicrystal formation.

  2. Three-Dimensional Icosahedral Phase Field Quasicrystal.

    PubMed

    Subramanian, P; Archer, A J; Knobloch, E; Rucklidge, A M

    2016-08-12

    We investigate the formation and stability of icosahedral quasicrystalline structures using a dynamic phase field crystal model. Nonlinear interactions between density waves at two length scales stabilize three-dimensional quasicrystals. We determine the phase diagram and parameter values required for the quasicrystal to be the global minimum free energy state. We demonstrate that traits that promote the formation of two-dimensional quasicrystals are extant in three dimensions, and highlight the characteristics required for three-dimensional soft matter quasicrystal formation. PMID:27563973

  3. About the atomic structures of icosahedral quasicrystals

    NASA Astrophysics Data System (ADS)

    Quiquandon, Marianne; Gratias, Denis

    2014-01-01

    This paper is a survey of the crystallographic methods that have been developed these last twenty five years to decipher the atomic structures of the icosahedral stable quasicrystals since their discovery in 1982 by D. Shechtman. After a brief recall of the notion of quasiperiodicity and the natural description of Z-modules in 3-dim as projection of regular lattices in N>3-dim spaces, we give the basic geometrical ingredients useful to describe icosahedral quasicrystals as irrational 3-dim cuts of ordinary crystals in 6-dim space. Atoms are described by atomic surfaces (ASs) that are bounded volumes in the internal (or perpendicular) 3-dim space and the intersections of which with the physical space are the actual atomic positions. The main part of the paper is devoted to finding the major properties of quasicrystalline icosahedral structures. As experimentally demonstrated, they can be described with a surprisingly few high symmetry ASs located at high symmetry special points in 6-dim space. The atomic structures are best described by aggregations and intersections of high symmetry compact interpenetrating atomic clusters. We show here that the experimentally relevant clusters are derived from one generic cluster made of two concentric triacontahedra scaled by τ and an external icosidodecahedron. Depending on which ones of the orbits of this cluster are eventually occupied by atoms, the actual atomic clusters are of type Bergman, Mackay, Tsai and others….

  4. Magnetism in icosahedral quasicrystals: current status and open questions

    SciTech Connect

    Goldman, Alan I.

    2014-07-02

    Progress in our understanding of the magnetic properties of R-containing icosahedral quasicrystals (R = rare earth element) from over 20 years of experimental effort is reviewed. This includes the much studied R-Mg-Zn and R-Mg-Cd ternary systems, as well as several magnetic quasicrystals that have been discovered and investigated more recently including Sc-Fe-Zn, R-Ag-In, Yb-Au-Al, the recently synthesized R-Cd binary quasicrystals, and their periodic approximants. In many ways, the magnetic properties among these quasicrystals are very similar. However, differences are observed that suggest new experiments and promising directions for future research.

  5. The quasiperiodic average structure of highly disordered decagonal Zn-Mg-Dy and its temperature dependence.

    PubMed

    Ors, Taylan; Takakura, Hiroyuki; Abe, Eiji; Steurer, Walter

    2014-04-01

    A single-crystal X-ray diffraction structure analysis of decagonal Zn-Mg-Dy, a Frank-Kasper-type quasicrystal, was performed using the higher-dimensional approach. For this first Frank-Kasper (F-K) decagonal quasicrystal studied so far, significant differences to the decagonal Al-TM-based (TM: transition metal) phases were found. A new type of twofold occupation domain is located on certain edge centers of the five-dimensional unit cell. The structure can be described in terms of a two-cluster model based on a decagonal cluster (∼ 23 Å diameter) arranged on the vertices of a pentagon-Penrose tiling (PPT) and a star-like cluster covering the remaining space. This model is used for the five-dimensional refinements, which converged to an R value of 0.126. The arrangement of clusters is significantly disordered as indicated by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In order to check the structure and stability at higher temperatures, in-situ high-temperature (HT) single-crystal X-ray diffraction experiments were conducted at 598 and 648 K (i.e. slightly below the decomposition temperature). The structure does not change significantly, however, the best quasiperiodic order is found at 598 K. The implication of these results on the stabilization mechanism of quasicrystals is discussed. PMID:24675601

  6. The Icosahedral Ti-Zr-Ni Quasicrystal - A Ground State Quasicrystal?

    NASA Astrophysics Data System (ADS)

    Hennig, R. G.; Carlsson, A. E.; Kelton, K. F.; Henley, C. L.

    2001-03-01

    The icosahedral Ti-Zr-Ni quasicrystal is known to be thermodynamically stable [1]. Most stable quasicrystals form at high temperatures from the liquid phase. In contrast to those quasicrystals, however, the Ti-Zr-Ni quasicrystal forms at lower temperatures, near 570^circC, by a solid state transformation of crystal phases that are stable at higher temperatures. A decorated canonical cell tiling for the structure of this quasicrystal was determined by a refinement to x-ray and neutron diffraction data and results from ab initio calculations. The energetic stability of the icosahedral Ti-Zr-Ni quasicrystal was investigated by total energy calculations using the density-functional code VASP [2]. The ternary ground state phase diagram for Ti-Zr-Ni was determined. The energy of the structural model of the quasicrystal is found to be lower than the energy of any known competing phase. This result, coupled with the continued stability with long anneals at lower temperatures, strongly suggest that the icosahedral Ti-Zr-Ni quasicrystal is a ground state quasicrystal. [1] K. F. Kelton, W. J. Kim, and R. M. Stroud. Appl. Phys. Let. 70, 3230 (1997). [2] G. Kresse and J. Hafner, Phys. Rev. B47, RC 558 (1993); G. Kresse and J. Furthmüller, Phys. Rev. B54, 11169 (1996).

  7. Monte Carlo simulations of icosahedral quasicrystal growth and melting

    NASA Astrophysics Data System (ADS)

    Dmitrienko, V. E.; Astaf'ev, S. B.; Kléman, M.

    1999-01-01

    Three-dimensional Monte Carlo simulations for atomic growth and melting of icosahedral quasicrystals are presented. It is supposed that the atoms can be locally ordered both icosahedrally and dodecahedrally, and the preferred ordering arises during the growth according to statistical and energetical criteria. All the waiting positions (where an atom could be in principle added) are generated on the cluster surface at every stage of the growth. The binding energies of all atoms and all waiting positions are computed with an oscillating Friedel potential. Then an object, chosen at random from the joined list of surface atoms and waiting positions, is treated according to the Metropolis criterion. The suggested growth process is completely local. It is found that the speed and sign of the process and the resulting structures depend strongly on the growth parameters. Most frequently, the main structural motif of grown clusters is the dodecahedral local ordering (DLO) whereas the icosahedral local ordering (ILO) is usually rare. However, the latter becomes dominant for rather exotic interatomic potentials or for high growth rates. The phenomenon of critical seed size is observed: for those parameters, for which large clusters grow, small enough seeds stop to grow and may even melt. The grown quasicrystals are faceted and their sizes in perpendicular space are rather close to those predicted theoretically and observed experimentally.

  8. Atomic clusters and atomic surfaces in icosahedral quasicrystals.

    PubMed

    Quiquandon, Marianne; Portier, Richard; Gratias, Denis

    2014-05-01

    This paper presents the basic tools commonly used to describe the atomic structures of quasicrystals with a specific focus on the icosahedral phases. After a brief recall of the main properties of quasiperiodic objects, two simple physical rules are discussed that lead one to eventually obtain a surprisingly small number of atomic structures as ideal quasiperiodic models for real quasicrystals. This is due to the fact that the atomic surfaces (ASs) used to describe all known icosahedral phases are located on high-symmetry special points in six-dimensional space. The first rule is maximizing the density using simple polyhedral ASs that leads to two possible sets of ASs according to the value of the six-dimensional lattice parameter A between 0.63 and 0.79 nm. The second rule is maximizing the number of complete orbits of high symmetry to construct as large as possible atomic clusters similar to those observed in complex intermetallic structures and approximant phases. The practical use of these two rules together is demonstrated on two typical examples of icosahedral phases, i-AlMnSi and i-CdRE (RE = Gd, Ho, Tm).

  9. Multiple diffraction in an icosahedral Al-Cu-Fe quasicrystal

    NASA Astrophysics Data System (ADS)

    Fan, C. Z.; Weber, Th.; Deloudi, S.; Steurer, W.

    2011-07-01

    In order to reveal its influence on quasicrystal structure analysis, multiple diffraction (MD) effects in an icosahedral Al-Cu-Fe quasicrystal have been investigated in-house on an Oxford Diffraction four-circle diffractometer equipped with an Onyx™ CCD area detector and MoKα radiation. For that purpose, an automated approach for Renninger scans (ψ-scans) has been developed. Two weak reflections were chosen as the main reflections (called P) in the present measurements. As is well known for periodic crystals, it is also observed for this quasicrystal that the intensity of the main reflection may significantly increase if the simultaneous (H) and the coupling (P-H) reflections are both strong, while there is no obvious MD effect if one of them is weak. The occurrence of MD events during ψ-scans has been studied based on an ideal structure model and the kinematical MD theory. The reliability of the approach is revealed by the good agreement between simulation and experiment. It shows that the multiple diffraction effect is quite significant.

  10. Hydrogen Characteristics of Ti-Based Icosahedral Quasicrystals

    NASA Astrophysics Data System (ADS)

    Viano, A. M.; Hanneken, J. W.; Kelton, K. F.; Gibbons, P. C.

    1997-03-01

    The ability of Ti-based icosahedral quasicrystals to store significant amounts of hydrogen is now well-known. Up to 64 atomic percent of hydrogen can be stored in Ti_45Zr_38Ni_17 with only a small fraction of the sample transforming to crystalline hydrides. The amount of crystalline phase present depends on both the method of hydrogenation and the surface preparation of the sample. The surface oxide layer, which has been characterized in air-exposed samples, greatly influences the absorption and desorption kinetics. To accurately determine the hydrogen characteristics, studies were performed on unoxidized, powdered quasicrystalline Ti_xZr_yNiz This was accomplished by gently ball-milling the as-quenched quasicrystalline ribbons in a stainless-steel vessel which was then connected directly to a modified Sieverts' apparatus. Absorption and desorption rates for the quasicrystal will be discussed and compared to those for other related alloys. The saturation limit of hydrogen in the quasicrystal, as measured from a determination of the pressure-composition isotherms, will also be presented.

  11. Ideal structure of icosahedral Al-Cu-Li quasicrystals

    NASA Astrophysics Data System (ADS)

    Yamamoto, Akiji

    1992-03-01

    A structure model for the icosahedral Al-Cu-Li quasicrystal has been derived. This is described in six-dimensional space as a six-dimensional crystal, having four kinds of occupation domains with complicated polyhedral shape. A general structure-factor formula is derived for such polyhedral domains, and a simple description of the structure using the site symmetry is proposed. The model gives R factors of 0.076 and 0.085 for recent x-ray and neutron-single-crystal-diffraction data [Boissieu, Janot, Dubois, Audier, and Dubost, J. Phys. 3, 1 (1991)]. The structure consists of a large number of icosahedral clusters and linking atoms joining them. It leads to an ideal cubic R-Al-Cu-Li structure and a large number of other cubic crystals when appropriate phason strains are taken into account. Two structures, the ideal R-Al-Cu-Li structure and a fictitious structure with a period (1+ √5 )/2 times longer, are shown.

  12. Speculation of equilibrium pressure of Ti36Zr40Ni20Pd4 icosahedral quasicrystal

    NASA Astrophysics Data System (ADS)

    Huang, Huogen; Chen, Liang

    2015-08-01

    Ti-Zr-Ni quasicrystals have been demonstrated to store a large number of hydrogen atoms, which implies strong potential application in hydrogen energy field for them. However, the desorption of hydrogen atoms in the quasicrystals is quite difficult, with the indication of high desorption temperature and slow desorption rate. The shortage limits their use in the field to a large extent. But this kind of quasicrystals might be used in nuclear fusion energy field, because tritium as a coral fuel for nuclear fusion needs tight storage. However, equilibrium pressure at room temperature of Ti-Zr-Ni quasicrystals, important for their application in fusion energy field, has not been clear yet. In this work, we designed a gas-solid reaction system with the pressure resolution of 10-8Pa and carried out hydrogen desorption investigation at different temperatures on Ti36Zr40Ni20Pd4 icosahedral quasicrystal. Based on three Pressure-Composition-Temperature desorption curves, we speculate according to Van't Hoff theory about hydrogen storage that its equilibrium pressure at room temperature could be at the magnitude of 10-6Pa, displaying good stability of hydrogen in the quasicrystal and also implying application prospects in fusion energy field for quasicrystals of this type.

  13. Dynamical x-ray diffraction from an icosahedral Al-Pd-Mn quasicrystal

    SciTech Connect

    Kycia, S.

    1996-04-23

    Primary extinction effects in diffraction from single grains of Al-Pd- Mn, and presumably many other FCI alloys, may be significant and should be corrected for prior to use of diffraction data in structural determinations. Probes based on dynamical diffraction effects, such as x-ray standing wave fluorescence, multiple beam interference, and x-ray transmission topographs, may now be used to study the bulk and surface structure of some quasicrystals. The observation of dynamical diffraction from icosahedral Al-Pd-Mn is a striking confirmation of the fact that quasicrystals can present a degree of structural perfection comparable to that found in the best periodic intermetallic crystals.

  14. A group theoretical approach to structural transitions of icosahedral quasicrystals and point arrays

    NASA Astrophysics Data System (ADS)

    Zappa, Emilio; Dykeman, Eric C.; Geraets, James A.; Twarock, Reidun

    2016-04-01

    In this paper we describe a group theoretical approach to the study of structural transitions of icosahedral quasicrystals and point arrays. We apply the concept of Schur rotations, originally proposed by Kramer, to the case of aperiodic structures with icosahedral symmetry; these rotations induce a rotation of the physical and orthogonal spaces invariant under the icosahedral group, and hence, via the cut-and-project method, a continuous transformation of the corresponding model sets. We prove that this approach allows for a characterisation of such transitions in a purely group theoretical framework, and provide explicit computations and specific examples. Moreover, we prove that this approach can be used in the case of finite point sets with icosahedral symmetry, which have a wide range of applications in carbon chemistry (fullerenes) and biology (viral capsids).

  15. Generalized 2D problem of icosahedral quasicrystals containing an elliptic hole

    NASA Astrophysics Data System (ADS)

    Li, Lian-He

    2013-11-01

    The generalized 2D problem of icosahedral quasicrystals containing an elliptic hole is considered by using the extended Stroh formalism. The closed-form solutions for the displacements and stresses are obtained under general loading conditions. The solution of the Griffith crack problem as a special case of the results is also observed. The stress intensity factor and strain energy release rate are given. The effect of the phonon—phason coupling elastic constant on the mechanical behavior is also discussed.

  16. Orientation relationship between the T structure and the icosahedral quasicrystal in the Zn-Mg-Al alloy system

    NASA Astrophysics Data System (ADS)

    Nakayama, Kei; Watanabe, Junya; Koyama, Yasumasa

    2016-08-01

    To understand the crystallographic relation between the Bergman-type icosahedral quasicrystal and its approximant-T structure, we have investigated the crystallographic features of prepared Zn-Mg-Al alloy samples, mainly by transmission electron microscopy. It was found that there existed three kinds of regions: that is, C14-Laves, approximant-T, and icosahedral-quasicrystal regions, in Zn-Mg-Al alloy samples with the composition of Zn-36at.%Mg-9at.%Al. Among these regions, in particular, we tried to determine an orientation relationship between neighboring icosahedral-quasicrystal and approximant-T regions. Based on the determined relationship, for instance, four threefold rotatory-inversion axes in the T structure were found to be parallel to four of ten threefold rotatory-inversion axes in the icosahedral quasicrystal. It was thus understood that the atomic arrangements of the Bergman-type icosahedral quasicrystal and its approximant-T structure are likely to resemble each other.

  17. Titanium-based icosahedral quasicrystals and approximants: Phase formation, cluster structure, and hydrogenation

    NASA Astrophysics Data System (ADS)

    Majzoub, Eric Hish

    Equilibrium phase formation is reported for ternary Ti-Zr-Ni alloys near the icosahedral phase (i-phase) forming composition. The i-phase forms over a small compositional range from a high-temperature equilibrium phase mixture of the Laves and alpha(Ti/Zr) solid solution phases. Additions of small amounts of Pb, 1--2 at. %, are demonstrated to substantially effect the equilibrium phase formation and extend the stability of the i-phase to nearly 700°C. An electrochemical method was used to hydrogenate Ti-based quasicrystals and their crystal approximants. This technique gives a consistently high hydrogen to metal atom ratio of 1.9, without crystal hydride formation in the quasicrystal. Nuclear Magnetic Resonance (NMR) measurements of the hydrogen dipole-dipole interaction were made using hydrided i-phase samples. Comparisons with simulations based on hydrogen filling of the approximant-phase tetrahedral interstitials reveals that any filling order is consistent with the experimental data. Studies of the atomic structure of hydrided and unhydrided i-TiZrNi quasicrystal and its approximant are reported. We construct constrained icosahedral glass models using Bergman and Mackay clusters to describe the i-phase in Ti-Zr-Ni and Ti-TM-Si-O. A comparison of simulated and experimental diffraction reveals that, the Bergman and Mackay clusters are the fundamental clusters in i-TiZrNi and i-TiMnSiO, respectively.

  18. Surface structures of Al-Pd-Mn and Al-Cu-Fe icosahedral quasicrystals

    SciTech Connect

    Shen, Z.

    1999-02-12

    In this dissertation, the author reports on the surface structure of i-Al-Pd-Mn twofold, threefold, fivefold and i-Al-Cu-Fe fivefold surfaces. The LEED studies indicate the existence of two distinct stages in the regrowth of all four surfaces after Ar{sup +} sputtering. In the first stage, upon annealing at relatively low temperature: 500K--800K (depending on different surfaces), a cubic phase appears. The cubic LEED patterns transform irreversibly to unreconstructed quasicrystalline patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically-identical, but symmetrically-inequivalent surfaces, a model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of cubic close-packed and icosahedral-packed materials. These results may be general among Al-rich, icosahedral materials. STM study of Al-Pd-Mn fivefold surface shows that terrace-step-kink structures start to form on the surface after annealing above 700K. Large, atomic ally-flat terraces were formed after annealing at 900K. Fine structures with fivefold icosahedral symmetry were found on those terraces. Data analysis and comparison of the STM images and structure model of icosahedral Al-Pd-Mn suggest that the fine structures in the STM images may be the pseudo Mackay (PMI) clusters which are the structure units of the structure model. Based upon his results, he can conclude that quasicrystalline structures are the stable structures of quasicrystal surfaces. In other words, quasicrystalline structures extend from the bulk to the surface. As a result of the effort reported in this dissertation, he believes that he has increased his understanding of the surface structure of icosahedral quasicrystals to a new level.

  19. Scanning tunneling microscopy of cleaved AlPdMn icosahedral quasicrystals

    NASA Astrophysics Data System (ADS)

    Urban, K.

    1997-03-01

    Quasicrystal surfaces produced by in-situ cleavage in ultra-high vacuum have been investigated by scanning tunneling microscopy. Twofold and fivefold surfaces of icosahedral AlPdMn single-quasicrystals have been studied. The surfaces were found to be rough. Their structure is determined by cluster aggregates of various sizes formed on the basis of an elementary cluster whose contrast behavior and diameter of about 1 nm point to the Mackay-type cluster [1]. The surface of these elementary clusters exhibits a smooth density of electronic states. These observations agree with the predictions of recent models on the quasicrystal structure and electronic properties in which the Mackay-type clusters play a dominant role [2]. In particular, these clusters are believed to act as deep potential wells leading to electron states primarily bound to these. Crack propagation during cleavage occurs along zones of lower strength between the clusters indicating that these act as rigid entities. This corroborates the assumption made in modern treatments of quasicrystal plasticity that the Mackay-type clusters control the mechanical properties [3,4]. [1] Ph. Ebert, M. Feuerbacher, N. Tamura, M. Wollgarten, and K. Urban, Phys. Rev. Lett. 77, 3827 (1996). [2] C. Janot, Phys. Rev. B 53, 181 (1996). [3] M. Feuerbacher, B. Baufeld, R. Rosenfeld, M. Bartsch, G. Hanke, M. Beyss, M. Wollgarten, and K. Urban, Philos. Mag. Lett. 71, 91 (1995). [4] F. Krul, R. Mikulla, P. Gumbsch, and H.-R. Trebin (to be published).

  20. Section method for projected structures of icosahedral quasicrystals and its application to electron-microscopy-image and surface analyses.

    PubMed

    Yamamoto, Akiji

    2004-11-01

    A section method for projected structures of icosahedral quasicrystals (IQCs) is given. A structure projected along a specified direction can be calculated directly from a six-dimensional periodic structure by this method. The method concludes that all peaks in high-resolution transmission electron-microscopy images of an IQC have different projected atom densities in general and leads to different chemical compositions and densities for all atom layers, suggesting that all surfaces of an IQC are different. Its application to icosahedral Al-Pd-Mn quasicrystals is shown.

  1. Neutron-diffraction approach to the atomic decoration of the Al-Mn icosahedral quasicrystal

    NASA Astrophysics Data System (ADS)

    Janot, Chr.; Pannetier, J.; Dubois, J. M.; de Boissieu, M.

    1989-01-01

    Neutron-diffraction data were obtained from single-phase icosahedral powder of the system Al74Si5Mn21 and its modification by isomorphous substitution on the Mn sites. Amplitudes and phase differences of partial structure factors were determined. Within a strip-projection approach, phases were reconstructed. Atomic densities calculated in the physical three-dimensional space show that Mackay (1981) icosahedra, the structural units usually invoked for quasi-crystal models, do not emerge as the basic ingredients of the atomic arrangements.

  2. Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals

    NASA Astrophysics Data System (ADS)

    Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming

    2016-06-01

    The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. Thedifferences of the sequences can be explained by analyzing the parameters of the Gupta-type many-body inter-atomic potentials.

  3. Adsorption sites on icosahedral quasicrystal surfaces: Dark stars and white flowers

    SciTech Connect

    Unal, B.; Jenks, C.J.; Thiel, P.A.

    2009-01-12

    From other work, two preferred sites have been suggested for metals and semimetals adsorbed on the fivefold surfaces of icosahedral, Al-based quasicrystals. Because of their appearance in scanning tunneling microscopy (STM) images, these sites are known as dark stars and white flowers. In this paper, we analyze four bulk structural models in physical space to determine the types, chemical decorations, and densities of the dark star - and, to a lesser extent, the white flower - adsorption sites for the fivefold planes of icosahedral Al-Pd-Mn. We find that the chemical decorations of these sites are heterogeneous, even within a single model. Both features are also structurally heterogeneous, according to STM measurements, and the structural variation is consistent with the bulk structure models. Finally, from the models, the density of dark stars in the planes correlates with the step height. This may explain previous experimental observations of different properties for different terraces.

  4. Ab initio Ti-Zr-Ni phase diagram predicts stability of icosahedral TiZrNi quasicrystals

    NASA Astrophysics Data System (ADS)

    Hennig, R. G.; Carlsson, A. E.; Kelton, K. F.; Henley, C. L.

    2005-04-01

    The ab initio phase diagram determines the energetic stability of the icosahedral TiZrNi quasicrystal. The complete ab initio zero-temperature ternary phase diagram is constructed from the calculated energies of the elemental, binary and ternary Ti-Zr-Ni phases. For this, the icosahedral i -TiZrNi quasicrystal is approximated by periodic structures of up to 123 atoms/unit cell, based on a decorated-tiling model [R. G. Hennig, K. F. Kelton, A. E. Carlsson, and C. L. Henley, Phys. Rev. B 67, 134202 (2003)]. The approximant structures containing the 45-atom Bergman cluster are nearly degenerate in energy, and are all energetically stable against the competing phases. It is concluded that i -TiZrNi is a ground-state quasicrystal, as it is experimentally the low-temperature phase for its composition.

  5. Structure of icosahedral quasicrystals and density-matrix functional theory for correlation effects

    NASA Astrophysics Data System (ADS)

    Hennig, Richard Georg

    In the first part of this work, the atomic and electronic structure as well as the energetics of the icosahedral TiZrNi quasicrystal and the 1/1 approximant W-TiZrNi were determined. An atomic decoration model for the quasicrystal was developed invoking similarities to the structure of the 1/1 approximant. The structure of the quasicrystal was refined using a combined approach of diffraction refinement and ab initio calculations. The ternary ground state phase diagram was calculated using density-functional calculations. It was found that the TiZrNi quasicrystal is lower in energy than the competing phases indicating that it is a ground state quasicrystal. The electronic density of states of the quasicrystals shows a pseudogap. The hydrogen site energy distribution of the approximant was calculated and it was shown that a determination of the distribution by chemical potential measurements is impossible due to its complexity and the strong temperature and concentration dependent hydrogen-hydrogen interactions. In the second part of this work a density-matrix functional for isolated impurities was developed. The density-matrix functional for the electron interaction energy, was based on two theorems proved in this work. It was shown that the second-moment approximation yields the exact ground state for a dimer molecule with arbitrary on-site and inter-site Coulomb interactions. The second-moment approximation is implemented as a variational method. By comparison to results from exact diagonalization and the Hartree-Fock method it was shown that the functional was accurate in the case of isolated impurities. The combined effect of disorder and electron interactions for the model of an Anderson impurity in a random alloy were investigated and unexpected crossover behavior in the effects of disorder and electron interactions on the spin fluctuations was found. As a first application of the second-moment approximation, the electronic structure of dangling-bond defects

  6. Unified structure theory of icosahedral quasicrystals: Evidence from neutron powder diffraction patterns that AlCrFeMnSi, AlCuLiMg, and TiNiFeSi icosahedral quasicrystals are twins of cubic crystals containing about 820 or 1,012 atoms in a primitive unit cube

    SciTech Connect

    Pauling, L. )

    1988-11-01

    A unified structure theory of icosahedral quasicrystals, combining the twinned-cubic-crystal theory and the Penrose-tiling-six-dimensional-projection theory, is described. Values of the primitive-cubic lattice constant for several quasicrystals are evaluated from x-ray and neutron diffraction data. The fact that the low-angle diffraction maxima can be indexed with cubic unit cells provides additional support for the twinned-cubic-crystal theory of icosahedral quasicrystals.

  7. Optical reflectivity as a simple diagnostic method for testing structural quality of icosahedral quasicrystals

    NASA Astrophysics Data System (ADS)

    Brien, Valérie; Dauscher, Anne; Machizaud, Francis

    2006-08-01

    The optical reflectivity of Al-based and Ti-based quasicrystalline and approximant samples were investigated versus the quality of their structural morphology using optical reflectometry, x-ray diffraction, and transmission electron microscopy. The different structural morphologies were obtained using three different preparation processes: sintering, pulsed laser deposition, and reactive cathodic magnetron sputtering. The work demonstrates that the canonical behavior of icosahedral state in specular reflectivity is extremely sensitive to different and very fine aspects of the microstructure: sizes of grains smaller than 50nm, slight local diffuse disorder, and shifts away from the icosahedral crystallographic structure (approximants). The work explains why the optical properties of the same kind of quasicrystals found in literature sometimes reveal a different behavior from one author to another. The study then confirms the work of some authors and definitely shows that the canonical behavior of icosahedral state in specular reflectivity over the 30000-50000cm-1 domain is characterized by a decreasing function made of steps. It also shows that this behavior can be interpreted thanks to the cluster hierarchy of the model of Janot [Phys. Rev. B 53, 181 (1996)].

  8. Undercooling, local structure and phase transition in icosahedral quasicrystals forming titanium-zirconium-nickel alloy liquids

    NASA Astrophysics Data System (ADS)

    Lee, Geun Woo

    While lacking the long-range translationally periodic order of crystalline solids, liquids contain a significant amount of short-range order (SRO), which distinguishes them from gases. The local structure of a liquid is important to understand its chemical and physical properties. One of the remarkable phenomena related to the short-range order of liquids is undercooling. That is, liquids can be retained below their melting temperature for a long time without crystallization. Turnbull first demonstrated this for metallic liquids in 1952. To explain the surprising results, Frank hypothesized in 1952 that the local structure of liquid metals is icosahedral. This structure is quite different from those of crystal phases giving a large nucleation barrier and making the undercooling of liquids possible. However, a complete verification of Frank's hypothesis has not been possible thus far. In this dissertation, this goal has been achieved by demonstrating a direct connection between the nucleation barrier and the icosahedral SRO (ISRO) in Ti-Zr-Ni alloy liquids. Containerless environments and in-situ x-ray scattering experiments, essential for such studies, were possible because of the development of electrostatic levitation (ESL) and Beamline-ESL techniques. In addition, distorted icosahedral SRO in liquids will be shown, which has been expected but never observed. The other important topic related to the undercooled liquids is a liquid-liquid (L-L) transition. Since the undercooled liquids are essentially metastable, the L-L transition could be expected. However, L-L transitions in undercooled liquids have not been observed experimentally, although elemental liquids of P, C, and Si have shown first order transitions above the liquidus temperatures under high pressure. From specific heat measurements of a series of Ti-Zr-Ni alloys by the ESL technique, a maximum in the specific heat at constant pressure was observed in a few quasicrystal forming alloy compositions in

  9. Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal.

    PubMed

    Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Pay Gómez, Cesar; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc

    2016-07-01

    The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K 2/K 1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q perp' reflections. PMID:27437112

  10. Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal.

    PubMed

    Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Pay Gómez, Cesar; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc

    2016-07-01

    The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K 2/K 1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q perp' reflections.

  11. Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal

    PubMed Central

    Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Pay Gómez, Cesar; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc

    2016-01-01

    The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K 2/K 1 = −0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye–Waller factor, which explains the vanishing of ‘high-Q perp’ reflections. PMID:27437112

  12. Structural stability of the icosahedral AlCuFe quasicrystal under high-pressure and high-temperature

    NASA Astrophysics Data System (ADS)

    Takagi, S.; Kyono, A.; Nakamoto, Y.; Hirao, N.

    2015-12-01

    We report high-pressure and high-temperature in-situ X-ray diffraction study of icosahedral (i)-AlCuFe quasicrystal "icosahedrite" which is the first known naturally occurring quasicrystal mineral discovered in the Khatyrka meteorite. The i-AlCuFe quasicrystal was synthesized in laboratory from a powder mixture with an atomic ratio of Al : Cu : Fe = 65 : 20 : 15. The high-temperature and high-pressure X-ray diffraction experiments were performed using the laser-heated diamond anvil cell system installed at BL10XU, SPring-8, Japan. The i-AlCuFe showed a characteristic X-ray diffraction pattern of quasicrystal. With only compression, the diffraction patterns of the i-AlCuFe were continued until 75 GPa. At a pressure of 87 GPa two small new peaks occurred and then kept up to the maximum pressure of 104 GPa in the study. The results indicate that the pressure-induced structural phase transition of the i-AlCuFe occurs above 87 GPa, and the structure of the i-AlCuFe remains unchanged at least up to 75 GPa. Under simultaneously high pressure and high temperature, on the other hand, the i-AlCuFe was readily transformed to crystalline phase. It can be characterized by an irreversible transformation process. The structure of the i-AlCuFe is therefore more affected by thermal metamorphism than by pressure metamorphism. The present high-pressure and high-temperature experiments clearly revealed the thermal and pressure stability of the i-AlCuFe quasicrystal which may help to explain the formation of the naturally occurring quasicrystal in the solar system.

  13. Icosahedral AlCuFe quasicrystal at high pressure and temperature and its implications for the stability of icosahedrite.

    PubMed

    Stagno, Vincenzo; Bindi, Luca; Shibazaki, Yuki; Tange, Yoshinori; Higo, Yuji; Mao, H-K; Steinhardt, Paul J; Fei, Yingwei

    2014-01-01

    The first natural-occurring quasicrystal, icosahedrite, was recently discovered in the Khatyrka meteorite, a new CV3 carbonaceous chondrite. Its finding raised fundamental questions regarding the effects of pressure and temperature on the kinetic and thermodynamic stability of the quasicrystal structure relative to possible isochemical crystalline or amorphous phases. Although several studies showed the stability at ambient temperature of synthetic icosahedral AlCuFe up to ~35 GPa, the simultaneous effect of temperature and pressure relevant for the formation of icosahedrite has been never investigated so far. Here we present in situ synchrotron X-ray diffraction experiments on synthetic icosahedral AlCuFe using multianvil device to explore possible temperature-induced phase transformations at pressures of 5 GPa and temperature up to 1773 K. Results show the structural stability of i-AlCuFe phase with a negligible effect of pressure on the volumetric thermal expansion properties. In addition, the structural analysis of the recovered sample excludes the transformation of AlCuFe quasicrystalline phase to possible approximant phases, which is in contrast with previous predictions at ambient pressure. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite. PMID:25070248

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

    SciTech Connect

    Mompiou, F.; Caillard, D

    2004-07-12

    Transmission electron microscopy observations have been performed on icosahedral Al-Pd-Mn quasi-crystal samples deformed at 20 deg. 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.

  15. Scanning tunneling microscopy studies of surface structures of icosahedral aluminum-copper-iron quasicrystals

    NASA Astrophysics Data System (ADS)

    Cai, Tanhong

    2001-07-01

    We investigate the atomic structure of fivefold surface of icosahedral (i-) Al-Cu-Fe quasicrystal using scanning tunneling microscopy (STM) under ultra high vacuum (UHV). Annealing the sputtered surface at appropriate temperature produces a step-terrace structure on the surface. Our STM analysis indicates that the terraces are separated with primarily two stepheights in the ratio of t=5+1 /2 , a characteristic ratio in quasiperiodic structures. The measurements agree with the results from dynamical low energy electron diffraction (LEED) calculations. The spatial distribution of stepheights along the fivefold axis does not follow the quasiperiodic Fibonacci sequence. The existence of such stacking defects in the bulk structure is confirmed with the screw dislocations often observed in the STM scans. The first atomic resolution STM images on this type of material are obtained. The flat terraces are dominated with "ten-petal flower-like" motif, locally arranged with fivefold symmetry. Similar structural features can be identified in the atomically-dense planes generated from one of the available bulk structure models. Based on these results, we conclude that the fivefold i-AlCuFe surface corresponds to a two-dimensional cut of the bulk material. After examining the clean surface, we investigate the nucleation and growth of aluminium metallic thin films on the quasicrystalline i-Al-Cu-Fe fivefold surface. Upon deposition at room temperature, aluminium adatoms nucleate as pentagonal "starfish" with uniform size and in the same orientation. The same structure features are observed for different fluxes at low coverages. Based on the experimental results and the available bulk structure model, we identify the specific nucleation sites on the substrate and develop a model for the formation of the pentagonal starfish.

  16. Additional evidence from x-ray powder diffraction patterns that icosahedral quasi-crystals of intermetallic compounds are twinned cubic crystals

    SciTech Connect

    Pauling, L. )

    1988-07-01

    Analysis of the measured values of Q for the weak peaks (small maxima, usually considered to be background fluctuations, noise) on the x-ray powder diffraction curves for 17 rapidly quenched alloys leads directly to the conclusion that they are formed by an 820-atom or 1012-atom primitive cubic structure that by icosahedral twinning produces the so-called icosahedral quasi-crystals.

  17. Development of thermal rectifier using unusual electron thermal conductivity of icosahedral quasicrystals

    NASA Astrophysics Data System (ADS)

    Takeuchi, Tsunehiro

    2015-03-01

    The bulk thermal rectifiers usable at high temperature were developed using the unusual increase of electron thermal conductivity of icosahedral quasicrystals (ICQ's) at high temperature. Our previously performed analyses in terms of linear response theory suggested that the unusual increase of electron thermal conductivity of ICQ was brought about by the synergy effect of quasiperiodicity and narrow pseudogap at the Fermi level. Since the linear response theory suggests that the unusual increase of electron thermal conductivity is coupled with the small magnitude of Seebeck coefficient, the composition of Al-Cu-Fe ICQ, where the thermal conductivity shows the most significant increase with increasing temperature, was determined with a great help of Seebeck coefficient measurements. Consequently obtained Al61.5Cu26.5Fe12.0 ICQ, which was characterized by the small magnitude of Seebeck coefficient, possessed 9 times larger value of thermal conductivity at 1000 K than that observed at 300 K. The increasing tendency of electron thermal conductivity with increasing temperature was further enhanced by means of small amount of Re substitution for Fe. This substitution definitely reduced the lattice thermal conductivity while the electron thermal conductivity was kept unchanged. The lattice thermal conductivity was reduced by 35 % under the presence of 0.5 at.% Re, and the thermal conductivity at 1000 K consequently became about 11 times larger than that at 300 K. The thermal rectifiers were constructed using our newly developed ICQ (Al61.5Cu26.5Fe12.0 or Al61.0Si0.5Cu26.5Fe11.5Re0.5) together with one of the selected materials (Si, Al2O3, CuGeTe2 or Ag2Te) that possess thermal conductivity decreasing with increasing temperature. The heat current flowing in the rectifiers was confirmed to show significant direction dependence. The consequently obtained TRR =|Jlarge|/ |Jsmall | for the composite consisting of

  18. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    SciTech Connect

    Lowe, M.; McGrath, R.; Sharma, H. R.; Yadav, T. P.; Fournée, V.; Ledieu, J.

    2015-03-07

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe{sub 3}O{sub 4} rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol.

  19. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    NASA Astrophysics Data System (ADS)

    Lowe, M.; Yadav, T. P.; Fournée, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.

    2015-03-01

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol.

  20. Speculation of equilibrium pressure of Ti{sub 36}Zr{sub 40}Ni{sub 20}Pd{sub 4} icosahedral quasicrystal

    SciTech Connect

    Huang, Huogen; Chen, Liang

    2015-08-17

    Ti-Zr-Ni quasicrystals have been demonstrated to store a large number of hydrogen atoms, which implies strong potential application in hydrogen energy field for them. However, the desorption of hydrogen atoms in the quasicrystals is quite difficult, with the indication of high desorption temperature and slow desorption rate. The shortage limits their use in the field to a large extent. But this kind of quasicrystals might be used in nuclear fusion energy field, because tritium as a coral fuel for nuclear fusion needs tight storage. However, equilibrium pressure at room temperature of Ti-Zr-Ni quasicrystals, important for their application in fusion energy field, has not been clear yet. In this work, we designed a gas-solid reaction system with the pressure resolution of 10{sup −8}Pa and carried out hydrogen desorption investigation at different temperatures on Ti{sub 36}Zr{sub 40}Ni{sub 20}Pd{sub 4} icosahedral quasicrystal. Based on three Pressure-Composition-Temperature desorption curves, we speculate according to Van’t Hoff theory about hydrogen storage that its equilibrium pressure at room temperature could be at the magnitude of 10{sup −6}Pa, displaying good stability of hydrogen in the quasicrystal and also implying application prospects in fusion energy field for quasicrystals of this type.

  1. Step-terrace morphology and reactivity to C60 of the five-fold icosahedral Ag-In-Yb quasicrystal

    NASA Astrophysics Data System (ADS)

    Nugent, P. J.; Smerdon, J. A.; McGrath, R.; Shimoda, M.; Cui, C.; Tsai, A. P.; Sharma, H. R.

    2011-07-01

    The surface of the icosahedral i-Ag-In-Yb quasicrystal provides one of the first non-Al-based aperiodic surfaces that is suitable for study under ultra-high vacuum conditions. We present a scanning tunnelling microscopy (STM) study of the five-fold surface of this new quasicrystal demonstrating detailed structure of the terraces and steps. The analysis of the autocorrelation functions of STM images at opposite bias polarities and of the in-plane structure of the bulk model of i-Cd-Yb, which is isostructural to i-Ag-In-Yb, reveals that the surface terminations occur at the centres of the rhombic triacontrahedral (RTH) clusters, which are the basic building blocks of this material. The study further confirms that the unoccupied electronic states are located on Yb sites. Step edges display a Fibonacci sequence of truncated clusters, which can also be explained in terms of the model structure. Occasionally, a single terrace is found to display different structures at negative bias, whereas the same terrace shows a uniform structure at positive bias. Depositing C60 creates a disordered overlayer on the surface with no resulting FFT or LEED patterns.

  2. Strain-induced structural transformation of single-phase Al-Cu-Fe icosahedral quasicrystal during mechanical milling

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, N. K.; Ali, F.; Srivastava, V. C.; Yadav, T. P.; Sakaliyska, M.; Surreddi, K. B.; Scudino, S.; Uhlenwinkel, V.; Eckert, J.

    2011-07-01

    A single-phase stable icosahedral quasicrystalline sample of high quality with the composition Al62.5Cu25Fe12.5 was produced by the spray forming technique. The material was further investigated by mechanical milling under an argon atmosphere to avoid oxidation during milling. At the initial stages of milling (within 5 h) a significant broadening of the diffraction peaks was observed, indicating a reduction of crystallite size and the introduction of lattice strain, which can be linked to phason strain of the quasilattice. Line broadening was noticed to increase with increasing milling time and in the material milled for longer time only a few broad diffraction peaks, which can be identified as a nanoscale bcc phase (i.e. disordered B2 phase, a ∼ 2.9 Å), were visible. At this stage the diffraction signals belonging to the quasicrystals were no longer observable, indicating a complete transformation of the quasicrystals into the bcc phase. Finally, the bcc phase formed during milling transformed back to the quasicrystalline phase during subsequent annealing treatment. The microhardness measured on the milled powders was found to decrease with increasing milling time, most likely as a consequence of the increased volume fraction of the ductile bcc phase. Attempts are made to rationalize the structural transformation.

  3. Schottky effect in the i -Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant

    NASA Astrophysics Data System (ADS)

    Jazbec, S.; Kashimoto, S.; Koželj, P.; Vrtnik, S.; Jagodič, M.; Jagličić, Z.; Dolinšek, J.

    2016-02-01

    The analysis of low-temperature specific heat of rare-earth (RE)-containing quasicrystals and periodic approximants and consequent interpretation of their electronic properties in the T →0 limit is frequently hampered by the Schottky effect, where crystalline electric fields lift the degeneracy of the RE-ion Hund's rule ground state and introduce additional contribution to the specific heat. In this paper we study the low-temperature specific heat of a thulium-containing i -Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant, both being classified as "Schottky" systems. We have derived the crystal-field Hamiltonian for pentagonal symmetry of the crystalline electric field, pertinent to the class of Tsai-type icosahedral quasicrystals and their approximants, where the RE ions are located on fivefold axes of the icosahedral atomic cluster. Using the leading term of this Hamiltonian, we have calculated analytically the Schottky specific heat in the presence of an external magnetic field and made comparison to the experimental specific heat of the investigated quasicrystal and approximant. When the low-temperature specific heat C is analyzed in a C /T versus T2 scale (as it is customarily done for metallic specimens), the Schottky specific heat yields an upturn in the T →0 limit that cannot be easily distinguished from a similar upturn produced by the electron-electron interactions in exchange-enhanced systems and strongly correlated systems. Our results show that extraction of the electronic properties of RE-containing quasicrystals from their low-temperature specific heat may be uncertain in the presence of the Schottky effect.

  4. Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc.

    PubMed

    Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Kaneko, Y; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M

    2013-03-20

    A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn(6)Sc. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a 'single molecule' and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to T(c) = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system.

  5. Quasicrystals

    PubMed Central

    Cahn, John W.

    2001-01-01

    The discretely diffracting aperiodic crystals termed quasicrystals, discovered at NBS in the early 1980s, have led to much interdisciplinary activity involving mainly materials science, physics, mathematics, and crystallography. It led to a new understanding of how atoms can arrange themselves, the role of periodicity in nature, and has created a new branch of crystallography. PMID:27500058

  6. Scanning Tunneling Microscopy Studies of Surface Structures of Icosahedral Al-Cu-Fe Quasicrystals

    SciTech Connect

    Tanhong Cai

    2002-12-31

    Three papers are included in this dissertation. The first paper: ''Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED studies'', is in press with ''Surface Science''. The second paper: ''An STM study of the atomic structure of the icosahedral Al-Cu-Fe fivefold surface'' is submitted to ''Physical Review B, Rapid Communication''. The third paper: ''Pseudomorphic starfish: arrangement of extrinsic metal atoms on a quasicrystalline substrate'' is submitted to ''Nature''. Following the third paper are general conclusions and appendices that document the published paper ''Structural aspects of the three-fold surface of icosahedral Al-Pd-Mn'' (appearing in volume 461, issue 1-3 of ''Surface Science'' on page L521-L527, 2000), the design as well as the specifications of the aluminum evaporator used in the aluminum deposition study in this dissertation, an extended discussion of the aluminum deposition on the quasicrystalline surface, and the STM database.

  7. Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap

    SciTech Connect

    Maniraj, M; Rai, Abhishek; Barman, S R; Krajci, M; Schlagel, Deborah L; Lograsso, Thomas A; Horn, K

    2014-09-01

    We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15±0.1)me and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i-Al-Pd-Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i-Al-Pd-Mn with the free-electron-like image potential states. Our investigation of the energy region immediately above EF provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.

  8. Quasicrystals

    SciTech Connect

    DuBois, J.M.; Thiel, P.A.; Tsai, A.P.; Urban, K.

    1999-11-01

    Recent developments indicate that quasicrystals are promising candidates for applications such as coatings, metal-matrix components, hydrogen storage materials, thermal barriers, infrared sensors, and other functions. This volume provides an update on the field of quasicrystals for members of the materials research community. More specifically, it focuses on progress in the preparation and properties of quasicrystalline for use in technological applications. Papers address commercial application, physical properties, electronic structure, atomic-scale structure, phase equilibria, and growth of high-quality samples. Highlights include some of the first applications, or near applications, of quasicrystalline materials. One such product is a high-strength steel currently used in surgical tools and electric shavers. The steel contains quasicrystalline precipitates which are unusually stable against Ostwald ripening. This stability is attributed to the low interfacial energy of the precipitates, and provides flexibility in processing by making the steel resistant to overaging. A second product, an aluminum alloy that meets or exceeds the specific US Air Force goal of high strength at elevated temperatures, is also discussed. And a third product, not yet on the market, is a quasicrystalline thermal barrier coating. Here, two attractive properties of quasicrystals combine--low thermal conductivity and plastic behavior at high temperatures. These materials are being tested on turbine blades in aircraft engines. New hypotheses about atomic-scale structure are also presented. This book contains 66 papers.

  9. Terrace-dependent nucleation of small Ag clusters on a five-fold icosahedral quasicrystal surface

    SciTech Connect

    Unal, B.; Evans, J.W.; Lograsso, T.A.; Ross, A.R.; Jenks, C.J.; Thiel, P.A.

    2007-07-21

    Nucleation of Ag islands on the five-fold surface of icosahedral Al-Pd-Mn is influenced strongly by trap sites. Submonolayers of Ag prepared by deposition at 365 K and with a flux of 1 x 10{sup -3} monolayers/s exhibit a variation in Ag island densities across different terraces. Comparisons with previous work and with rate equation analysis indicate that trap sites are not saturated under these experimental conditions and that the difference in island densities is not necessarily due to variation in trap densities. While it could have a number of different origins, our results point to a terrace-dependent value of the effective diffusion barrier for Ag adatoms.

  10. Magnetoresistance in i-R-Cd icosahedral quasicrystals (R=Y, Gd)

    NASA Astrophysics Data System (ADS)

    Saraswat, Garima; Popović, Dragana; Kong, Tai; Bud'Ko, Sergey L.; Canfield, Paul C.

    We use magnetoresistance (MR) to probe the electronic properties of the recently discovered binary quasicrystals (QCs) i-Gd-Cd and i-Y-Cd, with and without local magnetic moments, respectively. DC magnetization has revealed spin-glass freezing in i-Gd-Cd at a temperature Tf = 4 . 6 K. MR was measured at 1 . 6 <= T (K) <= 300 and in magnetic fields H up to 12 T. The most interesting behavior is observed in i-Gd-Cd, in which the MR exhibits thermo-magnetic history dependence at low T. In particular, there is a clear difference between the ZFC and FC values of the low-field positive MR. In contrast, the i-Y-Cd MR does not depend on magnetic history. The onset of the history dependent MR at T ~ 20 K >Tf , when the QC with local magnetic moments is cooled in a high field of 12 T, may be related to the formation of magnetic clusters above Tf, as inferred from the magnetization and specific heat studies. Possible mechanisms responsible for the striking coupling between charge transport and local magnetic environment observed in the MR will be discussed. Work at the NHMFL supported by NSF Grant No. DMR-1307075, the NSF Cooperative Agreement No. DMR-0654118 and the State of Florida. Work at Ames Lab (TK, SLB and PCC) supported by the U.S. D.O.E / B.E.S under Contract No. DE-AC02-07CH11358.

  11. Development of an icosahedral quasicrystal and two approximants in the Ca-Au-Sn system: syntheses and structural analyses.

    PubMed

    Lin, Qisheng; Corbett, John D

    2010-11-15

    The realm of Tsai-type (YCd(6)-type) quasicrystals (QCs) and their approximants (ACs) continues to expand to the east in the periodic table. The heavy tetrel Sn is now one of the major components in the new Ca(15.0(5))Au(60.0(4))Sn(25.0(2)) (atom %) icosahedral QC and in the corresponding 1/1 and 2/1 ACs. (The 2/1 AC with Yb is also established.) Single-crystal X-ray diffraction on a 1/1 AC gives the refined formula of Ca(3)Au(14.36(3))Sn(4.38(5)) in space group Im3, a = 15.131(1) Å, whereas a representative 2/1 AC gives Ca(13)Au(47.2(1))Sn(28.1(1)), Pa3 and a = 24.444(1) Å. Both ACs contain five-shell multiply endohedral triacontahedral clusters as the common building blocks, as in the parent structure of YCd(6). The 2/1 AC also contains four Ca(2)-dimer-centered prolate rhombohedra (PRs) in the unit cell. The long-range order between triacontahedra and PRs in the 2/1 AC is the same as those in Bergman-type 2/1 ACs. A TB-LMTO-ASA calculation on an ideal 1/1 AC model reveals a shallow pseudogap in the total densities-of-states data around the Fermi energy, as expected. The depth of the pseudogap is considerably enhanced through interactions between the Ca 3d states and s and p states of Au and Sn. PMID:20939550

  12. Development of an icosahedral quasicrystal and two approximants in the Ca-Au-Sn system: syntheses and structural analyses.

    PubMed

    Lin, Qisheng; Corbett, John D

    2010-11-15

    The realm of Tsai-type (YCd(6)-type) quasicrystals (QCs) and their approximants (ACs) continues to expand to the east in the periodic table. The heavy tetrel Sn is now one of the major components in the new Ca(15.0(5))Au(60.0(4))Sn(25.0(2)) (atom %) icosahedral QC and in the corresponding 1/1 and 2/1 ACs. (The 2/1 AC with Yb is also established.) Single-crystal X-ray diffraction on a 1/1 AC gives the refined formula of Ca(3)Au(14.36(3))Sn(4.38(5)) in space group Im3, a = 15.131(1) Å, whereas a representative 2/1 AC gives Ca(13)Au(47.2(1))Sn(28.1(1)), Pa3 and a = 24.444(1) Å. Both ACs contain five-shell multiply endohedral triacontahedral clusters as the common building blocks, as in the parent structure of YCd(6). The 2/1 AC also contains four Ca(2)-dimer-centered prolate rhombohedra (PRs) in the unit cell. The long-range order between triacontahedra and PRs in the 2/1 AC is the same as those in Bergman-type 2/1 ACs. A TB-LMTO-ASA calculation on an ideal 1/1 AC model reveals a shallow pseudogap in the total densities-of-states data around the Fermi energy, as expected. The depth of the pseudogap is considerably enhanced through interactions between the Ca 3d states and s and p states of Au and Sn.

  13. Scanning tuneeling microscopy studies of fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals and of thin silver films on those surfaces

    SciTech Connect

    Unal, Baris

    2008-01-01

    The present work in this dissertation mainly focuses on the clean fivefold surfaces of i-Al-Pd-Mn quasicrystals as well as the nucleation and growth of Ag films on these surfaces. In addition, Ag film growth on NiAl(110) has been explored in the frame of this dissertation. First, we have investigated the equilibration of a fivefold surface of icosahedral Al-Pd-Mn quasicrystal at 900-915 K and 925-950 K, using Omicron variable temperature scanning tunneling microscope (STM). Annealing at low temperatures resulted in many voids on some terraces while the others were almost void-free. After annealing at 925-950K, void-rich terraces became much rarer. Our STM images suggest that through growth and coalescence of the voids, a different termination becomes exposed on host terraces. All of these observations in our study indicate that even after the quasicrystalline terrace-step structure appears, it evolves with time and temperature. More specifically, based on the STM observations, we conclude that during the annealing a wide range of energetically similar layers nucleate as surface terminations, however, with increasing temperature (and time) this distribution gets narrower via elimination of the metastable void-rich terraces. Next, we have examined the bulk structural models of icosahedral Al-Pd-Mn quasicrystal in terms of the densities, compositions and interplanar spacings for the fivefold planes that might represent physical surface terminations. In our analyses, we mainly have focused on four deterministic models which have no partial or mixed occupancy but we have made some comparisons with an undeterministic model. We have compared the models with each other and also with the available experimental data including STM, LEED-IV, XPD and LEIS. In all deterministic models, there are two different families of layers (a pair of planes), and the nondeterministic model contains similar group of planes. These two families differ in terms of the chemical decoration of

  14. Magnetic and transport properties of i-R-Cd icosahedral quasicrystals (R=Y, Gd-Tm)

    SciTech Connect

    Kong, Tai; Bud'ko, Sergey L.; Jesche, Anton; McArthur, John; Kreyssig, Andreas; Goldman, Alan I.; Canfield, Paul C.

    2014-07-01

    We present a detailed characterization of the recently discovered i-R-Cd (R=Y,Gd-Tm) binary quasicrystals by means of x-ray diffraction, temperature-dependent dc and ac magnetization, temperature-dependent resistance, and temperature-dependent specific heat measurements. Structurally, the broadening of x-ray diffraction peaks found for i-R-Cd is dominated by frozen-in phason strain, which is essentially independent of R. i-Y-Cd is weakly diamagnetic and manifests a temperature-independent susceptibility. i-Gd-Cd can be characterized as a spin glass below 4.6 K via dc magnetization cusp, a third order nonlinear magnetic susceptibility peak, a frequency-dependent freezing temperature, and a broad maximum in the specific heat. i-R-Cd (R=Ho-Tm) is similar to i-Gd-Cd in terms of features observed in thermodynamic measurements. i-Tb-Cd and i-Dy-Cd do not show a clear cusp in their zero-field-cooled dc magnetization data, but instead show a more rounded, broad local maximum. The resistivity for i-R-Cd is of order 300μΩ cm and weakly temperature dependent. The characteristic freezing temperatures for i-R-Cd (R=Gd-Tm) deviate from the de Gennes scaling, in a manner consistent with crystal electric field splitting induced local moment anisotropy.

  15. Location and energy of interstitial hydrogen in the 1/1 approximant W-TiZrNi of the icosahedral TiZrNi quasicrystal: Rietveld refinement of x-ray and neutron diffraction data and density-functional calculations

    SciTech Connect

    Hennig, R. G.; Majzoub, E. H.; Kelton, K. F.

    2006-05-01

    We present a determination of hydrogen sites in the 1/1 approximant structure of the icosahedral TiZrNi quasicrystal. A Rietveld refinement of neutron and x-ray diffraction data determines the locations of interstitial hydrogen atoms. Density-functional methods calculate the energy of hydrogen on all possible interstitial sites. The Rietveld refinement shows that the hydrogen atoms are preferentially located in the two lowest-energy sites. The filling of the remaining hydrogen sites is dominated by the repulsive hydrogen-hydrogen interaction at short distances.

  16. A comparative study of the magnetic properties of the 1/1 approximant Ag(50)In(36)Gd(14) and the icosahedral quasicrystal Ag(50)In(36)Gd(14).

    PubMed

    Wang, P; Stadnik, Z M; Al-Qadi, K; Przewoźnik, J

    2009-10-28

    We report on measurements of the dc and ac magnetic susceptibility, (155)Gd Mössbauer spectra, and specific heat of the 1/1 approximant Ag(50)In(36)Gd(14), and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag(50)In(36)Gd(14). These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag(50)In(36)Gd(14), spin freezing occurs at T(f) = 4.3 K, and the frequency dependence of T(f) is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag(50)In(36)Gd(14) occurs in two stages: at T(f(1)) = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T(f(2)) = 2.4 K. The frequency dependences of T(f(1)) and T(f(2)) can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The (155)Gd Mössbauer spectra of the 1/1 approximant Ag(50)In(36)Gd(14) confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T(f(1)), but the temperature derivative of the magnetic entropy peaks at T(f(1)). The Debye temperature of the 1/1 approximant Ag(50)In(36)Gd(14) is 199(1) K as determined from the Mössbauer data, and 205(2) K as determined from the specific heat data.

  17. A comparative study of the magnetic properties of the 1/1 approximant Ag(50)In(36)Gd(14) and the icosahedral quasicrystal Ag(50)In(36)Gd(14).

    PubMed

    Wang, P; Stadnik, Z M; Al-Qadi, K; Przewoźnik, J

    2009-10-28

    We report on measurements of the dc and ac magnetic susceptibility, (155)Gd Mössbauer spectra, and specific heat of the 1/1 approximant Ag(50)In(36)Gd(14), and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag(50)In(36)Gd(14). These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag(50)In(36)Gd(14), spin freezing occurs at T(f) = 4.3 K, and the frequency dependence of T(f) is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag(50)In(36)Gd(14) occurs in two stages: at T(f(1)) = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T(f(2)) = 2.4 K. The frequency dependences of T(f(1)) and T(f(2)) can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The (155)Gd Mössbauer spectra of the 1/1 approximant Ag(50)In(36)Gd(14) confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T(f(1)), but the temperature derivative of the magnetic entropy peaks at T(f(1)). The Debye temperature of the 1/1 approximant Ag(50)In(36)Gd(14) is 199(1) K as determined from the Mössbauer data, and 205(2) K as determined from the specific heat data. PMID:21832453

  18. Quasicrystal-Crystal Transformation in Zn-Mg-Rare-Earth Alloys

    NASA Astrophysics Data System (ADS)

    Abe, Eiji; Tsai, An Pang

    1999-07-01

    We report a reversible phase transformation between the icosahedral Zn-Mg-rare-earth(RE) quasicrystal and the hexagonal crystal being not composed of any giant icosahedral atomic cluster. This clearly shows that the large atomic cluster is not an essential atomic configuration for quasicrystal formation. A structural unit of the Zn-Mg-RE icosahedral quasicrystal is suggested to be not an icosahedral atomic cluster such as the Mackay or Bergman type which have been successfully used for the structural description of the Al-based icosahedral quasicrystalline phases.

  19. A crystallographic approach to structural transitions in icosahedral viruses.

    PubMed

    Indelicato, Giuliana; Cermelli, Paolo; Salthouse, David G; Racca, Simone; Zanzotto, Giovanni; Twarock, Reidun

    2012-04-01

    Viruses with icosahedral capsids, which form the largest class of all viruses and contain a number of important human pathogens, can be modelled via suitable icosahedrally invariant finite subsets of icosahedral 3D quasicrystals. We combine concepts from the theory of 3D quasicrystals, and from the theory of structural phase transformations in crystalline solids, to give a framework for the study of the structural transitions occurring in icosahedral viral capsids during maturation or infection. As 3D quasicrystals are in a one-to-one correspondence with suitable subsets of 6D icosahedral Bravais lattices, we study systematically the 6D-analogs of the classical Bain deformations in 3D, characterized by minimal symmetry loss at intermediate configurations, and use this information to infer putative viral-capsid transition paths in 3D via the cut-and-project method used for the construction of quasicrystals. We apply our approach to the Cowpea Chlorotic Mottle virus (CCMV) and show that the putative transition path between the experimentally observed initial and final CCMV structures is most likely to preserve one threefold axis. Our procedure suggests a general method for the investigation and prediction of symmetry constraints on the capsids of icosahedral viruses during structural transitions, and thus provides insights into the mechanisms underlying structural transitions of these pathogens. PMID:21611828

  20. Approximation of virus structure by icosahedral tilings.

    PubMed

    Salthouse, D G; Indelicato, G; Cermelli, P; Keef, T; Twarock, R

    2015-07-01

    Viruses are remarkable examples of order at the nanoscale, exhibiting protein containers that in the vast majority of cases are organized with icosahedral symmetry. Janner used lattice theory to provide blueprints for the organization of material in viruses. An alternative approach is provided here in terms of icosahedral tilings, motivated by the fact that icosahedral symmetry is non-crystallographic in three dimensions. In particular, a numerical procedure is developed to approximate the capsid of icosahedral viruses by icosahedral tiles via projection of high-dimensional tiles based on the cut-and-project scheme for the construction of three-dimensional quasicrystals. The goodness of fit of our approximation is assessed using techniques related to the theory of polygonal approximation of curves. The approach is applied to a number of viral capsids and it is shown that detailed features of the capsid surface can indeed be satisfactorily described by icosahedral tilings. This work complements previous studies in which the geometry of the capsid is described by point sets generated as orbits of extensions of the icosahedral group, as such point sets are by construction related to the vertex sets of icosahedral tilings. The approximations of virus geometry derived here can serve as coarse-grained models of viral capsids as a basis for the study of virus assembly and structural transitions of viral capsids, and also provide a new perspective on the design of protein containers for nanotechnology applications. PMID:26131897

  1. Multiple scattering of light in three-dimensional photonic quasicrystals.

    PubMed

    Ledermann, Alexandra; Wiersma, Diederik S; Wegener, Martin; von Freymann, Georg

    2009-02-01

    Recent experiments on three-dimensional icosahedral dielectric photonic quasicrystals have shown several unexpected features: transmitted femtosecond pulses developed a trailing "diffusive" exponential tail and the sum of (zeroth-order) transmittance and reflectance was well below unity. These experimental findings have previously been ascribed to sample imperfections. Here, we analyze these findings by using 3D periodic approximants of the ideal photonic quasicrystals. We show that the experimental observations can be explained in terms of multiple scattering of light within these structures, i.e., in terms of intrinsic rather than purely extrinsic quasicrystal properties.

  2. A stable Ti-based quasicrystal

    SciTech Connect

    Kelton, K.F.; Kim, W.J.; Stroud, R.M.

    1997-06-01

    The thermal stability of the icosahedral phase (i phase) in Ti{sub 45}Zr{sub 38}Ni{sub 17} alloys is demonstrated. As-cast alloys containing initially only the C14 hexagonal Laves and {alpha}-solid-solution phases transformed primarily to the icosahedral phase upon annealing in vacuum for 64 h at 570{degree}C. This confirms previous evidence for i-phase stability and firmly establishes this quasicrystal as the first nonaluminum stable icosahedral phase. Diffraction data show that this stable i phase is primitive; energy dispersive x-ray spectroscopy measurements place its composition near Ti{sub 41.5}Zr{sub 41.5}Ni{sub 17}. These and other results suggest that the structure of this i phase is similar to that of i(AlLiCu). {copyright} {ital 1997 American Institute of Physics.}

  3. Local growth of icosahedral quasicrystalline tilings

    NASA Astrophysics Data System (ADS)

    Hann, Connor T.; Socolar, Joshua E. S.; Steinhardt, Paul J.

    2016-07-01

    Icosahedral quasicrystals (IQCs) with extremely high degrees of translational order have been produced in the laboratory and found in naturally occurring minerals, yet questions remain about how IQCs form. In particular, the fundamental question of how locally determined additions to a growing cluster can lead to the intricate long-range correlations in IQCs remains open. In answer to this question, we have developed an algorithm that is capable of producing a perfectly ordered IQC yet relies exclusively on local rules for sequential, face-to-face addition of tiles to a cluster. When the algorithm is seeded with a special type of cluster containing a defect, we find that growth is forced to infinity with high probability and that the resultant IQC has a vanishing density of defects. The geometric features underlying this algorithm can inform analyses of experimental systems and numerical models that generate highly ordered quasicrystals.

  4. Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy

    PubMed Central

    Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang

    2015-01-01

    Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn 6 Mg 3 Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn 6 Mg 3 Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn 3 MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn 3 MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn:Mg:Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn 3 MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials. PMID:26066096

  5. Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy.

    PubMed

    Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang

    2015-06-12

    Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn6Mg3Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn6Mg3Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn3MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn3MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn:Mg:Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn3MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials.

  6. Studies of Hydrogen in Ti-Based Quasicrystals

    NASA Astrophysics Data System (ADS)

    Viano, A. M.; Gibbons, P. C.; Kelton, K. F.

    1996-03-01

    The presumed polytetrahedral order and the favorable hydrogen-metal chemistry make Ti-based quasicrystals candidate materials for hydrogen storage applications. The icosahedral phase in tzn453817 has been shown to absorb up to 62 atomic percent of hydrogen with no structural transformation. This is accompanied by a 7% increase in the quasilattice parameter. An oxide layer on the surface of the rapidly quenched quasicrystalline ribbons acts as a barrier to hydrogen absorption by direct gas exposure, and thus alternative loading techniques have been developed and will be discussed. The absorption kinetics and storage capacity are far better for the quasicrystal than for the associated amorphous and crystalline phases in TiZrNi. Two distinct types of fundamental clusters have been propsed for icosahedral phases, the Mackay icoasahedron and the Pauling triacontahedron. Calculations of the distances between tetrahedral interstitial sites in these clusters permits a determination of the maximum number of hydrogen atoms allowed in each cluster. Hydrogen storage ability, then, can be used to determine the cluster type for various icosahedral phase alloys. Hydrogenated quasicrystals constitute a novel metal-hydride system that allows new basic studies and has technological potential for energy applications.

  7. New horizon in quasicrystals

    NASA Astrophysics Data System (ADS)

    Samavat, F.; Kiani, M.

    2015-11-01

    Quasicrystals (QCs) are aperiodic intermetallic alloys that possess a long range positional order. They often exhibit crystallographically forbidden symmetries, most commonly fivefold and tenfold. The forbidden symmetry is related to the fact that the atoms are arranged quasiperiodically. Quasiperiodic translational order has physical consequences. For example, since electrons and phonons in quasicrystals do not encounter a periodic potential, quasicrystals have unusual resistive and elastic properties, and these have been exploited in several applications. The purpose of this introduction is to present certain properties that are relevant to the surface science of quasicrystals, as a launching point for the other articles in this special issue of progress in surface science.

  8. X-Ray and Electrostatic Levitation Undercooling Studies in Ti-Zr-Ni Quasicrystals Forming Alloys

    NASA Technical Reports Server (NTRS)

    Rogers, J. R.; Hyers, R. W.; Rathz, T. J.; Kelton, K. F.; Gangopadhyay, A. K.; Woo, G. L.; Hannet, L.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The first undercooling nucleation measurements of electrostatic-levitated droplets of TiZrNi alloys that form the icosahedral quasicrystal phase (i-phase) are presented. The reduced undercooling for crystallization decreases with an increasing polytetrahedral order of the primary solidifying phase, supporting the existence of a developing icosahedral short-range order in the undercooled liquid. X-ray diffraction measurements made at the Advance Photon Source on levitated liquid droplets of these alloys at their liquidus temperatures, however, show no evidence for increased icosahedral order. This suggests that significant ordering only occurs below the melting temperature.

  9. Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.; Rathz, T. J.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The local atomic structures of undercooled liquid metals are presumed to be icosahedral; this order is incompatible with translational periodicity, constituting a barrier to the nucleation of the crystal phase. The extended atomic structure of the icosahedral quasicrystal (i-phase) is similar to that presumed in the undercooled liquid. Therefore, a comparison of the maximum undercooling in alloys that form the i-phase with those that form crystal phases provides a probe of the liquid structure.

  10. Soft-x-ray, heat-capacity, and transport measurements on icosahedral and crystalline alloys

    NASA Astrophysics Data System (ADS)

    Bruhwiler, P. A.; Wagner, J. L.; Biggs, B. D.; Shen, Y.; Wong, K. M.; Schnatterly, S. E.; Poon, S. J.

    1988-04-01

    Soft-x-ray emission, heat-capacity, and resistivity measurements are reported for icosahedral and Frank-Kasper phases of Al-Cu-Li and Al-Cu-Mg. This is the first extensive comparison of electronic properties of periodic and quasiperiodic lattices generated by packing similar structural units. Results are compared with theories of quasicrystals and provide a guideline for the observability of Van Hove singularities in quasicrystals. The density of states N(0) is a factor of 3 less in Al-Cu-Li than in Al-Cu-Mg alloys; this is spectroscopically confirmed.

  11. Quasicrystals: Making invisible materials

    NASA Astrophysics Data System (ADS)

    Boriskina, Svetlana V.

    2015-07-01

    All-dielectric photonic quasicrystals may act as zero-refractive-index homogeneous materials despite their lack of translational symmetry and periodicity, stretching wavelengths to infinity and offering applications in light wavefront sculpting and optical cloaking.

  12. Quasicrystal surfaces: structure and growth of atomic overlayers

    NASA Astrophysics Data System (ADS)

    Sharma, H. R.; Shimoda, M.; Tsai, A. P.

    2007-05-01

    We review recent developments in surface studies of single-grain quasicrystals under ultra high-vacuum conditions, focusing on two different topics: surface structure and growth of atomic overlayers on surfaces. Quasicrystalline phases are currently used for investigation of the first topic are icosahedral (i) Al-Pd-Mn, i-Al-Cu-Fe, i-Al-Cu-Ru, i-Ag-In-Yb and decagonal (d) Al-Ni-Co, and d-Al-Cu-Co. We report the progress made with all of these phases. The second topic covers the study of single-element overlayer growth by vapor deposition.

  13. Crystal electric field excitations in quasicrystal approximant TbCd6 studied by inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Das, Pinaki; Flint, R.; Kong, T.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.; de Boissieu, M.; Lory, P.-F.; Beutier, G.; Hiroto, T.

    All of the known quasicrystals with local moments exhibit frustration and spin glass-like behavior at low temperature. The onset of the spin freezing temperature is believed to be affected by the crystal electric field (CEF) splitting of the local moments. The quasicrystal approximant TbCd6 and its related icosahedral quasicrystal phase, i-Tb-Cd, form a set of model systems to explore how magnetism evolves from a conventional lattice (approximant phase) to an aperiodic quasicrystal. Though TbCd6 shows long-range antiferromagnetic ordering (TN = 24 K), only spin glass like behavior is observed in i-Tb-Cd with a spin freezing temperature of TF = 6 K. To investigate further, we have performed inelastic neutron scattering measurements on powder samples of TbCd6 and observed two distinct CEF excitations at low energies which points to a high degeneracy of the CEF levels related to the Tb surrounding with almost icosahedral symmetry. Work at Ames Laboratory was supported by the DOE, BES, Division of Materials Sciences & Engineering, under Contract No. DE-AC02-07CH11358. This research used resources at Institut Laue-Langevin, France.

  14. The Crystallography of Quasicrystals

    NASA Astrophysics Data System (ADS)

    Rabson, David Alan

    A century ago, E. S. Fedorov, A. Schonflies, and W. Barlow, working independently, classified the 230 distinct symmetry groups of objects repeated periodically in three-dimensional space. The 230 space groups determine the symmetries of macroscopic properties and provide crystallographers with their most important tool in deducing structure; as such, they find use in biology, organic chemistry, and virology as well as in physics, geology, and materials science. With the discovery in 1984 of quasicrystals, well-ordered but aperiodic metallic alloys with crystallographically forbidden rotational symmetries, the need arose to develop a space-group theory for these new materials. Based on the work by Rokhsar, Wright, and Mermin^1 in two dimensions, Rabson, Mermin, Rokhsar, and Wright have classified all quasicrystal and crystal three -dimensional axial space groups.^2 Our classification, proceeding in reciprocal space, is elementary, does not rely on projecting higher-dimensional crystallographic space groups, and is valid for arbitrary rotational symmetry. As an additional illustration of quasicrystallographic space groups, I derive and demonstrate algorithms that produce two-dimensional tilings of rhombi with each of the possible plane-group symmetries.^3 While the analogous task for crystallographic plane groups is trivial, the lack of translational symmetry in a quasicrystal tiling makes these constructions interesting. Since the symmetry of a quasicrystal appears more naturally in reciprocal than in direct space, it is not surprising that some of the resulting tilings seem intricate, although in fact their symmetries are quite simple. ftn^1 Acta Cryst. A44, 197-211 (1988). ^2 "The Space Groups of Axial Crystals and Quasicrystals," preprint. ^3See also Rabson, Ho, and Mermin, Acta Cryst. A44, 678 (1988) and Acta Cryst. A45, 538 (1989).

  15. Optics of photonic quasicrystals

    NASA Astrophysics Data System (ADS)

    Vardeny, Z. Valy; Nahata, Ajay; Agrawal, Amit

    2013-03-01

    The physics of periodic systems are of fundamental importance and result in various phenomena that govern wave transport and interference. However, deviations from periodicity may result in higher complexity and give rise to a number of surprising effects. One such deviation can be found in the field of optics in the realization of photonic quasicrystals, a class of structures made from building blocks that are arranged using well-designed patterns but lack translational symmetry. Nevertheless, these structures, which lie between periodic and disordered structures, still show sharp diffraction patterns that confirm the existence of wave interference resulting from their long-range order. In this Review, we discuss the beautiful physics unravelled in photonic quasicrystals of one, two and three dimensions, and describe how they can influence optical transmission and reflectivity, photoluminescence, light transport, plasmonics and laser action.

  16. The interest of x-ray imaging for the study of defects in real quasicrystals

    NASA Astrophysics Data System (ADS)

    Gastaldi, J.; Mancini, L.; Reinier, E.; Cloetens, P.; Ludwig, W.; Janot, C.; Baruchel, J.; Härtwig, J.; Schlenker, M.

    1999-05-01

    The understanding of defects in quasicrystals has improved through x-ray imaging at ESRF, one of the first operating third-generation synchrotron radiation sources. These sources, while enhancing the possibilities of x-ray topography, opened the way to new techniques like phase contrast radiography and tomography. The combination of these techniques makes it possible to visualize and characterize both structural defects and inhomogeneities in the bulk of real quasicrystals. Defects exhibiting a loop-shaped contrast, previously observed by x-ray topography in both AlCuFe and AlPdMn quasicrystals, were related to inhomogeneities (holes and precipitates) revealed by phase radiography and tomography. The evolution of the defects after annealing provides clues on their nature and formation. The experimental results are discussed with reference to the existing structural models for quasicrystals. Those concerning holes are in fair agreement with the predictions of a theoretical model introduced by Janot et al to describe the structure of icosahedral AlPdMn quasicrystals in terms of hierarchical self-similar packing of overlapping atomic clusters.

  17. Shock synthesis of quasicrystals with implications for their origin in asteroid collisions.

    PubMed

    Asimow, Paul D; Lin, Chaney; Bindi, Luca; Ma, Chi; Tschauner, Oliver; Hollister, Lincoln S; Steinhardt, Paul J

    2016-06-28

    We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe(2+) 0.25)2SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68-73Fe11-16Cu10-12Cr1-4Ni1-2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.

  18. Shock synthesis of quasicrystals with implications for their origin in asteroid collisions

    NASA Astrophysics Data System (ADS)

    Asimow, Paul D.; Lin, Chaney; Bindi, Luca; Ma, Chi; Tschauner, Oliver; Hollister, Lincoln S.; Steinhardt, Paul J.

    2016-06-01

    We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe2+0.25)2SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68-73Fe11-16Cu10-12Cr1-4Ni1-2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.

  19. Shock synthesis of quasicrystals with implications for their origin in asteroid collisions.

    PubMed

    Asimow, Paul D; Lin, Chaney; Bindi, Luca; Ma, Chi; Tschauner, Oliver; Hollister, Lincoln S; Steinhardt, Paul J

    2016-06-28

    We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe(2+) 0.25)2SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68-73Fe11-16Cu10-12Cr1-4Ni1-2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors. PMID:27298357

  20. Quasicrystals and Quantum Computing

    NASA Astrophysics Data System (ADS)

    Berezin, Alexander A.

    1997-03-01

    In Quantum (Q) Computing qubits form Q-superpositions for macroscopic times. One scheme for ultra-fast (Q) computing can be based on quasicrystals. Ultrafast processing in Q-coherent structures (and the very existence of durable Q-superpositions) may be 'consequence' of presence of entire manifold of integer arithmetic (A0, aleph-naught of Georg Cantor) at any 4-point of space-time, furthermore, at any point of any multidimensional phase space of (any) N-particle Q-system. The latter, apart from quasicrystals, can include dispersed and/or diluted systems (Berezin, 1994). In such systems such alleged centrepieces of Q-Computing as ability for fast factorization of long integers can be processed by sheer virtue of the fact that entire infinite pattern of prime numbers is instantaneously available as 'free lunch' at any instant/point. Infinitely rich pattern of A0 (including pattern of primes and almost primes) acts as 'independent' physical effect which directly generates Q-dynamics (and physical world) 'out of nothing'. Thus Q-nonlocality can be ultimately based on instantaneous interconnectedness through ever- the-same structure of A0 ('Platonic field' of integers).

  1. Single crystal growth of Al-based intermetallic phases being approximants to quasicrystals

    NASA Astrophysics Data System (ADS)

    Gille, Peter; Bauer, Birgitta; Hahne, Michael; Smontara, Ana; Dolinšek, Janez

    2011-03-01

    Decagonal (d) quasicrystals are formed in a number of Al-based ternary systems with d-AlCoNi being the best studied decagonal phase. They are highly anisotropic showing unusual properties of e.g. electric and thermal transport when measured along the periodic or quasiperiodic directions. For a long time, this has been attributed to the lack of periodicity in certain crystallographic orientations. Some neighbouring phases in the Al-Co-Ni system as well as in related ternaries consist of the same type of large icosahedral clusters, but are periodic in all three directions, sometimes with very large unit cells. Therefore, they are called approximants to the decagonal quasicrystals. They allow comparative studies of these phases as to judge whether some unusual properties of quasicrystals arise from the lack of periodicity or from the common atomic arrangements. Additional to decagonal AlCoNi quasicrystals, various approximants (monoclinic Al13(Co,Ni)4, orthorhombic Al13Co4, orthorhombic Al4(Cr,Fe), monoclinic Al13Fe4 and its ternary extensions Al13(Fe,Cr)4 and Al13(Fe,Ni)4) were grown by the Czochralski method as large single crystals as to carry out transport orientation-dependent measurements. It could be found that transport properties show remarkably similar anisotropic features when comparing corresponding crystallographic directions in these phases that can be related to the periodic stacking of layers.

  2. NMR and NQR study of the thermodynamically stable quasicrystals

    SciTech Connect

    Shastri, A.

    1995-02-10

    {sup 27}Al and {sup 61,65}Cu NMR measurements are reported for powder samples of stable AlCuFe and AlCuRu icosahedral quasicrystals and their crystalline approximants, and for a AlPdMn single grain quasicrystal. Furthermore, {sup 27}Al NQR spectra at 4.2 K have been observed in the AlCuFe and AlCuRu samples. From the quadrupole perturbed NMR spectra at different magnetic fields, and from the zero field NQR spectra, a wide distribution of local electric field gradient (EFG) tensor components and principal axis system orientations was found at the Al site. A model EFG calculation based on a 1/1 AlCuFe approximant was successful in explaining the observed NQR spectra. It is concluded that the average local gradient is largely determined by the p-electron wave function at the Al site, while the width of the distribution is due to the lattice contribution to the EFG. Comparison of {sup 63}Cu NMR with {sup 27}Al NMR shows that the EFG distribution at the two sites is similar, but that the electronic contribution to the EFG is considerably smaller at the Cu site, in agreement with a more s-type wave function of the conduction electrons.

  3. Evidence for the extraterrestrial origin of a natural quasicrystal

    PubMed Central

    Bindi, Luca; Eiler, John M.; Guan, Yunbin; Hollister, Lincoln S.; MacPherson, Glenn; Steinhardt, Paul J.; Yao, Nan

    2012-01-01

    We present evidence that a rock sample found in the Koryak Mountains in Russia and containing icosahedrite, an icosahedral quasicrystalline phase with composition Al63Cu24Fe13, is part of a meteorite, likely formed in the early solar system about 4.5 Gya. The quasicrystal grains are intergrown with diopside, forsterite, stishovite, and additional metallic phases [khatyrkite (CuAl2), cupalite (CuAl), and β-phase (AlCuFe)]. This assemblage, in turn, is enclosed in a white rind consisting of diopside, hedenbergite, spinel (MgAl2O4), nepheline, and forsterite. Particularly notable is a grain of stishovite (from the interior), a tetragonal polymorph of silica that only occurs at ultrahigh pressures (≥10 Gpa), that contains an inclusion of quasicrystal. An extraterrestrial origin is inferred from secondary ion mass spectrometry 18O/16O and 17O/16O measurements of the pyroxene and olivine intergrown with the metal that show them to have isotopic compositions unlike any terrestrial minerals and instead overlap those of anhydrous phases in carbonaceous chondrite meteorites. The spinel from the white rind has an isotopic composition suggesting that it was part of a calcium-aluminum-rich inclusion similar to those found in CV3 chondrites. The mechanism that produced this exotic assemblage is not yet understood. The assemblage (metallic copper-aluminum alloy) is extremely reduced, and the close association of aluminum (high temperature refractory lithophile) with copper (low temperature chalcophile) is unexpected. Nevertheless, our evidence indicates that quasicrystals can form naturally under astrophysical conditions and remain stable over cosmic timescales, giving unique insights on their existence in nature and stability. PMID:22215583

  4. Evidence for the extraterrestrial origin of a natural quasicrystal.

    PubMed

    Bindi, Luca; Eiler, John M; Guan, Yunbin; Hollister, Lincoln S; MacPherson, Glenn; Steinhardt, Paul J; Yao, Nan

    2012-01-31

    We present evidence that a rock sample found in the Koryak Mountains in Russia and containing icosahedrite, an icosahedral quasicrystalline phase with composition Al(63)Cu(24)Fe(13), is part of a meteorite, likely formed in the early solar system about 4.5 Gya. The quasicrystal grains are intergrown with diopside, forsterite, stishovite, and additional metallic phases [khatyrkite (CuAl(2)), cupalite (CuAl), and β-phase (AlCuFe)]. This assemblage, in turn, is enclosed in a white rind consisting of diopside, hedenbergite, spinel (MgAl(2)O(4)), nepheline, and forsterite. Particularly notable is a grain of stishovite (from the interior), a tetragonal polymorph of silica that only occurs at ultrahigh pressures (≥ 10 Gpa), that contains an inclusion of quasicrystal. An extraterrestrial origin is inferred from secondary ion mass spectrometry (18)O/(16)O and (17)O/(16)O measurements of the pyroxene and olivine intergrown with the metal that show them to have isotopic compositions unlike any terrestrial minerals and instead overlap those of anhydrous phases in carbonaceous chondrite meteorites. The spinel from the white rind has an isotopic composition suggesting that it was part of a calcium-aluminum-rich inclusion similar to those found in CV3 chondrites. The mechanism that produced this exotic assemblage is not yet understood. The assemblage (metallic copper-aluminum alloy) is extremely reduced, and the close association of aluminum (high temperature refractory lithophile) with copper (low temperature chalcophile) is unexpected. Nevertheless, our evidence indicates that quasicrystals can form naturally under astrophysical conditions and remain stable over cosmic timescales, giving unique insights on their existence in nature and stability. PMID:22215583

  5. Experimental evidence of icosahedral and decahedral packing in one-dimensional nanostructures.

    PubMed

    Velázquez-Salazar, J Jesús; Esparza, Rodrigo; Mejía-Rosales, Sergio Javier; Estrada-Salas, Rubén; Ponce, Arturo; Deepak, Francis Leonard; Castro-Guerrero, Carlos; José-Yacamán, Miguel

    2011-08-23

    The packing of spheres is a subject that has drawn the attention of mathematicians and philosophers for centuries and that currently attracts the interest of the scientific community in several fields. At the nanoscale, the packing of atoms affects the chemical and structural properties of the material and, hence, its potential applications. This report describes the experimental formation of 5-fold nanostructures by the packing of interpenetrated icosahedral and decahedral units. These nanowires, formed by the reaction of a mixture of metal salts (Au and Ag) in the presence of oleylamine, are obtained when the chemical composition is specifically Ag/Au = 3:1. The experimental images of the icosahedral nanowires have a high likelihood with simulated electron micrographs of structures formed by two or three Boerdijk-Coxeter-Bernal helices roped on a single structure, whereas for the decahedral wires, simulations using a model of adjacent decahedra match the experimental structures. To our knowledge, this is the first report of the synthesis of nanowires formed by the packing of structures with 5-fold symmetry. These icosahedral nanowire structures are similar to those of quasicrystals, which can only be formed if at least two atomic species are present and in which icosahedral and decahedral packing has been found for bulk crystals.

  6. Octonacci photonic quasicrystals

    NASA Astrophysics Data System (ADS)

    Brandão, E. R.; Costa, C. H.; Vasconcelos, M. S.; Anselmo, D. H. A. L.; Mello, V. D.

    2015-08-01

    We study theoretically the transmission spectra in one-dimensional photonic quasicrystals, made up of SiO2(A) and TiO2(B) materials, organized following the Octonacci sequence, where the nth-stage of the multilayer Sn is given by the rule Sn =Sn-1Sn-2Sn-1 , for n ⩾ 3 and with S1 = A and S2 = B . The expression for transmittance was obtained by employing a theoretical calculation based on the transfer-matrix method. For normally incident waves, we observe that, for a same generation, the transmission spectra for transverse electric (TE) and transverse magnetic (TM) waves are equal, at least qualitatively, and they present a scaling property where a self-similar behavior is obtained, as an evidence that these spectra are fractals. The spectra show regions where the omnidirectional band gaps emerges for specific generations of Octonacci photonic structure, except to TM waves. For TE waves, we note that all of them have almost the same width, for different generations. We also report the localization of modes as a consequence of the quasiperiodicity of the heterostructure.

  7. Al{sub 70}Pd{sub 21.5}Mn{sub 8.5}: A quasicrystal showing the de haas-van Alphen effect

    SciTech Connect

    Haanappel, E.G.; Kycia, S.W.; Harmon, B.N.; Canfield, P.C.; Goldman, A.I.; Rabson, D.A.; Thompson, J.D.; Mueller, F.M.

    1995-07-01

    We have measured the de Haas-van Alphen effect in the icosahedral quasicrystal Al{sub 70}Pd{sub 21.5}Mn{sub 8.5}. We have found two well-defined frequencies with the magnetic field parallel to a five-fold axis, and two different ones with the field parallel to a two-fold axis. On increasing the temperature, the amplitude of the oscillations substantially decreased, suggesting that the carriers have large masses.

  8. Natural quasicrystal with decagonal symmetry

    PubMed Central

    Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.

    2015-01-01

    We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al71Ni24Fe5, was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal to be identified, was found in the same meteorite. The new quasicrystal was found associated with steinhardtite (Al38Ni32Fe30), Fe-poor steinhardtite (Al50Ni40Fe10), Al-bearing trevorite (NiFe2O4) and Al-bearing taenite (FeNi). Laboratory studies of decagonal Al71Ni24Fe5 have shown that it is stable over a narrow range of temperatures, 1120 K to 1200 K at standard pressure, providing support for our earlier conclusion that the Khatyrka meteorite reached heterogeneous high temperatures [1100 < T(K) ≤ 1500] and then rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 Gya. The occurrences of metallic Al alloyed with Cu, Ni, and Fe raises new questions regarding conditions that can be achieved in the early solar nebula. PMID:25765857

  9. Natural quasicrystal with decagonal symmetry.

    PubMed

    Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S; Andronicos, Christopher L; Distler, Vadim V; Eddy, Michael P; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J; Steinhardt, William M; Yudovskaya, Marina; Steinhardt, Paul J

    2015-01-01

    We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al71Ni24Fe5, was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal to be identified, was found in the same meteorite. The new quasicrystal was found associated with steinhardtite (Al38Ni32Fe30), Fe-poor steinhardtite (Al50Ni40Fe10), Al-bearing trevorite (NiFe2O4) and Al-bearing taenite (FeNi). Laboratory studies of decagonal Al71Ni24Fe5 have shown that it is stable over a narrow range of temperatures, 1120 K to 1200 K at standard pressure, providing support for our earlier conclusion that the Khatyrka meteorite reached heterogeneous high temperatures [1100 < T(K) ≤ 1500] and then rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 Gya. The occurrences of metallic Al alloyed with Cu, Ni, and Fe raises new questions regarding conditions that can be achieved in the early solar nebula. PMID:25765857

  10. Subcellular neuronal quasicrystals: Implications for consciousness

    PubMed Central

    Gardiner, John

    2015-01-01

    Neuron neurotransmitter receptors are in general pentameric. This enables them to form pentagonal components in biological quasicrystals (similar to mathematical aperiodic tilings). As quasicrystals have been proposed to require quantum effects to exist this might introduce such effects as a component of neurotransmission and thus consciousness. Microtubules may play a role in the clustering of the receptors into quasicrystals, thus modulating their function and may even form quasicrystals themselves. Other quaiscrystals in neurons are potentially formed by water, cholera toxin complexes, and the cytoskeletal components actin and ankyrin. PMID:26629259

  11. Subcellular neuronal quasicrystals: Implications for consciousness.

    PubMed

    Gardiner, John

    2015-01-01

    Neuron neurotransmitter receptors are in general pentameric. This enables them to form pentagonal components in biological quasicrystals (similar to mathematical aperiodic tilings). As quasicrystals have been proposed to require quantum effects to exist this might introduce such effects as a component of neurotransmission and thus consciousness. Microtubules may play a role in the clustering of the receptors into quasicrystals, thus modulating their function and may even form quasicrystals themselves. Other quaiscrystals in neurons are potentially formed by water, cholera toxin complexes, and the cytoskeletal components actin and ankyrin. PMID:26629259

  12. Subcellular neuronal quasicrystals: Implications for consciousness

    PubMed Central

    Gardiner, John

    2015-01-01

    Neuron neurotransmitter receptors are in general pentameric. This enables them to form pentagonal components in biological quasicrystals (similar to mathematical aperiodic tilings). As quasicrystals have been proposed to require quantum effects to exist this might introduce such effects as a component of neurotransmission and thus consciousness. Microtubules may play a role in the clustering of the receptors into quasicrystals, thus modulating their function and may even form quasicrystals themselves. Other quaiscrystals in neurons are potentially formed by water, cholera toxin complexes, and the cytoskeletal components actin and ankyrin. PMID:26478770

  13. Atomic structure of the i-R -Cd quasicrystals and consequences for magnetism

    NASA Astrophysics Data System (ADS)

    Yamada, T.; Takakura, H.; Kong, T.; Das, P.; Jayasekara, W. T.; Kreyssig, A.; Beutier, G.; Canfield, P. C.; de Boissieu, M.; Goldman, A. I.

    2016-08-01

    We report on the six-dimensional (6D) structural refinement of three members of the i-R -Cd quasicrystals (R = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-YbCd5.7 quasicrystal. However, our refinements suggest that the R occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-R -Cd series and i-ScZn7.33, and their differences with i-YbCd5.7 and i-Ca15Cd85 , indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show from x-ray resonant magnetic scattering (XRMS) measurements on a set of closely related Tb1 -xYxCd6 1/1 approximants that the dilution of the magnetic R ions on the icosahedron within the Tsai-type cluster by nonmagnetic Y disrupts the commensurate magnetic ordering in the approximant phase.

  14. Synthesis and Characterization of Bulk Al-Cu-Fe Based Quasicrystals and Composites by Spray Forming

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, N. K.; Uhlenwinkel, V.; Srivastava, V. C.

    2015-06-01

    The bulk quasicrystalline (QC) materials and their composites have attracted considerable interest due to their promising mechanical properties. In the present investigation, spray forming has been used to synthesize bulk single-phase icosahedral quasicrystals and composites in Al62.5Cu25Fe12.5 system as well as in quaternary system containing 10% Sn. The elemental materials were induction melted under nitrogen cover and a billet of 250 mm in diameter and 350 mm in height was spray formed. The phase constitution of the spray-formed materials showed a bulk single-phase icosahedral quasicrystal as a major phase along with other crystalline phases. A large number of annealing twins were observed in the microstructure in ternary AlCuFe alloys. It is interesting to note that due to addition of Sn, the volume fraction of β-Al(CuFe) phase was found to increase and annealing twins were almost absent. The hardness of the single-phase AlCuFe alloy and Sn-containing composites was found to be 8.6 and 6.0 GPa, respectively, at a load of 300 g. In general, the hardness decreases with heat treatment at high temperatures. However, in case of Sn-containing alloy, hardness increases with low-temperature heat treatment. Long and hair-like cracks (Palmqvist type) are observed to form from the corner of the indentations of the ternary alloys, whereas in Sn-containing composites, the cracks are not sharp and long suggesting the enhancement of fracture toughness in the composites. Attempts have been made to understand the effect of Sn on the evolution of icosahedral phase, other crystalline phases and their composite effects on the mechanical properties.

  15. Precipitates in a quasicrystal-strengthened Al–Mn–Be–Cu alloy

    SciTech Connect

    Zupanič, Franc; Wang, Di; Gspan, Cristian; Bončina, Tonica

    2015-08-15

    In this work, an Al–Mn–Be–Cu alloy was studied containing a primary and eutectic icosahedral quasicrystalline phase in the as-cast microstructure. Special attention was given to a transmission electron microscopy investigation of precipitates formed within the aluminium solid solution (Al{sub ss}) at different temperatures. At 200 °C, only binary Al–Cu precipitates (θ′) were formed. At 300 °C, icosahedral quasicrystalline (IQC) precipitates prevailed with a crystallographic orientation relationship with the Al{sub ss.} The rods of the T-phase (Al{sub 20}Mn{sub 3}Cu{sub 2}) which were precipitated above 400 °C, also had a specific orientation relationship with the Al{sub ss}. The primary and eutectic IQC microstructural constituent started to transform rapidly to the T-phase and Be{sub 4}Al(Mn,Cu) at 500 °C. - Highlights: • In a quasicrystal-strengthened Al-alloy several types of precipitates can form. • At 200 °C, only binary Al–Cu precipitates formed (Al{sub 2}Cu-θ′). • The icosahedral quasicrystalline (IQC) precipitates prevailed at 300 °C. • T-phase (Al{sub 20}Mn{sub 3}Cu{sub 2}) precipitated at temperatures above 400 °C. • The precipitation of different phases did not have a strong effect on hardness.

  16. Topological States and Adiabatic Pumping in Quasicrystals

    NASA Astrophysics Data System (ADS)

    Kraus, Yaakov; Lahini, Yoav; Ringel, Zohar; Verbin, Mor; Zilberberg, Oded

    2012-02-01

    We find a connection between quasicrystals and topological matter, namely that quasicrystals exhibit non-trivial topological phases attributed to dimensions higher than their own [1]. Quasicrystals are materials which are neither ordered nor disordered, i.e. they exhibit only long-range order [2]. This long-range order is usually expressed as a projection from a higher dimensional ordered system. Recently, the unrelated discovery of Topological Insulators [3] defined a new type of materials classified by their topology. We show theoretically and experimentally using photonic lattices, that one-dimensional quasicrystals exhibit topologically-protected boundary states equivalent to the edge states of the two-dimensional Integer Quantum Hall Effect. We harness this property to adiabatically pump light across the quasicrystal, and generalize our results to higher dimensional systems. Hence, quasicrystals offer a new platform for the study of topological phases while their topology may better explain their surface properties.[4pt] [1] Y. E. Kraus, Y. Lahini, Z. Ringel, M. Verbin, and O. Zilberberg, arXiv:1109.5983 (2011).[0pt] [2] C. Janot, Quasicrystals (Clarendon, Oxford, 1994), 2nd ed.[0pt] [3] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010).

  17. Disorder-Enhanced Transport in Photonic Quasicrystals

    NASA Astrophysics Data System (ADS)

    Levi, Liad; Rechtsman, Mikael; Freedman, Barak; Schwartz, Tal; Manela, Ofer; Segev, Mordechai

    2011-06-01

    Quasicrystals are aperiodic structures with rotational symmetries forbidden to conventional periodic crystals; examples of quasicrystals can be found in aluminum alloys, polymers, and even ancient Islamic art. Here, we present direct experimental observation of disorder-enhanced wave transport in quasicrystals, which contrasts directly with the characteristic suppression of transport by disorder. Our experiments are carried out in photonic quasicrystals, where we find that increasing disorder leads to enhanced expansion of the beam propagating through the medium. By further increasing the disorder, we observe that the beam progresses through a regime of diffusive-like transport until it finally transitions to Anderson localization and the suppression of transport. We study this fundamental phenomenon and elucidate its origins by relating it to the basic properties of quasicrystalline media in the presence of disorder.

  18. Ordering and dynamics of the central tetrahedron in the 1/1 Zn6Sc periodic approximant to quasicrystal.

    PubMed

    Euchner, Holger; Yamada, Tsunetomo; Schober, Helmut; Rols, Stephane; Mihalkovič, Marek; Tamura, Ryuji; Ishimasa, Tsutomu; de Boissieu, Marc

    2012-10-17

    Periodic approximants to quasicrystals offer a unique opportunity to better understand the structure, physical properties and stabilizing mechanisms of their quasicrystal counterparts. We present a detailed study of the order-disorder phase transition occurring at about 160 K in the Zn(6)Sc cubic approximant to the icosahedral quasicrystal i-MgZnSc. This transition goes along with an anti-parallel ordering of the tetrahedra located at the centres of large atomic clusters, which are packed on a bcc lattice. Single crystal x-ray diffuse scattering shows that the tetrahedra display pre-transitional short range ordering above T(c) (Yamada et al 2012 in preparation). Using quasielastic neutron scattering (QENS) we clearly evidence this short range order to be dynamical in nature above T(c). The QENS data are consistent with a model of tetrahedra 'jumping' between almost equivalent positions, which is supported by molecular dynamics simulations. This demonstrates a unique dynamical flexibility of the Zn(6)Sc structure even at room temperature.

  19. Observation of topological phase transitions in photonic quasicrystals.

    PubMed

    Verbin, Mor; Zilberberg, Oded; Kraus, Yaacov E; Lahini, Yoav; Silberberg, Yaron

    2013-02-15

    Topological insulators and topological superconductors are distinguished by their bulk phase transitions and gapless states at a sharp boundary with the vacuum. Quasicrystals have recently been found to be topologically nontrivial. In quasicrystals, the bulk phase transitions occur in the same manner as standard topological materials, but their boundary phenomena are more subtle. In this Letter we directly observe bulk phase transitions, using photonic quasicrystals, by constructing a smooth boundary between topologically distinct one-dimensional quasicrystals. Moreover, we use the same method to experimentally confirm the topological equivalence between the Harper and Fibonacci quasicrystals. PMID:25166388

  20. The formation, structure, and hydrogen storage properties of titanium/zironcium/hafnium based quasicrystals and related phases

    NASA Astrophysics Data System (ADS)

    Huett, Van Thi

    Previous studies of hydrogen storage in Ti-Zr-Ni quasicrystals are reviewed and expanded. Based on the new results presented in this thesis hydrogen may be used as a probe of local structure if elastic and electronic interactions of the hydrogen atom with the lattice and other hydrogen atoms in the lattice are better understood. As-cast and as-quenched phases found in the Ti-Hf-Ni ternary system are surveyed. A high order (3/2) rational approximant to the quasicrystal and a metallic glass were some of the phases found in the as-quenched survey. These two phases were further studied showing that the 3/2 rational approximant is metastable, transforming to a stable Ti2Ni-type phase upon heating. The metallic glass found in this system has a 65°C separation between the glass transition and the first crystallization event to a nano-domained icosahedrally ordered phase. Hydrogenation studies of the 3/2 rational approximant and the metallic glass in Ti-Hf-Ni were also performed. These studies show that the structures around the hydrogen atoms are similar in both phases. The structures are also similar to the Ti-Zr-Ni quasicrystals. Other hydrogen storage methods were explored. Mechanically alloyed Ti-Zr-Ni quasicrystals and metallic glasses have a potential to be used as hydrogen storage materials. These mechanically alloyed phases do not need to have their surfaces prepared or activated for hydrogenation to occur, and show little formation of the irreversible hydride phase. Pressure composition isotherms at higher pressures than have been performed before on these alloys were examined. This required a new high-pressure Sievart's type apparatus to be built. The initial results from pressure composition isotherm measurements show that there is another pressure plateau, above the one previously found at low pressures. This higher pressure plateau is a region of pressure and temperature suitable for hydrogen storage applications.

  1. Beta cell device using icosahedral boride compounds

    DOEpatents

    Aselage, Terrence L.; Emin, David

    2002-01-01

    A beta cell for converting beta-particle energies into electrical energy having a semiconductor junction that incorporates an icosahedral boride compound selected from B.sub.12 As.sub.2, B.sub.12 P.sub.2, elemental boron having an .alpha.-rhombohedral structure, elemental boron having a .beta.-rhombohedral structure, and boron carbides of the chemical formula B.sub.12-x C.sub.3-x, where 0.15icosahedral boride compound self-heals, resisting degradation from radiation damage.

  2. Crystalline and quasicrystalline allotropes of Pb formed on the fivefold surface of icosahedral Ag-In-Yb

    SciTech Connect

    Sharma, H. R. Smerdon, J. A.; Nugent, P. J.; Ribeiro, A.; McGrath, R.; McLeod, I.; Dhanak, V. R.; Shimoda, M.; Tsai, A. P.

    2014-05-07

    Crystalline and quasicrystalline allotropes of Pb are formed by evaporation on the fivefold surface of the icosahedral (i) Ag-In-Yb quasicrystal under ultra-high vacuum. Lead grows in three dimensional quasicrystalline order and subsequently forms fivefold-twinned islands with the fcc(111) surface orientation atop of the quasicrystalline Pb. The islands exhibit specific heights (magic heights), possibly due to the confinement of electrons in the islands. We also study the adsorption behavior of C{sub 60} on the two allotropes of Pb. Scanning tunneling microcopy reveals that a high corrugation of the quasicrystalline Pb limits the diffusion of the C{sub 60} molecules and thus produces a disordered film, similar to adsorption behavior of the same molecules on the clean substrate surface. However, the sticking coefficient of C{sub 60} molecules atop the Pb islands approaches zero, regardless of the overall C{sub 60} coverage.

  3. Liquid to quasicrystal transition in bilayer water

    NASA Astrophysics Data System (ADS)

    Johnston, Jessica C.; Kastelowitz, Noah; Molinero, Valeria

    2010-10-01

    The phase behavior of confined water is a topic of intense and current interest due to its relevance in biology, geology, and materials science. Nevertheless, little is known about the phases that water forms even when confined in the simplest geometries, such as water confined between parallel surfaces. Here we use molecular dynamics simulations to compute the phase diagram of two layers of water confined between parallel non hydrogen bonding walls. This study shows that the water bilayer forms a dodecagonal quasicrystal, as well as two previously unreported bilayer crystals, one tiled exclusively by pentagonal rings. Quasicrystals, structures with long-range order but without periodicity, have never before been reported for water. The dodecagonal quasicrystal is obtained from the bilayer liquid through a reversible first-order phase transition and has diffusivity intermediate between that of the bilayer liquid and ice phases. The water quasicrystal and the ice polymorphs based on pentagons are stabilized by compression of the bilayer and are not templated by the confining surfaces, which are smooth. This demonstrates that these novel phases are intrinsically favored in bilayer water and suggests that these structures could be relevant not only for confined water but also for the wetting and properties of water at interfaces.

  4. Surfaces of Intermetallics: Quasicrystals and Beyond

    SciTech Connect

    Yuen, Chad

    2012-01-01

    The goal of this work is to characterize surfaces of intermetallics, including quasicrystals. In this work, surface characterization is primarily focused on composition and structure using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) performed under ultrahigh vacuum (UHV) conditions.

  5. Omnidirectional reflection from generalized Fibonacci quasicrystals.

    PubMed

    Barriuso, Alberto G; Monzón, Juan J; Yonte, Teresa; Felipe, Angel; Sánchez-Soto, Luis L

    2013-12-01

    We determine the optimal thicknesses for which omnidirectional reflection from generalized Fibonacci quasicrystals occurs. By capitalizing on the idea of wavelength- and angle-averaged reflectance, we assess in a consistent way the performance of the different systems. Our results indicate that some of these aperiodic arrangements can largely over-perform the conventional photonic crystals as omnidirectional reflection is concerned. PMID:24514554

  6. Structural refinement of 1/1 bcc approximants to quasicrystals: Bergman-type W(TiZrNi) and Mackay-type M(TiZrFe)

    NASA Astrophysics Data System (ADS)

    Kim, W. J.; Gibbons, P. C.; Kelton, K. F.; Yelon, W. B.

    1998-08-01

    We report the structural refinement of large-unit-cell bcc crystalline phases found in Ti-Zr-Ni and Ti-Zr-Fe alloys, which are 1/1 rational approximants of icosahedral quasicrystals in the same alloys. The structure of the stable 1/1 phase W(TiZrNi), lattice constant ao=14.317 Å, determined by a Rietveld analysis of x-ray and neutron powder diffraction data, is closely related to that of the 1/1 phases R(AlLiCu) and Bergman(AlMgZn), containing Bergman-type icosahedral clusters of atoms. Despite the similar chemistry of the 1/1 phases in Ti-Zr-Ni and Ti-Zr-Fe alloys, the 1/1 phase M(TiZrFe) contains double-shell Mackay icosahedra, like those found in the 1/1 phase α(TiCrSiO). These results provide starting structures for six-dimensional refinements of the related quasicrystals.

  7. Disordered structures of the TM-Mg-Zn 1/1 quasicrystal approximants (TM = Hf, Zr, or Ti) and chemical intergrowth.

    PubMed

    Gómez, Cesar Pay; Ohhashi, Satoshi; Yamamoto, Akiji; Tsai, An Pang

    2008-09-15

    The structures of three quasicrystal approximant phases in the TM-Mg-Zn (TM = Hf, Zr, Ti) systems with the analyzed compositions Hf5Mg18Zn77, Zr5Mg18Zn77, and Ti5.5Mg17.5Zn77 have been synthesized, and their structures have been analyzed by single-crystal X-ray diffraction. The structure analyses revealed that these cubic phases with the space group Pm3 contain two different rhombic-triacontahedral clusters. These clusters are so-called Bergman-type atomic clusters and previously known approximants of face-centered icosahedral (F-type) quasicrystals are composed only of Mackay-type clusters, thus these compounds are seen as new prototype structures. Electron density maps calculated by the maximum entropy method (MEM) show that one of the atomic clusters displays characteristic structural disorder. The disorder in these phases is related to the chemical intergrowth of different Friauf polyhedra, and the prospects of new guide lines for finding quasicrystals composed of such polyhedra are discussed.

  8. Two-Band Fibonacci Quasicrystal with Hybridization:. Exact Local GREEN’S Function Using the Renormalization-Group Method

    NASA Astrophysics Data System (ADS)

    Chakrabarti, A.; Karmakar, S. N.; Moitra, R. K.

    In this paper we present a study of the electronic properties of a one-dimensional Fibonacci chain with two hybridizing bands. Our study is motivated by recent experiments with quasicrystals in which transition metal atoms occupy positions of icosahedral symmetry. Using a recently proposed real space renormalization group scheme we make an exact analytical study of the two-band problem. We examine the effect of hybridization on the energy spectrum, the wave functions and the density of states of the Fibonacci chain. We find that the spectrum continues to remain a Cantor set even in the presence of hybridization. We conclude therefore this property of the spectrum is a purely structural effect. We present our results on the electronic density of states and show how hybridization produces additional structures in the energy spectrum.

  9. DNA Cages with Icosahedral Symmetry in Bionanotechnology

    NASA Astrophysics Data System (ADS)

    Jonoska, Nataša; Taormina, Anne; Twarock, Reidun

    Blueprints for polyhedral cages with icosahedral symmetry made of circular DNA molecules are provided. The basic rule is that every edge of the cage is met twice in opposite directions by the DNA strand(s), and vertex junctions are realized by a set of admissible junction types. As nanocontainers for cargo storage and delivery, the icosidodecahedral cages are of special interest because they have the largest volume per surface ratio of all cages discussed here.

  10. Eighteenth-century forms of quasicrystals.

    PubMed

    Pina, Carlos M; López-Acevedo, Victoria

    2016-01-01

    A careful inspection of the drawings and baked clay models created by the mineralogist Romé de L'Isle in the 18th century has revealed the existence of a number of intriguing forms with pentagonal symmetries. These forms cannot be classified in any of the 32 crystal classes. They can thus be considered the first crystallographic descriptions of polyhedral forms found in quasicrystals two centuries later. This paper presents a symmetry analysis of the fascinating drawings and clay models with pentagonal symmetries described in the book Cristallographie published in 1783 by Romé de L'Isle, as well as a comparison with quasicrystals recently synthesized. The paper also briefly discusses what could induce Romé de L'Isle to consider forms with pentagonal symmetries as plausible crystal forms. PMID:26697870

  11. Discussion on the surface science of quasicrystals

    SciTech Connect

    Thiel, P.A.

    2008-05-01

    This paper contains a short review of four aspects of the surface science of quasicrystals, together with a list of challenges for the scientific community in the near future. The first issue concerns the ability of surface science to shed light on bulk atomic structure. The second is the use of surfaces as quasiperiodic templates, particularly for films of periodic metals. Here, enforcing quasiperiodicity in the film may lead to unusual magnetic, tribological or adsorption properties. The third aspect concerns the effects of surface phasons and phonons on dynamical interactions with adsorbates, such as sticking coefficient, as well as on diffusion between the surface and near-surface region. The final area is tribology, where studies of quasicrystals have suggested that both adhesion and phononic friction may be important.

  12. Phase formation, liquid structure, and physical properties of amorphous and quasicrystal-forming alloys

    NASA Astrophysics Data System (ADS)

    Wessels, Victor Medgar

    2009-12-01

    Since the discovery of quasicrystals in 1985 and the development of commercially viable bulk metallic glasses (BMGs) in the mid 1990's a great deal of attention has been given to the characterization of new alloys with desirable properties, such as larger amorphous casting thickness, higher mechanical strength, or hydrogen storage capacity. Here, the results of a number of investigations into the structures and properties of some noncrystalline solid alloys will be presented and analyzed. Beamline electrostatic levitation (BESL), a method for determining supercooled liquid structure and phase formation in-situ, was used. Using BESL, the development of structural and chemical inhomogeneity was observed in supercooled liquid Cu46Zr 54 (a BMG when cast) with an onset at 845 +/- 5°C, providing experimental support for structural changes determined from molecular dynamics (MD) simulations of these liquids. Differing segregation of Hf and Zr atoms was observed in solidified Ti45Zr(38-x)HfxNi 17 using scanning electron microscopy (SEM), and correlated to a previously observed, sharp boundary in phase formation near x = 19 that was further investigated using BESL. In addition to the BESL studies, results will be presented and discussed on changes in microstructure and devitrification mechanisms with the addition of Ag in Mg65Cu(25-x)AgxGd 10 BMGs, interesting for their light weight and resistance to oxygen during casting, using transmission electron microscopy (TEM), SEM, and differential scanning calorimetry (DSC). Previous, preliminary results on the hydrogen storage capacity of icosahedral quasicrystal Ti45Zr38Ni 17 were re-examined, using an improved apparatus and analysis method developed as part of this work, and the previous results found to be in error.

  13. Photonic quasi-crystal terahertz lasers

    NASA Astrophysics Data System (ADS)

    Vitiello, Miriam Serena; Nobile, Michele; Ronzani, Alberto; Tredicucci, Alessandro; Castellano, Fabrizio; Talora, Valerio; Li, Lianhe; Linfield, Edmund H.; Davies, A. Giles

    2014-12-01

    Quasi-crystal structures do not present a full spatial periodicity but are nevertheless constructed starting from deterministic generation rules. When made of different dielectric materials, they often possess fascinating optical properties, which lie between those of periodic photonic crystals and those of a random arrangement of scatterers. Indeed, they can support extended band-like states with pseudogaps in the energy spectrum, but lacking translational invariance, they also intrinsically feature a pattern of ‘defects’, which can give rise to critically localized modes confined in space, similar to Anderson modes in random structures. If used as laser resonators, photonic quasi-crystals open up design possibilities that are simply not possible in a conventional periodic photonic crystal. In this letter, we exploit the concept of a 2D photonic quasi crystal in an electrically injected laser; specifically, we pattern the top surface of a terahertz quantum-cascade laser with a Penrose tiling of pentagonal rotational symmetry, reaching 0.1-0.2% wall-plug efficiencies and 65 mW peak output powers with characteristic surface-emitting conical beam profiles, result of the rich quasi-crystal Fourier spectrum.

  14. Local density fluctuations and hyperuniformity in quasicrystals

    NASA Astrophysics Data System (ADS)

    Oğuz, Erdal Celal; Torquato, Salvatore

    2015-03-01

    Local density fluctuations in many-body systems are of fundamental importance throughout various scientific disciplines, including physics, materials science, number theory and biology. In a point pattern, let the variance associated with the number of points contained in a spherical window of radius R be denoted by σ2 (R) . Hyperuniform point patterns in d dimensions do not possess infinite-wavelength fluctuations or, equivalently, possess a number variance that grows more slowly than the window volume, i.e., Rd. Hyperuniform systems include all infinite periodic structures, aperiodic quasicrystals, and some special disordered systems. Previous investigations showed that the number variance for large R in hyperuniform systems serves as a useful metric to rank order systems according to the degree to which large-scale density fluctuations are suppressed. In this work, we investigate the number variance of two-dimensional quasicrystals with a variety of different rotational symmetries. We study how the number variance depends on the rotational symmetry and local isomorphism class of the quasicrystal. We compare these results to a number of different periodic systems as well as disordered hyperuniform systems. ECO acknowledges the support from the German Research Foundation (DFG).

  15. Negative Refraction and Imaging with Quasicrystals

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangdong; Feng, Zhifang; Wang, Yiquan; Li, Zhi-Yuan; Cheng, Bingying; Zhang, Dao-Zhong

    Recently, negative refraction of electromagnetic waves in photonic crystals was demonstrated experimentally and subwavelength images were observed. However, these investigations all focused on the periodic structure. In fact, the negative refraction exists not only in periodic structure, but also in nonperiodic structures such as quasicrystalline arrangement of dielectric. Here, we discuss the negative refraction and imaging based on some transparent quasicrystalline photonic structures. The high-symmetric photonic quasicrystals (PQCs) can exhibit an effective refractive index close to -1 in a certain frequency window. The index shows small spatial dispersion, consistent with the nearly homogeneous geometry of the quasicrystal. Thus, a flat lens based on the 2D PQCs can form a non-near-field image whose position varies with the thickness of the sample and the source distance. At the same time, the focus and image for both polarized waves at the same structure and parameters can also be realized by such a flat lens. In addition, the negative refraction behaviors of acoustic wave in phononic quasicrystal are also discussed.

  16. Photonic quasi-crystal terahertz lasers

    PubMed Central

    Vitiello, Miriam Serena; Nobile, Michele; Ronzani, Alberto; Tredicucci, Alessandro; Castellano, Fabrizio; Talora, Valerio; Li, Lianhe; Linfield, Edmund H.; Davies, A. Giles

    2014-01-01

    Quasi-crystal structures do not present a full spatial periodicity but are nevertheless constructed starting from deterministic generation rules. When made of different dielectric materials, they often possess fascinating optical properties, which lie between those of periodic photonic crystals and those of a random arrangement of scatterers. Indeed, they can support extended band-like states with pseudogaps in the energy spectrum, but lacking translational invariance, they also intrinsically feature a pattern of ‘defects’, which can give rise to critically localized modes confined in space, similar to Anderson modes in random structures. If used as laser resonators, photonic quasi-crystals open up design possibilities that are simply not possible in a conventional periodic photonic crystal. In this letter, we exploit the concept of a 2D photonic quasi crystal in an electrically injected laser; specifically, we pattern the top surface of a terahertz quantum-cascade laser with a Penrose tiling of pentagonal rotational symmetry, reaching 0.1–0.2% wall-plug efficiencies and 65 mW peak output powers with characteristic surface-emitting conical beam profiles, result of the rich quasi-crystal Fourier spectrum. PMID:25523102

  17. Levitated crystals and quasicrystals of metamaterials

    SciTech Connect

    Wang, Zhehui; Morris, Christopher; Goree, John A

    2012-07-25

    New scientific and technological opportunities exist by marrying dusty plasma research with metamaterials. Specifically, by balancing control and self-assembly, certain laboratory plasmas can become a generic levitation platform for novel structure formation and nanomaterial synthesis. We propose to experimentally investigate two dimensional (2D) and three dimensional (3D) levitated structures of metamaterials and their properties. Such structures can self assemble in laboratory plasmas, similar to levitated dust crystals which were discovered in the mid 1990's. Laboratory plasma platform for metamaterial formation eliminates substrates upon which most metamaterials have to be supported. Three types of experiments, with similar setups, are discussed here. Levitated crystal structures of metamaterials using anisotropic microparticles are the most basic of the three. The second experiment examines whether quasicrystals of metamaterials are possible. Quasicrystals, discovered in the 1980's, possess so-called forbidden symmetries according to the conventional crystallography. The proposed experiment could answer many fundamental questions about structural, thermal and dynamical properties of quasicrystals. And finally, how to use nanoparticle coated microparticles to synthesize very long carbon nanotubes is also described. All of the experiments can fit inside a standard International Space Station locker with dimensions of 8-inch x 17-inch X 18-inch. Microgravity environment is deemed essential in particular for large 3D structures and very long carbon nanotube synthesis.

  18. Thin Films of Quasicrystals: Optical, Electronic, and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Symko, Orest G.

    1998-03-01

    In order to extend some of the unusual properties of quasicrystals toward practical applications and to study fundamental aspects of these properties, we have developed a technology for the deposition of high quality thin films of quasicrystals on a variety of substrates. Mechanical support for the thin films is provided by the substrate as bulk quasicrystals are brittle. We have applied the thin films to studies of their optical, electrical, and mechanical properties as well as to coatings of biomedical devices. An important characteristic of a quasicrystal is its pseudogap in the electronic density of states; it is determined directly from optical transmission measurements. Optical and mechanical characteristics of the thin films provide strong support for the cluster nature of quasicrystals and emphasize their importance for coatings. When used in biomedical devices, thin film quasicrystalline coatings show remarkable strength, low friction, and non-stick behavior. This work was in collaboration with W. Park, E. Abdel-Rahman, and T. Klein.

  19. Topological Quantum Hashing with the Icosahedral Group

    NASA Astrophysics Data System (ADS)

    Burrello, Michele; Xu, Haitan; Mussardo, Giuseppe; Wan, Xin

    2010-04-01

    We study an efficient algorithm to hash any single-qubit gate into a braid of Fibonacci anyons represented by a product of icosahedral group elements. By representing the group elements by braid segments of different lengths, we introduce a series of pseudogroups. Joining these braid segments in a renormalization group fashion, we obtain a Gaussian unitary ensemble of random-matrix representations of braids. With braids of length O(log⁡2(1/ɛ)), we can approximate all SU(2) matrices to an average error ɛ with a cost of O(log⁡(1/ɛ)) in time. The algorithm is applicable to generic quantum compiling.

  20. Method of making an icosahedral boride structure

    DOEpatents

    Hersee, Stephen D.; Wang, Ronghua; Zubia, David; Aselage, Terrance L.; Emin, David

    2005-01-11

    A method for fabricating thin films of an icosahedral boride on a silicon carbide (SiC) substrate is provided. Preferably the icosahedral boride layer is comprised of either boron phosphide (B.sub.12 P.sub.2) or boron arsenide (B.sub.12 As.sub.2). The provided method achieves improved film crystallinity and lowered impurity concentrations. In one aspect, an epitaxially grown layer of B.sub.12 P.sub.2 with a base layer or substrate of SiC is provided. In another aspect, an epitaxially grown layer of B.sub.12 As.sub.2 with a base layer or substrate of SiC is provided. In yet another aspect, thin films of B.sub.12 P.sub.2 or B.sub.12 As.sub.2 are formed on SiC using CVD or other vapor deposition means. If CVD techniques are employed, preferably the deposition temperature is above 1050.degree. C., more preferably in the range of 1100.degree. C. to 1400.degree. C., and still more preferably approximately 1150.degree. C.

  1. Fibonacci optical lattices for tunable quantum quasicrystals

    NASA Astrophysics Data System (ADS)

    Singh, K.; Saha, K.; Parameswaran, S. A.; Weld, D. M.

    2015-12-01

    We describe a quasiperiodic optical lattice, created by a physical realization of the abstract cut-and-project construction underlying all quasicrystals. The resulting potential is a generalization of the Fibonacci tiling. Calculation of the energies and wave functions of ultracold atoms loaded into such a lattice demonstrate a multifractal energy spectrum, a singular continuous momentum-space structure, and the existence of controllable edge states. These results open the door to cold atom quantum simulation experiments in tunable or dynamic quasicrystalline potentials, including topological pumping of edge states and phasonic spectroscopy.

  2. Preparation and wear resistance of Ti-Zr-Ni quasicrystal and polyamide composite materials

    NASA Astrophysics Data System (ADS)

    Wang, Xinlu; Li, Xuesong; Zhang, Zhenjiang; Zhang, Shanshan; Liu, Wanqiang; Wang, Limin

    2011-07-01

    Ti-Zr-Ni icosahedral quasicrystal powders (Ti-QC), prepared by mechanical alloying and then annealing in a vacuum furnace, were used as a novel filler material in polyamide 12 (PA12). The melt processability of the composite was studied using a Haake torque rheometer. This indicates that PA12/Ti-QC composites can be melt-processed into a wear-resistant material. Further, these composites, fabricated by compression molding, were tested in sliding wear against a polished bearing steel counterface. The results from wear testing show that the addition of Ti-QC filler to PA12 enhances wear resistance and reduces volume loss by half compared with neat PA12. Furthermore, it is found that the hardness of the composite increases with increasing content of Ti-QC filler. In addition, PA12/Ti-QC composites exhibit a slightly higher crystallization temperature and better thermal stability than PA12. These combined results demonstrate that Ti-QC filler may be a desirable alternative when attempting to increase the wear resistance of PA12.

  3. Emergent quasicrystals in strongly correlated systems

    NASA Astrophysics Data System (ADS)

    Sagi, Eran; Nussinov, Zohar

    2016-07-01

    Commensurability is of paramount importance in numerous strongly interacting electronic systems. In the fractional quantum Hall effect, a rich cascade of increasingly narrow plateaux appear at larger denominator filling fractions. Rich commensurate structures also emerge, at certain filling fractions, in high temperature superconductors and other electronic systems. A natural question concerns the character of these and other electronic systems at irrational filling fractions. Here we demonstrate that quasicrystalline structures naturally emerge in these situations, and trigger behaviors not typically expected of periodic systems. We first show that irrationally filled quantum Hall systems cross over into quasiperiodically ordered configuration in the thin-torus limit. Using known properties of quasicrystals, we argue that these states are unstable against the effects of disorder, in agreement with the existence of quantum Hall plateaux. We then study analogous physical situations in a system of cold Rydberg atoms placed on an optical lattice. Such an experimental setup is generally disorder free, and can therefore be used to detect the emergent quasicrystals we predict. We discuss similar situations in the Falicov-Kimball model, where known exact results can be used to establish quasicrystalline structures in one and two dimensions. We briefly speculate on possible relations between our theoretical findings and the existence of glassy dynamics and other features of strongly correlated electronic systems.

  4. Mechanical properties of icosahedral virus capsids

    NASA Astrophysics Data System (ADS)

    Vliegenthart, G. A.; Gompper, G.

    2007-12-01

    Virus capsids are self-assembled protein shells in the size range of 10 to 100 nanometers. The shells of DNA-viruses have to sustain large internal pressures while encapsulating and protecting the viral DNA. We employ computer simulations to study the mechanical properties of crystalline shells with icosahedral symmetry that serve as a model for virus capsids. The shells are positioned on a substrate and deformed by a uni-axial force excerted by a small bead. We predict the elastic response for small deformations, and the buckling transitions at large deformations. Both are found to depend strongly on the number N of elementary building blocks (capsomers), and the Föppl-von Kármán number γ which characterizes the relative importance of shear and bending elasticity.

  5. Highly symmetric Mn sites in icosahedral Ti-Mn

    SciTech Connect

    Jeong, E.; Holzer, J.C.; Carlsson, A.E.; Conradi, M.S.; Fedders, P.A.; Kelton, K.F. )

    1990-01-15

    We find that the {sup 55}Mn NMR linewidth and Knight shift of icosahedral Ti{sub 63}Mn{sub 37} ({ital i}-TiMn) are identical to those of the crystalline phases obtained upon annealing. Comparison of the linewidth in {ital i}-TiMn and a bcc Ti-Mn solid solution shows that the Mn sites in both phases have a nearly cubic or higher symmetry. These measurements and our analysis provide strong evidence for a large density of structurally ordered, highly symmetric sites in an icosahedral alloy and demonstrate that a high degree of structural disorder is not an intrinsic property of the icosahedral phase.

  6. Dynamical Diffraction and X-Ray Standing Waves from Atomic Planes Normal to a Twofold Symmetry Axis of the Quasicrystal AlPdMn

    SciTech Connect

    Jach, T.; Zhang, Y.; Colella, R.; de Boissieu, M.; Boudard, M.; Goldman, A.I.; Lograsso, T.A.; Delaney, D.W.; Kycia, S.

    1999-04-01

    We have observed dynamical diffraction in the 0240{ovr 2}4 and 0460{ovr 4}6 reflections of the icosahedral quasicrystal AlPdMn in the back-reflection geometry ({theta}{sub B}=90{degree} ). The x-ray fluorescence from the Al and Pd atoms exhibits strong standing wave behavior, similar to that observed in crystalline materials. The data indicate a long-range order of each species of atoms, with the coherent positions attributable to distributions of the Al and Pd, which we compare to a centrosymmetric model. We observe deviations from the model which imply small departures from inversion symmetry along the twofold symmetry axis and from the expected coherent fractions for Al. {copyright} {ital 1999} {ital The American Physical Society}

  7. Surface-reconstructed icosahedral structures for lead clusters

    NASA Astrophysics Data System (ADS)

    Hendy, Shaun C.; Doye, Jonathan P.

    2002-12-01

    We describe a family of icosahedral structures for lead clusters. In general, structures in this family contain a Mackay icosahedral core with a reconstructed two-shell outer-layer. This family includes the anti-Mackay icosahedra, which has a Mackay icosahedral core but with most of the surface atoms in hexagonal close-packed positions. Using a many-body glue potential for lead, we identify two icosahedral structures in this family which have the lowest energies of any known structure in the size range from 900 to 15 000 lead atoms. We show that these structures are stabilized by a feature of the many-body glue part of the interatomic potential.

  8. Relaxed crystalline and icosahedral molecular clusters - CO2

    NASA Astrophysics Data System (ADS)

    van de Waal, B. W.

    1987-05-01

    The differences between the icosahedral arrangement and crystalline packing following the addition of more molecule shells are examined. The applicability of the Mackay (1962) procedure for constructing concentric icosahedra is evaluated. The relaxation of molecule crystal fragments by shifting molecular positions following deformation is studied. The relative energy difference between relaxed crystalline and icosahedral structure as a function of cluster size is calculated as ranging from 2.4 to 0.8 percent. The evolution of shells in the relaxed crystalline growth sequence reveals that the inner shells become crystalline when more shells are added; the icosahedral deformation is more prominent in the outer shell, but decreases with increasing cluster size. It is suggested that, when multilayer icosahedral structures are larger than critical size, they do not transform as a whole into a crystalline arrangement but develop a growing crystalline core.

  9. Syntheses optimization, structural and thermoelectric properties of 1/1 Tsai-type quasicrystal approximants in RE-Au-SM systems (RE=Yb, Gd and SM=Si, Ge).

    PubMed

    Gebresenbut, Girma Hailu; Tamura, Ryuji; Eklöf, Daniel; Gómez, Cesar Pay

    2013-04-01

    Yb-Cd (Tsai-type) quasicrystals constitute the largest icosahedral quasicrystal family where Yb can be replaced by other rare earth elements (RE) and Cd by pairs of p- and d-block elements. YbCd6 is a prototype 1/1 Tsai-type approximant phase which has a similar local structure to the Yb-Cd quasicrystal. In this study, the syntheses of Yb15.78Au65.22Ge19.00, Gd14.34Au67.16Ge18.5 and Gd14.19Au69.87Si15.94 Tsai-type 1/1 quasicrystal approximants are optimized using the self-flux technique. The crystal structures of the compounds are refined by collecting single crystal x-ray diffraction data. The structural refinements indicated that the compounds are essentially isostructural with some differences at their cluster centers. The basic polyhedral cluster unit in all the three compounds can be described by concentric shells of icosahedra symmetry and of disordered tetrahedra and/or a rare earth atom at the cluster center. Furthermore, the thermoelectric properties of the compounds are probed and their dimensionless figures of merit are calculated at different temperatures. A significant difference is observed in their thermoelectric properties, which could arise due to the slight difference in their crystal structure and chemical composition, as we move from Ge to Si and/or Gd to Yb. Therefore, this study shows the systematic effect of the chemical substitution of structurally similar materials on their thermoelectric properties.

  10. Magnetic moments and non-Fermi-liquid behavior in quasicrystals

    NASA Astrophysics Data System (ADS)

    Andrade, Eric

    Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15, we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures, leading to a power-law distribution of Kondo temperatures, accompanied by a non-Fermi-liquid behavior, in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. This work was supported by FAPESP (Brazil) Grant No. 2013/00681-8.

  11. Spin waves in one-dimensional bicomponent magnonic quasicrystals

    NASA Astrophysics Data System (ADS)

    Rychły, J.; Kłos, J. W.; Mruczkiewicz, M.; Krawczyk, M.

    2015-08-01

    We studied a finite Fibonacci sequence of Co and Py stripes aligned side by side and in direct contact with each other. Calculations based on a continuous model, including exchange and dipole interactions, were performed for structures feasible for fabrication and characterization of the main properties of magnonic quasicrystals. We have shown the fractal structure of the magnonic spectrum with a number of magnonic gaps of different widths. Moreover, localization of spin waves in quasicrystals and the existence of surface spin waves in finite quaiscrystal structure is demonstrated.

  12. The RNA of turnip yellow mosaic virus exhibits icosahedral order

    SciTech Connect

    Larson, Steven B.; Lucas, Robert W.; Greenwood, Aaron; McPherson, Alexander . E-mail: amcphers@uci.edu

    2005-04-10

    Difference electron density maps, based on structure factor amplitudes and experimental phases from crystals of wild-type turnip yellow mosaic virus and those of empty capsids prepared by freeze-thawing, show a large portion of the encapsidated RNA to have an icosahedral distribution. Four unique segments of base-paired, double-helical RNA, one to two turns in length, lie between 33-A and 101-A radius and are organized about either 2-fold or 5-fold icosahedral axes. In addition, single-stranded loops of RNA invade the pentameric and hexameric capsomeres where they contact the interior capsid surface. The remaining RNA, not seen in electron density maps, must serve as connecting links between these secondary structural elements and is likely icosahedrally disordered. The distribution of RNA observed crystallographically appears to be in agreement with models based on biochemical data and secondary structural analyses.

  13. Group Representations and Multinomial Combinatorics of the Icosahedral Symmetry

    SciTech Connect

    Balasubramanian, K

    2004-02-02

    The icosahedral symmetry is one of the most intriguing symmetries, as it not only presents challenge but it appears in many fullerenes and high energetic materials such as the dodecahedral N{sub 20}. We have considered the combinatorics of all irreducible representations of the icosahedral symmetry for a number of multinomial partitions for vertex, face and edge colorings in this work. We have constructed the combinatorial tables for all irreducible representations for various multinomial partitions of colorings for the vertices, edge and faces of the icosahedron. These techniques should have important applications to enumerations and spectroscopy of fullerenes and high-energy materials such as N{sub 20}.

  14. Degenerate Quasicrystal of Hard Triangular Bipyramids Stabilized by Entropic Forces

    NASA Astrophysics Data System (ADS)

    Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon

    2012-02-01

    The assembly of hard polyhedra into novel ordered structures has recently received much attention. Here we focus on triangular bipyramids (TBPs)- i.e. dimers of hard tetrahedra- which pack densely in a simple triclinic crystal with two particles per unit cell [1]. This packing is referred to as the TBP crystal. We show that hard TBPs do not form this densest packing in simulation. Instead, they assemble into a different, far more complicated structure, a dodecagonal quasicrystal, which, in the level of monomers, is identical to the quasicrystal recently discovered in the hard tetrahedron system [2], but the way that tetrahedra pair into TBPs in the nearest neighbor network is random, making it the first degenerate quasicrystal reported in the literature [3]. This notion of degeneracy is in the level of decorating individual tiles and is different from the degeneracy of a quasiperiodic random tiling arising from phason flips [4]. The (3.4.3^2.4) approximant of the quasicrystal is shown to be more stable than the TBP crystal at densities below 79.7%.[4pt] [1] Chen ER, Engel M, Sharon SC, Disc. Comp. Geom. 44:253 (2010).[0pt] [2] Haji-Akbari A, Engel M, et al. Nature 462:773 (2009).[0pt] [3] Haji-Akbari A, Engel M, Glotzer SC, arXiv:1106.5561 [PRL, in press].[0pt] [4] Elser V, PRL 54: 1730 (1985)

  15. Properties- and applications of quasicrystals and complex metallic alloys.

    PubMed

    Dubois, Jean-Marie

    2012-10-21

    This article aims at an account of what is known about the potential for applications of quasicrystals and related compounds, the so-called family of Complex Metallic Alloys (CMAs‡). Attention is focused at aluminium-based CMAs, which comprise a large number of crystalline compounds and quasicrystals made of aluminium alloyed with transition metals (like Fe or Cu) or normal metals like Mg. Depending on composition, the structural complexity varies from a few atoms per unit cell up to thousands of atoms. Quasicrystals appear then as CMAs of ultimate complexity and exhibit a lattice that shows no periodicity anymore in the usual 3-dimensional space. Properties change dramatically with lattice complexity and turn the metal-type behaviour of simple Al-based crystals into a far more complex behaviour, with a fingerprint of semi-conductors that may be exploited in various applications, potential or realised. An account of the ones known to the author is given in the light of the relevant properties, namely light absorption, reduced adhesion and friction, heat insulation, reinforcement of composites for mechanical devices, and few more exotic ones. The role played by the search for applications of quasicrystals in the development of the field is briefly addressed in the concluding section.

  16. TOPICAL REVIEW: Raman effect in icosahedral boron-rich solids

    NASA Astrophysics Data System (ADS)

    Werheit, Helmut; Filipov, Volodymyr; Kuhlmann, Udo; Schwarz, Ulrich; Armbrüster, Marc; Leithe-Jasper, Andreas; Tanaka, Takaho; Higashi, Iwami; Lundström, Torsten; Gurin, Vladimir N.; Korsukova, Maria M.

    2010-04-01

    We present Raman spectra of numerous icosahedral boron-rich solids having the structure of α-rhombohedral, β-rhombohedral, α-tetragonal, β-tetragonal, YB66, orthorhombic or amorphous boron. The spectra were newly measured and, in some cases, compared with reported data and discussed. We emphasize the importance of a high signal-to-noise ratio in the Raman spectra for detecting weak effects evoked by the modification of compounds, accommodation of interstitial atoms and other structural defects. Vibrations of the icosahedra, occurring in all the spectra, are interpreted using the description of modes in α-rhombohedral boron by Beckel et al. The Raman spectrum of boron carbide is largely clarified. Relative intra- and inter-icosahedral bonding forces are estimated for the different structural groups and for vanadium-doped β-rhombohedral boron. The validity of Badger's rule is demonstrated for the force constants of inter-icosahedral B-B bonds, whereas the agreement is less satisfactory for the intra-icosahedral B-B bonds.

  17. Icosahedral phase stabilities in Al-Cu-Ru alloys

    SciTech Connect

    Shield, J.E.; Hoppe, C.; McCallum, R.W.; Goldman, A.I. ); Kelton, K.F.; Gibbons, P.C. )

    1992-02-01

    By examining a wide region of the Al-Cu-Ru phase diagram, a thorough analysis of the compositional and thermal stability of the icosahedral phase has been completed. The primary solidification product of rapid solidification was a topologically and chemically disordered icosahedral phase with an extensive compositional region. Crystallization through exothermic events of the as-solidified materials produced crystalline phases, without the formation of the face-centered-icosahedral (FCI) phase. However, the FCI phase does form at higher temperatures through an endothermic reaction, indicating that it is a stable phase of the system, but only at elevated temperatures. Of the alloys studied, the FCI phase field was found to encompass Al{sub 65}Cu{sub 23}Ru{sub 12}, Al{sub 65}Cu{sub 20}Ru{sub 15}, Al{sub 70}Cu{sub 20}Ru{sub 10}, and Al{sub 70}Cu{sub 15}Ru{sub 15}. The transformation to the FCI phase involves an intermediate approximant phase that is very similar to the FCI structure. Also, a cubic approximant containing atomic arrangements with local icosahedral symmetry similar to {alpha}-Al Mn Si was determined to exist near the FCI phase field.

  18. Crystallography of decahedral and icosahedral particles. II - High symmetry orientations

    NASA Technical Reports Server (NTRS)

    Yang, C. Y.; Yacaman, M. J.; Heinemann, K.

    1979-01-01

    Based on the exact crystal structure of decahedral and icosahedral particles, high energy electron diffraction patterns and image profiles have been derived for various high symmetry orientations of the particles with respect to the incident beam. These results form a basis for the identification of small metal particle structures with advanced methods of transmission electron microscopy.

  19. Coherent coexistence of nanodiamonds and carbon onions in icosahedral core-shell particles

    SciTech Connect

    Shevchenko, Vladimir Ya. Madison, Alexey E.; Mackay, Alan L.

    2007-03-01

    In icosahedral carbon nanoparticles, the diamond-like core can undergo a reversible topological transition into and coexist coherently with the onion shells. The general approach for describing and designing complex hierarchical icosahedral structures is discussed. Structural models of icosahedral carbon nanoparticles in which the local arrangement of atoms is virtually identical to that in diamond are derived. It is shown that icosahedral diamond-like particles can be transformed into onion-like shell structures (and vice versa) by the consecutive smoothing (puckering) of atomic networks without disturbance of their topological integrity. The possibility of coherent coexistence of icosahedral diamond-like core with onion shells is shown.

  20. Green's functions of one-dimensional quasicrystal bi-material with piezoelectric effect

    NASA Astrophysics Data System (ADS)

    Zhang, Liangliang; Wu, Di; Xu, Wenshuai; Yang, Lianzhi; Ricoeur, Andreas; Wang, Zhibin; Gao, Yang

    2016-09-01

    Based on the Stroh formalism of one-dimensional quasicrystals with piezoelectric effect, the problems of an infinite plane composed of two different quasicrystal half-planes are taken into account. The solutions of the internal and interfacial Green's functions of quasicrystal bi-material are obtained. Moreover, numerical examples are analyzed for a quasicrystal bi-material subjected to line forces or line dislocations, showing the contour maps of the coupled fields. The impacts of changing material constants on the coupled field components are investigated.

  1. Influence factors of polarization-independent focusing by octagonal photonic quasicrystal

    NASA Astrophysics Data System (ADS)

    Ren, K.; Ren, X. B.

    2011-04-01

    The focusing property of electromagnetic wave is investigated by a flat slab made of octagonal photonic quasicrystal. We obtain polarization-independent focusing by use of the all-dielectric photonic quasicrystal. The influence of geometrical factors of photonic quasicrystal on the focusing property for TM and TE polarizations is explored in detail. The results show that two orthogonal polarizations have a common focus point only under certain proper condition. Our results may be a useful guidance for the fabrication of lens devices capable of polarization-independent focusing by photonic quasicrystal.

  2. Composition-driven spin glass to ferromagnetic transition in the quasicrystal approximant Au-Al-Gd

    NASA Astrophysics Data System (ADS)

    Ishikawa, A.; Hiroto, T.; Tokiwa, K.; Fujii, T.; Tamura, R.

    2016-01-01

    We investigated the composition dependence of the magnetic susceptibility of the quasicrystal approximant Au-Al-Gd. A composition-driven ferromagnetic transition is observed in a quasicrystal approximant, which is attributed to the Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation via a variation in the Fermi wave vector. The ferromagnetic transition is most simply understood as a result of the close matching of the nearest and second-nearest spin distances with the maximum positions of the RKKY potential. The present work provides an idea that allows us to tailor the magnetic order via the electron concentration in quasicrystal approximants as well as in quasicrystals.

  3. Optical Mode Control by Geometric Phase in Quasicrystal Metasurface

    NASA Astrophysics Data System (ADS)

    Yulevich, Igor; Maguid, Elhanan; Shitrit, Nir; Veksler, Dekel; Kleiner, Vladimir; Hasman, Erez

    2015-11-01

    We report on the observation of optical spin-controlled modes from a quasicrystalline metasurface as a result of an aperiodic geometric phase induced by anisotropic subwavelength structure. When geometric phase defects are introduced in the aperiodic structured surface, the modes exhibit polarization helicity dependence resulting in the optical spin-Hall effect. The radiative thermal dispersion bands from a quasicrystal structure are studied where the observed bands arise from the optical spin-orbit interaction induced by the aperiodic space-variant orientations of anisotropic antennas. The optical spin-flip behavior of the revealed modes that arise from the geometric phase pickup is experimentally observed within the visible spectrum by measuring the spin-projected diffraction patterns. The introduced ability to manipulate the light-matter interaction of quasicrystals in a spin-dependent manner provides the route for molding light via spin-optical aperiodic artificial planar surfaces.

  4. Optical Mode Control by Geometric Phase in Quasicrystal Metasurface.

    PubMed

    Yulevich, Igor; Maguid, Elhanan; Shitrit, Nir; Veksler, Dekel; Kleiner, Vladimir; Hasman, Erez

    2015-11-13

    We report on the observation of optical spin-controlled modes from a quasicrystalline metasurface as a result of an aperiodic geometric phase induced by anisotropic subwavelength structure. When geometric phase defects are introduced in the aperiodic structured surface, the modes exhibit polarization helicity dependence resulting in the optical spin-Hall effect. The radiative thermal dispersion bands from a quasicrystal structure are studied where the observed bands arise from the optical spin-orbit interaction induced by the aperiodic space-variant orientations of anisotropic antennas. The optical spin-flip behavior of the revealed modes that arise from the geometric phase pickup is experimentally observed within the visible spectrum by measuring the spin-projected diffraction patterns. The introduced ability to manipulate the light-matter interaction of quasicrystals in a spin-dependent manner provides the route for molding light via spin-optical aperiodic artificial planar surfaces.

  5. Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals

    NASA Astrophysics Data System (ADS)

    Otsuki, Junya; Kusunose, Hiroaki

    2016-07-01

    A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.

  6. Encapsulation of a polymer by an icosahedral virus

    PubMed Central

    Elrad, Oren M.; Hagan, Michael F.

    2011-01-01

    The coat proteins of many viruses spontaneously form icosahedral capsids around nucleic acids or other polymers. Elucidating the role of the packaged polymer in capsid formation could promote biomedical efforts to block viral replication and enable use of capsids in nanomaterials applications. To this end, we perform Brownian dynamics on a coarse-grained model that describes the dynamics of icosahedral capsid assembly around a flexible polymer. We identify several mechanisms by which the polymer plays an active role in its encapsulation, including cooperative polymer-protein motions. These mechanisms are related to experimentally controllable parameters such as polymer length, protein concentration, and solution conditions. Furthermore, the simulations demonstrate that assembly mechanisms are correlated to encapsulation efficiency, and we present a phase diagram that predicts assembly outcomes as a function of experimental parameters. We anticipate that our simulation results will provide a framework for designing in vitro assembly experiments on single-stranded RNA virus capsids. PMID:21149971

  7. Electronic transport in polycrystalline samples of icosahedral phases

    NASA Astrophysics Data System (ADS)

    Vekilov, Yu. Kh.; Chernikov, M. A.; Dolinichek, Ya.

    2016-01-01

    The low-temperature electronic transport in polycrystals of quasicrystalline phases with an icosahedral structure has been analyzed within the model of the granular electronic system. In this model, the grains (drops) of a metallic icosahedral phase are surrounded by extended defects and grain boundaries, which create an insulating environment. The electron transport in this model is determined by the size quantization of electronic states inside metallic grains, by intergranular tunneling, and by electrostatic barriers. Depending on the temperature and structural state of the system, the hopping conductivity with variable lengths of jumps in the Efros-Shklovskii or Mott regime is observed with predominantly elastic cotunneling. In the case of strong intergranular coupling, the system passes into the metallic regime with the exponential temperature dependence of the electrical conductivity.

  8. Virus templated plasmonic nanoclusters with icosahedral symmetry via directed assembly

    NASA Astrophysics Data System (ADS)

    Ratna, Banahalli; Fontana, Jake; Dressick, Walter; Phelps, Jamie; Johnson, John; Sampson, Travian; Rendell, Ronald; Soto, Carissa

    2015-03-01

    Controlling the spatial and orientational order of plasmonic nanoparticles may lead to structures with novel electromagnetic properties and applications such as sub-wavelength imaging and ultra-sensitive chemical sensors. Here we report the directed assembly of three-dimensional, icosahedral plasmonic nanoclusters with resonances at visible wavelengths. We show using transmission electron microcopy and in situ dynamic light scattering the nanoclusters consist of twelve gold nanospheres attached to thiol groups at predefined locations on the surface of a genetically engineered cowpea mosaic virus with icosahedral symmetry. We measured the bulk absorbance from aqueous suspensions of nanoclusters and reproduced the major features of the spectrum using finite-element simulations. Furthermore, because the viruses are easily produced in gram quantities the directed assembly approach is capable of high-throughput, providing a strategy to realize large quantities for applications. NRL summer intern under the HBCU/MI Summer Research Program.

  9. Crystallography of decahedral and icosahedral particles. I - Geometry of twinning

    NASA Technical Reports Server (NTRS)

    Yang, C. Y.

    1979-01-01

    The crystal structure of the tetrahedral twins in multiply-twinned particles with decahedral and icosahedral point group symmetries has been examined and correlated with the face-centered cubic structure. Details on the crystal structure as well as the geometrical relationships among twins in each particle are presented. These crystallographic facts serve as a basis for the interpretation of small particle images obtained with advanced methods of transmission electron microscopy.

  10. Superior room-temperature ductility of typically brittle quasicrystals at small sizes

    NASA Astrophysics Data System (ADS)

    Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

    2016-08-01

    The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ~4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals--dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices.

  11. Theory of quasicrystal surfaces: Probing the chemical reactivity by atomic and molecular adsorption

    NASA Astrophysics Data System (ADS)

    Krajčí, M.; Hafner, J.

    The adsorption of oxygen and carbon atoms and of carbon monoxide molecules on a fivefold surface of icosahedral Al-Pd-Mn quasicrystals has been investigated using ab initio density-functional calculations. The quasicrystalline surface has been modeled by periodically repeated slabs cut from rational approximants to the quasicrystalline structure. Atomic and molecular adsorption have been studied for a large number of possible adsorption sites by performing three-dimensional static relaxations of the adsorbate/substrate complex. Four different scenarios for the dissociative adsorption of the CO molecule have been investigated via nudged-elastic band calculations of the transition states. Al and Mn-metal atoms present at the surface bind C and O atoms rather strongly, while Pd atoms are unstable adsorption sites: during relaxation, the adsorbate drifts to the nearest strong-binding site. The chemical reactivity with respect to a CO molecule varies very strongly across the surface. The adsorption close to Mn sites is promoted by rather strong covalent effects, but CO is only physisorbed at Al sites via weak polarization forces. On the basis of the observed local variations of the adsorption strength, we develop scenarios for dissociation and determine the potential energy barriers for this processes. We find that CO adsorbed close to a transition-metal atom can dissociate via an activated process, but the dissociation rate is expected to be rather low because of a high dissociation barrier and a "late" transition state. CO adsorbed close to Al atoms will desorb before dissociation. Surface vacancies present as a consequence of the irregular coordination of the Mackay cluster in the quasiperiodic structure will act as strongly attractive traps for diffusing molecules. Mn surface atoms are located in the center of truncated Mackay clusters. In scanning tunneling electron microscopy (STM) these truncated clusters are imaged as "white flowers". Surface vacancies are

  12. Growth and electronic structure of alkali-metal adlayers on icosahedral Al{sub 70.5}Pd{sub 21}Mn{sub 8.5}

    SciTech Connect

    Shukla, A. K.; Dhaka, R. S.; Biswas, C.; Banik, S.; Barman, S. R.; Horn, K.; Ebert, Ph.; Urban, K.

    2006-02-01

    We report x-ray photoelectron spectroscopy (XPS) study of Na and K adlayers on icosahedral Al{sub 70.5}Pd{sub 21}Mn{sub 8.5} (i-Al-Pd-Mn) quasicrystal. The Na 1s core-level exhibits a continuous linear shift of 0.8 eV towards lower binding energies (BE) with increasing coverage up to one monolayer (ML) saturation coverage. In the case of K/i-Al-Pd-Mn, a similar linear shift in the K 2p spectra towards lower BE is observed. In both cases, the plasmon related loss features are observed only above 1 ML. The substrate core-level peaks, such as Al 2p, do not exhibit any shift with the adlayer deposition up to the highest coverage. Based on these experimental observations and previous studies of alkali metal growth on metals, we conclude that below 1 ML, both Na and K form a dispersed phase on i-Al-Pd-Mn and there is hardly any charge transfer to the substrate. The variation of the adlayer and substrate core-level intensities with coverage indicates layer by layer growth.

  13. Soft materials design via self assembly of functionalized icosahedral particles

    NASA Astrophysics Data System (ADS)

    Muthukumar, Vidyalakshmi Chockalingam

    In this work we simulate self assembly of icosahedral building blocks using a coarse grained model of the icosahedral capsid of virus 1m1c. With significant advancements in site-directed functionalization of these macromolecules [1], we propose possible application of such self-assembled materials for drug delivery. While there have been some reports on organization of viral particles in solution through functionalization, exploiting this behaviour for obtaining well-ordered stoichiometric structures has not yet been explored. Our work is in well agreement with the earlier simulation studies of icosahedral gold nanocrystals, giving chain like patterns [5] and also broadly in agreement with the wet lab works of Finn, M.G. et al., who have shown small predominantly chain-like aggregates with mannose-decorated Cowpea Mosaic Virus (CPMV) [22] and small two dimensional aggregates with oligonucleotide functionalization on the CPMV capsid [1]. To quantify the results of our Coarse Grained Molecular Dynamics Simulations I developed analysis routines in MATLAB using which we found the most preferable nearest neighbour distances (from the radial distribution function (RDF) calculations) for different lengths of the functional groups and under different implicit solvent conditions, and the most frequent coordination number for a virus particle (histogram plots further using the information from RDF). Visual inspection suggests that our results most likely span the low temperature limits explored in the works of Finn, M.G. et al., and show a good degree of agreement with the experimental results in [1] at an annealing temperature of 4°C. Our work also reveals the possibility of novel stoichiometric N-mer type aggregates which could be synthesized using these capsids with appropriate functionalization and solvent conditions.

  14. Dynamic and Kinetic Assembly Studies of an Icosahedral Virus Capsid

    NASA Astrophysics Data System (ADS)

    Lee, Kelly

    2011-03-01

    Hepatitis B virus has an icosahedrally symmetrical core particle (capsid), composed of either 90 or 120 copies of a dimeric protein building block. We are using time-resolved, solution small-angle X-ray scattering and single-molecule fluorescence microscopy to probe the core particle assembly reaction at the ensemble and individual assembly levels. Our experiments to date reveal the assembly process to be highly cooperative with minimal population of stable intermediate species. Solution conditions, particularly salt concentration, appears to influence the partitioning of assembly products into the two sizes of shells. Funding from NIH R00-GM080352 and University of Washington.

  15. Melting of icosahedral gold nanoclusters from molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Wang, Yanting; Teitel, S.; Dellago, Christoph

    2005-06-01

    Molecular dynamics simulations show that gold clusters with about 600-3000 atoms crystallize into a Mackay icosahedron upon cooling from the liquid. A detailed surface analysis shows that the facets on the surface of the Mackay icosahedral gold clusters soften but do not premelt below the bulk melting temperature. This softening is found to be due to the increasing mobility of vertex and edge atoms with temperature, which leads to inter-layer and intra-layer diffusion, and a shrinkage of the average facet size, so that the average shape of the cluster is nearly spherical at melting.

  16. Melting of bcc Transition Metals and Icosahedral Clustering

    SciTech Connect

    Ross, M; Boehler, R; Japel, S

    2006-05-26

    In contrast to polyvalent metals, transition metals have low melting slopes(dT/dP) that are due to partially filled d-bands that allow for a lowering of liquid phase energy through s-d electron transfer and the formation of local structures. In the case of bcc transition metals we show the apparent discrepancy of DAC melting measurements with shock melting of Mo can be understood by reexamining the shock data for V and Ta and introducing the presence of an icosahedral short range order (ISRO) melt phase.

  17. Modeling liquid-liquid phase transitions and quasicrystal formation

    NASA Astrophysics Data System (ADS)

    Skibinsky, Anna

    In this thesis, studies which concern two different subjects related to phase transitions in fluids and crystalline solids are presented. Condensed matter formation, structure, and phase transitions are modeled using molecular dynamics simulations of simple discontinuous potentials with attractive and repulsive interactions. Novel phase diagrams are proposed for quasicrystals, crystals, and liquids. In the first part of the thesis, the formation of a quasicrystal in a two dimensional monodisperse system is investigated using molecular dynamics simulations of hard sphere particles interacting via a two-dimensional square-well potential. It is found that for certain values of the square-well parameters more than one stable crystalline phase can form. By quenching the liquid phase at a very low temperature, an amorphous phase is obtained. When this the amorphous phase is heated, a quasicrystalline structure with five-fold symmetry forms. From estimations of the Helmholtz potentials of the stable crystalline phases and of the quasicrystal, it is concluded that within a specific temperature range, the observed quasicrystal phase can be the stable phase. The second part of the thesis concerns a study of the liquid-liquid phase transition for a single-component system in three dimensions, interacting via an isotropic potential with a repulsive soft-core shoulder at short distance and an attractive well at an intermediate distance. The potential is similar to potentials used to describe such liquid systems as colloids, protein solutions, or liquid metals. It is shown that the phase diagram for such a potential can have two lines of first-order fluid-fluid phase transitions: one separating a gas and a low-density liquid (LDL), and another between the LDL and a high-density liquid (HDL). Both phase transition lines end in a critical point, a gas-LDL critical point and, depending on the potential parameters, either a gas-HDL critical point or a LDL-HDL critical point. A

  18. Thermal conductivity of one-dimensional Fibonacci quasicrystals

    NASA Astrophysics Data System (ADS)

    Maciá, Enrique

    2000-03-01

    We consider a general Fibonacci quasicrystal (FQC) in which both the masses and the elastic constants are aperiodically arranged. Making use of a suitable decimation scheme, inspired by real-space renormalization-group concepts, we obtain closed analytical expressions for the global transfer matrix and transmission coefficient for several resonant critical normal modes. The fractal structure of the frequency spectrum significantly influences both the cumulative contribution of the different normal modes to the thermal transport and the dependence of the thermal conductivity with the temperature over a wide temperature range. The role of resonant effects in the heat transport through the FQC is numerically and analytically discussed.

  19. Observation and Structure Determination of an Oxide Quasicrystal Approximant

    NASA Astrophysics Data System (ADS)

    Förster, S.; Trautmann, M.; Roy, S.; Adeagbo, W. A.; Zollner, E. M.; Hammer, R.; Schumann, F. O.; Meinel, K.; Nayak, S. K.; Mohseni, K.; Hergert, W.; Meyerheim, H. L.; Widdra, W.

    2016-08-01

    We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 32 .4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO3 clusters, leading to a fundamental edge length of the tiling 6.7 Å.

  20. Photonic quasi-crystal fiber with high birefringence

    NASA Astrophysics Data System (ADS)

    Liu, Hongfei; Xiao, Wei; Cai, Weicheng; Liu, Exian; Feng, Bo; Wang, Ziming; Liang, Taiyuan; Wang, Shuo; Liu, Jianjun

    2016-03-01

    A high-birefringence photonic quasi-crystal fiber (HB-PQF) based on SiO2 is proposed. The relationships between birefringence and structure parameters and between beat length and structure parameters are researched by finite difference beam propagation method. With the optimization of fiber structure parameters, the birefringence is 1.4207×10-2, which is two orders of magnitude higher than the normally used fiber when the wavelength is 1.55 μm. The radius of the fiber is 6.5 μm. The HB-PQF in a communication sensor will have important application prospects.

  1. Observation and Structure Determination of an Oxide Quasicrystal Approximant.

    PubMed

    Förster, S; Trautmann, M; Roy, S; Adeagbo, W A; Zollner, E M; Hammer, R; Schumann, F O; Meinel, K; Nayak, S K; Mohseni, K; Hergert, W; Meyerheim, H L; Widdra, W

    2016-08-26

    We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 3^{2}.4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO_{3} clusters, leading to a fundamental edge length of the tiling 6.7 Å. PMID:27610863

  2. What periodicities can be found in diffraction patterns of quasicrystals?

    PubMed

    Wolny, Janusz; Kozakowski, Bartlomiej; Kuczera, Pawel; Pytlik, Lucjan; Strzalka, Radoslaw

    2014-03-01

    The structure of quasicrystals is aperiodic. Their diffraction patterns, however, can be considered periodic. They are composed solely of series of peaks which exhibit a fully periodic arrangement in reciprocal space. Furthermore, the peak intensities in each series define the so-called `envelope function'. A Fourier transform of the envelope function gives an average unit cell, whose definition is based on the statistical distribution of atomic coordinates in physical space. If such a distribution is lifted to higher-dimensional space, it becomes the so-called atomic surface - the most fundamental feature of higher-dimensional analysis. PMID:24572319

  3. Unusual properties of icosahedral boron-rich solids

    NASA Astrophysics Data System (ADS)

    Emin, David

    2006-09-01

    Icosahedral boron-rich solids are materials containing boron-rich units in which atoms reside at an icosahedron's 12 vertices. These materials are known for their exceptional bonding and the unusual structures that result. This article describes how the unusual bonding generates other distinctive and useful effects. In particular, radiation-induced atomic vacancies and interstitials spontaneously recombine to produce the "self-healing" that underlies these materials' extraordinary radiation tolerance. Furthermore, boron carbides, a group of icosahedral boron-rich solids, possess unusual electronic, magnetic and thermal properties. For example, the charge carriers, holes, localize as singlet pairs on icosahedra. The unusual origin of this localization is indicated by the absence of a concomitant photo-ionization. The thermally assisted hopping of singlet pairs between icosahedra produces Seebeck coefficients that are unexpectedly large and only weakly dependent on carrier concentration. These properties are exploited in devices: (1) long-lived high-power high-capacity beta-voltaic cells, (2) very high temperature thermoelectrics and (3) solid-state neutron detectors.

  4. Shell and subshell periodic structures of icosahedral nickel nanoclusters

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi; Hu, Wangyu; Xiao, Shifang

    2005-06-01

    Using the modified analytic embedded atom method and molecular dynamics, the binding energies and their second order finite differences (stability functions) of icosahedral Ni clusters with shell and subshell periodicity are studied in detail via atomic evolution. The results exhibit shell and subshell structures of the clusters with atoms from 147 to 250 000, and the atomic numbers corresponding to shell or subshell structures are in good agreement with the experimental magic numbers obtained in time-of-flight mass spectra of threshold photoionization, and Martin's theoretical proposition of progressive formation of atomic umbrellas. Clusters with size from 147 to 561 atoms are energetically investigated via one-by-one atomic evolution and their magic numbers are theoretically proved. For medium-size Ni clusters with 561 to 2057 atoms, the prediction of magic numbers with atomic numbers is performed on the basis of umbrellalike subshell growth in near face-edge-vertex order. The similarity of the energy curves makes it possible to extend the prediction to even larger Ni nanoclusters in hierarchical Mackay icosahedral configurations.

  5. Two-Dimensional Crystals of Icosahedral Viruses at Liquid interfaces

    NASA Astrophysics Data System (ADS)

    Fukuto, Masafumi; Yang, Lin; Checco, Antonio; Kuzmenko, Ivan; Nguyen, Quyen; Mank, Nick; Wang, Qian

    2012-02-01

    Two-dimensional (2D) assembly of turnip yellow mosaic virus (TYMV) on cationic lipid monolayers is investigated at the air-water interface. TYMV, an icosahedral virus with a diameter of 28 nm, exhibits well-defined roughness, charge distribution, and hydrophilic/hydrophobic patches on its surface. The electrostatic attraction to the lipid-coated aqueous interface provides means to impose a specific virus orientation and hence reduce the number of possible inter-particle interactions. The 2D geometry is particularly advantageous in dissecting the role of anisotropy in aqueous-media assembly, which involves various types of similarly weak interactions. We show that the assembly approach used not only facilitates crystallization but also provides insights on how complex anisotropic interactions can be exploited to generate long-range order. Specifically, we report an in situ x-ray scattering observation of novel 2D crystal forms of TYMV that reflect the virus' icosahedral symmetry. The symmetry, shape, and surface heterogeneities of TYMV suggest a mechanism by which these crystals are stabilized by a combination of hydrophobic, electrostatic, and steric interactions.

  6. Nonhydrostatic icosahedral atmospheric model (NICAM) for global cloud resolving simulations

    NASA Astrophysics Data System (ADS)

    Satoh, M.; Matsuno, T.; Tomita, H.; Miura, H.; Nasuno, T.; Iga, S.

    2008-03-01

    A new type of ultra-high resolution atmospheric global circulation model is developed. The new model is designed to perform "cloud resolving simulations" by directly calculating deep convection and meso-scale circulations, which play key roles not only in the tropical circulations but in the global circulations of the atmosphere. Since cores of deep convection have a few km in horizontal size, they have not directly been resolved by existing atmospheric general circulation models (AGCMs). In order to drastically enhance horizontal resolution, a new framework of a global atmospheric model is required; we adopted nonhydrostatic governing equations and icosahedral grids to the new model, and call it Nonhydrostatic ICosahedral Atmospheric Model (NICAM). In this article, we review governing equations and numerical techniques employed, and present the results from the unique 3.5-km mesh global experiments—with O(10 9) computational nodes—using realistic topography and land/ocean surface thermal forcing. The results show realistic behaviors of multi-scale convective systems in the tropics, which have not been captured by AGCMs. We also argue future perspective of the roles of the new model in the next generation atmospheric sciences.

  7. Self-similarity and self-inversion of quasicrystals

    NASA Astrophysics Data System (ADS)

    Madison, A. E.

    2014-08-01

    The discovery of quasicrystals played a revolutionary role in the condensed matter science and forced to renounce the dogma of the classical crystallography that the regular filling of the space by identical blocks is reduced solely to the Fedorov space groups. It is shown that aperiodic crystals, apart from the similarity, exhibit the self-inversion property. In a broadened sense, the self-inversion implies the possible composition of the inversion with translations, rotations, and homothety, whereas pure reflection by itself in a circle can be absent as an independent symmetry element. It is demonstrated that the symmetry of aperiodic tilings is described by Schottky groups (which belong to a particular type of Kleinian groups generated by the linear fractional Möbius transformations); in the theory of aperiodic crystals, the Schottky groups play the same role that the Fedorov groups play in the theory of crystal lattices. The local matching rules for the Penrose fractal tiling are derived, the problem of choice of the fundamental region of the group of motions of a quasicrystal is discussed, and the relation between the symmetry of aperiodic tilings and the symmetry of constructive fractals is analyzed.

  8. Vortex quasi-crystals in mesoscopic superconducting samples

    NASA Astrophysics Data System (ADS)

    Wang, Jing-Kun; Zhang, Wei; R, Sá de Melo C. A.

    2016-08-01

    There seems to be a one to one correspondence between the phases of atomic and molecular matter (AMOM) and vortex matter (VM) in superfluids and superconductors. Crystals, liquids, and glasses have been experimentally observed in both AMOM and VM. Here, we propose a vortex quasi-crystal state which can be stabilized due to boundary and surface energy effects for samples of special shapes and sizes. For finite sized pentagonal samples, it is proposed that a phase transition between a vortex crystal and a vortex quasi-crystal occurs as a function of magnetic field and temperature as the sample size is reduced. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274009, 11434011, and 111522436), the National Key Basic Research Program of China (Grant No. 2013CB922000), the Research Funds of Renmin University of China (Grant Nos. 10XNL016 and 16XNLQ03), and the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices (Grant No. KF201404).

  9. Strongly localized modes in one-dimensional defect-free magnonic quasicrystals

    SciTech Connect

    Chen, C. H.; Qiu, R. Z.; Chang, C. H.; Hsueh, W. J.

    2014-08-15

    Signal storage in magnonic quasicrystals using a slow spin-wave mode, rather than the quasinormal mode of traditional periodic magnonic crystals, is proposed, which is analogous to the slow light mode in the field of optics. Compared to traditional materials, richer and more wavelength-selective sharp resonances are achieved using the quasicrystals with a fewer number of layers, because of the peculiar fractal transmission spectra of quasicrystals. The number of sharp resonance and the quality factor for the sharp resonances in the transmission spectra also increases as the generation order of the magnonic quasicrystal increases. This generic nature allows the storage of signals using spin wave, for a wide range of quasiperiodic systems.

  10. Lasing from organic quasicrystal fabricated by seven- and nine-beam interference.

    PubMed

    Luo, D; Li, Y; Xu, X W; Du, Q G

    2016-05-30

    We demonstrate mirrorless lasers based on all organic nanostructure fabricated by seven- and nine-beam interference using low contrast material, holographic polymer dispersed liquid crystals (H-PDLC). A finite-difference time-domain (FDTD) simulation is used to study the transmission of quasicrystal. The wavelengths of lasing peak are determined by both of local structure of quasicrystal that the pumping light experienced as well as the photoluminescence of laser dye doped. Features of mirrorless laser from quasicrystal based on H-PDLC include directional light source, low threshold, simple fabrication process, low cost and tunability. These properties make H-PDLC photonic quasicrystal promising for a new type of all organic miniature lasers. PMID:27410148

  11. Thermal stability of Al-Cu-Fe icosahedral alloys

    NASA Astrophysics Data System (ADS)

    Bessière, M.; Quivy, A.; Lefebvre, S.; Devaud-Rzepski, J.; Calvayrac, Y.

    1991-12-01

    A stable ideally quasiperiodic phase exists in a small range of concentration, close to the composition Al{62}Cu{25.5}Fe{12.5}. Reducing the iron content, or replacing small amounts of copper by aluminium, lead to icosahedral alloys which exhibit around 650 ^{circ}C structural transformations of unclear nature: in the X-ray powder diffraction pattern, the peak profiles become purely Lorentzian (Al{62.3}Cu{25.3}Fe{12.4}) or diffuse “side-bands” appear in the tails of the Bragg peaks (Al{63}Cu{24.5}Fe{12.5}). In the last case long annealing treatments eventually transform the Bragg peaks into diffuse peaks located at positions clearly off the ideal icosahedral symmetry. Small deviations from this composition range lead to Bragg peaks with shoulders whatever the heat-treatment may be; perfect icosahedral order is never obtained for these compositions (Al{63,25}Cu{24,5}Fe{12,25}, Al{64}Cu{24}Fe{12}, Al{63}Cu{25}Fe{12}). Une phase stable idéalement quasipériodique existe dans un petit domaine de concentration, au voisinage de la composition Al{62}Cu{25,5}Fe{12,5}. La diminution de la teneur en fer, ou le remplacement de faibles quantités de cuivre par de l'aluminium, conduisent à des alliages icosaédriques qui subissent vers 650 ^{circ}C des transformations structurales dont la nature n'est pas clairement identifiée: dans le diagramme de diffraction des rayons X sur poudre, les profils de raies deviennent purement Lorentziens (Al{62,3}Cu{25,3}Fe{12,4}) ou bien des raies diffuses apparaissent dans le pied des pics de Bragg (Al{63}Cu{24,5}Fe{12,5}). Dans ce dernier cas un long traitement de recuit transforme finalement les pics de Bragg en des pics diffus localisés à des positions clairement en dehors de celles correspondant à la symétrie icosaédrique idéale. De faibles écarts à ce domaine de compositions conduisent à des diagrammes de rayons X où les pics de Bragg sont épaulés quel que soit le traitement thermique ; l'ordre icosaédrique parfait n

  12. Radial vibrations of a sodium ion inside icosahedral C60

    NASA Technical Reports Server (NTRS)

    Ballester, J. L.; Dunlap, B. I.

    1992-01-01

    The very high symmetry of icosahedral C60 suggests that, as a first approximation, an atom trapped inside C60 would be subject to a potential that is radially symmetric about the center. All-electron local-density-functional calculations of the total energy of a sodium ion as a function of radial displacement from the center along the fivefold axis of C60 serve to refine such a radial potential. In particular, the calculations suggest studying potentials that have minima displaced from the center. An analytic functional form for a radial potential having a positive cusp at the origin is proposed, and the s-wave radial solutions of the corresponding Schroedinger equation are examined.

  13. Melting of icosahedral nickel clusters under hydrostatic pressure.

    PubMed

    Fu, Bing; Chen, Li; Wang, Feifei; Xie, Yiqun; Ye, Xiang

    2014-12-01

    The thermal stabilities and melting behavior of icosahedral nickel clusters under hydrostatic pressure have been studied by constant-pressure molecular dynamics simulation. The potential energy and Lindemann index are calculated. The overall melting temperature exhibits a strong dependence on pressure. The Lindemann index of solid structure before melting varies slowly and is almost independent of pressure. However, after the clusters melt completely, the Lindemann index at the overall melting point strongly depends on pressure. The overall melting temperature is found to be increasing nonlinearly with increasing pressure, while the volume change during melting decreases linearly with increasing pressure. Under a high pressure and temperature environment, similar angular distributions were found between liquid and solid structures, indicating the existence of a converging local structure.

  14. Many-molecule encapsulation by an icosahedral shell.

    PubMed

    Perlmutter, Jason D; Mohajerani, Farzaneh; Hagan, Michael F

    2016-01-01

    We computationally study how an icosahedral shell assembles around hundreds of molecules. Such a process occurs during the formation of the carboxysome, a bacterial microcompartment that assembles around many copies of the enzymes ribulose 1,5-bisphosphate carboxylase/ oxygenase and carbonic anhydrase to facilitate carbon fixation in cyanobacteria. Our simulations identify two classes of assembly pathways leading to encapsulation of many-molecule cargoes. In one, shell assembly proceeds concomitantly with cargo condensation. In the other, the cargo first forms a dense globule; then, shell proteins assemble around and bud from the condensed cargo complex. Although the model is simplified, the simulations predict intermediates and closure mechanisms not accessible in experiments, and show how assembly can be tuned between these two pathways by modulating protein interactions. In addition to elucidating assembly pathways and critical control parameters for microcompartment assembly, our results may guide the reengineering of viruses as nanoreactors that self-assemble around their reactants. PMID:27166515

  15. Dynamico, an Icosahedral Dynamical Core Designed for Consistency and Versatility

    NASA Astrophysics Data System (ADS)

    Dubos, T.

    2014-12-01

    The design of the icosahedral-hexagonal dynamical core DYNAMICO is presented. DYNAMICO solves the multi-layer rotating shallow-water equations, a compressible variant of the same equivalent to a discretization of the hydrostatic primitive equations (HPE) in a Lagrangian vertical coordinate, and the HPE in a hybrid mass-based vertical coordinate. In line with more general lines of thought known as physics-preserving discretizations and discrete differential geometry, kinematics and dynamics are separated as strictly as possible. This separation means that the transport of mass, scalars and potential temperature uses no information regarding the specific momentum equation being solved. This disregarded information includes the equation of state as well as any metric information, and is used only for certain terms of the momentum budget, written in Hamiltonian, vector-invariant form. The common Hamiltonian structure of the various equations of motion (Tort and Dubos, 2014 ; Dubos and Tort, 2014) is exploited to formulate energy-conserving spatial discretizations in a unified way. Furthermore most of the model code is common to the three sets of equations solved, making it easier to develop and validate each piece of the model separately. This design permits to consider several extensions in the near future, especially to deep-atmosphere, moist and non-hydrostatic equations. Representative academic three-dimensional benchmarks are run and analyzed, showing correctness of the model (Figure : time-zonal statistics from Held and Suarez (1994) simulations). Hopefully preliminary full-physics results will be presented as well. References : T. Dubos and M. Tort, "Equations of atmospheric motion in non-Eulerian vertical coordinates : vector-invariant form and Hamiltonian formulation", accepted by Mon. Wea. Rev. M. Tort and T. Dubos, "Usual approximations to the equations of atmospheric motion : a variational perspective" accepted by J. Atmos. Sci T. Dubos et al., "DYNAMICO

  16. Difference in Icosahedral Short-Range Order in Early and Late Transition Metal Liquids

    NASA Technical Reports Server (NTRS)

    Lee, G. W.; Gangopadbyay, A. K.; Kelton, K. F.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.

    2004-01-01

    New short-range order data are presented for equilibrium and undercooled liquids of Ti and Ni. These were obtained from in-situ synchrotron x-ray diffraction measurements of electrostatically-levitated droplets. While the short-range order of liquid Ni is icosahedral, consistent with Frank's hypothesis, significantly distorted icosahedral order is observed in liquid Ti. This is the first experimental observation of distorted icosahedral short-range order in any liquid. although this has been predicted by theoretical studies on atomic clusters.

  17. Difference in Icosahedral Short-Range Order in Early and Late Transition Metals Liquids

    NASA Technical Reports Server (NTRS)

    Lee, G. W.; Gangopadhyay, A. K.; Kelton, K. F.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.

    2003-01-01

    New short-range order data are presented for equilibrium and undercooled liquids of Ti and Ni. These were obtained from in-situ synchrotron x-ray diffraction measurements of electrostatically-levitated droplets. While the short-range order of liquid Ni is icosahedral, consistent with Frank's hypothesis, significantly distorted icosahedral order is observed in liquid Ti. This is the first experimental observation of distorted icosahedral short-range order in any liquid, although this has been predicted by theoretical studies on atomic clusters.

  18. Tri-icosahedral Gold Nanocluster [Au37(PPh3)10(SC2H4Ph)10X2](+): Linear Assembly of Icosahedral Building Blocks.

    PubMed

    Jin, Renxi; Liu, Chong; Zhao, Shuo; Das, Anindita; Xing, Hongzhu; Gayathri, Chakicherla; Xing, Yan; Rosi, Nathaniel L; Gil, Roberto R; Jin, Rongchao

    2015-08-25

    The [Au37(PPh3)10(SR)10X2](+) nanocluster (where SR = thiolate and X = Cl/Br) was theoretically predicted in 2007, but since then, there has been no experimental success in the synthesis and structure determination. Herein, we report a kinetically controlled, selective synthesis of [Au37(PPh3)10(SC2H4Ph)10X2](+) (counterion: Cl(-) or Br(-)) with its crystal structure characterized by X-ray crystallography. This nanocluster shows a rod-like structure assembled from three icosahedral Au13 units in a linear fashion, consistent with the earlier prediction. The optical absorption and the electrochemical and catalytic properties are investigated. The successful synthesis of this new nanocluster allows us to gain insight into the size, structure, and property evolution of gold nanoclusters that are based upon the assembly of icosahedral units (i.e., cluster of clusters). Some interesting trends are identified in the evolution from the monoicosahedral [Au13(PPh3)10X2](3+) to the bi-icosahedral [Au25(PPh3)10(SC2H4Ph)5X2](2+) and to the tri-icosahedral [Au37(PPh3)10(SC2H4Ph)10X2](+) nanocluster, which also points to the possibility of achieving even longer rod nanoclusters based upon assembly of icosahedral building blocks. PMID:26214221

  19. Archaeal Haloarcula californiae Icosahedral Virus 1 Highlights Conserved Elements in Icosahedral Membrane-Containing DNA Viruses from Extreme Environments

    PubMed Central

    Demina, Tatiana A.; Pietilä, Maija K.; Svirskaitė, Julija; Ravantti, Janne J.; Atanasova, Nina S.; Bamford, Dennis H.

    2016-01-01

    ABSTRACT Despite their high genomic diversity, all known viruses are structurally constrained to a limited number of virion morphotypes. One morphotype of viruses infecting bacteria, archaea, and eukaryotes is the tailless icosahedral morphotype with an internal membrane. Although it is considered an abundant morphotype in extreme environments, only seven such archaeal viruses are known. Here, we introduce Haloarcula californiae icosahedral virus 1 (HCIV-1), a halophilic euryarchaeal virus originating from salt crystals. HCIV-1 also retains its infectivity under low-salinity conditions, showing that it is able to adapt to environmental changes. The release of progeny virions resulting from cell lysis was evidenced by reduced cellular oxygen consumption, leakage of intracellular ATP, and binding of an indicator ion to ruptured cell membranes. The virion contains at least 12 different protein species, lipids selectively acquired from the host cell membrane, and a 31,314-bp-long linear double-stranded DNA (dsDNA). The overall genome organization and sequence show high similarity to the genomes of archaeal viruses in the Sphaerolipoviridae family. Phylogenetic analysis based on the major conserved components needed for virion assembly—the major capsid proteins and the packaging ATPase—placed HCIV-1 along with the alphasphaerolipoviruses in a distinct, well-supported clade. On the basis of its virion morphology and sequence similarities, most notably, those of its core virion components, we propose that HCIV-1 is a member of the PRD1-adenovirus structure-based lineage together with other sphaerolipoviruses. This addition to the lineage reinforces the notion of the ancient evolutionary links observed between the viruses and further highlights the limits of the choices found in nature for formation of a virion. PMID:27435460

  20. Atomistic simulation of frictional anisotropy on quasicrystal approximant surfaces

    NASA Astrophysics Data System (ADS)

    Ye, Zhijiang; Martini, Ashlie; Thiel, Patricia; Lovelady, Heather H.; McLaughlin, Keith; Rabson, David A.

    2016-06-01

    J. Y. Park et al. [Science 309, 1354 (2005), 10.1126/science.1113239] have reported eight times greater atomic-scale friction in the periodic than in the quasiperiodic direction on the twofold face of a decagonal Al-Ni-Co quasicrystal. We present results of molecular-dynamics simulations intended to elucidate mechanisms behind this giant frictional anisotropy. Simulations of a bare atomic-force-microscope tip on several model substrates and under a variety of conditions failed to reproduce experimental results. On the other hand, including the experimental passivation of the tip with chains of hexadecane thiol, we reproduce qualitatively the experimental anisotropy in friction, finding evidence for entrainment of the organic chains in surface furrows parallel to the periodic direction.

  1. Atomistic simulation of frictional anisotropy on quasicrystal approximant surfaces

    DOE PAGES

    Ye, Zhijiang; Martini, Ashlie; Thiel, Patricia; Lovelady, Heather H.; McLaughlin, Keith; Rabson, David A.

    2016-06-23

    J. Y. Park et al. [Science 309, 1354 (2005)] have reported eight times greater atomic-scale friction in the periodic than in the quasiperiodic direction on the twofold face of a decagonal Al-Ni-Co quasicrystal. Here we present results of molecular-dynamics simulations intended to elucidate mechanisms behind this giant frictional anisotropy. Simulations of a bare atomic-force-microscope tip on several model substrates and under a variety of conditions failed to reproduce experimental results. On the other hand, including the experimental passivation of the tip with chains of hexadecane thiol, we reproduce qualitatively the experimental anisotropy in friction, finding evidence for entrainment of themore » organic chains in surface furrows parallel to the periodic direction.« less

  2. Friction Anisotropy: A unique and intrinsic property of decagonal quasicrystals

    SciTech Connect

    Mulleregan, Alice; Park, Jeong Young; Salmeron, Miquel; Ogetree, D.F.; Jenks, C.J.; Thiel, P.A.; Brenner, J.; Dubois, J.M.

    2008-06-25

    We show that friction anisotropy is an intrinsic property of the atomic structure of Al-Ni-Co decagonal quasicrystals and not only of clean and well-ordered surfaces that can be prepared in vacuum [J.Y. Park et al., Science (2005)]. Friction anisotropy is manifested both in nanometer size contacts obtained with sharp atomic force microscope (AFM) tips as well as in macroscopic contacts produced in pin-on-disc tribometers. We show that the friction anisotropy, which is not observed when an amorphous oxide film covers the surface, is recovered when the film is removed due to wear. Equally important is the loss of the friction anisotropy when the quasicrystalline order is destroyed due to cumulative wear. These results reveal the intimate connection between the mechanical properties of these materials and their peculiar atomic structure.

  3. Acid-base chemistry in the formation of Mackay-type icosahedral clusters: μ3-acidity analysis of Sc-rich phases of the Sc-Ir system.

    PubMed

    Guo, Yiming; Stacey, Timothy E; Fredrickson, Daniel C

    2014-05-19

    The crystal structures of intermetallic phases offer a wealth of geometrical features (helices, multishelled clusters, and host-guest motifs) whose formation has yet to be explained or predicted by chemical theory. A recently developed extension of the acid-base concept to metallic systems, the μ3-acidity model, provides an avenue for developing this understanding for intermetallics formed from transition metals. In this Article, we illustrate how this approach can be used to understand one of the most striking geometrical entities to emerge in intermetallic chemistry, the Mackay cluster of icosahedral quasicrystals. We present μ3-acidity analyses, based on DFT-calibrated Hückel calculations, for a series of Sc-Ir intermetallics: ScIr (CsCl-type), Sc2Ir (Ti2Ni-type), Sc11Ir4, and the Mackay cluster containing phases Sc57Ir13 and Sc44Ir7. We begin by illustrating that a μ3-acidity model correctly predicts that each of these phases is stable relative to disproportionation into their neighboring compounds when a common set of Hückel parameters and d-orbital occupancies is used. Next, we explain these results by developing a relationship between the distance distribution of homoatomic contacts within an atom's coordination sphere and the μ3-neutralization it experiences. For a given average homoatomic distance, the role of heteroatomic contacts is higher when the distribution of homoatomic contacts is narrower. This effect is key to the strength of the acid-base neutralization of the Sc-rich phases, where the Sc atoms find a scarcity of Ir atoms from which to obtain neutralization. Under these circumstances, Sc-Ir contacts should be maximized, whereas the number and distance variations of the Sc-Sc contacts should be minimized. These expectations are borne out by the observed crystal structures. In particular, the Mackay clusters of Sc57Ir13 and Sc44Ir7, in which a central Ir atom is icosahedrally coordinated by a pentagonal dodecahedral array of face-sharing Sc

  4. Metal-organic framework materials based on icosahedral boranes and carboranes

    DOEpatents

    Mirkin, Chad A.; Hupp, Joseph T.; Farha, Omar K.; Spokoyny, Alexander M.; Mulfort, Karen L.

    2010-11-02

    Disclosed herein are metal-organic frameworks of metals and boron rich ligands, such as carboranes and icosahedral boranes. Methods of synthesizing and using these materials in gas uptake are disclosed.

  5. Van Hove singularities of some icosahedral boron-rich solids by differential reflectivity spectra

    NASA Astrophysics Data System (ADS)

    Werheit, Helmut

    2015-09-01

    Differential reflectivity spectra of some icosahedral boron rich solids, β-rhombohedral boron, boron carbide and YB66-type crystals, were measured. The derivatives yield the van Hove singularities, which are compared with results obtained by other experimental methods.

  6. A face-sharing bi-icosahedral model for Al₂₃⁻.

    PubMed

    Koyasu, K; Tsukuda, T

    2014-10-21

    A face-sharing bi-icosahedral motif is proposed as a candidate structure of the magic cluster, Al23(-), on the basis of DFT calculations. The structure can be viewed as a quasi-molecule made of two Al13 (D3d) superatoms with an open electronic configuration via constructive overlap of 1F and 2P superatomic orbitals. A face-sharing tri-icosahedral motif is also predicted for Al33(-). PMID:25199061

  7. Thermal expansion of a Au-Al-Yb intermediate valence quasicrystal

    NASA Astrophysics Data System (ADS)

    Watanuki, T.; Kashimoto, S.; Ishimasa, T.; Machida, A.; Yamamoto, S.; Tanaka, Y.; Mizumaki, M.; Kawamura, N.; Watanabe, S.

    2015-06-01

    The thermal expansion of a Au-Al-Yb intermediate-valence quasicrystal has been studied. X-ray diffraction measurements showed zero thermal expansion below 50 K. By comparison with an isostructural Au-Al-Tm quasicrystal, the contribution of the Yb valence variation was extracted, and it was shown that its negative thermal expansion component compensated for the positive thermal expansion of the original lattice. On cooling, the Yb contribution grew steeply below approximately 155 K down to the lowest experimental temperature of 5 K, due to enlargement of the Yb atomic radius, which was caused by the valence shift toward the divalent state. Additionally, a larger Yb contribution to the thermal expansion was demonstrated in a crystalline approximant to this quasicrystal. The magnitude of this contribution was approximately 1.4 times larger than in the case of the quasicrystal itself, resulting in a slight negative thermal expansion below 50 K. A heterogeneous valence model for the quasicrystal that we proposed previously accounts for this magnitude difference.

  8. Superior room-temperature ductility of typically brittle quasicrystals at small sizes.

    PubMed

    Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

    2016-01-01

    The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ∼4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals-dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices. PMID:27515779

  9. Stable Ti-based quasicrystal offers prospect for improved hydrogen storage

    SciTech Connect

    Stroud, R.M.; Viano, A.M.; Gibbons, P.C.; Kelton, K.F.; Misture, S.T.

    1996-11-01

    The desorption of hydrogen from a novel material, a Ti{sub 45}Zr{sub 38}Ni{sub 17}-H quasicrystal, was observed using high-temperature powder x-ray diffraction, demonstrating the potential utility of Ti-based quasicrystals in place of crystalline or amorphous hydrides for hydrogen storage applications. The maximum observed change in hydrogen concentration was from 61 at.{percent}, corresponding to a hydrogen-to-metal ratio (H/M) of 1.54, at 91{degree}C to less than 2.5 at.{percent} (H/M=0.025) at 620{degree}C. The onset temperature of desorption is below 350{degree}C. Surface oxidation was found to promote the formation of crystalline hydride phases. Highly oxidized samples transformed to a mixture of the C14 Laves and C15 Laves crystalline hydrides, and the Ti{sub 2}Ni phase. When the oxidation was less severe, a reversible transformation between the quasicrystal and crystalline hydride phases was clearly observed, demonstrating the stability of the Ti{sub 45}Zr{sub 38}Ni{sub 17} quasicrystal at very low hydrogen concentrations, and temperatures as high as 661{degree}C. This is the first evidence for a stable Ti-based quasicrystal and for reversible hydrogen storage in a quasicrystalline phase. {copyright} {ital 1996 American Institute of Physics.}

  10. Many-molecule encapsulation by an icosahedral shell

    PubMed Central

    Perlmutter, Jason D; Mohajerani, Farzaneh; Hagan, Michael F

    2016-01-01

    We computationally study how an icosahedral shell assembles around hundreds of molecules. Such a process occurs during the formation of the carboxysome, a bacterial microcompartment that assembles around many copies of the enzymes ribulose 1,5-bisphosphate carboxylase/ oxygenase and carbonic anhydrase to facilitate carbon fixation in cyanobacteria. Our simulations identify two classes of assembly pathways leading to encapsulation of many-molecule cargoes. In one, shell assembly proceeds concomitantly with cargo condensation. In the other, the cargo first forms a dense globule; then, shell proteins assemble around and bud from the condensed cargo complex. Although the model is simplified, the simulations predict intermediates and closure mechanisms not accessible in experiments, and show how assembly can be tuned between these two pathways by modulating protein interactions. In addition to elucidating assembly pathways and critical control parameters for microcompartment assembly, our results may guide the reengineering of viruses as nanoreactors that self-assemble around their reactants. DOI: http://dx.doi.org/10.7554/eLife.14078.001 PMID:27166515

  11. Quantum transport through single and multilayer icosahedral fullerenes

    NASA Astrophysics Data System (ADS)

    Lovey, Daniel A.; Romero, Rodolfo H.

    2013-10-01

    We use a tight-binding Hamiltonian and Green functions methods to calculate the quantum transmission through single-wall fullerenes and bilayered and trilayered onions of icosahedral symmetry attached to metallic leads. The electronic structure of the onion-like fullerenes takes into account the curvature and finite size of the fullerenes layers as well as the strength of the intershell interactions depending on to the number of interacting atom pairs belonging to adjacent shells. Misalignment of the symmetry axes of the concentric iscosahedral shells produces breaking of the level degeneracies of the individual shells, giving rise some narrow quasi-continuum bands instead of the localized discrete peaks of the individual fullerenes. As a result, the transmission function for non symmetrical onions is rapidly varying functions of the Fermi energy. Furthermore, we found that most of the features of the transmission through the onions are due to the electronic structure of the outer shell with additional Fano-like antiresonances arising from coupling with or between the inner shells.

  12. Electronic Properties of Ordered Quasicrystals and Related Phases

    NASA Astrophysics Data System (ADS)

    Biggs, Byron Davis

    An extensive, systematic study of the electronic properties of the well-ordered icosahedral (i-) phases and related crystalline and amorphous phases is presented. Barely metallic behavior is observed in the ordered i-crystals, including high resistivities with large temperature coefficients, low electronic densities of states at the Fermi energy, large values of the low-temperature Hall coefficients, and unusual temperature dependences of the Hall coefficients and the thermoelectric powers. In addition, rapid variations of these properties with small changes in composition are observed. Similar behavior is seen in crystalline approximant structures, which are close crystalline analogues of the i-phase. With increasing structural disorder in disordered i-phases and in the totally disordered amorphous (a-) phases, the familiar metallic-glass-like electronic properties are restored. This striking electronic behavior is shown to be due to band structure effects. The high resistivities, low densities of states, and low carrier densities are shown to be due to the structural scattering mechanism of the Fermi-surface-Jones-zone interaction, which is enhanced due to the high degree of structural ordering and, in the i-phases, due to the icosahedral symmetry. The unusual temperature dependences of the Hall coefficients and thermoelectric powers, as well as the rapid variation of the electronic properties with small changes in composition, support the existence of a rapidly varying density of states on a fine energy scale, on the order of 26 meV. The existence of these band structure effects is further supported by the effects of structural disorder on the electronic properties, with disorder restoring the free-electron metallic-glass -like electronic properties. The temperature dependence of the conductivity at high temperatures displays novel concave upward curvature in a wide variety of icosahedral, amorphous, and crystalline phases which have high resistivity values

  13. Hardness of Al-based quasicrystals evaluated via cluster-plus-glue-atom model

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Luo, Lingjie; Qiang, Jianbing; Wang, Yingmin; Dong, Chuang

    2014-05-01

    In this paper, the hardness of ternary Al-based quasicrystals was assessed through an application of the cluster-plus-glue-atom model. In this model, any structure is decomposed into a first-neighbour strongly bonded cluster part and second-neighbour weakly bonded glue-atom part so that the overall structural information is condensed into a local structural unit [cluster](glue atom)x. For quasicrystals, the averaged local units are formulated as [icosahedron] TM0,1(Transition Metal) and could be visualized as single icosahedron packing. Then, the hardness of quasicrystals was related to the rupture of weak inter-cluster bonds. Typically, theoretical hardness values of 8-9 GPa were obtained using 19 broken inter-cluster bonds, which accounts for about half of all the surface bonds of an icosahedron in the Mackay-type environment. The unit cluster formulas would act as rigid units during deformation and cracking.

  14. Theoretical investigation on a general class of 2D quasicrystals with the rectangular projection method

    NASA Astrophysics Data System (ADS)

    Yue, Yang-Yang; Lu, Rong-er; Yang, Bo; Huang, Huang; Hong, Xu-Hao; Zhang, Chao; Qin, Yi-Qiang; Zhu, Yong-Yuan

    2016-10-01

    We take a theoretical investigation on the reciprocal property of a class of 2D nonlinear photonic quasicrystal proposed by Lifshitz et al. in PRL 95, 133901 (2005). Using the rectangular projection method, the analytical expression for the Fourier spectrum of the quasicrystal structure is obtained explicitly. It is interesting to find that the result has a similar form to the corresponding expression of the well-known 1D Fibonacci lattice. In addition, we predict a further extension of the result to higher dimensions. This work is of practical importance for the photonic device design in nonlinear optical conversion progresses.

  15. Surface Tension and Viscosity of Quasicrystal-Forming Ti-Zr-Ni Alloys

    NASA Technical Reports Server (NTRS)

    Hyers, R. W.; Bradshaw, R. C.; Rogers, J. R.; Rathz, T. J.; Lee, G. W.; Kelton, K. F.; Gangopadhyay, A. K.

    2003-01-01

    The surface tension and viscosity of quasicrystal-forming Ti-Zr-Ni alloys were measured over a range of temperature, including both stable and undercooled liquids by an Electrostatic Levitation (ESL) technique. ESL is a containerless technique which allows processing of samples without contact, greatly reducing contamination and increasing access to the metastable undercooled liquid. The measured viscosity is typical of glass-forming alloys of similar composition to the quasicrystal-forming alloys studied here, while the surface tension shows an anomaly at deep undercoolings.

  16. Excitation of Bloch-like surface waves in quasi-crystals and aperiodic dielectric multilayers.

    PubMed

    Koju, Vijay; Robertson, William M

    2016-07-01

    The existence of Bloch surface waves in periodic dielectric multilayer structures with a surface defect is well known. Not yet recognized is that quasi-crystals and aperiodic dielectric multilayers can also support Bloch-like surface waves. In this work, we numerically show the excitation of Bloch-like surface waves in Fibonacci quasi-crystals and Thue-Morse aperiodic dielectric multilayers using the prism coupling method. We report improved surface electric field intensity and penetration depth of Bloch-like surface waves in the air side in such structures compared to their periodic counterparts. PMID:27367064

  17. Measuring the Thermophysical and Structural Properties of Glass-Forming and Quasicrystal-Forming Liquids

    NASA Technical Reports Server (NTRS)

    Hyers, Robert W.; Bradshaw, Richard C.; Rogers, Jan R.; Gangopadhyay, Anup K.; Kelton, Ken F.

    2006-01-01

    The thermophysical properties of glass-forming and quasicrystal-forming alloys show many interesting features in the undercooled liquid range. Some of the features in the thermophysical property curves are expected to reflect changes in the structure and coordination of the liquid. These measurements require containerless processing such as electrostatic levitation to access the undercooled liquid regime. An overview of the state of the art in measuring the thermophysical properties and structure of undercooled liquid glass-forming and quasicrystal-forming alloys will be presented, along with the status of current measurements.

  18. Comparative Study of Non-Enveloped Icosahedral Viruses Size

    PubMed Central

    Nikitin, Nikolai; Trifonova, Ekaterina; Evtushenko, Evgeniy; Kirpichnikov, Mikhail; Atabekov, Joseph; Karpova, Olga

    2015-01-01

    Now, as before, transmission electron microscopy (TEM) is a widely used technique for the determination of virions size. In some studies, dynamic light scattering (DLS) has also been applied for this purpose. Data obtained by different authors and using different methods could vary significantly. The process of TEM sample preparation involves drying on the substrate, which can cause virions to undergo morphology changes. Therefore, other techniques should be used for measurements of virions size in liquid, (i.e. under conditions closer to native). DLS and nanoparticle tracking analysis (NTA) provide supplementary data about the virions hydrodynamic diameter and aggregation state in liquid. In contrast to DLS, NTA data have a higher resolution and also are less sensitive to minor admixtures. In the present work, the size of non-enveloped icosahedral viruses of different nature was analyzed by TEM, DLS and NTA: the viruses used were the encephalomyocarditis virus (animal virus), and cauliflower mosaic virus, brome mosaic virus and bean mild mosaic virus (plant viruses). The same, freshly purified, samples of each virus were used for analysis using the different techniques. The results were compared with earlier published data and description databases. DLS data about the hydrodynamic diameter of bean mild mosaic virus, and NTA data for all examined viruses, were obtained for the first time. For all virus samples, the values of size obtained by TEM were less than virions sizes determined by DLS and NTA. The contribution of the electrical double layer (EDL) in virions hydrodynamic diameter was evaluated. DLS and NTA data adjusted for EDL thickness were in better agreement with TEM results. PMID:26545232

  19. Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrehedral-Phase-Forming Alloys

    NASA Technical Reports Server (NTRS)

    2003-01-01

    By investigating the properties of quasicrystals and quasicrystal-forming liquid alloys, we may determine the role of ordering of the liquid phase in the formation of quasicrystals, leading to a better fundamental understanding of both the quasicrystal and the liquid. A quasicrystal is solid characterized by a symmetric but non-periodic arrangement of atoms, usually in the form of an icosahedron (12 atoms, 20 triangular faces). It is theorized that the short-range order in liquids takes this same form. The degree of ordering depends on the temperature of the liquid, and affects many of the liquid s properties, including specific heat, viscosity, and electrical resistivity. The MSFC role in this project includes solidification studies, phase diagram determination, and thermophysical property measurements on the liquid quasicrystal-forming alloys, all by electrostatic levitation (ESL). The viscosity of liquid quasicrystal-forming alloys is measured by the oscillating drop method, both in the stable and undercooled liquid state. The specific heat of solid, undercooled liquid, and stable liquid are measured by the radiative cooling rate of the droplets.

  20. Dodecagonal Quasicrystal Phase in a Diblock Copolymer Melt

    NASA Astrophysics Data System (ADS)

    Bates, Frank; Gillard, Timothy; Lee, Sangwoo

    Recent experiments with low molecular weight asymmetric poly(isoprene- b-lactide) (PI-PLA) diblock copolymers have established an equilibrium Frank-Kasper σ-phase at compositions between 18 and 22 percent by volume PLA, which transforms to a BCC phase followed by disordering with increasing temperature. This presentation will describe synchrotron small-angle x-ray scattering and dynamic mechanical spectroscopy experiments conducted following rapid temperature quenches from the disordered state to temperatures associated with the σ-phase. We document the development of a long-lived dodecagonal quasicrystalline (DQC) phase that transforms with time into the associated quasicrystal approximate σ-phase at a rate that is highly temperature dependent. Remarkably, the DQC does not form from either the σ-phase or BCC state. These finding will be discussed in the context of an apparent spontaneous structural transition that occurs when the disordered melt is supercooled below a threshold temperature coincident with the BCC to σ-phase order-order transition temperature. Support provided by the National Science Foundation (1104368).

  1. The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases

    NASA Technical Reports Server (NTRS)

    Curreri, Peter A. (Technical Monitor); Kelton, K. F.; Gangopadhyay, A.; Lee, G. W.; Hyers, R. W.; Rathz, R. J.; Rogers, J.; Schenk, T.; Simonet, V.; Holland-Moritz, D.

    2003-01-01

    Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si, for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

  2. The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.; Holland-Moritz, D.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si(3), for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron X-ray and high flux neutron facilities.

  3. The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation Behavior of Ordered Phases

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.

    2003-01-01

    Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si[3], for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

  4. Accurate design of megadalton-scale two-component icosahedral protein complexes.

    PubMed

    Bale, Jacob B; Gonen, Shane; Liu, Yuxi; Sheffler, William; Ellis, Daniel; Thomas, Chantz; Cascio, Duilio; Yeates, Todd O; Gonen, Tamir; King, Neil P; Baker, David

    2016-07-22

    Nature provides many examples of self- and co-assembling protein-based molecular machines, including icosahedral protein cages that serve as scaffolds, enzymes, and compartments for essential biochemical reactions and icosahedral virus capsids, which encapsidate and protect viral genomes and mediate entry into host cells. Inspired by these natural materials, we report the computational design and experimental characterization of co-assembling, two-component, 120-subunit icosahedral protein nanostructures with molecular weights (1.8 to 2.8 megadaltons) and dimensions (24 to 40 nanometers in diameter) comparable to those of small viral capsids. Electron microscopy, small-angle x-ray scattering, and x-ray crystallography show that 10 designs spanning three distinct icosahedral architectures form materials closely matching the design models. In vitro assembly of icosahedral complexes from independently purified components occurs rapidly, at rates comparable to those of viral capsids, and enables controlled packaging of molecular cargo through charge complementarity. The ability to design megadalton-scale materials with atomic-level accuracy and controllable assembly opens the door to a new generation of genetically programmable protein-based molecular machines. PMID:27463675

  5. Icosahedral quasiperiodic packing of fibres parallel to fivefold and threefold axes.

    PubMed

    Audier, M; Duneau, M

    2000-01-01

    Building rules are examined for an icosahedral quasiperiodic packing of fibres with axes parallel to the ten threefold axes, first employing an experimental construction and afterwards a mathematical demonstration using the cut-and-project method applied in hyperspace. As a result of this latter approach, very simple two-dimensional (2D) building rules are proposed. Similar simple 2D rules have also been proposed for the case of an icosahedral quasiperiodic packing with fibre axes parallel to the six fivefold axes [Duneau & Audier (1999). Acta Cryst. A55, 746-754]. Finally, the construction of another icosahedral quasiperiodic packing resulting from a combination of two groups of fibres respectively parallel to six fivefold and ten threefold axes is reported. A brief discussion is given on different particular mechanical behaviours which might a priori be expected from the various enantiomorphic properties of these packings.

  6. An analytic solution of initial boundary value problem for 3D quasicrystals in half space

    NASA Astrophysics Data System (ADS)

    Akmaz, Hakan K.; Korkmaz, Alper

    2012-10-01

    In this article, initial boundary value problem for 3D quasicrystals in half space is considered. An analytic method is proposed for special form of initial conditions and nonhomogeneous term. It is explained that a weak solution of the problem can be constructed in the similar form of data by using symbolic calculations.

  7. Interactions among K+-Ca2+ Exchange, Sorption of m-Dinitrobenzene, and Smectite Quasicrystal Dynamics

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The fate of organic compounds in soils and sediments is influenced by sorption of the compounds on surfaces of soil materials. We investigated the interaction among sorption of an organic compound, cation exchange reactions, and both the size and swelling of smectite quasicrystals. Two reference sme...

  8. Superior room-temperature ductility of typically brittle quasicrystals at small sizes

    PubMed Central

    Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

    2016-01-01

    The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ∼4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals—dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices. PMID:27515779

  9. Group theory of icosahedral virus capsid vibrations: a top-down approach.

    PubMed

    Peeters, Kasper; Taormina, Anne

    2009-02-21

    We explore the use of a top-down approach to analyse the dynamics of icosahedral virus capsids and complement the information obtained from bottom-up studies of viral vibrations available in the literature. A normal mode analysis based on protein association energies is used to study the frequency spectrum, in which we reveal a universal plateau of low-frequency modes shared by a large class of Caspar-Klug capsids. These modes break icosahedral symmetry and are potentially relevant to the genome release mechanism. We comment on the role of viral tiling theory in such dynamical considerations. PMID:19014954

  10. Development of thermally-sprayed Al-Cu-Fe-Cr quasicrystal coating

    NASA Astrophysics Data System (ADS)

    Setiamarga, Budi Hartono

    A class of quasicrystal alloys that has drawn a lot of attention is aluminum based quasicrystal alloys because they are hard, light weight, wear resistant, and have a non-stick property. Quasicrystalline materials in the form of coatings produced by thermal spray techniques have been developed to utilize their properties. The goal of this research has been to develop the knowledge necessary to produce good thermally sprayed Al-Cu-Fe-Cr quasicrystal coatings. Boron has been found to improve ductility, reduce porosity and increase hardness when added to other thermally sprayed powders, therefore, as part of this research, quasicrystal coatings containing boron will also be produced and evaluated. The first phase of this research utilized a fine QC-1 quasicrystal powder of Alsb{70.5}Cusb{10.1}Fesb{8.8}Crsb{10.6}. The addition of boron was done using mechanical mixing. The addition of boron in fused QC-1 powders shows that boron can reduce porosity and increase hardness. Due to difficulties with thermal spraying the fine QC-1 powder and evaporation of aluminum, a coarser QC-2 powder with similar composition to QC-1 powder was produced. QC-2 and boron modified QC-2 coatings have similar hardness and levels of porosity, around 11%, although boron modified QC-2 coatings proved to be more wear resistant than plain QC-2 coatings. Both coatings demonstrated a weak coating-substrate interface bonding. Laser heat treatment was used to reduce the porosity and strengthen the coating-substrate interface bonding. Laser treatment of QC-2 quasicrystal coatings resulted in harder and lower porosity coatings with better coating-substrate interface bonding. Unfortunately, hot-cracks in the coatings were also produced. Hot-cracks are undesireable because they decrease the coating's corrosion resistance. Thermal spraying using High Velocity Oxygen Fuel (HVOF) technique was done. It was used on QC-2 powder and QC-3 powder of composition Alsb{68.6}Cusb{10.8}Fesb{8.9}Crsb{9.7}Bsb{2.0}. This

  11. Topologically induced semiconductivity in icosahedral Al-Pd-Re and its approximants

    NASA Astrophysics Data System (ADS)

    Krajčí, M.; Hafner, J.

    2007-01-01

    We demonstrate that the opening of a semiconducting band-gap in the electronic spectrum of the i-Al-Pd-Re quasicrystal and its approximants is due to the formation of a topological band-gap, in analogy to the band-gap found in the FeSi (B20) structure. In both systems we have identified a network of linear chains of alternating Si(Al) and transition-metal (TM) atoms extending along twofold symmetry directions. In i-Al-Pd-Re the chains of alternating Al and TM atoms extend from a center of the pseudo-Mackay (M) cluster over the surface of the Bergman cluster to the center of another neighboring M cluster. Substitutional Al/Pd defects and a fragmentation of the chains by phason defects lead to the formation of localized states in the band-gap. The band-gap of the real i-Al-Pd-Re quasicrystal is filled by localized states. The i-Al-Pd-Re quasicrystal thus behaves as a disordered semiconductor.

  12. Hydrogen absorption and structural analysis of TiZrNiV quasicrystals.

    PubMed

    Lee, Sang-Hwa; Jo, Youngsoo; Kim, Jaeyong

    2014-12-01

    Ti-based quasicrystals are known to store a high capacity of hydrogen exceeding the density of liquid hydrogen. Because TiZrNi quasicrystals contain a large number of tetrahedral sites formed with Ti and Zr atoms that are chemically favorable to hydrogen, these materials retain strong advantages for hydrogen storage applications in structurally and chemically. In fact, TiZrNi quasicrystals are known to absorb hydrogen maximum of the hydrogen to host metal ratio (H/M) value of near 2.0. The critical disadvantage, however, is that the equilibrium vapor pressure of hydrogen is very low (less than 1 Torr). To overcome this engineering drawback, we added a small amount of vanadium (V) in Ti(53-x)Zr27Ni20V(x), alloys (where x = 0 to 15) and rapidly quenched the molten ingots to form quasicrystals, and investigated the effects of V in terms of changes of structure, the H/M values, and an equilibrium vapor pressure of hydrogen. As the results, an equilibrium vapor pressure significantly increased from 0.84 to 2.16 Torr while the maximum H/M value decreased from 1.32 to 1.11 as increasing x = 0 to 8. After hydrogenation, the main peaks shifted evenly to the lower angle of 20 in X-ray diffraction patterns with uniform expansion of the quasilattice constants which demonstrates that hydrogen atoms homogeneously diffused into the samples. A Laves phase starts to form at x = 13 and the samples completely transformed to the phase at x = 15 suggesting the similarity between the quasicrystal and the Laves phase. PMID:25971068

  13. Crystallographic Features and State Stability of the Decagonal Quasicrystal in the Al-Co-Cu Alloy System

    NASA Astrophysics Data System (ADS)

    Nakayama, Kei; Mizutani, Akito; Koyama, Yasumasa

    2016-11-01

    In the Al-Co-Cu alloy system, both the decagonal quasicrystal with the space group of Poverline{10}m2 and its approximant Al13Co4 phase with monoclinic Cm symmetry are present around 20 at. % Co-10 at. % Cu. In this study, we examined the crystallographic features of prepared Al-(30 - x) at. % Co-x at. % Cu samples mainly by transmission electron microscopy in order to make clear the crystallographic relation between the decagonal quasicrystal and the monoclinic Al13Co4 structure. The results revealed a coexistence state consisting of decagonal quasicrystal and approximant Al13Co4 regions in Al-20 at. % Co-10 at. % Cu alloy samples. With the help of the coexistence state, the orientation relationship was established between the monoclinic Al13Co4 structure and the decagonal quasicrystal. In the determined relationship, the crystallographic axis in the quasicrystal was found to be parallel to the normal direction of the (010)m plane in the Al13Co4 structure, where the subscript m denotes the monoclinic system. Based on data obtained experimentally, the state stability of the decagonal quasicrystal was also examined in terms of the Hume-Rothery (HR) mechanism on the basis of the nearly-free-electron approximation. It was found that a model based on the HR mechanism could explain the crystallographic features such as electron diffraction patterns and atomic arrangements found in the decagonal quasicrystal. In other words, the HR mechanism is most likely appropriate for the stability of the decagonal quasicrystal in the Al-Co-Cu alloy system.

  14. Icosahedral packing of B12 icosahedra in boron suboxide (B6O)

    NASA Astrophysics Data System (ADS)

    Hubert, Hervé; Devouard, Bertrand; Garvie, Laurence A. J.; O'Keeffe, Michael; Buseck, Peter R.; Petuskey, William T.; McMillan, Paul F.

    1998-01-01

    Objects with icosahedral symmetry (Ih) bear a special fascination; natural examples are rare, but include radiolaria and virus particles (virions). The discovery of C60, a molecule in the shape of a truncated icosahedron with Ih symmetry, has aroused widespread interest. In 1962, Mackay described a radiating packing of spheres in Ih symmetry, in which the centres of successive shells of spheres lie on the surfaces of icosahedra. There has been extensive investigation of the conditions under which such packing might be realized in assemblies of atoms or of molecules such as C60 (ref. 5). Here we report the preparation, at high temperatures and pressures, of boron suboxide (B6O) in which the preferred form of the material is as macroscopic, near-perfect, regular icosahedra, similar to the multiply-twinned particles observed in some cubic materials. A major difference is that B6O has a rhombohedral structure that nearly exactly fits the geometrical requirements needed to obtain icosahedral twins. These icosahedral particles have a structure that can be described as a Mackay packing of icosahedral B12 units, and thus has long-ranged order without translational symmetry.

  15. Nucleation and Growth of Icosahedral Boron Suboxide Clusters at High Pressure

    NASA Astrophysics Data System (ADS)

    McMillan, Paul F.; Hubert, Hervé; Chizmeshya, Andrew; Petuskey, William T.; Garvie, Lawrence A. J.; Devouard, Bertrand

    1999-10-01

    The stoichiometry of boron suboxide (B6O1-δ) synthesized from mixtures of boron and boron oxide (B2O3) at high pressure lies closer to the nominal composition (δ=0) than materials obtained at atmospheric pressure. The materials obtained in the high pressure syntheses in the presence of molten B2O3 also have a higher degree of crystallinity than for sintered powders. For syntheses at temperatures of 1700-1800°C at pressures between 4 and approximately 5.5 GPa, the well-crystallized particles are dominated by icosahedral multiply-twinned particles up to approximately 40 μm in diameter. This unusual morphology is obtained by Mackay packing, i.e., by assembly of successive shells of icosahedral B12 units around a central icosahedral nucleus to give a multiply twinned particle in which each of the 20 elements has the Roverline3m space group of the rhombohedral α-B structure. We examine the thermodynamic and kinetic factors associated with the development of this morphology during high pressure growth and use ab initio calculations to investigate the energetic driving forces for initiation of the Mackay packing around the central icosahedral nucleus.

  16. Studies of Inactivation Mechanism of non-enveloped icosahedral viruses by a visible ultrashort pulsed laser

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The inactivation mechanism of ultrashort pulsed laser irradiation at a wavelength of 425 nm has been studied using two different-sized, non-enveloped icosahedral viruses, murine norovirus-1 (MNV-1) and human papillomavirus-16 (HPV-16) pseudovirions. Our experimental results are consistent with a mo...

  17. Stability of monatomic and diatomic quasicrystals and the influence of noise

    NASA Astrophysics Data System (ADS)

    Roth, J.; Schilling, R.; Trebin, H.-R.

    1990-02-01

    The stability of quasicrystals endowed with atomic Lennard-Jones-like pair potentials was investigated with use of the method of steepest descent. Starting from two- and three-dimensional Penrose patterns, the basic units were decorated in various fashions with one or two sorts of atoms. In accord with previous studies, all monatomic two-dimensional quasicrystals decay to a hexagonal periodic crystal with defects; diatomic systems remain stable when the relative size of the atoms is suitably chosen. In three dimensions, the monatomic quasicrystalline unit-sphere packing was proven stable as well as the structure of truncated icosahedra, even if in the initial configuration the atoms were displaced statistically up to 7% and 25%, respectively, of the edge length (noise). A series of decorations (among them one involving Mackay icosahedra) relaxed to the amorphous state. In these transitions the atoms arrange in families of Fibonacci planes whose separations scale down to atomic distances in a self-similar fashion.

  18. A simple configuration for fabrication of 2D and 3D photonic quasicrystals with complex structures

    NASA Astrophysics Data System (ADS)

    Sun, XiaoHong; Wang, Shuai; Liu, Wei; Jiang, LiuDi

    2016-06-01

    A simple method using a single-prism common-path interferometer is presented for the fabrication of complex quasicrystals in sub-micrometer scales. Multiple types of two-dimensional (2D) and three-dimensional (3D) quasicrystalline structures are designed and their diffraction patterns are obtained by using Fourier Transform method. Multi-fold rotational symmetries are demonstrated and compared. By using this method, a wide range of quasicrystals types can be produced with arbitrary complexities and rotational symmetries. The transmittance studies of 12-fold and 18-fold structures also reveal the existence of complete photonic bandgaps, which also demonstrates increased symmetry and significantly improved characteristics of photonic band-gaps.

  19. Harmonic response of multilayered one-dimensional quasicrystal plates subjected to patch loading

    NASA Astrophysics Data System (ADS)

    Waksmanski, Natalie; Pan, Ernian; Yang, Lian-Zhi; Gao, Yang

    2016-08-01

    Dynamic analyses of a multilayered one-dimensional quasicrystal plate subjected to a patch harmonic loading with simply supported lateral boundary conditions are presented. The pseudo-Stroh formulation and propagator matrix method are used to obtain the exact three-dimensional response of the plate. In order to avoid resonance, the frequency of the patch loading is chosen away from the natural frequencies by introducing a small imaginary part. The patch loading is expressed in the form of a double Fourier series expansion. Comprehensive numerical results are shown for a sandwich plate with two different stacking sequences. The results reveal the influence of layering, loading area, phonon-phason coupling coefficient and input frequency. This work is the first step towards understanding quasicrystals under intricate loading conditions such as indentation and impact, and the exact closed-form solution can serve as a reference in convergence studies of other numerical methods and for verification of existing or future plate theories.

  20. Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

    NASA Astrophysics Data System (ADS)

    Brajuskovic, V.; Barrows, F.; Phatak, C.; Petford-Long, A. K.

    2016-10-01

    Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. Additionally, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1D avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism.

  1. Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

    PubMed Central

    Brajuskovic, V.; Barrows, F.; Phatak, C.; Petford-Long, A. K.

    2016-01-01

    Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. Additionally, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1D avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism. PMID:27694973

  2. X-ray Reflectivity Study of AlPdMn Quasicrystal Fivefold Surface Oxidation

    NASA Astrophysics Data System (ADS)

    Gu, Tianqu; Goldman, Alan I.; Pinhero, P. J.

    1997-03-01

    By means of X-ray reflectivity measurement, a fivefold surface of AlPdMn single quasicrystal is studied after being treated in different environments: normal air, humid air and water. An electron density profile of the surface is acquired after each treatment. The difference of the density profile obtained with different treatment indicates that water molecule plays an important role in the oxidation of quasicrystal surface. The surface exposed to normal air has a sharper electron density profile and less surface oxidation thickness than that exposed to humid air and immersed in water. The thickness of the oxidation layer is about 30Åand 58Åfor normal air treatment and humid air and water treatment, respectively.

  3. Antiplane analysis for an elliptical inclusion in 1D hexagonal piezoelectric quasicrystal composites

    NASA Astrophysics Data System (ADS)

    Guo, Junhong; Zhang, Zhiying; Xing, Yongming

    2016-02-01

    An elliptical inclusion embedded in an infinite 1D hexagonal piezoelectric quasicrystal matrix is analysed in the framework of linear piezoelasticity of quasicrystals. Using the technique of conformal mapping, the closed-form solutions of the complex potentials, all the field quantities in the matrix and the inclusion are obtained under far-field antiplane mechanical loads of the phonon and phason fields and an inplane electrical load. Several special cases, such as a homogeneous material, a soft and permeable inclusion, an impermeable inclusion, a line inclusion, a rigid inclusion and a crack are reduced by the present results. Some numerical examples are provided to shows the variations of the stresses of the phonon and phason fields and the electric field with the shape of hole/inclusion, the dielectric permittivity and the distance from the hole/inclusion.

  4. Icosahedral stereographic projections in three dimensions for use in dark field TEM.

    PubMed

    Bourdillon, Antony J

    2013-08-01

    Thermodynamics require that rapidly cooled crystals and quasicrystals are relatively defective. Yet, without convenient 3-dimensional indexation both at crystal poles and in diffraction planes, or Kikuchi maps, it is difficult to identify the defects by dark field transmission electron microscopy. For two phase Al6Mn, these maps are derived. They relate i-Al6Mn to the standard face centered cubic, matrix crystals. An example of their usefulness in determining interfacial characteristics is described. Indices are integral powers on an irrational number.

  5. Opening of an icosahedral boron framework: A combined infrared spectroscopic and computational study

    NASA Astrophysics Data System (ADS)

    Fagiani, Matias R.; Liu Zeonjuk, L.; Esser, Tim K.; Gabel, Detlef; Heine, Thomas; Asmis, Knut R.; Warneke, Jonas

    2015-04-01

    The opening of an icosahderal boron cage in the periodinated closo-dodecaborate B12I122- upon deiodination is studied using cryogenic ion trap vibrational spectroscopy combined with electronic structure calculations. Comparison of simulated vibrational spectra to the infrared photodissociation spectra of messenger-tagged B12I122- and B12In- (n = 7-9) formed by skimmer collision induced dissociation shows that the larger clusters absorb exclusively below 975 cm-1 and hence exhibit quasi-icosahedral B12-cage structures, while the higher energy absorptions in-between 1000 and 1300 cm-1 observed for n = 7 can only be recovered by considering a breakup of the icosahedral cage upon deiodination from n = 8 to n = 7.

  6. Dual-phase glassy/nanoscale icosahedral phase materials in Cu–Zr–Ti–Pd system alloys

    SciTech Connect

    Louzguine-Luzgin, Dmitri V.; Churyumov, A.Yu.

    2014-10-15

    The present work is devoted to an investigation of the formation kinetics, stability and homogeneity area of the nanoscale icosahedral phase formed on heating in the dual-phase glassy/quasicrystalline phase Cu–Zr–Ti–Pd alloys. The data obtained indicate that the Cu–Zr–Ti–Pd icosahedral phase is not a Cu-rich part of the compositional homogeneity area of the Zr–Cu–Pd one. Moreover, Ti, as well as Pd, is found to be an important element stabilizing quasicrystalline phase in the Cu–Zr–Ti–Pd alloys. The formation criteria for Cu- and Zr/Hf-based icosahedral phases are discussed based on the quasilattice constant to average atomic diameter ratio. Deviation from a certain ratio leads to destabilization of the icosahedral phase. By using the isothermal calorimetry traces transformation kinetics above and below the glass-transition region was analyzed. Some difference in the transformation kinetics above and below the glass-transition region allows us to suggest that possible structure changes occur upon glass-transition. - Highlights: • Formation kinetics, stability and homogeneity area of nanoscale icosahedral phase • Cu–Zr–Ti–Pd icosahedral phase is not a Cu-rich part of Zr–Cu–Pd one. • Ti, as well as Pd, is an important element stabilizing quasicrystalline phase. • Difference in transformation kinetics above and below glass-transition region.

  7. Experimental observation and computer simulation of HOLZ line patterns of quasicrystalline icosahedral phase

    NASA Astrophysics Data System (ADS)

    Dai, Mingxing; Wang, Renhui

    1990-01-01

    Higher-order Laue zone (HOLZ) line patterns of an Al 76Si 4Mn 20 quasi- crystalline icosahedral phase (I phase) have been obtained experimentally with a large angular range by connecting a series of conventional convergent-beam electron diffraction patterns. The computer simulated HOLZ line patterns covering the whole orientation triangle of the I phase, which were calculated by using cut and projection method and the simple quasilattice model, show principle agreement with the experimental ones.

  8. Icosahedral symmetry breaking: C(60) to C(84), C(108) and to related nanotubes.

    PubMed

    Bodner, Mark; Bourret, Emmanuel; Patera, Jiri; Szajewska, Marzena

    2015-05-01

    This paper completes the series of three independent articles [Bodner et al. (2013). Acta Cryst. A69, 583-591, (2014), PLOS ONE, 10.1371/journal.pone.0084079] describing the breaking of icosahedral symmetry to subgroups generated by reflections in three-dimensional Euclidean space {\\bb R}^3 as a mechanism of generating higher fullerenes from C60. The icosahedral symmetry of C60 can be seen as the junction of 17 orbits of a symmetric subgroup of order 4 of the icosahedral group of order 120. This subgroup is noted by A1 × A1, because it is isomorphic to the Weyl group of the semi-simple Lie algebra A1 × A1. Thirteen of the A1 × A1 orbits are rectangles and four are line segments. The orbits form a stack of parallel layers centered on the axis of C60 passing through the centers of two opposite edges between two hexagons on the surface of C60. These two edges are the only two line segment layers to appear on the surface shell. Among the 24 convex polytopes with shell formed by hexagons and 12 pentagons, having 84 vertices [Fowler & Manolopoulos (1992). Nature (London), 355, 428-430; Fowler & Manolopoulos (2007). An Atlas of Fullerenes. Dover Publications Inc.; Zhang et al. (1993). J. Chem. Phys. 98, 3095-3102], there are only two that can be identified with breaking of the H3 symmetry to A1 × A1. The remaining ones are just convex shells formed by regular hexagons and 12 pentagons without the involvement of the icosahedral symmetry.

  9. Vibration isolation support system for a truncated icosahedral gravitational wave antenna

    NASA Astrophysics Data System (ADS)

    Velloso, W. F.; Melo, J. L.; Aguiar, O. D.

    2000-06-01

    We designed a mechanical isolation system for an icosahedral resonant gravitational wave detector we plan to construct in Brazil. We have used the NASTRAN finite element software to perform the numerical analysis. Our results show that the designed system could allow a damping factor better than -200 dB in the spectral range of interest, which is adequate to the sensibility level we want for the antenna.

  10. Antiferromagnetic order in the Cd6R (R = rare earth) quasicrystal approximants

    NASA Astrophysics Data System (ADS)

    Goldman, Alan; Kim, Min Gyu; Beutier, Guillaume; Kreyssig, Andreas; Hiroto, Takanobu; Yamada, Tsunetomo; Kim, Jong Woo; de Boissieu, Marc; Tamura, Ryuji

    2013-03-01

    Many theoretical treatments of spins on aperiodic lattices support the notion of long-range antiferromagnetic order. However, to date, there has been no experimental confirmation of long-range magnetic order in quasicrystalline systems. The absence of long-range magnetic order extends to crystalline approximant phases of the icosahedral structures as well. Surprisingly, the 1/1 approximant to the Cd-Mg-R icosahedral phases, Cd6 R , appears to be an exception to the rule. Here, we report on the results of x-ray resonant magnetic scattering measurements on Cd6 R approximants which show that long range antiferromagnetic order is, indeed, realized. For R = Tb and Ho, viewing the structure as a body-centered cubic packing of Tsai clusters, we find that the R ions associated with the icosahedral cluster at the corner of the unit cell are antiferromagnetically correlated with the R ions associated with the icosahedral cluster at the body-center of the unit cell. Work at the Ames Laboratory was supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, US Department of Energy. Work at the Tokyo University of Science was supported by KAKENHI (Grant No. 20045017)

  11. Interactions among K+-Ca2+ exchange, sorption of m-dinitrobenzene, and smectite quasicrystal dynamics.

    PubMed

    Chatterjee, Ritushree; Laird, David A; Thompson, Michael L

    2008-12-15

    The fate of organic contaminants in soils and sediments is influenced by sorption of the compounds to surfaces of soil materials. We investigated the interaction among sorption of an organic compound, cation exchange reactions, and both the size and swelling of smectite quasicrystals. Two reference smectites that vary in location and amount of layer charge, SPV (a Wyoming bentonite) and SAz-1 were initially Ca- and K-saturated and then equilibrated with mixed 0.01 M KCl and 0.005 M CaCl2 salt solutions both with and without the presence of 200 mg L(-1) m-dinitrobenzene (m-DNB). In general, sorption of m-DNB increased with the amount of K+ in the system for both clays, and the SPV sorbed more m-DNB than the SAz-1. Sorption of m-DNB increased the preference of Ca-SPV for K+ relative to Ca2+ but had little effect on K+-Ca2+ selectivity for K-SPV. Selectivity for K+ relative to Ca2+ was slightly higher for both K-SAz-1 and Ca-SAz-1 in the presence of m-DNB than in its absence. Distinct hysteresis loops were observed for the K+-Ca2+ cation exchange reactions for both clays, and the legacy of having been initially Ca- or K-saturated influenced sorption of m-DNB by SPV but had little effect for SAz-1. Suspension X-ray diffraction was used to measure changes in d-spacing and the relative thickness of smectite quasicrystals during the cation exchange and m-DNB sorption reactions. The results suggest that interactions among cation exchange and organic sorption reactions are controlled byan inherently hysteretic complex feedback process that is regulated by changes in the size and extent of swelling of smectite quasicrystals. PMID:19174877

  12. Fundamental solutions in a half space of two-dimensional hexagonal quasicrystal and their applications

    SciTech Connect

    Wang, T.; Li, X. Y.; Zhang, X.; Müller, R.

    2015-04-21

    Fundamental phonon-phason field in a half-infinite space of two-dimensional hexagonal quasicrystal is derived, on the basis of general solutions in terms of quasi-harmonic functions, by virtue of the trial-and-error technique. Extended Boussinesq and Cerruti problems are studied. Appropriate potential functions are assumed and corresponding fundamental solutions are explicitly derived in terms of elementary functions. The boundary integral equations governing the contact and crack problems are constructed from the present fundament solutions. The obtained analytical solutions can serve as guidelines for future indentation tests via scanning probe microscopy and atomic force microscopy methods.

  13. Insights into plant consciousness from neuroscience, physics and mathematics: a role for quasicrystals?

    PubMed

    Gardiner, John

    2012-09-01

    There is considerable debate over whether plants are conscious and this, indeed, is an important question. Here I look at developments in neuroscience, physics and mathematics that may impact on this question. Two major concomitants of consciousness in animals are microtubule function and electrical gamma wave synchrony. Both these factors may also play a role in plant consciousness. I show that plants possess aperiodic quasicrystal structures composed of ribosomes that may enable quantum computing, which has been suggested to lie at the core of animal consciousness. Finally I look at whether a microtubule fractal suggests that electric current plays a part in conventional neurocomputing processes in plants.

  14. Electronic structure and magnetism for a supercell model of Al-Mn quasicrystals

    NASA Astrophysics Data System (ADS)

    Jaswal, S. S.; He, X.-G.

    1992-07-01

    Self-consistent spin-polarized electronic-structure calculations are carried out on a supercell of a 54-atom Mackay icosahedron used to simulate a Al78Mn22 quasicrystal. When the 12 Mn atoms are placed at the corners of the inner icosahedron, they do not develop any magnetic moment. When they are placed at the corners of the outer icosahedron, the magnetic moment per manganese atom is 1.39μB, which is in very good agreement with the experimental data for this composition.

  15. Icosahedral boron clusters: a perfect tool for the enhancement of polymer features.

    PubMed

    Núñez, R; Romero, I; Teixidor, F; Viñas, C

    2016-10-01

    Boron clusters and organic molecules display manifestly different electronic, physical, chemical and geometrical characteristics. These differences highlight the complementarity of organic synthons and boron clusters, and therefore the feasibility of producing hybrid polymers incorporating both types of fragments. This review focuses on the development of hybrid organic-inorganic π conjugated, silane, siloxane and coordination polymers containing icosahedral boron clusters in the last few decades, which have received considerable academic and technological interest due to the combination of the electronic, optical and thermal properties of traditional inorganic materials with many of the desirable properties of organic plastics, including mechanical flexibility and low production costs.

  16. High Pressure X-ray Diffraction Study on Icosahedral Boron Arsenide (B12As2)

    SciTech Connect

    J Wu; H Zhu; D Hou; C Ji; C Whiteley; J Edgar; Y Ma

    2011-12-31

    The high pressure properties of icosahedral boron arsenide (B12As2) were studied by in situ X-ray diffraction measurements at pressures up to 25.5 GPa at room temperature. B12As2 retains its rhombohedral structure; no phase transition was observed in the pressure range. The bulk modulus was determined to be 216 GPa with the pressure derivative 2.2. Anisotropy was observed in the compressibility of B12As2-c-axis was 16.2% more compressible than a-axis. The boron icosahedron plays a dominant role in the compressibility of boron-rich compounds.

  17. Human Rhinovirus Subviral A Particle Binds to Lipid Membranes over a Twofold Axis of Icosahedral Symmetry

    PubMed Central

    Kumar, Mohit

    2013-01-01

    Minor group human rhinoviruses bind low-density lipoprotein (LDL) receptors for endocytosis. Once they are inside endosomes, the acidic pH triggers their dissociation from the receptors and conversion into hydrophobic subviral A particles; these attach to the membrane and transfer their single-strand, positive-sense RNA genome into the cytosol. Here, we allowed human rhinovirus 2 (HRV2) A particles, produced in vitro by incubation at pH 5.4, to attach to liposomes; cryo-electron microscopy 3-dimensional single-particle image reconstruction revealed that they bind to the membrane around a 2-fold icosahedral symmetry axis. PMID:23946453

  18. Stability comparison of several icosahedral structure units of Al-Cr alloys

    NASA Astrophysics Data System (ADS)

    Liu, Da; Wang, Renhui; Ye, Yiying

    1991-02-01

    Total energies for three types of icosahedral structure units of Al-Cr alloys have been calculated based on the embedded-atom method. The results show that the most stable structure unit is the small icosahedron with a Cr atom at its center, and the hypothetical structures based on the Mackay icosahedron and Bergman rhombic triacontahedron possess higher energies compared with those of the face-centered-cubic-solid solutions and the mechanical mixtures of pure Al and Cr crystals. These results are found to be consistent with experiment.

  19. 3 nj-symbols and harmonic superposition coefficients: an icosahedral abacus

    NASA Astrophysics Data System (ADS)

    Aquilanti, Vincenzo; Coletti, Cecilia

    2001-08-01

    Angular momentum recoupling coefficients of angular momentum theory and matrix elements for basis set transformation of hyperspherical harmonics enjoy properties and sum rules crucial for applications but complicated without the guidance of graphical techniques. These coefficients being related to Racah's polynomials, the graphs also apply to polynomials of the hypergeometric family, their q-analogues and their `elliptic' extensions. A useful `abacus' exploiting the connections with presentations of icosahedral and related symmetries is introduced. Particular and limiting cases, such as those of the semiclassical type, allow a unified view of properties of angular and hyperangular momentum algebra, including relationships among vector coupling coefficients and rotation matrix elements.

  20. Studies of inactivation mechanism of non-enveloped icosahedral virus by a visible ultrashort pulsed laser

    PubMed Central

    2014-01-01

    Background Low-power ultrashort pulsed (USP) lasers operating at wavelengths of 425 nm and near infrared region have been shown to effectively inactivate viruses such as human immunodeficiency virus (HIV), M13 bacteriophage, and murine cytomegalovirus (MCMV). It was shown previously that non-enveloped, helical viruses such as M13 bacteriophage, were inactivated by a USP laser through an impulsive stimulated Raman scattering (ISRS) process. Recently, enveloped virus like MCMV has been shown to be inactivated by a USP laser via protein aggregation induced by an ISRS process. However, the inactivation mechanism for a clinically important class of viruses – non-enveloped, icosahedral viruses remains unknown. Results and discussions We have ruled out the following four possible inactivation mechanisms for non-enveloped, icosahedral viruses, namely, (1) inactivation due to ultraviolet C (UVC) photons produced by non-linear optical process of the intense, fundamental laser beam at 425 nm; (2) inactivation caused by thermal heating generated by the direct laser absorption/heating of the virion; (3) inactivation resulting from a one-photon absorption process via chromophores such as porphyrin molecules, or indicator dyes, potentially producing reactive oxygen or other species; (4) inactivation by the USP lasers in which the extremely intense laser pulse produces shock wave-like vibrations upon impact with the viral particle. We present data which support that the inactivation mechanism for non-enveloped, icosahedral viruses is the impulsive stimulated Raman scattering process. Real-time PCR experiments show that, within the amplicon size of 273 bp tested, there is no damage on the genome of MNV-1 caused by the USP laser irradiation. Conclusion We conclude that our model non-enveloped virus, MNV-1, is inactivated by the ISRS process. These studies provide fundamental knowledge on photon-virus interactions on femtosecond time scales. From the analysis of the transmission

  1. STM study of the atomic structure of the icosahedral Al-Cu-Fe fivefold surface

    NASA Astrophysics Data System (ADS)

    Cai, T.; Fournée, V.; Lograsso, T.; Ross, A.; Thiel, P. A.

    2002-04-01

    We use scanning tunneling microscopy (STM) to investigate the atomic structure of the icosahedral (i-) Al-Cu-Fe fivefold surface in ultra high vacuum (UHV). Studies show that large, atomically flat terraces feature many ten-petal ``flowers'' with internal structure. The observed flower patterns can be associated with features on Al rich dense atomic planes generated from two-dimensional cuts of bulk models based on x-ray and neutron diffraction experiments. The results confirm that the fivefold surface of i-Al-Cu-Fe corresponds to a bulk-terminated plane.

  2. A Vertically Flow-Following, Icosahedral Grid Model for Medium-Range and Seasonal Prediction. Part 1: Model Description

    NASA Technical Reports Server (NTRS)

    Bleck, Rainer; Bao, Jian-Wen; Benjamin, Stanley G.; Brown, John M.; Fiorino, Michael; Henderson, Thomas B.; Lee, Jin-Luen; MacDonald, Alexander E.; Madden, Paul; Middlecoff, Jacques; Rosinski, James; Smirnova, Tanya G.; Sun, Shan; Wang, Ning

    2015-01-01

    A hydrostatic global weather prediction model based on an icosahedral horizontal grid and a hybrid terrain following/ isentropic vertical coordinate is described. The model is an extension to three spatial dimensions of a previously developed, icosahedral, shallow-water model featuring user-selectable horizontal resolution and employing indirect addressing techniques. The vertical grid is adaptive to maximize the portion of the atmosphere mapped into the isentropic coordinate subdomain. The model, best described as a stacked shallow-water model, is being tested extensively on real-time medium-range forecasts to ready it for possible inclusion in operational multimodel ensembles for medium-range to seasonal prediction.

  3. Icosahedral Order, Frustration, and the Glass Transition: Evidence from Time-Dependent Nucleation and Supercooled Liquid Structure Studies

    SciTech Connect

    Shen, Y.T.; Kim, T.H.; Gangopadhyay, A.K.; Kelton, K.F.

    2009-06-05

    One explanation for the glass transition is a geometrical frustration owing to the development of non-space-filling short-range order (icosahedral, tetrahedral). However, experimental demonstrations of this are lacking. Here, the first quantitative measurements of the time-dependent nucleation rate in a Zr59Ti3Cu20Ni8Al10 bulk metallic glass are combined with the first measurements of the evolution of the supercooled liquid structure to near the glass transition temperature to provide strong support for an icosahedral-order-based frustration model for the glass transition in Zr-based glasses.

  4. An NMR Evidence of Sharp Features in the Pseudogap of Quasicrystals

    NASA Astrophysics Data System (ADS)

    Tang, X.-P.; Wonnell, S. K.; Hill, E. A.; Wu, Y.; Poon, S. J.

    1997-03-01

    The electronic properties of the quasicrystals have been studied by ^27Al, ^63Cu and ^65Cu NMR. The nuclear spin- lattice relaxation rate was found to obey a universal T^2 temperature dependence over a wide temperature range (90K-500K) in quasicrystalline i-AlCuRu, i-AlCuFe, i-AlPdRe and crystalline approximant α-AlMnSi. The relaxation mechanism was proven to be electronic in origin. This unconventional temperature dependence is a clear evidence of a sharp feature in the electronic density-of-state (DOS) near the Fermi level E_F, N(E)=N_0[1+(|E-E_F|/Δ)^1/2]. A weak temperature dependence of the Knight shift K ∝ T^1/2, as a result of this type of DOS was also observed. Such DOS was expected for a Van Hove-type singularity as well as theoretical predictions based on the model of hierarchy of clusters(C. Janot et. al., Phys. Rev. Lett. 72, 1674(1994)). Our NMR study suggests that it is a common feature in quasicrystals. It was found that i-AlPdRe, i- AlCuRu possess sharper pseudogaps and smaller N(E_F) than in the other samples, in agreement with the established heat capacity, electric conductivity measurements.

  5. NMR charaterization of the pseudogap at the Fermi level in Quasicrystals

    NASA Astrophysics Data System (ADS)

    Tang, X.-P.; Wonnell, S. K.; Hill, E. A.; Wu, Y.; Poon, S. J.

    1996-11-01

    The electronic properties of quasicrystals and their crystalline approximants have been studied by ^27Al nuclear magnetic resonance. An anomalous temperature dependence of the spin-lattice relaxation rate (T_1-1), T_1-1 ~ T^2, was observed in a broad temperature range in i-AlCuFe, R-AlCuFe, i-AlCuRu, i-AlPdRe, and α-AlMnSi. This temperature dependence can be explained by the presence of a pseudogap described by g(E) ~ |E-E_F|^1/2. This type of density-of-state was predicted by a recent theoretical calculation(C. Janot et. al., Phys. Rev. Lett. 72, 1674(1994)) and also was indicated by a recent photonemission measurement (X. Wu et. al., Phys. Rev. Lett. 75, 4540(1995)) in i-AlPdMn. Our NMR results gave the first experimental evidence that this special electronic density-of-state is a common feature in quasicrystals. For all these samples, reasonable width of the pseudogap has been obtained from the temperature dependence of the spin-lattice relaxation rate. A weak temperature dependence of the Knight shift K ~ T^1/2, as a result of g(E) ~ |E-E_F|^1/2 is also consistent with our ^27Al measurements.

  6. First observation of ferromagnetic order in an artificial 2D quasicrystal

    NASA Astrophysics Data System (ADS)

    Farmer, Barry; Bhat, Vinayak; Balk, Andrew; Unguris, John; de Long, Lance

    2015-03-01

    Magnetic order in bulk quasicrystals is not well understood and known materials exhibit short-range, spin-glass order. We patterned ferromagnetic (FM) thin films into artificial quasicrystals, a new class of metamaterials that exhibits complex magnetic reversal and dynamics that can be controlled via tiling design. We analyzed two-dimensional SEMPA images of magnetization textures of Penrose P2 tilings (P2T) patterned into Permalloy. The diverse, asymmetric vertex coordinations drive novel, non-stochastic switching and complex spin-ice behaviors that reflect the influence of vertex domain wall energies. Monte Carlo and OOMMF simulation analyses of SEMPA images of slowly grown, never-field-cycled P2T reveal low energy, long-range ordered sublattices that form building blocks of a ground state. A fully ordered ground state is unresolved without long-range dipolar interactions that stabilize a magnetically ordered state with a net moment. Our P2T constitute a set of quasicrystalline metamaterials in which frustration and magnetic order among classical Ising spins can be directly studied. Kentucky research supported by U.S. DoE Grant DE-FG02-97ER45653 and NSF Grant EPS-0814194. ALB acknowledges support under the Cooperative Research Agreement between the University of Maryland and NIST.

  7. David Adler Lectureship Award in the Field of Materials Physics Talk: Surfaces of Quasicrystals

    NASA Astrophysics Data System (ADS)

    Thiel, Patricia

    2010-03-01

    Quasiperiodic order is recognized (in a utilitarian, rather than a mathematical sense) by the absence of periodicity, concurrent with a classically-forbidden rotational symmetry. It is quite beautiful, having captured the attention of scientists and artists alike. Following the discovery of quasiperiodic order in a real system,footnotetextD. Shechtman, I. Blech, D. Gratias, and J.W. Cahn, Phys. Rev. Lett. 53, 1951 (1984). many metallic alloys and intermetallics were found to exhibit this type of order on the atomic scale. More recently ``soft'' quasicrystals were discovered,footnotetextL. Bindi, P.J. Steinhardt, N. Yao, and P.J. Lu, Science 324, 1306 (2009). and nanocrystalline arrays were found to spontaneously adopt quasiperiodic order.footnotetextD.V. Talapin, E.V. Shevchenko, M.I. Bodnarchuk, X. Ye, J. Chen, and C.B. Murray, Nature 461 , 964 (2009). From a scientific perspective, quasicrystals are alluring because they allow us to test the relationship between atomic structure and physical properties. This talk deals with the ways in which our understanding of solid surfaces has been both enriched and challenged by these complex materials.footnotetextP. Thiel, Annu. Rev. Phys. Chem. (2008).^,footnotetextV. Fourn'ee, J. Ledieu, and P. Thiel, J. Phys: Condens. Matter. 20, 3310301 (2008). properties of the metallic quasicrystals originally generated interest because they were unusual.footnotetextJ.M. Dubois, Useful Quasicrystals(World Scientific, Singapore, 2005). For instance, among Al-rich alloys, the Al-based quasicrystalline phases exhibit puzzling resistance to surface oxidation. Also, Al-rich quasicrystals have surprisingly good and promising catalytic properties (e.g. for steam reforming of methanol).footnotetextA.P. Tsai and M. Yoshimura, Appl. Cat. A: General 214 , 237 (2001). Perhaps most famously, they exhibit low friction.^7 Comparisons with crystalline materials have established that these features are deeply related to the quasiperiodic atomic

  8. Origin of Quantum Criticality in Yb-Al-Au Approximant Crystal and Quasicrystal

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinji; Miyake, Kazumasa

    2016-06-01

    To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb15Al34Au51, the approximant crystal Yb14Al35Au51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits χ ˜ T-0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.

  9. Hierarchy of bond stiffnesses within icosahedral-based gold clusters protected by thiolates

    PubMed Central

    Yamazoe, Seiji; Takano, Shinjiro; Kurashige, Wataru; Yokoyama, Toshihiko; Nitta, Kiyofumi; Negishi, Yuichi; Tsukuda, Tatsuya

    2016-01-01

    Unique thermal properties of metal clusters are believed to originate from the hierarchy of the bonding. However, an atomic-level understanding of how the bond stiffnesses are affected by the atomic packing of a metal cluster and the interfacial structure with the surrounding environment has not been attained to date. Here we elucidate the hierarchy in the bond stiffness in thiolate-protected, icosahedral-based gold clusters Au25(SC2H4Ph)18, Au38(SC2H4Ph)24 and Au144(SC2H4Ph)60 by analysing Au L3-edge extended X-ray absorption fine structure data. The Au–Au bonds have different stiffnesses depending on their lengths. The long Au–Au bonds, which are more flexible than those in the bulk metal, are located at the icosahedral-based gold core surface. The short Au–Au bonds, which are stiffer than those in the bulk metal, are mainly distributed along the radial direction and form a cyclic structural backbone with the rigid Au–SR oligomers. PMID:26778685

  10. Coupled ocean-atmosphere modeling on horizontally icosahedral and vertically hybrid-isentropic/isopycnic grids.

    NASA Astrophysics Data System (ADS)

    Bleck, Rainer; Sun, Shan; Li, Haiqin; Benjamin, Stan

    2016-04-01

    Current efforts to close the gap between weather prediction and climate models have led to the construction of a coupled ocean-atmosphere system consisting of two high-resolution component models, operating on matching icosahedral grids and utilizing adaptive, near-isentropic/isopycnic vertical coordinates. The two components models, FIM and HYCOM (the latter converted to an icosahedral mesh for this purpose), have been tested extensively in twice-daily global medium-range weather prediction (http://fim.noaa.gov) and in real-time ocean data assimilation (http://hycom.org), respectively. The use of matching horizontal grids, currently at resolutions of 15km, 30km and 60km, avoids coastline ambiguities and interpolation errors at the air-sea interface. The intended purpose of the coupled model being subseasonal-to-seasonal prediction, our focus is on mid-term precipitation biases and the statistical steadiness of the atmospheric circulation (blocking frequency, Rossby wave breaking, meridional heat transport, etc.), as well as on possible causes of ocean model drift. An attempt is made to isolate the weather model's role in modifying water mass properties and ocean circulations (including meridional overturning) by comparing coupled model results to ocean-only experiments forced by observed atmospheric boundary conditions. A multi-decadal run at 60km resolution is used to illustrate ENSO variability in the coupled system.

  11. Symmetry-adapted digital modeling III. Coarse-grained icosahedral viruses.

    PubMed

    Janner, A

    2016-05-01

    Considered is the coarse-grained modeling of icosahedral viruses in terms of a three-dimensional lattice (the digital modeling lattice) selected among the projected points in space of a six-dimensional icosahedral lattice. Backbone atomic positions (Cα's for the residues of the capsid and phosphorus atoms P for the genome nucleotides) are then indexed by their nearest lattice point. This leads to a fine-grained lattice point characterization of the full viral chains in the backbone approximation (denoted as digital modeling). Coarse-grained models then follow by a proper selection of the indexed backbone positions, where for each chain one can choose the desired coarseness. This approach is applied to three viruses, the Satellite tobacco mosaic virus, the bacteriophage MS2 and the Pariacoto virus, on the basis of structural data from the Brookhaven Protein Data Bank. In each case the various stages of the procedure are illustrated for a given coarse-grained model and the corresponding indexed positions are listed. Alternative coarse-grained models have been derived and compared. Comments on related results and approaches, found among the very large set of publications in this field, conclude this article. PMID:27126109

  12. The Marine Algal Virus PpV01 Has an Icosahedral Capsid with T=219 Quasisymmetry

    PubMed Central

    Yan, Xiaodong; Chipman, Paul R.; Castberg, Tonje; Bratbak, Gunnar; Baker, Timothy S.

    2005-01-01

    Phaeocystis pouchetii virus (PpV01) infects and lyses the haptophyte Phaeocystis pouchetii (Hariot) Lagerheim and was first isolated from Norwegian coastal waters. We have used electron cryomicroscopy and three-dimensional image reconstruction methods to examine the native morphology of PpV01 at a resolution of 3 nm. The icosahedral capsid of PpV01 has a maximum diameter of 220 nm and is composed of 2,192 capsomers arranged with T=219 quasisymmetry. One specific capsomer in each asymmetric unit contains a fiber-like protrusion. Density attributed to the presence of a lipid membrane appears just below (inside) the capsid. PpV01 is the largest icosahedral virus whose capsid structure has been determined in three dimensions from images of vitrified samples. Striking similarities in the structures of PpV01 and a number of other large double-stranded DNA viruses are consistent with a growing body of evidence that they share a common evolutionary origin. PMID:15994818

  13. Molecular dynamics simulation of radiation damage in CaCd{sub 6} quasicrystal cubic approximant up to 10 keV

    SciTech Connect

    Chen, P. H.; Avchachov, K.; Nordlund, K.; Pussi, K.

    2013-06-21

    Due to the peculiar nature of the atomic order in quasicrystals, examining phase transitions in this class of materials is of particular interest. Energetic particle irradiation can provide a way to modify the structure locally in a quasicrystal. To examine irradiation-induced phase transitions in quasicrystals on the atomic scale, we have carried out molecular dynamics simulations of collision cascades in CaCd{sub 6} quasicrystal cubic approximant with energies up to 10 keV at 0 and 300 K. The results show that the threshold energies depend surprisingly strongly on the local coordination environments. The energy dependence of stable defect formation exhibits a power-law dependence on cascade energy, and surviving defects are dominated by Cd interstitials and vacancies. Only a modest effect of temperature is observed on defect survival, while irradiation temperature increases lead to a slight increase in the average size of both vacancy clusters and interstitial clusters.

  14. Covalent bonds and their crucial effects on pseudogap formation in α-Al(Mn,Re)Si icosahedral quasicrystalline approximant

    NASA Astrophysics Data System (ADS)

    Kirihara, K.; Nagata, T.; Kimura, K.; Kato, K.; Takata, M.; Nishibori, E.; Sakata, M.

    2003-07-01

    X-ray charge densities of Al-based icosahedral quasicrystalline approximant crystals α-AlReSi, α-AlMnSi, and Al12Re were observed by a combination of the maximum entropy method with the Rietveld method. We successfully obtained the clear images of interatomic covalent bonds between Al and transition metals (Mn, Re) and those in the Al (or Si) icosahedron in Mackay icosahedral clusters of both α-AlReSi and α-AlMnSi approximant crystals. The bonding nature of the three kinds of glue atom sites connecting Mackay icosahedral clusters was also clarified. This covalent bonding nature should strongly relate with the enhancement of the electron density-of-states pseudogap near the Fermi level. In addition, the interatomic covalent bonds of α-AlReSi are stronger than those of α-AlMnSi. This fact leads to the low effective carrier density of α-AlReSi in comparison with that of α-AlMnSi. Unlike the covalent bonding nature of an icosahedron in α-AlReSi and α-AlMnSi crystals, the Al icosahedron with an Re center atom exhibits no Al-Al interatomic covalent bonds in the Al12Re crystal. The tendency for metallic-covalent bonding conversion in the Al icosahedron, which is related to the atom site occupancy of the icosahedral cluster center, is also strongly supported.

  15. Performance Analysis of high-order remap-type advection scheme on icosahedral-hexagonal grid

    NASA Astrophysics Data System (ADS)

    Mittal, Rashmi; Dubey, Sarvesh; Saxena, Vaibhav; Meurdesoif, Yann

    2014-05-01

    A comparative performance analysis on computational cost of second order advection schemes FF-CSLAM (Flux form conservative semi-Lagrangian multi-tracer transport scheme) and it's two simplifications on Icosahedral grid has been presented. Tracer transport is one of the main building blocks in atmospheric models and hence their performance greatly determines the overall performance of the model. FF-CSLAM falls in the category of arbitrary Lagrangian Eulerian (ALE) scheme. It exploits the finite volume formulation and therefore it is inherently conservative. Flux-area through edges are approximated with great circle arcs in an upwind fashion. Bi-quadratic sub-grid scale reconstructions using weighted least-squares method is employed to approximate trace field. Area integrals on the overlapped region of flux-area and static Eulerian meshes are evaluated via line-integrals. A brief description of implementation of FF-CSLAM on icosahedral -hexagonal meshes along with and its numerical accuracy in terms of standard test cases will be presented. A comparative analysis of the computational overhead is necessary to assess the suitability of FF-CSLAM for massively parallel and multi-threading computer architectures in comparison to other advection schemes implemented on icosahedral grids. The main focus of this work is to present the implementation of the shared memory parallelization and to describe the memory access pattern of the numerical scheme. FF-CSLAM is a remap-type advection scheme, thus extra calculation are done in comparison to the other advection schemes. The additional computations are associated with the search required to find the overlap area between the area swept through the edge and the underlining grid. But the experiments shows that the associated computational overhead is minimal for multi-tracer transport. It will be shown that for the Courant Number less than one, FF-CSLAM, the computations are not expensive. Since the grid cells are arranged in

  16. The Three-Dimensional Finite-Volume Non-Hydrostatic Icosahedral Model (NIM)

    NASA Astrophysics Data System (ADS)

    Lee, J. L.; MacDonald, A. E.

    2014-12-01

    A multi-scales Non-hydrostatic Icosahedral Model (NIM) has been developed at Earth System Research Laboratory (ESRL) to meet NOAA's future prediction mission ranging from mesoscale short-range, high-impact weather forecasts to longer-term intra-seasonal climate prediction. NIM formulates the latest numerical innovation of the three-dimensional finite-volume control volume on the quasi-uniform icosahedral grid suitable for ultra-high resolution simulations. NIM is designed to utilize the state-of-art computing architecture such as Graphic Processing Units (GPU) processors to run globally at kilometer scale resolution to explicitly resolve convective storms and complex terrains. The novel features of NIM numerical design include: 1.1. A local coordinate system upon which finite-volume integrations are undertaken. The use of a local Cartesian coordinate greatly simplifies the mathematic formulation of the finite-volume operators and leads to the finite-volume integration along straight lines on the plane, rather than along curved lines on the spherical surface. 1.2. A general indirect addressing scheme developed for modeling on irregular grid. It arranges the icosahedral grid with a one-dimensional vector loop structure, table specified memory order, and an indirect addressing scheme that yields very compact code despite the complexities of this grid. 1.3. Use of three-dimensional finite-volume integration over control volumes constructed on the height coordinates. Three-dimensional finite-volume integration accurately represents the Newton Third Law over terrain and improves pressure gradient force over complex terrain. 1.4. Use of the Runge-Kutta 4th order conservative and positive-definite transport scheme 1.5. NIM dynamical solver has been implemented on CPU as well as GPU. As one of the potential candidates for NWS next generation models, NIM dynamical core has been successfully verified with various benchmark test cases including those proposed by DCMIP

  17. Protruding Features of Viral Capsids Are Clustered on Icosahedral Great Circles.

    PubMed

    Wilson, David P

    2016-01-01

    Spherical viruses are remarkably well characterized by the Triangulation (T) number developed by Casper and Klug. The T-number specifies how many viral capsid proteins are required to cover the virus, as well as how they are further subdivided into pentamer and hexamer subunits. The T-number however does not constrain the orientations of these proteins within the subunits or dictate where the proteins should place their protruding features. These protrusions often take the form of loops, spires and helices, and are significant because they aid in stability of the capsid as well as recognition by the host organism. Until now there has be no overall understanding of the placement of protrusions for spherical viruses, other than they have icosahedral symmetry. We constructed a set of gauge points based upon the work affine extensions of Keef and Twarock, which have fixed relative angular locations with which to measure the locations of these features. This work adds a new element to our understanding of the geometric arrangement of spherical viral capsid proteins; chiefly that the locations of protruding features are not found stochastically distributed in an icosahedral manner across the viral surface, but instead these features are found only in specific locations along the 15 icosahedral great circles. We have found that this result holds true as the T number and viral capsids size increases, suggesting an underlying geometric constraint on their locations. This is in spite of the fact that the constraints on the pentamers and hexamer orientations change as a function of T-number, as you need to accommodate more hexamers in the same solid angle between pentamers. The existence of this angular constraint of viral capsids suggests that there is a fitness or energetic benefit to the virus placing its protrusions in this manner. This discovery may have profound impacts on identifying and eliminating viral pathogens, understanding evolutionary constraints as well as

  18. Protruding Features of Viral Capsids Are Clustered on Icosahedral Great Circles

    PubMed Central

    Wilson, David P.

    2016-01-01

    Spherical viruses are remarkably well characterized by the Triangulation (T) number developed by Casper and Klug. The T-number specifies how many viral capsid proteins are required to cover the virus, as well as how they are further subdivided into pentamer and hexamer subunits. The T-number however does not constrain the orientations of these proteins within the subunits or dictate where the proteins should place their protruding features. These protrusions often take the form of loops, spires and helices, and are significant because they aid in stability of the capsid as well as recognition by the host organism. Until now there has be no overall understanding of the placement of protrusions for spherical viruses, other than they have icosahedral symmetry. We constructed a set of gauge points based upon the work affine extensions of Keef and Twarock, which have fixed relative angular locations with which to measure the locations of these features. This work adds a new element to our understanding of the geometric arrangement of spherical viral capsid proteins; chiefly that the locations of protruding features are not found stochastically distributed in an icosahedral manner across the viral surface, but instead these features are found only in specific locations along the 15 icosahedral great circles. We have found that this result holds true as the T number and viral capsids size increases, suggesting an underlying geometric constraint on their locations. This is in spite of the fact that the constraints on the pentamers and hexamer orientations change as a function of T-number, as you need to accommodate more hexamers in the same solid angle between pentamers. The existence of this angular constraint of viral capsids suggests that there is a fitness or energetic benefit to the virus placing its protrusions in this manner. This discovery may have profound impacts on identifying and eliminating viral pathogens, understanding evolutionary constraints as well as

  19. Thermal Conductivity and Seebeck Coefficients of Icosahedral Boron Arsenide Films on Silicon Carbide

    SciTech Connect

    Y Gong; Y Zhang; M Dudley; Y Zhang; J Edgar; P Heard; M Kuball

    2011-12-31

    The thermal conductivity of icosahedral boron arsenide (B{sub 12}As{sub 2}) films grown on (0001) 6H-SiC substrates by chemical vapor deposition was studied by the 3{omega} technique. The room temperature thermal conductivity decreased from 27.0 to 15.3 W/m K as the growth temperature was decreased from 1450 to 1275 C. This is mainly attributed to the differences in the impurity concentration and microstructure, determined from secondary ion mass spectrometry and high resolution transmission electron microscopy, respectively. Callaway's theory was applied to calculate the temperature-dependent thermal conductivity, and the results are in good agreement with the experimental data. Seebeck coefficients were determined as 107 {micro}V/K and 136 {micro}V/K for samples grown at 1350 C with AsH{sub 3}/B{sub 2}H{sub 6} flow ratio equals to 1:1 and 3:5, respectively.

  20. Reinterpretation of the zero-temperature conductivity in icosahedral AlPdRe

    NASA Astrophysics Data System (ADS)

    Rapp, Ö.

    2016-07-01

    The zero-temperature conductivity σ (0 ) of icosahedral (i )-AlPdRe has been found to be simply related to the resistance ratio R =ρ4.2 K/ρ295 K by a power law, σ (0 ) ˜R-1.74 , over four orders of magnitude in σ (0 ) . This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R . Electronic transport properties of single grain i -AlPdRe samples are thus found to be on common ground with polygrain i -AlPdRe. The relation between R and σ (0 ) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants.

  1. Defining criteria for oligomannose immunogens for HIV using icosahedral virus capsid scaffolds.

    PubMed

    Astronomo, Rena D; Kaltgrad, Eiton; Udit, Andrew K; Wang, Sheng-Kai; Doores, Katie J; Huang, Cheng-Yuan; Pantophlet, Ralph; Paulson, James C; Wong, Chi-Huey; Finn, M G; Burton, Dennis R

    2010-04-23

    The broadly neutralizing antibody 2G12 recognizes a conserved cluster of high-mannose glycans on the surface envelope spike of HIV, suggesting that the "glycan shield" defense of the virus can be breached and may, under the right circumstances, serve as a vaccine target. In an attempt to recreate features of the glycan shield semisynthetically, oligomannosides were coupled to surface lysines on the icosahedral capsids of bacteriophage Q beta and cowpea mosaic virus (CPMV). The Q beta glycoconjugates, but not CPMV, presented oligomannose clusters that bind the antibody 2G12 with high affinity. However, antibodies against these 2G12 epitopes were not detected in immunized rabbits. Rather, alternative oligomannose epitopes on the conjugates were immunodominant and elicited high titers of anti-mannose antibodies that do not crossreact with the HIV envelope. The results presented reveal important design considerations for a carbohydrate-based vaccine component for HIV. PMID:20416507

  2. Defining criteria for oligomannose immunogens for HIV using icosahedral virus capsid scaffolds.

    PubMed

    Astronomo, Rena D; Kaltgrad, Eiton; Udit, Andrew K; Wang, Sheng-Kai; Doores, Katie J; Huang, Cheng-Yuan; Pantophlet, Ralph; Paulson, James C; Wong, Chi-Huey; Finn, M G; Burton, Dennis R

    2010-04-23

    The broadly neutralizing antibody 2G12 recognizes a conserved cluster of high-mannose glycans on the surface envelope spike of HIV, suggesting that the "glycan shield" defense of the virus can be breached and may, under the right circumstances, serve as a vaccine target. In an attempt to recreate features of the glycan shield semisynthetically, oligomannosides were coupled to surface lysines on the icosahedral capsids of bacteriophage Q beta and cowpea mosaic virus (CPMV). The Q beta glycoconjugates, but not CPMV, presented oligomannose clusters that bind the antibody 2G12 with high affinity. However, antibodies against these 2G12 epitopes were not detected in immunized rabbits. Rather, alternative oligomannose epitopes on the conjugates were immunodominant and elicited high titers of anti-mannose antibodies that do not crossreact with the HIV envelope. The results presented reveal important design considerations for a carbohydrate-based vaccine component for HIV.

  3. Single particle analysis integrated with microscopy: a high-throughput approach for reconstructing icosahedral particles.

    PubMed

    Yan, Xiaodong; Cardone, Giovanni; Zhang, Xing; Zhou, Z Hong; Baker, Timothy S

    2014-04-01

    In cryo-electron microscopy and single particle analysis, data acquisition and image processing are generally carried out in sequential steps and computation of a three-dimensional reconstruction only begins once all the micrographs have been acquired. We are developing an integrated system for processing images of icosahedral particles during microscopy to provide reconstructed density maps in real-time at the highest possible resolution. The system is designed as a combination of pipelines to run in parallel on a computer cluster and analyzes micrographs as they are acquired, handling automatically all the processing steps from defocus estimation and particle picking to origin/orientation determination. An ab initio model is determined independently from the first micrographs collected, and new models are generated as more particles become available. As a proof of concept, we simulated data acquisition sessions using three sets of micrographs of good to excellent quality that were previously recorded from different icosahedral viruses. Results show that the processing of single micrographs can keep pace with an acquisition rate of about two images per minute. The reconstructed density map improves steadily during the image acquisition phase and its quality at the end of data collection is only moderately inferior to that obtained by expert users who processed semi-automatically all the micrographs after the acquisition. The current prototype demonstrates the advantages of integrating three-dimensional image processing with microscopy, which include an ability to monitor acquisition in terms of the final structure and to predict how much data and microscope resources are needed to achieve a desired resolution.

  4. Single particle analysis integrated with microscopy: a high-throughput approach for reconstructing icosahedral particles

    PubMed Central

    Zhang, Xing; Zhou, Z. Hong; Baker, Timothy S.

    2014-01-01

    In cryo-electron microscopy and single particle analysis, data acquisition and image processing are generally carried out in sequential steps and computation of a three-dimensional reconstruction only begins once all the micrographs have been acquired. We are developing an integrated system for processing images of icosahedral particles during microscopy to provide reconstructed density maps in real-time at the highest possible resolution. The system is designed as a combination of pipelines to run in parallel on a computer cluster and analyzes micrographs as they are acquired, handling automatically all the processing steps from defocus estimation and particle picking to origin/orientation determination. An ab-initio model is determined independently from the first micrographs collected, and new models are generated as more particles become available. As a proof of concept, we simulated data acquisition sessions using three sets of micrographs of good to excellent quality that were previously recorded from different icosahedral viruses. Results show that the processing of single micrographs can keep pace with an acquisition rate of about two images per minute. The reconstructed density map improves steadily during the image acquisition phase and its quality at the end of data collection is only moderately inferior to that obtained by expert users who processed semi-automatically all the micrographs after the acquisition. The current prototype demonstrates the advantages of integrating three-dimensional image processing with microscopy, which include an ability to monitor acquisition in terms of the final structure and to predict how much data and microscope resources are needed to achieve a desired resolution. PMID:24613762

  5. Three-dimensional reconstruction of icosahedral particles from single micrographs in real time at the microscope

    PubMed Central

    Cardone, Giovanni; Yan, Xiaodong; Sinkovits, Robert S.; Tang, Jinghua; Baker, Timothy S.

    2013-01-01

    Single particle analysis is a valuable tool in cryo-electron microscopy for determining the structure of biological complexes. However, the conformational state and the preparation of the sample are factors that play a critical role in the ultimate attainable resolution. In some cases extensive analysis at the microscope of a sample under different conditions is required to derive the optimal acquisition conditions. Currently this analysis is limited to raw micrographs, thus conveying only limited information on the structure of the complex. We are developing a computing system that generates a three-dimensional reconstruction from a single micrograph acquired under cryogenic and low dose conditions, and containing particles with icosahedral symmetry. The system provides the microscopist with immediate structural information from a sample, while it is in the microscope and during the preliminary acquisition stage. The system is designed to run without user intervention on a multi-processor computing resource and integrates all the processing steps required for the analysis. Tests performed on experimental data sets show that the probability of obtaining a reliable reconstruction from one micrograph is primarily determined by the quality of the sample, with success rates close to 100% when sample conditions are optimal, and decreasing to about 60% when conditions are sub-optimal. The time required to generate a reconstruction depends significantly on the diameter of the particles, and in most instances takes about one minute. The proposed approach can provide valuable three-dimensional information, albeit at low resolution, on conformational states, epitope binding, and stoichiometry of icosahedral multi-protein complexes. PMID:23891839

  6. Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology

    PubMed Central

    Legendre, Matthieu; Bartoli, Julia; Shmakova, Lyubov; Jeudy, Sandra; Labadie, Karine; Adrait, Annie; Lescot, Magali; Poirot, Olivier; Bertaux, Lionel; Bruley, Christophe; Couté, Yohann; Rivkina, Elizaveta; Abergel, Chantal; Claverie, Jean-Michel

    2014-01-01

    The largest known DNA viruses infect Acanthamoeba and belong to two markedly different families. The Megaviridae exhibit pseudo-icosahedral virions up to 0.7 μm in diameter and adenine–thymine (AT)-rich genomes of up to 1.25 Mb encoding a thousand proteins. Like their Mimivirus prototype discovered 10 y ago, they entirely replicate within cytoplasmic virion factories. In contrast, the recently discovered Pandoraviruses exhibit larger amphora-shaped virions 1 μm in length and guanine–cytosine-rich genomes up to 2.8 Mb long encoding up to 2,500 proteins. Their replication involves the host nucleus. Whereas the Megaviridae share some general features with the previously described icosahedral large DNA viruses, the Pandoraviruses appear unrelated to them. Here we report the discovery of a third type of giant virus combining an even larger pandoravirus-like particle 1.5 μm in length with a surprisingly smaller 600 kb AT-rich genome, a gene content more similar to Iridoviruses and Marseillevirus, and a fully cytoplasmic replication reminiscent of the Megaviridae. This suggests that pandoravirus-like particles may be associated with a variety of virus families more diverse than previously envisioned. This giant virus, named Pithovirus sibericum, was isolated from a >30,000-y-old radiocarbon-dated sample when we initiated a survey of the virome of Siberian permafrost. The revival of such an ancestral amoeba-infecting virus used as a safe indicator of the possible presence of pathogenic DNA viruses, suggests that the thawing of permafrost either from global warming or industrial exploitation of circumpolar regions might not be exempt from future threats to human or animal health. PMID:24591590

  7. Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology.

    PubMed

    Legendre, Matthieu; Bartoli, Julia; Shmakova, Lyubov; Jeudy, Sandra; Labadie, Karine; Adrait, Annie; Lescot, Magali; Poirot, Olivier; Bertaux, Lionel; Bruley, Christophe; Couté, Yohann; Rivkina, Elizaveta; Abergel, Chantal; Claverie, Jean-Michel

    2014-03-18

    The largest known DNA viruses infect Acanthamoeba and belong to two markedly different families. The Megaviridae exhibit pseudo-icosahedral virions up to 0.7 μm in diameter and adenine-thymine (AT)-rich genomes of up to 1.25 Mb encoding a thousand proteins. Like their Mimivirus prototype discovered 10 y ago, they entirely replicate within cytoplasmic virion factories. In contrast, the recently discovered Pandoraviruses exhibit larger amphora-shaped virions 1 μm in length and guanine-cytosine-rich genomes up to 2.8 Mb long encoding up to 2,500 proteins. Their replication involves the host nucleus. Whereas the Megaviridae share some general features with the previously described icosahedral large DNA viruses, the Pandoraviruses appear unrelated to them. Here we report the discovery of a third type of giant virus combining an even larger pandoravirus-like particle 1.5 μm in length with a surprisingly smaller 600 kb AT-rich genome, a gene content more similar to Iridoviruses and Marseillevirus, and a fully cytoplasmic replication reminiscent of the Megaviridae. This suggests that pandoravirus-like particles may be associated with a variety of virus families more diverse than previously envisioned. This giant virus, named Pithovirus sibericum, was isolated from a >30,000-y-old radiocarbon-dated sample when we initiated a survey of the virome of Siberian permafrost. The revival of such an ancestral amoeba-infecting virus used as a safe indicator of the possible presence of pathogenic DNA viruses, suggests that the thawing of permafrost either from global warming or industrial exploitation of circumpolar regions might not be exempt from future threats to human or animal health.

  8. A parametric study of the lensing properties of dodecagonal photonic quasicrystals

    NASA Astrophysics Data System (ADS)

    Di Gennaro, E.; Morello, D.; Miletto, C.; Savo, S.; Andreone, A.; Castaldi, G.; Galdi, V.; Pierro, V.

    2008-04-01

    We present a study of the lensing properties of two-dimensional (2-D) photonic quasicrystal (PQC) slabs made of dielectric cylinders arranged according to a 12-fold-symmetric square-triangle aperiodic tiling. Our full-wave numerical analysis confirms the results recently emerged in the technical literature and, in particular, the possibility of achieving focusing effects within several frequency regions. However, contrary to the original interpretation, such focusing effects turn out to be critically associated to local symmetry points in the PQC slab, and strongly dependent on its thickness and termination. Nevertheless, our study reveals the presence of some peculiar properties, like the ability to focus the light even for slabs with a reduced lateral width, or beaming effects, which render PQC slabs potentially interesting and worth of deeper investigation.

  9. Simultaneous large band gaps and localization of electromagnetic and elastic waves in defect-free quasicrystals.

    PubMed

    Yu, Tianbao; Wang, Zhong; Liu, Wenxing; Wang, Tongbiao; Liu, Nianhua; Liao, Qinghua

    2016-04-18

    We report numerically large and complete photonic and phononic band gaps that simultaneously exist in eight-fold phoxonic quasicrystals (PhXQCs). PhXQCs can possess simultaneous photonic and phononic band gaps over a wide range of geometric parameters. Abundant localized modes can be achieved in defect-free PhXQCs for all photonic and phononic polarizations. These defect-free localized modes exhibit multiform spatial distributions and can confine simultaneously electromagnetic and elastic waves in a large area, thereby providing rich selectivity and enlarging the interaction space of optical and elastic waves. The simulated results based on finite element method show that quasiperiodic structures formed of both solid rods in air and holes in solid materials can simultaneously confine and tailor electromagnetic and elastic waves; these structures showed advantages over the periodic counterparts.

  10. Negative refraction and localized states of a classical wave in high-symmetry quasicrystals

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangdong; Zhong, Wei; Feng, Zhifang; Wang, Yiquan; Li, Zhi-Yuan; Zhang, Dao-Zhong

    2011-07-01

    Recently, negative refraction of electromagnetic waves in periodic photonic crystals has been demonstrated experimentally and sub-wavelength images observed. A theoretical and experimental investigation is reported of the electromagnetic wave transport in high-symmetry photonic quasicrystals (QCs). It is shown that negative refraction can appear in these transparent quasicrystalline photonic structures. It is interesting that highly symmetric two-dimensional photonic QCs possess a universal feature for non-near-field focus of two kinds of polarized waves (S wave and P wave). That is, the non-near-field focus for two kinds of polarized waves can be realized by using flat lenses, which consist of some high-symmetric two-dimensional photonic QCs with the same structures and parameters. In addition, some two-dimensional and three-dimensional localized states in defect-free photonic QCs have been found. It is evident that these unusual localized states can be explored by means of electron energy loss spectroscopy.

  11. Long-range magnetic order in models for rare-earth quasicrystals

    NASA Astrophysics Data System (ADS)

    Thiem, Stefanie; Chalker, J. T.

    2015-12-01

    We take a two-step theoretical approach to study magnetism of rare-earth quasicrystals by considering Ising spins on quasiperiodic tilings, coupled via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. First, we compute RKKY interactions from a tight-binding Hamiltonian defined on the two-dimensional quasiperiodic tilings. We find that the magnetic interactions are frustrated and strongly dependent on the local environment. This results in the formation of clusters with strong bonds at certain patterns of the tilings that repeat quasiperiodically. Second, we examine the statistical mechanics of Ising spins with these RKKY interactions, using extensive Monte Carlo simulations. Although models that have frustrated interactions and lack translational invariance might be expected to display spin-glass behavior, we show that the spin system has a phase transition to low-temperature states with long-range quasiperiodic magnetic order. Additionally, we find that in some of the systems spin clusters can fluctuate much below the ordering temperature.

  12. Self-generation of dissipative solitons in magnonic quasicrystal active ring resonator

    SciTech Connect

    Grishin, S. V. Beginin, E. N.; Morozova, M. A.; Sharaevskii, Yu. P.; Nikitov, S. A.

    2014-02-07

    Self-generation of dissipative solitons in the magnonic quasicrystal (MQC) active ring resonator is studied theoretically and experimentally. The developed magnonic crystal has quasiperiodic Fibonacci type structure. Frequency selectivity of the MQC together with the parametric three-wave decay of magnetostatic surface spin wave (MSSW) leads to the dissipative soliton self-generation. The transfer matrix method is used to describe MQC transmission responses. Besides, the model of MQC active ring resonator is suggested. The model includes three coupled differential equations describing the parametric decay of MSSW and two differential equations of linear oscillators describing the frequency selectivity of MQC. Numerical simulation results of dissipative soliton self-generation are in a fair agreement with experimental data.

  13. Evidence from x-ray and neutron powder diffraction patterns that the so-called icosahedral and decagonal quasicrystals of MnAl/sub 6/ and other alloys are twinned cubic crystals

    SciTech Connect

    Pauling, L.

    1987-06-01

    It is shown that the x-ray powder diffraction patterns of rapidly quenched MnAl/sub 6/ and Mg/sub 32/(Al,Zn)/sub 49/ and the neutron powder diffraction pattern of MnAl/sub 5/ are compatible with the proposed 820-atom primitive cubic structure. The values found for the edge of the unit cube are 23.365 A (x-ray) and 23.416 A (neutron) for MnAl/sub 6/ and 24.313 A (x-ray) for Mg/sub 32/(Al,Zn)/sub 49/.

  14. Studies of Nucleation, Growth, Specific Heat, and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Croat, T. K.; Gangopadhyay, A.; Holland-Moritz, D.; Hyers, Robert W.; Rathz, Thomas J.; Robinson, Michael B.; Rogers, Jan R.

    2001-01-01

    Undercooling experiments and thermal physical property measurements of metallic alloys on the International Space Station (ISS) are planned. This recently-funded research focuses on fundamental issues of the formation and structure of highly-ordered non-crystallographic phases (quasicrystals) and related crystal phases (crystal approximants), and the connections between the atomic structures of these phases and those of liquids and glasses. It extends studies made previously by us of the composition dependence of crystal nucleation processes in silicate and metallic glasses, to the case of nucleation from the liquid phase. Motivating results from rf-levitation and drop-tube measurements of the undercooling of Ti/Zr-based liquids that form quasicrystals and crystal approximants are discussed. Preliminary measurements by electrostatic levitation (ESL) are presented.

  15. Atomic Scale coexistence of Periodic and quasiperiodic order in a2-fold A1-Ni-Co decagonal quasicrystal surface

    SciTech Connect

    Park, Jeong Young; Ogletree, D. Frank; Salmeron, Miquel; Ribeiro,R.A.; Canfield, P.C.; Jenks, C.J.; Thiel, P.A.

    2005-11-14

    Decagonal quasicrystals are made of pairs of atomic planes with pentagonal symmetry periodically stacked along a 10-fold axis. We have investigated the atomic structure of the 2-fold surface of a decagonal Al-Ni-Co quasicrystal using scanning tunneling microscopy (STM). The surface consists of terraces separated by steps of heights 1.9, 4.7, 7.8, and 12.6{angstrom} containing rows of atoms parallel to the 10-fold direction with an internal periodicity of 4{angstrom}. The rows are arranged aperiodically, with separations that follow a Fibonacci sequence and inflation symmetry. The results indicate that the surfaces are preferentially Al-terminated and in general agreement with bulk models.

  16. Oliver E. Buckley Condensed Matter Prize Talk: Once upon a time in Kamchatka: The Search for Natural Quasicrystals

    NASA Astrophysics Data System (ADS)

    Steinhardt, Paul

    2010-03-01

    Twenty-five years ago, soon after the concept of quasicrystals was introducedfootnotetextD. Levine and P.J. Steinhardt, PRL 53, 2477 (1984). and the first examples were synthesized in the laboratory,footnotetextD. Shechtman, I. Blech, D. Gratias and J.W. Cahn, PRL 53, 1951 (1984). the search for a naturally-forming quasicrystal began. For many years, the search was informal. However, beginning about a decade ago,footnotetextP.J. Lu, K. Deffeyes, P.J. Steinhardt, and N. Yao, PRL 87, 275507 (2001). a systematic search was developed that, through planning and much serendipity, led to the discovery this past year of a natural candidate embedded in a rock reported to have been found in a remote region on the northern Kamchatka peninsula.footnotetextL. Bindi, P.J. Steinhardt, N. Yao and P.J. Lu, Science 324, 1306 (2009). The talk will describe the search for natural quasicrystals and the implications for physics and geology.

  17. Fundamentals in generalized elasticity and dislocation theory of quasicrystals: Green tensor, dislocation key-formulas and dislocation loops

    NASA Astrophysics Data System (ADS)

    Lazar, Markus; Agiasofitou, Eleni

    2014-12-01

    The present work provides fundamental quantities in generalized elasticity and dislocation theory of quasicrystals. In a clear and straightforward manner, the three-dimensional Green tensor of generalized elasticity theory and the extended displacement vector for an arbitrary extended force are derived. Next, in the framework of dislocation theory of quasicrystals, the solutions of the field equations for the extended displacement vector and the extended elastic distortion tensor are given; that is, the generalized Burgers equation for arbitrary sources and the generalized Mura-Willis formula, respectively. Moreover, important quantities of the theory of dislocations as the Eshelby stress tensor, Peach-Koehler force, stress function tensor and the interaction energy are derived for general dislocations. The application to dislocation loops gives rise to the generalized Burgers equation, where the displacement vector can be written as a sum of a line integral plus a purely geometric part. Finally, using the Green tensor, all other dislocation key-formulas for loops, known from the theory of anisotropic elasticity, like the Peach-Koehler stress formula, Mura-Willis equation, Volterra equation, stress function tensor and the interaction energy are derived for quasicrystals.

  18. Neutron scattering study of the vibrational density of states in icosahedral and crystalline Al0.80Mn0.20

    NASA Astrophysics Data System (ADS)

    Miceli, P. F.; Youngquist, S. E.; Neumann, D. A.; Zabel, H.; Rush, J. J.; Rowe, J. M.

    1986-12-01

    We present an inelastic neutron scattering study of the vibrational density of states, g¯(E), for the icosahedral and crystalline phases of Al0.80Mn0.20. At low energy transfers we find nearly identical g¯(E)~E2 dependences indicating that the two materials are elastically similar. In the intermediate energy range, 20-35 meV, the crystalline g¯(E) shows weak structure while that of the icosahedral phase remains smooth. Above 40 meV there is an excess of the icosahedral g¯(E) compared to that of the crystalline material. These results provide a direct test for models of the interatomic forces and dynamics of the icosahedral phase.

  19. Structural determination of a 1/1 rational approximant to the icosahedral phase in Ti-Cr-Si alloys

    NASA Astrophysics Data System (ADS)

    Libbert, J. L.; Kelton, K. F.; Goldman, A. I.; Yelon, W. B.

    1994-05-01

    We report the discovery and structural refinement of a large unit cell bcc crystalline phase in a Ti-Cr-Si alloy that is a 1/1 rational approximant to the icosahedral phase in that system. The crystal structure was determined from a Rietveld analysis of x-ray and neutron powder diffraction data. Our results demonstrate that this phase is closely related to the α(Al-Mn-Si) phase, which in turn, is closely related to the structure of the icosahedral phase in the Al-transition-metal alloys. The neutron data indicate that the structure contains a significant amount of oxygen located in the Mackay clusters. Partial ordering of this oxygen may provide an explanation for the localized diffuse scattering often observed in the i phase and related crystalline phases in Ti-transitional-metal alloys.

  20. A control volume method on an icosahedral grid for numerical integration of the shallow-water equations on the sphere

    SciTech Connect

    Chern, I-Liang

    1994-08-01

    Two versions of a control volume method on a symmetrized icosahedral grid are proposed for solving the shallow-water equations on a sphere. One version expresses of the equations in the 3-D Cartersian coordinate system, while the other expresses the equations in the northern/southern polar sterographic coordinate systems. The pole problem is avoided because of these expressions in both versions and the quasi-homogenity of the icosahedral grid. Truncation errors and convergence tests of the numerical gradient and divergent operators associated with this method are studied. A convergence tests of the numerical gradient and divergent operators associated with this method are studied. A convergence test for a steady zonal flow is demonstrated. Several simulations of Rossby-Haurwitz waves with various numbers are also performed.

  1. Structural determination of a 1/1 rational approximant to the icosahedral phase in Ti-Cr-Si alloys

    SciTech Connect

    Libbert, J.L.; Kelton, K.F. ); Goldman, A.I. ); Yelon, W.B. )

    1994-05-01

    We report the discovery and structural refinement of a large unit cell bcc crystalline phase in a Ti-Cr-Si alloy that is a 1/1 rational approximant to the icosahedral phase in that system. The crystal structure was determined from a Rietveld analysis of x-ray and neutron powder diffraction data. Our results demonstrate that this phase is closely related to the [alpha](Al-Mn-Si) phase, which in turn, is closely related to the structure of the icosahedral phase in the Al-transition-metal alloys. The neutron data indicate that the structure contains a significant amount of oxygen located in the Mackay clusters. Partial ordering of this oxygen may provide an explanation for the localized diffuse scattering often observed in the [ital i] phase and related crystalline phases in Ti-transitional-metal alloys.

  2. Pattern formation in icosahedral virus capsids: the papova viruses and Nudaurelia capensis beta virus.

    PubMed Central

    Marzec, C J; Day, L A

    1993-01-01

    The capsids of the spherical viruses all show underlying icosahedral symmetry, yet they differ markedly in capsomere shape and in capsomere position and orientation. The capsid patterns presented by the capsomere shapes, positions, and orientations of three viruses (papilloma, SV40, and N beta V) have been generated dynamically through a bottom-up procedure which provides a basis for understanding the patterns. A capsomere shape is represented in two-dimensional cross-section by a mass or charge density on the surface of a sphere, given by an expansion in spherical harmonics, and referred to herein as a morphological unit (MU). A capsid pattern is represented by an icosahedrally symmetrical superposition of such densities, determined by the positions and orientations of its MUs on the spherical surface. The fitness of an arrangement of MUs is measured by an interaction integral through which all capsid elements interact with each other via an arbitrary function of distance. A capsid pattern is generated by allowing the correct number of approximately shaped MUs to move dynamically on the sphere, positioning themselves until an extremum of the fitness function is attained. The resulting patterns are largely independent of the details of both the capsomere representation and the interaction function; thus the patterns produced are generic. The simplest useful fitness function is sigma 2, the average square of the mass (or charge) density, a minimum of which corresponds to a "uniformly spaced" MU distribution; to good approximation, the electrostatic free energy of charged capsomeres, calculated from the linearized Poisson-Boltzmann equation, is proportional to sigma 2. With disks as MUs, the model generates the coordinated lattices familiar from the quasi-equivalence theory, indexed by triangulation numbers. Using fivefold MUs, the model generates the patterns observed at different radii within the T = 7 capsid of papilloma and at the surface of SV40; threefold MUs

  3. Atomistic modeling of the low-frequency mechanical modes and Raman spectra of icosahedral virus capsids

    NASA Astrophysics Data System (ADS)

    Dykeman, Eric C.; Sankey, Otto F.

    2010-02-01

    We describe a technique for calculating the low-frequency mechanical modes and frequencies of a large symmetric biological molecule where the eigenvectors of the Hessian matrix are determined with full atomic detail. The method, which follows order N methods used in electronic structure theory, determines the subset of lowest-frequency modes while using group theory to reduce the complexity of the problem. We apply the method to three icosahedral viruses of various T numbers and sizes; the human viruses polio and hepatitis B, and the cowpea chlorotic mottle virus, a plant virus. From the normal-mode eigenvectors, we use a bond polarizability model to predict a low-frequency Raman scattering profile for the viruses. The full atomic detail in the displacement patterns combined with an empirical potential-energy model allows a comparison of the fully atomic normal modes with elastic network models and normal-mode analysis with only dihedral degrees of freedom. We find that coarse-graining normal-mode analysis (particularly the elastic network model) can predict the displacement patterns for the first few (˜10) low-frequency modes that are global and cooperative.

  4. The icosahedral RNA virus as a grotto: organizing the genome into stalagmites and stalactites.

    PubMed

    Harvey, Stephen C; Zeng, Yingying; Heitsch, Christine E

    2013-03-01

    There are two important problems in the assembly of small, icosahedral RNA viruses. First, how does the capsid protein select the viral RNA for packaging, when there are so many other candidate RNA molecules available? Second, what is the mechanism of assembly? With regard to the first question, there are a number of cases where a particular RNA sequence or structure--often one or more stem-loops--either promotes assembly or is required for assembly, but there are others where specific packaging signals are apparently not required. With regard to the assembly pathway, in those cases where stem-loops are involved, the first step is generally believed to be binding of the capsid proteins to these "fingers" of the RNA secondary structure. In the mature virus, the core of the RNA would then occupy the center of the viral particle, and the stem-loops would reach outward, towards the capsid, like stalagmites reaching up from the floor of a grotto towards the ceiling. Those viruses whose assembly does not depend on protein binding to stem-loops could have a different structure, with the core of the RNA lying just under the capsid, and the fingers reaching down into the interior of the virus, like stalactites. We review the literature on these alternative structures, focusing on RNA selectivity and the assembly mechanism, and we propose experiments aimed at determining, in a given virus, which of the two structures actually occurs.

  5. Soft-core particles freezing to form a quasicrystal and a crystal-liquid phase.

    PubMed

    Archer, A J; Rucklidge, A M; Knobloch, E

    2015-07-01

    Systems of soft-core particles interacting via a two-scale potential are studied. The potential is responsible for peaks in the structure factor of the liquid state at two different but comparable length scales and a similar bimodal structure is evident in the dispersion relation. Dynamical density functional theory in two dimensions is used to identify two unusual states of this system: a crystal-liquid state, in which the majority of the particles are located on lattice sites but a minority remains free and so behaves like a liquid, and a 12-fold quasicrystalline state. Both are present even for deeply quenched liquids and are found in a regime in which the liquid is unstable with respect to modulations on the smaller scale only. As a result, the system initially evolves towards a small-scale crystal state; this state is not a minimum of the free energy, however, and so the system subsequently attempts to reorganize to generate the lower-energy larger-scale crystals. This dynamical process generates a disordered state with quasicrystalline domains and takes place even when this large scale is linearly stable, i.e., it is a nonlinear process. With controlled initial conditions, a perfect quasicrystal can form. The results are corroborated using Brownian dynamics simulations. PMID:26274178

  6. Wavelength dependence of focusing properties of two-dimensional photonic quasicrystal flat lens.

    PubMed

    Liu, Jianjun; Fan, Zhigang; Hu, Haili; Yang, Maohua; Guan, Chunying; Yuan, Libo; Guo, Hao; Zhang, Xiong

    2012-05-15

    We investigated the wavelength dependence of the focusing properties of a germanium-cylinder-based two-dimensional (2D) decagonal Penrose-type photonic quasicrystal (PQC) flat lens for the first time, to the best of our knowledge. We found that near the second bandgap and in the high-frequency side (between the bandgap boundary and the first light intensity peak) of the pass band, the flat lens can exhibit a focusing effect for a point light source and that the focusing wavelengths can directly be drawn from the photonic band structure. For all the focusing wavelengths, the summation of the object distance and the image distance is less than the thickness of the flat lens when the object distance is half the thickness of the flat lens. As the wavelength increases, the image distance, the image quality, and the effective refractive index of the flat lens increase, whereas the image power of the point light source decreases. The effective refractive index of the flat lens is less than -1.

  7. Nanoscale SEMPA imaging of an artificial quasicrystal spin ice at remanence

    NASA Astrophysics Data System (ADS)

    Balk, Andrew; Bhat, Vinayak; Farmer, Barry; Delong, Lance; Unguris, John; Electron Physics Group, CNST Team

    2015-03-01

    Artificial spin ice has emerged in the past decade as a model metamaterial for studying frustrated magnetic ordering at length scales large enough to be experimentally probed in real space. Recently, complex designs have been engineered to explore exotic behavior in non-square lattices. However, direct measurements of the actual moment directions have not been very common, and interpretation from techniques such as magnetic force microscopy and magneto-optical Kerr effect magnetometry can be complicated by the more complex geometries. Here we demonstrate using SEMPA (scanning electron microscopy with polarization analysis) as a method to robustly measure the ordering direction of elements in a connected artificial quasicrystal. We discuss the applicability of SEMPA to this system, details of the imaging and potential artifacts, and conclusions that can be drawn from the nanoscale two dimensional maps of the moment direction. This work is partially funded by DoE Grant #DE-FG02-97ER45653. ALB acknowledges support of this research under the Cooperative Research Agreement between the University of Maryland and NIST.

  8. Impact-induced shock and the formation of natural quasicrystals in the early solar system.

    PubMed

    Hollister, Lincoln S; Bindi, Luca; Yao, Nan; Poirier, Gerald R; Andronicos, Christopher L; MacPherson, Glenn J; Lin, Chaney; Distler, Vadim V; Eddy, Michael P; Kostin, Alexander; Kryachko, Valery; Steinhardt, William M; Yudovskaya, Marina; Eiler, John M; Guan, Yunbin; Clarke, Jamil J; Steinhardt, Paul J

    2014-06-13

    The discovery of a natural quasicrystal, icosahedrite (Al63Cu24Fe13), accompanied by khatyrkite (CuAl2) and cupalite (CuAl) in the CV3 carbonaceous chondrite Khatyrka has posed a mystery as to what extraterrestrial processes led to the formation and preservation of these metal alloys. Here we present a range of evidence, including the discovery of high-pressure phases never observed before in a CV3 chondrite, indicating that an impact shock generated a heterogeneous distribution of pressures and temperatures in which some portions reached at least 5 GPa and 1,200 °C. The conditions were sufficient to melt Al-Cu-bearing minerals, which then rapidly solidified into icosahedrite and other Al-Cu metal phases. The meteorite also contains heretofore unobserved phases of iron-nickel and iron sulphide with substantial amounts of Al and Cu. The presence of these phases in Khatyrka provides further proof that the Al-Cu alloys are natural products of unusual processes that occurred in the early solar system.

  9. Two-dimensional photonic crystals constructed with a portion of photonic quasicrystals.

    PubMed

    Yang, Yi; Wang, Guo Ping

    2007-05-14

    Photonic quasicrystals (PQs) can produce interesting photonic properties but the lack of periodicity in structures makes exact prediction on their photonic band structures (PBSs) a fundamental challenge currently. Here, we propose a kind of complex two-dimensional photonic crystal (PC) structures constructed with a small portion of different PQs for the purposes of overcoming the difficulty of numerical calculations on the PBSs but maintaining photonic properties of the original PQs owned. Theoretically calculated results on PBSs of the complex PC with a local feature consistent with 12-fold rotational symmetry show that, in the cases of dielectric cylinders in air, air-holes in a dielectric, and metal cylinders in air, respectively, the complex PC can indeed produce similar photonic properties of the original 12-fold PQ such as uniform or isotropic PBGs under much lower dielectric contrast etc. The complex PCs can be constructed with the local parts of n-fold symmetric PQs and should provide a way for creating novel photonic functional materials.

  10. Impact-induced shock and the formation of natural quasicrystals in the early solar system.

    PubMed

    Hollister, Lincoln S; Bindi, Luca; Yao, Nan; Poirier, Gerald R; Andronicos, Christopher L; MacPherson, Glenn J; Lin, Chaney; Distler, Vadim V; Eddy, Michael P; Kostin, Alexander; Kryachko, Valery; Steinhardt, William M; Yudovskaya, Marina; Eiler, John M; Guan, Yunbin; Clarke, Jamil J; Steinhardt, Paul J

    2014-01-01

    The discovery of a natural quasicrystal, icosahedrite (Al63Cu24Fe13), accompanied by khatyrkite (CuAl2) and cupalite (CuAl) in the CV3 carbonaceous chondrite Khatyrka has posed a mystery as to what extraterrestrial processes led to the formation and preservation of these metal alloys. Here we present a range of evidence, including the discovery of high-pressure phases never observed before in a CV3 chondrite, indicating that an impact shock generated a heterogeneous distribution of pressures and temperatures in which some portions reached at least 5 GPa and 1,200 °C. The conditions were sufficient to melt Al-Cu-bearing minerals, which then rapidly solidified into icosahedrite and other Al-Cu metal phases. The meteorite also contains heretofore unobserved phases of iron-nickel and iron sulphide with substantial amounts of Al and Cu. The presence of these phases in Khatyrka provides further proof that the Al-Cu alloys are natural products of unusual processes that occurred in the early solar system. PMID:24925481

  11. Multiple Bragg diffraction in quasicrystals: The issue of centrosymmetry in Al-Pd-Mn

    SciTech Connect

    Lee, H.; Colella, R.; Shen, Q.

    1996-07-01

    When a crystal is rotated around the scattering vector for a Bragg reflection {bold P}, another reflection {bold H} may be simultaneously excited for a particular value {psi} of the azimuthal angle. The plot of the intensity {ital I}{sub {bold P}} vs {psi} (called the {open_quote}{open_quote}azimuthal plot{close_quote}{close_quote}) shows peaks with asymmetric features from which phases of structure factors can be obtained. Multibeam diffraction data have been obtained with a high-quality Al-Pd-Mn quasicrystal using synchrotron x rays. Rocking widths of 36 arcsec have been obtained, which made it possible to obtain data that could be interpreted using dynamical theory without any need of smearing functions to take into account the mosaic spread or other instrumental resolution effects. The asymmetric features and the peak intensity of all azimuthal plots could be fitted with phases consistent with a noncentrosymmetric structure. This conclusion was reinforced by the results of a multibeam experiment with circularly polarized x rays. This is in contrast with several other diffraction experiments based on intensity measurements in the two-beam case. Possible reasons for this discrepancy are discussed. {copyright} {ital 1996 The American Physical Society.}

  12. Stable Icosahedral Hollow Cage Clusters: Stannapherene (Sn12 2-) and Plumbaspherene (Pb12 2-)

    SciTech Connect

    Cui, Lifeng; Wang, Lai S.

    2008-01-01

    One of the major objectives of cluster science is to discover stable atomic clusters, which may be used as building blocks for cluster-assembled nanomaterials. The discovery and bulk synthesis of the fullerenes have sprouted new research disciplines in chemistry and nanoscience and precipitated intense interests to search for other similar stable clusters. However, despite major research efforts, no other analogous gas-phase clusters have been found and yielded to bulk syntheses. In this article, we review our recent discoveries in cluster beam experiments of stannaspherene (Sn12 2–) and plumbaspherene (Pb12 2–), which are highly stable and symmetric cage clusters. The names for these two clusters derive from their icosahedral (Ih) symmetry and delocalized spherical π-bonding that are characteristics of buckminsterfullerene C60. Stannaspherene and plumbaspherene have diameters comparable to that of C60 and can be considered as inorganic analogs of the buckyball. The large internal space in Sn12 2– has been shown to be able to trap any transition metal atom to form new endohedral cage clusters, M@Sn12 –, analogous to endohedral fullerenes. The doped atom in M@Sn12 – keeps its quasi-atomic nature with large magnetic moments. These endohedral cages form a rich class of new building blocks for cluster-assembled materials with tunable magnetic, electronic, and chemical properties. During our attempt to synthesize endohedral stannaspherenes, we crystallized a new Pd2@Sn18 4– cluster, which can be viewed as the fusion of two Pd@Sn12 2– clusters. This result suggests that stannaspherene, plumbaspherene, and a large number of their endohedrally doped species can be synthesized in the bulk.

  13. Transmission properties of a Fibonacci quasi-crystals containing single-negative materials and their usage as multi-channel filters

    NASA Astrophysics Data System (ADS)

    Charkhesht, Ali; Pashaei Adl, Hamid; Roshan Entezar, Samad

    2014-03-01

    One of the interesting phenomena appearing in Fibonacci quasi-crystals is wave localization, so that the field becomes spatially confined in some suitable regions, or delocalized in some other parts. Many theoretical works have been written on this interesting subject. The periodic Fibonacci structure properties lead to a transmission spectrum that exhibits some band gap, and it is possible to control these band gaps by the generation number of this structures. All these properties make Fibonacci quasi-crystals materials very attractive from an optical point of view. Accordingly, the transmission properties of Fibonacci quasi-crystals containing single-negative materials are investigated with the transfer matrix method. It is shown that the periodic structures created by repeating the Fibonacci quasi-crystal generations, have some omnidirectional band gaps at the single-negative frequency region. Moreover, it is shown these band gaps depends on the number of Fibonacci photonic crystal unit cell. In other words, when generation number of Fibonacci photonic crystal unit cell increases, some sub band gaps appears within this omnidirectional band gap. In this work by using Fibonacci quasi-periodic structures we demonstrate that by increasing Generation Number of Unit cell, some omnidirectional sub-gaps will appear which can be used as a multichannel filter.

  14. Analysis of structure and P-c-T curve of hydrogenated Ti53Zr27xNi20Pd(x) quasicrystals.

    PubMed

    Jo, Youngsoo; Lee, Sang-Hwa; Shin, Hong Sik; Kim, Jaeyong

    2013-12-01

    The potential application of TiZrNi quasicrystals was evaluated by measuring the pressure-composition-temperature curves after replacing Zr by Pd to the limit maintaining the host structure for the samples made with Ti53Zr27(-x)Ni20Pd(x), where 0 < or = x < or = 8. The results of X-ray diffraction data revealed that the samples keep the pure quasicrystal structure to the maximum value of x = 8. All diffracted peaks uniformly shifted to the low angle of 2 theta in X-ray diffraction pattern suggesting that hydrogen atoms homogeneously diffuse in the quasicrystals and uniformly expand the quasilattice constants without modification of the structure. After hydrogenation at elevated temperature, the quasi-lattice constants increased from 5.12 to 5.34 angstroms for the samples made with x = 0 without appearing an impurity phase. When Zr was replaced by 8 at.% of Pd, the equilibrium vapor pressures significantly increased to 3.41 from 0.41 Torr at 300 degrees C although the total amount of hydrogen decreased as increasing Pd concentration. These results demonstrate that Pd will play a critical role in application for the TiZrNi quasicrystals as hydrogen storage materials. PMID:24266172

  15. Atomic structure of icosahedral B4C boron carbide from a first principles analysis of NMR spectra.

    PubMed

    Mauri, F; Vast, N; Pickard, C J

    2001-08-20

    Density functional theory is demonstrated to reproduce the 13C and 11B NMR chemical shifts of icosahedral boron carbides with sufficient accuracy to extract previously unresolved structural information from experimental NMR spectra. B4C can be viewed as an arrangement of 3-atom linear chains and 12-atom icosahedra. According to our results, all the chains have a CBC structure. Most of the icosahedra have a B11C structure with the C atom placed in a polar site, and a few percent have a B (12) structure or a B10C2 structure with the two C atoms placed in two antipodal polar sites.

  16. Icositetrahedral and icosahedral atomic configurations observed in the Nb-Ag metallic glasses synthesized by ion beam mixing

    SciTech Connect

    Tai, K. P.; Gao, N.; Dai, X. D.; Li, J. H.; Lai, W. S.; Liu, B. X.

    2006-08-28

    Metallic glasses are obtained in an immiscible Nb-Ag system by ion beam mixing and an atomic configuration in the amorphous structure is discovered, i.e., an icositetrahedral ordering, which, together with an icosahedral ordering also observed in the Nb-Ag metallic glasses and in some previously reported systems, helps in formulating a structural spectrum of the amorphous solids. The experimental characterization and atomistic modeling with an ab initio derived Nb-Ag potential demonstrate the significance of structural heredity, i.e., the crystalline structures of the constituent metals play a decisive role in determining the atomic structure of the metallic glasses in the system.

  17. Microstructural analysis of a FeAl/quasicrystal-based composite prepared using a focused ion beam miller.

    PubMed

    Cairney, J. M.; Munroe, P. R.; Sordelet, D. J.

    2001-02-01

    A composite consisting of a brittle multiphase matrix containing both an Al-based quasicrystalline phase (psi) and an ordered body centred cubic phase (beta) and a relatively ductile ordered body centred cubic intermetallic FeAl phase has been developed as an abrasive wear-resistant coating material. It is applied as a 500 µm thick layer onto stainless steel substrates through plasma spray processing. The microstructure of such materials can be readily examined by optical and scanning electron microscopy, but the inherent difficulty of preparing transmission electron microscope (TEM) samples has inhibited higher resolution studies. However, the relatively recent development of the focused ion beam (FIB) miller as a tool in materials science provides a method ideal for the preparation of TEM specimens of these materials. In this study a coating consisting of a mixture of an Al-Cu-Fe based quasicrystal and FeAl+Cr was deposited on to a 304 stainless steel substrate. TEM specimens were prepared using a FIB and subjected to detailed microstructural characterization. The structure consisted of elongated bands of a FeAl phase about 100 nm in width and several micrometres in length, which enclosed more equiaxed regions about 1 µm in diameter that consisted of fine mixtures of quasicrystal and two Al-Fe-Cu phases isostructurally related to FeAl.

  18. Critical scaling of icosahedral medium-range order in CuZr metallic glass-forming liquids

    PubMed Central

    Wu, Z. W.; Li, F. X.; Huo, C. W.; Li, M. Z.; Wang, W. H.; Liu, K. X.

    2016-01-01

    The temperature evolution of icosahedral medium-range order formed by interpenetrating icosahedra in CuZr metallic glassforming liquids was investigated via molecular dynamics simulations. Scaling analysis based on percolation theory was employed, and it is found that the size distribution of clusters formed by the central atoms of icosahedra at various temperatures follows a very good scaling law with the cluster number density scaled by S−τ and the cluster size S scaled by |1 − Tc/T|−1/σ, respectively. Here Tc is scaling crossover-temperature. τ and σ are scaling exponents. The critical scaling behaviour suggests that there would be a structural phase transition manifested by percolation of locally favoured structures underlying the glass transition, if the liquid could be cooled slowly enough but without crystallization intervening. Furthermore, it is revealed that when icosahedral short-range order (ISRO) extends to medium-range length scale by connection, the atomic configurations of ISROs will be optimized from distorted ones towards more regular ones gradually, which significantly lowers the energies of ISROs and introduces geometric frustration simultaneously. Both factors make key impacts on the drastic dynamic slow-down of supercooled liquids. Our findings provide direct structure-property relationship for understanding the nature of glass transition. PMID:27779239

  19. Adding the Third Dimension to Virus Life Cycles: Three-Dimensional Reconstruction of Icosahedral Viruses from Cryo-Electron Micrographs

    PubMed Central

    Baker, T. S.; Olson, N. H.; Fuller, S. D.

    1999-01-01

    Viruses are cellular parasites. The linkage between viral and host functions makes the study of a viral life cycle an important key to cellular functions. A deeper understanding of many aspects of viral life cycles has emerged from coordinated molecular and structural studies carried out with a wide range of viral pathogens. Structural studies of viruses by means of cryo-electron microscopy and three-dimensional image reconstruction methods have grown explosively in the last decade. Here we review the use of cryo-electron microscopy for the determination of the structures of a number of icosahedral viruses. These studies span more than 20 virus families. Representative examples illustrate the use of moderate- to low-resolution (7- to 35-Å) structural analyses to illuminate functional aspects of viral life cycles including host recognition, viral attachment, entry, genome release, viral transcription, translation, proassembly, maturation, release, and transmission, as well as mechanisms of host defense. The success of cryo-electron microscopy in combination with three-dimensional image reconstruction for icosahedral viruses provides a firm foundation for future explorations of more-complex viral pathogens, including the vast number that are nonspherical or nonsymmetrical. PMID:10585969

  20. Structure of A197 from Sulfolobus Turreted Icosahedral Virus: a Crenarchaeal Viral Glycosyltransferase Exhibiting the GT-A Fold

    PubMed Central

    Larson, Eric T.; Reiter, Dirk; Young, Mark; Lawrence, C. Martin

    2006-01-01

    Sulfolobus turreted icosahedral virus (STIV) was the first icosahedral virus characterized from an archaeal host. It infects Sulfolobus species that thrive in the acidic hot springs (pH 2.9 to 3.9 and 72 to 92°C) of Yellowstone National Park. The overall capsid architecture and the structure of its major capsid protein are very similar to those of the bacteriophage PRD1 and eukaryotic viruses Paramecium bursaria Chlorella virus 1 and adenovirus, suggesting a viral lineage that predates the three domains of life. The 17,663-base-pair, circular, double-stranded DNA genome contains 36 potential open reading frames, whose sequences generally show little similarity to other genes in the sequence databases. However, functional and evolutionary information may be suggested by a protein's three-dimensional structure. To this end, we have undertaken structural studies of the STIV proteome. Here we report our work on A197, the product of an STIV open reading frame. The structure of A197 reveals a GT-A fold that is common to many members of the glycosyltransferase superfamily. A197 possesses a canonical DXD motif and a putative catalytic base that are hallmarks of this family of enzymes, strongly suggesting a glycosyltransferase activity for A197. Potential roles for the putative glycosyltransferase activity of A197 and their evolutionary implications are discussed. PMID:16840342

  1. Formation of three types of quasi-crystals in Al-Pd-Mg system

    NASA Astrophysics Data System (ADS)

    Koshikawa, Naokiyo; Edagawa, Keiichi; Honda, Yuko; Takeuchi, Shin

    1993-04-01

    In the Al-Pd-Mg system, a Mackay-Icosahedron (MI) type Icosahedral (I) phase with the F-type superlattice order and a Decagonal (D) phase were found to form in a melt-quenched state, in addition to the Frank-Kasper (FK) type stable I-phase reported previously. This is the first example in which the three types of quasi-crystalline phases are formed in the same alloy system. The formation range of the FK-type I-phase in melt-quenched state is rather wide: 5 - 20 at percent Pd and 20 - 45 at percent Mg. In contrast, the MI-type, I-phase and D-phase are formed in small composition ranges around Al52Pd31Mg17 and Al74Pd21Mg5, respectively. Electron diffraction studies showed that the period along the tenfold axis of the D-phase is about 1.6 nm. The formation and stability of the MI-type and FK-type I-phases were discussed in terms of a Hume-Rothery rule.

  2. Spectroscopic, structural, computational and (spectro)electrochemical studies of icosahedral carboranes bearing fluorinated aryl groups.

    PubMed

    Tricas, Hugo; Colon, Marta; Ellis, David; Macgregor, Stuart A; McKay, David; Rosair, Georgina M; Welch, Alan J; Glukhov, Ivan V; Rossi, Fulvio; Laschi, Franco; Zanello, Piero

    2011-04-28

    The icosahedral carboranes 1-C(6)F(5)-2-Ph-1,2-closo-C(2)B(10)H(10) (1), 1-(4'-F(3)CC(6)H(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (2), 1,2-(4'-F(3)CC(6)H(4))(2)-1,2-closo-C(2)B(10)H(10) (3), 1-(4'-H(3)CC(6)F(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (4), 1-(4'-F(3)CC(6)F(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (5), 1,2-(4'-F(3)CC(6)F(4))(2)-1,2-closo-C(2)B(10)H(10) (6), 1,7-(4'-F(3)CC(6)F(4))(2)-1,7-closo-C(2)B(10)H(10) (7) and 1,12-(4'-F(3)CC(6)F(4))(2)-1,12-closo-C(2)B(10)H(10) (8), with fluorinated aryl substituents on cage carbon atoms, have been prepared in good to high yields and characterised by microanalysis, (1)H, (11)B and (19)F NMR spectroscopies, mass spectrometry, single-crystal X-ray diffraction and (spectro)electrochemistry. By analysis of <δ(11)B>, the weighted average (11)B chemical shift, a ranking order for the ortho carboranes 1-6 is established based on the combined electron-withdrawing properties of the C-substituents, and is in perfect agreement with that established independently by electrochemical study. In a parallel computational study the effects of a wide range of different substituents on the redox properties of carboranes have been probed by comparison of ΔE values, where ΔE is the energy gap between the DFT-optimised [7,9-R(2)-7,9-nido-C(2)B(10)](2-) anion and its DFT-optimised basket-shaped first oxidation product. The overall conclusion from the NMR spectroscopic, electrochemical and computational studies is that strongly electron withdrawing substituents significantly stabilise [7,9-nido-C(2)B(10)](2-) dianions with respect to oxidation, and that the best practical substituent is 4-F(3)CC(6)F(4). Thus attention focussed on the reduction of 1,2-(4'-F(3)CC(6)F(4))(2)-1,2-closo-C(2)B(10)H(10), compound 6. The sequence 6/[6](-)/[6](2-) appears reversible on the cyclic voltammetric timescale but on the longer timescale of macroelectrolysis the radical anion is only partially stable. EPR study of the electrogenerated monoanions from the ortho

  3. Electrochemically shape-controlled synthesis in deep eutectic solvents: triambic icosahedral platinum nanocrystals with high-index facets and their enhanced catalytic activity.

    PubMed

    Wei, Lu; Zhou, Zhi-You; Chen, Sheng-Pei; Xu, Chang-Deng; Su, Dangsheng; Schuster, Manfred Erwin; Sun, Shi-Gang

    2013-12-11

    Pt triambic icosahedral nanocrystals (TIH NCs) enclosed by {771} high-index facets were successfully synthesized electrochemically, for the first time, in ChCl-urea based deep eutectic solvents, and exhibited higher electrocatalytic activity and stability towards ethanol electrooxidation than a commercial Pt black catalyst. PMID:24084858

  4. Electrochemically shape-controlled synthesis in deep eutectic solvents: triambic icosahedral platinum nanocrystals with high-index facets and their enhanced catalytic activity.

    PubMed

    Wei, Lu; Zhou, Zhi-You; Chen, Sheng-Pei; Xu, Chang-Deng; Su, Dangsheng; Schuster, Manfred Erwin; Sun, Shi-Gang

    2013-12-11

    Pt triambic icosahedral nanocrystals (TIH NCs) enclosed by {771} high-index facets were successfully synthesized electrochemically, for the first time, in ChCl-urea based deep eutectic solvents, and exhibited higher electrocatalytic activity and stability towards ethanol electrooxidation than a commercial Pt black catalyst.

  5. Tailoring Magnetic Behavior in the Tb-Au-Si Quasicrystal Approximant System.

    PubMed

    Gebresenbut, Girma H; Andersson, Mikael S; Nordblad, Per; Sahlberg, Martin; Pay Gómez, Cesar

    2016-03-01

    A novel synthesis method, "arc-melting-self-flux", has been developed and a series of five Tsai-type 1/1 approximant crystals in the Tb-Au-Si system have been synthesized. The synthesis method, by employing a temperature program which oscillates near the melting and nucleation points of the approximants, has provided high-quality and large single crystals in comparison to those obtained from the standard arc-melting-annealing and self-flux methods. The atomic structures of the approximants have been determined from single-crystal X-ray diffraction data and described using concentric atomic clusters with icosahedral symmetry. The compounds are nearly isostructural with subtle variations; two types of atomic clusters which mainly vary at their cluster centers are observed. One type contains a Tb site at the center, and the other contains a disordered tetrahedron decorated with Au/Si mixed sites. Both cluster types can be found coexisting in the approximants. The compounds have different average weighted ratios of central Tb to disordered tetrahedron in the bulk material. Furthermore, a strategy for chemically tuning magnetic behavior is presented. Magnetic property measurements on the approximants revealed that the magnetic transition temperature (Tc) decreases as the occupancy of the central Tb site increases. Tc decreased from 11.5 K for 0% occupancy of the central Tb to 8 K for 100% occupancy. Enhanced magneto crystalline anisotropy is observed for the approximants with higher central Tb occupancy in comparison to their low central Tb occupancy counterparts. Hence, the previously reported "ferrimagnetic-like" magnetic structure model remains valid.

  6. Planar scanning method for detecting refraction characteristics of two-dimensional photonic quasi-crystal wedge-shaped prisms.

    PubMed

    Liu, Jianjun; Tan, Wei; Liu, Exian; Hu, Haili; Fan, Zhigang; Zhang, Tianhua; Zhang, Xiong

    2016-05-01

    In this study, a planar scanning method is proposed. This novel method adapts two monitors moving along double planar tracks that can be used to detect refraction characteristics of two-dimensional (2D) photonic quasi-crystal (PQC) wedge-shaped prisms. Refraction of a decagonal Penrose-type PQC prism is analyzed for a given incident beam and two polarization modes at different incident positions in the prism using this method. Refraction from the prism is irregular, indicating that nonuniformity in the arrangement of scatterers in the prism causes Bragg-like scattering irregularities. Numerical results show that this method can be used for guiding the design of a 2D PQC prism and for the analysis of its refraction characteristics. PMID:27140896

  7. Self-imaging effect in photonic quasicrystal waveguides: Application to 3 dB power splitter for terahertz waves

    NASA Astrophysics Data System (ADS)

    Xu, Feixiang; Zou, Qiushun; Zhou, Quancheng; Wang, Tongbiao; Yu, Tianbao; Liu, Nianhua

    2016-05-01

    We report that self-imaging effect still can be achieved in photonic quasicrystal waveguides (PtQCWs) just as it does in photonic crystal waveguides. As a possible application of the results, a new kind of compact 3 dB PtQCWs-based power splitters based on this effect for terahertz waves with symmetric interference is presented and analyzed. The finite element method is used to calculate the distributions of stable-state electric field and evaluate transmission efficiency of these structures. The calculated results show that the proposed device provides a new compact model for exporting efficiently THz wave with a broad bandwidth to two channels averagely and can be extended to new designs of PtQCW devices.

  8. New type of Al-based decagonal quasicrystal in Al60Cr20Fe10Si10 alloy

    NASA Astrophysics Data System (ADS)

    He, Zhanbing; Ma, Haikun; Li, Hua; Li, Xingzhong; Ma, Xiuliang

    2016-03-01

    A new kind of decagonal quasicrystal (DQC) with a periodicity of 1.23 nm was observed in the as-cast quaternary Al60Cr20Fe10Si10 alloy. The intensity distribution of some spots in the selected-area electron diffraction pattern along the tenfold zone axis was found to be different from other Al-based DQCs. High-angle annular dark-field scanning transmission electron microscopy was adopted to reveal the structural features at an atomic level. Both the tenfold symmetry and symmetry-broken decagonal (D) clusters of 1.91 nm in diameter were found, but with structural characteristics different from the corresponding D clusters in the other Al-based DQCs. The neighboring D clusters are connected by sharing one edge rather than covering, suggesting the tiling model is better than the covering model for structural description.

  9. Elastic constants and anisotropic internal frictions of decagonal Al72Ni18Co8 single quasicrystal at low temperatures

    NASA Astrophysics Data System (ADS)

    Tarumi, R.; Ledbetter, H.; Shiomi, S.; Ogi, H.; Hirao, M.; Tsai, A. P.

    2010-07-01

    We studied the complete set of elastic constants Cij and internal frictions tensor Qij-1 of anisotropic decagonal Al72Ni18Co8 single quasicrystal by electromagnetic acoustic resonance at low temperatures, to 5 K. Most Cij(T ) showed usual stiffening upon cooling and their temperature behaviors are well characterized by an Einstein-lattice-vibration model. The average Grüneisen parameter estimated from the bulk modulus is 2.4, almost identical to crystalline Al. Ambient temperature Qij-1 show a linear relationship to the elastic-constants temperature derivatives |dCij/dT|/Cij with a slope of 1.28 K-1, suggesting that lattice anharmonicity plays a dominant role for Qij-1. The longitudinal modulus for the decagonal axis C33 and corresponding internal friction Q33-1, however, showed significant deviation from such ideal behavior, suggesting additional low-frequency phonon-excitation modes along the decagonal axis.

  10. Low index-contrast aperiodically ordered photonic quasicrystals for the development of isotropic photonic band-gap devices

    NASA Astrophysics Data System (ADS)

    Priya Rose, T.; Di Gennaro, E.; Andreone, A.; Abbate, G.

    2010-05-01

    Photonic quasicrystals (PQCs) have neither true periodicity nor translational symmetry, however they can exhibit symmetries that are not achievable by conventional periodic structures. The arbitrarily high rotational symmetry of these materials can be practically exploited to manufacture isotropic band gap materials, which are perfectly suitable for hosting waveguides or cavities. In this work, formation and development of the photonic bandgap (PBG) in twodimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low dielectric contrast (0.4-0.6) were measured in the microwave region and compared with the PBG properties of a conventional hexagonal crystal. Band-gap properties were also investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0° to 30° were used in order to investigate the isotropic nature of the band-gap.

  11. Non-near-field focus and imaging of an unpolarized electromagnetic wave through high-symmetry quasicrystals

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangdong; Li, Zhiyuan; Cheng, Bingying; Zhang, Dao-Zhong

    2007-02-01

    The focus behaviors of electromagnetic wave through two-dimensional (2D) high-symmetry photonic quasicrystals (PQCs) have been investigated by using exact multi-scattering numerical simulation. We have found that the high-symmetry PQC flat lenses possess universal feature for non-near-field focus of two kinds of polarized waves. That is to say, the non-near-field focus for two kinds of polarized waves can be realized by using these flat lenses, which are consisting of 12-fold, 10-fold and 8-fold 2D PQCs with the same structures and parameters. Such a superior feature originates from higher rotational symmetry and negative refraction in the PQCs. Thus, potential applications of such a phenomenon to optical devices can be anticipated.

  12. Non-near-field focus and imaging of an unpolarized electromagnetic wave through high-symmetry quasicrystals.

    PubMed

    Zhang, Xiangdong; Li, Zhiyuan; Cheng, Bingying; Zhang, Dao-Zhong

    2007-02-01

    The focus behaviors of electromagnetic wave through two-dimensional (2D) high-symmetry photonic quasicrystals (PQCs) have been investigated by using exact multi-scattering numerical simulation. We have found that the high-symmetry PQC flat lenses possess universal feature for non-near-field focus of two kinds of polarized waves. That is to say, the non-near-field focus for two kinds of polarized waves can be realized by using these flat lenses, which are consisting of 12-fold, 10-fold and 8-fold 2D PQCs with the same structures and parameters. Such a superior feature originates from higher rotational symmetry and negative refraction in the PQCs. Thus, potential applications of such a phenomenon to optical devices can be anticipated.

  13. Planar scanning method for detecting refraction characteristics of two-dimensional photonic quasi-crystal wedge-shaped prisms.

    PubMed

    Liu, Jianjun; Tan, Wei; Liu, Exian; Hu, Haili; Fan, Zhigang; Zhang, Tianhua; Zhang, Xiong

    2016-05-01

    In this study, a planar scanning method is proposed. This novel method adapts two monitors moving along double planar tracks that can be used to detect refraction characteristics of two-dimensional (2D) photonic quasi-crystal (PQC) wedge-shaped prisms. Refraction of a decagonal Penrose-type PQC prism is analyzed for a given incident beam and two polarization modes at different incident positions in the prism using this method. Refraction from the prism is irregular, indicating that nonuniformity in the arrangement of scatterers in the prism causes Bragg-like scattering irregularities. Numerical results show that this method can be used for guiding the design of a 2D PQC prism and for the analysis of its refraction characteristics.

  14. New type of Al-based decagonal quasicrystal in Al60Cr20Fe10Si10 alloy

    PubMed Central

    He, Zhanbing; Ma, Haikun; Li, Hua; Li, Xingzhong; Ma, Xiuliang

    2016-01-01

    A new kind of decagonal quasicrystal (DQC) with a periodicity of 1.23 nm was observed in the as-cast quaternary Al60Cr20Fe10Si10 alloy. The intensity distribution of some spots in the selected-area electron diffraction pattern along the tenfold zone axis was found to be different from other Al-based DQCs. High-angle annular dark-field scanning transmission electron microscopy was adopted to reveal the structural features at an atomic level. Both the tenfold symmetry and symmetry-broken decagonal (D) clusters of 1.91 nm in diameter were found, but with structural characteristics different from the corresponding D clusters in the other Al-based DQCs. The neighboring D clusters are connected by sharing one edge rather than covering, suggesting the tiling model is better than the covering model for structural description. PMID:26928759

  15. Direct observations of local electronic states in an Al-based quasicrystal by STEM-EELS.

    PubMed

    Seki, Takehito; Abe, Eiji

    2014-11-01

    Most quasicrystals (QCs) reveal pseudogaps in their density of states around Fermi level, and hence the stability of QCs have been discussed in terms of energetic gains in electron systems. In fact, many QCs have been discovered by tuning valence electron density based on Hume-Rothery rule. Therefore, understanding electronic structures in QCs may provide an important clue for their stabilization mechanism. Generally, it has been frequently discussed based on an interaction between Fermi surface and Brillouin zone boundary within the framework of nearly free electron model, which is believed to be an underlying physics of a Hume-Rothery's empirical criteria. However the hybridization effect also stabilize electron system, particularly in Al-transition metal system, in which a lot of quasicrystalline phases were discovered. Therefore, the electronic structures of QCs have not yet been fully understood, whereas their atomic structures have been studied well in terms of configuration entropy by scanning transmission electron microscopy (STEM) [1]. In the present work, we investigate local electronic states in Al-based QCs using electron energy loss spectroscopy (EELS) combined with STEM, by which EELS spectra with sub-Å probe and atomic structure can be obtained simultaneously. We report STEM-EELS results on AlCuIr decagonal phases [2].jmicro;63/suppl_1/i17-a/DFU069F1F1DFU069F1Fig. 1.Core-loss edges obtained from cluster-centers and cluster-edges. Al L1 (left) Ir O23, Ir N67 (center) and Cu L23 (right). Principal components analysis clearly shows up the atomic-site dependence of plasmon loss spectra in a two-dimensional map. Qualitatively, there seems to be certain correlations between the plasmon peaks and the core-loss edges, Al L1, Ir O23, Ir N67 and Cu L23, all of which reveal different behaviors at the cluster centers and the edges (Fig. 1). All results indicate the cluster centers have metallic states and the cluster edges have covalent states in comparison

  16. A Winged-Helix Protein From Sulfolobus Turreted Icosahedral Virus Points Toward Stabilizing Disulfide Bonds in the Intracellular Proteins of a Hyperthermophilic Virus

    SciTech Connect

    Larson, E.T.; Eilers, B.; Menon, S.; Reiter, D.; Ortmann, A.; Young, M.J.; Lawrence, C.M.

    2009-06-03

    Sulfolobus turreted icosahedral virus (STIV) was the first non-tailed icosahedral virus to be isolated from an archaeal host. Like other archaeal viruses, its 37 open reading frames generally lack sequence similarity to genes with known function. The roles of the gene products in this and other archaeal viruses are thus largely unknown. However, a protein's three-dimensional structure may provide functional and evolutionary insight in cases of minimal sequence similarity. In this vein, the structure of STIV F93 reveals a homodimer with strong similarity to the winged-helix family of DNA-binding proteins. Importantly, an interchain disulfide bond is found at the dimer interface, prompting analysis of the cysteine distribution in the putative intracellular proteins of the viral proteome. The analysis suggests that intracellular disulfide bonds are common in cellular STIV proteins, where they enhance the thermostability of the viral proteome.

  17. Effects of Superfine Structure Level-Cluster Crossing on Amplitude and Phase Revival Dynamics: Comparing Tetrahedral and Octahedral Spherical Rotors with Icosahedral Rotors

    NASA Astrophysics Data System (ADS)

    Harter, William G.; Li, Alvason Zhenhua

    2013-06-01

    Quantum revivals or "super-beats" are predicted to occur when angularly localized symmetric tops states are free to evolve. Similar types of dynamics are expected to involve spherical top superfine and superhyperfine level clusters that are labeled by induced representations of octahedral or tetrahedral symmetries for XY_4, XY_6, and related molecules. A considerably more complicated set of effects are expected for the icosahedral molecule C_ {60} and its related isotopomers. An important difference for icosahedral symmetry is that its superfine splitting ratios are most-irrational (Golden-ratio) fractions that preclude perfect Poincare recurrence of quantum phase while the octahedral splitting ratios are rational. William Harter and Justin Mitchell, International Journal of Molecular Science, 14, 714 (2013).

  18. Reconstruction of the Disassembly Pathway of an Icosahedral Viral Capsid and Shape Determination of Two Successive Intermediates.

    PubMed

    Law-Hine, Didier; Sahoo, Anil K; Bailleux, Virginie; Zeghal, Mehdi; Prevost, Sylvain; Maiti, Prabal K; Bressanelli, Stéphane; Constantin, Doru; Tresset, Guillaume

    2015-09-01

    Viral capsids derived from an icosahedral plant virus widely used in physical and nanotechnological investigations were fully dissociated into dimers by a rapid change of pH. The process was probed in vitro at high spatiotemporal resolution by time-resolved small-angle X-ray scattering using a high brilliance synchrotron source. A powerful custom-made global fitting algorithm allowed us to reconstruct the most likely pathway parametrized by a set of stoichiometric coefficients and to determine the shape of two successive intermediates by ab initio calculations. None of these two unexpected intermediates was previously identified in self-assembly experiments, which suggests that the disassembly pathway is not a mirror image of the assembly pathway. These findings shed new light on the mechanisms and the reversibility of the assembly/disassembly of natural and synthetic virus-based systems. They also demonstrate that both the structure and dynamics of an increasing number of intermediate species become accessible to experiments. PMID:27120684

  19. A molecular dynamics study on the structural and electronic properties of two-dimensional icosahedral B12 cluster based structures

    NASA Astrophysics Data System (ADS)

    Kah, Cherno Baba; Yu, M.; Jayanthi, C. S.; Wu, S. Y.

    2014-03-01

    Our previous study on one-dimensional icosahedral B12 cluster (α-B12) based chain [Bulletin of APS Annual Meeting, p265 (2013)] and ring structures has prompted us to study the two-dimensional (2D) α-B12 based structures. Recently, we have carried out a systematic molecular dynamics study on the structural stabilities and electronic properties of the 2D α-B12 based structures using the SCED-LCAO method [PRB 74, 15540 (2006)]. We have considered several types of symmetry for these 2D structures such as δ3, δ4, δ6 (flat triangular), and α' types. We have found that the optimized structures are energetically in the order of δ6 < α' < δ3 < δ4 which is different from the energy order of α'< δ6 < δ4 < δ3 found in the 2D boron monolayer sheets [ACS Nano 6, 7443 (2012)]. A detailed discussion of this study will be presented. The first author acknowledges the McSweeny Fellowship for supporting his research in this work.

  20. Optical reflectance and omnidirectional bandgaps in Fibonacci quasicrystals type 1-D multilayer structures containing exponentially graded material

    NASA Astrophysics Data System (ADS)

    Singh, Bipin K.; Thapa, Khem B.; Pandey, Praveen C.

    2013-06-01

    A theoretical study of optical reflectance and reflection bands of 1-D photonic quasi-crystals (Fibonacci type arrangement) composed of exponentially graded material is presented. The proposed structures consist of two different layers, one of them is of constant refractive index (L) and the other one is of exponentially graded refractive index (S) dielectric materials. Four different generations (2nd, 3rd, 4th and 5th) of the Fibonacci sequence for 10 periods in one dimension (1-D) are considered and compared in view of their optical reflectance and bandgaps for both TE and TM polarisations. Also, we proposed some heterostructures made by the combination of different Fibonacci generations and their periods to obtain suitable omnidirectional reflection band. We used the transfer matrix method (TMM) to obtain the reflectance, bandgaps and omnidirectional reflectional bandgaps (ODR) of such structures in near infrared spectrum (800-2200 nm) at different angles of incidence. We show that ODR exists in these types of structures. The number of ODRs and total bandgap depend on the Fibonacci generations. Extraordinary ODR bandgaps are obtained in the case of heterostructures formed by the combination of different generations of the Fibonacci sequence. The ODR for these structures is similar to the ODR of photonic crystals containing left-handed materials. This work would be useful to study the Fibonacci type photonic crystals having graded index materials and also it will open new window to design several photonic crystal devices like sensors, reflectors, etc. in the infrared region.

  1. Giant Surfactants based on Precisely Functionalized POSS Nano-atoms: Tuning from Crystals to Frank-Kasper Phases and Quasicrystals

    NASA Astrophysics Data System (ADS)

    Cheng, Stephen Z. D.

    In creating new functional materials for advanced technologies, precisely control over functionality and their hierarchical ordered structures are vital for obtaining the desired properties. Giant polyhedra are a class of materials which are designed and constructed via deliberately placing precisely functionalized polyhedral oligomeric silsesquioxane (POSS) and fullerene (C60) molecular nano-particles (MNPs) (so-called ``nano-atoms'') at the vertices of a polyhedron. Giant surfactants are consisted of polymer tail-tethered ``nano-atoms'' which are deliberately and precisely functionalized POSS or C60 molecular nano-particles (MNPs). The ``nano-atom'' heads and polymer tails thus have drastic chemical differences to impart amphiphilicity. These giant surfactants capture the essential structural features of their small-molecule counterparts in many ways but possess much larger sizes, and therefore, they are recognized as size-amplified versions of small molecule surfactants. Two of the most illustrating examples are a series of novel giant tetrahedra and a series of giant giant surfactants as building blocks to construct into hierarchical ordered super-lattice structures ranging from crystals, Frank-Kasper phases and quasicrystals in the condensed bulk states, reveals evidently the interconnections between soft matters and hard matters in sharing their common structures and fundamental knowledge. This work was supported by National Science Foundation (DMR-1409972).

  2. Atomic structure solution of the complex quasicrystal approximant Al77Rh15Ru8 from electron diffraction data.

    PubMed

    Samuha, Shmuel; Mugnaioli, Enrico; Grushko, Benjamin; Kolb, Ute; Meshi, Louisa

    2014-12-01

    The crystal structure of the novel Al77Rh15Ru8 phase (which is an approximant of decagonal quasicrystals) was determined using modern direct methods (MDM) applied to automated electron diffraction tomography (ADT) data. The Al77Rh15Ru8 E-phase is orthorhombic [Pbma, a = 23.40 (5), b = 16.20 (4) and c = 20.00 (5) Å] and has one of the most complicated intermetallic structures solved solely by electron diffraction methods. Its structural model consists of 78 unique atomic positions in the unit cell (19 Rh/Ru and 59 Al). Precession electron diffraction (PED) patterns and high-resolution electron microscopy (HRTEM) images were used for the validation of the proposed atomic model. The structure of the E-phase is described using hierarchical packing of polyhedra and a single type of tiling in the form of a parallelogram. Based on this description, the structure of the E-phase is compared with that of the ε6-phase formed in Al-Rh-Ru at close compositions.

  3. Understanding the interface of six-shell cuboctahedral and icosahedral palladium clusters on reduced graphene oxide: experimental and theoretical study.

    PubMed

    Gracia-Espino, Eduardo; Hu, Guangzhi; Shchukarev, Andrey; Wågberg, Thomas

    2014-05-01

    Studies on noble-metal-decorated carbon nanostructures are reported almost on a daily basis, but detailed studies on the nanoscale interactions for well-defined systems are very rare. Here we report a study of reduced graphene oxide (rGOx) homogeneously decorated with palladium (Pd) nanoclusters with well-defined shape and size (2.3 ± 0.3 nm). The rGOx was modified with benzyl mercaptan (BnSH) to improve the interaction with Pd clusters, and N,N-dimethylformamide was used as solvent and capping agent during the decoration process. The resulting Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are fully consistent with six-shell cuboctahedral and icosahedral clusters containing ~600 Pd atoms, where 45% of these are located at the surface. According to X-ray photoelectron spectroscopy analysis, the Pd clusters exhibit an oxidized surface forming a PdO(x) shell. Given the well-defined experimental system, as verified by electron microscopy data and theoretical simulations, we performed ab initio simulations using 10 functionalized graphenes (with vacancies or pyridine, amine, hydroxyl, carboxyl, or epoxy groups) to understand the adsorption process of BnSH, their further role in the Pd cluster formation, and the electronic properties of the graphene-nanoparticle hybrid system. Both the experimental and theoretical results suggest that Pd clusters interact with functionalized graphene by a sulfur bridge while the remaining Pd surface is oxidized. Our study is of significant importance for all work related to anchoring of nanoparticles on nanocarbon-based supports, which are used in a variety of applications.

  4. Energetics, relative stabilities, and size-dependent properties of nanosized carbon clusters of different families: fullerenes, bucky-diamond, icosahedral, and bulk-truncated structures.

    PubMed

    Yu, M; Chaudhuri, I; Leahy, C; Wu, S Y; Jayanthi, C S

    2009-05-14

    Structures and relative stabilities of carbon clusters belonging to different families have been investigated for diameters d < or = 5 nm based on an efficient semiempirical molecular dynamics (MD) scheme as well as a density functional theory based simulation. Carbon clusters studied include fullerenes and fullerene-derived structures (e.g., cages and onions), icosahedral structures, bucky-diamond structures, and clusters cut from the bulk diamond with spherical and facetted truncations. The reason for using a semiempirical MD is partly due to the large number of different cases (or carbon allotropes) investigated and partly due to the size of the clusters investigated in this work. The particular flavor of the semiempirical MD scheme is based on a self-consistent and environment-dependent Hamiltonian developed in the framework of linear combination of atomic orbitals. We find that (i) among the families of carbon clusters investigated, fullerene structures have the lowest energy with the relative energy ordering being E(fullerene) < E(onion) < E(icosahedral) < E(bucky-diamond) < E(bulk-truncated), (ii) a crossover between bucky-diamond and icosahedral structures is likely at d approximately 8 nm, (iii) the highest occupied molecular orbital-lowest unoccupied molecular orbital gap as a function of the diameter for the case of fullerenes shows an oscillatory behavior with the gap ranging from 2 eV to 6 meV, and the gap approaching that of gapless graphite for d > 3.5 nm, and (iv) there can be three types of phase transformations depending on the manner of heating and cooling in our simulated annealing studies: (a) a bucky-diamond structure --> an onionlike structure, (b) an onionlike --> a cage structure, and (c) a bucky-diamond --> a cage structure.

  5. Characterization of the Archaeal Thermophile Sulfolobus Turreted Icosahedral Virus Validates an Evolutionary Link among Double-Stranded DNA Viruses from All Domains of Life

    PubMed Central

    Maaty, Walid S. A.; Ortmann, Alice C.; Dlakić, Mensur; Schulstad, Katie; Hilmer, Jonathan K.; Liepold, Lars; Weidenheft, Blake; Khayat, Reza; Douglas, Trevor; Young, Mark J.; Bothner, Brian

    2006-01-01

    Icosahedral nontailed double-stranded DNA (dsDNA) viruses are present in all three domains of life, leading to speculation about a common viral ancestor that predates the divergence of Eukarya, Bacteria, and Archaea. This suggestion is supported by the shared general architecture of this group of viruses and the common fold of their major capsid protein. However, limited information on the diversity and replication of archaeal viruses, in general, has hampered further analysis. Sulfolobus turreted icosahedral virus (STIV), isolated from a hot spring in Yellowstone National Park, was the first icosahedral virus with an archaeal host to be described. Here we present a detailed characterization of the components forming this unusual virus. Using a proteomics-based approach, we identified nine viral and two host proteins from purified STIV particles. Interestingly, one of the viral proteins originates from a reading frame lacking a consensus start site. The major capsid protein (B345) was found to be glycosylated, implying a strong similarity to proteins from other dsDNA viruses. Sequence analysis and structural predication of virion-associated viral proteins suggest that they may have roles in DNA packaging, penton formation, and protein-protein interaction. The presence of an internal lipid layer containing acidic tetraether lipids has also been confirmed. The previously presented structural models in conjunction with the protein, lipid, and carbohydrate information reported here reveal that STIV is strikingly similar to viruses associated with the Bacteria and Eukarya domains of life, further strengthening the hypothesis for a common ancestor of this group of dsDNA viruses from all domains of life. PMID:16840341

  6. Carbon-rich icosahedral boron carbides beyond B4C and their thermodynamic stabilities at high temperature and pressure from first principles

    NASA Astrophysics Data System (ADS)

    Ektarawong, A.; Simak, S. I.; Alling, B.

    2016-08-01

    We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from B4C to B2C , using first-principles calculations. Apart from B4C , generally addressed in the literature, B2.5C , represented by B10C2p (C-C), where Cp and (C-C) denote a carbon atom occupying the polar site of the icosahedral cluster and a diatomic carbon chain, respectively, is predicted to be thermodynamically stable under high pressures with respect to B4C as well as pure boron and carbon phases. The thermodynamic stability of B2.5C is determined by the Gibbs free energy G as a function of pressure p and temperature T , in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. The stability range of B2.5C is then illustrated through the p -T phase diagrams. Depending on the temperatures, the stability range of B2.5C is predicted to be within the range between 40 and 67 GPa. At T ≳ 500 K, the icosahedral Cp atoms in B2.5C configurationally disorder at the polar sites. By investigating the properties of B2.5C , e.g., elastic constants and phonon and electronic density of states, we demonstrate that B2.5C is both mechanically and dynamically stable at zero pressure, and is an electrical semiconductor. Furthermore, based on the sketched phase diagrams, a possible route for experimental synthesis of B2.5C as well as a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

  7. Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystal and Polytetrahedral-Phase Forming Alloys

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Gangopadhyay, Anup K.; Lee, G. W.; Hyers, Robert W.; Rathz, T. J.; Robinson, Michael B.; Rogers, Jan R.

    2003-01-01

    From extensive ground based work on the phase diagram and undercooling studies of Ti-Zr-Ni alloys, have clearly identified the composition of three different phases with progressively increasing polytetrahedral order such as, (Ti/Zr), the C14 Laves phase, and the i-phase, that nucleate directly from the undercooled liquid. The reduced undercooling decreases progressively with increasing polytetrahedral order in the solid, supporting Frank s hypothesis. A new facility for direct measurements of the structures and phase transitions in undercooled liquids (BESL) was developed and has provided direct proof of the primary nucleation of a metastable icosahedral phase in some Ti-Zr-Ni alloys. The first measurements of specific heat and viscosity in the undercooled liquid of this alloy system have been completed. Other than the importance of thermo-physical properties for modeling nucleation and growth processes in these materials, these studies have also revealed some interesting new results (such as a maximum of C(sup q, sub p) in the undercooled state). These ground-based results have clearly established the necessary background and the need for conducting benchmark nucleation experiments at the ISS on this alloy system.

  8. The structure of alfalfa mosaic virus capsid protein assembled as a T=1 icosahedral particle at 4.0-A resolution.

    PubMed Central

    Kumar, A; Reddy, V S; Yusibov, V; Chipman, P R; Hata, Y; Fita, I; Fukuyama, K; Rossmann, M G; Loesch-Fries, L S; Baker, T S; Johnson, J E

    1997-01-01

    K. Fukuyama, S. S. Abdel-Meguid, J. E. Johnson, and M. G. Rossmann (J. Mol. Biol. 167:873-984, 1983) reported the structure of alfalfa mosaic virus assembled from the capsid protein as a T=1 icosahedral empty particle at 4.5-A resolution. The information contained in the structure included the particle size, protein shell thickness, presence of wide holes at the icosahedral fivefold axes, and a proposal that the capsid protein adopts a beta-barrel structure. In the present work, the X-ray diffraction data of Fukuyama et al. as well as the data subsequently collected by I. Fita, Y. Hata, and M. G. Rossmann (unpublished) were reprocessed to 4.0-A resolution, and the structure was solved by molecular replacement. The current structure allowed the tracing of the polypeptide chain of the capsid protein confirming the beta-sandwich fold and provides information on intersubunit interactions in the particle. However, it was not possible to definitively assign the amino acid sequence to the side chain density at 4-A resolution. The particle structure was also determined by cryoelectron microscopy and image reconstruction methods and found to be in excellent agreement with the X-ray model. PMID:9311881

  9. Acidities of closo-1-COOH-1,7-C2B10H11 and amino acids based on icosahedral carbaboranes.

    PubMed

    Dávalos, Juan Z; González, Javier; Ramos, Rocío; Hnyk, Drahomír; Holub, Josef; Santaballa, J Arturo; Canle-L, Moisés; Oliva, Josep M

    2014-04-17

    Carborane clusters are not found in Nature and are exclusively man-made. In this work we study, both experimentally and computationally, the gas-phase acidity (measured GA = 1325 kJ·mol(-1), computed GA = 1321 kJ·mol(-1)) and liquid-phase acidity (measured pKa = 2.00, computed pKa = 1.88) of the carborane acid closo-1-COOH-1,7-C2B10H11. The experimental gas-phase acidity was determined with electrospray tandem mass spectrometry (ESI/MS), by using the extended Cooks kinetic method (EKM). Given the similar spatial requirements of the title icosahedral cage and benzene and the known importance of aminoacids as a whole, such a study is extended, within an acid-base context, to corresponding ortho, meta, and para amino acids derived from icosahedral carborane cages, 1-COOH-n-NH2-1, n-R with {R = C2B10H10, n = 2, 7, 12}, and from benzene {R = C6H4, n = 2, 3, 4}. A remarkable difference is found between the proportion of neutral versus zwitterion structures in water for glycine and the carborane derived amino acids.

  10. An icosahedral array of methyl groups supported by an aromatic borane scaffold: The [closo-B{sub 12}(CH{sub 3}){sub 12}]{sup 2{minus}} ion

    SciTech Connect

    Peymann, T.; Knobler, C.B.; Hawthorne, M.F.

    1999-06-16

    The quest for globular structures possessing both hydrophobic surfaces and extraordinary kinetic stability stems from the search for novel modules with which to synthesize supramolecular structures, weakly coordinating anions, and space-controlling drug components. The fullerenes, characterized by unique chemistry and physical properties, represent one family of such precursors. Another family of globular hydrophobes, described by the authors as ``camouflaged`` carboranes, has been described. These species may approach the van der Waals diameter of C{sub 60} by attachment of methyl groups and functionalized methyl substituents to the icosahedral scaffolding of the aromatic [closo-C{sub n}B{sub 12{minus}n}H{sub 12}]{sup n{minus}2} (n = 0--2). Whereas hydrophobic and amphiphilic derivatives of this sort are known with n = 1 and 2, the fully methylated derivative of the parent species, dodecamethyl-closo-dodecaborate(2{minus}), (n = 0), is now reported for the first time. The authors describe a new permethylation technique for icosahedral closo-boranes employing trimethylaluminium and methyl iodide in the absence of a solvent.

  11. Design of Three-shell Icosahedral Matryoshka Clusters A@B12@A20 (A = Sn, Pb; B = Mg, Zn, Cd, Mn)

    PubMed Central

    Huang, Xiaoming; Zhao, Jijun; Su, Yan; Chen, Zhongfang; King, R. Bruce

    2014-01-01

    We propose a series of icosahedral matryoshka clusters of A@B12@A20 (A = Sn, Pb; B = Mg, Zn, Cd), which possess large HOMO-LUMO gaps (1.29 to 1.54 eV) and low formation energies (0.06 to 0.21 eV/atom). A global minimum search using a genetic algorithm and density functional theory calculations confirms that such onion-like three-shell structures are the ground states for these A21B12 binary clusters. All of these icosahedral matryoshka clusters, including two previously found ones, i.e., [As@Ni12@As20]3− and [Sn@Cu12@Sn20]12−, follow the 108-electron rule, which originates from the high Ih symmetry and consequently the splitting of superatom orbitals of high angular momentum. More interestingly, two magnetic matryoshka clusters, i.e., Sn@Mn12@Sn20 and Pb@Mn12@Pb20, are designed, which combine a large magnetic moment of 28 µB, a moderate HOMO-LUMO gap, and weak inter-cluster interaction energy, making them ideal building blocks in novel magnetic materials and devices. PMID:25376938

  12. Solute-derived thermal stability of nanocrystalline aluminum and processing factor influence on the formation of Al6Mn quasicrystals in melt-spinning

    NASA Astrophysics Data System (ADS)

    Baker, Andrew H.

    Thermal stability of nanograined metals can be difficult to attain due to the large driving force for grain growth that arises from the significant boundary area constituted by the nanostructure. Kinetic approaches for stabilization of the nanostructure effective at low homologous temperatures often fail at higher homologous temperatures. Thermodynamic approaches for thermal stabilization may offer higher temperature stability. In this research, modest alloying of aluminum with solute (1 at.% Sc, Yb, or Sr) was examined as a means to thermodynamically stabilize a bulk nanostructure at elevated temperatures. After using melt-spinning and ball-milling to create an extended solid-solution and nanostructure with average grain size on the order of 30-45 nm, 1 h annealing treatments at 673 K (0.72 Tm) , 773 K (0.83 Tm) , and 873 K (0.94 Tm) were applied. The alloys remain nanocrystalline (<100 nm) as measured by Warren-Averbach Fourier analysis of x-ray diffraction peaks and direct observation of TEM dark field micrographs, with the efficacy of stabilization: Sr>Yb>Sc. Disappearance of intermetallic phases in the Sr and Yb alloys in the x-ray diffraction spectra are observed to occur coincident with the stabilization after annealing, suggesting that precipitates dissolve and the boundaries are enriched with solute. Melt-spinning has also been shown to be an effective process to produce a class of ordered, but non-periodic crystals called quasicrystals. However, many of the factors related to the creation of the quasicrystals through melt-spinning are not optimized for specific chemistries and alloy systems. In a related but separate aspect of this research, melt-spinning was utilized to create metastable quasicrystalline Al6Mn in an alpha-Al matrix through rapid solidification of Al-8Mn (by mol) and Al-10Mn (by mol) alloys. Wheel speed of the melt-spinning wheel and orifice diameter of the tube reservoir were varied to determine their effect on the resulting volume

  13. Atomic structure of the 75 MDa extremophile Sulfolobus turreted icosahedral virus determined by CryoEM and X-ray crystallography.

    PubMed

    Veesler, David; Ng, Thiam-Seng; Sendamarai, Anoop K; Eilers, Brian J; Lawrence, C Martin; Lok, Shee-Mei; Young, Mark J; Johnson, John E; Fu, Chi-yu

    2013-04-01

    Sulfolobus turreted icosahedral virus (STIV) was isolated in acidic hot springs where it infects the archeon Sulfolobus solfataricus. We determined the STIV structure using near-atomic resolution electron microscopy and X-ray crystallography allowing tracing of structural polypeptide chains and visualization of transmembrane proteins embedded in the viral membrane. We propose that the vertex complexes orchestrate virion assembly by coordinating interactions of the membrane and various protein components involved. STIV shares the same coat subunit and penton base protein folds as some eukaryotic and bacterial viruses, suggesting that they derive from a common ancestor predating the divergence of the three kingdoms of life. One architectural motif (β-jelly roll fold) forms virtually the entire capsid (distributed in three different gene products), indicating that a single ancestral protein module may have been at the origin of its evolution.

  14. Comparison of the icosahedral and α structures of Al-Mn-Si with the use of soft-x-ray emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Bruhwiler, P. A.; Shen, Y.; Schnatterly, S. E.; Poon, S. J.

    1987-11-01

    We have measured the soft-x-ray emission spectra of icosahedral-phase (I) Al74Mn20Si6 and α-phase Al100Mn24Si14. In addition, we present measurements of elemental Al and Si and of the solid solution Al97Si3. All spectra represent emission from single-phase samples. α- and I-phase spectra are quite similar in overall structure. Mn is seen to play a central role in determining the local electronic structure associated with Al and Si in the ternary alloys. Analysis of the differences in the lower Al emission band of these alloys supports the idea that there is more than one Mn site in both phases. The electronic structure of Si in the two systems is anomalous. Comparisons of L-emission spectra of Al and Si in various alloys are made, and the validity of the equivalent core approximation is discussed.

  15. Energy Band Structure and Optical Response Function of Icosahedral B12As2: A Spectroscopic Ellipsometry and First-principles Calculational Study

    SciTech Connect

    Bakalova, S.; Gong, Y; Cobet, C; Esser, N; Zhang, Y; Edgar, J; Zhang, Y; Dudley, M; Kuball, M

    2010-01-01

    An experimental and theoretical study on the dielectric-response function of icosahedral B{sub 12}As{sub 2} in the spectral region between 1.24 and 9.8 eV is presented. Comprehensive experimental information on the energy band structure from the analysis of features in the optical dispersion was complemented by spin-orbit first-principles calculations. The lowest indirect band gap width is 3.2 eV; the two lowest direct interband transitions are at 3.46 and 3.9 eV. High-energy critical points are assigned to specific electron transitions in the Brillouin zone and their dimensionality was determined. The static dielectric constant of B{sub 12}As{sub 2} is uniaxially anisotropic with values of 7.84 and 9.02 for polarization perpendicular and parallel to the trigonal axis. Hole and electron effective masses are derived from the band dispersions.

  16. Identification of a major intermediate along the self-assembly pathway of an icosahedral viral capsid by using an analytical model of a spherical patch.

    PubMed

    Law-Hine, Didier; Zeghal, Mehdi; Bressanelli, Stéphane; Constantin, Doru; Tresset, Guillaume

    2016-08-10

    Viruses are astonishing edifices in which hundreds of molecular building blocks fit into the final structure with pinpoint accuracy. We established a robust kinetic model accounting for the in vitro self-assembly of a capsid shell derived from an icosahedral plant virus by using time-resolved small-angle X-ray scattering (TR-SAXS) data at high spatiotemporal resolution. By implementing an analytical model of a spherical patch into a global fitting algorithm, we managed to identify a major intermediate species along the self-assembly pathway. With a series of data collected at different protein concentrations, we showed that free dimers self-assembled into a capsid through an intermediate resembling a half-capsid. The typical lifetime of the intermediate was a few seconds and yet the presence of so large an oligomer was not reported before. The progress in instrumental detection along with the development of powerful algorithms for data processing contribute to shedding light on nonequilibrium processes in highly complex systems such as viruses. PMID:27444997

  17. Averaging Tens to Hundreds of Icosahedral Particle Images to Resolve Protein Secondary Structure Elements using a Multi-Path Simulated Annealing Optimization Algorithm

    PubMed Central

    Liu, Xiangan; Jiang, Wen; Jakana, Joanita; Chiu, Wah

    2007-01-01

    Accurately determining a cryoEM particle’s alignment parameters is crucial to high resolution single particle 3-D reconstruction. We developed Multi-Path Simulated Annealing, a Monte Carlo type of optimization algorithm, for globally aligning the center and orientation of a particle simultaneously. A consistency criterion was developed to ensure the alignment parameters are correct and to remove some bad particles from a large pool of images of icosahedral particles. Without using any a priori model, this procedure is able to reconstruct a structure from a random initial model. Combining the procedure above with a new empirical double threshold particle selection method, we are able to pick tens of best quality particles to reconstruct a subnanometer resolution map from scratch. Using the best 62 particles of rice dwarf virus, the reconstruction reached 9.6Å resolution at which 4 helices of the P3A subunit of RDV are resolved. Furthermore, with the 284 best particles, the reconstruction is improved to 7.9Å resolution, and 21 of 22 helices and 6 of 7 beta sheets are resolved. PMID:17698370

  18. A mimetic, semi-implicit, forward-in-time, finite volume shallow water model: comparison of hexagonal-icosahedral and cubed-sphere grids

    NASA Astrophysics Data System (ADS)

    Thuburn, J.; Cotter, C. J.; Dubos, T.

    2014-05-01

    A new algorithm is presented for the solution of the shallow water equations on quasi-uniform spherical grids. It combines a mimetic finite volume spatial discretization with a Crank-Nicolson time discretization of fast waves and an accurate and conservative forward-in-time advection scheme for mass and potential vorticity (PV). The algorithm is implemented and tested on two families of grids: hexagonal-icosahedral Voronoi grids, and modified equiangular cubed-sphere grids. Results of a variety of tests are presented, including convergence of the discrete scalar Laplacian and Coriolis operators, advection, solid body rotation, flow over an isolated mountain, and a barotropically unstable jet. The results confirm a number of desirable properties for which the scheme was designed: exact mass conservation, very good available energy and potential enstrophy conservation, consistent mass, PV and tracer transport, and good preservation of balance including vanishing ∇ × ∇, steady geostrophic modes, and accurate PV advection. The scheme is stable for large wave Courant numbers and advective Courant numbers up to about 1. In the most idealized tests the overall accuracy of the scheme appears to be limited by the accuracy of the Coriolis and other mimetic spatial operators, particularly on the cubed-sphere grid. On the hexagonal grid there is no evidence for damaging effects of computational Rossby modes, despite attempts to force them explicitly.

  19. A mimetic, semi-implicit, forward-in-time, finite volume shallow water model: comparison of hexagonal-icosahedral and cubed sphere grids

    NASA Astrophysics Data System (ADS)

    Thuburn, J.; Cotter, C. J.; Dubos, T.

    2013-12-01

    A new algorithm is presented for the solution of the shallow water equations on quasi-uniform spherical grids. It combines a mimetic finite volume spatial discretization with a Crank-Nicolson time discretization of fast waves and an accurate and conservative forward-in-time advection scheme for mass and potential vorticity (PV). The algorithm is implemented and tested on two families of grids: hexagonal-icosahedral Voronoi grids, and modified equiangular cubed-sphere grids. Results of a variety of tests are presented, including convergence of the discrete scalar Laplacian and Coriolis operators, advection, solid body rotation, flow over an isolated mountain, and a barotropically unstable jet. The results confirm a number of desirable properties for which the scheme was designed: exact mass conservation, very good available energy and potential enstrophy conservation, consistent mass, PV and tracer transport, and good preservation of balance including vanishing ∇ × ∇, steady geostrophic modes, and accurate PV advection. The scheme is stable for large wave Courant numbers and advective Courant numbers up to about 1. In the most idealized tests the overall accuracy of the scheme appears to be limited by the accuracy of the Coriolis and other mimetic spatial operators, particularly on the cubed sphere grid. On the hexagonal grid there is no evidence for damaging effects of computational Rossby modes, despite attempts to force them explicitly.

  20. Correlation between dynamic slowing down and local icosahedral ordering in undercooled liquid Al{sub 80}Ni{sub 20} alloy

    SciTech Connect

    Jakse, N.; Pasturel, A.

    2015-08-28

    We use ab initio molecular dynamics simulations to study the correlation between the local ordering and the dynamic properties of liquid Al{sub 80}Ni{sub 20} alloy upon cooling. Our results evidence a huge increase of local icosahedral ordering (ISRO) in the undercooled regime which is more developed around Ni than Al atoms. We show that ISRO has a strong impact on self-diffusion coefficients of both species and is at the origin of their crossover from Arrhenius to non-Arrhenius behavior around a crossover temperature T{sub X} = 1000 K, located in the undercooled region. We also clearly identify that this temperature corresponds to the development of dynamic heterogeneities and to the breakdown of the Stokes-Einstein relation. At temperatures below this crossover, we find that the behavior of the diffusion and relaxation dynamics is mostly incompatible with predictions of the mode-coupling theory. Finally, an analysis of the van Hove function indicates that the crossover temperature T{sub X} marks the onset of a change in the diffusion mechanism from a normal flow to an activated process with hopping. From these results, the glass-forming ability of the alloy is discussed.

  1. Structure, electronic density of states and electric field gradients of icosahedral AlCuFe: An ab initio study of the original and a modified Cockayne model

    NASA Astrophysics Data System (ADS)

    Zijlstra, E. S.; Kortus, J.; Krajčí, M.; Stadnik, Z. M.; Bose, S. K.

    2004-03-01

    We present a detailed analysis of electronic properties of the Cockayne model of icosahedral AlCuFe, both in its original form and after a structural relaxation using the ab initio density functional approach. The electronic density of states (DOS) and electric field gradients (EFG’s) of the Al and Fe atoms in the original and the relaxed Cockayne models were calculated and compared with available photoemission, Mössbauer, and nuclear quadrupole resonance spectroscopy data. The relaxed and the original models show significantly different electronic properties. Both models are deficient in describing the available experimental data. The DOS’s show two Fe-d peaks, where there is only one such peak in the photoemission spectroscopy data. These models also cannot account for the shape of the Mössbauer spectra. We show that the interchange between 12 Cu and 12 Fe atoms, each belonging to a single symmetry class, results in a smaller number of Cu-Fe nearest-neighbor pairs and a lowering of the total energy by an amount of ΔE˜50 meV/atom. This “modified” version of the Cockayne model was further relaxed for the final comparison between the calculation and experimental results. The modified model shows a considerable improvement: The DOS has only one Fe-d peak, in agreement with photoemission spectroscopy data, and the calculated EFG’s account very well for the experimental Mössbauer spectra.

  2. Identification of a major intermediate along the self-assembly pathway of an icosahedral viral capsid by using an analytical model of a spherical patch.

    PubMed

    Law-Hine, Didier; Zeghal, Mehdi; Bressanelli, Stéphane; Constantin, Doru; Tresset, Guillaume

    2016-08-10

    Viruses are astonishing edifices in which hundreds of molecular building blocks fit into the final structure with pinpoint accuracy. We established a robust kinetic model accounting for the in vitro self-assembly of a capsid shell derived from an icosahedral plant virus by using time-resolved small-angle X-ray scattering (TR-SAXS) data at high spatiotemporal resolution. By implementing an analytical model of a spherical patch into a global fitting algorithm, we managed to identify a major intermediate species along the self-assembly pathway. With a series of data collected at different protein concentrations, we showed that free dimers self-assembled into a capsid through an intermediate resembling a half-capsid. The typical lifetime of the intermediate was a few seconds and yet the presence of so large an oligomer was not reported before. The progress in instrumental detection along with the development of powerful algorithms for data processing contribute to shedding light on nonequilibrium processes in highly complex systems such as viruses.

  3. Electron microscopic imaging revealed the flexible filamentous structure of the cell attachment protein P2 of Rice dwarf virus located around the icosahedral 5-fold axes.

    PubMed

    Miyazaki, Naoyuki; Higashiura, Akifumi; Higashiura, Tomoko; Akita, Fusamichi; Hibino, Hiroyuki; Omura, Toshihiro; Nakagawa, Atsushi; Iwasaki, Kenji

    2016-02-01

    The minor outer capsid protein P2 of Rice dwarf virus (RDV), a member of the genus Phytoreovirus in the family Reoviridae, is essential for viral cell entry. Here, we clarified the structure of P2 and the interactions to host insect cells. Negative stain electron microscopy (EM) showed that P2 proteins are monomeric and flexible L-shaped filamentous structures of ∼20 nm in length. Cryo-EM structure revealed the spatial arrangement of P2 in the capsid, which was prescribed by the characteristic virion structure. The P2 proteins were visualized as partial rod-shaped structures of ∼10 nm in length in the cryo-EM map and accommodated in crevasses on the viral surface around icosahedral 5-fold axes with hydrophobic interactions. The remaining disordered region of P2 assumed to be extended to the radial direction towards exterior. Electron tomography clearly showed that RDV particles were away from the cellular membrane at a uniform distance and several spike-like densities, probably corresponding to P2, connecting a viral particle to the host cellular membrane during cell entry. By combining the in vitro and in vivo structural information, we could gain new insights into the detailed mechanism of the cell entry of RDV.

  4. A hybrid simulated method for analyzing the optical efficiency of a head-mounted display with a quasi-crystal OLED panel.

    PubMed

    Chang, Kao-Der; Li, Chang-Yi; Pan, Jui-Wen; Cheng, Kuei-Yuan

    2014-03-10

    Organic light emitting diodes (OLEDs) with a quasi-crystal (QC) structure are analyzed and applied in a head-mounted display (HMD) system in this study. We adopt a hybrid simulated method to evaluate the light extraction efficiency (LEE) and far-field pattern in the air, and study the relationship between them. The simulation results show that OLEDs implanted with the QC structure can provide a collimated far-field pattern to increase the brightness. Using this 10-fold QC arrangement the maxima LEE of the OLEDs can be increased by 1.20 times. Compared with conventional OLEDs, the viewing angle of the OLED panel decreases from 120 degrees to 26 degrees with an improvement in the optical efficiency of the HMD system by 2.66 times. Moreover, the normalized on-axis intensity in the pupil of the eyepiece can be enlarged up to 3.95 times which suggests that the OLED panel can save 74.68% energy while achieving the same on-axis intensity as conventional OLEDs.

  5. Sign of canted ferromagnetism in the quasicrystal approximants Au-SM-R (SM = Si, Ge and Sn / R = Tb, Dy and Ho).

    PubMed

    Hiroto, T; Tokiwa, K; Tamura, R

    2014-05-28

    Magnetic susceptibility and magnetization of the quasicrystal approximants Au-SM-R (SM = Si, Ge or Sn / R = Gd, Tb, Dy or Ho) are investigated. Ferromagnetic transitions are observed in all of these compounds, in contrast to the spin-glass behavior reported in similar compounds, Ag-In-R (R = Eu, Gd, Tb or Dy). Au-SM-Gd (SM = Si, Ge or Sn) exhibit a simple ferromagnetic transition at 22.5, 13 and 9 K, respectively, whereas Au-Si-(Tb, Dy or Ho) show indications of a canted ferromagnetic transition at 8.3, 5.9 and 3.8 K, respectively. The latter are attributed to a crystal electric field effect that is absent in the Gd-bearing compounds. The ferromagnetic behavior in Au-SM-R may be understood to be a consequence of the short R-R distances compared to those for Cd-R and Ag-In-R.

  6. Quantum diffusion of electrons in quasiperiodic and periodic approximant lattices in the rare earth-cadmium system

    NASA Astrophysics Data System (ADS)

    Armstrong, N. M. R.; Mortimer, K. D.; Kong, T.; Bud'ko, S. L.; Canfield, P. C.; Basov, D. N.; Timusk, T.

    2016-04-01

    Icosahedral quasicrystals are characterised by the absence of a distinct Drude peak in their low-frequency optical conductivity and the same is true of their crystalline approximants. We have measured the optical conductivity of i-GdCd?, an icosahedral quasicrystal, and two approximants, GdCd? and YCd?. We find that there is a significant difference in the optical properties of these compounds. The approximants have a zero frequency peak, characteristic of a metal, whereas the quasicrystal has a striking minimum. This is the first example where the transport properties of a quasicrystal and its approximant differ in such a fundamental way. Using a generalised Drude model introduced by Mayou, we find that our data are well described by this model. It implies that the quantum diffusion of electron wave packets through the periodic and quasiperiodic lattices is responsible for these dramatic differences: in the approximants, the transport is superdiffusive, whereas the quasicrystals show subdiffusive motion of the electrons.

  7. Mutations at the base of the icosahedral five-fold cylinders of minute virus of mice induce 3'-to-5' genome uncoating and critically impair entry functions.

    PubMed

    Cotmore, Susan F; Tattersall, Peter

    2012-01-01

    The linear single-stranded DNA genome of minute virus of mice can be ejected, in a 3'-to-5' direction, via a cation-linked uncoating reaction that leaves the 5' end of the DNA firmly complexed with its otherwise intact protein capsid. Here we compare the phenotypes of four mutants, L172T, V40A, N149A, and N170A, which perturb the base of cylinders surrounding the icosahedral 5-fold axes of the virus, and show that these structures are strongly implicated in 3'-to-5' release. Although noninfectious at 37°C, all mutants were viable at 32°C, showed a temperature-sensitive cell entry defect, and, after proteolysis of externalized VP2 N termini, were unable to protect the VP1 domain, which is essential for bilayer penetration. Mutant virus yields from multiple-round infections were low and were characterized by the accumulation of virions containing subgenomic DNAs of specific sizes. In V40A, these derived exclusively from the 5' end of the genome, indicative of 3'-to-5' uncoating, while L172T, the most impaired mutant, had long subgenomic DNAs originating from both termini, suggesting additional packaging portal defects. Compared to the wild type, genome release in vitro following cation depletion was enhanced for all mutants, while only L172T released DNA, in both directions, without cation depletion following proteolysis at 37°C. Analysis of progeny from single-round infections showed that uncoating did not occur during virion assembly, release, or extraction. However, unlike the wild type, the V40A mutant extensively uncoated during cell entry, indicating that the V40-L172 interaction restrains an uncoating trigger mechanism within the endosomal compartment.

  8. A hybrid plant RNA virus made by transferring the noncapsid movement protein from a rod-shaped to an icosahedral virus is competent for systemic infection.

    PubMed

    De Jong, W; Ahlquist, P

    1992-08-01

    For many plant RNA viruses, multiple viral gene products, including noncapsid movement proteins and capsid proteins, contribute to the spread of infection within plants. The extent to which these factors interact to support infection spread is not known, but, for movement protein mutants of certain viruses, the inability of coinoculated "helper" viruses to complement defective movement has suggested a possible requirement for coadaptation between noncapsid movement proteins and other virus factors. To test directly for required coadaptation, the 3a movement protein gene of cowpea chlorotic mottle virus, an icosahedral bromovirus, was replaced with the nonhomologous 30-kDa movement protein gene of sunn-hemp mosaic virus, a rod-shaped, cowpea-adapted tobamovirus. The resulting hybrid virus is competent for systemic infection of cowpea, with systemic infection dependent upon expression of the 30-kDa gene. In view of the dramatic differences between cowpea chlorotic mottle virus and sunn-hemp mosaic virus in genetic organization and particle morphology, the ability of the hybrid to systemically infect cowpea implies that the tobamovirus 30-kDa movement protein functions independently of sequence-specific interactions with other viral components or sequences. Similarly, the required contribution of bromovirus capsid protein to infection movement appears to be independent of specific interaction with the natural 3a movement protein. In addition to other implications concerning movement protein and coat protein function, the results are consistent with the possibility that two or more distinguishable transfer processes may be involved in crossing different tissue barriers to achieve full systemic spread of infection. PMID:1495969

  9. A diagnostic interface for the ICOsahedral Non-hydrostatic (ICON) modelling framework based on the Modular Earth Submodel System (MESSy v2.50)

    NASA Astrophysics Data System (ADS)

    Kern, Bastian; Jöckel, Patrick

    2016-10-01

    Numerical climate and weather models have advanced to finer scales, accompanied by large amounts of output data. The model systems hit the input and output (I/O) bottleneck of modern high-performance computing (HPC) systems. We aim to apply diagnostic methods online during the model simulation instead of applying them as a post-processing step to written output data, to reduce the amount of I/O. To include diagnostic tools into the model system, we implemented a standardised, easy-to-use interface based on the Modular Earth Submodel System (MESSy) into the ICOsahedral Non-hydrostatic (ICON) modelling framework. The integration of the diagnostic interface into the model system is briefly described. Furthermore, we present a prototype implementation of an advanced online diagnostic tool for the aggregation of model data onto a user-defined regular coarse grid. This diagnostic tool will be used to reduce the amount of model output in future simulations. Performance tests of the interface and of two different diagnostic tools show, that the interface itself introduces no overhead in form of additional runtime to the model system. The diagnostic tools, however, have significant impact on the model system's runtime. This overhead strongly depends on the characteristics and implementation of the diagnostic tool. A diagnostic tool with high inter-process communication introduces large overhead, whereas the additional runtime of a diagnostic tool without inter-process communication is low. We briefly describe our efforts to reduce the additional runtime from the diagnostic tools, and present a brief analysis of memory consumption. Future work will focus on optimisation of the memory footprint and the I/O operations of the diagnostic interface.

  10. Interpenetration of a 3D Icosahedral M@Ni12 (M=Al, Ga) Framework with Porphyrin-Reminiscent Boron Layers in MNi9 B8.

    PubMed

    Zheng, Qiang; Wagner, Frank R; Ormeci, Alim; Prots, Yurii; Burkhardt, Ulrich; Schmidt, Marcus; Schnelle, Walter; Grin, Yuri; Leithe-Jasper, Andreas

    2015-11-01

    Two ternary borides MNi9 B8 (M=Al, Ga) were synthesized by thermal treatment of mixtures of the elements. Single-crystal X-ray diffraction data reveal AlNi9 B8 and GaNi9 B8 crystallizing in a new type of structure within the space group Cmcm and the lattice parameters a=7.0896(3) Å, b=8.1181(3) Å, c=10.6497(4) Å and a=7.0897(5) Å, b=8.1579(4) Å, c=10.6648(7) Å, respectively. The boron atoms build up two-dimensional layers, which consist of puckered [B16 ] rings with two tailing B atoms, whereas the M atoms reside in distorted vertices-condensed [Ni12 ] icosahedra, which form a three-dimensional framework interpenetrated by boron porphyrin-reminiscent layers. An unusual local arrangement resembling a giant metallo-porphyrin entity is formed by the [B16 ] rings, which, due to their large annular size of approximately 8 Å, chelate four of the twelve icosahedral Ni atoms. An analysis of the chemical bonding by means of the electron localizability approach reveals strong covalent B-B interactions and weak Ni-Ni interactions. Multi-center dative B-Ni interaction occurs between the Al-Ni framework and the boron layers. In agreement with the chemical bonding analysis and band structure calculations, AlNi9 B8 is a Pauli-paramagnetic metal. PMID:26418894

  11. The Effect of Icosahedral Phase on Dynamic Recrystallization Evolution and Hot Workability of Mg-2.0Zn-0.3Zr-0.2Y Alloy

    NASA Astrophysics Data System (ADS)

    Lv, Bin-Jiang; Peng, Jian; Chu, Zhong

    2015-09-01

    The effect of Icosahedral phase (I-phase) on hot deformation behavior, dynamic recrystallization (DRX) evolution, and hot workability of Mg-2.0Zn-0.3Zr-0.2Y alloy has been investigated in the temperature range of 300-500 °C and strain rate range of 0.001-1 s-1 using Gleeble 3500D thermo-mechanical simulator. Based on regression analysis for Arrhenius-type equation of flow behavior, the average activation energy of deformation was determined as Q = 277.8 kJ/mol. The model of DRX evolution is . The DRX model agreed well with the microstructure evolution of the alloy at all deformation conditions. At lower strain rates (0.001-0.01 s-1), continuous DRX (CDRX) is the main DRX mechanism that occurred near the original grain boundaries. Twin-dynamic recrystallization (TDRX) began to occur at lower deformation temperatures and higher strain rates (0.1-1 s-1). At a deformation temperature range of 250 to 350 °C and a strain rate of 1 s-1, the main DRX mechanism is TDRX, and the density of twins decreased, and CDRX began to occur near the original grain boundaries. When the deformation temperature increased to 400 °C, TDRX disappeared and CDRX occurred near original grain boundaries and I-phase particles. According to the flow stress behavior and DRX model, the processing maps have exhibited the optimum deformation conditions to be 450 °C and the strain rate range of 0.01-0.001 s-1.

  12. The structure of an Al-Rh-Cu decagonal quasicrystal studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Hiraga, Kenji; Yasuhara, Akira; Yamamoto, Kazuki; Yubuta, Kunio

    2015-05-01

    The structure of an Al-Rh-Cu decagonal quasicrystal formed with two quasiperiodic planes along the periodic axis in an Al63Rh18.5Cu18.5 alloy has been studied by spherical aberration (Cs)-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM). Heavy atoms of Rh and mixed sites (MSs) of Al and Cu atoms projected along the periodic axis can be clearly represented as separate bright dots in observed HAADF-STEM images, and consequently arrangements of Rh atoms and MSs on the two quasiperiodic planes can be directly determined from those of bright dots in the observed HAADF-STEM image. The Rh atoms are arranged in pentagonal tiling formed with pentagonal and star-shaped pentagonal tiles with an edge-length of 0.76 nm, and also MSs with a pentagonal arrangement are located in the pentagonal tiles with definite orientations. The star-shaped pentagonal tiles in the pentagonal tiling are arranged in τ2(τ: golden ratio)-inflated pentagonal tiling with a bond-length of 2 nm. From arrangements of Rh atoms placed in pentagonal tilings with a bond-length of 2 nm, which are generated by the projection of a five-dimensional hyper-cubic lattice, occupation domains in the perpendicular space are derived. Al atoms as well as Rh atoms and MSs are represented as dark dots in an observed ABF-STEM image, and arrangements of Al atoms in well-symmetric regions are discussed.

  13. Structure-Based Mutagenesis of Sulfolobus Turreted Icosahedral Virus B204 Reveals Essential Residues in the Virion-Associated DNA-Packaging ATPase

    PubMed Central

    Dellas, Nikki; Snyder, Jamie C.; Dills, Michael; Nicolay, Sheena J.; Kerchner, Keshia M.; Brumfield, Susan K.; Lawrence, C. Martin

    2015-01-01

    ABSTRACT Sulfolobus turreted icosahedral virus (STIV), an archaeal virus that infects the hyperthermoacidophile Sulfolobus solfataricus, is one of the most well-studied viruses of the domain Archaea. STIV shares structural, morphological, and sequence similarities with viruses from other domains of life, all of which are thought to belong to the same viral lineage. Several of these common features include a conserved coat protein fold, an internal lipid membrane, and a DNA-packaging ATPase. B204 is the ATPase encoded by STIV and is thought to drive packaging of viral DNA during the replication process. Here, we report the crystal structure of B204 along with the biochemical analysis of B204 mutants chosen based on structural information and sequence conservation patterns observed among members of the same viral lineage and the larger FtsK/HerA superfamily to which B204 belongs. Both in vitro ATPase activity assays and transfection assays with mutant forms of B204 confirmed the essentiality of conserved and nonconserved positions. We also have identified two distinct particle morphologies during an STIV infection that differ in the presence or absence of the B204 protein. The biochemical and structural data presented here are not only informative for the STIV replication process but also can be useful in deciphering DNA-packaging mechanisms for other viruses belonging to this lineage. IMPORTANCE STIV is a virus that infects a host from the domain Archaea that replicates in high-temperature, acidic environments. While STIV has many unique features, there exist several striking similarities between this virus and others that replicate in different environments and infect a broad range of hosts from Bacteria and Eukarya. Aside from structural features shared by viruses from this lineage, there exists a significant level of sequence similarity between the ATPase genes carried by these different viruses; this gene encodes an enzyme thought to provide energy that drives

  14. Chemical ordering of Co and Ni in a W-(AlCoNi) crystalline approximant related to Al-Co-Ni decagonal quasicrystals studied by atomic resolution energy-dispersive X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Yasuhara, Akira; Hiraga, Kenji

    2015-01-01

    A W-(AlCoNi) crystalline approximant, which is closely related to Al-Co-Ni decagonal quasicrystals, in an Al72.5Co20Ni7.5 alloy has been studied by atomic resolution energy-dispersive X-ray spectroscopy (EDS), in an instrument attached to a spherical aberration (Cs)-corrected scanning transmission electron microscope. On high-resolution EDS maps of Co and Ni elements, obtained by integrating many sets of EDS data taken from undamaged areas, chemical ordering of Co and Ni is clearly detected. In the structure of the W-(AlCoNi) phase, consisting of arrangements of transition-metal (TM) atoms located at vertices of pentagonal tilings and pentagonal arrangements of mixed sites (MSs) of TM and Al atoms, Co atoms occupy the TM atom positions with the pentagonal tiling and Ni is enriched in part of the pentagonal arrangements of MSs.

  15. New icosahedral nanoclusters in crystal structures of intermetallic compounds: Topological types of 50-atom deltahedra D50 in samson phases β-Mg2Al3 and ɛ-Mg23Al30

    NASA Astrophysics Data System (ADS)

    Blatov, V. A.; Ilyushin, G. D.

    2012-12-01

    A database of intermetallic compounds has been compiled using the TOPOS program package. This database includes 514 topological types, containing 12- and 13-atom icosahedral i clusters. An isolated group of 1649 i clusters is described by 14 point groups and their maximum symmetry D 3 d (bar 3 m) and T h ( m bar 3) is established, respectively, in 47 and 25 types of crystal structures. A structural analysis of the outer quasispherical shells showed that local 63-atom i configurations 1@12@50, which contain 50 atoms in the second layer, are implemented in 8 out of 19 cases. Examples of new topologically different types of 50-atom D50 deltahedra in the Samson phases ɛ-Mg23Al30 and β-Mg2Al3 are presented. Four topologically different sites with coordination numbers of 5, 6, 6, or 7 are established in the ɛ shell and seven sites with coordination numbers of 5, 5, 6, 6, 6, 6, or 7 are found in the β shell. The inner i clusters for the β-Mg2Al3 structure (with the symmetry bar 3 m) and the ɛ-Mg23Al30 structure (with the symmetry bar 3) have a similar chemical composition, i.e., Mg7Al6 and Mg6Al7, and their 50-atom shells are chemically identical to 18Mg + 32Al. The configurations found supplement the series of known two-layer icosahedral Bergman and Mackay clusters in the form of deltahedra with 32- and 42-atom shells.

  16. Electronic spectrum of the three-dimensional quasi crystal

    NASA Astrophysics Data System (ADS)

    Olenev, Dmitri; Isaev, Eyvaz; Slobodianiuk, Pavel; Vekilov, Yuri

    1999-05-01

    The electronic spectrum of icosahedral quasicrystal with central atom decoration of Amman-Mackay network is investigated in the tight-binding approximation. Quasicrystal is described as a structural limit of the optimal cubic approximants with increasing period. The electronic spectra for the first four optimal cubic approximants do not contain hierarchical gap structure which is typical for Cantor set of the spectrum of one-dimensional quasicrystal. At the same time the spectrum with increasing the order of approximant becomes singular on the whole energy scales.

  17. Enhancement of light output power of GaN-based light-emitting diodes with photonic quasi-crystal patterned on p-GaN surface and n-side sidewall roughing.

    PubMed

    Lai, Fang-I; Yang, Jui-Fu

    2013-05-17

    In this paper, GaN-based light-emitting diodes (LEDs) with photonic quasi-crystal (PQC) structure on p-GaN surface and n-side roughing by nano-imprint lithography are fabricated and investigated. At an injection current of 20 mA, the LED with PQC structure on p-GaN surface and n-side roughing increased the light output power of the InGaN/GaN multiple quantum well LEDs by a factor of 1.42, and the wall-plug efficiency is 26% higher than the conventional GaN-based LED type. After 500-h life test (55°C/50 mA), it was found that the normalized output power of GaN-based LED with PQC structure on p-GaN surface and n-side roughing only decreased by 6%. These results offer promising potential to enhance the light output powers of commercial light-emitting devices using the technique of nano-imprint lithography.

  18. Enhancement of light output power of GaN-based light-emitting diodes with photonic quasi-crystal patterned on p-GaN surface and n-side sidewall roughing

    PubMed Central

    2013-01-01

    In this paper, GaN-based light-emitting diodes (LEDs) with photonic quasi-crystal (PQC) structure on p-GaN surface and n-side roughing by nano-imprint lithography are fabricated and investigated. At an injection current of 20 mA, the LED with PQC structure on p-GaN surface and n-side roughing increased the light output power of the InGaN/GaN multiple quantum well LEDs by a factor of 1.42, and the wall-plug efficiency is 26% higher than the conventional GaN-based LED type. After 500-h life test (55°C/50 mA), it was found that the normalized output power of GaN-based LED with PQC structure on p-GaN surface and n-side roughing only decreased by 6%. These results offer promising potential to enhance the light output powers of commercial light-emitting devices using the technique of nano-imprint lithography. PMID:23683526

  19. Structural, elastic, and electronic properties of icosahedral boron subcarbides (B12C3, B13C2), subnitride B12N2, and suboxide B12O2 from data of SCC-DFTB calculations

    NASA Astrophysics Data System (ADS)

    Enyashin, A. N.; Ivanovskii, A. L.

    2011-08-01

    The structural, elastic, and electronic properties of a series of icosahedral phases, such as boron subcarbides B12C3 and B13C2, subnitride B12N2, and suboxide B12O2, have been studied in the framework of the SCC-DFTB method. It has been found that the B12C2 and B13C2 phases manifest metal-like properties, while B12C3 and B12O2 are semiconductors. The estimates have shown that the insertion of 2 p atoms (C, N, or O) into intericosahedral pores of elemental boron can cause both a decrease in its elastic modulus (an increase in the compressibility of B12N2) and a sharp increase in the modulus B (in subcarbides B12C3 and B12BCC). On the other hand, the insertion of 2 p atoms into α-B12 will favor an increase in its hardness (suboxide B12O2 will have a maximum hardness).

  20. Synthesis and characterization of (H2dab)2Cu8Ge4S14·2H2O: An expanded framework based on icosahedral Cu8S12 cluster

    NASA Astrophysics Data System (ADS)

    Zhang, Ren-Chun; Zhang, Chi; Ji, Shou-Hua; Ji, Min; An, Yong-Lin

    2012-02-01

    A new three-dimensional framework copper-thiogermanate, (H2dab)2Cu8Ge4S14·2H2O (1), was prepared under solvothermal condition and characterized by elemental analysis, single-crystal and powder X-ray diffraction, thermogravimetric analysis and UV-vis diffuse reflectance spectroscopy. Compound 1 crystallizes in the monoclinic space group P2(1)/c, a=11.444(4) Å, b=12.984(4) Å, c=12.455(6) Å, β=91.527(1)°, V=1850.2(3) Å3, Z=2. It contains a new three-dimensional Cu-Ge-S framework constructed from icosahedral [Cu8S12]16- clusters linked by [GeS4]4- and dimeric [Ge2S6]4- units, with diprotonated 1,4-dab (1,4-diaminobutane) and H2O molecules located in the intersecting channels. UV-vis reflectance spectroscopy reveals the band gap of compound 1 is 2.5 eV.

  1. Cluster self-organization of crystal-forming systems: Suprapolyhedral cluster precursors and self-assembly of the icosahedral structure of ZrZn22( cF184)

    NASA Astrophysics Data System (ADS)

    Ilyushin, G. D.; Blatov, V. A.

    2009-07-01

    The mechanism of self-assembly of symmetrically and topologically different chains and microlayers (in the form of planar nets) from cyclic three-node clusters A 3 is considered in the model system. The obtained nets correspond to the uninodal Shubnikov nets N 3 12 12 and N 3 6 3 6 and the new binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2). A complete three-dimensional reconstruction of the self-assembly of the icosahedral structure of the ZrZn22 compound ( cF184) is performed using computer methods (with the TOPOS program package) according to the following scheme: cluster precursor → primary chain → microlayer → microframework (supraprecursor) → ... → framework. It is revealed that the suprapolyhedral cluster precursor (nanocluster ˜12 Å in size) of the AB 2 composition is formed by three polyhedra shared by vertices in a cyclic manner: the A-ZrZn16 polyhedron (sixteen-vertex polyhedron with the point symmetry bar 4 3 m) and two B-ZrZn12 polyhedra (icosahedra with the point symmetry bar 3 m). The AB 2 cluster precursor in the structure retains the symmetry m. It is established that the structural mechanism of self-assembly of the two-dimensional layer in the ZrZn22 structure is described by the binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2) constructed in the modeling.

  2. Synthesis and characterization of (H{sub 2}dab){sub 2}Cu{sub 8}Ge{sub 4}S{sub 14}{center_dot}2H{sub 2}O: An expanded framework based on icosahedral Cu{sub 8}S{sub 12} cluster

    SciTech Connect

    Zhang Renchun; Zhang Chi; Ji Shouhua; Ji Min; An Yonglin

    2012-02-15

    A new three-dimensional framework copper-thiogermanate, (H{sub 2}dab){sub 2}Cu{sub 8}Ge{sub 4}S{sub 14}{center_dot}2H{sub 2}O (1), was prepared under solvothermal condition and characterized by elemental analysis, single-crystal and powder X-ray diffraction, thermogravimetric analysis and UV-vis diffuse reflectance spectroscopy. Compound 1 crystallizes in the monoclinic space group P2(1)/c, a=11.444(4) A, b=12.984(4) A, c=12.455(6) A, {beta}=91.527(1) Degree-Sign , V=1850.2(3) A{sup 3}, Z=2. It contains a new three-dimensional Cu-Ge-S framework constructed from icosahedral [Cu{sub 8}S{sub 12}]{sup 16-} clusters linked by [GeS{sub 4}]{sup 4-} and dimeric [Ge{sub 2}S{sub 6}]{sup 4-} units, with diprotonated 1,4-dab (1,4-diaminobutane) and H{sub 2}O molecules located in the intersecting channels. UV-vis reflectance spectroscopy reveals the band gap of compound 1 is 2.5 eV. - Graphical abstract: Compound 1 contains a 3D expanded framework constructed from icosahedral Cu{sub 8}S{sub 12} clusters linked by GeS{sub 4} and dimeric Ge{sub 2}S{sub 6} units, with diprotonated 1,4-dab and H{sub 2}O molecules located in the channels. Highlights: Black-Right-Pointing-Pointer A new 3-D framework copper-thiogermanate was prepared under solvothermal condition. Black-Right-Pointing-Pointer The framework is built up from icosahedral Cu{sub 8}S{sub 12} clusters linked by GeS{sub 4} and dimeric Ge{sub 2}S{sub 6} units. Black-Right-Pointing-Pointer The result provides a new strategy to expand octahedral SBUs-based framework. Black-Right-Pointing-Pointer Compound 1 is a semiconductor with the band gap of 2.5 eV.

  3. Diffraction studies of the structure of glasses and liquids

    SciTech Connect

    Moss, S.C.

    1989-01-01

    At the University of Houston, our program on glasses and liquids has continued with emphasis on melanin; vitreous TiO{sub 2}; metallic glasses/quasicrystals, including the computer modelling of quasicrystals via icosahedral glass models; and the structure of C{sup +} ion-beam deposited carbon films. The development of a dedicated glass and liquid diffractometer (GLAD) at the Argonne IPNS, under the direction of Dr. David L. Price, has entered the prototype stage. We are now quite close to a fully operating facility and commissioning should take place in the Spring 1990 with beam time available for participating scientists, on state-of-the-art experiments, shortly thereafter.

  4. Topological pumping over a photonic Fibonacci quasicrystal

    NASA Astrophysics Data System (ADS)

    Verbin, Mor; Zilberberg, Oded; Lahini, Yoav; Kraus, Yaacov E.; Silberberg, Yaron

    2015-02-01

    Quasiperiodic lattices have recently been shown to be a nontrivial topological phase of matter. Charge pumping—one of the hallmarks of topological states of matter—was recently realized for photons in a one-dimensional off-diagonal Harper model implemented in a photonic waveguide array. However, if the relationship between topological pumps and quasiperiodic systems is generic, one might wonder how to observe it in the canonical and most studied quasicrystalline system in one dimension—the Fibonacci chain. This chain is expected to facilitate a similar phenomenon, yet its discrete nature hinders the experimental study of such topological effects. Here, we overcome this obstacle by utilizing the topological equivalence of a family of quasiperiodic models which ranges from the Fibonacci chain to the Harper model. Implemented in photonic waveguide arrays, we observe the topological properties of this family, and perform a topological pumping of photons across a Fibonacci chain.

  5. Basis for Synthesis of Spiral Lattice Quasicrystals

    NASA Astrophysics Data System (ADS)

    Bursill, L. A.; Ryan, George; Fan, Xudong; Rouse, J. L.; Peng, Julin; Perkins, Anne

    Observations of the sunflower Helianthus tuberosus reveal the occurrence of both Fibonacci and Lucas numbers of visible spirals (parastichies). This species is multi-headed, allowing a quantitative study of the relative abundance of these two types of phyllotaxis. The florets follow a spiral arrangement. It is remarkable that the Lucas series occurred, almost invariably, in the first-flowering heads of individual plants. The occurrence of left-and right-handed chirality was found to be random, within experimental error, using an appropriate chirality convention. Quantitative crystallographic studies allow the average growth law to be derived (r = alτ-1 θ = 2πl/(τ + 1), where a is a constant, l is the seed cell number and τ is the golden mean (1 +√ {5})/2). They also reveal departures from classical theoretical models of phyllotaxis, taking the form of persistent oscillations in both divergence angle and radius. The experimental results are discussed in terms of a new theoretical model for the close-packing of growing discs. Finally, a basis for synthesis of (inorganic) spiral lattice structures is proposed.

  6. Are there bipolarons in icosahedral boron-rich solids?

    PubMed

    Werheit, H

    2007-05-01

    The charge transport of boron carbide, often incorrectly denoted as B(4)C, has been controversially discussed. It is shown that the bipolaron hypothesis is not compatible with numerous experimental results. In particular, the determined real microstructure of boron carbide and its related electronic properties disprove several assumptions, which are fundamental to the bipolaron hypothesis. In contrast, the actual energy band scheme derived mainly from optical investigations is confirmed by careful evaluation of the high-temperature electrical conductivity, and allows a consistent description at most of the experimental results.

  7. Carbon-rich icosahedral boron carbide designed from first principles

    SciTech Connect

    Jay, Antoine; Vast, Nathalie; Sjakste, Jelena; Duparc, Olivier Hardouin

    2014-07-21

    The carbon-rich boron-carbide (B{sub 11}C)C-C has been designed from first principles within the density functional theory. With respect to the most common boron carbide at 20% carbon concentration B{sub 4}C, the structural modification consists in removing boron atoms from the chains linking (B{sub 11}C) icosahedra. With C-C instead of C-B-C chains, the formation of vacancies is shown to be hindered, leading to enhanced mechanical strength with respect to B{sub 4}C. The phonon frequencies and elastic constants turn out to prove the stability of the carbon-rich phase, and important fingerprints for its characterization have been identified.

  8. Isolation and Structural Characterization of a Mackay 55-Metal-Atom Two-Shell Icosahedron of Pseudo-Ih Symmetry, Pd55L12(μ3-CO)20 (L = PR3, R = Isopropyl): Comparative Analysis with Interior Two-Shell Icosahedral Geometries in Capped Three-Shell Pd145, Pt-Centered Four-Shell Pd-Pt M165, and Four-Shell Au133 Nanoclusters.

    PubMed

    Erickson, Jeremiah D; Mednikov, Evgueni G; Ivanov, Sergei A; Dahl, Lawrence F

    2016-02-10

    We present the first successful isolation and crystallographic characterization of a Mackay 55-metal-atom two-shell icosahedron, Pd55L12(μ3-CO)20 (L = PPr(i)3) (1). Its two-shell icosahedron of pseudo-Ih symmetry (without isopropyl substituents) enables a structural/bonding comparison with interior 55-metal-atom two-shell icosahedral geometries observed within the multi-shell capped 145-metal-atom three-shell Pd145(CO)72(PEt3)30 and 165-metal-atom four-shell Pt-centered (μ12-Pt)Pd164-xPtx(CO)72(PPh3)20 (x ≈ 7) nanoclusters, and within the recently reported four-shell Au133(SC6H4-p-Bu(t))52 nanocluster. DFT calculations carried out on a Pd55(CO)20(PH3)12 model analogue, with triisopropyl phosphine substituents replaced by H atoms, revealed a positive +0.84 e charge for the entire Pd55 core, with a highly positive second-shell Pd42 surface of +1.93 e.

  9. Nanosized (mu12-Pt)Pd164-xPtx(CO)72(PPh3)20 (x approximately 7) containing Pt-centered four-shell 165-atom Pd-Pt core with unprecedented intershell bridging carbonyl ligands: comparative analysis of icosahedral shell-growth patterns with geometrically related Pd145(CO)x(PEt3)30 (x approximately 60) containing capped three-shell Pd145 core.

    PubMed

    Mednikov, Evgueni G; Jewell, Matthew C; Dahl, Lawrence F

    2007-09-19

    Presented herein are the preparation and crystallographic/microanalytical/magnetic/spectroscopic characterization of the Pt-centered four-shell 165-atom Pd-Pt cluster, (mu(12)-Pt)Pd(164-x)Pt(x)(CO)(72)(PPh(3))(20) (x approximately 7), 1, that replaces the geometrically related capped three-shell icosahedral Pd(145) cluster, Pd(145)(CO)(x)(PEt(3))(30) (x approximately 60), 2, as the largest crystallographically determined discrete transition metal cluster with direct metal-metal bonding. A detailed comparison of their shell-growth patterns gives rise to important stereochemical implications concerning completely unexpected structural dissimilarities as well as similarities and provides new insight concerning possible synthetic approaches for generation of multi-shell metal clusters. 1 was reproducibly prepared in small yields (<10%) from the reaction of Pd(10)(CO)(12)(PPh(3))(6) with Pt(CO)(2)(PPh(3))(2). Its 165-atom metal-core geometry and 20 PPh(3) and 72 CO ligands were established from a low-temperature (100 K) CCD X-ray diffraction study. The well-determined crystal structure is attributed largely to 1 possessing cubic T(h) (2/m3) site symmetry, which is the highest crystallographic subgroup of the noncrystallographic pseudo-icosahedral I(h) (2/m35) symmetry. The "full" four-shell Pd-Pt anatomy of 1 consists of: (a) shell 1 with the centered (mu(12)-Pt) atom encapsulated by the 12-atom icosahedral Pt(x)Pd(12-x) cage, x = 1.2(3); (b) shell 2 with the 42-atom nu(2) icosahedral Pt(x)Pd(42-x) cage, x = 3.5(5); (c) shell 3 with the anti-Mackay 60-atom semi-regular rhombicosidodecahedral Pt(x)Pd(60-x) cage, x = 2.2(6); (d) shell 4 with the 50-atom nu(2) pentagonal dodecahedral Pd(50) cage. The total number of crystallographically estimated Pt atoms, 8 +/- 3, which was obtained from least-squares (Pt(x)/Pd(1-x))-occupancy analysis of the X-ray data that conclusively revealed the central atom to be pure Pt (occupancy factor, x = 1.00(3)), is fortuitously in agreement

  10. The determination of the solidification paths and the liquidus surface in the quasicrystalline region of the Al-Cu-Ru systems

    SciTech Connect

    Haines, S.

    1995-12-06

    Objective is to determine if conventional slow-growth methods will be successful for growing single quasicrystals in this system. Reaction schemes, isopleths, and a ternary liquidus diagram were constructed using DTA, XRD, microscopy, and energy dispersive spectroscopy. Results suggest a peak in the liquidus near the predicted compositions of Al{sub 65}Cu{sub 23}Ru{sub 12} or Al{sub 65}Cu{sub 20}Ru{sub 15} in the face-centered icosahedral phase field. Further study is needed to verify the existence of a congruently melting phase. There appears to be composition for which slow-growth methods will produce a single-quasicrystal. Directional solidification studies were done on 65Al25Cu10Ru.

  11. Extra-electron induced covalent strengthening and generalization of intrinsic ductile-to-brittle criterion

    PubMed Central

    Niu, Haiyang; Chen, Xing-Qiu; Liu, Peitao; Xing, Weiwei; Cheng, Xiyue; Li, Dianzhong; Li, Yiyi

    2012-01-01

    Traditional strengthening ways, such as strain, precipitation, and solid-solution, come into effect by pinning the motion of dislocation. Here, through first-principles calculations we report on an extra-electron induced covalent strengthening mechanism, which alters chemical bonding upon the introduction of extra-valence electrons in the matrix of parent materials. It is responsible for the brittle and high-strength properties of Al12W-type compounds featured by the typical fivefold icosahedral cages, which are common for quasicrystals and bulk metallic glasses (BMGs). In combination with this mechanism, we generalize ductile-to-brittle criterion in a universal hyperbolic form by integrating the classical Pettifor's Cauchy pressure with Pugh's modulus ratio for a wide variety of materials with cubic lattices. This study provides compelling evidence to correlate Pugh's modulus ratio with hardness of materials and may have implication for understanding the intrinsic brittleness of quasicrystals and BMGs. PMID:23056910

  12. Caged clusters in Al11Ir4: Structural transition and insulating phase

    NASA Astrophysics Data System (ADS)

    Mihalkovič, Marek; Henley, C. L.

    2013-08-01

    Using pair potentials fitted to an ab initio database, combined with replica-exchange simulated annealing, we show that the complex, quasicrystal-related Al11Ir4 compound contains a nonstandard version of the “pseudo-Mackay” icosahedral cluster, with nonicosahedral inner Al10Ir and/or Al9Ir clusters that exist in various orientations and account for partial occupancies in the reported structure. We found two different compositions with different orientationally ordered grounds, each doubling the (cubic) unit cell and each reached by a first-order thermal transition. One of these is metallic and the other is insulating.

  13. Dynamical implications of Viral Tiling Theory.

    PubMed

    ElSawy, K M; Taormina, A; Twarock, R; Vaughan, L

    2008-05-21

    The Caspar-Klug classification of viruses whose protein shell, called viral capsid, exhibits icosahedral symmetry, has recently been extended to incorporate viruses whose capsid proteins are exclusively organised in pentamers. The approach, named 'Viral Tiling Theory', is inspired by the theory of quasicrystals, where aperiodic Penrose tilings enjoy 5-fold and 10-fold local symmetries. This paper analyses the extent to which this classification approach informs dynamical properties of the viral capsids, in particular the pattern of Raman active modes of vibrations, which can be observed experimentally. PMID:18353372

  14. Embedding quasicrystals in a periodic cell: dynamics in quasiperiodic structures.

    PubMed

    Kraemer, Atahualpa S; Sanders, David P

    2013-09-20

    We introduce a construction to "periodize" a quasiperiodic lattice of obstacles, i.e., embed it into a unit cell in a higher-dimensional space, reversing the projection method used to form quasilattices. This gives an algorithm for simulating dynamics, as well as a natural notion of uniform distribution, in quasiperiodic structures. It also shows the generic existence of channels, where particles travel without colliding, up to a critical obstacle radius, which we calculate for a Penrose tiling. As an application, we find superdiffusion in the presence of channels, and a subdiffusive regime when obstacles overlap.

  15. Method of making quasicrystal alloy powder, protective coatings and articles

    DOEpatents

    Shield, Jeffrey E.; Goldman, Alan I.; Anderson, Iver E.; Ellis, Timothy W.; McCallum, R. William; Sordelet, Daniel J.

    1995-07-18

    A method of making quasicrystalline alloy particulates wherein an alloy is superheated and the melt is atomized to form generally spherical alloy particulates free of mechanical fracture and exhibiting a predominantly quasicrystalline in the atomized condition structure. The particulates can be plasma sprayed to form a coating or consolidated to form an article of manufacture.

  16. Method of making quasicrystal alloy powder, protective coatings and articles

    DOEpatents

    Shield, J.E.; Goldman, A.I.; Anderson, I.E.; Ellis, T.W.; McCallum, R.W.; Sordelet, D.J.

    1995-07-18

    A method of making quasicrystalline alloy particulates is disclosed wherein an alloy is superheated and the melt is atomized to form generally spherical alloy particulates free of mechanical fracture and exhibiting a predominantly quasicrystalline in the atomized condition structure. The particulates can be plasma sprayed to form a coating or consolidated to form an article of manufacture. 3 figs.

  17. Bandgap isotropy in photonic quasicrystals with low-index contrast

    NASA Astrophysics Data System (ADS)

    Andreone, Antonello; Abbate, Giancarlo; Di Gennaro, Emiliano; Rose Thankamani, Priya

    2012-05-01

    Formation and development of the photonic band gap in two-dimensional 8-, 10-, and 12-fold symmetry quasicrystalline lattices of low-index contrast are reported. Finite-size structures made of dielectric cylindrical rods are studied and measured in the microwave region, and their properties are compared with a conventional hexagonal crystal. Band-gap characteristics are investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence are used to investigate the isotropic nature of the band gap.

  18. No inherent glassiness in a Penrose tiling quasicrystal

    SciTech Connect

    Strandburg, K.J.; Dressel, P.R.

    1988-11-01

    Consideration of the structure of the Penrose pattern has led to speculation that a system with a Penrose tiling ground state might be subject to inherent glassy behavior. Monte Carol simulations show, using a simple model of the energetics, that there is no inherent glassiness in the Penrose tiling. Thermodynamic quantities measured are completely reversible, displaying no observable hysterisis, and the system may be easily cooled from a highly disordered configuration into its lowest energy state. 11 refs., 7 figs.

  19. The Mpemba Effect, Shechtman's Quasicrystals and Student Exploration Activities

    ERIC Educational Resources Information Center

    Balazovic, Marek; Tomasik, Boris

    2012-01-01

    In the 1960s, Tanzanian student Erasto Mpemba and his teacher published a paper with the title "Cool?" in this journal (Mpemba and Osborne 1969 "Phys. Educ." 4 172-5). They claimed that hot water freezes more quickly than cold water. The paper not only led to a wave of discussion, and more publications about this topic, but also to a whole series…

  20. Novel Kac-Moody-type affine extensions of non-crystallographic Coxeter groups

    NASA Astrophysics Data System (ADS)

    Dechant, Pierre-Philippe; Bœhm, Céline; Twarock, Reidun

    2012-07-01

    Motivated by recent results in mathematical virology, we present novel asymmetric {Z}[\\tau ]-integer-valued affine extensions of the non-crystallographic Coxeter groups H2, H3 and H4 derived in a Kac-Moody-type formalism. In particular, we show that the affine reflection planes which extend the Coxeter group H3 generate (twist) translations along two-, three- and five-fold axes of icosahedral symmetry, and we classify these translations in terms of the Fibonacci recursion relation applied to different start values. We thus provide an explanation of previous results concerning affine extensions of icosahedral symmetry in a Coxeter group context, and extend this analysis to the case of the non-crystallographic Coxeter groups H2 and H4. These results will enable new applications of group theory in physics (quasicrystals), biology (viruses) and chemistry (fullerenes).

  1. Neutron diffraction determination of hydrogen atom locations in the α(TiCrSiO) 1/1 crystal approximant

    NASA Astrophysics Data System (ADS)

    Kim, J. Y.; Kim, W. J.; Gibbons, P. C.; Kelton, K. F.; Yelon, W. B.

    1999-08-01

    Titanium/zirconium-based quasicrystals and their related crystal approximants have been identified as potential new materials for hydrogen storage applications. To better understand the local chemistry and atomic ordering in these phases, preferential interstitial sites for hydrogen/deuterium were determined for α(TiCrSiO). This is a bcc 1/1 crystal approximant to the icosahedral quasicrystal phase that contains a two-shell, Mackay-icosahedral cluster of atoms at each bcc site. It absorbs hydrogen or deuterium, without formation of other hydride phases, to a maximum hydrogen to metal atom ratio (H/M) of 0.26. For fully deuterated samples, both tetrahedral and octahedral interstitial sites are occupied with fractions of 0.14 and 0.12, respectively. Here, the hydrogen/deuterium sites are determined from a Rietveld analysis of x-ray and neutron powder diffraction data taken from samples of α(TiCrSiO) loaded with deuterium. Only the octahedral sites are occupied in the partially deuterated samples (D/M=0.11). A decrease in the oxygen concentration below the stoichiometric value for α(TiCrSiO) leads to an increase in the total amount of hydrogen that can be absorbed, suggesting that these interstitial atoms are competing for the same octahedral interstitial sites.

  2. Transient nucleation and local structure in zirconium-based metallic glasses

    NASA Astrophysics Data System (ADS)

    Shen, Youtao

    Over the past decade, there has been increasing attention in metallic glasses due to their scientific and engineering significance. One particular interest in metallic glasses is the frequent nanocrystallization upon devitrification. However, the full understanding of such nanostructure formation during devitrification remains incomplete. In this thesis, nanocrystallization upon annealing is studied in Zr-based metallic glasses. Quantitative transient nucleation rate data during glass crystallization to an icosahedral quasicrystal phase (i-phase) were obtained for the first time by measuring the crystal density following two-step annealing treatments by transmission electron microscopy. The data fit well to the classical theory of nucleation. The extremely small interfacial free energy (sigma = 0.006 J/m2) between the i-phase and the glass obtained from fits to the nucleation data indicates a significant icosahedral order in the glass. Taken together with high energy X-ray diffraction studies of the glass, these data provide the strongest evidence to date of the significant icosahedral order in metallic glasses. The addition of a few atomic percent of elements can change the glass formation and crystallization behavior significantly in these glasses. We report the discovery of Zr65Cu27Ti8 bulk metallic glasses with diameters up to 1 mm produced by suction casting. The effects of structural relaxation on the glass transition and crystallization kinetics, investigated by differential scanning calorimetry, are discussed. The effects of the addition of small amounts of Ti on the local order in Zr-based metallic glasses were investigated by high energy synchrotron X-ray diffraction and fluctuation electron microscopy. An increasing icosahedral order with increasing Ti content explains the bulk metallic glass formation in the Zr-Cu-Ti alloys. However, this is not true in a related, but more complex, Zr-Ti-Cu-Ni-Al alloy.

  3. Science Using an Electrostatic Levitation Furnace in the MUCAT Sector at the APS

    NASA Technical Reports Server (NTRS)

    Goldman, A.; Kelton, K. F.; Rogers, J. R.

    2004-01-01

    The original motivation for the construction of the BESL prototype was to obtain the first proof of a 50-year-old hypothesis regarding the solidification of liquid metals. Since the 1950s it has been known that under proper conditions liquid metals can be cooled below their melting temperature (undercooled) without crystallizing to the stable solid phase. In 1952 Frank proposed that this was because the atoms in the metallic liquid were arranged with the symmetry of an icosahedron, a Platonic solid consisting of 20 tetrahedra (4-sided pyramid-shaped polyhedra) arranged around a common center. Since this local atomic order is incompatible with the long-range translational periodicity of crystal phases, a barrier is formed to the formation of small regions of the crystal phase, the nucleation barrier. A proof of Frank's hypothesis required a direct correlation between measured icosahedral order in the undercooled liquid and the nucleation barrier. The tendency of sample containers to catalyze nucleation obscured this relation, requiring containerless techniques. Combining containerless processing techniques for electrostatically levitated droplets (ESL) with x-ray synchrotron methods, a team from Washington University, St. Louis, MO, NASA Marshall Space Flight Center, and MUCAT at the APS demonstrated an increasing icosahedral order in TiZrNi liquids with decreasing temperature below the melting temperature. The increased icosahedral order caused the transformation of the liquid to a metastable icosahedral quasicrystal phase, instead of the stable tetrahedrally-coordinated crystal intermetallic, giving the first clear demonstration of the connection between the nucleation barrier and the local structure of the liquid, verifying Frank's hypothesis for this alloy.

  4. Chalcogen and pnicogen bonds in complexes of neutral icosahedral and bicapped square-antiprismatic heteroboranes.

    PubMed

    Pecina, Adam; Lepšík, Martin; Hnyk, Drahomír; Hobza, Pavel; Fanfrlík, Jindřich

    2015-02-26

    A systematic quantum mechanical study of σ-hole (chalcogen, pnicogen, and halogen) bonding in neutral experimentally known closo-heteroboranes is performed. Chalcogens and pnicogens are incorporated in the borane cage, whereas halogens are considered as exo-substituents of dicarbaboranes. The chalcogen and pnicogen atoms in the heteroborane cages have partial positive charge and thus more positive σ-holes. Consequently, these heteroboranes form very strong chalcogen and pnicogen bonds. Halogen atoms in dicarbaboranes also have a highly positive σ-hole, but only in the case of C-bonded halogen atoms. In such cases, the halogen bond of heteroboranes is also strong and comparable to halogen bonds in organic compounds with several electron-withdrawing groups being close to the halogen atom involved in the halogen bond.

  5. Protruding knob-like proteins violate local symmetries in an icosahedral marine virus

    PubMed Central

    Gipson, Preeti; Baker, Matthew L.; Raytcheva, Desislava; Haase-Pettingell, Cameron; Piret, Jacqueline; King, Jonathan A.; Chiu, Wah

    2014-01-01

    Marine viruses play crucial roles in shaping the dynamics of oceanic microbial communities and in the carbon cycle on Earth. Here we report a 4.7-Å structure of a cyanobacterial virus, Syn5, by electron cryo-microscopy and modelling. A Cα backbone trace of the major capsid protein (gp39) reveals a classic phage protein fold. In addition, two knob-like proteins protruding from the capsid surface are also observed. Using bioinformatics and structure analysis tools, these proteins are identified to correspond to gp55 and gp58 (each with two copies per asymmetric unit). The non 1:1 stoichiometric distribution of gp55/58 to gp39 breaks all expected local symmetries and leads to non-quasi-equivalence of the capsid subunits, suggesting a role in capsid stabilization. Such a structural arrangement has not yet been observed in any known virus structures. PMID:24985522

  6. Heat capacity and thermal expansion of icosahedral lutetium boride LuB66

    SciTech Connect

    Novikov, V V; Avdashchenko, D V; Matovnikov, A V; Mitroshenkov, N V; Bud’ko, S L

    2014-01-07

    The experimental values of heat capacity and thermal expansion for lutetium boride LuB66 in the temperature range of 2-300 K were analysed in the Debye-Einstein approximation. It was found that the vibration of the boron sub-lattice can be considered within the Debye model with high characteristic temperatures; low-frequency vibration of weakly connected metal atoms is described by the Einstein model.

  7. THOR-ISO: a Global Circulation Model for Exoplanets on an Icosahedral Grid

    NASA Astrophysics Data System (ADS)

    Mendonca, J.; Grimm, S.; Heng, K.

    2015-10-01

    In this presentation I will describe the details and first results of our new dynamical code for exoplanet atmospheres. This model is part of the Exoclimes Simulation Platform (ESP), and is a project of the Exoplanet and Exoclimes Group (see www.exoclime.org). The model I will present solves the complex physical and dynamical equations that include fundamental principles of atmospheric fluid dynamics and various idealisations of radiative transfer and dry convection, among others. I will also show the results of the first successful benchmark tests for this model, where we explore the results of the model for Earth-like and Hot-Jupiter like conditions. The analysis of the results from this complex and detailed model, will help us to have a better understanding of the diversity of climates and atmospheric circulations that we expect to find in the multitude of exoplanets already discovered.

  8. The effects of stoichiometry on the mechanical properties of icosahedral boron carbide under loading.

    PubMed

    Taylor, DeCarlos E; McCauley, James W; Wright, T W

    2012-12-19

    The effects of stoichiometry on the atomic structure and the related mechanical properties of boron carbide (B(4)C) have been studied using density functional theory and quantum molecular dynamics simulations. Computational cells of boron carbide containing up to 960 atoms and spanning compositions ranging from 6.7% to 26.7% carbon were used to determine the effects of stoichiometry on the atomic structure, elastic properties, and stress-strain response as a function of hydrostatic, uniaxial, and shear loading paths. It was found that different stoichiometries, as well as variable atomic arrangements within a fixed stoichiometry, can have a significant impact on the yield stress of boron carbide when compressed uniaxially (by as much as 70% in some cases); the significantly reduced strength of boron carbide under shear loading is also demonstrated.

  9. Epitaxial Growth of Icosahedral Boride Semiconductors for Novel Energy Conversion Devices

    SciTech Connect

    Edgar, J.H.

    2006-01-03

    The chemical vapor deposition and properties of the boron-rich semiconductors B12As2 and B12P2 on 6H-SiC(0001) and silicon substrates were investigated. Crystalline, stoichiometric films were deposited between 1200 C and 1500 C using two types of reactants, hydrides (B2H6 and AsH3) for B12As2 and halides (BBr3 and PBr3) for B12P2. 6H-SiC proved to be the better substrate for B12As2 heteroepitaxy, in terms of the residual impurity concentrations. Films on Si substrates suffered from high concentrations of Si (up to 4at.%); in contrast, the Si and C concentrations in the B12As2 films deposited on 6H-SiC at 1300 C were at or below the detection limits of secondary ion mass spectrometry (SIMS). The deposition temperature was significant as films deposited at 1450 C contained high residual C and Si concentrations (>1020 cm-3), probably due to the decomposition of the substrate. The hydrogen concentration in all B12As2 films was relatively high, with a minimum concentration of 3x1019 cm-3 in undoped B12As2. SIMS measurements showed that the hydrogen concentration was directly proportional to and tracked the Si concentration, reaching values as high as 3 x 1020 cm-3. The structural properties of the B12As2 films were characterized by x-ray diffraction and transmission electron microscopy. The FWHM of typical high resolution x-ray rocking curves for the (333) peaks of the B12As2 films were 800 arcsec. The films are under tensile strain due the higher coefficient of thermal expansion for B12As2 than SiC. Rotational twins were present in B12As2 films deposited on (0001) oriented 6H-SiC substrates, as revealed by cross-sectional TEM and x-ray diffraction pole figures. While the c-plane 6H-SiC has six-fold rotational symmetry, rhombohedral B12As2 has only 3-fold symmetry (along its (111) axis), thus it randomly nucleates with two different in-plane orientations. The electrical properties of undoped and silicon-doped B12As2 deposited on semi-insulating 6H-SiC substrates were characterized by Hall effect measurements. The resistivity of p-type B12As2 films on semi-insulating 6H-SiC(0001) substrates was controllably varied over nearly four orders of magnitude by changing the concentrations of silicon into the films, incorporated by adding silane during deposition. The electrical properties of the B12As2 suffered from low hole mobilities, typically less than 3 cm2/V's. This was possibly a consequence of structural defects in the films. The resistivity of as-deposited undoped and silicon-doped B12As2 films decreased by two or more orders of magnitude after annealing at temperatures above 600 C in argon. This unexpected but reproducible effect of annealing on the resistivity of the semiconductor warrants further investigation. The properties of palladium, platinum, and chromium/platinum electrical contacts to B12As2 were tested at Pennsylvania State University. The Pd and Pt contacts exhibited nonlinear I-V characteristics and severe agglomeration upon annealing, but the Cr/Pt contacts were ohmic and remained smooth even after they were annealed at 750 C. The specific contact resistance of the Cr/Pt contacts dropped four orders of magnitude after samples were annealed in Ar for 30 s at 750 C. This reduction in specific contact resistance was linked to a simultaneous drop in the resistivity of B12As2 upon annealing. In subsequent experiments, a low specific contact resistance was also achieved when Cr/Pt was deposited on B12As2 films that were annealed prior to metallization instead of afterwards.

  10. Na9K16TI~25: A New Phase Containing Naked Icosahedral Cluster Fragments Ti99-

    SciTech Connect

    Li, Bin; Corbett, John D.

    2007-12-05

    The phase Na{sub 9}K{sub 16}Tl{sub 25.25(2)} was synthesized by fusion of the elements in sealed Ta containers followed by quenching and annealing at 250 C. The structure established by single crystal X-ray diffraction means (P6{sub 3}/m, Z = 2, a = 19.376(3) {angstrom}, c = 11.480(2) {angstrom}) features Tl{sub 9}{sup 9-} clusters. These are well separated by cations that bridge between, faces, edges, and vertices of the clusters; sodium appears to be essential in this role. This is the third compound known to contain Tl{sub 9} clusters, but here two of nine sites are partially occupied, which can be interpreted as a 70:30 mixture of Tl{sub 9} and Tl{sub 7} units in the same cavity. This Tl{sub 9} example also displays lower symmetry (C{sub s}) but requires the same 2n skeletal electrons. EHTB electronic structure calculations indicate that the Fermi level intersects a finite densities-of-states (DOS), and only some bonds are optimized at E{sub F}, giving some insight regarding the site of Tl deficiency. Direct geometric relationships are found among Tl{sub 13}, Tl{sub 9}, Tl{sub 7} and Tl{sub 5} clusters through systematic removal of vertices.

  11. Synonymous Mutations Reduce Genome Compactness in Icosahedral ssRNA Viruses

    PubMed Central

    Tubiana, Luca; Božič, Anže Lošdorfer; Micheletti, Cristian; Podgornik, Rudolf

    2015-01-01

    Recent studies have shown that single-stranded (ss) viral RNAs fold into more compact structures than random RNA sequences with similar chemical composition and identical length. Based on this comparison, it has been suggested that wild-type viral RNA may have evolved to be atypically compact so as to aid its encapsidation and assist the viral assembly process. To further explore the compactness selection hypothesis, we systematically compare the predicted sizes of >100 wild-type viral sequences with those of their mutants, which are evolved in silico and subject to a number of known evolutionary constraints. In particular, we enforce mutation synonynimity, preserve the codon-bias, and leave untranslated regions intact. It is found that progressive accumulation of these restricted mutations still suffices to completely erase the characteristic compactness imprint of the viral RNA genomes, making them in this respect physically indistinguishable from randomly shuffled RNAs. This shows that maintaining the physical compactness of the genome is indeed a primary factor among ssRNA viruses’ evolutionary constraints, contributing also to the evidence that synonymous mutations in viral ssRNA genomes are not strictly neutral. PMID:25564866

  12. Extremely small thermal conductivity of the Al-based Mackay-type 1/1 -cubic approximants

    NASA Astrophysics Data System (ADS)

    Takeuchi, Tsunehiro; Nagasako, Naoyuki; Asahi, Ryoji; Mizutani, Uichiro

    2006-08-01

    Thermal conductivity (κ) of the Al-based Mackay-type 1/1 -cubic approximants ( α -phase) was investigated over a wide temperature range from 2Kto300K . Behaviors of κ(T) observed for these 1/1 -cubic approximants were essentially the same with those reported for the corresponding icosahedral quasicrystals; very small magnitude lower than 4.5W/mK , small contribution of electrons, and possession of a local maximum and a local minimum around 30-50K and 100-200K , respectively. By analyzing measured lattice thermal conductivity κlat(T) in terms both of local atomic arrangements and phonon dispersions, we revealed that κlat(T) is greatly reduced by combination of the small group velocity of phonons and the enhanced umklapp process of phonon scattering. Those characteristics are brought about by the large lattice constant and vacancies in the structure.

  13. Diffraction studies of the structure of glasses and liquids: Technical progress report

    SciTech Connect

    Moss, S.C.

    1989-01-01

    The Houston program on glasses and liquids has continued over the year with an expanded activity into vitreous TiO/sub 2/ and amorphous metals/quasicrystals. The modeling study of vitreous SiO/sub 2/ has been published and the study of amorphous melanin is well underway in-house. We have also begun some promising modeling work on the icosahedral glass model (IGM) for quasicrystals and have completed a preliminary study of epitaxial diamond crystal growth on the (111) silicon crystal surface (initially undertaken to study the expected ''amorphous'' diamond-like phase). The work on GLAD at the Argonne IPNS continues on schedule under the direction of Dr. David L. Price. The status of the Phase I instrument has been published and the Phase II development is underway with an evacuated flight path, additional detectors and a final data acquisition system in progress. It is our expectation that the final instrument will be the most advanced of its kind in the world for the study of a wide variety of problems in glasses, liquids and amorphous materials.

  14. Ion beam-irradiation induced structure transformation in α-AlMnSi

    NASA Astrophysics Data System (ADS)

    Guo, Y. X.; Wang, L. M.; Chen, L. F.; Ewing, R. C.

    1997-05-01

    Structure changes of an α-AlMnSi phase, irradiated with 1.5 MeV Xe + ions at room temperature, have been studied by transmission electron microscopy (TEM). At an irradiation dose of 3.4 × 10 13 ions/cm 2, the primitive cubic α-AlMnSi phase transformed to a bcc phase. But the unit cell parameter ( a = 1.268 nm) remained the same. With an increase of irradiation dose, the bcc phase became amorphous at 3.4 × 10 14 ions/cm 2. The bcc phase structure consists of two MacKay icosahedral atomic clusters in each unit cell. A pseudo ten-fold rotational axis has also been obtained via electron diffraction in the specimens irradiated to 5.1 × 10 13 ions/cm 2. This quasicrystal-like structure was found for the first time during the radiation-induced crystalline-to-amorphous phase transformation. Annealing of the fully amorphized specimens was performed with in situ TEM. The α-AlMnSi phase started to form at 350°C and was fully crystallized at 500°C. The bcc phase and quasicrystal-like structures were not observed during the crystallization processes.

  15. Self-assembly of hydrogen-bonded two-dimensional quasicrystals

    NASA Astrophysics Data System (ADS)

    Wasio, Natalie A.; Quardokus, Rebecca C.; Forrest, Ryan P.; Lent, Craig S.; Corcelli, Steven A.; Christie, John A.; Henderson, Kenneth W.; Kandel, S. Alex

    2014-03-01

    The process of molecular self-assembly on solid surfaces is essentially one of crystallization in two dimensions, and the structures that result depend on the interplay between intermolecular forces and the interaction between adsorbates and the underlying substrate. Because a single hydrogen bond typically has an energy between 15 and 35 kilojoules per mole, hydrogen bonding can be a strong driver of molecular assembly; this is apparent from the dominant role of hydrogen bonding in nucleic-acid base pairing, as well as in the secondary structure of proteins. Carboxylic acid functional groups, which provide two hydrogen bonds, are particularly promising and reliable in creating and maintaining surface order, and self-assembled monolayers of benzoic acids produce structure that depends on the number and relative placement of carboxylic acid groups. Here we use scanning tunnelling microscopy to study self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH), and find that, rather than producing dimeric or linear structures typical of carboxylic acids, FcCOOH forms highly unusual cyclic hydrogen-bonded pentamers, which combine with simultaneously formed FcCOOH dimers to form two-dimensional quasicrystallites that exhibit local five-fold symmetry and maintain translational and rotational order (without periodicity) for distances of more than 400 ångströms.

  16. Electronic structure in the Al-Mn alloy crystalline analog of quasicrystals

    NASA Astrophysics Data System (ADS)

    Fujiwara, Takeo

    1989-07-01

    Electronic structure in crystalline α-(Al114Mn24) is calculated by the linear muffin-tin orbital-atomic-sphere approximation method with the local-density-functional theory. The density of states consists of a set of spiky peaks. The electronic structure is discussed for quasicrystalline Al-Mn alloy from the viewpoint of the stability and the role of the vacant center of the Mackay icosahedron. The stability is actually owing to the pseudogap of the Mn 3d band and the deep s,p-bonding bands of the Al glue atoms.

  17. Evidence of local effects in anomalous refraction and focusing properties of dodecagonal photonic quasicrystals

    NASA Astrophysics Data System (ADS)

    di Gennaro, Emiliano; Miletto, Carlo; Savo, Salvatore; Andreone, Antonello; Morello, Davide; Galdi, Vincenzo; Castaldi, Giuseppe; Pierro, Vincenzo

    2008-05-01

    We present the key results from a comprehensive study of the refraction and focusing properties of a two-dimensional dodecagonal photonic “quasicrystal” (PQC), which was carried out via both full-wave numerical simulations and microwave measurements on a slab made of alumina rods inserted in a parallel-plate waveguide. We observe an anomalous refraction and focusing in several frequency regions, which confirm some recently published results. However, our interpretation, which is based on numerical and experimental evidence, substantially differs from the one in terms of “effective negative refractive index” that was originally proposed. Instead, our study highlights the critical role played by short-range interactions associated with local order and symmetry.

  18. Mode confinement in photonic quasicrystal point-defect cavities for particle accelerators

    NASA Astrophysics Data System (ADS)

    Di Gennaro, E.; Savo, S.; Andreone, A.; Galdi, V.; Castaldi, G.; Pierro, V.; Masullo, M. Rosaria

    2008-10-01

    In this letter, we present a study of the confinement properties of point-defect resonators in finite-size photonic-bandgap structures composed of aperiodic arrangements of dielectric rods, with special emphasis on their use for the design of cavities for particle accelerators. Specifically, for representative geometries, we study the properties of the fundamental mode (as a function of the filling fraction, structure size, and losses) via two-dimensional and three-dimensional full-wave numerical simulations, as well as microwave measurements at room temperature. Results indicate that for reduced-size structures, aperiodic geometries exhibit superior confinement properties by comparison with periodic ones.

  19. Isotropic properties of the photonic band gap in quasicrystals with low-index contrast

    NASA Astrophysics Data System (ADS)

    Priya Rose, T.; di Gennaro, E.; Abbate, G.; Andreone, A.

    2011-09-01

    We report on the formation and development of the photonic band gap in two-dimensional 8-, 10-, and 12-fold symmetry quasicrystalline lattices of low-index contrast. Finite-size structures made of dielectric cylindrical rods were studied and measured in the microwave region, and their properties were compared with a conventional hexagonal crystal. Band-gap characteristics were investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0∘ to 30∘ were used to investigate the isotropic nature of the band gap. The arbitrarily high rotational symmetry of aperiodically ordered structures could be practically exploited to manufacture isotropic band-gap materials, which are perfectly suitable for hosting waveguides or cavities.

  20. Ionic Strength-Induced Formation of Smectite Quasicrystals Enhances Nitroaromatic Compound Sorption

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The influence of ionic strength on nitroaromatic compound sorption from water by K+- and Ca2+-saturated smectite (SWy-2) was examined. The results indicated that sorption of 1,3-dinitrobenzene by K-SWy-2 increased up to 2.2 times as KCl ionic strength increased from 0.01 to 0.30 M. In contrast, sorp...

  1. A Sodium-Containing Quasicrystal: Using Gold To Enhance Sodium's Covalency in Intermetallic Compounds

    SciTech Connect

    Smetana, Volodymyr; Lin, Qisheng; Pratt, Daniel K.; Kreyssig, Andreas; Ramazanoglu, Mehmet; Corbett, John D.; Goldman, Alan I.; Miller, Gordon J.

    2013-09-26

    Gold macht stabil: Na13Au12Ga15, ein natriumhaltiges thermodynamisch stabiles quasikristallines Material, wurde bei einer systematischen Studie des polaren Na-Au-Ga-Intermetallsystems entdeckt. Sein Elektron/Atom-Verhältnis von 1.75 ist für Bergman-Ikosaederphasen extrem klein, doch der substanzielle Au-Anteil sorgt für eine Hume-Rothery-Stabilisierung und neuartige polar-kovalente Na-Au-Wechselwirkungen.

  2. Anisotropy of the electric transport properties of decagonal Al-Cu-Co(Fe) quasicrystals

    NASA Astrophysics Data System (ADS)

    Shulyatev, D. A.; Klyueva, M. V.; Devaradjan, U.

    2016-09-01

    The method of growth from a melt solution was used to obtain iron-alloyed (0.08 at %) Al-Cu-Co single crystals with a decagonal symmetry. The temperature dependences of the electrical resistivity in magnetic fields of 0-18 T were measured using samples oriented in the periodic direction (ρ p ( T)) and in the quasi-periodic plane (ρ q ( T)). A strong anisotropy of the resistivity was observed; the ρ p ( T) curve is linear, whereas the ρ q ( T) curve is approximated well by a second-order polynomial. A strong anisotropy of the magnetoresistance was also observed; a positive magnetoresistance Δρ/ρ ~ 10-3 for the current flowing in the quasiperiodic plane; and a weak (close to zero) negative magnetoresistance for the current flowing along the periodic direction.

  3. Quasicrystals and the Penrose Patterns: A Geometric Activity with a Scientific Application.

    ERIC Educational Resources Information Center

    Clason, Robert; And Others

    1993-01-01

    Penrose tile patterns are created using regular pentagon-based rhombi. Provides instructions for assembling Penrose patterns, plus activities for secondary school students and preservice elementary teachers. Compares the two-dimensional process of placing pattern blocks to form Penrose patterns to the symmetries of crystals formed in nature.…

  4. Surfaces of complex intermetallic compounds: insights from density functional calculations.

    PubMed

    Hafner, Jürgen; Krajčí, Marian

    2014-11-18

    . Detailed results are presented for two intermetallic compounds that have recently attracted much attention as active and highly selective catalysts for the semihydrogenation of alkynes to alkenes, but the identification of the catalytically active surfaces was found to be very difficult. The crystal structure of B20-type GaPd can be interpreted as the lowest order approximant of icosahedral Al-Pd-Mn quasicrystals. Among the low-index surfaces, the {100} surface shows 2-fold symmetry and the {210} surface pseudo-5-fold symmetry; for both the surface stoichiometry is identical to that of the bulk. Because the structure lacks inversion symmetry, the {111} surfaces have polar character and permit terminations of widely different chemical composition. Results for all three surfaces are presented and compared with the available experiments. The crystal structure of orthorhombic Al13Co4 is built by pentagonal clusters similar to those found in decagonal Al-Co and Al-Ni-Co quasicrystals. A simulated cleavage experiment shows that the constituent clusters remain intact upon cleavage, resulting in the formation of a highly corrugated (100) surface. The calculated STM images are found to be in very good agreement with experiment and permit in addition identification of possible surface modifications by the desorption of individual atoms. Pentagonal motifs on the {210} surface of GaPd and on the (100) surface of Al13Co4 consisting of simple- and transition-metal atoms have been identified as the catalytically active centers for the semihydrogenation of acetylene to ethylene. PMID:24741993

  5. Structural study of supercooled liquids and metallic glasses by high-energy x-ray diffraction and reverse Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Kim, Tae Ho

    2007-12-01

    By employing the technique of electrostatic levitation, coupled with high-energy x-ray diffraction and rapid data acquisition, this study obtained high quality structural data in the supercooled regime of liquids. The experimental x-ray diffraction data for supercooled liquids such as Si, Ti, Ni and Zr were analyzed using the Reverse Monte Carlo method to determine realistic atomic structures. No change in the coordination number of supercooled liquid Si was observed over the measured temperature range of supercooling. This result calls into question previous experimental claims of structural evidence for the existence of a liquid-liquid phase transition. Instead, based on the Honeycutt Andersen index and bond orientational order parameter analyses of the RMC structure, the fraction of regions with white-tin (A5) and diamond cubic (A4) order remain nearly constant with supercooling; however, the coherence length of the A5 order increases. This study proposes local structural models for supercooled liquid transition metals (Ti, Ni and Zr). All analyses suggest that an icosahedral short-range order is present in these supercooled liquids, but this short-range order is distorted in liquid Ti. These results support the observed evolution of the high-q shoulder on the second peak in the structure factor, S(q). The structures of metallic glasses (such as the Zr-based glasses) were investigated by the same techniques to provide further insight into the atomic structure of liquids. The relation between glass forming ability and the local structure of these metallic glasses was explored. Interestingly, Zr-based metallic glasses with different glass forming abilities showed similarly strong icosahedral order in liquid and glassy states. An investigation of the structural behavior near the glass transition temperature (Tg) in these glasses demonstrated an evolution of icosahedral order with supercooling. The evolution was arrested on approaching the Tg and thereafter became

  6. Liquid-solid transitions with applications to self-assembly

    NASA Astrophysics Data System (ADS)

    Keys, Aaron S.

    We study the thermodynamic and kinetic pathways by which liquids transform into solids, and their relation to the metastable states that commonly arise in self-assembly applications. As a case study in the formation of ordered metastable solids, we investigate the atomistic mechanism by which quasicrystals form. We show that the aperiodic growth of quasicrystals is controlled by the ability of the growing quasicrystal "nucleus" to incorporate kinetically trapped atoms into the solid phase with minimal rearrangement. In a related study, we propose a two-part mechanism for forming 3d dodecagonal quasicrystals by self-assembly. Our mechanism involves (1) attaching small mobile particles to the surface of spherical particles to encourage icosahedral packing and (2) allowing a subset of particles to deviate from the ideal spherical shape, to discourage close-packing In addition to studying metastable ordered solids, we investigate the phenomenology and mechanism of the glass transition. We report measurements of spatially heterogeneous dynamics in a system of air-driven granular beads approaching a jamming transition, and show that the dynamics in our granular system are quantitatively indistinguishable from those for a supercooled liquid approaching a glass transition. In a second study of the glass transition, we use transition path sampling to study the structure, statistics and dynamics of localized excitations for several model glass formers. We show that the excitations are sparse and localized, and their size is temperature-independent. We show that their equilibrium concentration is proportional to exp[- Ja (1/T-1/T o)], where Ja is the energy scale for irreversible particle displacements of length a, and T o is an onset temperature. We show that excitation dynamics is facilitated by the presence of other excitations, causing dynamics to slow in a hierarchical way as temperature is lowered. To supplement our studies of liquid-solid transitions, we introduce a

  7. Total-energy calculations for crystalline approximants of quasicrystalline structures: Occupation of the centers of the icosahedral units

    NASA Astrophysics Data System (ADS)

    Sikka, S. K.; Sharma, Surinder M.; Chidambaram, R.

    1993-02-01

    Motivated by recent positron-annihilation experiments on quasicrystalline materials, we have investigated whether the centers of packing units [of Mackay's icosahedron for the Al-Mn system and cuboctahedron for the Mg-Zn (Al) system] are empty or filled. Our pseudopotential-based total-energy calculations suggest that the centers are occupied, in agreement with experimental positron-annihilation results. Possible reasons for discrepancies with the diffraction results are discussed.

  8. Charge Detection Mass Spectrometry Identifies Preferred Non-Icosahedral Polymorphs in the Self-Assembly of Woodchuck Hepatitis Virus Capsids.

    PubMed

    Pierson, Elizabeth E; Keifer, David Z; Kukreja, Alexander A; Wang, Joseph C-Y; Zlotnick, Adam; Jarrold, Martin F

    2016-01-29

    Woodchuck hepatitis virus (WHV) is prone to aberrant assembly in vitro and can form a broad distribution of oversized particles. Characterizing aberrant assembly products is challenging because they are both large and heterogeneous. In this work, charge detection mass spectrometry (CDMS) is used to measure the distribution of WHV assembly products. CDMS is a single-particle technique where the masses of individual ions are determined from simultaneous measurement of each ion's charge and m/z (mass-to-charge) ratio. Under relatively aggressive, assembly promoting conditions, roughly half of the WHV assembly products are T=4 capsids composed of exactly 120 dimers while the other half are a broad distribution of larger species that extends to beyond 210 dimers. There are prominent peaks at around 132 dimers and at 150 dimers. In part, the 150 dimer complex can be attributed to elongating a T=4 capsid along its 5-fold axis by adding a ring of hexamers. However, most of the other features cannot be explained by existing models for hexameric defects. Cryo-electron microscopy provides evidence of elongated capsids. However, image analysis reveals that many of them are not closed but have "spiral-like" morphologies. The CDMS data indicate that oversized capsids have a preference for growth by addition of 3 or 4 dimers, probably by completion of hexameric vertices.

  9. Investigations of the Electronic Properties and Surface Structures of Aluminium-Rich Quasicrystalline Alloys

    SciTech Connect

    Jason A. Barrow

    2003-08-05

    The work presented in this dissertation has investigated three distinct areas of interest in the field of quasicrystals: bulk structure, transport properties, and electronic structure. First, they have described the results of a study which explored the fundamental interactions between the atomic species of the icosahedral Al-Pd-Mn quasicrystal. The goal of this work was to determine whether the pseudo-MacKay or Bergman type clusters have a special stability or are merely a geometric coincidence. This was carried out by using laser vaporization to produce gas-phase metal clusters, which were analyzed using time-of-flight mass spectrometry. Both the kinetic and thermodynamic stabilities of the clusters were probed. The data indicated no special stability for either pseudo-MacKay or Bergman type clusters as isolated units. This, however, is not proof that these clusters are simply a geometric coincidence. It is possible that such clusters only have stability in the framework of the bulk matrix and do not exist as isolated units. Next, they have reported their investigations of the bulk thermal transport properties of a decagonal Al-Ni-Co two dimensional quasicrystal in the temperature range 373K-873K. The properties of a sample oriented along the periodic axis and another oriented along the aperiodic axis were measured. A high degree of anisotropy was observed between the aperiodic and periodic directions. Additionally, the properties were measured for a sample miscut to an orientation 45{sup o} off-axis. The properties of the miscut sample were shown to have good agreement with a theoretical model used to describe thermal transport in metallic single crystals. This model only considers thermal transport by a free-electron gas; therefore, agreement with experimental data suggests the validity of the Drude free-electron model for the decagonal Al-Ni-Co at these temperatures. Consequently, the observed anisotropy may be adequately described using classical transport

  10. Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} and Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63}: The diversity of pseudo 5-fold symmetries in the Na–Au–Ga system

    SciTech Connect

    Smetana, Volodymyr; Corbett, John D. Miller, Gordon J.

    2013-11-15

    The Na-rich part (∼30% Na) of the Na–Au–Ga system between NaAu{sub 2}, NaGa{sub 4}, and Na{sub 22}Ga{sub 39} has been found to contain the ternary phases Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} (I) and Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63} (II), according to the results of single crystal X-ray diffraction measurements. I is orthorhombic, Cmcm, a=5.3040(1), b=24.519(5), c=14.573(3) Å, and contains a network of clusters with local 5-fold symmetry along the a-axis. Such clusters are frequent building units in decagonal quasicrystals and their approximants. II is rhombohedral, R3{sup ¯}m, a=16.325(2), c=35.242(7) Å, and contains building blocks that are structurally identical to the Bergman-type clusters as well as fused icosahedral units known with active metals, triels and late transition elements. II also contains a polycationic network with elements of the clathrate V type structure. Tight-binding electronic structure calculations using linear muffin–tin-orbital (LMTO) methods on idealized models of I and II indicate that both compounds are metallic with evident pseudogaps at the corresponding Fermi levels. The overall Hamilton bond populations are generally dominated by Au–Ga and Au–Au bonds in I and by Ga–Ga bonds in II; moreover, the Na–Au and Na–Ga contributions in I are unexpectedly large, ∼20% of the total. A similar involvement of sodium in covalent bonding has also been found in the electron-richer i-Na{sub 13}Au{sub 12}Ga{sub 15} quasicrystal approximant. - Graphical abstract: Multiply-endohedral Bergman-related clusters in the structure of Na{sub 17}Au{sub 5.9(1)}Ga{sub 46.6.} Display Omitted - Highlights: • Two new compounds with the local 5-fold symmetry have been investigated. • Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} is an orthorhombic approximant of the Na{sub 13}Au{sub 12}Ga{sub 15} quasicrystal. • Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63} represents a rhombohedral distortion of the Bergman-type phases.

  11. Huygens and Barrow, Newton and Hooke. Pioneers in mathematical analysis and catastrophe theory from evolvents to quasicrystals.

    NASA Astrophysics Data System (ADS)

    Arnol'D, V. I.

    This book is an English translation of the Russian original of 1989. It is based on a college lecture commemorating the tercentenary of Newton's book Philosophiae Naturalis Principia Mathematica. The author retraces the beginnings of mathematical analysis and theoretical physics in the works of the great scientists of the 17th century, and recounts the history of the discovery of the law of gravitation, discussions Newton had with Hooke and Leibniz, and much more. Some of Huygens' and Newton's ideas, several centuries ahead of their time, were developed only recently. The author follows the link between their inception and the break-throughs in contemporary mathematics and physics. The book provides present-day generalizations of Newton's theorems on the elliptical shape of orbits, attraction of spheres, and on the transcendence of Abelian integrals; it offers a brief review of the theory of regular and chaotic movement in celestial mechanics, including, for example, the problem of ports in the distribution of smaller planets and a discussion of the structure of planetary rings.

  12. Band gaps and transmission spectra in generalized Fibonacci σ(p,q) one-dimensional magnonic quasicrystals.

    PubMed

    Costa, C H O; Vasconcelos, M S

    2013-07-17

    We employ a microscopic theory to investigate spin wave (magnon) propagation through their dispersion and transmission spectra in magnonic crystals arranged to display deterministic disorder. In this work the quasiperiodic arrangement investigated is the well-known generalized Fibonacci sequence, which is characterized by the σ(p,q) parameter, where p and q are non-zero integers. In order to determine the bulk modes and transmission spectra of the spin waves, the calculations are carried out for the exchange dominated regime within the framework of the Heisenberg model and taking into account the random phase approximation. We have considered magnetic materials that have a ferromagnetic order, and the transfer-matrix treatment is applied to simplify the algebra. The results reveal that spin wave spectra display a rich and interesting magnonic pass- and stop-bands structures, including an almost symmetric band gap distribution around of a mid-gap frequency, which depends on the Fibonacci sequence type. PMID:23779133

  13. Power-law scaling and fractal nature of medium-range order in metallic glasses.

    PubMed

    Ma, D; Stoica, A D; Wang, X-L

    2009-01-01

    The atomic structure of metallic glasses has been a long-standing scientific problem. Unlike crystalline metals, where long-range ordering is established by periodic stacking of fundamental building blocks known as unit cells, a metallic glass has no long-range translational or orientational order, although some degrees of short- and medium-range order do exist. Previous studies have identified solute- (minority atom)-centred clusters as the fundamental building blocks or short-range order in metallic glasses. Idealized cluster packing schemes, such as efficient cluster packing on a cubic lattice and icosahedral packing as in a quasicrystal, have been proposed and provided first insights on the medium-range order in metallic glasses. However, these packing schemes break down beyond a length scale of a few clusters. Here, on the basis of neutron and X-ray diffraction experiments, we propose a new packing scheme-self-similar packing of atomic clusters. We show that the medium-range order has the characteristics of a fractal network with a dimension of 2.31, and is described by a power-law correlation function over the medium-range length scale. Our finding provides a new perspective of order in disordered materials and has broad implications for understanding their structure-property relationship, particularly those involving a change in length scales.

  14. First-principles phonon calculation for Al-(Re,Mn)-Si 1/1-1/1-1/1 approximants

    NASA Astrophysics Data System (ADS)

    Nagasako, N.; Asahi, R.; Takeuchi, T.

    2006-03-01

    A very low thermal conductivity (˜1 W/Km) and a relatively large Seebeck coefficient in Al-based Mackay-type icosahedral quasicrystal have attracted much interest aiming for thermoelectric applications. We performed first-principles phonon calculations for the Al-(Re,Mn)-Si 1/1-1/1-1/1 approximants [1] to elucidate mechanism of their low thermal conductivity. The total energy and atomic force were calculated for a modeled Al17(Re,Mn)4Si2 unit cell containing 138 atoms using the projector augmented wave method implemented in VASP code [2], and were then utilized for obtaining a phonon dispersion by the direct method [3]. The calculated lattice specific heat showed very good agreement with experiment, confirming validity of the present calculations. We found localized optical modes with a relatively low frequency (˜2 THz) in the phonon dispersion. We discuss the low thermal conductivity in comparison between the Al-Re-Si and Al-Mn-Si systems via averaged group velocity and umklapp phonon scattering related to these optical modes. [1] Takeuchi et al., Phys. Rev. B70, 144202 (2004). [2] G. Kresse, J. Furthmuller, Phys. Rev. B54, 11169 (1996). [3] MedeA-Phonon, Materials Design, Inc. (2003) based on K. Parlinski, Phonon 3.11 (2002).

  15. Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples

    DOE PAGES

    Canfield, Paul C.; Kong, Tai; Kaluarachchi, Udhara S.; Jo, Na Hyun

    2016-01-05

    Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibres. In this paper, we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the cleanmore » separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this article, we provide examples of the growth of isotopically substituted TbCd6 and icosahedral i-RCd quasicrystals, as well as the separation of (i) the closely related Bi2Rh3S2 and Bi2Rh3.5S2 phases and (ii) and PrZn11 and PrZn17.« less

  16. Digital Alchemy for Materials Design: Colloids and Beyond.

    PubMed

    van Anders, Greg; Klotsa, Daphne; Karas, Andrew S; Dodd, Paul M; Glotzer, Sharon C

    2015-10-27

    Starting with the early alchemists, a holy grail of science has been to make desired materials by modifying the attributes of basic building blocks. Building blocks that show promise for assembling new complex materials can be synthesized at the nanoscale with attributes that would astonish the ancient alchemists in their versatility. However, this versatility means that making a direct connection between building-block attributes and bulk structure is both necessary for rationally engineering materials and difficult because building block attributes can be altered in many ways. Here we show how to exploit the malleability of the valence of colloidal nanoparticle "elements" to directly and quantitatively link building-block attributes to bulk structure through a statistical thermodynamic framework we term "digital alchemy". We use this framework to optimize building blocks for a given target structure and to determine which building-block attributes are most important to control for self-assembly, through a set of novel thermodynamic response functions, moduli, and susceptibilities. We thereby establish direct links between the attributes of colloidal building blocks and the bulk structures they form. Moreover, our results give concrete solutions to the more general conceptual challenge of optimizing emergent behaviors in nature and can be applied to other types of matter. As examples, we apply digital alchemy to systems of truncated tetrahedra, rhombic dodecahedra, and isotropically interacting spheres that self-assemble diamond, fcc, and icosahedral quasicrystal structures, respectively. Although our focus is on colloidal systems, our methods generalize to any building blocks with adjustable interactions. PMID:26401754

  17. Orbits of crystallographic embedding of non-crystallographic groups and applications to virology.

    PubMed

    Twarock, Reidun; Valiunas, Motiejus; Zappa, Emilio

    2015-11-01

    The architecture of infinite structures with non-crystallographic symmetries can be modelled via aperiodic tilings, but a systematic construction method for finite structures with non-crystallographic symmetry at different radial levels is still lacking. This paper presents a group theoretical method for the construction of finite nested point sets with non-crystallographic symmetry. Akin to the construction of quasicrystals, a non-crystallographic group G is embedded into the point group P of a higher-dimensional lattice and the chains of all G-containing subgroups are constructed. The orbits of lattice points under such subgroups are determined, and it is shown that their projection into a lower-dimensional G-invariant subspace consists of nested point sets with G-symmetry at each radial level. The number of different radial levels is bounded by the index of G in the subgroup of P. In the case of icosahedral symmetry, all subgroup chains are determined explicitly and it is illustrated that these point sets in projection provide blueprints that approximate the organization of simple viral capsids, encoding information on the structural organization of capsid proteins and the genomic material collectively, based on two case studies. Contrary to the affine extensions previously introduced, these orbits endow virus architecture with an underlying finite group structure, which lends itself better to the modelling of dynamic properties than its infinite-dimensional counterpart. PMID:26522406

  18. Digital Alchemy for Materials Design: Colloids and Beyond.

    PubMed

    van Anders, Greg; Klotsa, Daphne; Karas, Andrew S; Dodd, Paul M; Glotzer, Sharon C

    2015-10-27

    Starting with the early alchemists, a holy grail of science has been to make desired materials by modifying the attributes of basic building blocks. Building blocks that show promise for assembling new complex materials can be synthesized at the nanoscale with attributes that would astonish the ancient alchemists in their versatility. However, this versatility means that making a direct connection between building-block attributes and bulk structure is both necessary for rationally engineering materials and difficult because building block attributes can be altered in many ways. Here we show how to exploit the malleability of the valence of colloidal nanoparticle "elements" to directly and quantitatively link building-block attributes to bulk structure through a statistical thermodynamic framework we term "digital alchemy". We use this framework to optimize building blocks for a given target structure and to determine which building-block attributes are most important to control for self-assembly, through a set of novel thermodynamic response functions, moduli, and susceptibilities. We thereby establish direct links between the attributes of colloidal building blocks and the bulk structures they form. Moreover, our results give concrete solutions to the more general conceptual challenge of optimizing emergent behaviors in nature and can be applied to other types of matter. As examples, we apply digital alchemy to systems of truncated tetrahedra, rhombic dodecahedra, and isotropically interacting spheres that self-assemble diamond, fcc, and icosahedral quasicrystal structures, respectively. Although our focus is on colloidal systems, our methods generalize to any building blocks with adjustable interactions.

  19. Orbits of crystallographic embedding of non-crystallographic groups and applications to virology.

    PubMed

    Twarock, Reidun; Valiunas, Motiejus; Zappa, Emilio

    2015-11-01

    The architecture of infinite structures with non-crystallographic symmetries can be modelled via aperiodic tilings, but a systematic construction method for finite structures with non-crystallographic symmetry at different radial levels is still lacking. This paper presents a group theoretical method for the construction of finite nested point sets with non-crystallographic symmetry. Akin to the construction of quasicrystals, a non-crystallographic group G is embedded into the point group P of a higher-dimensional lattice and the chains of all G-containing subgroups are constructed. The orbits of lattice points under such subgroups are determined, and it is shown that their projection into a lower-dimensional G-invariant subspace consists of nested point sets with G-symmetry at each radial level. The number of different radial levels is bounded by the index of G in the subgroup of P. In the case of icosahedral symmetry, all subgroup chains are determined explicitly and it is illustrated that these point sets in projection provide blueprints that approximate the organization of simple viral capsids, encoding information on the structural organization of capsid proteins and the genomic material collectively, based on two case studies. Contrary to the affine extensions previously introduced, these orbits endow virus architecture with an underlying finite group structure, which lends itself better to the modelling of dynamic properties than its infinite-dimensional counterpart.

  20. Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED Studies

    SciTech Connect

    Cai, T.; Shi, F.; Shen, Z.; Gierer, M.; Goldman, A.I.; Kramer, M.J.; Jenks, C.J.; Lograsso, T.A.; Delaney, D.W.; Thiel, P.A.; Van, M.A.

    2001-04-15

    We investigate the atomic structure of the fivefold surface of an icosahedral Al-Cu-Fe alloy, using scanning tunneling microscopy (STM) imaging and a special dynamical low energy-electron diffraction (LEED) method. STM indicates that the step heights adopt (primarily) two values in the ratio of tau, but the spatial distribution of these two values does not follow a Fibonacci sequence, thus breaking the ideal bulk-like quasicrystalline layer stacking order perpendicular to the surface. The appearance of screw dislocations in the STM images is another indication of imperfect quasicrystallinity. On the other hand, the LEED analysis, which was successfully applied to Al-Pd-Mn in a previous study, is equally successful for Al-Cu-Fe. Similar structural features are found for both materials, in particular for interlayer relaxations and surface terminations. Although there is no structural periodicity, there are clear atomic planes in the bulk of the quasicrystal, some of which can be grouped in recurring patterns. The surface tends to form between these grouped layers in both alloys. For Al-Cu-Fe, the step heights measured by STM are consistent with the thicknesses of the grouped layers favored in LEED. These results suggest that the fivefold Al-Cu-Fe surface exhibits a quasicrystalline layering structure, but with stacking defects.

  1. Structural organization of icosahedral coordination polyhedra in a molecular dynamics model of the Ni{sub 60}Ag{sub 40} metallic glass

    SciTech Connect

    Pryadilshchikov, A. Yu. Kosilov, A. T.; Evteev, A. V.; Levchenko, E. V.

    2008-09-15

    Features of the formation of a percolation cluster structure composed of interpenetrating and contacting icosahedra during the glass transition in an amorphous Ni{sub 60}Ag{sub 40} alloy have been studied using the molecular-dynamics method and statistical geometric analysis. Data on the morphology of clusters composed entirely of the interpenetrating icosahedra and on the character of their conjugation in the percolation cluster are presented.

  2. Fivefold i-Al-Pd-Mn surface as template for growing monatomic quasiperiodic layers: First-principles simulations for adatoms from groups one to three

    NASA Astrophysics Data System (ADS)

    Krajčí, Marian; Hafner, J.

    2008-04-01

    By using ab initio density-functional calculations, we have explored the conditions for the formation of quasiperiodic overlayers on top of a fivefold surface of an icosahedral Al-Pd-Mn quasicrystal. We calculate binding energies of single adatoms at special sites of the surface, with the aim to construct the potential-energy landscape of the quasiperiodic surface. We show that the energetically favorable adsorption sites are located at the vertices of a DHBS tiling [consisting of decagons (D), hexagons (H), boats (B), and stars (S)] describing the quasiperiodic ordering of the surface. An idealized structural model for the adlayer is constructed by decorating the interior of these tiles such that atoms are placed again in energetically favorable locations and that the local arrangement does not break the fivefold symmetry of the underlying substrate. The stability of this idealized structure is probed for elements from groups one to three of the Periodic Table by performing a conjugate-gradient relaxation under the action of the ab initio calculated forces. We demonstrate that in addition to a strong binding of the adatoms to the substrate, the size of the adatoms and the achievement of a dense surface coverage are the most important factors influencing the stability of quasiperiodic ordering in the adsorbed monolayer. From the analysis of the geometrical distribution of the adsorption sites, we conclude that a dense quasiperiodic overlayer with a density of 0.066atoms/Å2 (corresponding to a coverage Θ≈0.50 monolayers) can be formed by adatoms with an atomic size of 3.7ű0.4Å . Atoms with this size are Na, Ca, Y, and La. We suggest that these elements and presumably also most rare-earth elements are good candidates for the formation of highly regular quasiperiodic adlayers with a structure described by a decagonal DHBS tiling consisting of decagons, hexagons, boats, and pentagonal stars.

  3. A Novel Liquid-Liquid Transition in Undercooled Ti-Zr-Ni Liquids

    NASA Technical Reports Server (NTRS)

    Lee, G. W.; Gangopadhyay, A. K.; Kelton, K. F.; Bradshaw, R. C.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.

    2004-01-01

    If crystallization can be avoided, liquids enter a metastable (undercooled) state below their equilibrium liquidus temperatures, T(sub l), finally 'freezing' into a glass below a characteristic temperature called the glass transition temperature, T(sub g). In rare cases, the undercooled liquid may undergo a liquid-liquid phase transition (liquid polymorphism) before entering the glassy state. This has been suggested from experimental studies of H2O and Si. Such phase transitions have been predicted in some stable liquids, ie. above T(sub l) at atmospheric pressure, for SiO2 and BeF2, but these have not been verified experimentally. They have been observed in liquids of P, Si and C, but only under high pressure. In this letter we present the first experimental evidence for a phase transition in a low viscosity metallic liquid that is driven by an approach to a constant entropy configuration state and correlated with a growing icosahedral order in the liquid. A maximum in the specific heat at constant pressure, similar to what is normally observed near T(sub g), is reported for undercooled liquids of quasicrystal-forming Ti-Zr-Ni alloys. A two-state excitation model that includes cooperativity by incorporating a temperature-dependent excitation energy, fits the specific heat data well, signaling a phase transition. An inflection in the liquid density with decreasing temperature instead of a discontinuity indicates that this is not a typical first order phase transition; it could be a weakly first order or higher order transition. While showing many similarities to a glass transition, this liquid-liquid phase transition occurs in a mobile liquid, making it novel.

  4. Role of Hf on Phase Formation in Ti45Zr(38-x)Hf(x)Ni17 Liquids and Solids

    NASA Technical Reports Server (NTRS)

    Wessels, V.; Sahu, K. K.; Gangopadhyay, A. K.; Huett, V. T.; Canepari, S.; Goldman, A. I.; Hyers, R. W.; Kramer, M. J.; Rogers, J. R.; Kelton, K. F.; Robinson, D.

    2008-01-01

    Hafnium and zirconium are very similar, with almost identical sizes and chemical bonding characteristics. However, they behave differently when alloyed with Ti and Ni. A sharp phase formation boundary near 18-21 at.% Hf is observed in rapidly-quenched and as-cast Ti45Zr38-xHfxNi17 alloys. Rapidly-quenched samples that contain less than 18 at.% Hf form the icosahedral quasicrystal phase, whiles samples containing more than 21 at.% form the 3/2 rational approximant phase. In cast alloys, a C14 structure is observed for alloys with Hf lower than the boundary concentration, while a large-cell (11.93 ) FCC Ti2Ni-type structure is found in alloys with Hf concentrations above the boundary. To better understand the role of Hf on phase formation, the structural evolution with supercooling and the solidification behavior of liquid Ti45Zr38-xHfxNi17 alloys (x=0, 12, 18, 21, 38) were studied using the Beamline Electrostatic Levitation (BESL) technique using 125keV x-rays on the 6ID-D beamline at the Advanced Photon Source, Argonne National Laboratory. For all liquids primary crystallization was to a BCC solid solution phase; interestly, an increase in Hf concentration leads to a decrease in the BCC lattice parameter in spite of the chemical similarity between Zr and Hf. A Reitveld analysis confirmed that as in the cast alloys, the secondary phase that formed was the C14 below the phase formation boundary and a Ti2Ni-type structure at higher Hf concentrations. Both the liquidus temperature and the reduced undercooling change sharply on traversing the phase formation boundary concentration, suggesting a change in the liquid structure. Structural information from a Honeycutt-Anderson index analysis of reverse Monte Carlo fits to the S(q) liquid data will be presented to address this issue.

  5. Containerless measurements of thermophysical properties of Zr54Ti8Cu20Al10Ni8.

    PubMed

    Bradshaw, R C; Warren, M E; Rogers, J R; Rathz, T J; Gangopadhyay, A K; Kelton, K F; Hyers, R W

    2006-09-01

    High-temperature measurement and study of reactive materials can be difficult with conventional processing methods because contamination from the measuring apparatus and container walls can adversely affect measurements. Containerless processing techniques can be employed to isolate samples from their environment, reducing contamination. Benefits of containerless processing include reduction in heterogeneous nucleation sites, which in turn delays the onset of solidification and allows the study of meta-stable undercooled phases. However, property measurements must use noncontact methods as well. Fortunately, several optical-based methods have been developed and successfully employed to measure thermophysical properties, including surface tension, viscosity, density, and thermal expansion. Combining these techniques with the electrostatic levitator (ESL) located at the NASA Marshall Space Flight Center (MSFC) has resulted in an excellent facility to perform containerless material studies which support microgravity flight projects. Currently, studies of the thermophysical properties of liquid quasi-crystal forming and related alloys ranging from superheated to deeply undercooled states are being done with this facility in support of the NASA-funded flight project Quasi-crystalline Undercooled Alloys for Space Investigation (QUASI). While the primary purpose of these measurements is to support planned flight experiments, they are also a desirable resource for future manufacturing considerations and for fundamental insight in the physics of icosahedral ordering in liquids and solids. Presented here is an overview of the contactless measuring methods for surface tension, viscosity, density, and thermal expansion applied to Zr54Ti8Cu20Al10Ni8, for the superheated and meta-stable undercooled liquid phases, in support of QUASI. PMID:17124115

  6. Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics

    NASA Astrophysics Data System (ADS)

    Ektarawong, A.; Simak, S. I.; Hultman, L.; Birch, J.; Tasnádi, F.; Wang, F.; Alling, B.

    2016-04-01

    The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)1-x(B13C2)x, as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)1-x(B13C2)x is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young's and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)1-x(B13C2)x system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)1-x(B13C2)x. The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

  7. Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics.

    PubMed

    Ektarawong, A; Simak, S I; Hultman, L; Birch, J; Tasnádi, F; Wang, F; Alling, B

    2016-04-01

    The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)(1-x)(B13C2)(x), as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)(1-x)(B13C2)(x) is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young's and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)(1-x)(B13C2)(x) system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)(1-x)(B13C2)(x). The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

  8. Formation of the icosahedral quasicrystalline phase in a rapidly solidified Al{sub 52}Cu{sub 25.5}Fe{sub 12.5}Si{sub 1} alloy

    SciTech Connect

    Wang Yan; Zhang Zhonghua . E-mail: zh_zhang@sdu.edu.cn; Geng Haoran; Yang Zhongxi

    2006-04-15

    In the present work, the effect of wheel speed (quenching rate) on the formation of the quasicrystalline phase in a rapidly solidified Al{sub 52}Cu{sub 25.5}Fe{sub 12.5}Si{sub 1} alloy has been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results show that rapid solidification has no effect on the phase constitution of the Al{sub 52}Cu{sub 25.5}Fe{sub 12.5}Si{sub 1} alloy. The addition of Si decreases the stability of the quasicrystalline phase in the conventionally cast Al{sub 52}Cu{sub 25.5}Fe{sub 12.5}Si{sub 1} alloy. The thermal stability of the quasicrystalline phase in the melt-spun alloy depends upon the quenching rate. Moderate-rate rapid solidification can improve the thermal stability of the quasicrystalline phase in the melt-spun alloy. Higher quenching rate instigates the transformation of the quasicrystalline phase into the cubic approximant phase and decreases the stability of the quasicrystalline phase. Furthermore, the transformation temperature decreases with increasing Si addition into the Al{sub (62-x)}Cu{sub 25.5}Fe{sub 12.5}Si{sub x}.

  9. PREFACE: 6th International Conference on Aperiodic Crystals (APERIODIC'09)

    NASA Astrophysics Data System (ADS)

    Grimm, Uwe; McGrath, Rónán; Degtyareva, Olga; Sharma, Hem Raj

    2010-04-01

    on quasicrystals (Eiji Abe), complex metal alloys (Alessandra Beni) and incommensurately modulated structures (Gervais Chapuis). While these were mainly aimed at younger researchers in the field, the lectures were very well attended and appreciated by the participants. The main programme ran from Monday morning until Friday lunchtime. It comprised 13 invited and 40 contributed plenary talks, and more than 40 posters, which were presented at two afternoon/evening poster sessions. The topics covered in the programme range from mathematical foundations, mathematical models, new materials, sample preparation, structure determination, physical properties and surface properties to industrial applications. Every presenter was invited to submit an article for this proceedings volume, and the 36 peer-reviewed papers in this volume present a cross-section of the range of presentations at the conference. They have been arranged into four categories, (i) quasicrystals, (ii) modulated structures, (iii) mathematical and theoretical aspects of aperiodic order, and (iv) approximants and complex phases. Prizes for best student presentations were awarded to Heinrich Orsini-Rosenberg (ETH Zurich) for his poster Tailor-made sevenfold approximants: ab-initio investigations on formation and stability and to Holger Euchner (Universität Stuttgart) for his contributed talk on Lattice dynamics in complex metallic alloys - vibrational properties of Zn11Mg2. In addition to a cash prize, Heinrich Orsini-Rosenberg received an icosahedral teapot, which was manufactured and donated by David Warrington, and Holger Euchner received a book prize. The meeting started with a welcome reception in the University's recently refurbished Victoria Gallery and Museum. A public lecture Simple sets of shapes that tile the plane but cannot ever repeat by Professor Sir Roger Penrose FRS attracted a wide audience and gave a fascinating insight into the discovery of the Penrose tiling, which is still the paradigm

  10. [Non-empirical interatomic potentials for transition metals]. Progress report

    SciTech Connect

    Not Available

    1993-05-01

    The report is divided into the following sections: potential-energy functions for d-band metals, potential-energy functions for aluminides and quasicrystals, electronic structure of complex structures and quasicrystals, potential-energy functions in transition-metal oxides, applications to defect structure and mechanical properties, and basic theory of interatomic potentials.

  11. [Non-empirical interatomic potentials for transition metals

    SciTech Connect

    Not Available

    1993-01-01

    The report is divided into the following sections: potential-energy functions for d-band metals, potential-energy functions for aluminides and quasicrystals, electronic structure of complex structures and quasicrystals, potential-energy functions in transition-metal oxides, applications to defect structure and mechanical properties, and basic theory of interatomic potentials.

  12. Structure, stability, and electronic properties of the i -AlPdMn quasicrystalline surface

    NASA Astrophysics Data System (ADS)

    Krajčí, M.; Hafner, J.

    2005-02-01

    The structure, stability, and electronic properties of a fivefold surface of an icosahedral (i) Al-Pd-Mn alloy have been investigated using ab initio density-functional methods. Structural models for a series of rational approximants to the quasicrystalline structure of bulk i -AlPdMn have been constructed using the cut-and-projection technique with triacontahedral acceptance domains in the six-dimensional hyperspace according to the Katz-Gratias-Boudard model. This leads to a real-space structure describable in terms of interpenetrating Mackay and Bergman clusters. A fivefold surface has been prepared by cleaving the bulk structure along a plane perpendicular to a fivefold axis. The position of the cleavage plane has been chosen such as to produce a surface layer with a high atomic density. The atomic structure of these surfaces can be described by a P1 tiling by pentagons, thin rhombi, pentagonal stars, and a “boat”—in terms of a cut-and-projection model the decagonal acceptance domain of the P1 tiling corresponds to the maximal cross section of the triacontahedra defining the three-dimensional quasicrystal. The vertices of the P1 tiling are occupied by Pd atoms surrounded by pentagonal motifs of Al atoms. For the ab initio calculations we have prepared slab models of the surface based on the 3/2 and 2/1 approximants and containing up to 357 atoms in the computational cell. The analysis of the surface charge density shows flat minima at the vertices of the P1 tiling and strong charge depletion in some of the pentagonal tiles (“surface vacancies”). Both observations are in agreement with scanning tunneling microscopy studies of these surfaces. Structural relaxations have been performed only for the 2/1 models with up to 205 atoms/cell. The calculations demonstrate that the skeleton of the P1 tiling fixed by the transition-metal atoms represents a stable surface termination, but considerable rearrangement of the Al atoms and large relaxations of the

  13. Crystallization of Zr2PdxCu1-x and Zr2NixCu1-x Metallic Glass

    SciTech Connect

    Xu, Min

    2008-01-01

    One interesting aspect of rretallic glasses is the numerous instances of the deviation of the phase selection from the amorphous state to thermodynamically stable phases during the crystallization process. Their devitrification pathways allow us to study the relationship between the original amorphous structure and their crystalline counter parts. Among the various factors of phase selections, size and electronic effects have been most extensively studied. Elucidating the phase selection process of a glassy alloy will be helpful to fill in the puzzle of the changes from disordered to ordered structures. In this thesis, Two model Zr2PdxCu1-x and Zr2NixCu1-x (x = 0, 0.25, 0.5, 0.75 and 1) glassy systems were investigated since: (1) All of the samples can be made into a homogenous metallic glass; (2) The atomic radii differ from Pd to Cu is by 11%, while Ni has nearly the identical atomic size compare to Cu. Moreover, Pd and Ni differ by only one valence electron from Cu. Thus, these systems are ideal to test the idea of the effects of electronic structure and size factors; (3) The small number of components in these pseudo binary systems readily lend themselves to theoretical modeling. Using high temperature X-ray diffraction (HTXRD) and thermal analysis, topological, size, electronic, bond and chemical distribution factors on crystallization selections in Zr2PdxCu1-x and Zr2NixCu1-x metallic glass have been explored. All Zr2PdxCu1-x compositions share the same Cu11b phase with different pathways of meta-stable, icosahedral quasicrystalline phase (i-phase), and C16 phase formations. The quasicrystal phase formation is topologically related to the increasing icosahedral short range order (SRO) with Pd content in Zr2PdxCu1-x system. Meta-stable C16 phase is competitive with

  14. Gap solitons and soliton trains in finite-sized two-dimensional periodic and quasiperiodic photonic crystals.

    PubMed

    Xie, Ping; Zhang, Zhao-Qing; Zhang, Xiangdong

    2003-02-01

    We demonstrate the existence of the gap solitons and soliton trains in finite-sized two-dimensional periodic nonlinear photonic crystals by using the mutiple-scattering approach with an iterative scheme. In 12-fold symmetric nonlinear quasicrystals, we also demonstrated the existence of symmetric, regular gap solitons, asymmetric single-soliton states, and two-solitons states. We revealed that the existence of symmetric, regular gap solitons in a 12-fold quasicrystal is limited by the geometrical size of the hexagon that forms the core of the dodecahedral cell, which is the building block of the quasicrystal.

  15. L'Oréal and UNESCO Award Women Physicists $500 000

    NASA Astrophysics Data System (ADS)

    Feder, Toni

    2003-03-01

    Not just cosmetic: L'Oréal and UNESCO are rewarding five women from around the globe for their scientific contributions in crystallography, disordered materials, scaling laws of fluids and complex systems, and electron microscopy of crystals and quasicrystals.

  16. Multi-body forces and the energetics of transition metals, alloys, and semiconductors

    SciTech Connect

    Carlsson, A.E.

    1992-01-01

    Progress over the past year is divided into 3 areas: potential-energy functions for transition-metal aluminides; electronic structure and energetics of complex structures and quasicrystals; and ceramic materials (PdO, PtO).

  17. Multi-body forces and the energetics of transition metals, alloys, and semiconductors. Annual progress report, (1991--1992)

    SciTech Connect

    Carlsson, A.E.

    1992-11-01

    Progress over the past year is divided into 3 areas: potential-energy functions for transition-metal aluminides; electronic structure and energetics of complex structures and quasicrystals; and ceramic materials (PdO, PtO).

  18. Exploring the symmetry and mechanism of virus capsid maturation via an ensemble of pathways.

    PubMed

    May, Eric R; Feng, Jun; Brooks, Charles L

    2012-02-01

    Many icosahedral viruses undergo large-scale conformational transitions between icosahedrally symmetric conformations during their life cycles. However, whether icosahedral symmetry is maintained along the transition pathways for this process is unknown. By employing a simplified and directed structure-based potential we compute an ensemble of transition pathways for the maturation transition of bacteriophage HK97. We observe localized symmetry-breaking events, but find that the large-scale displacements are dominated by icosahedrally symmetric deformation modes. We find that all pathways obey a common mechanism characterized by formation of pentameric contacts early in the transition. PMID:22325284

  19. Cubic Icosahedra? A Problem in Assigning Symmetry

    ERIC Educational Resources Information Center

    Lloyd, D. R.

    2010-01-01

    There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…

  20. Single particle cryo-electron microscopy and 3-D reconstruction of viruses.

    PubMed

    Guo, Fei; Jiang, Wen

    2014-01-01

    With fast progresses in instrumentation, image processing algorithms, and computational resources, single particle electron cryo-microscopy (cryo-EM) 3-D reconstruction of icosahedral viruses has now reached near-atomic resolutions (3-4 Å). With comparable resolutions and more predictable outcomes, cryo-EM is now considered a preferred method over X-ray crystallography for determination of atomic structure of icosahedral viruses. At near-atomic resolutions, all-atom models or backbone models can be reliably built that allow residue level understanding of viral assembly and conformational changes among different stages of viral life cycle. With the developments of asymmetric reconstruction, it is now possible to visualize the complete structure of a complex virus with not only its icosahedral shell but also its multiple non-icosahedral structural features. In this chapter, we will describe single particle cryo-EM experimental and computational procedures for both near-atomic resolution reconstruction of icosahedral viruses and asymmetric reconstruction of viruses with both icosahedral and non-icosahedral structure components. Procedures for rigorous validation of the reconstructions and resolution evaluations using truly independent de novo initial models and refinements are also introduced.

  1. Single Particle Cryo-electron Microscopy and 3-D Reconstruction of Viruses

    PubMed Central

    Guo, Fei; Jiang, Wen

    2014-01-01

    With fast progresses in instrumentation, image processing algorithms, and computational resources, single particle electron cryo-microscopy (cryo-EM) 3-D reconstruction of icosahedral viruses has now reached near-atomic resolutions (3–4 Å). With comparable resolutions and more predictable outcomes, cryo-EM is now considered a preferred method over X-ray crystallography for determination of atomic structure of icosahedral viruses. At near-atomic resolutions, all-atom models or backbone models can be reliably built that allow residue level understanding of viral assembly and conformational changes among different stages of viral life cycle. With the developments of asymmetric reconstruction, it is now possible to visualize the complete structure of a complex virus with not only its icosahedral shell but also its multiple non-icosahedral structural features. In this chapter, we will describe single particle cryo-EM experimental and computational procedures for both near-atomic resolution reconstruction of icosahedral viruses and asymmetric reconstruction of viruses with both icosahedral and non-icosahedral structure components. Procedures for rigorous validation of the reconstructions and resolution evaluations using truly independent de novo initial models and refinements are also introduced. PMID:24357374

  2. Modeling quasi-lattice with octagonal symmetry

    SciTech Connect

    Girzhon, V. V.; Smolyakov, O. V.; Zakharenko, M. I.

    2014-11-15

    We prove the possibility to use the method of modeling of a quasi-lattice with octagonal symmetry similar to that proposed earlier for the decagonal quasicrystal. The method is based on the multiplication of the groups of basis sites according to specified rules. This model is shown to be equivalent to the method of the periodic lattice projection, but is simpler because it considers merely two-dimensional site groups. The application of the proposed modeling procedure to the reciprocal lattice of octagonal quasicrystals shows a fairly good matching with the electron diffraction pattern. Similarly to the decagonal quasicrystals, the possibility of three-index labeling of the diffraction reflections is exhibited in this case. Moreover, the ascertained ratio of indices provides information on the intensity of diffraction reflections.

  3. Role of Ti in the formation of Zr-Ti-Cu-Ni-Al glasses

    SciTech Connect

    Kim, T H; Gangopadhyay, A K; Xing, L Q; Lee, G W; Shen, Y T; Kelton, K F; Goldman, A I; Hyers, R W; Rogers, J R

    2010-07-19

    It has been widely reported that glass formation improves in Zr{sub 62}Cu{sub 20}Ni{sub 8}Al{sub 10} alloys when small amounts of Ti are substituted for Zr. Glasses containing greater than 3 at. % Ti crystallize to a metastable icosahedral phase, suggesting that Ti enhances icosahedral short-range order in the liquid/glass, making crystallization more difficult during cooling. However, based on containerless solidification and in situ high-energy synchrotron diffraction studies of electrostatically levitated supercooled liquids of these alloys, we demonstrate that Ti inhibits surface crystallization but neither increases the icosahedral short-range order nor improves glass formation.

  4. Fabrication of ten-fold photonic quasicrystalline structures

    SciTech Connect

    Sun, XiaoHong Wu, YuLong; Liu, Wen; Liu, Wei; Han, Juan; Jiang, Lei

    2015-05-15

    Compared to periodic crystals, quasicrystals have higher point group symmetry and are more favorable in achieving complete band-gaps. In this report, a top-cut prism interferometer is designed to fabricate ten-fold photonic quasicrystalline structures. By optimizing the exposing conditions and material characteristics, appropriate quasicrystals have been obtained in the SU8 photoresist films. Atomic Force Microscopy and laser diffraction are used to characterize the fabricated structures. The measurement results show the consistence between the theoretical design and experiments. This will provide guidance for the large-area and fast production of ten-fold quasicrystalline structures with high quality.

  5. Channel-drop filter based on a photonic crystal ring resonator

    NASA Astrophysics Data System (ADS)

    Mehdizadeh, Farhad; Alipour-Banaei, Hamed; Serajmohammadi, Somaye

    2013-07-01

    In this paper combining a square lattice photonic crystal with a 12-fold quasicrystal, we proposed a new design for an optical channel-drop filter. Our proposed structure has a transmission efficiency very close to 1 and the band width and quality factor values for this structure are 4.5 nm and 344. After designing the channel-drop filter we investigated the effect of different parameters on the output wavelength of the filter. It has been shown that by changing the dielectric rods’ refractive index, radius of initial structure rods and the radius of the 12-fold quasicrystal rods we can obtain different output wavelengths of the filter.

  6. Grain size softening effect in Al62.5Cu25Fe12.5 nanoquasicrystals

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, N. K.; Ali, F.; Scudino, S.; Samadi Khoshkhoo, M.; Stoica, M.; Srivastava, V. C.; Uhlenwinkel, V.; Vaughan, G.; Suryanarayana, C.; Eckert, J.

    2013-11-01

    Inverse Hall-Petch (IHP) behavior in nano-quasicrystalline Al62.5Cu25Fe12.5 is reported. Powders with varying grain sizes were produced by mechanical milling of spray-formed quasicrystals. The hardness of the milled powders increased with decreasing grain size down to about 40 nm and decreased with further refinement, demonstrating the IHP behavior. This critical grain size was found to be larger compared to other metallic nanocrystalline alloys. This IHP behaviour has been attributed to the structural complexity in quasicrystals and to thermally activated shearing events of atoms at the grain boundaries.

  7. Origin of the log-periodic oscillations in the quantum dynamics of electrons in quasiperiodic systems

    NASA Astrophysics Data System (ADS)

    Thiem, Stefanie

    2015-04-01

    Recently, the occurrence of log-periodic oscillations in the quantum dynamics of electrons was reported for the one-dimensional Fibonacci quasicrystal by Lifshitz and Even-Dar Mandel. We apply a real-space renormalization group approach to show that these log-periodic oscillations are related to the underlying quasiperiodic structure of the Fibonacci quasicrystal. We find that they originate from the superposition of bonding and antibonding states associated to strongly coupled atoms in the chains, and that they show a hierarchical structure closely related to the atomic configurations.

  8. Raman Effect in Boron and Boron-Rich Compounds

    NASA Astrophysics Data System (ADS)

    Werheit, Helmut; Filipov, Volodimir

    High-resolution Raman spectra of different allotropes of elemental boron and of some selected representatives of boron-rich solids are presented and discussed. Often, the number of modes exceeds that, which is group theoretically predicted for idealized structures. The reason is intrinsic defects, which are typical for most of these structures. Specific Raman modes in the spectra of different groups of icosahedral structures are attributed to inter-icosahedral and intra-icosahedral B-B vibrations respectively and allow assessing the bonding forces related. Badger's rule is satisfactorily fulfilled across all icosahedral structure groups. - Depending on the penetration depth of the exciting radiation, Raman spectra can be significantly different as shown for boron carbide and lanthanum hexaboride.

  9. Synthesis of a new boron carbonitride with a B4C-like structure from the thermolysis of N-alkylated borazines.

    PubMed

    Brydson, Rik; Daniels, Howard; Fox, Mark A; Greatrex, Robert; Workman, Christopher

    2002-04-01

    Thermolysis of N-trialkyl borazines at 500 degrees C produces homogeneous, amorphous boron carbonitride phases, whose compositions are dependent upon the borazine substituent, and whose structures are similar to that of icosahedral boron carbide, B4C.

  10. Temperature-dependent stability of supported five-fold twinned copper nanocrystals.

    PubMed

    Silly, Fabien; Castell, Martin R

    2009-04-28

    The temperature-dependent structure transition of supported Cu nanocrystals on SrTiO3(001)-(2 x 1) is investigated by scanning tunneling microscopy (STM). We experimentally determine the phase map of supported Cu icosahedral, decahedral, and truncated octahedral nanocrystal shapes as a function of substrate temperature during Cu deposition. We show that a supported nanocrystal of 8500 atoms at a nucleation temperature of 480 degrees C has the same probability of adopting an icosahedral or octahedral shape. PMID:19323548

  11. Experimental and ab initio structural studies of liquid Zr[subscript 2]Ni

    SciTech Connect

    Hao, S.G.; Kramer, M.J.; Wang, C.Z.; Ho, K.M.; Nandi, S.; Kreyssig, A.; Goldman, A.I.; Wessels, V.; Sahu, K.K.; Kelton, K.F.; Hyers, R.W.; Canepari, S.M.; Rogers, J.R.

    2009-05-01

    High-energy x-ray diffraction and ab initio molecular-dynamics simulations demonstrate that the short-range order in the deeply undercooled Zr{sub 2}Ni liquid is quite nuanced. The second diffuse scattering peak in the total structure factory sharpens with supercooling, revealing a shoulder on the high-Q side that is often taken to be a hallmark of increasing icosahedral order. However, a Voronoi tessellation indicates that only approximately 3.5% of all the atoms are in an icosahedral or icosahedral-like environment. In contrast, a Honeycutt-Andersen analysis indicates that a much higher fraction of the atoms is in icosahedral (15%--18%) or distorted icosahedral (25%--28%) bond-pair environments. These results indicate that the liquid contains a large population of fragmented clusters with pentagonal and distorted pentagonal faces, but the fully developed icosahedral fragments are rare. Interestingly, in both cases, the ordering changes little over the 500 K of cooling. All metrics show that the nearest-neighbor atomic configurations of the most deeply supercooled simulated liquid (1173 K) differ topologically and chemically from those in the stable C16 compound, even though the partial pair distributions are similar. The most significant structural change upon decreasing the temperature from 1673 to 1173 K is an increase in the population of Zr in Ni-centered clusters. The structural differences between the liquid and the C16 increase the nucleation barrier, explaining glass formation in the rapidly quenched alloys.

  12. (X-ray diffraction experiments with condenser matter)

    SciTech Connect

    Coppens, P.

    1990-01-01

    This report discusses research on the following topics: high-{Tc} superconductors; The response of crystal to an applied electric field; quasicrystals; surface structure and kinetics of surface layer formation; EXAFS studies of superconductors and heterostructures; effect of iron on the crystal structure of perovskite; x-ray detector development; and SAXS experiments. (LSP)

  13. High temperature x-ray and calorimetric studies of phase transformations in quasicrystalline Ti{endash}Zr{endash}Ni alloys

    SciTech Connect

    Stroud, R.M.; Kelton, K.F.; Misture, S.T.

    1997-02-01

    We present the first high temperature x-ray diffraction (HTXRD) studies of {ital in situ} quasicrystal-crystal and crystal-crystal transformations in Ti{endash}Zr{endash}Ni alloys. Together with differential scanning calorimetry studies, these x-ray measurements indicate three separate paths for the Ti{endash}Zr{endash}Ni quasicrystal-crystal transformation: single exothermic, single endothermic, or multiple endothermic. The mode of transformation depends on the alloy composition and the level of environmental oxygen. The crystalline products include the Ti{sub 2}Ni, MgZn{sub 2} Laves, {alpha}{endash}(Ti,Zr) and {beta}{endash}(Ti,Zr) phases. In the absence of oxygen, the endothermic transformation of the quasicrystal demonstrates that it is the lowest free energy (stable) phase at the Ti{sub 53}Zr{sub 27}Ni{sub 20} composition. Oxygen stabilizes the Ti{sub 2}Ni phase, eliminating both the quasicrystal and the MgZn{sub 2} Laves phase, at partial pressures as low as a few hundred ppm. {copyright} {ital 1997 Materials Research Society.}

  14. Discovery of New Al-Cu-Fe Minerals in the Khatyrka CV3 Meteorite

    NASA Astrophysics Data System (ADS)

    Ma, C.; Lin, C.; Bindi, L.; Steinhardt, P. J.

    2016-08-01

    Our nanomineralogy investigation of Khatyrka has revealed two new alloy minerals (AlCu with a Pm-3m CsCl structure and Al3Fe with a C2/m structure) and associated icosahedrite (quasicrystal Al63Cu26Fe11 with a five-fold symmetry) in section 126A of USNM 7908.

  15. Dirac Sea and its Evolution

    NASA Astrophysics Data System (ADS)

    Volfson, Boris

    2013-09-01

    The hypothesis of transition from a chaotic Dirac Sea, via highly unstable positronium, into a Simhony Model of stable face-centered cubic lattice structure of electrons and positrons securely bound in vacuum space, is considered. 13.75 Billion years ago, the new lattice, which, unlike a Dirac Sea, is permeable by photons and phonons, made the Universe detectable. Many electrons and positrons ended up annihilating each other producing energy quanta and neutrino-antineutrino pairs. The weak force of the electron-positron crystal lattice, bombarded by the chirality-changing neutrinos, may have started capturing these neutrinos thus transforming from cubic crystals into a quasicrystal lattice. Unlike cubic crystal lattice, clusters of quasicrystals are "slippery" allowing the formation of centers of local torsion, where gravity condenses matter into galaxies, stars and planets. In the presence of quanta, in a quasicrystal lattice, the Majorana neutrinos' rotation flips to the opposite direction causing natural transformations in a category comprised of three components; two others being positron and electron. In other words, each particle-antiparticle pair "e-" and "e+", in an individual crystal unit, could become either a quasi- component "e- ve e+", or a quasi- component "e+ - ve e-". Five-to-six six billion years ago, a continuous stimulation of the quasicrystal aetherial lattice by the same, similar, or different, astronomical events, could have triggered Hebbian and anti-Hebbian learning processes. The Universe may have started writing script into its own aether in a code most appropriate for the quasicrystal aether "hardware": Eight three-dimensional "alphabet" characters, each corresponding to the individual quasi-crystal unit shape. They could be expressed as quantum Turing machine qubits, or, alternatively, in a binary code. The code numerals could contain terminal and nonterminal symbols of the Chomsky's hierarchy, wherein, the showers of quanta, forming the

  16. From structure of the complex to understanding of the biology

    SciTech Connect

    Rossmann, Michael G.; Arisaka, Fumio; Battisti, Anthony J.; Bowman, Valorie D.; Chipman, Paul R.; Fokine, Andrei; Hafenstein, Susan; Kanamaru, Shuji; Kostyuchenko, Victor A.; Mesyanzhinov, Vadim V.; Shneider, Mikhail M.; Palermo, Laura M.; Parrish, Colin R.; Xiao, Chuan

    2007-01-01

    The most extensive structural information on viruses relates to apparently icosahedral virions and is based on X-ray crystallography and on cryo-electron microscopy single-particle reconstructions. This paper concerns itself with the study of the macromolecular complexes that constitute viruses, using structural hybrid techniques. The most extensive structural information on viruses relates to apparently icosahedral virions and is based on X-ray crystallography and on cryo-electron microscopy (cryo-EM) single-particle reconstructions. Both techniques lean heavily on imposing icosahedral symmetry, thereby obscuring any deviation from the assumed symmetry. However, tailed bacteriophages have icosahedral or prolate icosahedral heads that have one obvious unique vertex where the genome can enter for DNA packaging and exit when infecting a host cell. The presence of the tail allows cryo-EM reconstructions in which the special vertex is used to orient the head in a unique manner. Some very large dsDNA icosahedral viruses also develop special vertices thought to be required for infecting host cells. Similarly, preliminary cryo-EM data for the small ssDNA canine parvovirus complexed with receptor suggests that these viruses, previously considered to be accurately icosahedral, might have some asymmetric properties that generate one preferred receptor-binding site on the viral surface. Comparisons are made between rhinoviruses that bind receptor molecules uniformly to all 60 equivalent binding sites, canine parvovirus, which appears to have a preferred receptor-binding site, and bacteriophage T4, which gains major biological advantages on account of its unique vertex and tail organelle.

  17. Analysis of boron carbides' electronic structure

    NASA Technical Reports Server (NTRS)

    Howard, Iris A.; Beckel, Charles L.

    1986-01-01

    The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

  18. Topology in Ordered Phases

    NASA Astrophysics Data System (ADS)

    Tanda, Satoshi; Matsuyama, Toyoki; Oda, Migaku; Asano, Yasuhiro; Yakubo, Kousuke

    2006-08-01

    .]. Nanofibers of hydrogen storage alloy / I. Saita ... [et al.]. Synthesis of stable icosahedral quasicrystals in Zn-Sc based alloys and their magnetic properties / S. Kashimoto and T. Ishimasa. One-armed spiral wave excited by eam pressure in accretion disks in Be/X-Ray binaries / K. Hayasaki and A. T. Okazaki -- IV. Topological defects and excitations. Topological excitations in the ground state of charge density wave systems / P. Monceau. Soliton transport in nanoscale charge-density-wave systems / K. Inagaki, T. Toshima and S. Tanda. Topological defects in triplet superconductors UPt3, Sr[symbol]RuO[symbol], etc. / K. Maki ... [et al.]. Microscopic structure of vortices in type II superconductors / K. Machida ... [et al.]. Microscopic neutron investigation of the Abrikosov state of high-temperature superconductors / J. Mesot. Energy dissipation at nano-scale topological defects of high-Tc superconductors: microwave study / A. Maeda. Pressure induced topological phase transition in the heavy Fermion compound CeAl[symbol] / H. Miyagawa ... [et al.]. Explanation for the unusual orientation of LSCO square vortex lattice in terms of nodal superconductivity / M. Oda. Local electronic states in Bi[symbol]Sr[symbol]CaCu[symbol]O[symbol] / A. Hashimoto ... [et al.] -- V. Topology in quantum phenomena. Topological vortex formation in a Bose-Einstein condensate of alkali-metal atoms / M. Nakahara. Quantum phase transition of [symbol]He confined in nano-porous media / K. Shirahama, K. Yamamoto and Y. Shibayama. A new mean-field theory for Bose-Einstein condensates / T. Kita. Spin current in topological cristals / Y. Asano. Antiferromagnetic defects in non-magnetic hidden order of the heavy-electron system URu[symbol]Si[symbol] / H. Amitsuka, K. Tenya and M. Yokoyama. Magnetic-field dependences of thermodynamic quantities in the vortex state of Type-II superconductors / K. Watanabe, T. Kita and M. Arai. Three-magnon-mediated nuclear spin relaxation in quantum ferrimagnets of topological

  19. Structure and magnetism of quasicrystalline and crystalline Al1-xMnx alloys

    NASA Astrophysics Data System (ADS)

    Youngquist, S. E.; Miceli, P. F.; Wiesler, D. G.; Zabel, H.; Fraser, H. L.

    1986-08-01

    We have performed x-ray structural studies of quenched and annealed Al1-xMnx alloys in the range of 0.14<=x<=0.20. The quenched samples exhibit a coexistence of Al with an icosahedral phase, the latter having a maximum volume fraction at x=0.20. Magnetic susceptibility measurements for x=0.14 and 0.20 show a dramatically enhanced magnetic moment in the icosahedral phase (p=0.747 and 1.27, respectively) as compared to the annealed samples (p=0 and 0.617, respectively). The increase of magnetic moment per Mn ion with increasing Mn concentration indicates a range of stoichiometries and microstructures over which the icosahedral phase can exist.

  20. Highly uniform platinum icosahedra made by hot injection-assisted GRAILS method.

    PubMed

    Zhou, Wei; Wu, Jianbo; Yang, Hong

    2013-06-12

    Highly uniform Pt icosahedral nanocrystals with an edge length of 8.8 nm were synthesized in nonhydrolytic systems using the hot injection-assisted GRAILS (gas reducing agent in liquid solution) method. The results show the key factors for the shape control include fast nucleation, kinetically controlled growth, and protection from oxidation by air. The effect of oxygen molecules on the Pt morphology was experimentally confirmed based on the study of shape evolution of icosahedral crystals upon exposure to oxygen gas. The Pt icosahedral catalysts obtained had an area-specific activity of 0.83 mA/cm(2) Pt, four times that of 0.20 mA/cm(2) Pt for typical Pt/C catalysts, in an oxygen reduction reaction (ORR).

  1. Why Are Buckyonions Round?

    NASA Technical Reports Server (NTRS)

    Bates, Kevin R.; Scuseria, Gustavo E.

    1997-01-01

    Multi-layered round carbon particles (onions) containing tens to hundreds of thousands of atoms form during electron irradiation of graphite carbon. However, theoretical models of large icosahedral fullerenes predict highly faceted shapes for molecules with more than a few hundred atoms. This discrepancy in shape may be explained by the presence of defects during the formation of carbon onions. Here, we use the semi-empirical tight-binding method for carbon to simulate the incorporation of pentagon-heptagon defects on to the surface of large icosahedral fullerenes. We show a simple mechanism that results in energetically competitive derivative structures and a global change in molecular shape from faceted to round. Our results provide a plausible explanation of the apparent discrepancy between experimental observations of round buckyonions and theoretical predictions of faceted icosahedral fullerenes.

  2. Why are Buckyonions Round?

    NASA Technical Reports Server (NTRS)

    Bates, Kevin R.; Scuseria, Gustavo E.

    1998-01-01

    Multi-layered round carbon particles (onions) containing tens to hundreds of thousands of atoms form during electron irradiation of graphite. However. theoretical models or large icosahedral fullerenes predict highly faceted shapes for molecules with more than a few hundred atoms. This discrepancy in shape may be explained by the presence of defects during the formation of carbon onions. Here, we use the semi-empirical tight-binding method for carbon to simulate the incorporation of pentagon-heptagon defects on to the surface of large icosahedral fullerenes. We show a simple mechanism that results in energetically competitive derivative structures and a global change in molecular shape from faceted to round. Our results provide a plausible explanation of the apparent discrepancy between experimental observations or round buckyonions and theoretical predictions of faceted icosahedral fullerenes.

  3. Microstructure Evolution in Al-Cu-Fe Quasicrystalline Thin Films

    NASA Astrophysics Data System (ADS)

    Widjaja, Edy; Marks, Laurence

    2003-03-01

    Transmission Electron Microscopy (TEM) was performed to study the microstructure evolution in Al-Cu-Fe quasicrystalline thin films. Thin films were grown by magnetron sputtering on sodium chloride crystals which were subsequently dissolved in water to acquire free-standing films. Nanocrystalline films were found in the as-deposited sample. When annealed at 400oC the films changed to metastable crystalline phases that transformed into icosahedral phases upon further annealing at 500oC. TEM imaging combined with electron diffraction revealed various features associated with the phase evolution in the crystalline-quasicrystalline phase transformation. Some grains in the film functioned as sacrificial grains allowing others to grow into icosahedral phases. Elements near the boundary of the sacrificial grains diffused to form the icosahedral phases, resulting in fragments in the center of the grain. The oxide layer of the film was amorphous aluminum oxide that exhibited poor adhesion to the quasicrystalline films.

  4. Formation of fivefold axes in the FCC-metal nanoclusters

    NASA Astrophysics Data System (ADS)

    Myasnichenko, Vladimir S.; Starostenkov, Mikhail D.

    2012-11-01

    Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu-Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000 K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu-Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

  5. Unlocking Internal Prestress from Protein Nanoshells

    NASA Astrophysics Data System (ADS)

    Klug, W. S.; Roos, W. H.; Wuite, G. J. L.

    2012-10-01

    The capsids of icosahedral viruses are closed shells assembled from a hexagonal lattice of proteins with fivefold angular defects located at the icosahedral vertices. Elasticity theory predicts that these disclinations are subject to an internal compressive prestress, which provides an explanation for the link between size and shape of capsids. Using a combination of experiment and elasticity theory we investigate the question of whether macromolecular assemblies are subject to residual prestress, due to basic geometric incompatibility of the subunits. Here we report the first direct experimental test of the theory: by controlled removal of protein pentamers from the icosahedral vertices, we measure the mechanical response of so-called “whiffle ball” capsids of herpes simplex virus, and demonstrate the signature of internal prestress locked into wild-type capsids during assembly.

  6. Surface Reactivity of Quasicrystalline Materials

    NASA Astrophysics Data System (ADS)

    Jenks, Cynthia J.

    1997-03-01

    A fundamental knowledge and understanding of the reactivity of quasicrystalline materials is of great interest because of certain practical properties these materials possess, namely low coefficients of friction and oxidation resistance. A recent "hierarchical cluster" model proposed by Janot(C. Janot Phys. Rev. B 56 (1996) 181.) predicts that quasicrystal surfaces should be intrinsically inert and rough, and is useful in explaining their interesting properties. Surface structure and preparation may play a role in the applicability of this model. In this talk, we examine these factors and present experimental measurements of the surface reactivity of some Al-based quasicrystalline materials under ultra-high vacuum conditions (less than 2 x 10-10 Torr). To gain an understanding of what properties are unique to quasicrystals, we make comparisons with the surface reactivity of crystalline alloys of similar composition and pure, crystalline aluminum. note number.

  7. Light Localisation and Lasing

    NASA Astrophysics Data System (ADS)

    Ghulinyan, Mher; Pavesi, Lorenzo

    2014-12-01

    List of contributors; Preface; 1. Light propagation and emission in complex photonic media W. L. Vos, A. Lagendijk and A. P. Mosk; 2. Transport of localized waves via modes and channels A. Genack and Z. Shi; 3. Modes structure and interaction in random lasers M. Leonetti and C. Lopez; 4. Ordered and disordered light transport in couple microring resonators S. Mookherjea; 5. One-dimensional photonic quasicrystals M. Ghulinyan; 6. 2D pseudo-random and deterministic aperiodic lasers H. Cao, H. Noh and L. Dal Negro; 7. 3D photonic quasicrystal and deterministic aperiodic structures A. Ledermann, M. Renner and G. von Freymann; 8. Cavity quantum electrodynamics with three-dimensional photonic bandgap crystals W. L. Vos and L. A. Woldering; References; Index.

  8. Holographic fabrication of 3D photonic crystal templates with 4, 5, and 6-fold rotational symmetry using a single beam and single exposure

    NASA Astrophysics Data System (ADS)

    Lowell, David; George, David; Lutkenhaus, Jeffery; Philipose, Usha; Zhang, Hualiang; Lin, Yuankun

    2016-03-01

    A method of fabricating large-volume three-dimensional (3D) photonic crystal and quasicrystal templates using holographic lithography is presented. Fabrication is accomplished using a single-beam and single exposure by a reflective optical element (ROE). The ROE is 3D printed support structure which holds reflecting surfaces composed of silicon or gallium arsenide. Large-volume 3D photonic crystal and quasicrystal templates with 4-fold, 5-fold, and 6-fold symmetry were fabricated and found to be in good agreement with simulation. Although the reflective surfaces were setup away from the Brewster's angle, the interference among the reflected s and p-polarizations still generated bicontinuous structures, demonstrating the flexibility of the ROE. The ROE, being a compact and inexpensive alternative to diffractive optical elements and top-cut prisms, facilitates the large-scale integration of holographically fabricated photonic structures into on-chip applications.

  9. One dimensional 1H, 2H and 3H

    NASA Astrophysics Data System (ADS)

    Vidal, A. J.; Astrakharchik, G. E.; Vranješ Markić, L.; Boronat, J.

    2016-05-01

    The ground-state properties of one-dimensional electron-spin-polarized hydrogen 1H, deuterium 2H, and tritium 3H are obtained by means of quantum Monte Carlo methods. The equations of state of the three isotopes are calculated for a wide range of linear densities. The pair correlation function and the static structure factor are obtained and interpreted within the framework of the Luttinger liquid theory. We report the density dependence of the Luttinger parameter and use it to identify different physical regimes: Bogoliubov Bose gas, super-Tonks-Girardeau gas, and quasi-crystal regimes for bosons; repulsive, attractive Fermi gas, and quasi-crystal regimes for fermions. We find that the tritium isotope is the one with the richest behavior. Our results show unambiguously the relevant role of the isotope mass in the properties of this quantum system.

  10. Containerless Measurement of Thermophysical Properties of Ti-Zr-Ni Alloys

    NASA Technical Reports Server (NTRS)

    Hyers, Robert; Bradshaw, Richard C.; Rogers, Jan C.; Rathz, Thomas J.; Lee, Geun W.; Gangopadhyay, Anup K.; Kelton, Kenneth F.

    2004-01-01

    The surface tension, viscosity, density, and thermal expansion of Ti-Zr-Ni alloys were measured for a number of compositions by electrostatic levitation methods. Containerless methods greatly reduce heterogeneous nucleation, increasing access to the undercooled liquid regime at finite cooling rates. The density and thermal expansion are measured optically, while the surface tension and viscosity are measured by the oscillating drop method. The measured alloys include compositions which form a metastable quasicrystal phase from the undercooled liquid, and alloys close to the composition of several multi-component bulk metallic glass-forming alloys. Measurements of surface tension show behavior typical of transition metals at high temperature, but a sudden decrease in the deeply undercooled liquid for alloys near the quasicrystal-forming composition range, but not for compositions which form the solid-solution phase first.

  11. Fabrication of photonic quasicrystalline structures in the sub-micrometer scale

    NASA Astrophysics Data System (ADS)

    Wang, Shuai; Sun, XiaoHong; Li, WenYang; Liu, Wei; Jiang, Lei; Han, Juan

    2016-05-01

    Compared to periodic crystals, photonic quasicrystals (PQC) have higher point group symmetry and are more favorable in achieving complete band-gaps. In this report, a top-cut prism interferometer is designed to fabricate ten-fold photonic quasicrystalline structures in the sub-micro scale. Based on the difference of production conditions, a variety of quasicrystals have been obtained in the SU8 photoresist films. Scanning Probe Microscopy and laser diffraction are used to characterize the produced structures. The corresponding theoretical analysis is also provided to compare with the experimental results. This will provide guidance for the large-area and fast production of ten-fold quasicrystalline structures with high quality.

  12. Determination of three-dimensional low-resolution viral structure from solution x-ray scattering data.

    PubMed Central

    Zheng, Y; Doerschuk, P C; Johnson, J E

    1995-01-01

    The capsid is modeled as a region of constant electron density located between inner and outer envelopes that exhibit icosahedral symmetry. For computational purposes the envelopes are represented as truncated sums of weighted icosahedral harmonics. Methods are described for estimating the weights from x-ray solution scattering patterns based on nonlinear least squares, and two examples of the procedure, for viruses with known atomic-resolution structures, are given. Images FIGURE 8 FIGURE 9 FIGURE 14 FIGURE 17 FIGURE 20 FIGURE 23 PMID:8527677

  13. Structure determination of enterovirus 71

    SciTech Connect

    Plevka, Pavel; Perera, Rushika; Cardosa, Jane; Kuhn, Richard J.; Rossmann, Michael G.

    2013-02-20

    Enterovirus 71 is a picornavirus that causes hand, foot and mouth disease but may induce fatal neurological illness in infants and young children. Enterovirus 71 crystallized in a body-centered orthorhombic space group with two particles in general orientations in the crystallographic asymmetric unit. Determination of the particle orientations required that the locked rotation function excluded the twofold symmetry axes from the set of icosahedral symmetry operators. This avoided the occurrence of misleading high rotation-function values produced by the alignment of icosahedral and crystallographic twofold axes. Once the orientations and positions of the particles had been established, the structure was solved by molecular replacement and phase extension.

  14. High energy x-ray scattering studies of the local order in liquid Al

    SciTech Connect

    Mauro, N.A.; Bendert, J.C.; Vogt, A.J.; Gewin, J.M.; Kelton, K.F.

    2012-10-23

    The x-ray structure factors and densities for liquid aluminum from 1123 K to 1273 K have been measured using the beamline electrostatic levitator. Atomic structures as a function of temperature have been constructed from the diffraction data with reverse Monte Carlo simulations. An analysis of the local atomic structures in terms of the Honeycutt-Andersen indices indicates a high degree of icosahedral and distorted icosahedral order, a modest amount of body-centered cubic order, and marginal amounts of face-centered cubic and hexagonal close-packed order.

  15. Physical, mechanical, and tribological properties of quasicrystalline Al-Cu-Fe coatings prepared by plasma spraying

    NASA Astrophysics Data System (ADS)

    Lepeshev, A. A.; Rozhkova, E. A.; Karpov, I. V.; Ushakov, A. V.; Fedorov, L. Yu.

    2013-12-01

    The physical, mechanical, and tribological properties of quasicrystalline coatings based on the Al65Cu23Fe12 alloy prepared by plasma spraying have been investigated. The specific features of the phase formation due to the competitive interactions of the icosahedral ψ and cubic β phases have been elucidated. A correlation between the microhardness and the content of the icosahedral phase in the coating has been determined. The decisive role of the quasicrystalline phase in the formation of high tribological characteristics of the coatings has been revealed and tested.

  16. SimulaTEM: multislice simulations for general objects.

    PubMed

    Gómez-Rodríguez, A; Beltrán-Del-Río, L M; Herrera-Becerra, R

    2010-01-01

    In this work we present the program SimulaTEM for the simulation of high resolution micrographs and diffraction patterns. This is a program based on the multislice approach that does not assume a periodic object. It can calculate images from finite objects, from amorphous samples, from crystals, quasicrystals, grain boundaries, nanoparticles or arbitrary objects provided the coordinates of all the atoms can be supplied.

  17. Quasicrystalline particulate reinforced aluminum composite

    SciTech Connect

    Anderson, I.E.; Biner, S.B.; Sordelet, D.J.; Unal, O.

    1997-07-01

    Particulate reinforced aluminum and aluminum alloy composites are rapidly emerging as new commercial materials for aerospace, automotive, electronic packaging and other high performance applications. However, their low processing ductility and difficulty in recyclability have been the key concern. In this study, two composite systems having the same aluminum alloy matrix, one reinforced with quasicrystals and the other reinforced with the conventional SiC reinforcements were produced with identical processing routes. Their processing characteristics and tensile mechanical properties were compared.

  18. Quantum and spectral properties of the Labyrinth model

    NASA Astrophysics Data System (ADS)

    Takahashi, Yuki

    2016-06-01

    We consider the Labyrinth model, which is a two-dimensional quasicrystal model. We show that the spectrum of this model, which is known to be a product of two Cantor sets, is an interval for small values of the coupling constant. We also consider the density of states measure of the Labyrinth model and show that it is absolutely continuous with respect to Lebesgue measure for almost all values of coupling constants in the small coupling regime.

  19. A correspondence principle

    NASA Astrophysics Data System (ADS)

    Hughes, Barry D.; Ninham, Barry W.

    2016-02-01

    A single mathematical theme underpins disparate physical phenomena in classical, quantum and statistical mechanical contexts. This mathematical "correspondence principle", a kind of wave-particle duality with glorious realizations in classical and modern mathematical analysis, embodies fundamental geometrical and physical order, and yet in some sense sits on the edge of chaos. Illustrative cases discussed are drawn from classical and anomalous diffusion, quantum mechanics of single particles and ideal gases, quasicrystals and Casimir forces.

  20. Diffraction pattern of modulated structures described by Bessel functions

    NASA Astrophysics Data System (ADS)

    Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw

    2016-05-01

    We performed detailed analysis of 1D modulated structure (MS) with harmonic modulation within the statistical approach. By applying two-mode Fourier transform, we were able to derive analytically the structure factor for MS with single harmonic modulation component. We confirmed in a very smooth way that ordinary Bessel functions of the first kind define envelopes tuning the intensities of the diffraction peaks. This applies not only to main reflections of the diffraction pattern but also to all satellites. In the second part, we discussed in details the similarities between harmonically modulated structures with multiple modulations and 1D model quasicrystal. The Fourier expansion of the nodes' positions in the Fibonacci chain gives direct numerical definition of the atomic arrangement in MS. In that sense, we can define 1D quasicrystal as a MS with infinite number of harmonic modulations. We prove that characteristic measures (like v(u) relation typical for statistical approach and diffraction pattern) calculated for MS asymptotically approach their counterparts for 1D quasicrystal as large enough number of modulation terms is taken into account.

  1. Quasi crystals: Studies of stability and phason relaxation

    SciTech Connect

    Gronlund, L.D.

    1989-01-01

    This dissertation is in two distinct parts. In chapter I the author considers a simple model of solidification based on Landau theory and investigates whether this model can have stable or metastable quasicrystalline solutions. The model is that proposed by Kalugin, Kitaev, and Levitov with an additional local quartic term in the free energy. In this case, the body-centered cubic (bcc) crystal is the global minimum. He assesses the stability of the quasicrystalline solutions and shows that they are not even metastable, being unstable against a collapse to the bcc crystal. In chapter II he proposes a simple model for phason dynamics in quasicrystals. Phason shifts in the Penrose tiling model of quasicrystals appear as flips of rows of tiles, known as worms. When worms cross one another a hierarchy is established in which some of the worms cannot flip until others have. A complex set of constraints on worm flips is thereby introduced by the intricate pattern of worm crossings in quasicrystalline tilings. He introduces a simple model of interacting sets of one-dimensional Ising chains that mimics this set of constraints and study the possible consequences of these constraints for phason dynamics and the relaxation of phason strain in quasicrystals.

  2. Draft Genome Sequence of Tokyovirus, a Member of the Family Marseilleviridae Isolated from the Arakawa River of Tokyo, Japan

    PubMed Central

    2016-01-01

    Members of the Marseilleviridae family are large DNA viruses with icosahedral particles that infect Acanthamoeba cells. This report presents a new Marseilleviridae family member discovered in a water/soil sample from a river in Tokyo, named Tokyovirus, with genome size of 370 to 380 kb. PMID:27284144

  3. Effects of Oxygen Impurities on Glass-Formation Ability in Zr2Cu Alloy.

    PubMed

    Wang, Zhanyu; Huang, Li; Yue, G Q; Shen, B; Dong, F; Zhang, R J; Zheng, Y X; Wang, S Y; Wang, C Z; Kramer, M J; Ho, K M; Chen, L Y

    2016-09-01

    Using ab initio molecular dynamics simulations, we show that oxygen (O) impurities have a noticeable influence on the glass-formation ability (GFA) in Zr2Cu alloy. Cu-centered icosahedral clusters and Zr-centered Kasper polyhedra are the dominate short-range orders in undercooled Zr2Cu liquid which are most likely to be responsible for the glass formation in Zr2Cu systems. When O is introduced, a Zr octahedron is formed around the O impurity. Most of the Zr atoms in the octahedron also serve as the bridging atoms for cross-linked Kasper polyhedral network, resulting in an O-centered medium range order (MRO) structure. Meanwhile, Cu atoms are moved away from the first shell of O-centered octahedral clusters. With 1 at. % O impurities, the fractions of Zr-centered clusters are less affected, while the increase of ideal icosahedral order and decrease of distorted icosahedral order lead to a more stable atomic structure. This result suggests that a low concentration of O impurities would improve the GFA in Zr2Cu alloy. However, when ∼5 at. % O impurities are included, the ideal icosahedral clusters and Zr-centered Kasper polyhedra are seriously suppressed by the formation of O-centered MRO, which can lead to deterioration of GFA. Our analyses provide useful insight into glass formation behavior in O-doped metallic alloy systems. PMID:27509394

  4. Smooth scaling of valence electronic properties in fullerenes: From one carbon atom, to C60, to graphene

    NASA Astrophysics Data System (ADS)

    Lewis, Greyson R.; Bunting, William E.; Zope, Rajendra R.; Dunlap, Brett I.; Ellenbogen, James C.

    2013-05-01

    Scaling of quantum capacitances and valence electron detachment energies is studied for icosahedral and nonicosahedral fullerenes. Scaling trends are considered from zero to infinite average radius, where a fullerene's local surface properties are similar to those of graphene. Detailed density-functional-theory calculations are performed to determine the geometries and detachment energies of icosahedral fullerenes, while values of these quantities are obtained for nonicosahedral species from previously published experimental results. Strongly linear, quasiclassical scaling versus average radii r¯n is seen for the quantum capacitances, but on two different scaling lines for icosahedral and nonicosahedral species, respectively. By contrast, nonclassical, nonlinear scaling versus 1/r¯n is seen for the electron detachment energies, i.e., the valence ionization potentials and electron affinities. This nonlinearity is not accounted for by classical theories that are used to explain trends in electronic properties of fullerenes and usually give accurate quantitative estimates. Instead, simple quantum equations are derived to account for nonlinearities in the metal-particle-like electron detachment energy scaling and to show that these are responsible for nonclassical, nonzero intercepts in the capacitance scaling lines of the fullerenes. Last, it is found that points representing the carbon atom and the graphene limit lie on scaling lines for icosahedral fullerenes, so their quantum capacitances and their detachment energies scale smoothly from one C atom, to C60, to graphene.

  5. Design of a hyperstable 60-subunit protein icosahedron.

    PubMed

    Hsia, Yang; Bale, Jacob B; Gonen, Shane; Shi, Dan; Sheffler, William; Fong, Kimberly K; Nattermann, Una; Xu, Chunfu; Huang, Po-Ssu; Ravichandran, Rashmi; Yi, Sue; Davis, Trisha N; Gonen, Tamir; King, Neil P; Baker, David

    2016-07-01

    The icosahedron is the largest of the Platonic solids, and icosahedral protein structures are widely used in biological systems for packaging and transport. There has been considerable interest in repurposing such structures for applications ranging from targeted delivery to multivalent immunogen presentation. The ability to design proteins that self-assemble into precisely specified, highly ordered icosahedral structures would open the door to a new generation of protein containers with properties custom-tailored to specific applications. Here we describe the computational design of a 25-nanometre icosahedral nanocage that self-assembles from trimeric protein building blocks. The designed protein was produced in Escherichia coli, and found by electron microscopy to assemble into a homogenous population of icosahedral particles nearly identical to the design model. The particles are stable in 6.7 molar guanidine hydrochloride at up to 80 degrees Celsius, and undergo extremely abrupt, but reversible, disassembly between 2 molar and 2.25 molar guanidinium thiocyanate. The icosahedron is robust to genetic fusions: one or two copies of green fluorescent protein (GFP) can be fused to each of the 60 subunits to create highly fluorescent ‘standard candles’ for use in light microscopy, and a designed protein pentamer can be placed in the centre of each of the 20 pentameric faces to modulate the size of the entrance/exit channels of the cage. Such robust and customizable nanocages should have considerable utility in targeted drug delivery, vaccine design and synthetic biology. PMID:27309817

  6. Advanced quadratures and periodic boundary conditions in parallel 3D S{sub n} transport

    SciTech Connect

    Manalo, K.; Yi, C.; Huang, M.; Sjoden, G.

    2013-07-01

    Significant updates in numerical quadratures have warranted investigation with 3D Sn discrete ordinates transport. We show new applications of quadrature departing from level symmetric (S{sub 2}o). investigating 3 recently developed quadratures: Even-Odd (EO), Linear-Discontinuous Finite Element - Surface Area (LDFE-SA), and the non-symmetric Icosahedral Quadrature (IC). We discuss implementation changes to 3D Sn codes (applied to Hybrid MOC-Sn TITAN and 3D parallel PENTRAN) that can be performed to accommodate Icosahedral Quadrature, as this quadrature is not 90-degree rotation invariant. In particular, as demonstrated using PENTRAN, the properties of Icosahedral Quadrature are suitable for trivial application using periodic BCs versus that of reflective BCs. In addition to implementing periodic BCs for 3D Sn PENTRAN, we implemented a technique termed 'angular re-sweep' which properly conditions periodic BCs for outer eigenvalue iterative loop convergence. As demonstrated by two simple transport problems (3-group fixed source and 3-group reflected/periodic eigenvalue pin cell), we remark that all of the quadratures we investigated are generally superior to level symmetric quadrature, with Icosahedral Quadrature performing the most efficiently for problems tested. (authors)

  7. Theory of morphological transformation of viral capsid shell during the maturation process in the HK97 bacteriophage and similar viruses

    NASA Astrophysics Data System (ADS)

    Konevtsova, O. V.; Lorman, V. L.; Rochal, S. B.

    2016-05-01

    We consider the symmetry and physical origin of collective displacement modes playing a crucial role in the morphological transformation during the maturation of the HK97 bacteriophage and similar viruses. It is shown that the experimentally observed hexamer deformation and pentamer twist in the HK97 procapsid correspond to the simplest irreducible shear strain mode of a spherical shell. We also show that the icosahedral faceting of the bacteriophage capsid shell is driven by the simplest irreducible radial displacement field. The shear field has the rotational icosahedral symmetry group I while the radial field has the full icosahedral symmetry Ih. This difference makes their actions independent. The radial field sign discriminates between the icosahedral and the dodecahedral shapes of the faceted capsid shell, thus making the approach relevant not only for the HK97-like viruses but also for the parvovirus family. In the frame of the Landau-Ginzburg formalism we propose a simple phenomenological model valid for the first reversible step of the HK97 maturation process. The calculated phase diagram illustrates the discontinuous character of the virus shape transformation. The characteristics of the virus shell faceting and expansion obtained in the in vitro and in vivo experiments are related to the decrease in the capsid shell thickness and to the increase of the internal capsid pressure.

  8. Theory of morphological transformation of viral capsid shell during the maturation process in the HK97 bacteriophage and similar viruses.

    PubMed

    Konevtsova, O V; Lorman, V L; Rochal, S B

    2016-05-01

    We consider the symmetry and physical origin of collective displacement modes playing a crucial role in the morphological transformation during the maturation of the HK97 bacteriophage and similar viruses. It is shown that the experimentally observed hexamer deformation and pentamer twist in the HK97 procapsid correspond to the simplest irreducible shear strain mode of a spherical shell. We also show that the icosahedral faceting of the bacteriophage capsid shell is driven by the simplest irreducible radial displacement field. The shear field has the rotational icosahedral symmetry group I while the radial field has the full icosahedral symmetry I_{h}. This difference makes their actions independent. The radial field sign discriminates between the icosahedral and the dodecahedral shapes of the faceted capsid shell, thus making the approach relevant not only for the HK97-like viruses but also for the parvovirus family. In the frame of the Landau-Ginzburg formalism we propose a simple phenomenological model valid for the first reversible step of the HK97 maturation process. The calculated phase diagram illustrates the discontinuous character of the virus shape transformation. The characteristics of the virus shell faceting and expansion obtained in the in vitro and in vivo experiments are related to the decrease in the capsid shell thickness and to the increase of the internal capsid pressure.

  9. Fourth class of convex equilateral polyhedron with polyhedral symmetry related to fullerenes and viruses.

    PubMed

    Schein, Stan; Gayed, James Maurice

    2014-02-25

    The three known classes of convex polyhedron with equal edge lengths and polyhedral symmetry--tetrahedral, octahedral, and icosahedral--are the 5 Platonic polyhedra, the 13 Archimedean polyhedra--including the truncated icosahedron or soccer ball--and the 2 rhombic polyhedra reported by Johannes Kepler in 1611. (Some carbon fullerenes, inorganic cages, icosahedral viruses, geodesic structures, and protein complexes resemble these fundamental shapes.) Here we add a fourth class, "Goldberg polyhedra," which are also convex and equilateral. We begin by decorating each of the triangular facets of a tetrahedron, an octahedron, or an icosahedron with the T vertices and connecting edges of a "Goldberg triangle." We obtain the unique set of internal angles in each planar face of each polyhedron by solving a system of n equations and n variables, where the equations set the dihedral angle discrepancy about different types of edge to zero, and the variables are a subset of the internal angles in 6gons. Like the faces in Kepler's rhombic polyhedra, the 6gon faces in Goldberg polyhedra are equilateral and planar but not equiangular. We show that there is just a single tetrahedral Goldberg polyhedron, a single octahedral one, and a systematic, countable infinity of icosahedral ones, one for each Goldberg triangle. Unlike carbon fullerenes and faceted viruses, the icosahedral Goldberg polyhedra are nearly spherical. The reasoning and techniques presented here will enable discovery of still more classes of convex equilateral polyhedra with polyhedral symmetry.

  10. Complete genome sequence of the podoviral bacteriophage CP24R virulent for Clostridium perfringens

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Bacteriophage 'CP24R was isolated from raw sewage of a waste treatment plant and lytic activity was observed against a type C Clostridium perfringens isolate. Electron microscopy revealed a small virion (44nm diameter icosahedral capsid) with a short, non-contractile tail, indicative of the family ...

  11. First record of a mosquito iridescent virus in Culex pipiens L. (Diptera: Culicidae)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The mosquito iridescent viruses (MIVs) are large icosahedral DNA viruses that replicate and assemble in the cytoplasm of the host. Paracrystalline arrangements of virions that accumulate in the cytoplasm produce an iridescent color that is symptomatic of acute infections. In August 2010, we found ...

  12. The diversity of the orthoreoviruses: molecular taxonomy and phylogentic divides.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The family Reoviridae is a diverse group of viruses with double-stranded ribonucleic acid (RNA) genomes contained within icosahedral, layered protein capsids. Within the Reoviridae, the Orthoreovirus genus includes viruses that infect reptiles, birds and mammals (including humans). Recent sequencing...

  13. Relevance of capsid structure in the buckling and maturation of spherical viruses

    NASA Astrophysics Data System (ADS)

    Aznar, María; Luque, Antoni; Reguera, David

    2012-06-01

    The shape and mechanical properties of viral capsids play an important role in several biological processes during the virus life cycle. In particular, to become infective, many viruses require a maturation stage where the capsid undergoes a buckling transition, from an initial spherical procapsid into a final icosahedral faceted shell. Here we study, using a minimal physical model, how the capsid shape and the buckling transition depend on the triangulation number T and the icosahedral class P of the virus structure. We find that, for small shells, capsids with P = 1 are most likely to produce polyhedral shapes that minimize their energy and accumulated stress, whereas viruses with P = 3 prefer to remain spherical. For big capsids, all shells are more stable adopting an icosahedral shape, in agreement with continuum elastic theory. Moreover, spherical viruses show a buckling transition to polyhedral shells under expansion, in consonance with virus maturation. The resulting icosahedral shell is mechanically stiffer, tolerates larger expansions and withstands higher internal pressures before failing, which could explain why some dsDNA viruses, which rely on the pressurization of their genetic material to facilitate the infection, undergo a buckling transition. We emphasize that the results are general and could also be applied to non-biological systems.

  14. Relevance of capsid structure in the buckling and maturation of spherical viruses.

    PubMed

    Aznar, María; Luque, Antoni; Reguera, David

    2012-06-01

    The shape and mechanical properties of viral capsids play an important role in several biological processes during the virus life cycle. In particular, to become infective, many viruses require a maturation stage where the capsid undergoes a buckling transition, from an initial spherical procapsid into a final icosahedral faceted shell. Here we study, using a minimal physical model, how the capsid shape and the buckling transition depend on the triangulation number T and the icosahedral class P of the virus structure. We find that, for small shells, capsids with P = 1 are most likely to produce polyhedral shapes that minimize their energy and accumulated stress, whereas viruses with P = 3 prefer to remain spherical. For big capsids, all shells are more stable adopting an icosahedral shape, in agreement with continuum elastic theory. Moreover, spherical viruses show a buckling transition to polyhedral shells under expansion, in consonance with virus maturation. The resulting icosahedral shell is mechanically stiffer, tolerates larger expansions and withstands higher internal pressures before failing, which could explain why some dsDNA viruses, which rely on the pressurization of their genetic material to facilitate the infection, undergo a buckling transition. We emphasize that the results are general and could also be applied to non-biological systems.

  15. Three-dimensional structure of scaffolding-containing phage p22 procapsids by electron cryo-microscopy.

    PubMed

    Thuman-Commike, P A; Greene, B; Jakana, J; Prasad, B V; King, J; Prevelige, P E; Chiu, W

    1996-07-01

    The procapsids of bacterial viruses are the products of the polymerization of coat and scaffolding subunits, as well as the precursors in DNA packaging. Electron cryo-microscopy has been used to study the three-dimensional structures of bacteriophage P22 procapsids containing wild-type and mutant scaffolding proteins. The scaffolding mutant structure has been resolved to 19 A resolution and agrees with the 22 A resolution wild-type procapsid reconstruction. Both procapsid reconstructions contain an outer icosahedral coat protein shell and an inner scaffolding protein core. The outer core protein forms a T = 7 icosahedral lattice with distinctive channels present at the centers of the pentons and hexons. In addition, the hexons display a prominent skew. Computational isolation of the skewed hexon shows the presence of a local 2-fold axis that reduces the number of unique conformations in the asymmetric unit to four at this resolution. We have classified the four unique subunits into three distinct classes, based upon the shape of the upper domain and the presence of a channel leading to the inner coat protein surface. In addition, at the inner surface of the coat protein, finger-like regions that extend towards the scaffolding protein core are present in two of the subunits. The finger-like regions suggest the presence of an ordered interaction between the inner coat protein and the scaffolding protein. However, an icosahedral scaffolding protein shell is not formed, and the innermost scaffolding protein core does not pack with icosahedral symmetry. PMID:8676394

  16. Design of a hyperstable 60-subunit protein icosahedron

    NASA Astrophysics Data System (ADS)

    Hsia, Yang; Bale, Jacob B.; Gonen, Shane; Shi, Dan; Sheffler, William; Fong, Kimberly K.; Nattermann, Una; Xu, Chunfu; Huang, Po-Ssu; Ravichandran, Rashmi; Yi, Sue; Davis, Trisha N.; Gonen, Tamir; King, Neil P.; Baker, David

    2016-07-01

    The icosahedron is the largest of the Platonic solids, and icosahedral protein structures are widely used in biological systems for packaging and transport. There has been considerable interest in repurposing such structures for applications ranging from targeted delivery to multivalent immunogen presentation. The ability to design proteins that self-assemble into precisely specified, highly ordered icosahedral structures would open the door to a new generation of protein containers with properties custom-tailored to specific applications. Here we describe the computational design of a 25-nanometre icosahedral nanocage that self-assembles from trimeric protein building blocks. The designed protein was produced in Escherichia coli, and found by electron microscopy to assemble into a homogenous population of icosahedral particles nearly identical to the design model. The particles are stable in 6.7 molar guanidine hydrochloride at up to 80 degrees Celsius, and undergo extremely abrupt, but reversible, disassembly between 2 molar and 2.25 molar guanidinium thiocyanate. The icosahedron is robust to genetic fusions: one or two copies of green fluorescent protein (GFP) can be fused to each of the 60 subunits to create highly fluorescent ‘standard candles’ for use in light microscopy, and a designed protein pentamer can be placed in the centre of each of the 20 pentameric faces to modulate the size of the entrance/exit channels of the cage. Such robust and customizable nanocages should have considerable utility in targeted drug delivery, vaccine design and synthetic biology.

  17. Twenty-four near-instabilities of Caspar-Klug viruses

    NASA Astrophysics Data System (ADS)

    Englert, François; Peeters, Kasper; Taormina, Anne

    2008-09-01

    Group theoretical arguments combined with normal mode analysis techniques are applied to a coarse-grained approximation of icosahedral viral capsids which incorporates areas of variable flexibility. This highlights a remarkable structure of the low-frequency spectrum in this approximation, namely, the existence of a plateau of 24 near zero modes with universal group theory content.

  18. Twenty-four near-instabilities of Caspar-Klug viruses.

    PubMed

    Englert, François; Peeters, Kasper; Taormina, Anne

    2008-09-01

    Group theoretical arguments combined with normal mode analysis techniques are applied to a coarse-grained approximation of icosahedral viral capsids which incorporates areas of variable flexibility. This highlights a remarkable structure of the low-frequency spectrum in this approximation, namely, the existence of a plateau of 24 near zero modes with universal group theory content. PMID:18851066

  19. New insights into the enigma of boron carbide inverse molecular behavior

    SciTech Connect

    Dera, Przemyslaw; Manghnani, Murli H.; Hushur, Anwar; Hu, Yi; Tkachev, Sergey

    2014-07-01

    Equation of state and compression mechanism of nearly stoichiometric boron carbide B{sub 4}C were investigated using diamond anvil cell single crystal synchrotron X-ray diffraction technique up to a maximum quasi-hydrostatic pressure of 74.0(1) GPa in neon pressure transmitting medium at ambient temperature. No signatures of structural phase transitions were observed on compression. Crystal structure refinements indicate that the icosahedral units are less compressible (13% volume reduction at 60 GPa) than the unit cell volume (18% volume reduction at 60 GPa), contrary to expectations based on the inverse molecular behavior hypothesis, but consistent with spectroscopic evidence and first principles calculations. The high-pressure crystallographic refinements reveal that the nature of the chemical bonds (two, versus three centered character) has marginal effect on the bond compressibility and the compression of the crystal is mainly governed by the force transfer between the rigid icosahedral structural units. - Graphical abstract: Single crystal measurements of equation of state and compression mechanism of B{sub 4}C show that the icosahedral units are less compressibe than the unit cell volume, despite the threei-ceneterd nature of some icosahedral bonds. - Highlights: • Equation of state and compression mechanism of B{sub 4}C were measured to 75 GPa. • No signatures of structural phase transitions were observed on compression. • Icosahedral units are less compressibe than the unit cell volume. • The nature of the chemical bonds has mariginal effect on the bond compressibility. • The compression is governed by force transfer between the rigid icosahedra.

  20. EXAFS and Computer Modeling Studies of the Structures of Aperiodic Crystals.

    NASA Astrophysics Data System (ADS)

    Ma, Yanjun

    EXAFS technique and computer modeling are used to investigate the structures of the aperiodic alloys, including icosahedral Al-Mn-(Si), Al-(Fe,Mn)-Si, Al-Cu -Li and decagonal Al-Mn, Al-(Fe,Mn) alloys. Some related crystalline compounds, including Al_4Mn, beta-AlMnSi, and Al_ {12}Mn, are also studied. Through comparisons with closely related crystalline compounds, particularly alpha-AlMnSi and R-AlCuLi, a good understanding of the local structures of the aperiodic alloys around TM elements is obtained. We identified the structural units in i-AlMnSi and in i-AlCuLi type of icosahedral alloys as a Mackay icosahedron (MI) of 54 atoms and a truncated icosahedron of about 104 atoms, respectively. The dimensions of the units are given. In addition, information concerning the connection between these units in the icosahedral phases is obtained. It is found that in i-AlMnSi each MI has a coordination of about seven as opposed to the eight in alpha -AlMnSi. The connection between the MI in the i -phase is also somewhat disordered. A new technique of EXAFS data analysis is applied to yield the radial distribution function of the aperiodic alloys. This technique is especially effective in studying non-gaussian distributions, and will have wide applications in EXAFS studies of the structures of amorphous metals. Close similarities between the Mn shells of i -AlMnSi and those of alpha-AlMnSi indicate that the cubic distortion of the MI in alpha-MlMnSi remains in i-AlMnSi. It is thus concluded that small cubic regions of size about 40 A exist in the icosahedral phase. Based on the EXAFS results two models for the structure of the icosahedral phase are presented. One is a randomly connected icosahedra model. In the second model, microcrystallites are added to the first one to simulate the EXAFS results that small crystallites exist in the i-phase. It is found by computer simulation that the second model improves many properties of the first model and is in better agreement with