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Sample records for plastic crystal phase

  1. Plasticity and beyond microstructures, crystal-plasticity and phase transitions

    CERN Document Server

    Hackl, Klaus

    2014-01-01

    The book presents the latest findings in experimental plasticity, crystal plasticity, phase transitions, advanced mathematical modeling of finite plasticity and multi-scale modeling. The associated algorithmic treatment is mainly based on finite element formulations for standard (local approach) as well as for non-standard (non-local approach) continua and for pure macroscopic as well as for directly coupled two-scale boundary value problems. Applications in the area of material design/processing are covered, ranging from grain boundary effects in polycrystals and phase transitions to deep-drawing of multiphase steels by directly taking into account random microstructures.

  2. Intermittent dislocation density fluctuations in crystal plasticity from a phase-field crystal model

    DEFF Research Database (Denmark)

    Tarp, Jens M.; Angheluta, Luiza; Mathiesen, Joachim;

    2014-01-01

    Plastic deformation mediated by collective dislocation dynamics is investigated in the two-dimensional phase-field crystal model of sheared single crystals. We find that intermittent fluctuations in the dislocation population number accompany bursts in the plastic strain-rate fluctuations. Disloc...

  3. Phase field crystal study of deformation and plasticity in nanocrystalline materials.

    Science.gov (United States)

    Stefanovic, Peter; Haataja, Mikko; Provatas, Nikolas

    2009-10-01

    We introduce a modified phase field crystal (MPFC) technique that self-consistently incorporates rapid strain relaxation alongside the usual plastic deformation and multiple crystal orientations featured by the traditional phase field crystal (PFC) technique. Our MPFC formalism can be used to study a host of important phase transformation phenomena in material processing that require rapid strain relaxation. We apply the MPFC model to study elastic and plastic deformations in nanocrystalline materials, focusing on the "reverse" Hall-Petch effect. Finally, we introduce a multigrid algorithm for efficient numerical simulations of the MPFC model.

  4. Creating physically-based three-dimensional microstructures: Bridging phase-field and crystal plasticity models.

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Hojun [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Owen, Steven J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Abdeljawad, Fadi F. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Hanks, Byron [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Battaile, Corbett Chandler [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    In order to better incorporate microstructures in continuum scale models, we use a novel finite element (FE) meshing technique to generate three-dimensional polycrystalline aggregates from a phase field grain growth model of grain microstructures. The proposed meshing technique creates hexahedral FE meshes that capture smooth interfaces between adjacent grains. Three dimensional realizations of grain microstructures from the phase field model are used in crystal plasticity-finite element (CP-FE) simulations of polycrystalline a -iron. We show that the interface conformal meshes significantly reduce artificial stress localizations in voxelated meshes that exhibit the so-called "wedding cake" interfaces. This framework provides a direct link between two mesoscale models - phase field and crystal plasticity - and for the first time allows mechanics simulations of polycrystalline materials using three-dimensional hexahedral finite element meshes with realistic topological features.

  5. Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

    Science.gov (United States)

    Moore, John A.; Barton, Nathan R.; Florando, Jeff; Mulay, Rupalee; Kumar, Mukul

    2017-10-01

    Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material’s structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V’s mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments or lower fidelity models. The results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.

  6. A High-Rate, Single-Crystal Model including Phase Transformations, Plastic Slip, and Twinning

    Energy Technology Data Exchange (ETDEWEB)

    Addessio, Francis L. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Bronkhorst, Curt Allan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Bolme, Cynthia Anne [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Explosive Science and Shock Physics Division; Brown, Donald William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Cerreta, Ellen Kathleen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Lebensohn, Ricardo A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Lookman, Turab [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Luscher, Darby Jon [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Mayeur, Jason Rhea [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Morrow, Benjamin M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Rigg, Paulo A. [Washington State Univ., Pullman, WA (United States). Dept. of Physics. Inst. for Shock Physics

    2016-08-09

    An anisotropic, rate-­dependent, single-­crystal approach for modeling materials under the conditions of high strain rates and pressures is provided. The model includes the effects of large deformations, nonlinear elasticity, phase transformations, and plastic slip and twinning. It is envisioned that the model may be used to examine these coupled effects on the local deformation of materials that are subjected to ballistic impact or explosive loading. The model is formulated using a multiplicative decomposition of the deformation gradient. A plate impact experiment on a multi-­crystal sample of titanium was conducted. The particle velocities at the back surface of three crystal orientations relative to the direction of impact were measured. Molecular dynamics simulations were conducted to investigate the details of the high-­rate deformation and pursue issues related to the phase transformation for titanium. Simulations using the single crystal model were conducted and compared to the high-­rate experimental data for the impact loaded single crystals. The model was found to capture the features of the experiments.

  7. Crystal Structures and Phase Sequences of Metallocenium Salts with Fluorinated Anions: Effects of Molecular Size and Symmetry on Phase Transitions to Ionic Plastic Crystals.

    Science.gov (United States)

    Mochida, Tomoyuki; Funasako, Yusuke; Ishida, Mai; Saruta, Shingo; Kosone, Takashi; Kitazawa, Takafumi

    2016-10-24

    Sandwich compounds often exhibit various phase transitions, including those to plastic phases. To elucidate the general features of the phase transitions in metallocenium salts, the thermal properties and crystal structures of [Fe(C5 Me5 )2 ]X ([1]X), [Co(C5 Me5 )2 ]X ([2]X), and [Fe(C5 Me4 H)2 ]X ([3]X) have been investigated, where the counter anions (X) are Tf2 N (=(CF3 SO2 )2 N(-) ), OTf (=CF3 SO3(-) ), PF6 , and BF4 . The Tf2 N salts commonly undergo phase transitions from an ordered phase at low temperatures to an anion-disordered phase, followed by a plastic phase and finally melt at high temperatures. All these salts exhibit a phase transition to a plastic phase, and the transition temperature generally decreases with decreasing cation size and increasing anion size. The crystal structures of these salts comprise an alternating arrangement of cations and anions. About half of these salts exhibit phase transitions at low temperatures, which are mostly correlated with the order-disorder of the anion.

  8. Molecular disorder and translation/rotation coupling in the plastic crystal phase of hybrid perovskites.

    Science.gov (United States)

    Even, J; Carignano, M; Katan, C

    2016-03-28

    The complexity of hybrid organic perovskites calls for an innovative theoretical view that combines usually disconnected concepts in order to achieve a comprehensive picture: (i) the intended applications of this class of materials are currently in the realm of conventional semiconductors, which reveal the key desired properties for the design of efficient devices. (ii) The reorientational dynamics of the organic component resembles that observed in plastic crystals, therefore requiring a stochastic treatment that can be done in terms of pseudospins and rotator functions. (iii) The overall structural similarity with all inorganic perovskites suggests the use of the high temperature pseudo cubic phase as the reference platform on which further refinements can be built. In this paper we combine the existing knowledge on these three fields to define a general scenario based on which we can continue the quest towards a fundamental understanding of hybrid organic perovskites. With the introduction of group theory as the main tool to rationalize the different ideas and with the help of molecular dynamics simulations, several experimentally observed properties are naturally explained with possible suggestions for future work.

  9. Terahertz Conductivity and Hindered Molecular Reorientation of Lithium Salt Doped Succinonitrile in its Plastic Crystal Phase

    Science.gov (United States)

    Nickel, Daniel V.; Bian, Hongtao; Zheng, Junrong; Mittleman, Daniel M.

    2014-09-01

    The terahertz complex permittivity of the molecular plastic crystal succinonitrile (SN) or 1,2 dicyanoethane (N≡C-CH2-CH2-C≡N), doped with the lithium salts LiBF4, LiPF6, LiTFSI, and LiClO4 to form solid-state plastic crystal electrolytes, is measured and compared using temperature-dependent terahertz time-domain spectroscopy (THz-TDS). In contrast to the trends at low frequency, SN's terahertz conductivity decreases slightly when doped with Li-salts. This indicates that at high frequencies the dielectric response is not dominated by ionic charge transport, but instead by relaxational processes which are hindered by the presence of the ionic dopants. Assuming a single Cole-Cole distribution of Debye-like processes dominates the measured spectra, the average relaxation times τ and Arrhenius activation energies E a are extracted for each electrolyte and are shown to increase significantly relative to undoped SN's τ and E a, indicating the relaxational processes are hindered by the presence of the ionic dopants.

  10. Computational strain gradient crystal plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2014-01-01

    of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically...

  11. Glassy features of crystal plasticity

    Science.gov (United States)

    Lehtinen, Arttu; Costantini, Giulio; Alava, Mikko J.; Zapperi, Stefano; Laurson, Lasse

    2016-08-01

    Crystal plasticity occurs by deformation bursts due to the avalanchelike motion of dislocations. Here we perform extensive numerical simulations of a three-dimensional dislocation dynamics model under quasistatic stress-controlled loading. Our results show that avalanches are power-law distributed and display peculiar stress and sample size dependence: The average avalanche size grows exponentially with the applied stress, and the amount of slip increases with the system size. These results suggest that intermittent deformation processes in crystalline materials exhibit an extended critical-like phase in analogy to glassy systems instead of originating from a nonequilibrium phase transition critical point.

  12. Size effects in crystal plasticity

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    Numerical analyses of plasticity size effects have been carried out for different problems using a developed strain gradient crystal plasticiy theory. The theory employs higher order stresses as work conjugates to slip gradients and uses higher order boundary conditions. Problems on localization...... of plastic flow in a single crystal, grain boundary effects in a bicrystal, and grain size effects in a polycrystal are studied. Single crystals containing micro-scale voids have also been analyzed at different loading conditions with focus on the stress and deformation fields around the voids, on void...... growth and interaction between neighboring voids, and on a comparison between the developed strain gradient crystal plasticity theory and a discrete dislocation plasticity theory. Furthermore, voids and rigid inclusions in isotropic materials have been studied using a strain gradient plasticity theory...

  13. Coupled Crystal Plasticity-Phase Field Fracture Simulation Study on Damage Evolution Around a Void: Pore Shape Versus Crystallographic Orientation

    Science.gov (United States)

    Diehl, Martin; Wicke, Marcel; Shanthraj, Pratheek; Roters, Franz; Brueckner-Foit, Angelika; Raabe, Dierk

    2017-03-01

    Various mechanisms such as anisotropic plastic flow, damage nucleation, and crack propagation govern the overall mechanical response of structural materials. Understanding how these mechanisms interact, i.e. if they amplify mutually or compete with each other, is an essential prerequisite for the design of improved alloys. This study shows—by using the free and open source software DAMASK (the Düsseldorf Advanced Material Simulation Kit)—how the coupling of crystal plasticity and phase field fracture methods can increase the understanding of the complex interplay between crystallographic orientation and the geometry of a void. To this end, crack initiation and propagation around an experimentally obtained pore with complex shape is investigated and compared to the situation of a simplified spherical void. Three different crystallographic orientations of the aluminum matrix hosting the defects are considered. It is shown that crack initiation and propagation depend in a non-trivial way on crystallographic orientation and its associated plastic behavior as well as on the shape of the pore.

  14. Formation of a solid solution between [N(C2H5)4][BF4] and [N(C2H5)4][PF6] in crystal and plastic crystal phases.

    Science.gov (United States)

    Matsumoto, Kazuhiko; Nonaka, Ryojun; Wang, Yushen; Veryasov, Gleb; Hagiwara, Rika

    2017-01-18

    The phase behavior of [N2222][BF4] and [N2222][PF6] (N2222(+) = tetraethylammonium cation) binary systems has been investigated in the present study. Differential scanning calorimetry revealed that the crystal-to-plastic-crystal transition temperature decreases upon mixing the two salts, with a minimum at x([N2222][PF6]) = 0.4, where x([N2222][PF6]) denotes the molar fraction of [N2222][PF6]. Powder X-ray diffraction analysis indicated the formation of a solid solution with a rock-salt type structure in the plastic crystal phase at all ratios and the lattice parameter a changes according to Vegard's law. In the crystal phase, two solid solution phases based on the structures of the single salts are observed. Raman spectroscopy confirmed the changes in the solid-solid transition temperature as observed by differential scanning calorimetry. Consequently, in the resulting phase diagram, the solid solution is formed in a wide x([N2222][PF6]) range for both the crystal and plastic crystal phases.

  15. Multiple glass transitions in the plastic crystal phase of triphenylene derivates

    NARCIS (Netherlands)

    Yildirim, Z.; Wubbenhorst, M.; Mendes, E.; Picken, S.J.; Paraschiv, I.; Marcelis, A.T.M.; Zuilhof, H.; Sudhölter, E.J.R.

    2005-01-01

    The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a

  16. Computational Strain Gradient Crystal Plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2011-01-01

    A model for strain gradient crystal visco-plasticity is formulated along the lines proposed by Fleck andWillis (2009) for isotropic plasticity. Size-effects are included in the model due to the addition of gradient terms in both the free energy as well as through a dissipation potential. A finite...... element solution method is presented, which delivers the slip-rate field and the velocity-field based on two minimum principles. Some plane deformation problems relevant for certain specific orientations of a face centered cubic crystal under plane loading conditions are studied, and effective in......-plane parameters are developed based on the crystallographic properties of the material. The problem of cyclic shear of a single crystal between rigid platens is studied as well as void growth of a cylindrical void....

  17. Individual phase constitutive properties of a TRIP-assisted QP980 steel from a combined synchrotron X-ray diffraction and crystal plasticity approach

    Energy Technology Data Exchange (ETDEWEB)

    Hu, X. H.; Sun, X.; Hector, L. G.; Ren, Y.

    2017-06-01

    Microstructure-based constitutive models for multiphase steels require accurate constitutive properties of the individual phases for component forming and performance simulations. We address this requirement with a combined experimental/theoretical methodology which determines the critical resolved shear stresses and hardening parameters of the constituent phases in QP980, a TRIP assisted steel subject to a two-step quenching and partitioning heat treatment. High energy X-Ray diffraction (HEXRD) from a synchrotron source provided the average lattice strains of the ferrite, martensite, and austenite phases from the measured volume during in situ tensile deformation. The HEXRD data was then input to a computationally efficient, elastic-plastic self-consistent (EPSC) crystal plasticity model which estimated the constitutive parameters of different slip systems for the three phases via a trial-and-error approach. The EPSC-estimated parameters are then input to a finite element crystal plasticity (CPFE) model representing the QP980 tensile sample. The predicted lattice strains and global stress versus strain curves are found to be 8% lower that the EPSC model predicted values and from the HEXRD measurements, respectively. This discrepancy, which is attributed to the stiff secant assumption in the EPSC formulation, is resolved with a second step in which CPFE is used to iteratively refine the EPSC-estimated parameters. Remarkably close agreement is obtained between the theoretically-predicted and experimentally derived flow curve for the QP980 material.

  18. Changes in mobility of plastic crystal ethanol during its transformation into the monoclinic crystal state

    Energy Technology Data Exchange (ETDEWEB)

    Sanz, Alejandro, E-mail: alejandro.sanz@csic.es; Nogales, Aurora; Ezquerra, Tiberio A. [Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006 Madrid (Spain); Puente-Orench, Inés [Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9 (France); Instituto de Ciencia de Materiales de Aragón, ICMA-CSIC, Pedro Cerbuna 12, 50009 Zaragoza (Spain); Jiménez-Ruiz, Mónica [Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9 (France)

    2014-02-07

    Transformation of deuterated ethanol from the plastic crystal phase into the monoclinic one is investigated by means of a singular setup combining simultaneously dielectric spectroscopy with neutron diffraction. We postulate that a dynamic transition from plastic crystal to supercooled liquid-like configuration through a deep reorganization of the hydrogen-bonding network must take place as a previous step of the crystallization process. Once these precursor regions are formed, subsequent crystalline nucleation and growth develop with time.

  19. Plasticity size effects in voided crystals

    DEFF Research Database (Denmark)

    Hussein, M. I.; Borg, Ulrik; Niordson, Christian Frithiof;

    The shear and equi-biaxial straining responses of periodic voided single crystals are analysed using discrete dislocation plasticity and a continuum strain gradient crystal plasticity theory. In the discrete dislocation formulation the dislocations are all of edge character and are modelled as line...... predictions of the two formulations for all crystal types and void volume fractions considered when the material length scale in the non-local plasticity model chosen to be $0.325\\mu m$ (around ten times the slip plane spacing in the discrete dislocation models)....

  20. influence of the molecular structures on the high-pressure and low-temperature phase transitions of plastic crystals.

    Science.gov (United States)

    Wunschel, Markus; Dinnebier, Robert E; Carlson, Stefan; Bernatowicz, Piotr; van Smaalen, Sander

    2003-02-01

    The crystal structures of tert-butyl-tris(trimethylsilyl)silane, Si[C(CH(3))(3)](1)[Si(CH(3))(3)](3) (Bu1), and di-tert-butyl-bis(trimethylsilyl)silane, Si[C(CH(3))(3)](2)[Si(CH(3))(3)](2) (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm3m symmetry (Z = 4) with a = 13.2645 (2) A, V = 2333.87 (4) A(3) for Bu1 and a = 12.9673 (1) A, V = 2180.46 (3) A(3) for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational disorder. Upon cooling both compounds undergo a first-order phase transition at temperatures T(c) = 230 (5) K (Bu1) and T(c) = 250 (5) K (Bu2) into monoclinic structures with space group P2(1)/n. The structures at 105 K have a = 17.317 (1), b = 15.598 (1), c = 16.385 (1) A, gamma = 109.477 (4) degrees, V = 4172.7 (8) A(3) and Z = 8 for Bu1and a = 17.0089 (9), b = 15.3159 (8), c = 15.9325 (8) A, gamma = 110.343 (3) degrees, V = 3891.7 (5) A(3) and Z = 8 for Bu2. The severe disorder of the room-temperature phase is significantly decreased and only a two- or threefold rotational disorder of the molecules remains at 105 K. First-order phase transitions have been observed at pressures of 0.13-0.28 GPa for Bu1 and 0.20-0.24 GPa for Bu2. The high-pressure structures are isostructural to the low-temperature structures. The pressure dependencies of the unit-cell Volumes were fitted with Vinet equations of state and the bulk moduli were obtained. At still higher pressures further anomalies in the pressure dependencies of the lattice parameters were observed. These anomalies are explained as additional disorder-order phase transitions.

  1. New insights into the thermal behaviour of organic ionic plastic crystals: magnetic resonance imaging of polycrystalline morphology alterations induced by solid-solid phase transitions.

    Science.gov (United States)

    Romanenko, Konstantin; Pringle, Jennifer M; O'Dell, Luke A; Forsyth, Maria

    2015-07-15

    Organic ionic plastic crystals (OIPCs) show strong potential as solid-state electrolytes for lithium battery applications, demonstrating promising electrochemical performance and eliminating the need for a volatile and flammable liquid electrolyte. The ionic conductivity (σ) in these systems has recently been shown to depend strongly on polycrystalline morphology, which is largely determined by the sample's thermal history. [K. Romanenko et al., J. Am. Chem. Soc., 2014, 136, 15638]. Tailoring this morphology could lead to conductivities sufficiently high for battery applications, so a more complete understanding of how phenomena such as solid-solid phase transitions can affect the sample morphology is of significant interest. Anisotropic relaxation of nuclear spin magnetisation provides a new MRI based approach for studies of polycrystalline materials at both a macroscopic and molecular level. In this contribution, morphology alterations induced by solid-solid phase transitions in triisobutyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1444FSI) and diethyl(methyl)(isobutyl)phosphonium hexafluorophosphate (P1224PF6) are examined using magnetic resonance imaging (MRI), alongside nuclear magnetic resonance (NMR) spectroscopy, diffusion measurements and conductivity data. These observations are linked to molecular dynamics and structural behaviour crucial for the conductive properties of OIPCs. A distinct correlation is established between the conductivity at a given temperature, σ(T), and the intensity of the narrow NMR signal that is attributed to a mobile fraction, fm(T), of ions in the OIPC. To explain these findings we propose an analogy with the well-studied relationship between permeability (k) and void fraction (θ) in porous media, with k(θ) commonly quantified by a power-law dependence that can also be employed to describe σ(fm).

  2. Plasticity size effects in voided crystals

    DEFF Research Database (Denmark)

    Hussein, M. I.; Borg, Ulrik; Niordson, Christian Frithiof

    singularities in an elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and annihilation are incorporated through a set of constitutive rules. Over the range of length scales investigated, both the discrete dislocation and strain...... predictions of the two formulations for all crystal types and void volume fractions considered when the material length scale in the non-local plasticity model chosen to be $0.325\\mu m$ (around ten times the slip plane spacing in the discrete dislocation models)....

  3. Plasticity size effects in voided crystals

    DEFF Research Database (Denmark)

    Hussein, M.I.; Borg, Ulrik; Niordson, Christian Frithiof

    2008-01-01

    as line singularities in an elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and annihilation are incorporated through a set of constitutive rules. Over the range of length scales investigated, both the discrete dislocation...... between predictions of the two formulations for all crystal types and void volume fractions considered when the material length scale in the non-local plasticity model is chosen to be 0.325 mu m (about 10 times the slip plane spacing in the discrete dislocation models)....

  4. Crystal plasticity and grain crushing in high-porosity rocks

    Science.gov (United States)

    Rahmani, H.; Tjioe, M.; Borja, R. I.

    2012-12-01

    Previous studies show the significance of considering microstructure of individual crystals in modeling the inelastic behavior of high-porosity rocks. Plastic deformation of high-porosity crystalline rocks, exemplified by limestone, is mainly attributed to crystal plasticity and cataclastic flow. Crystal plasticity is defined as the plastic deformation along potential slip systems within the crystal lattice. In the context of continuum mechanics this micro-mechanism is modeled by a nonlinear relationship between stresses and strains. Two types of nonlinearity characterize the inelastic behavior of the crystal grains: material nonlinearity and geometric nonlinearity. Material nonlinearity defines the changes in stiffness matrix due to plastic slip along slip systems. Geometric nonlinearity contributes to the changes in stiffness matrix due to changes in the geometry of the crystal grains. Geometric nonlinearity is modeled using theory of finite deformation, which assumes the geometry of slip systems to be a function of crystal deformation. This type of nonlinearity is very important in modeling crystal deformation mainly because of plastic spin induced by anisotropy in the crystal structure. However, considering the geometry of slip systems as a function of crystal slip makes the equations highly nonlinear. As a result, many studies either ignore geometric nonlinearity or make other assumptions to simplify the equations. Cataclastic flow, on the other hand, is characterized by pervasive grain crushing in which larger grains are converted into smaller ones. We model cataclastic flow as strong discontinuity in the grain scale via an assumed enhanced strain method formulated within the context of nonlinear finite elements. The method allows the individual finite elements, identified to be in critical condition, to break into two pieces along a plane identified by theory of bifurcation. We show that modeling cataclastic flow combined with finite deformation crystal

  5. Strain gradient crystal plasticity effects on flow localization

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    In metal grains one of the most important failure mechanisms involves shear band localization. As the band width is small, the deformations are affected by material length scales. To study localization in single grains a rate-dependent crystal plasticity formulation for finite strains is presented...... in the absence of strain gradients. The model is used to study the effect of an internal material length scale on the localization of plastic flow in shear bands in a single crystal under plane strain tension. It is shown that the mesh sensitivity is removed when using the nonlocal material model considered...... for metals described by the reformulated Fleck-Hutchinson strain gradient plasticity theory. The theory is implemented numerically within a finite element framework using slip rate increments and displacement increments as state variables. The formulation reduces to the classical crystal plasticity theory...

  6. Influence Intensive Plastic Deformation on Phase Formation Process in Amorphous Alloys

    Directory of Open Access Journals (Sweden)

    V.I. Lysov

    2016-06-01

    Full Text Available The influence of intensive plastic deformation on structure and properties of amorphous alloys were investigated experimentally. Using highly sensitive dilatometer techniques shown that intensive plastic deformation of amorphous alloys leads to increased of thermal stability interval that can be explained by a shift of the phase equilibria in heterogeneous system: amorphous matrix - frozen crystallization centers. Thus there is a dissolution frozen crystallization centers present in the original sample that confirmed by electron researches.

  7. Polymer-stabilized ferroelectric liquid crystal for flexible displays using plastic substrates

    Science.gov (United States)

    Fujikake, Hideo; Murashige, Takeshi; Sato, Hiroto; Iino, Yoshiki; Kikuchi, Hiroshi; Kawakita, Masahiro; Tsuchiya, Yuzuru

    2001-12-01

    We have developed a ferroelectric liquid crystal device with a novel structure containing a polymer fiber network for flexible lightweight displays using thin plastic substrates. The aligned polymer fibers of sub-micrometers -diameter were formed under ultraviolet light irradiation in a heated nematic- phase solution consisting of liquid crystal and monofunctional acrylate monomer. The rigid polymer network was found to adhere to the two plastic substrates, and the uniform liquid crystal alignment provided a contrast ratio of 100:1 for a monomer concentration of 20 wt%. This device achieves a continuous grayscale capability as a result of change in the spatial distribution of small liquid crystal domains, and also exhibits a fast response time of 80 microsecond(s) due to high-purity separation of polymer and liquid crystal materials. It therefore has attractive features for flexible moving-image display applications.

  8. Plastic deformation modelling of tempered martensite steel block structure by a nonlocal crystal plasticity model

    Directory of Open Access Journals (Sweden)

    Martin Boeff

    2014-01-01

    Full Text Available The plastic deformations of tempered martensite steel representative volume elements with different martensite block structures have been investigated by using a nonlocal crystal plasticity model which considers isotropic and kinematic hardening produced by plastic strain gradients. It was found that pronounced strain gradients occur in the grain boundary region even under homogeneous loading. The isotropic hardening of strain gradients strongly influences the global stress–strain diagram while the kinematic hardening of strain gradients influences the local deformation behaviour. It is found that the additional strain gradient hardening is not only dependent on the block width but also on the misorientations or the deformation incompatibilities in adjacent blocks.

  9. Energetic materials: crystallization, characterization and insensitive plastic bonded explosives

    NARCIS (Netherlands)

    Heijden, A.E.D.M. van der; Creyghton, Y.L.M.; Marino, E.; Bouma, R.H.B.; Scholtes, G.J.H.G.; Duvalois, W.; Roelands, C.P.M.

    2008-01-01

    The product quality of energetic materials is predominantly determined by the crystallization process applied to produce these materials. It has been demonstrated in the past that the higher the product quality of the solid energetic ingredients, the less sensitive a plastic bonded explosive contain

  10. Energetic materials: crystallization, characterization and insensitive plastic bonded explosives

    NARCIS (Netherlands)

    Heijden, A.E.D.M. van der; Creyghton, Y.L.M.; Marino, E.; Bouma, R.H.B.; Scholtes, G.J.H.G.; Duvalois, W.; Roelands, C.P.M.

    2008-01-01

    The product quality of energetic materials is predominantly determined by the crystallization process applied to produce these materials. It has been demonstrated in the past that the higher the product quality of the solid energetic ingredients, the less sensitive a plastic bonded explosive

  11. An all-solid-state electrochemical double-layer capacitor based on a plastic crystal electrolyte

    Directory of Open Access Journals (Sweden)

    Ali eaabouimrane

    2015-08-01

    Full Text Available A plastic crystal, solid electrolyte was prepared by mixing tetrabutylammonium hexafluorophosphate salt, (C4H94NPF6, (10 molar % with succinonitrile, SCN, (N C−CH2−CH2−C N, [SCN-10%TBA-PF6]. The resultant waxy material shows a plastic crystalline phase that extend from -36 °C up to its melting at 23 °C. It shows a high ionic conductivity reaching 4 × 10−5 S/cm in the plastic crystal phase (15 °C and ~ 3 × 10−3 S/cm in the molten state (25 °C. These properties along with the high electrochemical stability rendered the use of this material as an electrolyte in an electrochemical double-layer capacitor (EDLC. The EDLC was assembled and its performance was tested by cyclic voltammetry, AC impedance spectroscopy and galvanostatic charge-discharge methods. Specific capacitance values in the range of 4-7 F/g. (of electrode active material were obtained in the plastic crystal phase at 15 °C, that although compare well with those reported for some polymer electrolytes, can be still enhanced with further development of the device and its components, and only demonstrate their great potential use for capacitors as a new application.

  12. Origin and use of crystallization phase diagrams.

    Science.gov (United States)

    Rupp, Bernhard

    2015-03-01

    Crystallization phase diagrams are frequently used to conceptualize the phase relations and also the processes taking place during the crystallization of macromolecules. While a great deal of freedom is given in crystallization phase diagrams owing to a lack of specific knowledge about the actual phase boundaries and phase equilibria, crucial fundamental features of phase diagrams can be derived from thermodynamic first principles. Consequently, there are limits to what can be reasonably displayed in a phase diagram, and imagination may start to conflict with thermodynamic realities. Here, the commonly used `crystallization phase diagrams' are derived from thermodynamic excess properties and their limitations and appropriate use is discussed.

  13. Crystal Plasticity Analysis on Compressive Loading of Magnesium with Suppression of Twinning

    Science.gov (United States)

    Mayama, Tsuyoshi; Ohashi, Tetsuya; Higashida, Kenji; Kawamura, Yoshihito

    The compressive loading behavior of single crystals and bicrystals of magnesium without consideration of deformation twinning has been investigated by crystal plasticity finite element analysis with the aim of fundamental understanding of kink band formation in magnesium alloys with long period stacking ordered structure (LPSO) phase. The basal plane of the single crystal model is set to be parallel to the compressive direction. The result of the compressive loading analysis of single crystals indicates the significant influence of suppression of twinning on the activation of nonbasal slip systems and stress-strain behavior. The compressive analysis of symmetric bicrystal is also performed to clarify the influence of the angle between basal plane and the loading axis. The influence of the introduction of grain boundary and the slight change of crystal orientation is discussed in terms of activated deformation modes.

  14. The stress statistics of the first pop-in or discrete plastic event in crystal plasticity

    Science.gov (United States)

    Derlet, P. M.; Maaß, R.

    2016-12-01

    The stress at which the first discrete plastic event occurs is investigated using extreme value statistics. It is found that the average of this critical stress is inversely related to the deforming volume, via an exponentially truncated power-law. This is demonstrated for the first pop-in event observed in experimental nano-indentation data as a function of the indenter volume, and for the first discrete plastic event seen in a dislocation dynamics simulation. When the underlying master distribution of critical stresses is assumed to be a power-law, it becomes possible to extract the density of discrete plastic events available to the crystal, and to understand the exponential truncation as a break-down of the asymptotic Weibull limit.

  15. Size effects in single crystal thin films : nonlocal crystal plasticity simulations

    NARCIS (Netherlands)

    Yefimov, S; van der Giessen, E

    2005-01-01

    Stress relaxation in single crystalline thin films on substrates subjected to thermal loading is studied using a recently proposed nonlocal continuum crystal plasticity theory. The theory is founded on a statistical-mechanics description of the collective behaviour of dislocations in multiple slip,

  16. On Slip Transmission Criteria in Experiments and Crystal Plasticity Models

    CERN Document Server

    Bayerschen, E; Reddy, B D; Böhlke, T

    2015-01-01

    A comprehensive overview is given on the slip transmission criteria for grain boundaries in the experimental literature, with a focus on slip system and grain boundary orientation. The use of these geometric criteria in continuum crystal plasticity models is briefly discussed. Perspectives on additional experimentally motivated criteria used in computational simulations are given. The theoretical framework of Gurtin (2008, J. Mech. Phys. Solids 56, p. 640) is reviewed for the single slip case with the aim of showing explicitly the connections to the experimentally developed criteria for slip transmission that are not discussed in the work itself.

  17. Strain gradient crystal plasticity analysis of a single crystal containing a cylindrical void

    DEFF Research Database (Denmark)

    Borg, Ulrik; Kysar, J.W.

    2007-01-01

    The effects of void size and hardening in a hexagonal close-packed single crystal containing a cylindrical void loaded by a far-field equibiaxial tensile stress under plane strain conditions are studied. The crystal has three in-plane slip systems oriented at the angle 60 degrees with respect...... to one another. Finite element simulations are performed using a strain gradient crystal plasticity formulation with an intrinsic length scale parameter in a non-local strain gradient constitutive framework. For a vanishing length scale parameter the non-local formulation reduces to a local crystal...... to three times higher for smaller void sizes than for larger void sizes in the non-local material....

  18. Plastic deformation of tubular crystals by dislocation glide

    Science.gov (United States)

    Beller, Daniel A.; Nelson, David R.

    2016-09-01

    Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.

  19. Single crystal plasticity by modeling dislocation density rate behavior

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, Benjamin L [Los Alamos National Laboratory; Bronkhorst, Curt [Los Alamos National Laboratory; Beyerlein, Irene [Los Alamos National Laboratory; Cerreta, E. K. [Los Alamos National Laboratory; Dennis-Koller, Darcie [Los Alamos National Laboratory

    2010-12-23

    The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

  20. Plastic deformation of tubular crystals by dislocation glide.

    Science.gov (United States)

    Beller, Daniel A; Nelson, David R

    2016-09-01

    Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.

  1. Crystal Plasticity Model of Reactor Pressure Vessel Embrittlement in GRIZZLY

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Pritam [Idaho National Laboratory (INL), Idaho Falls, ID (United States); Biner, Suleyman Bulent [Idaho National Laboratory (INL), Idaho Falls, ID (United States); Zhang, Yongfeng [Idaho National Laboratory (INL), Idaho Falls, ID (United States); Spencer, Benjamin Whiting [Idaho National Laboratory (INL), Idaho Falls, ID (United States)

    2015-07-01

    The integrity of reactor pressure vessels (RPVs) is of utmost importance to ensure safe operation of nuclear reactors under extended lifetime. Microstructure-scale models at various length and time scales, coupled concurrently or through homogenization methods, can play a crucial role in understanding and quantifying irradiation-induced defect production, growth and their influence on mechanical behavior of RPV steels. A multi-scale approach, involving atomistic, meso- and engineering-scale models, is currently being pursued within the GRIZZLY project to understand and quantify irradiation-induced embrittlement of RPV steels. Within this framework, a dislocation-density based crystal plasticity model has been developed in GRIZZLY that captures the effect of irradiation-induced defects on the flow stress behavior and is presented in this report. The present formulation accounts for the interaction between self-interstitial loops and matrix dislocations. The model predictions have been validated with experiments and dislocation dynamics simulation.

  2. A thermomechanical crystal plasticity constitutive model for ultrasonic consolidation

    KAUST Repository

    Siddiq, Amir

    2012-01-01

    We present a micromechanics-based thermomechanical constitutive model to simulate the ultrasonic consolidation process. Model parameters are calibrated using an inverse modeling approach. A comparison of the simulated response and experimental results for uniaxial tests validate and verify the appropriateness of the proposed model. Moreover, simulation results of polycrystalline aluminum using the identified crystal plasticity based material parameters are compared qualitatively with the electron back scattering diffraction (EBSD) results reported in the literature. The validated constitutive model is then used to simulate the ultrasonic consolidation process at sub-micron scale where an effort is exerted to quantify the underlying micromechanisms involved during the ultrasonic consolidation process. © 2011 Elsevier B.V. All rights reserved.

  3. On plastic flow in notched hexagonal close packed single crystals

    Science.gov (United States)

    Selvarajou, Balaji; Kondori, Babak; Benzerga, A. Amine; Joshi, Shailendra P.

    2016-09-01

    The micromechanics of anisotropic plastic flow by combined slip and twinning is investigated computationally in single crystal notched specimens. Constitutive relations for hexagonal close packed materials are used which take into account elastic anisotropy, thirty potential deformation systems, various hardening mechanisms and rate-sensitivity. The specimens are loaded perpendicular to the c-axis but the presence of a notch generates three-dimensional triaxial stress states. The study is motivated by recent experiments on a polycrystalline magnesium alloy. To enable comparisons with these where appropriate, three sets of activation thresholds for the various deformation systems are used. For the conditions that most closely mimic the alloy material, attention is focused on the relative roles of pyramidal and prismatic slip, as well as on the emergence of {1012bar}[101bar1] extension twinning at sufficiently high triaxiality. In all cases, the spatial variations of stress triaxiality and plastic strain, inclusive of various system activities, are quantified along with their evolution upon straining. The implications of these findings in fundamental understanding of ductile failure of HCP alloys in general and Mg alloys in particular are discussed.

  4. Double phase conjugation in tungsten bronze crystals.

    Science.gov (United States)

    Sharp, E J; Clark Iii, W W; Miller, M J; Wood, G L; Monson, B; Salamo, G J; Neurgaonkar, R R

    1990-02-20

    In this paper we report a new method for double phase conjugation particularly suited to the tungsten bronze crystal strontium barium niobate. It has also been observed to produce conjugate waves in BaTiO(3) and BSKNN. This new arrangement is called the bridge conjugator because the two beams enter opposing [100] crystal faces and fan together to form a bridge without reflection off a crystal face. Our measurements indicate that the bridge conjugator is competitive with previously reported double phase conjugate mirrors in reflectivity, response time, ease of alignment, and fidelity.

  5. Phase-field slip-line theory of plasticity

    Science.gov (United States)

    Freddi, Francesco; Royer-Carfagni, Gianni

    2016-09-01

    A variational approach to determine the deformation of an ideally plastic substance is proposed by solving a sequence of energy minimization problems under proper conditions to account for the irreversible character of plasticity. The flow is driven by the local transformation of elastic strain energy into plastic work on slip surfaces, once that a certain energetic barrier for slip activation has been overcome. The distinction of the elastic strain energy into spherical and deviatoric parts is used to incorporate in the model the idea of von Mises plasticity and isochoric plastic strain. This is a "phase field model" because the matching condition at the slip interfaces is substituted by the evolution of an auxiliary phase field that, similar to a damage field, is unitary on the elastic phase and null on the yielded phase. The slip lines diffuse in bands, whose width depends upon a material length-scale parameter. Numerical experiments on representative problems in plane strain give solutions with noteworthy similarities with the results from classical slip-line field theory, but the proposed model is much richer because, accounting for elastic deformations, it can describe the formation of slip bands at the local level, which can nucleate, propagate, widen and diffuse by varying the boundary conditions. In particular, the solution for a long pipe under internal pressure is very different from the one obtainable from the classical macroscopic theory of plasticity. For this case, the location of the plastic bands may be an insight to explain the premature failures that are sometimes encountered during the manufacturing process. This practical example enhances the importance of this new theory based on the mathematical sciences.

  6. Chiral Liquid Crystals: Structures, Phases, Effects

    Directory of Open Access Journals (Sweden)

    Ingo Dierking

    2014-06-01

    Full Text Available The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.

  7. Semantic modeling of the structural and process entities during plastic deformation of crystals and rocks

    Science.gov (United States)

    Babaie, Hassan; Davarpanah, Armita

    2016-04-01

    We are semantically modeling the structural and dynamic process components of the plastic deformation of minerals and rocks in the Plastic Deformation Ontology (PDO). Applying the Ontology of Physics in Biology, the PDO classifies the spatial entities that participate in the diverse processes of plastic deformation into the Physical_Plastic_Deformation_Entity and Nonphysical_Plastic_Deformation_Entity classes. The Material_Physical_Plastic_Deformation_Entity class includes things such as microstructures, lattice defects, atoms, liquid, and grain boundaries, and the Immaterial_Physical_Plastic_Deformation_Entity class includes vacancies in crystals and voids along mineral grain boundaries. The objects under the many subclasses of these classes (e.g., crystal, lattice defect, layering) have spatial parts that are related to each other through taxonomic (e.g., Line_Defect isA Lattice_Defect), structural (mereological, e.g., Twin_Plane partOf Twin), spatial-topological (e.g., Vacancy adjacentTo Atom, Fluid locatedAlong Grain_Boundary), and domain specific (e.g., displaces, Fluid crystallizes Dissolved_Ion, Void existsAlong Grain_Boundary) relationships. The dynamic aspect of the plastic deformation is modeled under the dynamical Process_Entity class that subsumes classes such as Recrystallization and Pressure_Solution that define the flow of energy amongst the physical entities. The values of the dynamical state properties of the physical entities (e.g., Chemical_Potential, Temperature, Particle_Velocity) change while they take part in the deformational processes such as Diffusion and Dislocation_Glide. The process entities have temporal parts (phases) that are related to each other through temporal relations such as precedes, isSubprocessOf, and overlaps. The properties of the physical entities, defined under the Physical_Property class, change as they participate in the plastic deformational processes. The properties are categorized into dynamical, constitutive

  8. Material characterization and finite element modelling of cyclic plasticity behavior for 304 stainless steel using a crystal plasticity model

    OpenAIRE

    Lu, Jiawa; Sun, Wei; Becker, Adib A.

    2016-01-01

    Low cycle fatigue tests were carried out for a 304 stainless steel at room temperature. A series of experimental characterisations, including SEM, TEM, and XRD were conducted for the 304 stainless steel to facilitate the understanding of the mechanical responses and microstructural behaviour of the material under cyclic loading including nanostructure, crystal structure and the fractured surface. The crystal plasticity finite element method (CPFEM) is a powerful tool for studying the microstr...

  9. Crystal Plasticity Modeling of Microstructure Evolution and Mechanical Fields During Processing of Metals Using Spectral Databases

    Science.gov (United States)

    Knezevic, Marko; Kalidindi, Surya R.

    2017-05-01

    This article reviews the advances made in the development and implementation of a novel approach to speeding up crystal plasticity simulations of metal processing by one to three orders of magnitude when compared with the conventional approaches, depending on the specific details of implementation. This is mainly accomplished through the use of spectral crystal plasticity (SCP) databases grounded in the compact representation of the functions central to crystal plasticity computations. A key benefit of the databases is that they allow for a noniterative retrieval of constitutive solutions for any arbitrary plastic stretching tensor (i.e., deformation mode) imposed on a crystal of arbitrary orientation. The article emphasizes the latest developments in terms of embedding SCP databases within implicit finite elements. To illustrate the potential of these novel implementations, the results from several process modeling applications including equichannel angular extrusion and rolling are presented and compared with experimental measurements and predictions from other models.

  10. A phase-field model for incoherent martensitic transformations including plastic accommodation processes in the austenite

    Science.gov (United States)

    Kundin, J.; Raabe, D.; Emmerich, H.

    2011-10-01

    If alloys undergo an incoherent martensitic transformation, then plastic accommodation and relaxation accompany the transformation. To capture these mechanisms we develop an improved 3D microelastic-plastic phase-field model. It is based on the classical concepts of phase-field modeling of microelastic problems (Chen, L.Q., Wang Y., Khachaturyan, A.G., 1992. Philos. Mag. Lett. 65, 15-23). In addition to these it takes into account the incoherent formation of accommodation dislocations in the austenitic matrix, as well as their inheritance into the martensitic plates based on the crystallography of the martensitic transformation. We apply this new phase-field approach to the butterfly-type martensitic transformation in a Fe-30 wt%Ni alloy in direct comparison to recent experimental data (Sato, H., Zaefferer, S., 2009. Acta Mater. 57, 1931-1937). It is shown that the therein proposed mechanisms of plastic accommodation during the transformation can indeed explain the experimentally observed morphology of the martensitic plates as well as the orientation between martensitic plates and the austenitic matrix. The developed phase-field model constitutes a general simulations approach for different kinds of phase transformation phenomena that inherently include dislocation based accommodation processes. The approach does not only predict the final equilibrium topology, misfit, size, crystallography, and aspect ratio of martensite-austenite ensembles resulting from a transformation, but it also resolves the associated dislocation dynamics and the distribution, and the size of the crystals itself.

  11. Strain gradient crystal plasticity: A continuum mechanics approach to modeling micro-structural evolution

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2015-01-01

    In agreement with dislocation theory, recent experiments show, both quantitatively and qualitatively, how geometrically necessary dislocations (GNDs) distribute in dislocation wall and cell structures. Hence, GND density fields are highly localized with large gradients and discontinuities occurring...... between the cells. This behavior is not typical for strain gradient crystal plasticity models. The present study employs a higher order extension of conventional crystal plasticity theory in which the viscous slip rate is influenced by the gradients of GND densities through a back stress...

  12. Strain gradient crystal plasticity: A continuum mechanics approach to modeling micro-structural evolution

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2015-01-01

    In agreement with dislocation theory, recent experiments show, both quantitatively and qualitatively, how geometrically necessary dislocations (GNDs) distribute in dislocation wall and cell structures. Hence, GND density fields are highly localized with large gradients and discontinuities occurring...... between the cells. This behavior is not typical for strain gradient crystal plasticity models. The present study employs a higher order extension of conventional crystal plasticity theory in which the viscous slip rate is influenced by the gradients of GND densities through a back stress...

  13. An incremental flow theory for crystal plasticity incorporating strain gradient effects

    DEFF Research Database (Denmark)

    Nellemann, Christopher; Niordson, Christian Frithiof; Nielsen, Kim Lau

    2017-01-01

    The present work investigates a new approach to formulating a rate-independent strain gradient theory for crystal plasticity. The approach takes as offset recent discussions published in the literature for isotropic plasticity, and a key ingredient of the present work is the manner in which a gra...

  14. Multiscale simulation and nanoindentation experimental study of initial plasticity of Fe single crystal

    Institute of Scientific and Technical Information of China (English)

    YUAN Lin; SHAN De-bin; GUO Bin

    2009-01-01

    It is very important to understand the initial plastic behavior of metals at microscale. In order to research the initial plasticity of body centered cubic metals in micro-/nano-scale, the multiscale simulation method and experimental study were used to study the nanoindentation process of Fe single crystal. The results show that the first abruption of load-displacement curve in nanoindentation of Fe single crystal can be attributed to the first transition from elastic to plastic deformation characterized by the dislocation emission.

  15. Multiscale Modeling of Structurally-Graded Materials Using Discrete Dislocation Plasticity Models and Continuum Crystal Plasticity Models

    Science.gov (United States)

    Saether, Erik; Hochhalter, Jacob D.; Glaessgen, Edward H.

    2012-01-01

    A multiscale modeling methodology that combines the predictive capability of discrete dislocation plasticity and the computational efficiency of continuum crystal plasticity is developed. Single crystal configurations of different grain sizes modeled with periodic boundary conditions are analyzed using discrete dislocation plasticity (DD) to obtain grain size-dependent stress-strain predictions. These relationships are mapped into crystal plasticity parameters to develop a multiscale DD/CP model for continuum level simulations. A polycrystal model of a structurally-graded microstructure is developed, analyzed and used as a benchmark for comparison between the multiscale DD/CP model and the DD predictions. The multiscale DD/CP model follows the DD predictions closely up to an initial peak stress and then follows a strain hardening path that is parallel but somewhat offset from the DD predictions. The difference is believed to be from a combination of the strain rate in the DD simulation and the inability of the DD/CP model to represent non-monotonic material response.

  16. Lyotropic Liquid Crystal Phases from Anisotropic Nanomaterials

    Directory of Open Access Journals (Sweden)

    Ingo Dierking

    2017-10-01

    Full Text Available Liquid crystals are an integral part of a mature display technology, also establishing themselves in other applications, such as spatial light modulators, telecommunication technology, photonics, or sensors, just to name a few of the non-display applications. In recent years, there has been an increasing trend to add various nanomaterials to liquid crystals, which is motivated by several aspects of materials development. (i addition of nanomaterials can change and thus tune the properties of the liquid crystal; (ii novel functionalities can be added to the liquid crystal; and (iii the self-organization of the liquid crystalline state can be exploited to template ordered structures or to transfer order onto dispersed nanomaterials. Much of the research effort has been concentrated on thermotropic systems, which change order as a function of temperature. Here we review the other side of the medal, the formation and properties of ordered, anisotropic fluid phases, liquid crystals, by addition of shape-anisotropic nanomaterials to isotropic liquids. Several classes of materials will be discussed, inorganic and mineral liquid crystals, viruses, nanotubes and nanorods, as well as graphene oxide.

  17. The Way to Phase Space Crystals

    Science.gov (United States)

    Guo, Lingzhen; Michael, Marthaler; Schön, Gerd

    A novel way to create a band structure of the quasienergy spectrum for driven systems is proposed based on the discrete symmetry in phase space. The system, e.g., an ion or ultracold atom trapped in a potential, shows no spatial periodicity, but it is driven by a time-dependent field. Under rotating wave approximation, the system can produce a periodic lattice structure in phase space. The band structure in quasienergy arises as a consequence of the n-fold discrete periodicity in phase space induced by this driving field. We propose explicit models to realize such a phase space crystal and analyze its band structure in the frame of a tightbinding approximation. The phase space lattice differs fundamentally from a lattice in real space, because its coordinate system, i.e., phase space, has a noncommutative geometry. The phase space crystal opens new ways to engineer energy band structures, with the added advantage that its properties can be changed in situ by tuning the driving field's parameters. Carl-Zeiss Stiftung.

  18. Simulation of cylindrical cup drawing of AZ31 sheet metal with crystal plasticity finite element method

    Science.gov (United States)

    Tang, Weiqin; Li, Dayong; Zhang, Shaorui; Peng, Yinghong

    2013-12-01

    As a light-weight structural material, magnesium alloys show good potential in improving the fuel efficiency of vehicles and reducing CO2 emissions. However, it is well known that polycrystalline Mg alloys develop pronounced crystallographic texture and plastic anisotropy during rolling, which leads to earing phenomenon during deep drawing of the rolled sheets. It is vital to predict this phenomenon accurately for application of magnesium sheet metals. In the present study, a crystal plasticity model for AZ31 magnesium alloy that incorporates both slip and twinning is established. Then the crystal plasticity model is implemented in the commercial finite element software ABAQUS/Explicit through secondary development interface (VUMAT). Finally, the stamping process of a cylindrical cup is simulated using the developed crystal plasticity finite element model, and the predicting method is verified by comparing with experimental results from both earing profile and deformation texture.

  19. Crystallization of acetaminophen form II by plastic-ball-assisted ultrasonic irradiation

    Science.gov (United States)

    Mori, Yoichiro; Maruyama, Mihoko; Takahashi, Yoshinori; Yoshikawa, Hiroshi Y.; Okada, Shino; Adachi, Hiroaki; Sugiyama, Shigeru; Takano, Kazufumi; Murakami, Satoshi; Matsumura, Hiroyoshi; Inoue, Tsuyoshi; Yoshimura, Masashi; Mori, Yusuke

    2017-02-01

    We report a novel method for crystallizing the metastable polymorph form II of acetaminophen by using a plastic ball during ultrasonic irradiation. The presence of a plastic ball during ultrasonic irradiation of aqueous acetaminophen solution effectively increased the probability and reduced the induction time of form II crystallization. This method facilitated both laboratory- and large-scale production of form II crystals. Our method has significant advantages for practical application of form II because it can reduce the time to production and enable large-scale production.

  20. Tensile plastic strain localization in single crystals of austenite steel electrolytically saturated with hydrogen

    Science.gov (United States)

    Barannikova, S. A.; Nadezhkin, M. V.; Mel'Nichuk, V. A.; Zuev, L. B.

    2011-09-01

    The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested Fe-18Cr-12Ni-2Mo single crystals of austenite steel with low stacking-fault energy has been studied using a double-exposure speckle photography technique. The main parameters of plastic-flow localization at various stages of the deformation hardening of crystals have been determined in single crystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at a controlled constant cathode potential.

  1. ON PLASTIC ANISOTROPY OF CONSTITUTIVE MODEL FOR RATE-DEPENDENT SINGLE CRYSTAL

    Institute of Scientific and Technical Information of China (English)

    张光; 张克实; 冯露

    2005-01-01

    An algorithm for single crystals was developed and implemented to simulate plastic anisotropy using a rate-dependent slip model. The proposed procedure was a slightly modified form of single crystal constitutive model of Sarma and Zacharia. Modified Euler method, together with Newton-Raphson method was used to integrate this equation which was stable and efficient. The model together with the developed algorithm was used to study three problems. First, plastic anisotropy was examined by simulating the crystal deformation in tension and plane strain compression, respectively. Secondly, the orientation effect of some material parameters in the model and applied strain rate on plastic anisotropy for single crystal also is investigated. Thirdly, the influence of loading direction on the active slip system was discussed.

  2. Modeling of elastic and plastic waves for HCP single crystals in a 3D formulation based on zinc single crystal

    Science.gov (United States)

    Krivosheina, Marina; Kobenko, Sergey; Tuch, Elena; Kozlova, Maria

    2016-11-01

    This paper investigates elastic and plastic waves in HCP single crystals through the numerical simulation of strain processes in anisotropic materials based on a zinc single crystal. Velocity profiles for compression waves in the back surfaces of single-crystal zinc plates with impact loading oriented in 0001 and 10 1 ¯0 are presented in this work as a part of results obtained in numerical simulations. The mathematical model implemented in this study reflects the following characteristics of the mechanical properties inherent in anisotropic (transtropic) materials: varying degree of anisotropy of elastic and plastic properties, which includes reverse anisotropy, dependence of distribution of all types of waves on the velocity orientation, and the anisotropy of compressibility. Another feature of elastic and plastic waves in HCP single crystals is that the shock wave does not split into an elastic precursor and "plastic" compression shock wave, which is inherent in zinc single crystals with loading oriented in 0001. The study compares numerical results obtained in a three-dimensional formulation with the results of velocity profiles from the back surfaces of target plates obtained in real experiments. These results demonstrate that the mathematical model is capable of describing the properties of the above-mentioned anisotropic (transtropic) materials.

  3. Plastic theory for the multi-crystal metals-From infinitesimal deformation to finite deformation

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Multi-crystal metals have the property of volume conservation in the plastic state. In the infinitesimal deformation plasticity the strain tensor can be split into a deviator part and a volumetric part. The vanishing of the first variant of the strain tensor is equivalent to the volume conservation. Furthermore, the split of the strain into an elastic part and a plastic part is also adopted widely. The flow rule is thus established. These two splits are not confirmed in the finite deformation plasticity. The plasticity criterion and the flow rule are thus facing great challenge. There are various definitions of strain measures in the finite deformation theory. Though the choosing of strain measure is arbitrary in the elastic problem, it is strongly restricted in the plastic problem. By theoretical and experimental studies, it is shown that the logarithmic strain is the only suitable strain measure in the metal forming problem.

  4. Eighth-order phase-field-crystal model for two-dimensional crystallization

    OpenAIRE

    Jaatinen, A.; Ala-Nissila, T.

    2010-01-01

    We present a derivation of the recently proposed eighth order phase field crystal model [Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase field crystal models. We find that among the phase field crystal models...

  5. Equilibrium crystal phases of triblock Janus colloids

    Science.gov (United States)

    Reinhart, Wesley F.; Panagiotopoulos, Athanassios Z.

    2016-09-01

    Triblock Janus colloids, which are colloidal spheres decorated with attractive patches at each pole, have recently generated significant interest as potential building blocks for functional materials. Their inherent anisotropy is known to induce self-assembly into open structures at moderate temperatures and pressures, where they are stabilized over close-packed crystals by entropic effects. We present a numerical investigation of the equilibrium phases of triblock Janus particles with many different patch geometries in three dimensions, using Monte Carlo simulations combined with free energy calculations. In all cases, we find that the free energy difference between crystal polymorphs is less than 0.2 kBT per particle. By varying the patch fraction and interaction range, we show that large patches stabilize the formation of structures with four bonds per patch over those with three. This transition occurs abruptly above a patch fraction of 0.30 and has a strong dependence on the interaction range. Furthermore, we find that a short interaction range favors four bonds per patch, with longer range increasingly stabilizing structures with only three bonds per patch. By quantifying the effect of patch geometry on the stability of the equilibrium crystal structures, we provide insights into the fundamental design rules for constructing complex colloidal crystals.

  6. Monodomain Blue Phase Liquid Crystal Layers for Phase Modulation

    Science.gov (United States)

    Oton, E.; Netter, E.; Nakano, T.; D.-Katayama, Y.; Inoue, F.

    2017-03-01

    Liquid crystal “Blue Phases” (BP) have evolved, in the last years, from a scientific curiosity to emerging materials for new photonic and display applications. They possess attractive features over standard nematic liquid crystals, like submillisecond switching times and polarization- independent optical response. However, BPs still present a number of technical issues that prevent their use in practical applications: their phases are only found in limited temperature ranges, thus requiring stabilization of the layers; stabilized BP layers are inhomogeneous and not uniformly oriented, which worsen the optical performance of the devices. It would be essential for practical uses to obtain perfectly aligned and oriented monodomain BP layers, where the alignment and orientation of the cubic lattice are organized in a single 3D structure. In this work we have obtained virtually perfect monodomain BP layers and used them in devices for polarization independent phase modulation. We demonstrate that, under applied voltage, well aligned and oriented layers generate smoother and higher values of the phase shift than inhomogeneous layers, while preserving polarization independency. All BP devices were successfully stabilized in BPI phase, maintaining the layer monodomain homogeneity at room temperature, covering the entire area of the devices with a unique BP phase.

  7. Monodomain Blue Phase Liquid Crystal Layers for Phase Modulation

    Science.gov (United States)

    Oton, E.; Netter, E.; Nakano, T.; D.-Katayama, Y.; Inoue, F.

    2017-01-01

    Liquid crystal “Blue Phases” (BP) have evolved, in the last years, from a scientific curiosity to emerging materials for new photonic and display applications. They possess attractive features over standard nematic liquid crystals, like submillisecond switching times and polarization- independent optical response. However, BPs still present a number of technical issues that prevent their use in practical applications: their phases are only found in limited temperature ranges, thus requiring stabilization of the layers; stabilized BP layers are inhomogeneous and not uniformly oriented, which worsen the optical performance of the devices. It would be essential for practical uses to obtain perfectly aligned and oriented monodomain BP layers, where the alignment and orientation of the cubic lattice are organized in a single 3D structure. In this work we have obtained virtually perfect monodomain BP layers and used them in devices for polarization independent phase modulation. We demonstrate that, under applied voltage, well aligned and oriented layers generate smoother and higher values of the phase shift than inhomogeneous layers, while preserving polarization independency. All BP devices were successfully stabilized in BPI phase, maintaining the layer monodomain homogeneity at room temperature, covering the entire area of the devices with a unique BP phase. PMID:28281691

  8. A finite deformation theory of higher-order gradient crystal plasticity

    DEFF Research Database (Denmark)

    Kuroda, Mitsutoshi; Tvergaard, Viggo

    2008-01-01

    crystal plasticity that is based on an assumption of the existence of higher-order stresses. Furthermore, a boundary-value problem for simple shear of a constrained thin strip is studied numerically, and some characteristic features of finite deformation are demonstrated through a comparison to a solution......For higher-order gradient crystal plasticity, a finite deformation formulation is presented. The theory does not deviate much from the conventional crystal plasticity theory. Only a back stress effect and additional differential equations for evolution of the geometrically necessary dislocation...... (GND) densities supplement the conventional theory within a non-work-conjugate framework in which there is no need to introduce higher-order microscopic stresses that would be work-conjugate to slip rate gradients. We discuss its connection to a work-conjugate type of finite deformation gradient...

  9. Features of plastic strain localization at the yield plateau in Hadfield steel single crystals

    Science.gov (United States)

    Barannikova, S. A.; Zuev, L. B.

    2008-07-01

    Spatiotemporal distributions of local components of the plastic distortion tensor in Hadfield steel single crystals oriented for single twinning have been studied under active tensile straining conditions using the double-exposure speckle photography technique. Features of the macroscopically inhomogeneous strain localization at the yield plateau are considered. Relations between local components of the plastic distortion tensor in the zone of strain localization are analyzed.

  10. SOME MISUNDERSTANDINGS ON ROTATION OF CRYSTALS AND REASONABLE PLASTIC STRAIN RATE

    Institute of Scientific and Technical Information of China (English)

    赵祖武

    2001-01-01

    It is pointed out that crystals are discrete but not continuous materials. Hence the rotation R in decomposition F = RU and spin W in F F-1 are not correct. Errors will arise in plastic deformation rate if it is directly expressed with amounts of velocity of slips in glide systems such as γv n . The geometrical figure of crystal lattices does not change after slips and based on this idea a simple way in mechanics of continuous media to get the plastic deformations rate induced by slips is proposed. Constitutive equations are recommended.

  11. Crystallization and X-ray diffraction of crystals formed in water-plasticized amorphous lactose.

    Science.gov (United States)

    Jouppila, K; Kansikas, J; Roos, Y H

    1998-01-01

    Effects of storage time and relative humidity on crystallization and crystal forms produced from amorphous lactose were investigated. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage relative humidity. Lactose crystallized mainly as alpha-lactose monohydrate and anhydrous crystals with alpha- and beta-lactose in a molar ratio of 5:3. The results suggested that the crystal form was defined by the early nucleation process. The crystallization data are important in modeling of crystallization phenomena and prediction of stability of lactose-containing food and pharmaceutical materials.

  12. Facilitating protein crystal cryoprotection in thick-walled plastic capillaries by high-pressure cryocooling.

    Science.gov (United States)

    Chen, Yi-Fan; Tate, Mark W; Gruner, Sol M

    2009-06-01

    Many steps in the X-ray crystallographic solution of protein structures have been automated. However, the harvesting and cryocooling of crystals still rely primarily on manual handling, frequently with consequent mechanical damage. An attractive alternative is to grow crystals directly inside robust plastic capillaries that may be cryocooled and mounted on the beamline goniometer. In this case, it is still desirable to devise a way to cryoprotect the crystals, which is difficult owing to the poor thermal conductivity of thick plastic capillary walls and the large thermal mass of the capillary and internal mother liquor. A method is described to circumvent these difficulties. It is shown that high-pressure cryocooling substantially reduced the minimal concentrations of cryoprotectants required to cryocool water inside capillaries without formation of ice crystals. The minimal concentrations of PEG 200, PEG 400 and glycerol necessary for complete vitrification under pressure cryocooling were determined.

  13. 1,2,4-Triazolium perfluorobutanesulfonate as an archetypal pure protic organic ionic plastic crystal electrolyte for all-solid-state fuel cells

    DEFF Research Database (Denmark)

    Luo, Jiangshui; Jensen, Annemette Hindhede; Brooks, Neil R.

    2015-01-01

    1,2,4-Triazolium perfluorobutanesulfonate (1), a novel, pure protic organic ionic plastic crystal (POIPC) with a wide plastic crystalline phase, has been explored as a proof-of-principle anhydrous proton conductor for all-solid-state high temperature hydrogen/air fuel cells. Its physicochemical...... weakening of hydrogen bonds at 82 C seems to be coupled with the onset of orientational or rotational disorder of the ions. The temperature dependence of ionic conductivity in the solid and molten states is measured via impedance spectroscopy and current interruption technique, respectively. The Arrhenius......), plastic crystalline (phase II and I) and melt phases successively from 173 C to 200 C. Differential scanning calorimetry and temperature dependent powder X-ray diffraction (XRD) measurements together with polarized optical microscopy and thermomechanical analysis reveal the two solid–solid phase...

  14. Dynamic behavior of oscillatory plastic flow in a smectic liquid crystal

    Science.gov (United States)

    Herke, Richard A.; Clark, 1., Noel A.; Handschy, Mark A.

    1997-09-01

    Dynamic surface force measurements are used to study the response of a smectic-A liquid crystal under layer-normal stress. The smectic A is confined in a spherical wedge between crossed cylindrical surfaces having a minimum gap spacing of 0.5-4 μm. The force transmitted between the surfaces by the liquid crystal is measured vs surface spacing using a capacitance micrometer-based surface force apparatus. Above a threshold stress plastic flow results, consisting of individual layers being excluded or included. Each layer flow event has an intriguing dynamical structure, beginning with an enhanced drift rate, which can last for many minutes, accelerating to a rapid separation change of ~1 or 2 s duration wherein the bulk of the relaxation occurs, and tapering off to a background drift rate over a period of a 100 s or more. The single-layer nature of the observed jumps in liquid crystal thickness indicates that they are topological in origin, i.e., slippage events in the phase of the smectic-A order parameter that must necessarily involve edge or screw dislocations. A model based on the Glaberson-Clem-Oswald-Kléman helical instability in screw dislocations is the only one found to explain the data, the layering events arising from a cascade of these helical instabilities sweeping radially outward through the smectic-A sample. The slow precursor acceleration is due to the nucleation of a few helices in the thin central portion of the sample. As time goes on, the force relieved is transferred to the rest of the sample, pushing larger and larger amounts of the area into the unstable regime, and a type of chain reaction occurs whereby the bulk of a layer is removed. In the end only the material at the edge of the droplet, where the thickness is largest, is left to slowly continue to nucleate, producing a long-term tail.

  15. On the localization of plastic strain under compression of LiF crystals

    Science.gov (United States)

    Barannikova, S. A.; Nadezhkin, M. V.; Zuev, L. B.

    2010-07-01

    The plastic flow localization patterns for alkali halide LiF crystals under compression have been investigated. The main spatiotemporal regularities of the strain localization at different stages of deformation hardening in the single crystals have been established. The relation has been traced between the orientation of localized strain zones and the crystallography of slip systems of the test specimens studied simultaneously by the double-exposure speckle photography and photoelasticity methods.

  16. Phase Relationship in Phenol-Insulin Crystal Growth System

    Institute of Scientific and Technical Information of China (English)

    梁栋材; 宋浪舟; 万柱礼; 常文瑞

    1994-01-01

    Based on the crystal growth system of rhombohedral 2Zn-insulin,the phase transition ofinsulin crystals has been investigated with the phenol concentration as an independent component.The dia-gram of the phase relationship in this crystal growth system was established,and two points of phase transi-tion were found.The transition point Ⅰ indicates the phase transition between rhombohedral 2Zn-insulin crys-tal and rhombohedral 4Zn-insulin crystal,and these two phases coexist within a narrow region of phenol con-centration (0.028%-0.029% (g/ml)).Point Ⅱ at 0.76%-0.77% (g/ml) of phenol concentration showsthe phase transition between rhombohcdral crystal and monoclinic crystals,and a new phase of monocliniccrystal (B-form monoclinic insulin crystal) has been observed.This paper reports the diagram of phase rela-tionship obtained from our experiments,and analyses and discusses the dependence of phase transition of in-sulin crystals on phenol concentration in crystal growth system.

  17. Crystal plasticity modeling of through-thickness texture heterogeneity in heavily rolled aluminum

    DEFF Research Database (Denmark)

    Delannay, Laurent; Mishin, Oleg V.

    2013-01-01

    The textures measured at different depths inside a cold rolled aluminium sheet are compared to results obtained by crystal plasticity predictions. Different assumptions about the micro-to-macro scale transitions are considered. The input texture reveals a through-thickness gradient that originate...

  18. Cathodoluminescence study of e-irradiated and plastically deformed ZnO crystals

    Energy Technology Data Exchange (ETDEWEB)

    Avella, M.; Hortelano, V.; Martinez, O.; Jimenez, J. [GdS Optronlab., Univ. de Valladolid, Paseo de Belen 1, 47011 Valladolid (Spain); Mass, J. [Grupo de Fisica Aplicada, Universidad del Norte, km 5, Via Pto. Colombia, Barranquilla (Colombia); Wang, B. [Solid State Scientific Corp., 27-2 Wright Rd., Hollis, NH 03049 (United States); Drevinsky, P.; Bliss, D. [Air Force Research Laboratory, Sensors Directorate, Hanscom AFB, MA 01731 (United States)

    2012-07-15

    Intrinsic defects are generated by e-irrradiation, and plastic deformation in ZnO crystals. Spectrally resolved cathodoluminescence (CL) experiments permit the analysis of the optical signature of those defects. We present herein a CL analysis of ZnO crystals irradiated with high energy electrons, and plastically deformed by Vickers indentation. Spectral changes around 3.3 eV and in the deep level emission are observed in the irradiated samples. These changes are compared to those observed around the extended defects introduced by Vickers indentation, which present a similar signature to the e-irradiated samples, suggesting relation between the defects generated by plastic deformation and e-irradiation. Zn vacancies seem to be the dominant defects generated in both processes (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Crystal plasticity finite element modelling of the extrusion texture of a magnesium alloy

    Science.gov (United States)

    Shao, Yichuan; Tang, Tao; Li, Dayong; Tang, Weiqin; Peng, Yinghong

    2015-07-01

    In this paper, a crystal plasticity finite-element model (CPFEM) is developed to simulate the hot extrusion texture of the magnesium alloy AZ31. The crystal plasticity model is implemented in ABAQUS™ via user interface VUMAT subroutine. The elasto-plastic self-consistent (EPSC) model is used as the basic polycrystal framework to simulate the slip and twinning during the extrusion. Furthermore, this framework is extended to account for the effects of the dynamically recrystallized (DRX) grains on the extrusion textures. Good agreement is found between the experimentally measured and simulated textures. The simulation results show that the presence of a secondary texture component around || extrusion direction (ED) can be attributed to the lattice rotation around the c-axis during the formation of the DRX grains. In addition, the shear strain imposed on the extruded material affects the resulting texture by enhancing the basal slip mode as the material passes through the extrusion opening.

  20. Studies of Phase Transformation in Molecular Crystals Using the Positron Annihilation Technique

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Lightbody, David; Sherwood, John N.

    1980-01-01

    An examination has been made of the brittle/plastic phase transformation in the molecular crystals cyclohexane, DL-camphene and succinonitrile using the positron annihilation technique. In each material, the transition is characterized by a distinct increase in ortho-positronium lifetime. The inf......An examination has been made of the brittle/plastic phase transformation in the molecular crystals cyclohexane, DL-camphene and succinonitrile using the positron annihilation technique. In each material, the transition is characterized by a distinct increase in ortho-positronium lifetime....... The influence of impurities on the transition was examined for DL-camphene. Addition of the impurity tricylene in concentrations in the range 0.14-4.0 mol % resulted in a lowering of the transition temperature from 176 to 167 K and a broadening of the transition region....

  1. Corundum Based Composite Block Containing Plastic Phase YB/T 4129-2005

    Institute of Scientific and Technical Information of China (English)

    Yu Lingyan; Chai Junlan

    2009-01-01

    @@ 1 Scope This standard specifies the definition, classifica-tion, technical requirements, test methods, inspection rules, packing, marking, transportation and quality certificate of corundum block containing plastic phase.

  2. Avalanches, plasticity, and ordering in colloidal crystals under compression.

    Science.gov (United States)

    McDermott, D; Reichhardt, C J Olson; Reichhardt, C

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

  3. Modeling texture development during cold rolling of IF steel by crystal plasticity finite element method

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    With the consideration of slip deformation mechanism and various slip systems of body centered cubic (BCC) metals,Taylor-type and finite element polycrystai models were embedded into the commercial finite element code ABAQUS to realize crystal plasticity finte element modeling,based on the rate dependent crystal constitutive equations.Initial orientations measured by electron backscatter diffraction (EBSD) were directly input into the crystal plasticity finite element model to simulate the development of rolling texture of interstitial-flee steel (IF steel) at various reductions.The modeled results show a good agreement with the experimental results.With increasing reduction,the predicted and experimental rolling textures tend to sharper,and the results simulated by the Taylor-type model are stronger than those simulated by finite element model.Conclusions are obtained that rolling textures calculated with 48 {110}+{ 112}+{123} slip systems are more approximate to EBSD results.

  4. Relationship between burgers vectors of dislocations and plastic strain localization patterns in compression-strained alkali halide crystals

    Science.gov (United States)

    Barannikova, S. A.; Nadezhkin, M. V.; Zuev, L. B.

    2011-08-01

    Plastic strain localization patterns in compression-strained alkali halide (NaCl, KCl, and LiF) crystals have been studied using a double-exposure speckle photography technique. The main parameters of strain localization autowaves at the linear stages of deformation hardening in alkali halide crystals have been determined. A quantitative relationship between the macroscopic parameters of plastic flow localization and microscopic parameters of strained alkali halide crystals has been established.

  5. Synergistic Effects of Nucleating Agents and Plasticizers on the Crystallization Behavior of Poly(lactic acid

    Directory of Open Access Journals (Sweden)

    Xuetao Shi

    2015-01-01

    Full Text Available The synergistic effect of nucleating agents and plasticizers on the thermal and mechanical performance of PLA nanocomposites was investigated with the objective of increasing the crystallinity and balancing the stiffness and toughness of PLA mechanical properties. Calcium carbonate, halloysite nanotubes, talc and LAK (sulfates were compared with each other as heterogeneous nucleating agents. Both the DSC isothermal and non-isothermal studies indicated that talc and LAK were the more effective nucleating agents among the selected fillers. Poly(D-lactic acid (PDLA acted also as a nucleating agent due to the formation of the PLA stereocomplex. The half crystallization time was reduced by the addition of talc to about 2 min from 37.5 min of pure PLA by the isothermal crystallization study. The dynamic mechanical thermal study (DMTA indicated that nanofillers acted as both reinforcement fillers and nucleating agents in relation to the higher storage modulus. The plasticized PLA studied by DMTA indicated a decreasing glass transition temperature with the increasing of the PEG content. The addition of nanofiller increased the Young’s modulus. PEG had the plasticization effect of increasing the break deformation, while sharply decreasing the stiffness and strength of PLA. The synergistic effect of nanofillers and plasticizer achieved the balance between stiffness and toughness with well-controlled crystallization.

  6. Eighth-order phase-field-crystal model for two-dimensional crystallization

    OpenAIRE

    Jaatinen, A.; Ala-Nissilä, Tapio

    2010-01-01

    We present a derivation of the recently proposed eighth-order phase-field crystal model [A. Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two-dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase-field crystal models. We find that among the phase-field crystal mod...

  7. Microstructural Characterization Of Quenched And Plastically Deformed Two-Phase α+β Titanium Alloys

    Directory of Open Access Journals (Sweden)

    Motyka M.

    2015-09-01

    Full Text Available Development of microstructure in two-phase α+β titanium alloys is realized by thermomechanical processing – sequence of heat treatment and plastic working operations. Analysis of achieved results indicates that hot plastic deformation – depending on deformation degree – causes significant elongation of α phase grains. Following heat treatment and plastic deformation processes lead to their fragmentation and spheroidization. Characterization of microstructure morphology changes during thermomechanical processing of quenched Ti-6Al-4V and Ti-6Al-2Mo-2Cr alloys is presented in the paper. The effect of martensitic phase α’(α” on microstructure development in plastic deformation process was confirmed.

  8. Formation of porous crystals via viscoelastic phase separation

    Science.gov (United States)

    Tsurusawa, Hideyo; Russo, John; Leocmach, Mathieu; Tanaka, Hajime

    2017-10-01

    Viscoelastic phase separation of colloidal suspensions can be interrupted to form gels either by glass transition or by crystallization. With a new confocal microscopy protocol, we follow the entire kinetics of phase separation, from homogeneous phase to different arrested states. For the first time in experiments, our results unveil a novel crystallization pathway to sponge-like porous crystal structures. In the early stages, we show that nucleation requires a structural reorganization of the liquid phase, called stress-driven ageing. Once nucleation starts, we observe that crystallization follows three different routes: direct crystallization of the liquid phase, the Bergeron process, and Ostwald ripening. Nucleation starts inside the reorganized network, but crystals grow past it by direct condensation of the gas phase on their surface, driving liquid evaporation, and producing a network structure different from the original phase separation pattern. We argue that similar crystal-gel states can be formed in monatomic and molecular systems if the liquid phase is slow enough to induce viscoelastic phase separation, but fast enough to prevent immediate vitrification. This provides a novel pathway to form nanoporous crystals of metals and semiconductors without dealloying, which may be important for catalytic, optical, sensing, and filtration applications.

  9. Phase Change Enthalpies and Entropies of Liquid Crystals

    National Research Council Canada - National Science Library

    Acree, William E; Chickos, James S

    2006-01-01

    .... A group additivity approach used to estimate total phase change entropies of organic molecules applied to 627 of these liquid crystals is found to significantly overestimate their total phase change entropies...

  10. Evolution of Dislocation Subsystem Components During Plastic Deformation Depending on Parameters of Strengthening Phase with L12 Superstructure

    Science.gov (United States)

    Daneyko, O. I.; Kovalevskaya, T. A.; Kulaeva, N. A.; Kolupaeva, S. N.; Shalygina, T. A.

    2017-09-01

    The paper presents results of mathematical modelling of plastic deformation in dispersion-hardened materials with FCC crystal system and L12 superstructure particles. Research results show that the size and the distance between particles of the strengthening phase affect the strain hardening and the evolution of the dislocation subsystem of the FCC alloy hardened with coherent L12 superstructure particles. It is found that increased size of ordered particles or decreased distance between them enhances the abnormal growth in the flow stress and the density of the dislocation subsystem components. Investigations show that prismatic dislocation loops predominate in the dislocation subsystem of materials having a nano-dispersion strengthening phase.

  11. Modeling the coupling between martensitic phase transformation and plasticity in shape memory alloys

    Science.gov (United States)

    Manchiraju, Sivom

    The thermo-mechanical response of NiTi shape memory alloys (SMAs) is predominantly dictated by two inelastic deformation processes---martensitic phase transformation and plastic deformation. This thesis presents a new microstructural finite element (MFE) model that couples these processes and anisotropic elasticity. The coupling occurs via the stress redistribution induced by each mechanism. The approach includes three key improvements to the literature. First, transformation and plasticity are modeled at a crystallographic level and can occur simultaneously. Second, a rigorous large-strain finite element formulation is used, thereby capturing texture development (crystal rotation). Third, the formulation adopts recent first principle calculations of monoclinic martensite stiffness. The model is calibrated to experimental data for polycrystalline NiTi (49.9 at% Ni). Inputs include anisotropic elastic properties, texture, and DSC data as well as a subset of pseudoelastic and load-biased thermal cycling data. This calibration process provides updated material values---namely, larger self-hardening between similar martensite plates. It is then assessed against additional pseudoelastic and load-biased thermal cycling experimental data and neutron diffraction measurements of martensite texture evolution. Several experimental trends are captured---in particular, the transformation strain during thermal cycling monotonically increases with increasing bias stress, reaching a peak and then decreasing due to intervention of plasticity---a trend which existing MFE models are unable to capture. Plasticity is also shown to enhance stress-induced martensite formation during loading and generate retained martensite upon unloading. The simulations even enable a quantitative connection between deformation processing and two-way shape memory effect. Some experimental trends are not captured---in particular, the ratcheting of macrostrain with repeated thermal cycling. This may

  12. Phase transformations during the growth of paracetamol crystals from the vapor phase

    Science.gov (United States)

    Belyaev, A. P.; Rubets, V. P.; Antipov, V. V.; Bordei, N. S.

    2014-07-01

    Phase transformations during the growth of paracetamol crystals from the vapor phase are studied by differential scanning calorimetry. It is found that the vapor-crystal phase transition is actually a superposition of two phase transitions: a first-order phase transition with variable density and a second-order phase transition with variable ordering. The latter, being a diffuse phase transition, results in the formation of a new, "pretransition," phase irreversibly spent in the course of the transition, which ends in the appearance of orthorhombic crystals. X-ray diffraction data and micrograph are presented.

  13. Fundamental display properties of flexible devices containing polymer-stabilized ferroelectric liquid crystal between plastic substrates

    Science.gov (United States)

    Fujikake, Hideo; Murashige, Takeshi; Sato, Hiroto; Iino, Yoshiki; Kawakita, Masahiro; Kikuchi, Hiroshi

    2002-09-01

    We describe several fundamental display properties of a flexible ferroelectric liquid crystal device containing polymer fibers between thin plastic substrates. The composite film of liquid crystal and polymer was created from a solution of liquid crystal and monomer materials between the plastic substrates under ultraviolet light irradiation. The dynamic electrooptic response to analog voltage pulses was examined with an incidence of laser beam light, and its light modulation property exhibited good linearity in continuous gray-scale capability. The excellent spatial uniformity of liquid crystal alignment formed between the flexible substrates resulted in high-contrast light modulation, although slight spontaneous bending of liquid crystal alignment in the device plane was recognized. When the laser light beam was obliquely incident on the flexible display device, the measured transmittance revealed that the device has a wide viewing angle of more than 100 deg without contrast reversal. This is considered to be caused by the molecular switching in the device plane and the thin electrooptic layer in the display device.

  14. Validation of a crystal plasticity model using high energy diffraction microscopy

    Science.gov (United States)

    Beaudoin, A. J.; Obstalecki, M.; Storer, R.; Tayon, W.; Mach, J.; Kenesei, P.; Lienert, U.

    2012-03-01

    High energy diffraction microscopy is used to measure the crystallographic orientation and evolution of lattice strain in an Al-Li alloy. The relative spatial arrangement of the several pancake-shaped grains in a tensile sample is determined through in situ and ex situ techniques. A model for crystal plasticity with continuity of lattice spin is posed, where grains are represented by layers in a finite element mesh following the arrangement indicated by experiment. Comparison is drawn between experiment and simulation.

  15. Validation of a Crystal Plasticity Model Using High Energy Diffraction Microscopy

    Science.gov (United States)

    Beaudoin, A. J.; Obstalecki, M.; Storer, R.; Tayon, W.; Mach, J.; Kenesei, P.; Lienert, U.

    2012-01-01

    High energy diffraction microscopy is used to measure the crystallographic orientation and evolution of lattice strain in an Al Li alloy. The relative spatial arrangement of the several pancake-shaped grains in a tensile sample is determined through in situ and ex situ techniques. A model for crystal plasticity with continuity of lattice spin is posed, where grains are represented by layers in a finite element mesh following the arrangement indicated by experiment. Comparison is drawn between experiment and simulation.

  16. Improvement for the steering performance of liquid crystal phased array

    Institute of Scientific and Technical Information of China (English)

    SONG Yan; KONG Ling-jiang; CHEN Jun; ZHU Ying; YANG Jian-yu

    2009-01-01

    Optical phased array technology is introduced and the steering performances of liquid crystal phased array are discussed, several factors affecting the beam steering performances arc analyzed completely, also simple models for some typical factors are developed. Then, a new method based on iterating and modifying the output phase pattern of liquid crystal phase shifters is proposed. Using this method, the modified voltages applied on electrodes of liquid crystal phase shifters can be obtained, after applying the voltages, the influence of factors can be compensated to some extent; the steering angle accu-racy and efficiency with liquid crystal phased array can be improved. Through the simulation for the angle range from 0° to -1°, the error of steering angle can be reduced three orders of magnitude, and the efficiency can be increased almost 30% after several iterations.

  17. Comparison of Lithium Gadolinium Borate Crystal Shards in Scintillating and Nonscintillating Plastic Matrices

    CERN Document Server

    Kazkaz, Kareem; Pedretti, Marisa

    2011-01-01

    We present a method for detecting neutrons using scintillating lithium gadolinium borate crystal shards in a plastic matrix while maintaining high gamma rejection. We have procured two cylindrical detectors, 5"\\times5", containing 1% crystal by mass. Crystal shards have a typical dimension of 1 mm. One detector was made with scintillating plastic, and one with nonscintillating plastic. Pulse shape analysis was used to reject gamma ray backgrounds. The scintillating detector was measured to have an intrinsic fast fission neutron efficiency of 0.4% and a gamma sensitivity of less than 2.3 \\times 10-9, while the nonscintillating detector had a neutron efficiency of 0.7% and gamma sensitivity of (4.75\\pm3.94)\\times10-9. We determine that increasing the neutron detection efficiency by a factor of 2 will make the detector competitive with moderated 3He tubes, and we discuss several simple and straightforward methods for obtaining or surpassing such an improvement. We end with a discussion of possible applications, ...

  18. Correlation between crystallization behaviour and interfacial interactions in plasticized PLA/POSS nanocomposites

    Science.gov (United States)

    Kodal, Mehmet; Şirin, Hümeyra; Özkoç, Güralp

    2016-03-01

    In this study, the correlation between crystallization behavior and surface chemistry of polyhedral oligomeric silsesquioxanes (POSS) for plasticized poly(lactic acid) (PLA)/POSS nanocomposites was investigated. Four different kinds of POSS particles having different chemical structures were used. Poly(ethylene glycol) (PEG, 8000 g/mol) was utilized as the plasticiser. The nanocomposites were melt-compounded in an Xplore Instruments 15 cc twin screw microcompounder at 180°C barrel temperature and 100 rpm screw speed. Non-isothermal crystallization behaviour of PLA/PEG/POSS nanocomposites were evaluated from common kinetic models such as Avrami and Avrami-Ozawa and Kissinger by using the thermal data obtained from differantial scanning calorimetry (DSC). A polarized optical microscope (POM) equipped with a hot-stage was used to examine the morphology during the crystal growth. In order to investigate the interfacial interactions between POSS particles and plasticized PLA, thermodynamic work of adhesion approach was adopted using the experimentally determined surface energies. A strong correlation was obtained between interfacial chemistry and the nucleation rate in plasticized PLA/POSS nanocomposites. It was found that the polar interactions were the dominating factor which determines the nucleation activity of the POSS particles.

  19. A Plastic-Crystal Electrolyte Interphase for All-Solid-State Sodium Batteries.

    Science.gov (United States)

    Gao, Hongcai; Xue, Leigang; Xin, Sen; Park, Kyusung; Goodenough, John B

    2017-05-08

    The development of all-solid-state rechargeable batteries is plagued by a large interfacial resistance between a solid cathode and a solid electrolyte that increases with each charge-discharge cycle. The introduction of a plastic-crystal electrolyte interphase between a solid electrolyte and solid cathode particles reduces the interfacial resistance, increases the cycle life, and allows a high rate performance. Comparison of solid-state sodium cells with 1) solid electrolyte Na3 Zr2 (Si2 PO4 ) particles versus 2) plastic-crystal electrolyte in the cathode composites shows that the former suffers from a huge irreversible capacity loss on cycling whereas the latter exhibits a dramatically improved electrochemical performance with retention of capacity for over 100 cycles and cycling at 5 C rate. The application of a plastic-crystal electrolyte interphase between a solid electrolyte and a solid cathode may be extended to other all-solid-state battery cells. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. MIR phasing using merohedrally twinned crystals

    NARCIS (Netherlands)

    Terwisscha van Scheltinga, Anke C.; Valegård, Karin; Hajdu, Janos; Andersson, Inger

    2003-01-01

    Merohedral twinning is a crystal-growth disorder that seriously hinders the determination of macromolecular crystal structures by isomorphous replacement. The strategies used in the structures solved so far are discussed. Several methods can be used to determine the extent of twinning, the twin frac

  1. Numerical implementation of a crystal plasticity model with dislocation transport for high strain rate applications

    Science.gov (United States)

    Mayeur, Jason R.; Mourad, Hashem M.; Luscher, Darby J.; Hunter, Abigail; Kenamond, Mark A.

    2016-05-01

    This paper details a numerical implementation of a single crystal plasticity model with dislocation transport for high strain rate applications. Our primary motivation for developing the model is to study the influence of dislocation transport and conservation on the mesoscale response of metallic crystals under extreme thermo-mechanical loading conditions (e.g. shocks). To this end we have developed a single crystal plasticity theory (Luscher et al (2015)) that incorporates finite deformation kinematics, internal stress fields caused by the presence of geometrically necessary dislocation gradients, advection equations to model dislocation density transport and conservation, and constitutive equations appropriate for shock loading (equation of state, drag-limited dislocation velocity, etc). In the following, we outline a coupled finite element-finite volume framework for implementing the model physics, and demonstrate its capabilities in simulating the response of a [1 0 0] copper single crystal during a plate impact test. Additionally, we explore the effect of varying certain model parameters (e.g. mesh density, finite volume update scheme) on the simulation results. Our results demonstrate that the model performs as intended and establishes a baseline of understanding that can be leveraged as we extend the model to incorporate additional and/or refined physics and move toward a multi-dimensional implementation.

  2. Photon Cascade from a Single Crystal Phase Nanowire Quantum Dot

    DEFF Research Database (Denmark)

    Bouwes Bavinck, Maaike; Jöns, Klaus D; Zieliński, Michal

    2016-01-01

    unprecedented potential to be controlled with atomic layer accuracy without random alloying. We show for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width...... quantum optical properties for single photon application and quantum optics.......We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer...

  3. Highly birefringent crystal for Raman transitions with phase modulators

    Science.gov (United States)

    Arias, Nieves; Abediyeh, Vahide; Hamzeloui, Saeed; Jeronimo-Moreno, Yasser; Gomez, Eduardo

    2016-05-01

    We present a system to excite Raman transitions with minimum phase noise. The system uses a phase modulator to generate the phase locked beams required for the transition. We use a long calcite crystal to filter out one of the sidebands, avoiding the cancellation that appears at high detunings for phase modulation. The measured phase noise is limited by the quality of the microwave synthesizer. We use the calcite crystal a second time to produce a co-propagating Raman pair with perpendicular polarizations to drive velocity insensitive Raman transitions. Support from CONACYT and Fundacion Marcos Moshinsky.

  4. Geometric constraints on phase coexistence in vanadium dioxide single crystals

    Science.gov (United States)

    McGahan, Christina; Gamage, Sampath; Liang, Jiran; Cross, Brendan; Marvel, Robert E.; Haglund, Richard F.; Abate, Yohannes

    2017-02-01

    The appearance of stripe phases is a characteristic signature of strongly correlated quantum materials, and its origin in phase-changing materials has only recently been recognized as the result of the delicate balance between atomic and mesoscopic materials properties. A vanadium dioxide (VO2) single crystal is one such strongly correlated material with stripe phases. Infrared nano-imaging on low-aspect-ratio, single-crystal VO2 microbeams decorated with resonant plasmonic nanoantennas reveals a novel herringbone pattern of coexisting metallic and insulating domains intercepted and altered by ferroelastic domains, unlike previous reports on high-aspect-ratio VO2 crystals where the coexisting metal/insulator domains appear as alternating stripe phases perpendicular to the growth axis. The metallic domains nucleate below the crystal surface and grow towards the surface with increasing temperature as suggested by the near-field plasmonic response of the gold nanorod antennas.

  5. Geometric constraints on phase coexistence in vanadium dioxide single crystals.

    Science.gov (United States)

    McGahan, Christina; Gamage, Sampath; Liang, Jiran; Cross, Brendan; Marvel, Robert E; Haglund, Richard F; Abate, Yohannes

    2017-02-24

    The appearance of stripe phases is a characteristic signature of strongly correlated quantum materials, and its origin in phase-changing materials has only recently been recognized as the result of the delicate balance between atomic and mesoscopic materials properties. A vanadium dioxide (VO2) single crystal is one such strongly correlated material with stripe phases. Infrared nano-imaging on low-aspect-ratio, single-crystal VO2 microbeams decorated with resonant plasmonic nanoantennas reveals a novel herringbone pattern of coexisting metallic and insulating domains intercepted and altered by ferroelastic domains, unlike previous reports on high-aspect-ratio VO2 crystals where the coexisting metal/insulator domains appear as alternating stripe phases perpendicular to the growth axis. The metallic domains nucleate below the crystal surface and grow towards the surface with increasing temperature as suggested by the near-field plasmonic response of the gold nanorod antennas.

  6. A dialogue about protein crystallization and phase diagrams.

    Science.gov (United States)

    Asherie, Neer

    2012-07-01

    A lighthearted researcher and a disheartened student discuss the challenges of protein crystallization and how phase diagrams can be used to address these challenges. The student feels a little better afterwards, but many proteins remain uncrystallized.

  7. Phase Field Modeling of Twinning in Indentation of Transparent Crystals

    Science.gov (United States)

    2011-09-01

    twin boundaries . Equilibrium configurations of deformed and twinned crystals are attained via direct energy minimization. The theory is framed in the...phases: (i) the original crystal (the parent) and (ii) the twin. Interfaces between phases are twin boundaries . Order parameter η generally exhibits the...following values: η(X, •) = 0∀X ∈ parent, = 1∀X ∈ twin, ∈ (0, 1)∀X ∈ twin boundaries . (1) In linear elasticity, kinematic field variables are

  8. Micro-Structural Evolution and Size-Effects in Plastically Deformed Single Crystals: Strain Gradient Continuum Modeling

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah

    , to focus on their ability to capture realistic micro-structural evolution. This challenge is the main focus of the present thesis, which takes as starting point a non-work conjugate type back stress based higher order crystal plasticity theory. Within this framework, several possibilities for the back......An extensive amount of research has been devoted to the development of micro-mechanics based gradient plasticity continuum theories, which are necessary for modeling micron-scale plasticity when large spatial gradients of plastic strain appear. While many models have proven successful in capturing...... the macroscopic effects related to strain gradients, most predict smooth micro-structures. The evolution of dislocation micro-structures, during plastic straining of ductile crystalline materials, is highly complex and nonuniform. Published experimental measurements on deformed metal crystals show distinct...

  9. Stability and plasticizing and crystallization effects of vitamins in amorphous sugar systems.

    Science.gov (United States)

    Zhou, Yankun; Roos, Yrjö H

    2012-02-01

    Increased molecular mobility and structural changes resulting from water plasticization of glassy solids may lead to loss of the entrapped compounds from encapsulant systems. In the present study, the stability of water-soluble vitamins, vitamin B(1) (vB(1), thiamin hydrochloride) and vitamin C (vC, ascorbic acid), in freeze-dried lactose and trehalose at various water activities was studied. Water sorption of lactose-vB(1), lactose-vC, trehalose-vB(1), and trehalose-vC systems was determined gravimetrically. Glass transition and crystallization of anhydrous and plasticized sugar-vitamin systems were determined using thermal analysis. Critical water activity was calculated using water sorption and glass transition data. The retention of the vitamins was measured spectrophotometrically. The results showed that the amorphous structure protected the entrapped vitamins at low a(w). Crystallization of lactose accelerated vitamin degradation, whereas trehalose retained much higher amounts of the vitamins. Glass transition and critical water activity of solids and crystallization of component sugars should be considered in the stabilization of sensitive components.

  10. A Study of Hardening Behavior Based on a Finite-Deformation Gradient Crystal-Plasticity Model

    CERN Document Server

    Pouriayevali, Habib

    2016-01-01

    A systematic study on the different roles of the governing components of a well-defined finite-deformation gradient crystal-plasticity model proposed by (Gurtin, 2008b) is carried out, in order to visualize the capability of the model in the prediction of a wide range of hardening behaviors as well as rate-dependent, scale-variation and Bauschinger-like responses in a single crystal. A function of accumulation rates of dislocations is employed and viewed as a measure of formation of short-range interactions which impede dislocation movements within a crystal. The model is first represented in the reference configuration for the purpose of numerical implementation, and then implemented in the FEM software ABAQUS via a user-defined subroutine (UEL). Our simulation results reveal that the dissipative gradient-strengthening is also identified as a source of isotropic-hardening behavior, which represents the effect of cold work introduced by (Gurtin and Ohno, 2011). Moreover, plastic flows in predefined slip syste...

  11. A Rate-Dependent Crystal Plasticity Analysis of Orientation Stability in Biaxial Tension of Magnesium

    Institute of Scientific and Technical Information of China (English)

    Donghong Zhang; Saiyi Li

    2011-01-01

    The development of texture during plastic deformation plays an important role in determining the stretch formability of magnesium alloy sheets. In this study, the orientation stability during equibiaxial tension of magnesium was analyzed based on three dimensional lattice rotations calculated by using a rate-dependent crystal plasticity model and assuming five different combinations of slip modes. The results show that no orientations can satisfy the stability criteria with both zero rotation velocity and convergent orientation flow in all dimensions. However, relatively stable orientations with zero rotation velocity and an overall convergence are found. They are featured by characteristic alignments of specific crystallographic directions in the macroscopic axis of contraction, depending on the slip modes involved in the deformation. It is also shown that the orientation stability varies significantly with the deviation of deformation mode from equibiaxial tension. The simulation results are briefly discussed in comparison with pre-existing experiments.

  12. Plastic vortex-creep in $YBa_{2}Cu_{3}O_{7-x}$ crystals

    CERN Document Server

    Abulafia, Y; Wolfus, Y; Prozorov, R; Burlachkov, L; Yeshurun, Y; Zeldov, D M E; Wühl, H; Geshkenbein, B V; Vinokur, V M

    1996-01-01

    Local magnetic relaxation measurements in YBa$_2$Cu$_3$O$_{7-x}$ crystals show evidence for plastic vortex-creep associated with the motion of dislocations in the vortex lattice. This creep mechanism governs the vortex dynamics in a wide range of temperatures and fields below the melting line and above the field corresponding to the peak in the ''fishtail'' magnetization. In this range the activation energy $U_{pl}$, which decreases with field, drops below the elastic (collective) creep activation energy, $U_{el}$, which increases with field. A crossover in flux dynamics from elastic to plastic creep is shown to be the origin of the fishtail in YBa$_2$Cu$_3$O$_{7-x}$.

  13. Crystallization: A phase transition process driving by chemical potential decrease

    Science.gov (United States)

    Sun, Congting; Xue, Dongfeng

    2017-07-01

    A chemical bonding model is established to describe the chemical potential decrease during crystallization. In the nucleation stage, in situ molecular vibration spectroscopy shows the increased vibration energy of constituent groups, indicating the shortened chemical bonding and the decreased chemical potential towards the formation of nuclei. Starting from the Gibbs free energy formula, the chemical potential decrease during crystallization is scaled, which depends on the released chemical bonding energy per unit phase transition zone. In the crystal growth, the direction-dependent growth rate of inorganic single crystals can be quantitatively determined, their anisotropic thermodynamic morphology can thus be constructed on the basis of relative growth rates.

  14. A defect density-based constitutive crystal plasticity framework for modeling the plastic deformation of Fe-Cr-Al cladding alloys subsequent to irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Patra, Anirban [Los Alamos National Laboratory; Wen, Wei [Los Alamos National Laboratory; Martinez Saez, Enrique [Los Alamos National Laboratory; Tome, Carlos [Los Alamos National Laboratory

    2016-02-05

    It is essential to understand the deformation behavior of these Fe-Cr-Al alloys, in order to be able to develop models for predicting their mechanical response under varied loading conditions. Interaction of dislocations with the radiation-induced defects governs the crystallographic deformation mechanisms. A crystal plasticity framework is employed to model these mechanisms in Fe-Cr-Al alloys. This work builds on a previously developed defect density-based crystal plasticity model for bcc metals and alloys, with necessary modifications made to account for the defect substructure observed in Fe-Cr-Al alloys. The model is implemented in a Visco-Plastic Self Consistent (VPSC) framework, to predict the mechanical behavior under quasi-static loading.

  15. Crystallization kinetics in liquid crystals with hexagonal precursor phases by calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Padmaja, Sunkara; Ajita, Narayanan; Potukuchi, Dakshina Murthy [Dept. of Physics, Jawaharlal Nehru Technological Univ., Kakinada (India); Srinivasulu, Maddasani; Girish, Sriram Ramchandra [Liquid Crystal Research Centre, Koneru Lakshmaiah Coll. of Engineering, Vaddeswaram (India); Pisipati, Venkata Gopala Krishna Murthy [Dept. of Chemistry, Manipal Inst. of Tech. (India)

    2010-08-15

    Design and characterization of Schiff based liquid crystalline nO.m compounds exhibiting hexagonal smectic phases are reported. Crystallization kinetics investigations are carried out in the liquid crystals (LCs) exhibiting hexagonal ordered orthogonal and tilted precursor LC phases by calorimetry. The Avrami theory is referred and results are analyzed. Influence of molecular ordering, structure, and dimensionality of the LC precursor phase on kinetics is studied. Effect of shape and flexibility of the molecule for nucleation and growth processes is investigated. Varying rate of kinetics reflects upon the transit of the system from constant type to independent type of nucleation. The trends in the Avrami parameter b and exponent n suggest sporadic nucleation. Crystal growth is interpreted as heterogeneous permeation of layered domains (or aggregates) formed by needle shaped calamitic molecules. Calorimetric observations at different crystallization temperatures CT and hold time t infer diffusion mediated crystallization. (orig.)

  16. Eighth-order phase-field-crystal model for two-dimensional crystallization

    Science.gov (United States)

    Jaatinen, A.; Ala-Nissila, T.

    2010-12-01

    We present a derivation of the recently proposed eighth-order phase-field crystal model [A. Jaatinen , Phys. Rev. E 80, 031602 (2009)10.1103/PhysRevE.80.031602] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two-dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase-field crystal models. We find that among the phase-field crystal models studied, the eighth-order fitting scheme gives results in good agreement with the density functional theory for both static and dynamic properties, suggesting it is an accurate and computationally efficient approximation to the density functional theory.

  17. Crystal plasticity finite element analysis of deformation behaviour in SAC305 solder joint

    Science.gov (United States)

    Darbandi, Payam

    Due to the awareness of the potential health hazards associated with the toxicity of lead (Pb), actions have been taken to eliminate or reduce the use of Pb in consumer products. Among those, tin (Sn) solders have been used for the assembly of electronic systems. Anisotropy is of significant importance in all structural metals, but this characteristic is unusually strong in Sn, making Sn based solder joints one of the best examples of the influence of anisotropy. The effect of anisotropy arising from the crystal structure of tin and large grain microstructure on the microstructure and the evolution of constitutive responses of microscale SAC305 solder joints is investigated. Insights into the effects of key microstructural features and dominant plastic deformation mechanisms influencing the measured relative activity of slip systems in SAC305 are obtained from a combination of optical microscopy, orientation imaging microscopy (OIM), slip plane trace analysis and crystal plasticity finite element (CPFE) modeling. Package level SAC305 specimens were subjected to shear deformation in sequential steps and characterized using optical microscopy and OIM to identify the activity of slip systems. X-ray micro Laue diffraction and high energy monochromatic X-ray beam were employed to characterize the joint scale tensile samples to provide necessary information to be able to compare and validate the CPFE model. A CPFE model was developed that can account for relative ease of activating slip systems in SAC305 solder based upon the statistical estimation based on correlation between the critical resolved shear stress and the probability of activating various slip systems. The results from simulations show that the CPFE model developed using the statistical analysis of activity of slip system not only can satisfy the requirements associated with kinematic of plastic deformation in crystal coordinate systems (activity of slip systems) and global coordinate system (shape changes

  18. On the formulations of higher-order strain gradient crystal plasticity models

    DEFF Research Database (Denmark)

    Kuroda, M.; Tvergaard, Viggo

    2008-01-01

    Recently, several higher-order extensions to the crystal plasticity theory have been proposed to incorporate effects of material length scales that were missing links in the conventional continuum mechanics. The extended theories are classified into work-conjugate and non-work-conjugate types...... backgrounds and very unlike mathematical representations. Nevertheless, both types of theories predict the same kind of material length scale effects. We have recently shown that there exists some equivalency between the two approaches in the special situation of two-dimensional single slip under small...

  19. Effects of microscopic boundary conditions on plastic deformations of small-sized single crystals

    DEFF Research Database (Denmark)

    Kuroda, Mitsutoshi; Tvergaard, Viggo

    2009-01-01

    The finite deformation version of the higher-order gradient crystal plasticity model proposed by the authors is applied to solve plane strain boundary value problems, in order to obtain an understanding of the effect of the higher-order boundary conditions. Numerical solutions are carried out...... effect of higher-order boundary conditions on the overall deformation mode of the block is observed. The bent foil has free surfaces through which dislocations can go out of the material, and we observe a strong size-dependent mechanical response resulting from the surface condition assumed....

  20. The effect of crystal-plastic deformation on Ti concentration in quartz

    Science.gov (United States)

    Nachlas, W. O.; Hirth, G.; Whitney, D. L.; Teyssier, C. P.

    2013-12-01

    Quartz is a dominant phase controlling crustal rheology and strain localization, and the sensitivity of its recrystallization mechanisms to variations in temperature, pressure, and fluid activity make evaluation of these parameters crucial to reconstructing the deformation history of quartz-bearing rocks in the lithosphere. The advent of Ti in quartz thermobarometry provides a technique with potentially powerful applications for understanding the conditions at which rocks deform plastically in the crust. However, it is unclear how ductile deformation, specifically dislocation creep, affects Ti substitution in quartz and whether the Ti concentration in quartz accurately records the conditions at which quartz recrystallized. This study addresses these questions through a series of high P-T rock deformation experiments on precisely synthesized Ti-doped quartz aggregates to investigate the influence of strain and dynamic recrystallization on the concentration of Ti in quartz. Laboratory rock deformation experiments provide an ideal opportunity to study Ti solubility in deformed quartz because they allow for recrystallization to occur in a controlled environment; deformation experiments are conducted under isothermal and isobaric conditions at constant strain rate for increasing intervals of time to isolate the effect of strain on Ti chemistry of quartz. This study employs a novel doping synthesis method to produce a quartz aggregate consisting of a large population of quartz crystals doped with a precise Ti concentration where each individual crystal has a uniform dopant distribution. Deformation of a homogeneous starting material enables simulation of a retrograde solubility path, in which a sample with an initially high, uniform concentration is modified during deformation at conditions where the solubility is substantially lower. This enables observations to be made of the mechanisms responsible for mobilizing Ti through diffusion and exsolution to adjust to the

  1. Bendable high-frequency microwave switches formed with single-crystal silicon nanomembranes on plastic substrates

    Science.gov (United States)

    Yuan, Hao-Chih; Qin, Guoxuan; Celler, George K.; Ma, Zhenqiang

    2009-07-01

    This letter presents realization of bendable rf switches operating at microwave frequencies formed with single-crystal Si nanomembranes (SiNMs) on a plastic substrate. Selectively doped 200-nm-thick SiNM is lifted off from silicon-on-insulator and transferred to a polymer substrate to form lateral P-intrinsic-N (PIN) diodes with minimized parasitic resistances. A single-pole single-throw switch, consisting of two PIN diodes connected in a shunt-series configuration, demonstrated very low insertion loss and high isolation from dc up to 20 GHz. The level of performance indicates a promise of properly processed single-crystal semiconductor nanomembranes for high-frequency applications in a number of consumer and military systems.

  2. Flexible photodetectors on plastic substrates by use of printing transferred single-crystal germanium membranes

    Science.gov (United States)

    Yuan, Hao-Chih; Shin, Jonghyun; Qin, Guoxuan; Sun, Lei; Bhattacharya, Pallab; Lagally, Max G.; Celler, George K.; Ma, Zhenqiang

    2009-01-01

    This letter presents studies of multiwavelength flexible photodetectors on a plastic substrate by use of printing transferred single-crystal germanium (Ge) membranes. Ge membranes of 250nm thickness with selectively ion-implantation doped regions were released from a germanium-on-insulator substrate and integrated with a 175-μm-thick polyethylene terephthalate substrate via a dry printing technique. Photodiodes configured in lateral p-i-n configuration using the flexible Ge membranes with an intrinsic region width of 10μm exhibit an external quantum efficiency that varies from 5% at 411nm to 42% at 633nm under -1V bias condition. These results demonstrate the potential of utilizing single-crystal Ge-membrane photodiodes for imaging applications and as solar cells on objects with arbitrary curvatures and shapes.

  3. The Plastic and Liquid Phases of CCl$_3$Br Studied by Molecular Dynamics Simulations

    CERN Document Server

    Caballero, Nirvana; Carignano, Marcelo; Serra, Pablo

    2013-01-01

    We present a molecular dynamics study of the liquid and plastic crystalline phases of CCl$_3$Br. We investigated the short-range orientational order using a recently developed classification method and we found that both phases behave in a very similar way. The only differences occur at very short molecular separations, which are shown to be very rare. The rotational dynamics was explored using time correlation functions of the molecular bonds. We found that the relaxation dynamics corresponds to an isotropic diffusive mode for the liquid phase, but departs from this behavior as the temperature is decreased and the system transitions into the plastic phase.

  4. The effect of crystal plasticity and mineral stability on the rheological properties of magma during spine extrusion at Unzen, Japan

    Science.gov (United States)

    Wallace, Paul A.; Kendrick, Jackie E.; Lavallée, Yan; Ashworth, James D.; Mariani, Elisabetta; von Aulock, Felix W.; Coats, Rebecca; Miwa, Takahiro

    2016-04-01

    The presence of crystals in silicic magmas is known to have a significant effect on the rheological properties inducing a non-Newtonian response. Plastic deformation of the crystalline phase in magmatic suspensions is believed to be partially responsible for this characteristic behaviour via accommodating strain, but little has been investigated on its role in volcanic processes. The spine extrusion following the final stages of endogenous growth of the 1991-95 lava dome eruption at Unzen volcano, Japan, has provided a unique opportunity to investigate the contribution of the different deformation mechanisms and varying petrological phenomena associated with magma ascent. The spine forms a shear zone consisting of four structurally discrete units over a 6 m transect including: gouge (1), a heavily sheared zone (2) to a moderately sheared zone (3), and an undeformed magmatic core (4). Here we report the first systematic study of the microstructures, mineralogy, crystal stability, geochemistry and crystal size distribution across this shear zone. The spine samples are porphyritic dacites with varying abundance of phenocrysts (20-30 vol.%), dominantly plagioclase, hornblende and biotite with minor quartz. The groundmass contains the same mineralogy plus pyroxene, magnetite and ilmenite. The microlites (35 vol.%) show a strong trachytic texture in areas of high shear, providing evidence of strain localisation. Brittle deformation is evident across the spine, with the higher sheared samples showing more crystal size reduction of the phenocrysts. By performing high-temperature (900° C) uniaxial compressive strength tests at constant strain rates (10-5 and 10-3 s-1), it can be inferred that crystals play a key role in the rheological properties, by forming a rigid but weak network that serves to partition stress and thus localise strain within the flowing melt. Electron backscatter diffraction (EBSD) enables the identification of crystal plasticity in both phenocrysts

  5. A test of cirrus ice crystal scattering phase functions

    Science.gov (United States)

    Field, P. R.; Baran, A. J.; Kaye, P. H.; Hirst, E.; Greenaway, R.

    2003-07-01

    In-situ ice crystal scattering has been measured in cirrus cloud with the Small Ice Detector laser scattering probe. Using light scattered from single particles (maximum dimension ~<100 μm) at 4-10° and 20-40° we have tested ice crystal scattering phase functions for spheres, hexagonal columns, hexagonal plates, polycrystals an aggregate of columns and an analytic function. We find that phase functions that lack a pronounced 22° halo are the best representatives for the example data presented here. Spherical ice particle phase functions do not satisfy the measurements.

  6. Crystallization phase diagram, the growth of large single crystals of bovine {beta}-Lactoglobulin A

    Energy Technology Data Exchange (ETDEWEB)

    Yagi, D; Ohnishi, Y; Tanaka, I; Niimura, N, E-mail: niimura@mx.ibaraki.ac.jp

    2010-11-01

    A crystallization phase diagram defining the meta-stable region of bovine {beta}-lactoglobulin A ({beta}-Lg) was firstly determined by a dialysis method. We have succeeded in growing a large single crystal of {beta}-Lg by selecting a crystal grown in this ''meta-stable region'' method described in the present paper. The quality of protein crystals was characterized quantitatively via rapid X-ray data collections, followed by the use of Wilson plots to analyze their resulting average B-factors.

  7. Crystallization phase diagram, the growth of large single crystals of bovine β-Lactoglobulin A

    Science.gov (United States)

    Yagi, D.; Ohnishi, Y.; Tanaka, I.; Niimura, N.

    2010-11-01

    A crystallization phase diagram defining the meta-stable region of bovine β-lactoglobulin A (β-Lg) was firstly determined by a dialysis method. We have succeeded in growing a large single crystal of β-Lg by selecting a crystal grown in this "meta-stable region" method described in the present paper. The quality of protein crystals was characterized quantitatively via rapid X-ray data collections, followed by the use of Wilson plots to analyze their resulting average B-factors.

  8. Large three-dimensional photonic crystals based on monocrystalline liquid crystal blue phases.

    Science.gov (United States)

    Chen, Chun-Wei; Hou, Chien-Tsung; Li, Cheng-Chang; Jau, Hung-Chang; Wang, Chun-Ta; Hong, Ching-Lang; Guo, Duan-Yi; Wang, Cheng-Yu; Chiang, Sheng-Ping; Bunning, Timothy J; Khoo, Iam-Choon; Lin, Tsung-Hsien

    2017-09-28

    Although there have been intense efforts to fabricate large three-dimensional photonic crystals in order to realize their full potential, the technologies developed so far are still beset with various material processing and cost issues. Conventional top-down fabrications are costly and time-consuming, whereas natural self-assembly and bottom-up fabrications often result in high defect density and limited dimensions. Here we report the fabrication of extraordinarily large monocrystalline photonic crystals by controlling the self-assembly processes which occur in unique phases of liquid crystals that exhibit three-dimensional photonic-crystalline properties called liquid-crystal blue phases. In particular, we have developed a gradient-temperature technique that enables three-dimensional photonic crystals to grow to lateral dimensions of ~1 cm (~30,000 of unit cells) and thickness of ~100 μm (~ 300 unit cells). These giant single crystals exhibit extraordinarily sharp photonic bandgaps with high reflectivity, long-range periodicity in all dimensions and well-defined lattice orientation.Conventional fabrication approaches for large-size three-dimensional photonic crystals are problematic. By properly controlling the self-assembly processes, the authors report the fabrication of monocrystalline blue phase liquid crystals that exhibit three-dimensional photonic-crystalline properties.

  9. Direct observation of plasticity and quantitative hardness measurements in single crystal cyclotrimethylene trinitramine by nanoindention

    Energy Technology Data Exchange (ETDEWEB)

    Ramos, Kyle J [Los Alamos National Laboratory; Hooks, David E [Los Alamos National Laboratory; Bahr, David F [WSU

    2008-01-01

    Investigation of deformation beginning with elasticity and continuing through the elastic-plastic transition to incipient cracking has been conducted for (210), (021), and (001) oriented single crystals of the explosive cyclotrimethylene trinitramine, commonly known as 'RDX' Instrumented indentation was performed with a conical tip over a range of loads. The resulting load-depth data exhibited distinct, reproducible, orientation dependent load excursions demonstrating elastic-plastic transitions. Indent impressions were imaged by scanning probe microscopy. Impressions on the (210) and (001) planes showed deformation pileup features associated with zone axes of slip planes. Clearly discernable slip traces were evident on the (210) plane. The (021) indentations produced significant material pile-up surrounding the impression, but did not contain discrete features associable with specific zone axes. All of the orientations exhibited cracking thresholds at very low loads. The reduced moduli were anisotropic and the hardness's were isotropic indicating limited plasticity. Maximum shear stresses estimated from a Hertzian model, at load excursions, were within a factor of 10 of published shear moduli indicating deformation initiated near the theoretical yield strength presumably by homogeneous nucleation of dislocations. The material strength parameters and apparent deformation pathways inferred from this work are compared to historical microhardness testing and interpretation of anisotropic hardness in which ambiguity of results can be attributed to the effects of cracking and simultaneous slip on multiple systems.

  10. Orientation dependence of the plastic slip near notches in ductile FCC single crystals

    Science.gov (United States)

    Crone, W. C.; Shield, T. W.; Creuziger, A.; Henneman, B.

    2004-01-01

    Results from experiments conducted on copper FCC single crystals are reported. Two symmetric crystallographic orientations and four nonsymmetric crystallographic orientations were tested. The slip line fields that form near a pre-existing notch in these specimens were observed. The changes in these patterns as the orientation of the notch in the crystal is rotated in an {101} plane are discussed. Sectors of similar slip line patterns are identified and the type of boundaries between these sectors are discussed. A type of sector boundary called mixed kink is identified. Specimen orientations that differ by 90° are found to have different slip line patterns, contrary to the predictions of perfectly plastic slip line theory. The locations of the first slip lines to form are compared to the predictions obtained using anisotropic linear elastic stress field solutions and the initial plane-strain yield surfaces. It is found that comparison of these surface slip line fields to plane strain crack tip solutions in the annular region between 350 and 750 μm is justified. The differences in anisotropic elastic solutions for orientations that are 90° apart explain the lack of agreement with perfectly plastic slip line theory.

  11. Structural recovery in plastic crystals by time-resolved non-linear dielectric spectroscopy.

    Science.gov (United States)

    Riechers, Birte; Samwer, Konrad; Richert, Ranko

    2015-04-21

    The dielectric relaxation of several different plastic crystals has been examined at high amplitudes of the ac electric fields, with the aim of exploring possible differences with respect to supercooled liquids. In all cases, the steady state high field loss spectrum appears to be widened, compared with its low field limit counterpart, whereas peak position and peak amplitude remain almost unchanged. This field induced change in the loss profile is explained on the basis of two distinct effects: an increased relaxation time due to reduced configurational entropy at high fields which affects the low frequency part of the spectrum, and accelerated dynamics at frequencies above the loss peak position resulting from the added energy that the sample absorbs from the external electric field. From the time-resolved assessment of the field induced changes in fictive temperatures at relatively high frequencies, we find that this structural recovery is slaved to the average rather than mode specific structural relaxation time. In other words, the very fast relaxation modes in the plastic crystal cannot adjust their fictive temperatures faster than the slower modes, the equivalent of time aging-time superposition. As a result, an explanation for this single fictive temperature must be consistent with positional order, i.e., translational motion or local density fluctuations do not govern the persistence time of local time constants.

  12. Hexatic, Wigner Crystal, and Superfluid Phases of Dipolar Bosons

    OpenAIRE

    Mitra, Kaushik; Williams, C J; de Melo, C. A. R. Sá

    2009-01-01

    The finite temperature phase diagram of two-dimensional dipolar bosons versus dipolar interaction strength is discussed. We identify the stable phases as dipolar superfluid (DSF), dipolar Wigner crystal (DWC), dipolar hexatic fluid (DHF), and dipolar normal fluid (DNF). We also show that other interesting phases like dipolar supersolid (DSS) and dipolar hexatic superfluid (DHSF) are at least metastable, and can potentially be reached by thermal quenching. In particular, for large densities or...

  13. Vitrification and Crystallization of Phase-Separated Metallic Liquid

    Directory of Open Access Journals (Sweden)

    Yun Cheng

    2017-02-01

    Full Text Available The liquid–liquid phase separation (LLPS behavior of Fe50Cu50 melt from 3500 K to 300 K with different rapid quenching is investigated by molecular dynamics (MD simulation based on the embedded atom method (EAM. The liquid undergoes metastable phase separation by spinodal decomposition in the undercooled regime and subsequently solidifies into three different Fe-rich microstructures: the interconnected-type structure is kept in the glass and crystal at a higher cooling rate, while the Fe-rich droplets are found to crystalize at a lower cooling rate. During the crystallization process, only Fe-rich clusters can act as the solid nuclei. The twinning planes can be observed in the crystal and only the homogeneous atomic stacking shows mirror symmetry along the twinning boundary. Our present work provides atomic-scale understanding of LLPS melt during the cooling process.

  14. Fabrication of Phase-Change Polymer Colloidal Photonic Crystals

    Directory of Open Access Journals (Sweden)

    Tianyi Zhao

    2014-01-01

    Full Text Available This paper presents the preparation of phase-change polymer colloidal photonic crystals (PCs by assembling hollow latex spheres encapsulated with dodecanol for the first time. The monodispersed hollow latex spheres were obtained by phase reversion of monodispersed core-shell latex spheres in the n-hexane, which dissolves the PS core and retains the PMMA/PAA shell. The as-prepared phase-change colloidal PCs show stable phase-change behavior. This fabrication of phase-change colloidal PCs would be significant for PC’s applications in functional coatings and various optic devices.

  15. Induced smectic phases in phase diagrams of binary nematic liquid crystal mixtures.

    Science.gov (United States)

    Huang, Tsang-Min; McCreary, Kathleen; Garg, Shila; Kyu, Thein

    2011-03-28

    To elucidate induced smectic A and smectic B phases in binary nematic liquid crystal mixtures, a generalized thermodynamic model has been developed in the framework of a combined Flory-Huggins free energy for isotropic mixing, Maier-Saupe free energy for orientational ordering, McMillan free energy for smectic ordering, Chandrasekhar-Clark free energy for hexagonal ordering, and phase field free energy for crystal solidification. Although nematic constituents have no smectic phase, the complexation between these constituent liquid crystal molecules in their mixture resulted in a more stable ordered phase such as smectic A or B phases. Various phase transitions of crystal-smectic, smectic-nematic, and nematic-isotropic phases have been determined by minimizing the above combined free energies with respect to each order parameter of these mesophases. By changing the strengths of anisotropic interaction and hexagonal interaction parameters, the present model captures the induced smectic A or smectic B phases of the binary nematic mixtures. Of particular importance is the fact that the calculated phase diagrams show remarkable agreement with the experimental phase diagrams of binary nematic liquid crystal mixtures involving induced smectic A or induced smectic B phase.

  16. Micromechanics of plastic deformation and phase transformation in a three-phase TRIP-assisted advanced high strength steel: Experiments and modeling

    Science.gov (United States)

    Srivastava, Ankit; Ghassemi-Armaki, Hassan; Sung, Hyokyung; Chen, Peng; Kumar, Sharvan; Bower, Allan F.

    2015-05-01

    The micromechanics of plastic deformation and phase transformation in a three-phase advanced high strength steel are analyzed both experimentally and by microstructure-based simulations. The steel examined is a three-phase (ferrite, martensite and retained austenite) quenched and partitioned sheet steel with a tensile strength of ~980 MPa. The macroscopic flow behavior and the volume fraction of martensite resulting from the austenite-martensite transformation during deformation were measured. In addition, micropillar compression specimens were extracted from the individual ferrite grains and the martensite particles, and using a flat-punch nanoindenter, stress-strain curves were obtained. Finite element simulations idealize the microstructure as a composite that contains ferrite, martensite and retained austenite. All three phases are discretely modeled using appropriate crystal plasticity based constitutive relations. Material parameters for ferrite and martensite are determined by fitting numerical predictions to the micropillar data. The constitutive relation for retained austenite takes into account contributions to the strain rate from the austenite-martensite transformation, as well as slip in both the untransformed austenite and product martensite. Parameters for the retained austenite are then determined by fitting the predicted flow stress and transformed austenite volume fraction in a 3D microstructure to experimental measurements. Simulations are used to probe the role of the retained austenite in controlling the strain hardening behavior as well as internal stress and strain distributions in the microstructure.

  17. Understanding the Cubic Phase Stabilization and Crystallization Kinetics in Mixed Cations and Halides Perovskite Single Crystals.

    Science.gov (United States)

    Xie, Li-Qiang; Chen, Liang; Nan, Zi-Ang; Lin, Hai-Xin; Wang, Tan; Zhan, Dong-Ping; Yan, Jia-Wei; Mao, Bing-Wei; Tian, Zhong-Qun

    2017-03-08

    The spontaneous α-to-δ phase transition of the formamidinium-based (FA) lead halide perovskite hinders its large scale application in solar cells. Though this phase transition can be inhibited by alloying with methylammonium-based (MA) perovskite, the underlying mechanism is largely unexplored. In this Communication, we grow high-quality mixed cations and halides perovskite single crystals (FAPbI3)1-x(MAPbBr3)x to understand the principles for maintaining pure perovskite phase, which is essential to device optimization. We demonstrate that the best composition for a perfect α-phase perovskite without segregation is x = 0.1-0.15, and such a mixed perovskite exhibits carrier lifetime as long as 11.0 μs, which is over 20 times of that of FAPbI3 single crystal. Powder XRD, single crystal XRD and FT-IR results reveal that the incorporation of MA(+) is critical for tuning the effective Goldschmidt tolerance factor toward the ideal value of 1 and lowering the Gibbs free energy via unit cell contraction and cation disorder. Moreover, we find that Br incorporation can effectively control the perovskite crystallization kinetics and reduce defect density to acquire high-quality single crystals with significant inhibition of δ-phase. These findings benefit the understanding of α-phase stabilization behavior, and have led to fabrication of perovskite solar cells with highest efficiency of 19.9% via solvent management.

  18. Multiple topological phase transitions in a gyromagnetic photonic crystal

    KAUST Repository

    Chen, Zeguo

    2017-04-19

    We present the design of a tunable two-dimensional photonic crystal that exhibits multiple topological phases, including a conventional insulator phase, a quantum spin Hall phase, and a quantum anomalous Hall phase under different combinations of geometric parameters and external magnetic fields. Our photonic crystal enables a platform to study the topology evolution attributed to the interplay between crystalline symmetry and time-reversal symmetry. A four-band tight-binding model unambiguously reveals that the topological property is associated with the pseudospin orientations and that it is characterized by the spin Chern number. The emerging quantum anomalous Hall phase features a single helical edge state that is locked by a specific pseudospin. Simulation results demonstrate that the propagation of such a single helical edge state is robust against magnetic impurities. Potential applications, such as spin splitters, are described.

  19. Diffractive devices based on blue phase liquid crystals

    Science.gov (United States)

    Li, Yan; Huang, Shuaijia; Su, Yikai

    2016-09-01

    Blue phase liquid crystal (BPLC) has been attractive for display and photonic applications for its sub-millisecond response time, no need for surface alignment, and an optically isotropic dark state. Because of these advantages, diffractive devices based on blue phase liquid crystals have great potential for wide applications. In this work, we present several BPLC diffractive devices. The operation principles, fabrication and experimental measurements will be discussed in details for two BPLC gratings realized by holographic method and a BPLC Fresnel lens using a spatial light modulator projector. All of these devices exhibit several attractive features such as sub-millisecond response, relatively high spatial resolution and polarization-independence.

  20. Extra phase noise from thermal fluctuations in nonlinear optical crystals

    DEFF Research Database (Denmark)

    César, J. E. S.; Coelho, A.S.; Cassemiro, K.N.

    2009-01-01

    We show theoretically and experimentally that scattered light by thermal phonons inside a second-order nonlinear crystal is the source of additional phase noise observed in optical parametric oscillators. This additional phase noise reduces the quantum correlations and has hitherto hindered the d...... the direct production of multipartite entanglement in a single nonlinear optical system. We cooled the nonlinear crystal and observed a reduction in the extra noise. Our treatment of this noise can be successfully applied to different systems in the literature....

  1. Enhanced diffusion of Uranium and Thorium linked to crystal plasticity in zircon

    Directory of Open Access Journals (Sweden)

    Reddy Steven M

    2006-12-01

    Full Text Available Abstract The effects of crystal-plasticity on the U-Th-Pb system in zircon is studied by quantitative microstructural and microchemical analysis of a large zircon grain collected from pyroxenite of the Lewisian Complex, Scotland. Electron backscatter diffraction (EBSD mapping reveals a c.18° variation in crystallographic orientation that comprises both a gradual change in orientation and a series of discrete low-angle (207Pb/206Pb ages for individual analyses show no significant variation across the grain, and define a concordant, combined mean age of 2451 ± 14 Ma. This indicates that the grain was deformed shortly after initial crystallization, most probably during retrograde Inverian metamorphism at amphibolite facies conditions. The elevated Th over U and consistent 207Pb/206Pb ages indicates that deformation most likely occurred in the presence of a late-stage magmatic fluid that drove an increase in the Th/U during deformation. The relative enrichment of Th over U implies that Th/U ratio may not always be a robust indicator of crystallization environment. This study provides the first evidence of deformation-related modification of the U-Th system in zircon and has fundamental implications for the application and interpretation of zircon trace element data.

  2. Multiscale Crystal Plasticity Modeling Considering Nucleation of Dislocations Based on Thermal Activation Process on Ultrafine-grained Aluminum

    Science.gov (United States)

    Aoyagi, Y.

    2017-05-01

    In this study, a crystal plasticity model expressing the behavior of the dislocation source and the mobile dislocations is proposed by considering a thermal activation process of dislocations. In order to predict the variation of critical resolved shear stress due to grain boundaries, mobile dislocations, or dislocation sources, information on these crystal defects is introduced into a hardening law of crystal plasticity. The crystal orientation and shape of ultrafine-grained (UFG) aluminum produced by accumulative roll bonding processes are measured by electron backscatter diffraction (EBSD). Mechanical properties of the UFG aluminum are estimated using tensile test and indentation test. Results obtained by EBSD are introduced into a computational model. Finite element simulation for polycrystal of aluminum investigates the effect of microstructure on mechanical properties of UFG aluminum.

  3. Crystal growth in a three-phase system: diffusion and liquid-liquid phase separation in lysozyme crystal growth.

    Science.gov (United States)

    Heijna, M C R; van Enckevort, W J P; Vlieg, E

    2007-07-01

    In the phase diagram of the protein hen egg-white lysozyme, a region is present in which the lysozyme solution demixes and forms two liquid phases. In situ observations by optical microscopy show that the dense liquid droplets dissolve when crystals grow in this system. During this process the demixed liquid region retracts from the crystal surface. The spatial distribution of the dense phase droplets present special boundary conditions for Fick's second law for diffusion. In combination with the cylindrical symmetry provided by the kinetically roughened crystals, this system allows for a full numerical analysis. Using experimental data for setting the boundary conditions, a quasi-steady-state solution for the time-dependent concentration profile was shown to be valid. Comparison of kinetically rough growth in a phase separated system and in a nonseparated system shows that the growth kinetics for a three-phase system differs from a two-phase system, in that crystals grow more slowly but the duration of growth is prolonged.

  4. Crystal-liquid-gas phase transitions and thermodynamic similarity

    CERN Document Server

    Skripov, Vladimir P; Schmelzer, Jurn W P

    2006-01-01

    Professor Skripov obtained worldwide recognition with his monograph ""Metastable liquids"", published in English by Wiley & Sons. Based upon this work and another monograph published only in Russia, this book investigates the behavior of melting line and the properties of the coexisting crystal and liquid phase of simple substances across a wide range of pressures, including metastable states of the coexisting phases. The authors derive new relations for the thermodynamic similarity for liquid-vapour phase transition, as well as describing solid-liquid, liquid-vapor and liquid-liquid phase tra

  5. Crystallization and Characterization of Galdieria sulphuraria RUBISCO in Two Crystal Forms: Structural Phase Transition Observed in P21 Crystal Form

    Directory of Open Access Journals (Sweden)

    Boguslaw Stec

    2007-10-01

    Full Text Available We have isolated ribulose-1,5-bisphosphate-carboxylase/oxygenase (RUBISCOfrom the red algae Galdieria Sulphuraria. The protein crystallized in two different crystalforms, the I422 crystal form being obtained from high salt and the P21 crystal form beingobtained from lower concentration of salt and PEG. We report here the crystallization,preliminary stages of structure determination and the detection of the structural phasetransition in the P21 crystal form of G. sulphuraria RUBISCO. This red algae enzymebelongs to the hexadecameric class (L8S8 with an approximate molecular weight 0.6MDa.The phase transition in G. sulphuraria RUBISCO leads from two hexadecamers to a singlehexadecamer per asymmetric unit. The preservation of diffraction power in a phasetransition for such a large macromolecule is rare.

  6. Phase sensitive amplification in silicon photonic crystal waveguides

    CERN Document Server

    Yanbing,; Husko, Chad; Schroder, Jochen; Lefrancois, Simon; Rey, Isabella H; Krauss, Thomas F; Eggleton, Benjamin J

    2013-01-01

    We experimentally demonstrate phase sensitive amplification (PSA) in a silicon photonic crystal waveguide based on pump-degenerate four-wave mixing. An 11 dB phase extinction ratio is obtained in a record compact 196 {\\mu}m nanophotonic device due to broadband slow-light, in spite of the presence of two-photon absorption and free-carriers. Numerical calculations show good agreement with the experimental results.

  7. Phase-sensitive amplification in silicon photonic crystal waveguides.

    Science.gov (United States)

    Zhang, Yanbing; Husko, Chad; Schröder, Jochen; Lefrancois, Simon; Rey, Isabella H; Krauss, Thomas F; Eggleton, Benjamin J

    2014-01-15

    We experimentally demonstrate phase-sensitive amplification in a silicon photonic crystal waveguide based on pump-degenerate four-wave mixing. An 11 dB phase-extinction ratio is obtained in a record compact 196 μm nanophotonic device due to broadband slow light, in spite of the presence of two-photon absorption and free carriers. Numerical calculations show good agreement with the experimental results.

  8. Tunable phase-only optical filters with a uniaxial crystal.

    Science.gov (United States)

    Xiao, Fanrong; Yuan, Jinghe; Wang, Guiying; Xu, Zhizhan

    2004-06-10

    A novel method of fabricating phase-only optical filters that is based on the properties of a uniaxial crystal is proposed. With these optical filters, the phase differences are tunable among the different filter zones. Many focal patterns can be obtained if these optical filters are placed in front of a lens; furthermore, these optical filters can also be used to make up for the distortions in fabrications in which they were used only as untunable optical filters.

  9. Dimension Changing Phase Transitions in Instanton Crystals

    CERN Document Server

    Kaplunovsky, Vadim

    2013-01-01

    We investigate lattices of instantons and the dimension-changing transitions between them. Our ultimate goal is the 3d->4D transition, which is holographically dual to the phase transition between the baryonic and the quarkyonic phases of cold nuclear matter. However, in this paper (just as in [1]) we focus on lower dimensions -- the 1D lattice of instantons in a harmonic potential V M_2^2x_2^2+M_3^2x_2^2+M_4^2x_4^2 and the zigzag-shaped lattice as a first stage of the 1D->2D transition. We prove that in the low- and moderate-density regimes, interactions between the instantons are dominated by two-body forces. This drastically simplifies finding the ground state of the instantons' orientations, so we made a numeric scan of the whole orientation space instead of assuming any particular ansatz. We find that depending on the M_2/M_3/M_4 ratios, the ground state of instanton orientations can follow a wide variety of patterns. For the straight 1D lattices, we found orientations periodically running over elements ...

  10. Crystal plasticity extend FEM implementation of thermal-tensile aluminum alloy

    Directory of Open Access Journals (Sweden)

    Liu Yang

    2016-01-01

    Full Text Available Multi-level approach has been used to simulate the thermal deformation of aluminium alloy at different temperature and strain rate. The crystal plasticity model is extended in the finite element method and the thermal behaviour is integrated in the constitutive equations. Moreover, the damage evolution is also reflected in the simulation using continuum damage mechanics model. Thus, the void evolution and thermal effect could both be shown in the simulation. A new shear strain rate model is constructed with the thermal activated mechanism to describe the rate dependent behaviours during tensile test. The thermal parameters are determined in a fitting test of representative volume element to compare with the experimental data. The results prove that the mechanical tensile behaviour of 5052 aluminium alloy could be well described at different temperatures. The damage evolution process is expressed by the stress concentration and strain concentration in the finite element simulation, which are also confirmed by the experiments.

  11. Simulation of ultra-thin sheet metal forming using phenomenological and crystal plasticity models

    Science.gov (United States)

    Adzima, F.; Manach, PY; Balan, T.; Tabourot, L.; Toutain, S.; Diot, JL

    2016-08-01

    Micro-forming of ultra-thin sheet metals raises numerous challenges. In this investigation, the predictions of state-of-the-art crystal plasticity (CP) and phenomenological models are compared in the framework of industrial bending-dominated forming processes. Sheet copper alloys 0.1mm-thick are considered, with more than 20 grains through the thickness. Consequently, both model approaches are valid on theoretical ground. The phenomenological models’ performance was conditioned by the experimental database used for parameter identification. The CP approach was more robust with respect to parameter identification, while allowing for a less flexible description of kinematic hardening, at the cost of finer mesh and specific grain-meshing strategies. The conditions for accurate springback predictions with CP-based models are investigated, in an attempt to bring these models at the robustness level required for industrial application.

  12. Reversible Nanoparticle Cubic Lattices in Blue Phase Liquid Crystals.

    Science.gov (United States)

    Gharbi, Mohamed Amine; Manet, Sabine; Lhermitte, Julien; Brown, Sarah; Milette, Jonathan; Toader, Violeta; Sutton, Mark; Reven, Linda

    2016-03-22

    Blue phases (BPs), a distinct class of liquid crystals (LCs) with 3D periodic ordering of double twist cylinders involving orthogonal helical director twists, have been theoretically studied as potential templates for tunable colloidal crystals. Here, we report the spontaneous formation of thermally reversible, cubic crystal nanoparticle (NP) assemblies in BPs. Gold NPs, functionalized to be highly miscible in cyanobiphenyl-based LCs, were dispersed in BP mixtures and characterized by polarized optical microscopy and synchrotron small-angle X-ray scattering (SAXS). The NPs assemble by selectively migrating to periodic strong trapping sites in the BP disclination lines. The NP lattice, remarkably robust given the small particle size (4.5 nm diameter), is commensurate with that of the BP matrix. At the BP I to BP II phase transition, the NP lattice reversibly switches between two different cubic structures. The simultaneous presence of two different symmetries in a single material presents an interesting opportunity to develop novel dynamic optical materials.

  13. Metastable crystal growth of acetaminophen using solution-mediated phase transformation

    Science.gov (United States)

    Mori, Yoichiro; Maruyama, Mihoko; Takahashi, Yoshinori; Yoshikawa, Hiroshi Y.; Okada, Shino; Adachi, Hiroaki; Sugiyama, Shigeru; Takano, Kazufumi; Murakami, Satoshi; Matsumura, Hiroyoshi; Inoue, Tsuyoshi; Yoshimura, Masashi; Mori, Yusuke

    2017-01-01

    We report a new method of obtaining the metastable phase form II crystals of acetaminophen. Solution-mediated phase transformation (SMPT) from trihydrate into form II is utilized to obtain form II crystals. SMPT is triggered by seeding form II crystals into a saturated solution including trihydrate crystals, which are less stable than form II crystals. Form II seed crystals gradually grew at the expense of the dissolving trihydrate crystals, and finally, all the trihydrate crystals in solution were transformed into form II crystals in about 4 h. Thus, we conclude that SMPT is effective for the production of form II crystals.

  14. Unified rotational dynamics of molecular crystals with orientational phase transition

    NARCIS (Netherlands)

    Michel, K.H.; Raedt, H. De

    1976-01-01

    A unified theory for the rotational dynamics of molecular crystals with orientational phase transitions is given. As basic secular variables one takes symmetry adapted functions, which describe the molecular orientations, and the angular momenta of the molecules. Using Mori’s projection operator tec

  15. Phase field simulations of ice crystal growth in sugar solutions

    NARCIS (Netherlands)

    Sman, Van Der R.G.M.

    2016-01-01

    We present the first model ever, that describes explicitly ice crystal growth in a sugar solution during freezing. This 2-D model uses the phase field method, supplemented with realistic, and predictive theories on the thermodynamics and (diffusion) kinetics of this food system. We have to make u

  16. Dwell fatigue in two Ti alloys: An integrated crystal plasticity and discrete dislocation study

    Science.gov (United States)

    Zheng, Zebang; Balint, Daniel S.; Dunne, Fionn P. E.

    2016-11-01

    It is a well known and important problem in the aircraft engine industry that alloy Ti-6242 shows a significant reduction in fatigue life, termed dwell debit, if a stress dwell is included in the fatigue cycle, whereas Ti-6246 does not; the mechanistic explanation for the differing dwell debit of these alloys has remained elusive for decades. In this work, crystal plasticity modelling has been utilised to extract the thermal activation energies for pinned dislocation escape for both Ti alloys based on independent experimental data. This then allows the markedly different cold creep responses of the two alloys to be captured accurately and demonstrates why the observed near-identical rate sensitivity under non-dwell loading is entirely consistent with the dwell behaviour. The activation energies determined are then utilised within a recently developed thermally-activated discrete dislocation plasticity model to predict the strain rate sensitivities of the two alloys associated with nano-indentation into basal and prism planes. It is shown that Ti-6242 experiences a strong crystallographic orientation-dependent rate sensitivity while Ti-6246 does not which is shown to agree with recently published independent measurements; the dependence of rate sensitivity on indentation slip plane is also well captured. The thermally-activated discrete dislocation plasticity model shows that the incorporation of a stress dwell in fatigue loading leads to remarkable stress redistribution from soft to hard grains in the classical cold dwell fatigue rogue grain combination in alloy Ti-6242, but that no such load shedding occurs in alloy Ti-6246. The key property controlling the behaviour is the time constant of the thermal activation process relative to that of the loading. This work provides the first mechanistic basis to explain why alloy Ti-6242 shows a dwell debit but Ti-6246 does not.

  17. Contribution of molecular flexibility to the elastic-plastic properties of molecular crystal α-RDX

    Science.gov (United States)

    Pal, Anirban; Picu, Catalin R.

    2017-01-01

    We show in this work that the mechanical properties of molecular crystals are strongly affected by the flexibility of the constituent molecules. To this end, we explore several kinematically restrained models of the molecular crystal cyclotrimethylene trinitramine in the α phase. We evaluate the effect of gradually removing the flexibility of the molecule on various crystal-scale parameters such as the elastic constants, the lattice parameters, the thermal expansion coefficients, the stacking fault energy and the critical stress for the motion of a dislocation (the Peierls-Nabarro stress). The values of these parameters evaluated with the fully refined, fully flexible atomistic model of the crystal are taken as reference. It is observed that the elastic constants, the lattice parameters and their dependence on pressure, and the thermal expansion coefficient can be accurately predicted with models that consider the NO2 and CH2 groups rigid, and the N-N bonds and the bonds of the triazine ring inextensible. Eliminating the dihedral flexibility of the ring leads to larger errors. The model in which the entire molecule is considered rigid or is mapped to a blob leads to even larger errors. Only the fully flexible, reference model provides accurate values for the stacking fault energy and the Peierls-Nabarro critical stress. Removing any component of the molecular flexibility leads to large errors in these parameters. These results also provide guidance for the development of coarse grained models of molecular crystals.

  18. Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

    Science.gov (United States)

    Javanbakht, Mahdi; Levitas, Valery I.

    2016-12-01

    Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP. When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect the stationary solution and the nanostructure. Consequently, there are multiple stationary solutions

  19. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Albert-Einstein Allee-11, Ulm University, 89069 Ulm (Germany); Burgermeister, Tobias; Keller, Jonas; Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Institute for Theoretical Physics, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Givat Ram (Israel); Zurek, Wojciech H. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87544 (United States); Campo, Adolfo del [Department of Physics, University of Massachusetts Boston, Boston, MA 02125 (United States); Mehlstäubler, Tanja E., E-mail: tanja.mehlstaeubler@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

    2015-03-01

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed nonadiabatically. For a second order phase transition, the Kibble–Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  20. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Ulm Univ., Ulm (Germany); Burgermeister, Tobias [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Keller, Jonas [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Ulm Univ., Ulm, (Germany):Institute for Theoretical Physics, Ulm Univ.,Ulm, (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram (Israel); Zurek, Wojciech Hubert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); del Campo, Adolfo [Univ. of Massachusetts, Amherst, MA (United States). Dept. of Physics; Mehlstaubler, Tanja E. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany)

    2014-11-19

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed non-adiabatically. For a second order phase transition, the Kibble-Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  1. Crystal plasticity finite element modeling of discrete twin evolution in polycrystalline magnesium

    Science.gov (United States)

    Cheng, Jiahao; Ghosh, Somnath

    2017-02-01

    This paper develops an advanced, image-based crystal plasticity finite element (CPFE) model, for predicting explicit twin formation and associated heterogeneous deformation in single crystal and polycrystalline microstructures of hexagonal close-packed or hcp materials, such as magnesium. Twin formation is responsible for premature failure of many hcp materials. The physics of nucleation, propagation and growth of explicit twins are considered in the CPFE formulation. The twin nucleation model is based on dissociation of sessile dislocations into stable twin loops, while propagation is assumed by atoms shearing on twin planes and shuffling to reduce the thermal activation energy barrier. The explicit twin evolution model however has intrinsic issues of low computational efficiency. Very fine simulation time steps with enormous computation costs are required to simulate the fast propagating twin bands and associated strain localization. To improve the computational efficiency, a multi-time scale subcycling algorithm is developed. It decomposes the computational domain into sub-domains of localized twins requiring very fine time-steps and complementary domains of relatively low resolution. Each sub-domain updates the stress and the deformation-dependent variables in different rates, followed by a coupling at the end of every coarse time step to satisfy global equilibrium. A 6-fold increase in computing speed is obtained for a polycrystalline Mg microstructure simulation in this paper. CPFE simulations of high purity Mg microstructures are compared with experiments with very good agreement in stress-strain response as well as heterogeneous twin formation with strain localization.

  2. A crystal plasticity smooth-particle hydrodynamics approach and its application to equal-channel angular pressing simulation

    Science.gov (United States)

    Ma, Anxin; Hartmaier, Alexander

    2016-12-01

    A crystal plasticity (CP) modelling approach based on smooth-particle hydrodynamics (SPH) has been developed to study severe plastic deformation of crystalline materials. The method has been implemented and validated by comparing the stress distribution and stress evolution of several SPH and FEM simulations for an anisotropic elastic material. The findings show that the SPH method produces an efficient and numerically robust solution for solid-mechanics boundary value problems. Furthermore, the approach has been extended to incorporate a CP model and employed to simulate FCC polycrystals under the equal-channel angular pressing (ECAP) condition. It was found that the polycrystal contains four distinct regions with different deformation mechanisms. For the case that friction between deformable particles and boundary particles was neglected, more than one half of the grains suffered severe plastic deformation. The CP-SPH developed here thus is demonstrated to be a powerful tool to study grain refinement under severe plastic deformation.

  3. Enhanced light extraction efficiency of plastic scintillator by photonic crystal prepared with a self-assembly method

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jinliang [State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Radiation Detection Research Center, Northwest Institute of Nuclear Technology, Xi’an, 710024 (China); Zhu, Zhichao [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Chen, Liang; Ouyang, Xiaoping [State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Radiation Detection Research Center, Northwest Institute of Nuclear Technology, Xi’an, 710024 (China); Liu, Bo, E-mail: lbo@tongji.edu.cn [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Cheng, Chuanwei [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Hu, Jing; He, Shiyi [State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Radiation Detection Research Center, Northwest Institute of Nuclear Technology, Xi’an, 710024 (China); Wang, Zewei [State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Radiation Detection Research Center, Northwest Institute of Nuclear Technology, Xi’an, 710024 (China); College of Materials Science and Engineering, Xiangtan University, Xiangtan 411105 (China); Gu, Mu; Chen, Hong [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China)

    2015-09-21

    Plastic scintillators are extensively used in various radiation measurement systems. However the total internal reflection decreases the scintillation light output, leading to a low detection efficiency especially in these weak signal detection situations. In the present investigation, we have designed a light extraction scheme based on the photonic crystal formed with a monolayer periodic array of polystyrene nanospheres by a self-assembly method. The photonic crystal coated on the surface of plastic scintillator can significantly enhance the light extraction by 120% compared with the plain reference sample under X-ray excitation, which is achieved by the principle of the coupling of evanescent field near the scintillator-air interface with the photonic crystal.

  4. Effects of plasticization and shear stress on phase structure development and properties of soy protein blends.

    Science.gov (United States)

    Chen, Feng; Zhang, Jinwen

    2010-11-01

    In this study, soy protein concentrate (SPC) was used as a plastic component to blend with poly(butylene adipate-co-terephthalate) (PBAT). Effects of SPC plasticization and blend composition on its deformation during mixing were studied in detail. Influence of using water as the major plasticizer and glycerol as the co-plasticizer on the deformation of the SPC phase during mixing was explored. The effect of shear stress, as affected by SPC loading level, on the phase structure of SPC in the blends was also investigated. Quantitative analysis of the aspect ratio of SPC particles was conducted by using ImageJ software, and an empirical model predicting the formation of percolated structure was applied. The experimental results and the model prediction showed a fairly good agreement. The experimental results and statistic analysis suggest that both SPC loading level and its water content prior to compounding had significant influences on development of the SPC phase structure and were correlated in determining the morphological structures of the resulting blends. Consequently, physical and mechanical properties of the blends greatly depended on the phase morphology and PBAT/SPC ratio of the blends.

  5. A mathematical formulation of the random phase approximation for crystals

    CERN Document Server

    Cances, Eric

    2011-01-01

    This works extends the recent study on the dielectric permittivity of crystals within the Hartree model [E. Cances and M. Lewin, Arch. Rational Mech. Anal., 197 (2010) 139--177] to the time-dependent setting. In particular, we prove the existence and uniqueness of the nonlinear Hartree dynamics, also called the random phase approximation in the physics literature, in a suitable functional space allowing to describe a local defect embedded in a perfect crystal. We also give a rigorous mathematical definition of the microscopic frequency-dependent polarization matrix, and derive the macroscopic Maxwell-Gauss equation for insulating and semiconducting crystals, from a first order approximation of the nonlinear Hartree model, by means of homogenization arguments.

  6. Two-phase modelling of equiaxed crystal sedimentation and thermomechanic stress development in the sedimented packed bed

    Science.gov (United States)

    Ludwig, A.; Vakhrushev, A.; Holzmann, T.; Wu, M.; Kharicha, A.

    2015-06-01

    During many industrial solidification processes equiaxed crystals form, grow and move. When those crystals are small they are carried by the melt, whereas when getting larger they sediment. As long as the volume fraction of crystals is below the packing limit, they are able to move relatively free. Crystals being backed in a so called packed bed form a semi-solid slurry, which may behave like a visco-plastic material. In addition, cooling-induced density increase of both, liquid and solid phases might lead to shrinkage of the whole casting domain. So deformation happens and gaps between casting and mold occur. In the present work, a two-phase Eulerian-Eulerian volume averaging model for describing the motion of equiaxed crystals in the melt is combined with a similar two-phase model for describing the dynamic of the packed bed. As constitutive equation for the solid skeleton in the packed bed Norton-Hoff law is applied. Shrinkage induced by density changes in the liquid or the solid phase is explicitly taken into account and handled by remeshing the calculation domain accordantly.

  7. A molecular dynamics study of dislocation density generation and plastic relaxation during shock of single crystal Cu

    Science.gov (United States)

    Sichani, Mehrdad M.; Spearot, Douglas E.

    2016-07-01

    The molecular dynamics simulation method is used to investigate the dependence of crystal orientation and shock wave strength on dislocation density evolution in single crystal Cu. Four different shock directions , , , and are selected to study the role of crystal orientation on dislocation generation immediately behind the shock front and plastic relaxation as the system reaches the hydrostatic state. Dislocation density evolution is analyzed for particle velocities between the Hugoniot elastic limit ( up H E L ) for each orientation up to a maximum of 1.5 km/s. Generally, dislocation density increases with increasing particle velocity for all shock orientations. Plastic relaxation for shock in the , , and directions is primarily due to a reduction in the Shockley partial dislocation density. In addition, plastic anisotropy between these orientations is less apparent at particle velocities above 1.1 km/s. In contrast, plastic relaxation is limited for shock in the orientation. This is partially due to the emergence of sessile stair-rod dislocations with Burgers vectors of 1/3 and 1/6. The nucleation of 1/6 dislocations at lower particle velocities is mainly due to the reaction between Shockley partial dislocations and twin boundaries. On the other hand, for the particle velocities above 1.1 km/s, the nucleation of 1/3 dislocations is predominantly due to reaction between Shockley partial dislocations at stacking fault intersections. Both mechanisms promote greater dislocation densities after relaxation for shock pressures above 34 GPa compared to the other three shock orientations.

  8. Phase-field-crystal model for fcc ordering.

    Science.gov (United States)

    Wu, Kuo-An; Adland, Ari; Karma, Alain

    2010-06-01

    We develop and analyze a two-mode phase-field-crystal model to describe fcc ordering. The model is formulated by coupling two different sets of crystal density waves corresponding to and reciprocal lattice vectors, which are chosen to form triads so as to produce a simple free-energy landscape with coexistence of crystal and liquid phases. The feasibility of the approach is demonstrated with numerical examples of polycrystalline and (111) twin growth. We use a two-mode amplitude expansion to characterize analytically the free-energy landscape of the model, identifying parameter ranges where fcc is stable or metastable with respect to bcc. In addition, we derive analytical expressions for the elastic constants for both fcc and bcc. Those expressions show that a nonvanishing amplitude of [200] density waves is essential to obtain mechanically stable fcc crystals with a nonvanishing tetragonal shear modulus (C11-C12)/2. We determine the model parameters for specific materials by fitting the peak liquid structure factor properties and solid-density wave amplitudes following the approach developed for bcc [K.-A. Wu and A. Karma, Phys. Rev. B 76, 184107 (2007)]. This procedure yields reasonable predictions of elastic constants for both bcc Fe and fcc Ni using input parameters from molecular dynamics simulations. The application of the model to two-dimensional square lattices is also briefly examined.

  9. Plastic phase change material and articles made therefrom

    Science.gov (United States)

    Abhari, Ramin

    2016-04-19

    The present invention generally relates to a method for manufacturing phase change material (PCM) pellets. The method includes providing a melt composition, including paraffin and a polymer. The paraffin has a melt point of between about 10.degree. C. and about 50.degree. C., and more preferably between about 18.degree. C. and about 28.degree. C. In one embodiment, the melt composition includes various additives, such as a flame retardant. The method further includes forming the melt composition into PCM pellets. The method further may include the step of cooling the melt to increase the melt viscosity before pelletizing. Further, PCM compounds are provided having an organic PCM and a polymer. Methods are provided to convert the PCM compounds into various form-stable PCMs. A method of coating the PCMs is included to provide PCMs with substantially no paraffin seepage and with ignition resistance properties.

  10. Plastic phase change material and articles made therefrom

    Energy Technology Data Exchange (ETDEWEB)

    Abhari, Ramin

    2016-04-19

    The present invention generally relates to a method for manufacturing phase change material (PCM) pellets. The method includes providing a melt composition, including paraffin and a polymer. The paraffin has a melt point of between about 10.degree. C. and about 50.degree. C., and more preferably between about 18.degree. C. and about 28.degree. C. In one embodiment, the melt composition includes various additives, such as a flame retardant. The method further includes forming the melt composition into PCM pellets. The method further may include the step of cooling the melt to increase the melt viscosity before pelletizing. Further, PCM compounds are provided having an organic PCM and a polymer. Methods are provided to convert the PCM compounds into various form-stable PCMs. A method of coating the PCMs is included to provide PCMs with substantially no paraffin seepage and with ignition resistance properties.

  11. Tunable Crystal-to-Crystal Phase Transition in a Cadmium Halide Chain Polymer

    Directory of Open Access Journals (Sweden)

    Ulli Englert

    2011-07-01

    Full Text Available The chain polymer [{Cd(μ-X2py2}1∞] (X = Cl, Br; py = pyridine undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and can be confirmed for the bulk by powder diffraction. The transition temperature can be adjusted by tuning the composition of the mixed-halide phase: Transition temperatures between 175 K up to the decomposition of the material at ca. 350 K are accessible. Elemental analysis, ion chromatography and site occupancy refinements from single-crystal X-ray diffraction agree with respect to the stoichiometric composition of the samples.

  12. Pyramidal ice crystal scattering phase functions and concentric halos

    Directory of Open Access Journals (Sweden)

    C. Liu

    Full Text Available Phase functions have been calculated using the Monte Carlo/geometric ray tracing method for single hexagonal pyramidal ice crystals (such as solid and hollow bullets randomly oriented in space and horizontal plane, in order to study the concentric halo formations. Results from three dimensional model calculations show that 9° halo can be as bright as the common 22° halo for pyramidal angle of 28°, and the 18°, 20°, 24° and 35° halos cannot be seen due to the strong 22° halo domination in the scattering phase function between 18° and 35°. For solid pyramidal ice crystals randomly oriented horizontally, the 35° arc can be produced and its intensity depends on the incident ray solar angle and the particle aspect ratio.

  13. Modeling of Shape Memory Alloys: Phase Transformation/Plasticity Interaction at the Nano Scale and the Statistics of Variation in Pseudoelastic Performance

    Science.gov (United States)

    Paranjape, Harshad Madhukar

    Shape memory alloys (SMA) show two remarkable properties- pseudoelasticity and shape memory effect. These properties make them an attractive material for a variety of commercial applications. However, the mechanism of austenite to martensite phase transformation, responsible for these properties also induces plastic deformation leading to structural and functional fatigue. Micron scale experiments suggest that the plastic deformation is induced in part due to the local stress field of the fine martensite microstructure. However, the results are qualitative and the nature of transformation-plasticity interaction is dependent on factors like the width of the interfaces. This thesis presents a new modeling approach to study the interaction between martensite correspondence variant scale microstructure and plastic deformation in austenite. A phase field method based evolution law is developed for phase transformation and reorientation of martensite CVs. This is coupled with a crystal plasticity law for austenite plastic deformation. The model is formulated with finite deformation and rotations. The effect of local crystal orientation is incorporated. An explicit time integration scheme is developed and implemented in a finite element method (FEM) based framework, allowing the modeling of complex boundary conditions and arbitrary loading conditions. Two systematic studies are carried out with the model. First, the interaction between plasticity and phase transformation is studied for load-free and load-biased thermal cycling of single crystals. Key outcomes of this study are that, the residual martensite formed during thermal cycling provides nucleation sites for the phase transformation in the subsequent cycles. Further, the distribution of slip on different slip systems is determined by the martensite texture. This is a strong evidence for transformation induced plasticity. In the second study, experimentally informed simulations of NiTi micropillar compression are

  14. Structure, Hydrodynamics, and Phase Transition of Freely Suspended Liquid Crystals

    Science.gov (United States)

    Clark, Noel A.

    2000-01-01

    Smectic liquid crystals are phases of rod shaped molecules organized into one dimensionally (1D) periodic arrays of layers, each layer being between one and two molecular lengths thick. In the least ordered smectic phases, the smectics A and C, each layer is a two dimensional (2D) liquid. Additionally there are a variety of more ordered smectic phases having hexatic short range translational order or 2D crystalline quasi long range translational order within the layers. The inherent fluid-layer structure and low vapor pressure of smectic liquid crystals enable the long term stabilization of freely suspended, single component, layered fluid films as thin as 30A, a single molecular layer. The layering forces the films to be an integral number of smectic layers thick, quantizing their thickness in layer units and forcing a film of a particular number of layers to be physically homogeneous with respect to its layer structure over its entire area. Optical reflectivity enables the precise determination of the number of layers. These ultrathin freely suspended liquid crystal films are structures of fundamental interest in condensed matter and fluid physics. They are the thinnest known stable condensed phase fluid structures and have the largest surface-to-volume ratio of any stable fluid preparation, making them ideal for the study of the effects of reduced dimensionality on phase behavior and on fluctuation and interface phenomena. Their low vapor pressure and quantized thickness enable the effective use of microgravity to extend the study of basic capillary phenomena to ultrathin fluid films. Freely suspended films have been a wellspring of new liquid crystal physics. They have been used to provide unique experimental conditions for the study of condensed phase transitions in two dimensions. They are the only system in which the hexatic has been unambiguously identified as a phase of matter, and the only physical system in which fluctuations of a 2D XY system and

  15. Self-polarizing terahertz liquid crystal phase shifter

    Directory of Open Access Journals (Sweden)

    Xiao-wen Lin

    2011-09-01

    Full Text Available Using sub-wavelength metallic gratings as both transparent electrodes and broadband high-efficiency polarizers, a highly-compact self-polarizing phase shifter is demonstrated by electrically tuning the effective birefringence of a nematic liquid crystal cell. The metal grating polarizers ensure a good polarizing efficiency in the range of 0.2 to 2 THz. Phase shift of more than π/3 is achieved in a 256 μm-thick cell with a saturation root mean square voltage of around 130 V in this integrated device.

  16. Crystal Phase Quantum Well Emission with Digital Control.

    Science.gov (United States)

    Assali, S; Lähnemann, J; Vu, T T T; Jöns, K D; Gagliano, L; Verheijen, M A; Akopian, N; Bakkers, E P A M; Haverkort, J E M

    2017-09-18

    One of the major challenges in the growth of quantum well and quantum dot heterostructures is the realization of atomically sharp interfaces. Nanowires provide a new opportunity to engineer the band structure as they facilitate the controlled switching of the crystal structure between the zinc-blende (ZB) and wurtzite (WZ) phases. Such a crystal phase switching results in the formation of crystal phase quantum wells (CPQWs) and quantum dots (CPQDs). For GaP CPQWs, the inherent electric fields due to the discontinuity of the spontaneous polarization at the WZ/ZB junctions lead to the confinement of both types of charge carriers at the opposite interfaces of the WZ/ZB/WZ structure. This confinement leads to a novel type of transition across a ZB flat plate barrier. Here, we show digital tuning of the visible emission of WZ/ZB/WZ CPQWs in a GaP nanowire by changing the thickness of the ZB barrier. The energy spacing between the sharp emission lines is uniform and is defined by the addition of single ZB monolayers. The controlled growth of identical quantum wells with atomically flat interfaces at predefined positions featuring digitally tunable discrete emission energies may provide a new route to further advance entangled photons in solid state quantum systems.

  17. Special phase transformation and crystal growth pathways observed in nanoparticles†

    Directory of Open Access Journals (Sweden)

    Finnegan Michael P

    2003-11-01

    Full Text Available Phase transformation and crystal growth in nanoparticles may happen via mechanisms distinct from those in bulk materials. We combine experimental studies of as-synthesized and hydrothermally coarsened titania (TiO2 and zinc sulfide (ZnS with thermodynamic analysis, kinetic modeling and molecular dynamics (MD simulations. The samples were characterized by transmission electron microscopy, X-ray diffraction, synchrotron X-ray absorption and scattering, and UV-vis spectroscopy. At low temperatures, phase transformation in titania nanoparticles occurs predominantly via interface nucleation at particle–particle contacts. Coarsening and crystal growth of titania nanoparticles can be described using the Smoluchowski equation. Oriented attachment-based crystal growth was common in both hydrothermal solutions and under dry conditions. MD simulations predict large structural perturbations within very fine particles, and are consistent with experimental results showing that ligand binding and change in aggregation state can cause phase transformation without particle coarsening. Such phenomena affect surface reactivity, thus may have important roles in geochemical cycling.

  18. Transparent nematic phase in a liquid-crystal-based microemulsion.

    Science.gov (United States)

    Yamamoto, J; Tanaka, H

    2001-01-18

    Complex fluids are usually produced by mixing together several distinct components, the interactions between which can give rise to unusual optical and rheological properties of the system as a whole. For example, the properties of microemulsions (composed of water, oil and surfactants) are determined by the microscopic structural organization of the fluid that occurs owing to phase separation of the component elements. Here we investigate the effect of introducing an additional organizing factor into such a fluid system, by replacing the oil component of a conventional water-in-oil microemulsion with an intrinsically anisotropic fluid--a nematic liquid crystal. As with the conventional case, the fluid phase-separates into an emulsion of water microdroplets (stabilized by the surfactant as inverse micelles) dispersed in the 'oil' phase. But the properties are further influenced by a significant directional coupling between the liquid-crystal molecules and the surfactant tails that emerge (essentially radially) from the micelles. The result is a modified bulk-liquid crystal that is an ordered nematic at the mesoscopic level, but which does not exhibit the strong light scattering generally associated with bulk nematic order: the bulk material here is essentially isotropic and thus transparent.

  19. Confined crystals of the smallest phase-change material.

    Science.gov (United States)

    Giusca, Cristina E; Stolojan, Vlad; Sloan, Jeremy; Börrnert, Felix; Shiozawa, Hidetsugu; Sader, Kasim; Rümmeli, Mark H; Büchner, Bernd; Silva, S Ravi P

    2013-09-11

    The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.

  20. Thermal fluctuations and phase diagrams of the phase-field crystal model with pinning.

    Science.gov (United States)

    Ramos, J A P; Granato, E; Achim, C V; Ying, S C; Elder, K R; Ala-Nissila, T

    2008-09-01

    We study the influence of thermal fluctuations in the phase diagram of a recently introduced two-dimensional phase field crystal model with an external pinning potential. The model provides a continuum description of pinned lattice systems allowing for both elastic deformations and topological defects. We introduce a nonconserved version of the model and determine the ground-state phase diagram as a function of lattice mismatch and strength of the pinning potential. Monte Carlo simulations are used to determine the phase diagram as a function of temperature near commensurate phases. The results show a rich phase diagram with commensurate, incommensurate, and liquidlike phases with a topology strongly dependent on the type of ordered structure. A finite-size scaling analysis of the melting transition for the c(2x2) commensurate phase shows that the thermal correlation length exponent nu and specific heat behavior are consistent with the Ising universality class as expected from analytical arguments.

  1. Plastic deformation of submicron-sized crystals studied by in-situ Kikuchi diffraction and dislocation imaging

    DEFF Research Database (Denmark)

    Zhang, Xiaodan; Godfrey, Andrew; Winther, Grethe

    2012-01-01

    The plastic deformation of submicron-size copper single crystals in the form of pillars has been characterized during in-situ compression in the transmission electron microscope up to strains of 28–33% using a state-of-the-art holder (PI-95 PicoIndenter). The dimensions of the crystals used were...... approx. 500×250×200 nm3 with the compression axis oriented 1.6° from [110]. Local crystallographic orientations have been determined with high accuracy using a Kikuchi diffraction method and glide of dislocations over a pillar has also been observed directly by dark field imaging. The variation...

  2. Nematic-like stable glasses without equilibrium liquid crystal phases.

    Science.gov (United States)

    Gómez, Jaritza; Gujral, Ankit; Huang, Chengbin; Bishop, Camille; Yu, Lian; Ediger, M D

    2017-02-07

    We report the thermal and structural properties of glasses of posaconazole, a rod-like molecule, prepared using physical vapor deposition (PVD). PVD glasses of posaconazole can show substantial molecular orientation depending upon the choice of substrate temperature, Tsubstrate, during deposition. Ellipsometry and IR measurements indicate that glasses prepared at Tsubstrate very near the glass transition temperature (Tg) are highly ordered. For these posaconazole glasses, the orientation order parameter is similar to that observed in macroscopically aligned nematic liquid crystals, indicating that the molecules are mostly parallel to one another and perpendicular to the interface. To our knowledge, these are the most anisotropic glasses ever prepared by PVD from a molecule that does not form equilibrium liquid crystal phases. These results are consistent with a previously proposed mechanism in which molecular orientation in PVD glasses is inherited from the orientation present at the free surface of the equilibrium liquid. This mechanism suggests that molecular orientation at the surface of the equilibrium liquid of posaconazole is nematic-like. Posaconazole glasses can show very high kinetic stability; the isothermal transformation of a 400 nm glass into the supercooled liquid occurs via a propagating front that originates at the free surface and requires ∼10(5) times the structural relaxation time of the liquid (τα). We also studied the kinetic stability of PVD glasses of itraconazole, which is a structurally similar molecule with equilibrium liquid crystal phases. While itraconazole glasses can be even more anisotropic than posaconazole glasses, they exhibit lower kinetic stability.

  3. Thin and flexible solid-state organic ionic plastic crystal-polymer nanofibre composite electrolytes for device applications.

    Science.gov (United States)

    Howlett, Patrick C; Ponzio, Florian; Fang, Jian; Lin, Tong; Jin, Liyu; Iranipour, Nahid; Efthimiadis, Jim

    2013-09-07

    All solid-state organic ionic plastic crystal-polymer nanofibre composite electrolytes are described for the first time. The new composite materials exhibit enhanced conductivity, excellent thermal, mechanical and electrochemical stability and allow the production of optically transparent, free-standing, flexible, thin film electrolytes (10's μms thick) for application in electrochemical devices. Stable cycling of a lithium cell incorporating the new composite electrolyte is demonstrated, including cycling at lower temperatures than previously possible with the pure material.

  4. Recrystallization and texture evolution during hot rolling of copper, studied by a multiscale model combining crystal plasticity and vertex models

    Science.gov (United States)

    Mellbin, Y.; Hallberg, H.; Ristinmaa, M.

    2016-10-01

    A multiscale modeling framework, combining a graph-based vertex model of microstructure evolution with a GPU-parallelized crystal plasticity model, was recently proposed by the authors. Considering hot rolling of copper, the full capabilities of the model are demonstrated in the present work. The polycrystal plasticity model captures the plastic response and the texture evolution during materials processing while the vertex model provides central features of grain structure evolution through dynamic recrystallization, such as nucleation and growth of individual crystals. The multiscale model makes it possible to obtain information regarding grain size and texture development throughout the workpiece, capturing the effects of recrystallization and heterogeneous microstructure evolution. Recognizing that recrystallization is a highly temperature dependent phenomenon, simulations are performed at different process temperatures. The results show that the proposed modeling framework is capable of simultaneously capturing central aspects of material behavior at both the meso- and macrolevel. Detailed investigation of the evolution of texture, grain size distribution and plastic deformation during the different processing conditions are performed, using the proposed model. The results show a strong texture development, but almost no recrystallization, for the lower of the investigated temperatures, while at higher temperatures an increased recrystallization is shown to weaken the development of a typical rolling texture. The simulations also show the influence of the shear deformation close to the rolling surface on both texture development and recrystallization.

  5. VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Rao Popuri, Srinivasa [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Artemenko, Alla [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Labrugere, Christine [CeCaMA, University of Bordeaux 1, ICMCB, 87 Avenue du Dr. A. Schweitzer, F-33608 Pessac (France); Miclau, Marinela [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Villesuzanne, Antoine [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Pollet, Michaël, E-mail: pollet@icmcb-bordeaux.cnrs.fr [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France)

    2014-05-01

    Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.

  6. Asymmetric dynamic phase holographic grating in nematic liquid crystal

    Science.gov (United States)

    Ren, Chang-Yu; Shi, Hong-Xin; Ai, Yan-Bao; Yin, Xiang-Bao; Wang, Feng; Ding, Hong-Wei

    2016-09-01

    A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal (NLC) was presented. An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating. The diffraction efficiency we achieved is more than 40%, exceeding the theoretical limit for symmetric profile gratings. Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC. Finally, physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented, based on the photo-refractive-like (PR-like) effect. Project supported by the Science and Technology Programs of the Educational Committee of Heilongjiang Province, China (Grant No. 12541730) and the National Natural Science Foundation of China (Grant No. 61405057).

  7. A plastic-composite-plastic structure high performance flexible energy harvester based on PIN-PMN-PT single crystal/epoxy 2-2 composite

    Science.gov (United States)

    Zeng, Zhou; Gai, Linlin; Wang, Xian; Lin, Di; Wang, Sheng; Luo, Haosu; Wang, Dong

    2017-03-01

    We present a high performance flexible piezoelectric energy harvester constituted by a Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal/epoxy 2-2 composite flake, a polyethylene terephthalate (PET) substrate, and a PET cover, which is capable of harvesting energy from biomechanical movements. Electrical properties of the device under different epoxy volume fractions, load resistances, and strains are studied systematically. Both theoretical and experimental results show that the plastic-composite-plastic structure contributes to the flexibility of the device, and a high performance bulk PIN-PMN-PT single crystal (a thickness of 50 μm) results in its high electrical output. At a low excitation frequency of 4.2 Hz, the optimal flexible energy harvester (with ve = 21%) can generate a peak voltage of 12.9 V and a maximum power density of 0.28 mW/cm3 under a bending radius of 10.5 mm, and maintain its performance after 40 000 bending-unbending cycles. High flexibility and excellent electrical output at low operational frequency demonstrate the promise of the device in biomechanical motion energy harvesting for wireless and portable low-power electronics.

  8. Influence of Cumulative Plastic Deformation on Microstructure of the Fe-Al Intermetallic Phase Base Alloy

    Directory of Open Access Journals (Sweden)

    Bednarczyk I.

    2014-10-01

    Full Text Available This article is part of the research on the microstructural phenomena that take place during hot deformation of intermetallic phase-based alloy. The research aims at design an effective thermo - mechanical processing technology for the investigated intermetallic alloy. The iron aluminides FeAl have been among the most widely studied intermetallics because their low cost, low density, good wear resistance, easy of fabrication and resistance to oxidation and corrosion. There advantages create wide prospects for their industrial applications for components of machines working at a high temperature and in corrosive environment. The problem restricting their application is their low plasticity and their brittle cracking susceptibility, hampers their development as construction materials. Consequently, the research of intermetallic-phase-based alloys focuses on improvement their plasticity by hot working proceses. The study addresses the influence of deformation parameters on the structure of an Fe-38% at. Al alloy with Zr, B Mo and C microadditions, using multi – axis deformation simulator. The influence of deformation parameters on microstructure and substructure was determined. It was revealed that application of cumulative plastic deformation method causes intensive reduction of grain size in FeAl phase base alloy.

  9. Ab initio molecular crystal structures, spectra, and phase diagrams.

    Science.gov (United States)

    Hirata, So; Gilliard, Kandis; He, Xiao; Li, Jinjin; Sode, Olaseni

    2014-09-16

    Conspectus Molecular crystals are chemists' solids in the sense that their structures and properties can be understood in terms of those of the constituent molecules merely perturbed by a crystalline environment. They form a large and important class of solids including ices of atmospheric species, drugs, explosives, and even some organic optoelectronic materials and supramolecular assemblies. Recently, surprisingly simple yet extremely efficient, versatile, easily implemented, and systematically accurate electronic structure methods for molecular crystals have been developed. The methods, collectively referred to as the embedded-fragment scheme, divide a crystal into monomers and overlapping dimers and apply modern molecular electronic structure methods and software to these fragments of the crystal that are embedded in a self-consistently determined crystalline electrostatic field. They enable facile applications of accurate but otherwise prohibitively expensive ab initio molecular orbital theories such as Møller-Plesset perturbation and coupled-cluster theories to a broad range of properties of solids such as internal energies, enthalpies, structures, equation of state, phonon dispersion curves and density of states, infrared and Raman spectra (including band intensities and sometimes anharmonic effects), inelastic neutron scattering spectra, heat capacities, Gibbs energies, and phase diagrams, while accounting for many-body electrostatic (namely, induction or polarization) effects as well as two-body exchange and dispersion interactions from first principles. They can fundamentally alter the role of computing in the studies of molecular crystals in the same way ab initio molecular orbital theories have transformed research practices in gas-phase physical chemistry and synthetic chemistry in the last half century. In this Account, after a brief summary of formalisms and algorithms, we discuss applications of these methods performed in our group as compelling

  10. Preparative crystallization of a single chain antibody using an aqueous two-phase system.

    Science.gov (United States)

    Huettmann, Hauke; Berkemeyer, Matthias; Buchinger, Wolfgang; Jungbauer, Alois

    2014-11-01

    A simultaneous crystallization and aqueous two-phase extraction of a single chain antibody was developed, demonstrating process integration. The process conditions were designed to form an aqueous two-phase system, and to favor crystallization, using sodium sulfate and PEG-2000. At sufficiently high concentrations of PEG, a second phase was generated in which the protein crystallization occurred simultaneously. The single chain antibody crystals were partitioned to the top, polyethylene glycol-rich phase. The crystal nucleation took place in the sodium sulfate-rich phase and at the phase boundary, whereas crystal growth was progressing mainly in the polyethylene glycol-rich phase. The crystals in the polyethylene glycol-rich phase grew to a size of >50 µm. Additionally, polyethylene glycol acted as an anti-solvent, thus, it influenced the crystallization yield. A phase diagram with an undersaturation zone, crystallization area, and amorphous precipitation zone was established. Only small differences in polyethylene glycol concentration caused significant shifts of the crystallization yield. An increase of the polyethylene glycol content from 2% (w/v) to 4% (w/v) increased the yield from approximately 63-87%, respectively. Our results show that crystallization in aqueous two-phase systems is an opportunity to foster process integration.

  11. Non-destructive testing of carbon reinforced plastics by means of phase retrieval

    CERN Document Server

    Agour, Mostafa; Kopylow, Christoph v; Bergmann, Ralf B

    2012-01-01

    In this work, the SLM-based phase retrieval system will be used to inspect carbon reinforced plastics samples (CFRP) under applying a thermal load. For this purpose, the system is used to capture a sequence of 8 spatially separated recording planes, where the distance between subsequent planes equals 2 mm. For detecting the hidden failures two sets of intensity observations are recorded. The first set for the initial state and the second set is captured after applying the load. To recover the phase information associated with the two states, the captured intensities have been subjected to an iterative algorithm based on the method of generalized projection.

  12. Thermal dispersion and secondary crystallization of phase change memory cells

    Science.gov (United States)

    Deng, Y. F.; Li, Z.; Peng, J. H.; Liu, C.; Miao, X. S.

    2013-12-01

    The heat accumulation effect associated with heat dispersion process in phase change memory cell was analyzed. The pulse operating scheme was optimized. The pulse sequences with different intervals show distinct heat accumulation effect. A compact model with pulse sequence expansion was proposed, and the simulation result is close to the experiment data for a pulse sequence with interval 20 ns. The simulated R-V curves show that threshold voltage reduces with the decreasing pulse interval. The secondary crystallization and amorphization were used to explain the heat accumulation effect for high speed operation, cycling, and so on.

  13. Kinetic Processes Crystal Growth, Diffusion, and Phase Transformations in Materials

    CERN Document Server

    Jackson, Kenneth A

    2004-01-01

    The formation of solids is governed by kinetic processes, which are closely related to the macroscopic behaviour of the resulting materials. With the main focus on ease of understanding, the author begins with the basic processes at the atomic level to illustrate their connections to material properties. Diffusion processes during crystal growth and phase transformations are examined in detail. Since the underlying mathematics are very complex, approximation methods typically used in practice are the prime choice of approach. Apart from metals and alloys, the book places special emphasis on th

  14. Crystal structure of the superconducting phase of sulfur hydride

    Science.gov (United States)

    Einaga, Mari; Sakata, Masafumi; Ishikawa, Takahiro; Shimizu, Katsuya; Eremets, Mikhail I.; Drozdov, Alexander P.; Troyan, Ivan A.; Hirao, Naohisa; Ohishi, Yasuo

    2016-09-01

    A superconducting critical temperature above 200 K has recently been discovered in H2S (or D2S) under high hydrostatic pressure. These measurements were interpreted in terms of a decomposition of these materials into elemental sulfur and a hydrogen-rich hydride that is responsible for the superconductivity, although direct experimental evidence for this mechanism has so far been lacking. Here we report the crystal structure of the superconducting phase of hydrogen sulfide (and deuterium sulfide) in the normal and superconducting states obtained by means of synchrotron X-ray diffraction measurements, combined with electrical resistance measurements at both room and low temperatures. We find that the superconducting phase is mostly in good agreement with the theoretically predicted body-centred cubic (bcc) structure for H3S. The presence of elemental sulfur is also manifest in the X-ray diffraction patterns, thus proving the decomposition mechanism of H2S to H3S + S under pressure.

  15. Ultrafast characterization of phase-change material crystallization properties in the melt-quenched amorphous phase.

    Science.gov (United States)

    Jeyasingh, Rakesh; Fong, Scott W; Lee, Jaeho; Li, Zijian; Chang, Kuo-Wei; Mantegazza, Davide; Asheghi, Mehdi; Goodson, Kenneth E; Wong, H-S Philip

    2014-06-11

    Phase change materials are widely considered for application in nonvolatile memories because of their ability to achieve phase transformation in the nanosecond time scale. However, the knowledge of fast crystallization dynamics in these materials is limited because of the lack of fast and accurate temperature control methods. In this work, we have developed an experimental methodology that enables ultrafast characterization of phase-change dynamics on a more technologically relevant melt-quenched amorphous phase using practical device structures. We have extracted the crystallization growth velocity (U) in a functional capped phase change memory (PCM) device over 8 orders of magnitude (10(-10) programmed PCM devices at very high heating rates (>10(8) K/s), which reveals the extreme fragility of Ge2Sb2Te5 in its supercooled liquid phase. Furthermore, these crystallization properties were studied as a function of device programming cycles, and the results show degradation in the cell retention properties due to elemental segregation. The above experiments are enabled by the use of an on-chip fast heater and thermometer called as microthermal stage (MTS) integrated with a vertical phase change memory (PCM) cell. The temperature at the PCM layer can be controlled up to 600 K using MTS and with a thermal time constant of 800 ns, leading to heating rates ∼10(8) K/s that are close to the typical device operating conditions during PCM programming. The MTS allows us to independently control the electrical and thermal aspects of phase transformation (inseparable in a conventional PCM cell) and extract the temperature dependence of key material properties in real PCM devices.

  16. The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

    Science.gov (United States)

    Ji, L. K.; Xu, T.; Zhang, J. M.; Wang, H. T.; Tong, M. X.; Zhu, R. H.; Zhou, G. S.

    2017-07-01

    Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10-5, 1.25 × 10-4, 2.5 × 10-3, and 1.25 × 10-2 s-1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10-3 s-1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10-5 s-1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10-3 s-1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.

  17. Determination of plasticizers included in balloon by solid phase microextraction and gas chromatography with mass spectrometric detection.

    Energy Technology Data Exchange (ETDEWEB)

    Park, H.M.; Kim, J.H.; Ryu, J.Ch.; Kim, Y.M.; Lee, K.B. [Korea Institute of Science and Technology, Seoul (Korea)

    2001-02-01

    Solid-phase microextraction (SPME) with 85 {mu}m polyacrylate fiber, coupled to gas chromatography-mass spectrometry was used to analyze the plasticizers contained in balloon samples. The balloons were identified to be made of polyisoprene by IR spectroscopy. The plasticizers extracted from the balloon samples soaked in acetone-added water solvent for an hour were quantified by external standard method using nine kinds of plasticizers. The quantification method was validated for standard plasticizers in the range of 0.25-25 {mu}g/g. The detection limits were 0.11-0.38 {mu}g/g for different plasticizers. The RSDs for the reproducibility of this quantitation method were 3.7-14.2%. A few of balloons included risky level of plasticizer concerned as an endocrine disrupter, and it is necessary to regulate these products. (author). 10 refs., 3 tabs., 4 figs.

  18. Crystal structure and phase transition of thermoelectric SnSe.

    Science.gov (United States)

    Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo

    2016-06-01

    Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.

  19. The prediction of differential hardening behaviour of steels by multi-scale crystal plasticity modelling

    NARCIS (Netherlands)

    Eyckens, P.; Mulder, J.; Gawad, J.; Vegter, H.; Roose, D.; Boogaard, van den A.H.; Van Bael, A.; Van Houtte, P.

    2015-01-01

    An essential aspect of materials modelling in the field of metal plasticity is hardening. The classical assumption of isotropic hardening in metal plasticity models is often too simplified to describe actual material behaviour. This paper focuses on the non-isotropic hardening termed differential ha

  20. Influence of plastic strain on the hydrogen evolution reaction on nickel (100) single crystal surfaces to improve hydrogen embrittlement

    Energy Technology Data Exchange (ETDEWEB)

    Lekbir, C., E-mail: choukri.lekbir@univ-lr.fr; Creus, J.; Sabot, R.; Feaugas, X.

    2013-08-20

    Hydrogen-induced embrittlement can be accountable for premature failure of structure in relation with physical and/or chemical processes occurring on material's surface or in the bulk of the material. Hydrogen Evolution Reaction (HER) corresponding to the early step of hydrogen ingress in the material is explored in present study in relation with plastic strain. HER on nickel (100) single crystal in sulphuric acid medium can be related by a Volmer–Heyrovsky mechanism. The corresponding elementary kinetic parameters as symmetry coefficients, activation enthalpies, and number of active sites have been identified via a thermokinetic model using experimental data. These parameters can be affected by defects associated with plastic strain. Irreversible plastic strain modifies the density and the distribution of storage dislocations affecting the surface roughness at atomic scale and generating additional active adsorption sites. Furthermore, surface emergence of mobile dislocations induces the formation of slip bands, which modify the surface roughness and the electronic state of the surface and increases the (111) surface density. The consequence of plastic strain on HER is explored and discussed in relation with both processes.

  1. Numerical modeling of two-phase high speed jet with non-equilibrium solid phase crystallization

    Science.gov (United States)

    Molchanov, A. M.; Yanyshev, D. S.; Bykov, L. V.

    2016-11-01

    The main purpose of the paper is to demonstrate that the Euler approach is fully applicable to the multiphase flows with discrete phase undergoing phase transitions. It is carried out using the example of a jet flow with aluminium oxide particles non-equilibrium crystallization. The jet is strongly underexpanded. The non-equilibrium molecular effects are being taken into account. The obtained results of the simulations are in good agreement with the works of the other authors. The developed Euler approach proved itself to be the most robust in flows with complex flow geometry.

  2. Strategies for the crystallization of viruses: using phase diagrams and gels to produce 3D crystals of Grapevine fanleaf virus.

    Science.gov (United States)

    Schellenberger, Pascale; Demangeat, Gérard; Lemaire, Olivier; Ritzenthaler, Christophe; Bergdoll, Marc; Oliéric, Vincent; Sauter, Claude; Lorber, Bernard

    2011-05-01

    The small icosahedral plant RNA nepovirus Grapevine fanleaf virus (GFLV) is specifically transmitted by a nematode and causes major damage to vineyards worldwide. To elucidate the molecular mechanisms underlying the recognition between the surface of its protein capsid and cellular components of its vector, host and viral proteins synthesized upon infection, the wild type GFLV strain F13 and a natural mutant (GFLV-TD) carrying a Gly₂₉₇Asp mutation were purified, characterized and crystallized. Subsequently, the geometry and volume of their crystals was optimized by establishing phase diagrams. GFLV-TD was twice as soluble as the parent virus in the crystallization solution and its crystals diffracted X-rays to a resolution of 2.7 Å. The diffraction limit of GFLV-F13 crystals was extended from 5.5 to 3 Å by growth in agarose gel. Preliminary crystallographic analyses indicate that both types of crystals are suitable for structure determination. Keys for the successful production of GFLV crystals include the rigorous quality control of virus preparations, crystal quality improvement using phase diagrams, and crystal lattice reinforcement by growth in agarose gel. These strategies are applicable to the production of well-diffracting crystals of other viruses and macromolecular assemblies.

  3. Raman study of the molecular motions of pivalic acid: the liquid—plastic phase transition

    Science.gov (United States)

    Balevičius, V.; Orel, B.; Hadži, D.

    Raman spectra of pivalic acid in the plastic and liquid phase have been measured. The reorientational correlation times have been evaluated from the ν asCH, νCO and νCC bands as a function of temperature. The reorientational correlation time corresponding to ν as CH and νCC bands is τ 4ps ( T = 20°C). The calculated activation energy is 26 KJ mol -1. The reorientation of the carboxylic groups which may be assisted by the proton transfer along the hydrogen bonds in dimers is discussed.

  4. Hardening in Two-Phase Materials. II. Plastic Strain and Mean Stress Hardening Rate

    DEFF Research Database (Denmark)

    Lilholt, Hans

    1977-01-01

    The strain parameters which are relevant in a tensile experiment, are analysed and related to the geometry of deformation and to the mean stress of two-phase materials. The hardening rate of the mean stress with respect to plastic strain is found to be useful in comparison between experiments and...... and theories, and it allows theories to be probed over a range of strains. Previous experiments on the fibre-reinforced material of copper-tungsten are analysed in relation to the geometry of deformation....

  5. Reductive renormalization of the phase-field crystal equation.

    Science.gov (United States)

    Oono, Y; Shiwa, Y

    2012-12-01

    It has been known for some time that singular perturbation and reductive perturbation can be unified from the renormalization-group theoretical point of view: Reductive extraction of space-time global behavior is the essence of singular perturbation methods. Reductive renormalization was proposed to make this unification practically accessible; actually, this reductive perturbation is far simpler than most reduction methods, such as the rather standard scaling expansion. However, a rather cryptic exposition of the method seems to have been the cause of some trouble. Here, an explicit demonstration of the consistency of the reductive renormalization-group procedure is given for partial differentiation equations (of a certain type, including time-evolution semigroup type equations). Then, the procedure is applied to the reduction of a phase-field crystal equation to illustrate the streamlined reduction method. We conjecture that if the original system is structurally stable, the reductive renormalization-group result and that of the original equation are diffeomorphic.

  6. Differential hardening in IF steel - Experimental results and a crystal plasticity based model

    NARCIS (Netherlands)

    Mulder, J.; Eyckens, P.; van den Boogaard, Antonius H.; Hora, P.

    2015-01-01

    Work hardening in metals is commonly described by isotropic hardening, especially for monotonically increasing proportional loading. The relation between different stress states in this case is determined by equivalent stress and strain definitions, based on equal plastic dissipation. However,

  7. Phase-field modeling on morphological landscape of isotactic polystyrene single crystals.

    Science.gov (United States)

    Xu, Haijun; Matkar, Rushikesh; Kyu, Thein

    2005-07-01

    Spatio-temporal growth of isotactic polystyrene single crystals during isothermal crystallization has been investigated theoretically based on the phase field model by solving temporal evolution of a nonconserved phase order parameter coupled with a heat conduction equation. In the description of the total free energy, an asymmetric double-well local free energy density has been adopted to represent the metastable melt and the stable solid crystal. Unlike the small molecule systems, polymer crystallization rarely reaches thermodynamic equilibrium; most polymer crystals are kinetically stabilized in some metastable states. To capture various metastable polymer crystals, the phase field crystal order parameter at the solidification potential has been treated to be supercooling dependent such that it can assume an intermediate value between zero (melt) and unity (perfect crystal), reflecting imperfect polycrystalline nature of polymer crystals. Two-dimensional simulations exhibit various single crystal morphologies of isotactic polystyrene crystals such as faceted hexagonal patterns transforming to nonfaceted snowflakes with increasing supercooling. Of particular interest is that heat liberation from the crystallizing front influences the curvature of the crystal-melt interface, leading to directional growth of lamellar tips and side branches. The landscape of these morphological textures has been established as a function of anisotropy of surface energy and supercooling. With increasing supercooling and decreasing anisotropy, the hexagonal single crystal transforms to the dense lamellar branching morphology in conformity with the experimental findings.

  8. Deformation Heterogeneity and Texture Evolution of NiTiFe Shape Memory Alloy Under Uniaxial Compression Based on Crystal Plasticity Finite Element Method

    Science.gov (United States)

    Liang, Yulong; Jiang, Shuyong; Zhang, Yanqiu; Zhao, Yanan; Sun, Dong; Zhao, Chengzhi

    2017-04-01

    Crystal plastic finite element method (CPFEM) is used to simulate microstructural evolution, texture evolution and macroscopic stress-strain response of polycrystalline NiTiFe shape memory alloy (SMA) with B2 austenite phase during compression deformation. A novel two-dimensional polycrystalline finite element model based on electron back-scattered diffraction (EBSD) experiment data is developed to represent virtual grain structures of polycrystalline NiTiFe SMA. In the present study, CPFEM plays a significant role in predicting texture evolution and macroscopic stress-strain response of NiTiFe SMA during compression deformation. The simulated results are in good agreement with the experimental ones. It can be concluded that intragranular and intergranular strain heterogeneities are of great importance in guaranteeing plastic deformation compatibility of NiTiFe SMA. CPFEM is able to capture the evolution of grain boundaries with various misorientation angles for NiTiFe SMA subjected to the various compression deformation degrees. During uniaxial compression of NiTiFe SMA, the microstructure evolves into high-energy substructure and consequently the well-defined subgrains are formed. Furthermore, the grain boundaries and the subgrain boundaries are approximately aligned with the direction in which metal flows.

  9. Study of crystal structure at high temperature phase in KIO sub 3 crystal by synchrotron powder X-ray diffraction

    CERN Document Server

    Kasatani, H; Kuroiwa, Y; Yagi, K; Katayama, R; Terauchi, H

    2003-01-01

    The accurate crystal structure of the I-phase in KIO sub 3 crystal has been obtained at 530 K, for the first time, by the MEM/Rietveld analysis from high-energy X-ray powder-diffraction data. The crystal structure of the I-phase is the rhombohedral perovskite structure (space group R3m; Z=1). The MEM charge-density distributions reveal that the shorter I-O bond exhibits a covalent bonding character and others (I-K, K-O and longer I-O bonds) an ionic.

  10. Phase transformations and phase equilibria in the Co-Sn-Ti system in the crystallization interval

    Science.gov (United States)

    Fartushna, Iu.; Bulanova, M.; Ayral, R. M.; Tedenac, J. C.; Meleshevich, K.

    2016-12-01

    The Co-Sn-Ti system was studied in the crystallization interval (below 50 at% Sn) by the methods of Scanning Electron Microscopy, microprobe analysis, Differential Thermal Analysis, X-ray diffraction. The liquidus and solidus projections and the melting diagram were constructed. Only Co2TiSn(τ1) ternary compound (Heusler phase-L12) was found in equilibria with the liquid in the concentration interval studied. Taking into account our recent data, the liquidus projection is characterized by the fields of primary crystallization of (βTi), (Co), binary-based phases Ti3Sn, Ti2Sn, Ti5Sn3, Ti6Sn5, Ti2Co, TiCo, TiCo2 (c), TiCo2 (h), TiCo3, βCo3Sn2, CoSn and ternary τ1. The solidus projection is characterized by thirteen three-phase fields, which result from invariant four-phase equilibria, five are of eutectic type (E) and eight of transition type (U) and the existence of one more region Ti2Sn3+βCoSn3+(Sn) in the solidus projection is discussed.

  11. Reversible crystal-to-amorphous-to-crystal phase transition and a large magnetocaloric effect in a spongelike metal organic framework material.

    Science.gov (United States)

    Tian, Chong-Bin; Chen, Rui-Ping; He, Chao; Li, Wei-Jin; Wei, Qi; Zhang, Xu-Dong; Du, Shao-Wu

    2014-02-21

    Reversible crystal-to-amorphous-to-crystal phase transition accompanied by changes in magnetic and NLO properties was first observed in a rigid non-porous spongelike MOF material. The crystal phase exhibits a high magnetocaloric effect, while the amorphous phase has potential application as a magnetic DMF sensor.

  12. The microstructural record of porphyroclasts and matrix of serpentinite mylonites – from brittle and crystal-plastic deformation to dissolution-precipitation creep

    Directory of Open Access Journals (Sweden)

    J. Bial

    2013-04-01

    Full Text Available We examine the microfabric development in high-pressure, low-temperature metamorphic serpentinite mylonites exposed in the Erro-Tobbio Unit (Voltri Massif, Italy using polarization microscopy and electron microscopy (SEM/EBSD, EMP. The mylonites are derived from mantle peridotites, were serpentinized at the ocean floor and underwent high pressure metamorphism during Alpine subduction. They contain diopside and olivine porphyroclasts embedded in a fine-grained matrix essentially consisting of antigorite. The porphyroclasts record brittle and crystal-plastic deformation of the original peridotites in the upper mantle at stresses of a few hundred MPa. After the peridotites became serpentinized, deformation occurred mainly by dissolution-precipitation creep resulting in a foliation with flattened olivine grains at phase boundaries with antigorite, crenulation cleavages and olivine and antigorite aggregates in strain shadows next to porphyroclasts. It is suggested that the fluid was provided by dehydration reactions of antigorite forming olivine and enstatite during subduction and prograde metamorphism. At sites of stress concentration around porphyroclasts antigorite reveals an associated SPO and CPO, characteristically varying grain sizes and sutured grain boundaries, indicating deformation by dislocation creep. Stresses were probably below a few tens of MPa in the serpentinites, which was not sufficiently high to allow for crystal-plastic deformation of olivine at conditions at which antigorite is stable. Accordingly, any intragranular deformation features of the newly precipitated olivine in strain shadows are absent. The porphyroclast microstructures are not associated with the microstructures of the mylonitic matrix, but are inherited from an independent earlier deformation. The porphyroclasts record a high-stress deformation in the upper mantle of the oceanic lithosphere probably related to rifting processes, whereas the antigorite matrix

  13. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition.

    Science.gov (United States)

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V; Stanley, H Eugene; Reguera, David; Franzese, Giancarlo

    2015-06-22

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments.

  14. Controlled in meso phase crystallization--a method for the structural investigation of membrane proteins.

    Directory of Open Access Journals (Sweden)

    Jan Kubicek

    Full Text Available We investigated in meso crystallization of membrane proteins to develop a fast screening technology which combines features of the well established classical vapor diffusion experiment with the batch meso phase crystallization, but without premixing of protein and monoolein. It inherits the advantages of both methods, namely (i the stabilization of membrane proteins in the meso phase, (ii the control of hydration level and additive concentration by vapor diffusion. The new technology (iii significantly simplifies in meso crystallization experiments and allows the use of standard liquid handling robots suitable for 96 well formats. CIMP crystallization furthermore allows (iv direct monitoring of phase transformation and crystallization events. Bacteriorhodopsin (BR crystals of high quality and diffraction up to 1.3 Å resolution have been obtained in this approach. CIMP and the developed consumables and protocols have been successfully applied to obtain crystals of sensory rhodopsin II (SRII from Halobacterium salinarum for the first time.

  15. Description of hard-sphere crystals and crystal-fluid interfaces: a comparison between density functional approaches and a phase-field crystal model.

    Science.gov (United States)

    Oettel, M; Dorosz, S; Berghoff, M; Nestler, B; Schilling, T

    2012-08-01

    In materials science the phase-field crystal approach has become popular to model crystallization processes. Phase-field crystal models are in essence Landau-Ginzburg-type models, which should be derivable from the underlying microscopic description of the system in question. We present a study on classical density functional theory in three stages of approximation leading to a specific phase-field crystal model, and we discuss the limits of applicability of the models that result from these approximations. As a test system we have chosen the three-dimensional suspension of monodisperse hard spheres. The levels of density functional theory that we discuss are fundamental measure theory, a second-order Taylor expansion thereof, and a minimal phase-field crystal model. We have computed coexistence densities, vacancy concentrations in the crystalline phase, interfacial tensions, and interfacial order parameter profiles, and we compare these quantities to simulation results. We also suggest a procedure to fit the free parameters of the phase-field crystal model. Thereby it turns out that the order parameter of the phase-field crystal model is more consistent with a smeared density field (shifted and rescaled) than with the shifted and rescaled density itself. In brief, we conclude that fundamental measure theory is very accurate and can serve as a benchmark for the other theories. Taylor expansion strongly affects free energies, surface tensions, and vacancy concentrations. Furthermore it is phenomenologically misleading to interpret the phase-field crystal model as stemming directly from Taylor-expanded density functional theory.

  16. Synthesis and Crystallization Studies of Thermo-plastic Polyster/Titania Nanocomposites

    Directory of Open Access Journals (Sweden)

    Harshita Agrawal

    2014-02-01

    Full Text Available The present work reports the non-isothermal crystallization kinetics of PETTiO2 nanocomposites. The average particle size of TiO2 nanoparticles, prepared by chemical route, has been calculated 32 nm using Debay-Scherrer’s formula in XRD peaks. PET-TiO2 nanocomposites have been synthesized using solution casting method. The investigation of non-isothermal crystallization behavior has been conducted by means of Differential Scanning Calorimeter (DSC. The crystallization temperature shift to lower temperature for both PET pristine and PET-TiO2 nanocomposites due to decrease in mobility of chain segments and heterogeneous nucleation. Also, the inclusion of TiO2 nanoparticles may accelerate nucleation rate in nanocomposites that causes the crystallization time and absolute crystallinity fraction. The thermal conductivity of inorganic filler TiO2 nanoparticles may affect the crystallization temperature.

  17. Crystallization of molecular systems from solution: phase diagrams, supersaturation and other basic concepts.

    Science.gov (United States)

    Coquerel, Gérard

    2014-04-07

    The aim of the tutorial review is to show that any crystallization from solution is guided by stable or metastable equilibria and thus can be rationalized by using phase diagrams. Crystallization conducted by cooling, by evaporation and by anti-solvent addition is mainly considered. The driving force of crystallization is quantified and the occurrence of transient metastable states is logically explained by looking at the pathways of crystallization and the progressive segregation which might occur in a heterogeneous system.

  18. Blue phase liquid crystal: strategies for phase stabilization and device development

    Directory of Open Access Journals (Sweden)

    Asiqur Rahman, Suhana Mohd Said and S Balamurugan

    2015-05-01

    Full Text Available The blue phase liquid crystal (BPLC is a highly ordered liquid crystal (LC phase found very close to the LC–isotropic transition. The BPLC has demonstrated potential in next-generation display and photonic technology due to its exceptional properties such as sub-millisecond response time and wide viewing angle. However, BPLC is stable in a very small temperature range (0.5–1 °C and its driving voltage is very high (~100 V. To overcome these challenges recent research has focused on solutions which incorporate polymers or nanoparticles into the blue phase to widen the temperature range from around few °C to potentially more than 60 °C. In order to reduce the driving voltage, strategies have been attempted by modifying the device structure by introducing protrusion or corrugated electrodes and vertical field switching mechanism has been proposed. In this paper the effectiveness of the proposed solution will be discussed, in order to assess the potential of BPLC in display technology and beyond.

  19. Thermodynamics around the first-order ferromagnetic phase transition of Fe2P single crystals

    NARCIS (Netherlands)

    Hudl, M.; Campanini, D.; Caron, L.; Höglin, V.; Sahlberg, M.; Nordblad, P.; Rydh, A.

    2014-01-01

    The specific heat and thermodynamics of Fe2P single crystals around the first-order paramagnetic to ferromagnetic (FM) phase transition at TC≃217K are empirically investigated. The magnitude and direction of the magnetic field relative to the crystal axes govern the derived H−T phase diagram. Striki

  20. Phase Transitions in a Non-Uniformly Stressed Iron Borate Single Crystal

    Science.gov (United States)

    Dzhuraev, D. R.; Niyazov, L. N.; Sokolov, B. Yu.

    2016-05-01

    Based on the Landau thermodynamic theory, phase transformations observed in a FeBO3 single crystal subject to spatially non-uniform mechanical stresses are analyzed. It is demonstrated that the main results of theoretical consideration of structural and magnetic phase transitions in the examined crystal do not contradict with the available experimental data.

  1. Influence of fat crystals in the oil phase on stability of oil-in-water emulsions

    NARCIS (Netherlands)

    Boekel, van M.A.J.S.

    1980-01-01

    Coalescence at rest and during flow was studied in emulsions of paraffin oil in water with several surfactants and with crystals of solid paraffin or tristearate in the oil phase. Solid fat in the oil phase was estimated by pulsed nuclear magnetic resonance. Without crystals, oil-in-water emulsions

  2. A Scanning Hologram Recorded by Phase Conjugate Property of Nonlinear Crystals

    DEFF Research Database (Denmark)

    Zi-Liang, Ping; Dalsgaard, Erik

    1996-01-01

    A methode of recording a scanning hologram with phase conjugate property of nonlinear crystal is provided. The principle of recording, setup and experiments are given.......A methode of recording a scanning hologram with phase conjugate property of nonlinear crystal is provided. The principle of recording, setup and experiments are given....

  3. Interface dynamics and crystal phase switching in GaAs nanowires

    OpenAIRE

    Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M

    2016-01-01

    This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature17148 Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) n...

  4. Influence of pressure on the ferroelectric phase transition in a symmetrical polymerizable diacetylene crystal DNP

    Science.gov (United States)

    Even, J.; Bertault, M.; Girard, A.; Délugeard, Y.

    1996-12-01

    DNP is a symmetrical disubstituted polymerizable diacetylene RCCCCR where R is CH 2O(NO 2) 2. The monomer crystal of DNP undergoes a ferroelectric phase transition at low temperature; it disappears in fully polymerized DNP crystal because polymerization changes the diacetylene backbone conformation. We show that hydrostatic isotropic pressure also stabilizes the ferroelectric phase in the DNP monomer crystal by enhancing van der Waals interactions between side groups.

  5. Prediction, simulation, and verification of the phase noise in 80-MHz low-phase-noise crystal oscillators.

    Science.gov (United States)

    Huang, Xianhe; Chen, Pingping; Fu, Wei; Jiao, Junjie

    2015-09-01

    To predict the phase noise in an 80-MHz crystal oscillator, on the basis of the classical Leeson model, we analyzed and selected the oscillator noise figure F and transistor corner frequency fc reasonably, and then calculated the loaded Q (QL) value of the oscillator according to the parameters in the selected Butler oscillation circuit. Thus, we obtained the predicted phase noise in an 80-MHz crystal oscillator according to the Leeson phase noise formula. Next, the simulation curve of the phase noise in this 80-MHz low-phase-noise crystal oscillator was obtained by establishing a transistor nonlinear model using commercial design software. Then, we debugged the 80-MHz low-phase-noise crystal oscillator prototype under the guidance of the prediction and simulation results and tested it. The measured results show that the phase noise predicted after selecting reasonable parameters for the Leeson model and the ADS simulation curve of the phase noise obtained by using the nonlinear transistor model are both close to the actual measured result. This result may be beneficial in simplifying the design process for low-phase-noise crystal oscillators.

  6. Phase-space properties of two-dimensional elastic phononic crystals and anharmonic effects in nano-phononic crystals

    Science.gov (United States)

    Swinteck, Nichlas Z.

    This dissertation contains research directed at investigating the behavior and properties of a class of composite materials known as phononic crystals. Two categories of phononic crystals are explicitly investigated: (I) elastic phononic crystals and (II) nano-scale phononic crystals. For elastic phononic crystals, attention is directed at two-dimensional structures. Two specific structures are evaluated (1) a two-dimensional configuration consisting of a square array of cylindrical Polyvinylchloride inclusions in air and (2) a two-dimensional configuration consisting of a square array of steel cylindrical inclusions in epoxy. For the first configuration, a theoretical model is developed to ascertain the necessary band structure and equi-frequency contour features for the realization of phase control between propagating acoustic waves. In contrasting this phononic crystal with a reference system, it is shown that phononic crystals with equifrequency contours showing non-collinear wave and group velocity vectors are ideal systems for controlling the phase between propagating acoustic waves. For the second configuration, it is demonstrated that multiple functions can be realized of a solid/solid phononic crystal. The epoxy/steel phononic crystal is shown to behave as (1) an acoustic wave collimator, (2) a defect-less wave guide, (3) a directional source for elastic waves, (4) an acoustic beam splitter, (5) a phase-control device and (6) a k-space multiplexer. To transition between macro-scale systems (elastic phononic crystals) and nano-scale systems (nano-phononic crystals), a toy model of a one-dimensional chain of masses connected with non-linear, anharmonic springs is utilized. The implementation of this model introduces critical ideas unique to nano-scale systems, particularly the concept of phonon mode lifetime. The nano-scale phononic crystal of interest is a graphene sheet with periodically spaced holes in a triangular array. It is found through equilibrium

  7. Analytical Round Robin for Elastic-Plastic Analysis of Surface Cracked Plates, Phase II Results

    Science.gov (United States)

    Allen, P. A.; Wells, D. N.

    2017-01-01

    The second phase of an analytical round robin for the elastic-plastic analysis of surface cracks in flat plates was conducted under the auspices of ASTM Interlaboratory Study 732. The interlaboratory study (ILS) had 10 participants with a broad range of expertise and experience, and experimental results from a surface crack tension test in 4142 steel plate loaded well into the elastic-plastic regime provided the basis for the study. The participants were asked to evaluate a surface crack tension test according to the version of the surface crack initiation toughness testing standard published at the time of the ILS, E2899-13. Data were provided to each participant that represent the fundamental information that would be provided by a mechanical test laboratory prior to evaluating the test result. Overall, the participant’s test analysis results were in good agreement and constructive feedback was received that has resulted in an improved published version of the standard E2899-15.

  8. Oscillations, phase-of-firing coding, and spike timing-dependent plasticity: an efficient learning scheme.

    Science.gov (United States)

    Masquelier, Timothée; Hugues, Etienne; Deco, Gustavo; Thorpe, Simon J

    2009-10-28

    Recent experiments have established that information can be encoded in the spike times of neurons relative to the phase of a background oscillation in the local field potential-a phenomenon referred to as "phase-of-firing coding" (PoFC). These firing phase preferences could result from combining an oscillation in the input current with a stimulus-dependent static component that would produce the variations in preferred phase, but it remains unclear whether these phases are an epiphenomenon or really affect neuronal interactions-only then could they have a functional role. Here we show that PoFC has a major impact on downstream learning and decoding with the now well established spike timing-dependent plasticity (STDP). To be precise, we demonstrate with simulations how a single neuron equipped with STDP robustly detects a pattern of input currents automatically encoded in the phases of a subset of its afferents, and repeating at random intervals. Remarkably, learning is possible even when only a small fraction of the afferents ( approximately 10%) exhibits PoFC. The ability of STDP to detect repeating patterns had been noted before in continuous activity, but it turns out that oscillations greatly facilitate learning. A benchmark with more conventional rate-based codes demonstrates the superiority of oscillations and PoFC for both STDP-based learning and the speed of decoding: the oscillation partially formats the input spike times, so that they mainly depend on the current input currents, and can be efficiently learned by STDP and then recognized in just one oscillation cycle. This suggests a major functional role for oscillatory brain activity that has been widely reported experimentally.

  9. The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior

    Directory of Open Access Journals (Sweden)

    Samo Kralj

    2009-09-01

    Full Text Available We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described.

  10. Non-Fermi liquid phase in metallic Skyrmion crystals

    Science.gov (United States)

    Watanabe, Haruki; Parameswaran, Siddharth; Raghu, Srinivas; Vishwanath, Ashvin

    2014-03-01

    Motivated by reports of a non-Fermi liquid state in MnSi, we examine the effect of coupling phonons of an incommensurate skyrmion crystal (SkX) to conduction electrons. We find that non-Fermi liquid behavior emerges in both two and three dimensions over the entire phase, due to an anomalous electron-phonon coupling that is linked to the net skyrmion density. A small parameter, the spiral wave vector in lattice units, allows us to exercise analytic control and ignore Landau damping of phonons over a wide energy range. At the lowest energy scales the problem is similar to electrons coupled to a gauge field. The best prospects for realizing these effects is in short period skyrmion lattice systems such as MnGe or epitaxial MnSi films. We also compare our results with the unusual T 3 / 2 scaling of temperature dependent resistivity seen in high pressure experiments on MnSi. We acknowledge support from the NSF via Grant DMR-0645691, the DOE Office of Basic Energy Sciences via contract DE-AC02-76SF00515, and the Simons, Templeton, and Alfred P. Sloan Foundations.

  11. The role of dissipation and defect energy in variational formulations of problems in strain-gradient plasticity. Part 2: single-crystal plasticity

    Science.gov (United States)

    Reddy, B. D.

    2011-11-01

    Variational formulations are constructed for rate-independent problems in small-deformation single-crystal strain-gradient plasticity. The framework, based on that of Gurtin (J Mech Phys Solids 50: 5-32, 2002), makes use of the flow rule expressed in terms of the dissipation function. Provision is made for energetic and dissipative microstresses. Both recoverable and non-recoverable defect energies are incorporated into the variational framework. The recoverable energies include those that depend smoothly on the slip gradients, the Burgers tensor, or on the dislocation densities (Gurtin et al. J Mech Phys Solids 55:1853-1878, 2007), as well as an energy proposed by Ohno and Okumura (J Mech Phys Solids 55:1879-1898, 2007), which leads to excellent agreement with experimental results, and which is positively homogeneous and therefore not differentiable at zero slip gradient. Furthermore, the variational formulation accommodates a non-recoverable energy due to Ohno et al. (Int J Mod Phys B 22:5937-5942, 2008), which is also positively homogeneous, and a function of the accumulated dislocation density. Conditions for the existence and uniqueness of solutions are established for the various examples of defect energy, with or without the presence of hardening or slip resistance.

  12. Microstructure Evolution and Mechanical Behavior of a Hot-Rolled High-Manganese Dual-Phase Transformation-Induced Plasticity/Twinning-Induced Plasticity Steel

    Science.gov (United States)

    Fu, Liming; Shan, Mokun; Zhang, Daoda; Wang, Huanrong; Wang, Wei; Shan, Aidang

    2017-05-01

    The microstructures and deformation behavior were studied in a high-temperature annealed high-manganese dual-phase (28 vol pct δ-ferrite and 72 vol pct γ-austenite) transformation-induced plasticity/twinning-induced plasticity (TRIP/TWIP) steel. The results showed that the steel exhibits a special Lüders-like yielding phenomenon at room temperature (RT) and 348 K (75 °C), while it shows continuous yielding at 423 K, 573 K and 673 K (150 °C, 300 °C and 400 °C) deformation. A significant TRIP effect takes place during Lüders-like deformation at RT and 348 K (75 °C) temperatures. Semiquantitative analysis of the TRIP effect on the Lüders-like yield phenomenon proves that a softening effect of the strain energy consumption of strain-induced transformation is mainly responsible for this Lüders-like phenomenon. The TWIP mechanism dominates the 423 K (150 °C) deformation process, while the dislocation glide controls the plasticity at 573 K (300 °C) deformation. The delta-ferrite, as a hard phase in annealed dual-phase steel, greatly affects the mechanical stability of austenite due to the heterogeneous strain distribution between the two phases during deformation. A delta-ferrite-aided TRIP effect, i.e., martensite transformation induced by localized strain concentration of the hard delta-ferrite, is proposed to explain this kind of Lüders-like phenomenon. Moreover, the tensile curve at RT exhibits an upward curved behavior in the middle deformation stage, which is principally attributed to the deformation twinning of austenite retained after Lüders-like deformation. The combination of the TRIP effect during Lüders-like deformation and the subsequent TWIP effect greatly enhances the ductility in this annealed high-manganese dual-phase TRIP/TWIP steel.

  13. Microstructure Evolution and Mechanical Behavior of a Hot-Rolled High-Manganese Dual-Phase Transformation-Induced Plasticity/Twinning-Induced Plasticity Steel

    Science.gov (United States)

    Fu, Liming; Shan, Mokun; Zhang, Daoda; Wang, Huanrong; Wang, Wei; Shan, Aidang

    2017-02-01

    The microstructures and deformation behavior were studied in a high-temperature annealed high-manganese dual-phase (28 vol pct δ-ferrite and 72 vol pct γ-austenite) transformation-induced plasticity/twinning-induced plasticity (TRIP/TWIP) steel. The results showed that the steel exhibits a special Lüders-like yielding phenomenon at room temperature (RT) and 348 K (75 °C), while it shows continuous yielding at 423 K, 573 K and 673 K (150 °C, 300 °C and 400 °C) deformation. A significant TRIP effect takes place during Lüders-like deformation at RT and 348 K (75 °C) temperatures. Semiquantitative analysis of the TRIP effect on the Lüders-like yield phenomenon proves that a softening effect of the strain energy consumption of strain-induced transformation is mainly responsible for this Lüders-like phenomenon. The TWIP mechanism dominates the 423 K (150 °C) deformation process, while the dislocation glide controls the plasticity at 573 K (300 °C) deformation. The delta-ferrite, as a hard phase in annealed dual-phase steel, greatly affects the mechanical stability of austenite due to the heterogeneous strain distribution between the two phases during deformation. A delta-ferrite-aided TRIP effect, i.e., martensite transformation induced by localized strain concentration of the hard delta-ferrite, is proposed to explain this kind of Lüders-like phenomenon. Moreover, the tensile curve at RT exhibits an upward curved behavior in the middle deformation stage, which is principally attributed to the deformation twinning of austenite retained after Lüders-like deformation. The combination of the TRIP effect during Lüders-like deformation and the subsequent TWIP effect greatly enhances the ductility in this annealed high-manganese dual-phase TRIP/TWIP steel.

  14. Identifying Structure-Property Relationships Through DREAM.3D Representative Volume Elements and DAMASK Crystal Plasticity Simulations: An Integrated Computational Materials Engineering Approach

    Science.gov (United States)

    Diehl, Martin; Groeber, Michael; Haase, Christian; Molodov, Dmitri A.; Roters, Franz; Raabe, Dierk

    2017-03-01

    Predicting, understanding, and controlling the mechanical behavior is the most important task when designing structural materials. Modern alloy systems—in which multiple deformation mechanisms, phases, and defects are introduced to overcome the inverse strength-ductility relationship—give raise to multiple possibilities for modifying the deformation behavior, rendering traditional, exclusively experimentally-based alloy development workflows inappropriate. For fast and efficient alloy design, it is therefore desirable to predict the mechanical performance of candidate alloys by simulation studies to replace time- and resource-consuming mechanical tests. Simulation tools suitable for this task need to correctly predict the mechanical behavior in dependence of alloy composition, microstructure, texture, phase fractions, and processing history. Here, an integrated computational materials engineering approach based on the open source software packages DREAM.3D and DAMASK (Düsseldorf Advanced Materials Simulation Kit) that enables such virtual material development is presented. More specific, our approach consists of the following three steps: (1) acquire statistical quantities that describe a microstructure, (2) build a representative volume element based on these quantities employing DREAM.3D, and (3) evaluate the representative volume using a predictive crystal plasticity material model provided by DAMASK. Exemplarily, these steps are here conducted for a high-manganese steel.

  15. Identifying Structure-Property Relationships Through DREAM.3D Representative Volume Elements and DAMASK Crystal Plasticity Simulations: An Integrated Computational Materials Engineering Approach

    Science.gov (United States)

    Diehl, Martin; Groeber, Michael; Haase, Christian; Molodov, Dmitri A.; Roters, Franz; Raabe, Dierk

    2017-05-01

    Predicting, understanding, and controlling the mechanical behavior is the most important task when designing structural materials. Modern alloy systems—in which multiple deformation mechanisms, phases, and defects are introduced to overcome the inverse strength-ductility relationship—give raise to multiple possibilities for modifying the deformation behavior, rendering traditional, exclusively experimentally-based alloy development workflows inappropriate. For fast and efficient alloy design, it is therefore desirable to predict the mechanical performance of candidate alloys by simulation studies to replace time- and resource-consuming mechanical tests. Simulation tools suitable for this task need to correctly predict the mechanical behavior in dependence of alloy composition, microstructure, texture, phase fractions, and processing history. Here, an integrated computational materials engineering approach based on the open source software packages DREAM.3D and DAMASK (Düsseldorf Advanced Materials Simulation Kit) that enables such virtual material development is presented. More specific, our approach consists of the following three steps: (1) acquire statistical quantities that describe a microstructure, (2) build a representative volume element based on these quantities employing DREAM.3D, and (3) evaluate the representative volume using a predictive crystal plasticity material model provided by DAMASK. Exemplarily, these steps are here conducted for a high-manganese steel.

  16. The non-equilibrium phase diagrams of flow-induced crystallization and melting of polyethylene.

    Science.gov (United States)

    Wang, Zhen; Ju, Jianzhu; Yang, Junsheng; Ma, Zhe; Liu, Dong; Cui, Kunpeng; Yang, Haoran; Chang, Jiarui; Huang, Ningdong; Li, Liangbin

    2016-09-09

    Combining extensional rheology with in-situ synchrotron ultrafast x-ray scattering, we studied flow-induced phase behaviors of polyethylene (PE) in a wide temperature range up to 240 °C. Non-equilibrium phase diagrams of crystallization and melting under flow conditions are constructed in stress-temperature space, composing of melt, non-crystalline δ, hexagonal and orthorhombic phases. The non-crystalline δ phase is demonstrated to be either a metastable transient pre-order for crystallization or a thermodynamically stable phase. Based on the non-equilibrium phase diagrams, nearly all observations in flow-induced crystallization (FIC) of PE can be well understood. The interplay of thermodynamic stabilities and kinetic competitions of the four phases creates rich kinetic pathways for FIC and diverse final structures. The non-equilibrium flow phase diagrams provide a detailed roadmap for precisely processing of PE with designed structures and properties.

  17. Two phase modeling of the influence of plastic strain on the magnetic and magnetostrictive behaviors of ferromagnetic materials

    Science.gov (United States)

    Hubert, Olivier; Lazreg, Said

    2017-02-01

    A growing interest of automotive industry in the use of high performance steels is observed. These materials are obtained thanks to complex manufacturing processes whose parameters fluctuations lead to strong variations of microstructure and mechanical properties. The on-line magnetic non-destructive monitoring is a relevant response to this problem but it requires fast models sensitive to different parameters of the forming process. The plastic deformation is one of these important parameters. Indeed, ferromagnetic materials are known to be sensitive to stress application and especially to plastic strains. In this paper, a macroscopic approach using the kinematic hardening is proposed to model this behavior, considering a plastic strained material as a two phase system. Relationship between kinematic hardening and residual stress is defined in this framework. Since stress fields are multiaxial, an uniaxial equivalent stress is calculated and introduced inside the so-called magneto-mechanical multidomain modeling to represent the effect of plastic strain. The modeling approach is complemented by many experiments involving magnetic and magnetostrictive measurements. They are carried out with or without applied stress, using a dual-phase steel deformed at different levels. The main interest of this material is that the mechanically hard phase, soft phase and the kinematic hardening can be clearly identified thanks to simple experiments. It is shown how this model can be extended to single phase materials.

  18. Phase Sensitive X-Ray Diffraction Imaging of Defects in Biological Macromolecular Crystals

    Science.gov (United States)

    Hu, Z. W.; Lai, B.; Chu, Y. S.; Cai, Z.; Mancini, D. C.; Thomas, B. R.; Chernov, A. A.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Characterization of defects and/or disorder in biological macromolecular crystals presents much greater challenges than in conventional small-molecule crystals. The lack of sufficient contrast of defects is often a limiting factor in x-ray diffraction topography of protein crystals. This has seriously hampered efforts to understand mechanisms and origins of formation of imperfections, and the role of defects as essential entities in the bulk of macromolecular crystals. In this report, we employ a phase sensitive x-ray diffraction imaging approach for augmenting the contrast of defects in protein crystals.

  19. Indentation Pileup Behavior of Ti-6Al-4V Alloy: Experiments and Nonlocal Crystal Plasticity Finite Element Simulations

    Science.gov (United States)

    Han, Fengbo; Tang, Bin; Yan, Xu; Peng, Yifei; Kou, Hongchao; Li, Jinshan; Deng, Ying; Feng, Yong

    2017-01-01

    This study reports on the indentation pileup behavior of Ti-6Al-4V alloy. Berkovich nanoindentation was performed on a specimen with equiaxed microstructure. The indented area was characterized by electron backscattered diffraction (EBSD) to obtain the indented grain orientations. Surface topographies of several indents were measured by atomic force microscopy (AFM). The pileup patterns on the indented surfaces show significant orientation dependence. Corresponding nonlocal crystal plasticity finite element (CPFE) simulations were carried out to predict the pileup patterns. Analysis of the cumulative shear strain distributions and evolutions for different slip systems around the indents found that the pileups are mainly caused by prismatic slip. The pileup patterns evolve with the loading and unloading process, and the change in pileup height due to the elastic recovery at unloading stage is significant. The density distributions of geometrically necessary dislocations (GNDs) around the indent were predicted. Simulation of nanoindentation on a tricrystal model was performed.

  20. Indentation Pileup Behavior of Ti-6Al-4V Alloy: Experiments and Nonlocal Crystal Plasticity Finite Element Simulations

    Science.gov (United States)

    Han, Fengbo; Tang, Bin; Yan, Xu; Peng, Yifei; Kou, Hongchao; Li, Jinshan; Deng, Ying; Feng, Yong

    2017-04-01

    This study reports on the indentation pileup behavior of Ti-6Al-4V alloy. Berkovich nanoindentation was performed on a specimen with equiaxed microstructure. The indented area was characterized by electron backscattered diffraction (EBSD) to obtain the indented grain orientations. Surface topographies of several indents were measured by atomic force microscopy (AFM). The pileup patterns on the indented surfaces show significant orientation dependence. Corresponding nonlocal crystal plasticity finite element (CPFE) simulations were carried out to predict the pileup patterns. Analysis of the cumulative shear strain distributions and evolutions for different slip systems around the indents found that the pileups are mainly caused by prismatic slip. The pileup patterns evolve with the loading and unloading process, and the change in pileup height due to the elastic recovery at unloading stage is significant. The density distributions of geometrically necessary dislocations (GNDs) around the indent were predicted. Simulation of nanoindentation on a tricrystal model was performed.

  1. Plastic yielding and work hardening of single crystals in a soft device

    Science.gov (United States)

    Le, K. C.; Nguyen, Q. S.

    2009-11-01

    An analytical solution to the problem of an anti-plane constrained shear of single crystals placed in a soft device within the continuum dislocation theory is found. The dependence of the nucleation stress on the grain size exhibits a modest deviation from the Hall-Petch relation. It is shown that, as soon as the dissipation is taken into account, the hardening behavior becomes nearly identical to that of single crystals in a hard device. To cite this article: K.C. Le, Q.S. Nguyen, C. R. Mecanique 337 (2009).

  2. Lattice Boltzmann Simulation of 3D Nematic Liquid Crystal near Phase Transition

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun; TAO Rui-Bao

    2002-01-01

    Phase transition between nematic and isotropic liquid crystal is a very weak first order phase transition.We avoid to use the normal Landau-de Gennes's free energy that reduces a strong first order transition, and set up adata base of free energy calculated by means of Tao-Sheng Lin's extended molecular field theory that can explain theexperiments of the equilibrium properties of nematic liquid crystal very well. Then we use the free energy method oflattice Boltzmann developed by Oxford group to study the phase decomposition, pattern formation in the flow of theliquid crystal near transition temperature.

  3. Two hardening mechanisms in single crystal thin films studied by discrete dislocation plasticity

    NARCIS (Netherlands)

    Nicola, L; Van der Giessen, E; Needleman, A

    2005-01-01

    thermal stress in single crystal thin films on a rigid substrate are used to study size effects. The relation between the residual stress and the dislocation structure in the films after cooling is analyzed using dislocation dynamics. A boundary layer characterized by a high stress gradient and a hi

  4. A facility for plastic deformation of germanium single-crystal wafers

    DEFF Research Database (Denmark)

    Lebech, B.; Theodor, K.; Breiting, B.

    1998-01-01

    . All movements and temperature changes are done by a robot via a PLC-control system. Two nine-crystal focusing monochromators (54 x 116 and 70 x 116 mm(2)) made from 100 wafers with average mosaicity similar to 13' have been constructed. Summaries of the test results are presented. (C) 1998 Elsevier...

  5. T Helper Subsets, Peripheral Plasticity, and the Acute Phase Protein, α1-Antitrypsin

    Directory of Open Access Journals (Sweden)

    Boris M. Baranovski

    2015-01-01

    Full Text Available The traditional model of T helper differentiation describes the naïve T cell as choosing one of several subsets upon stimulation and an added reciprocal inhibition aimed at maintaining the chosen subset. However, to date, evidence is mounting to support the presence of subset plasticity. This is, presumably, aimed at fine-tuning adaptive immune responses according to local signals. Reprograming of cell phenotype is made possible by changes in activation of master transcription factors, employing epigenetic modifications that preserve a flexible mode, permitting a shift between activation and silencing of genes. The acute phase response represents an example of peripheral changes that are critical in modulating T cell responses. α1-antitrypsin (AAT belongs to the acute phase responses and has recently surfaced as a tolerogenic agent in the context of adaptive immune responses. Nonetheless, AAT does not inhibit T cell responses, nor does it shutdown inflammation per se; rather, it appears that AAT targets non-T cell immunocytes towards changing the cytokine environment of T cells, thus promoting a regulatory T cell profile. The present review focuses on this intriguing two-way communication between innate and adaptive entities, a crosstalk that holds important implications on potential therapies for a multitude of immune disorders.

  6. Optical frequency conversion in quasi-phase-matched stacks of nonlinear crystals

    Science.gov (United States)

    Rustagi, K. C.; Mehendale, S. C.; Meenakshi, S.

    1982-06-01

    The paper presents a quantitative theory of nonlinear frequency conversion in stacks of crystals in which the phase mismatch due to dispersion is compensated by changing the sign of the nonlinear coupling coefficient in successive crystals. The effects of systematic and random departures in crystal lengths are studied with emphasis on the evolution of the relative phase. It is shown that with the appropriate choice of the signs of the nonlinear coupling coefficient in various crystals, high efficiency frequency conversion should be possible using almost any sufficiently large set of nonlinear crystals. In addition, the theory of second harmonic generation in periodic stacks and in rotating twinned crystals of zinc-blend structure is described.

  7. Optically induced structural phase transitions in ion Coulomb crystals

    DEFF Research Database (Denmark)

    Horak, Peter; Dantan, Aurelien Romain; Drewsen, Michael

    2012-01-01

    , such as body-centered cubic and face-centered cubic, can be suppressed by a proper choice of the potential depth and periodicity. Furthermore, by varying the harmonic trap parameters and/or the optical potential in time, controlled transitions between crystal structures can be obtained with close to unit......We investigate numerically the structural dynamics of ion Coulomb crystals confined in a three-dimensional harmonic trap when influenced by an additional one-dimensional optically induced periodical potential. We demonstrate that transitions between thermally excited crystal structures...

  8. Synthesis, crystal growth and characterization of a phase matchable nonlinear optical single crystal: p-chloro dibenzylideneacetone

    Science.gov (United States)

    Ravindra, H. J.; John Kiran, A.; Nooji, Satheesha Rai; Dharmaprakash, S. M.; Chandrasekharan, K.; Kalluraya, Balakrishna; Rotermund, Fabian

    2008-05-01

    Good quality single crystals of p-chloro dibenzylideneacetone (CDBA) of size 13 mm×8 mm×2 mm were grown by slow evaporation solution growth technique. The grown crystals were confirmed by elemental analysis, Fourier transform infrared (FTIR) analysis and single crystal X-ray diffraction techniques. From the thermo gravimetric/differential thermal (TG/DT) analysis, the CDBA was found to be thermally stable up to 250 °C. The mechanical stability of the crystal is comparable with that of the other reported chalcones. The lower optical cut-off wavelength for this crystal was observed at 440 nm. The laser damage threshold of the crystal was 0.6 GW/cm 2 at 532 nm. The second harmonic generation conversion efficiency of the powder sample of CDBA was found to be 4.5 times greater than that of urea. We also demonstrate the existence of the phase matching property in this crystal using Kurtz powder technique.

  9. Phase diagram of power law and Lennard-Jones systems: Crystal phases

    Energy Technology Data Exchange (ETDEWEB)

    Travesset, Alex [Ames Laboratory

    2014-10-28

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  10. Evaluation of phase bunching in the central region of a cyclotron by a radial probe with a plastic scintillator

    Energy Technology Data Exchange (ETDEWEB)

    Miyawaki, Nobumasa, E-mail: miyawaki.nobumasa@jaea.go.jp [Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Fukuda, Mitsuhiro [Research Center for Nuclear Physics, Osaka University, 10-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Kurashima, Satoshi; Kashiwagi, Hirotsugu; Okumura, Susumu [Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Arakawa, Kazuo [Gunma University Heavy Ion Medical Center, Gunma University, 3-39-22 Showa-Machi, Maebashi, Gunma, 371-8511 (Japan); Kamiya, Tomihiro [Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan)

    2014-12-11

    A new technique for evaluating the phase bunching performance in the central region of a cyclotron was developed. A newly-developed radial probe with a 6-mm-wide, 5-mm-height plastic scintillator was applied to analysis of the correlation between the internal beam phase distribution and the initial beam phase, defined by adjusting the relative RF phase of the beam buncher. The phase distribution measurement system, comprising the radial probe equipped with a plastic scintillator and the signal-processing modules, had a sufficiently good time resolution of 45 ps full-width at half-maximum for the phase bunching evaluation. The correlations between the buncher phase and the measured phase distribution for the acceleration harmonic number h=1 and 2 were consistent with the calculation result of the geometric trajectory analysis. For h=1 case of a 107 MeV {sup 4}He{sup 2+} beam, the internal beam phase region spread over 71 RF degrees full-width at quarter-maximum (FWQM) for the acceptable buncher phase region of 48 RF degrees, and no evidence of the phase bunching effect was observed. For h=2 case of a 260 MeV {sup 20}Ne{sup 7+} beam, the internal beam phase region for the acceptable buncher phase region of 59 RF degrees was compressed into 21 RF degrees FWQM. The phase bunching effect was sharply evident for h=2, and contributed to increase of the acceptable beam phase region and the beam intensity per phase width.

  11. Large Scale DD Simulation Results for Crystal Plasticity Parameters in Fe-Cr And Fe-Ni Systems

    Energy Technology Data Exchange (ETDEWEB)

    Zbib, Hussein M.; Li, Dongsheng; Sun, Xin; Khaleel, Mohammad A.

    2012-04-30

    The development of viable nuclear energy source depends on ensuring structural materials integrity. Structural materials in nuclear reactors will operate in harsh radiation conditions coupled with high level hydrogen and helium production, as well as formation of high density of point defects and defect clusters, and thus will experience severe degradation of mechanical properties. Therefore, the main objective of this work is to develop a capability that predicts aging behavior and in-service lifetime of nuclear reactor components and, thus provide an instrumental tool for tailoring materials design and development for application in future nuclear reactor technologies. Towards this end goal, the long term effort is to develop a physically based multiscale modeling hierarchy, validated and verified, to address outstanding questions regarding the effects of irradiation on materials microstructure and mechanical properties during extended service in the fission and fusion environments. The focus of the current investigation is on modern steels for use in nuclear reactors including high strength ferritic-martensitic steels (Fe-Cr-Ni alloys). The effort is to develop a predicative capability for the influence of irradiation on mechanical behavior. Irradiation hardening is related to structural information crossing different length scales, such as composition, dislocation, and crystal orientation distribution. To predict effective hardening, the influence factors along different length scales should be considered. Therefore, a hierarchical upscaling methodology is implemented in this work in which relevant information is passed between models at three scales, namely, from molecular dynamics to dislocation dynamics to dislocation-based crystal plasticity. The molecular dynamics (MD) was used to predict the dislocation mobility in body centered cubic (bcc) Fe and its Ni and Cr alloys. The results are then passed on to dislocation dynamics to predict the critical resolved

  12. Phase-locking regimes of photonic crystal nanocavity laser arrays

    DEFF Research Database (Denmark)

    Skovgård, Troels Suhr; Kristensen, Philip Trøst; Mørk, Jesper

    2011-01-01

    We model and analyze the dynamical properties of coupled photonic crystal nanocavity lasers. The model includes Purcell enhancement of the spontaneous emission and intercavity coupling. The coupling strength between neighboring cavities is an essential parameter, and by performing finite-differen......We model and analyze the dynamical properties of coupled photonic crystal nanocavity lasers. The model includes Purcell enhancement of the spontaneous emission and intercavity coupling. The coupling strength between neighboring cavities is an essential parameter, and by performing finite...

  13. Crystal size growth in the liquid phase methanol synthesis catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Sawant, A.; Lee, S.; Foos, A.

    1988-01-01

    The phenomenon of crystal growth in the methanol synthesis catalyst has been studied. Crystallite size distributions in the CuO/ZnO/Al/sub 2/O/sub 3/ methanol synthesis catalyst have been determined. The effects of temperature, reaction environment and time under reaction conditions have been studied. It is observed that water in the reaction mixture promotes crystal growth. 26 refs., 10 figs., 1 tab.

  14. Evolutionary crystal structure prediction and novel high-pressure phases

    OpenAIRE

    Oganov, A. R.; Ma, Y.; Lyakhov, A. O.; Valle, M.; C. Gatti

    2010-01-01

    Prediction of stable crystal structures at given pressure-temperature conditions, based only on the knowledge of the chemical composition, is a central problem of condensed matter physics. This extremely challenging problem is often termed "crystal structure prediction problem", and recently developed evolutionary algorithm USPEX (Universal Structure Predictor: Evolutionary Xtallography) made an important progress in solving it, enabling efficient and reliable prediction of structures with up...

  15. Local phase measurements of light in a one-dimensional photonic crystal

    NARCIS (Netherlands)

    Flück, E.; Otter, A.M.; Korterik, J.P.; Balistreri, M.L.M.; Kuipers, L.; Hulst, van N.F.

    2001-01-01

    For the first time the local optical phase evolution in and around a small, o­ne-dimensional photonic crystal has been visualized with a heterodyne interferometric photon scanning tunnelling microscope. The measurements show an exponential decay of the optical intensity inside the crystal, which con

  16. Mercury-induced crystallization and SAD phasing of the human Fe65-PTB1 domain

    OpenAIRE

    Radzimanowski, Jens; Ravaud, Stéphanie; Beyreuther, Konrad; Sinning, Irmgard; Wild, Klemens

    2008-01-01

    Crystals of the phosphotyrosine-binding domain 1 (PTB1) of the neuronal adaptor protein Fe65 grown in the presence of a mercury derivative show a dramatic improvement in resolution, permitting SAD phasing.

  17. Solving the Phase Problem in Crystal Structure Determination: A Simple Introduction to Direct Methods.

    Science.gov (United States)

    Schenk, H.

    1979-01-01

    Presents a simple way to introduce Direct Methods program systems to solve phase problems in x-ray crystal structure determination. It is intended for the undergraduate chemistry student laboratory. (Author/SA)

  18. Removal of vapour phase PCDD/Fs in electric arc furnace steelmaking emissions by sorption using plastics.

    Science.gov (United States)

    Ooi, Tze Chean; Ewan, Bruce C R; Cliffe, Keith R; Anderson, David R; Fisher, Raymond; Thompson, Dennis

    2008-08-01

    Plastics are potentially suitable for the removal of vapour phase PCDD/Fs in emissions from the electric arc furnace (EAF) steelmaking process. Three different commercial plastics, i.e. polypropylene BE170MO (Borealis A/S, Denmark), polypropylene in the form of 5 mm spheres (The Precision Plastic Ball Co. Ltd., UK) and polyethylene LD605BA (ExxonMobil Chemical, Belgium), have been studied using a novel experimental apparatus for the removal of vapour phase PCDD/Fs. Polypropylene BE170MO was identified to be the most suitable product amongst the three plastics in terms of PCDD/F sorption and potential industrial application. The optimum temperature for PCDD/F sorption on polypropylene BE170MO was below 90 degrees C for a removal efficiency of >99% at an average vapour phase PCDD/F concentration of 3.5 ng I-TEQ/Nm(3). At 130 degrees C, 53% of the PCDD/Fs trapped on polypropylene BE170MO were desorbed.

  19. PHASE ANALYSIS AND CRYSTAL STRUCTURE STUDIES ON BINARY ALLOYS OF ALUMINUM WITH TRANSITION METALS.

    Science.gov (United States)

    In order to provide the necessary background for detailed crystal-chemistry studies in the field of binary aluminum - transition metal systems, extensive investigations have been carried out on the phase relations of a large number of such systems. The results of these studies are briefly summarized, as are also the results of crystal structure determinations of a few alumi num - transition metal phases. (Author)

  20. Ground-State Phase Diagram of Transverse Spin-2 Ising Model with Longitudinal Crystal-Field

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal-field is studied within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. The ground-state phase diagram and the tricritical point are obtained in the transverse field Ω/z J-longitudinal crystal D/zJ field plane. We find that there are the first order-order phase transitions in a very smallrange of D/zJ besides the usual first order-disorder phase transitions and the second order-disorder phase transitions.

  1. Factors Affecting the Plasticity of Sodium Chloride, Lithium Fluoride, and Magnesium Oxide Single Crystals. 1

    Science.gov (United States)

    Stearns, Carl A.; Pack, Ann E.; Lad, Robert A.

    1959-01-01

    A study was made of the relative magnitude of the effects of various factors on the ductility of single crystals of sodium chloride (NaCl), lithium fluoride (LiF), and magnesium oxide (MgO). Specimen treatments included water-polishing, varying cleavage rate, annealing, quenching, X-irradiation, surface coating, aging, and combinations of some of these treatments. The mechanical behavior of the crystals was studied in flexure and in compression, the latter study being performed at both constant strain rate and constant load. Etch-pit studies were carried out to provide some pertinent information on the results of pretreatment on the dislocation concentration and distribution in the vicinity of the surface. The load deformation curves for these ionic single crystals show an initial region of very low slope which proved to be due to anelastic deformation. The extent of initial anelastic deformation is modified by specimen pretreatment in a way that suggests that this deformation is the result of expansion of cleaved-in dislocation loops, which can contract on the removal of the stress. The effects of the various pretreatments on the load and deflection at fracture are in accord with the prediction one might make with regard to their effect on the nucleation of fatal surface cracks. For NaCl, increases in ductility are always accompanied by increases in strength. The creep constants for NaCl are a function of treatments which affect the bulk structure but are not a function of treatments which only affect the surface.

  2. Phase Sensitive X-Ray Diffraction Imaging Study of Protein Crystals

    Science.gov (United States)

    Hu, Z. W.

    2003-01-01

    The study of defects and growth of protein crystals is of importance in providing a fundamental understanding of this important category of systems and the rationale for crystallization of better ordered crystals for structural determination and drug design. Yet, as a result of the extremely weak scattering power of x-rays in protein and other biological macromolecular crystals, the extinction lengths for those crystals are extremely large and, roughly speaking, of the order of millimeters on average compared to the scale of micrometers for most small molecular crystals. This has significant implication for x-ray diffraction and imaging study of protein crystals, and presents an interesting challenge to currently available x-ray analytical techniques. We proposed that coherence-based phase sensitive x-ray diffraction imaging could provide a way to augment defect contrast in x-ray diffraction images of weakly diffracting biological macromolecular crystals. I shall examine the principles and ideas behind this approach and compare it to other available x-ray topography and diffraction methods. I shall then present some recent experimental results in two model protein systems-cubic apofemtin and tetragonal lysozyme crystals to demonstrate the capability of the coherence-based imaging method in mapping point defects, dislocations, and the degree of perfection of biological macromolecular crystals with extreme sensitivity. While further work is under way, it is intended to show that the observed new features have yielded important information on protein crystal perfection and nucleation and growth mechanism otherwise unobtainable.

  3. About the Nature of Electroluminescence Centers in Plastically Deformed Crystals of p-type Silicon

    Directory of Open Access Journals (Sweden)

    B.V. Pavlyk

    2015-10-01

    Full Text Available The paper describes research of dislocation electroluminescence of single crystal p-type silicon with a high concentration of dislocations on the surface (111. It is shown the reaction of the luminescence spectra and capacitive-modulation spectra of samples after high-temperature annealing in an atmosphere of flowing oxygen. The analysis of the results lets us to establish the nature of recombination centers and their reorganization under high-temperature annealing. It is shown that deposition of Al film on the substrate p-Si leads to the formation of strain capacity and the localization of defects in the surface layer that corresponds to luminescence centers.

  4. New crystal phase of ammonium nitrate: First-principles prediction and characterization

    Science.gov (United States)

    Steele, Brad A.; Oleynik, Ivan I.

    2017-01-01

    First principles evolutionary crystal structure search found a new crystal phase of ammonium nitrate (AN). The calculated Raman spectra of this new phase is consistent with the recently reported experimental Raman spectrum that contains two peaks previously associated with a pressure-induced phase transition. The phase transition is reported to occur at a pressure of 17 GPa while the new phase is calculated to be lower in free energy than phase IV of AN (AN-IV) above a pressure of 10.83 GPa. The new phase has a monoclinic unit cell with the P21/m space group symmetry (AN-P21/m). This new phase is similar to AN-IV except the ammonium molecules are oriented differently relative to the nitrate molecules. The calculated Raman spectrum of both AN-P21/m and AN-IV as a function of pressure shows good agreement with experiment up to 33 GPa.

  5. Crystal Field Parameters and Phase Transitions in ErSb

    DEFF Research Database (Denmark)

    Shapiro, S. M.; Bak, P.

    1975-01-01

    The crystal field levels of the Er ion in a single crystal of ErSb have been measured by inelastic neutron scattering. The crystal field parameters obtained by a least squares fit to the spectra at several temperatures are: B4 = (0·473 ± 0·005) × 10−2°K and B6 = (0·59 ± 0·06) × 10−5°K, which differ...... considerably from the values o by interpolation from measurements on other compounds. In addition the temperature dependence of the magnetic scattering in the vicinity of the Néel temperature (TN = 3·55°K) clearly demonstrates that the transition is second order in contrast to the first order behavior...

  6. THERMODYNAMIC PARAMETERS OF LEAD SULFIDE CRYSTALS IN THE CUBIC PHASE

    Directory of Open Access Journals (Sweden)

    T. O. Parashchuk

    2016-07-01

    Full Text Available Geometric and thermodynamic parameters of cubic PbS crystals were obtained using the computer calculations of the thermodynamic parameters within density functional theory method DFT. Cluster models for the calculation based on the analysis of the crystal and electronic structure. Temperature dependence of energy ΔE and enthalpy ΔH, Gibbs free energy ΔG, heat capacity at constant pressure CP and constant volume CV, entropy ΔS were determined on the basis of ab initio calculations of the crystal structure of molecular clusters. Analytical expressions of temperature dependences of thermodynamic parameters which were approximated with quantum-chemical calculation points have been presented. Experimental results compared with theoretically calculated data.

  7. Atomically resolved images of I(h) ice single crystals in the solid phase.

    Science.gov (United States)

    Kobayashi, Keita; Koshino, Masanori; Suenaga, Kazu

    2011-05-20

    The morphology and crystal structure of nanoparticles of ice were examined by high-resolution transmission electron microscopy. Two different crystal structures were found and unambiguously assigned to hexagonal (I(h)) and cubic (I(c)) ice crystals. Direct observation of oxygen columns clearly revealed the hexagonal packing of water molecules. Electron energy-loss spectroscopy was used to monitor the electronic excitation in ice, suggesting possible dissociation of water molecules. Dynamic process of phase transition between I(h) and I(c) phases of individual ice nanoparticles under electron beam irradiation was also monitored by in situ transmission electron diffractometry.

  8. Effect of Crystal Quality on HCP-BCC Phase Transition in Solid 4He

    CERN Document Server

    Mikhin, N; Rudavskii, E; Vekhov, Y; Mikhin, Nikolay; Polev, Andrey; Rudavskii, Eduard; Vekhov, Yegor

    2006-01-01

    The kinetics of HCP-BCC structure phase transition is studied by precise pressure measurement technique in 4He crystals of different quality. An anomalous pressure behavior in bad quality crystals under constant volume conditions is detected just after HCP-BCC structure phase transition. A sharp pressure drop of 0.2 bar was observed at constant temperature. The subsequent pressure kinetics is a non-monotonic temperature function. The effect observed can be explained if we suppose that microscopic liquid droplets appear on the HCP-BCC interphase region in bad quality crystals. After the interphase region disappearance, these droplets are crystallized with pressure reduction. It is shown that this effect is absent in high quality thermal-treated crystals.

  9. Phase diagrams of mixtures of a polymer and a cholesteric liquid crystal under an external field.

    Science.gov (United States)

    Matsuyama, Akihiko

    2014-11-14

    We present a mean field theory to describe phase behaviors in mixtures of a polymer and a cholesteric liquid crystal under an external magnetic or electric field. Taking into account a chiral coupling between a polymer and a liquid crystal under the external field, we examine twist-untwist phase transitions and phase separations in the mixtures. It is found that a cholesteric-nematic phase transition can be induced by not only the external field but also concentration and temperature. Depending on the strength of the external field, we predict cholesteric-paranematic (Ch+pN), nematic-paranematic (N+pN), cholesteric-nematic (Ch+N) phase separations, etc., on the temperature-concentration plane. We also discuss mixtures of a non-chiral nematic liquid crystal and a chiral dopant.

  10. Controlling crystal phases in GaAs nanowires grown by Au-assisted molecular beam epitaxy.

    Science.gov (United States)

    Dheeraj, D L; Munshi, A M; Scheffler, M; van Helvoort, A T J; Weman, H; Fimland, B O

    2013-01-11

    Control of the crystal phases of GaAs nanowires (NWs) is essential to eliminate the formation of stacking faults which deteriorate the optical and electronic properties of the NWs. In addition, the ability to control the crystal phase of NWs provides an opportunity to engineer the band gap without changing the crystal material. We show that the crystal phase of GaAs NWs grown on GaAs(111)B substrates by molecular beam epitaxy using the Au-assisted vapor-liquid-solid growth mechanism can be tuned between wurtzite (WZ) and zinc blende (ZB) by changing the V/III flux ratio. As an example we demonstrate the realization of WZ GaAs NWs with a ZB GaAs insert that has been grown without changing the substrate temperature.

  11. Controlling Interface States in 1D Photonic Crystals by tuning Bulk Geometric Phases

    CERN Document Server

    Gao, Wensheng; Chen, Baojie; Pun, Edwin Y B; Chan, C T; Tam, Wing Yim

    2016-01-01

    Interface states in photonic crystals usually require defects or surface/interface decorations. We show here that one can control interface states in 1D photonic crystals through the engineering of geometrical phase such that interface states can be guaranteed in even or odd, or in all photonic bandgaps. We verify experimentally the designed interface states in 1D multilayered photonic crystals fabricated by electron beam vapor deposition. We also obtain the geometrical phases by measuring the reflection phases at the bandgaps of the PCs and achieve good agreement with the theory. Our approach could provide a platform for the design of using interface states in photonic crystals for nonlinear optic, sensing, and lasing applications

  12. Orientational phase transition in cubic liquid crystals with positional order

    OpenAIRE

    Pokrovsky, V.L.; Saidachmetov, P.A.

    1988-01-01

    An electric field can give rise to a shear deformation of a cubic liquid crystal with long-range positional order fixed by two plates. The critical value of the field does not depend on the size of the system and depends crucially on the orientation.

  13. Optically induced structural phase transitions in ion Coulomb crystals

    DEFF Research Database (Denmark)

    Horak, Peter; Dantan, Aurelien Romain; Drewsen, Michael

    2012-01-01

    , such as body-centered cubic and face-centered cubic, can be suppressed by a proper choice of the potential depth and periodicity. Furthermore, by varying the harmonic trap parameters and/or the optical potential in time, controlled transitions between crystal structures can be obtained with close to unit...

  14. Irradiation-initiated plastic deformation in prestrained single-crystal copper

    Energy Technology Data Exchange (ETDEWEB)

    Li, Bo [Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230027 (China); The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031 (China); Wang, Liang [The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031 (China); Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Jian, Wu-Rong [The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031 (China); Department of Engineering Mechanics, South China University of Technology, Guangzhou, Guangdong 510640 (China); E, Jun-Cheng [The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031 (China); Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Ma, Hong-Hao, E-mail: hhma@ustc.edu.cn [Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230027 (China); Luo, Sheng-Nian, E-mail: sluo@pims.ac.cn [The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031 (China); Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China)

    2016-02-01

    With large-scale molecular dynamics simulations, we investigate the response of elastically prestrained single-crystal Cu to irradiation as regards the effects of prestrain magnitude and direction, as well as PKA (primary knock-on atom) energy. Under uniaxial tension, irradiation induces such defects as Frenkel pairs, stacking faults, twins, dislocations, and voids. Given the high dislocation concentration, twins and quad-stacking faults form through overlapping of different stacking faults. Voids nucleate via liquid cavitation, and dislocations around void play a lesser role in the void nucleation and growth. Dislocation density increases with increasing prestrain and PKA energy. At a given prestrain, there exists a critical PKA energy for dislocation activation, which decreases with increasing prestrain and depends on crystallographic direction of the applied prestrain.

  15. Shock Compression of Metal Crystals: A Comparison of Eulerian and Lagrangian Elastic-Plastic Theories

    Science.gov (United States)

    2014-11-01

    temperature equation-of-state (EOS) [ Luscher et al., 2013] for the pressure. For isotropic (e.g., untextured polycrystalline) solids, nonlinear elasticity...elastoplasticity [ Luscher et al., 2013]. 1450048-12 2nd Reading October 15, 2014 11:4 WSPC-255-IJAM S1758-8251 1450048 Shock Compression of Metal Crystals...Clayton, 2011; Luscher et al., 2013] S̄ = ∂Ū ∂E = ∂Ψ̄ ∂E = JFE−1σFE−T, θ = ∂Ū/∂η, η = −∂Ψ̄/∂θ, χ̄ = −∂Ψ̄/∂ζ, (3.7) c̄θ̇ = ∑ α τ̄αγ̇α + θ ∂S̄ ∂θ : Ė

  16. Vapor-crystal phase transition in synthesis of paracetamol films by vacuum evaporation and condensation

    Science.gov (United States)

    Belyaev, A. P.; Rubets, V. P.; Antipov, V. V.; Bordei, N. S.; Zarembo, V. I.

    2014-03-01

    We report on the structural and technological investigations of the vapor-crystal phase transition during synthesis of paracetamol films of the monoclinic system by vacuum evaporation and condensation in the temperature range 220-320 K. The complex nature of the transformation accompanied by the formation of a gel-like phase is revealed. The results are interpreted using a model according to which the vapor-crystal phase transition is not a simple first-order phase transition, but is a nonlinear superposition of two phase transitions: a first-order transition with a change in density and a second-order phase transition with a change in ordering. Micrographs of the surface of the films are obtained at different phases of formation.

  17. Phase separation of monomer in liquid crystal mixtures and surface morphology in polymer-stabilized vertical alignment liquid crystal displays

    Energy Technology Data Exchange (ETDEWEB)

    Lyu, Jae Jin; Lee, Jun Hyup; Kim, Kyeong Hyeon [Development Center, LCD Business, SAMSUNG Electronics Co. LTD., Tangjeong-Myeon, Asan, Chungnam 336-741 (Korea, Republic of); Kikuchi, Hirotsuku; Higuchi, Hiroki [Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga-Koen, Kasuga 816-8580 (Japan); Kim, Dae Hyun; Lee, Seung Hee, E-mail: jsquare.lyu@samsung.com, E-mail: lsh1@chonbuk.ac.kr [Department of BIN Fusion Technology and Department of Polymer-Nano Science and Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of)

    2011-08-17

    The polymer-stabilized vertically aligned (PS-VA) liquid crystal display (LCD) driving mode has high potential for manufacturing low power consuming displays due to the higher transmittance and fast response as compared with the existing patterned vertically aligned and multi-domain vertically aligned modes. In this paper we have investigated the reaction mechanisms of monomer-liquid crystal blends to form a surface pre-tilt angle of liquid crystal in vertical alignment LCD associated with a fishbone electrode structure. The observed sizes of polymer bumps formed on the substrates were found to be dependent on the exposed UV wavelength and were almost equal in both top and bottom substrates. When a large UV wavelength was used, the phase separation mechanism of monomer in PS-VA mode was found nearly isotropic rather than anisotropic in contrast to the previous studies.

  18. Restudy of the unusual phase behavior of the mesogen-jacketed liquid crystal polymers

    Institute of Scientific and Technical Information of China (English)

    ZHAO; Yongfeng; FAN; Xinghe; CHEN; Xiaofang; WAN; Xinhua

    2006-01-01

    A series of poly{2,5-bis[(4-butoxyphenyl)-oxycarbonyl]styrenes} (PBPCS) with low molecular weight distribution was synthesized by atom transfer radical polymerization (ATRP). The mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and rheometer. PBPCS showed the phase transition from isotropic into liquid crystal (LC) phase, and the LC phase formed at high temperature and disappeared in the subsequent cooling procedure. Using the WAXD fiber pattern, the phase structure of the PBPCS at higher temperature showed hexagonal columnar nematic phase. Experimental results demonstrated that the driving force of the entropy is an important factor during the unusual LC phase formation of PBPCS.

  19. Nucleation of protein crystals: critical nuclei, phase behavior, and control pathways

    Science.gov (United States)

    Galkin, Oleg; Vekilov, Peter G.

    2001-11-01

    We have studied the nucleation of crystals of the model protein lysozyme using a novel technique that allows direct determinations of homogeneous nucleation rates. At constant temperature of 12.6°C we varied the thermodynamic supersaturation by changing the concentrations of protein and precipitant. We found a broken dependence of the homogeneous nucleation rate on supersaturation that is beyond the predictions of the classical nucleation theory. The nucleation theorem allows us to relate this to discrete changes of the size of the crystal nuclei with increasing supersaturation as (10 or 11)→(4 or 5)→(1 or 2). Furthermore, we observe that the existence of a second liquid phase at high protein concentrations strongly affects crystal nucleation kinetics. We show that the rate of homogeneous nucleation of lysozyme crystals passes through a maximum in the vicinity of the liquid-liquid phase boundary hidden below the liquidus (solubility) line in the phase diagram of the protein solution. We found that glycerol and polyethylene glycol (PEG), which do not specifically bind to proteins, shift this phase boundary and significantly suppress or enhance the crystal nucleation rates, although no simple correlation exists between the action of PEG on the phase diagram and the nucleation kinetics. This provides for a control mechanism which does not require changes in the protein concentration, or the acidity and ionicity of the solution. The effects of the two additives on the phase diagram strongly depend on their concentration and this provides opportunities for further tuning of nucleation rates.

  20. Ferroelectric phase transition in relaxor ferroelectric single crystals 0.76PMN-0.24PT

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The features of the single crystals 0.76PMN-0.24PT in dielectric, ferroelectric, pyroelectric properties and domain structures indicate that they are located between typical ferroelectrics and normal ones. The unpoled crystals present a transitional domain configuration between microdomains and typical macrodomains while the crystals on (001) cuts undergo field-induced phase transition under poling, showing two special temperature points Td and Tm during the succedent heating procedure. The dielectric constant starts to decrease drastically at Td during cooling, or the transformation from induced macrodomain to transitional domain takes place at Td during heating. Ferroelectric-paraelectric phase transition or depolarization continues within the whole temperature range of Td-Tm, where ferroelectric phase in the form of transitional macrodomains coexists with paraelectric phase. Then the crystals macroscopically transoform into paraelectric phase containing ferroelectric microdomains at a temperature above Tm. However, owing to the influence of crystallite orientation on field-induced phase transition, the temperature Td does not appear in the same temperature-electric field history in multicrystal ceramics with the same composition as the above single crystals.

  1. Crystallization Kinetics of GeSbTe Phase-Change Nanoparticles Resolved by Ultrafast Calorimetry

    NARCIS (Netherlands)

    Chen, Bin; Brink, ten Gert; Palasantzas, Georgios; Kooi, Bart J.

    2017-01-01

    Although nanostructured phase-change materials (PCMs) are considered as the building blocks of next-generation phase-change memory and other emerging optoelectronic applications, the kinetics of the crystallization, the central property in switching, remains ambiguous in the high-temperature regime.

  2. Microscopic dynamics of AC{sub 60} compounds in the plastic, polymer, and dimer phases investigated by inelastic neutron scattering

    Energy Technology Data Exchange (ETDEWEB)

    Schober, H.; Toelle, A. [Institut Laue-Langevin, F-38042 Grenoble (France); Renker, B.; Heid, R.; Gompf, F. [INFP, Forschungszentrum Karlsruhe, D-76021 Karlsruhe (Federal Republic of Germany)

    1997-09-01

    We present inelastic neutron-scattering results for AC{sub 60} (A=K,Rb,Cs) compounds. The spectra of the high-temperature fcc phases strongly resemble the ones of pristine C{sub 60} in the plastic phase. At equal temperatures we find identical rotational diffusion constants for pristine C{sub 60} and Rb{sub 1}C{sub 60} (D{sub r}=2.4 10{sup 10} s{sup {minus}1} at 400 K). The changes taking place in the inelastic part of the spectra on cooling AC{sub 60} indicate the formation of strong intermolecular bonds. The buildup of intensities in the gap region separating internal and external vibrations in pure C{sub 60} is the most prominent signature of this transition. The spectra of the low-temperature phases depend on their thermal history. The differences can be explained by the formation of a polymer phase (upon slow cooling from the fcc phase) and a dimer phase (upon fast cooling), respectively. The experimental data are analyzed on the basis of lattice dynamical calculations. The density-of-states are well modeled assuming a [2+2] bond for the polymer and a single intercage bond for the dimer. Indications for different intercage bonding are also found in the internal mode spectra, which, on the other hand, react only weakly to the charge transfer. The dimer phase is metastable and converts into the polymer phase with a strongly temperature-dependent time constant. The transition from the polymer to the fcc phase is accompanied by inelastic precursor effects which are interpreted as the signature of inhomogeneities arising from plastic monomer regions embedded in the polymer phase. In the polymer phase AC{sub 60} compounds show strong anharmonic behavior in the low-temperature region. The possible connection with the metal-to-insulator transition is discussed. {copyright} {ital 1997} {ital The American Physical Society}

  3. Crystal chemistry of three-component white dwarfs and neutron star crusts: phase stability, phase stratification, and physical properties

    CERN Document Server

    Engstrom, T A; Crespi, V H

    2015-01-01

    A systematic search for multicomponent crystal structures is carried out for five different ternary systems of nuclei in a polarizable background of electrons, representative of accreted neutron star crusts and some white dwarfs. Candidate structures are "bred" by a genetic algorithm, and optimized at constant pressure under the assumption of linear response (Thomas-Fermi) charge screening. Subsequent phase equilibria calculations reveal eight distinct crystal structures in the $T=0$ bulk phase diagrams, five of which are complicated multinary structures not before predicted in the context of compact object astrophysics. Frequent instances of geometrically similar but compositionally distinct phases give insight into structural preferences of systems with pairwise Yukawa interactions, including and extending to the regime of low density colloidal suspensions made in a laboratory. As an application of these main results, we self-consistently couple the phase stability problem to the equations for a self-gravit...

  4. Mapping mesoscale heterogeneity in the plastic deformation of a copper single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Magid, K. R.; Florando, J.N.; Lassila, D.H.; Leblanc, M.M.; Tamura, N.; Morris Jr, J. W.

    2008-10-01

    The work reported here is part of a 'multiscale characterization' study of heterogeneous deformation patterns in metals. A copper single crystal was oriented for single slip in the (111)[{bar 1}01] slip system and tested to {approx}10% strain in roughly uniaxial compression. The macroscopic strain field was monitored during the test by optical 'image correlation'. The strain field was measured on orthogonal surfaces, one of which (the x-face) was oriented perpendicular to [1{bar 2}1] and contained the [{bar 1}01] direction of the preferred slip system. The macroscopic strain developed in an inhomogeneous pattern of broad, crossed shear bands in the x-face. One, the primary band, lay parallel to (111). The second, the 'conjugate' band, was oriented perpendicular to (111) with an overall ({bar 1}01) habit that contains no common slip plane of the fcc crystal. The mesoscopic deformation pattern was explored with selected area diffraction, using a focused synchrotron radiation polychromatic beam with a resolution of 1-3 {micro}m. Areas within the primary, conjugate and mixed (primary + conjugate) strain regions of the x-face were identified and mapped for their orientation, excess defect density and shear stress. The mesoscopic defect structure was concentrated in broad, somewhat irregular primary bands that lay nominally parallel to (111) in an almost periodic distribution with a period of about 30 {micro}m. These primary bands were dominant even in the region of conjugate strain. There were also broad conjugate defect bands, almost precisely perpendicular to the primary bands, that tended to bridge primary bands and terminate at them. The residual shear stresses were large (ranging to well above 500 MPa) and strongly correlated with the primary shear bands; interband stresses were small. The maximum resolved shear stresses within the primary bands were oriented out of the plane of the bands, and, hence, could not recover the dislocation

  5. Reflectance and reflection phase of photonic crystal with anisotropic left-handed materials

    Science.gov (United States)

    Kang, Yongqiang; Zhang, Chunmin; Yao, Baoli

    2016-11-01

    The reflectance and reflection phase properties of one dimensional photonic crystals with anisotropic left-handed materials is investigated by transfer matrix method. It is demonstrated that the width of zero- n band gap is influenced by the incident angle, polarization, the proportion of lattice and the ratio of thickness which is different from the zero- n band gap with isotropic left hand materials. The value of reflection phase is affected by incident angle and polarization and not affected by the proportion of lattice and the ratio of thickness. These characteristic may be useful for making photonic crystal phase compensators and the dispersion compensators.

  6. Setting up a liquid crystal phase screen to simulate atmospheric turbulence

    Science.gov (United States)

    Giles, Michael K.; Seward, Anthony J.; Vorontsov, Mikhail A.; Rha, Jungtae; Jimenez, Ray

    2000-11-01

    Phase screens are often used to simulate atmospheric turbulence in systems designed to test adaptive optics techniques. This paper presents the design and implementation of a dynamic phase screen using a simple and inexpensive twisted nematic liquid crystal display taken from a video projector and placed in a pupil plane. The details of the optical system layout, the system alignment procedure, and the operating parameters of the liquid crystal display are discussed. Examples of turbulence (having strength and statistics similar to measured values of atmospheric turbulence in a variety of scenarios) are written to the phase screen, and the effects of the turbulence on image quality are measured and presented.

  7. Hyperresolving phase-only filters with an optically addressable liquid crystal spatial light modulator.

    Science.gov (United States)

    McOrist, J; Sharma, M D; Sheppard, C J R; West, E; Matsuda, K

    2003-01-01

    Hyperresolving (sometimes called 'superresolving' or 'ultraresolving') phase-only filters can be generated using an optically addressable liquid crystal spatial light modulator. This approach avoids the problems of low efficiency, and coupling between amplitude and phase modulation, that arise when using conventional liquid crystal modulators. When addressed by a programmed light intensity distribution, it allows filters to be changed rapidly to modify the response of a system or permit the investigation of different filter designs. In this paper we present experimental hyperresolved images obtained using an optically addressable parallel-aligned nematic LCD with two zone Toraldo type phase-only filters. The images are compared with theoretical predictions.

  8. Crystal growth of an organic non-linear optical material from the vapour phase

    CERN Document Server

    Hou, W

    1999-01-01

    Due to the potential applications of organic non-linear optical materials in the areas of optical processing and communication, the investigation of the crystal growth of new organic NLO materials has been an active field for the last 20 years. For such uses it is necessary to produce single crystals of high quality and perfection, free of strain and defects. When crystals are grown from the solution and the melt, solvent and the decomposition component in the melt can introduce impurities and imperfection to the as-grown crystals. For crystals grown from vapour phase, in the absence of the solvent, this cannot occur and the method promises to yield single crystals of higher quality. Despite this attraction, little attention has been paid to the vapour phase growth of organic NLO crystals. It was with this in mind that the following investigation was carried out. Using Methyl p-hydroxybenzoate (p-MHB), a potential organic NLO material, a comparison investigation was made of its crystal growth from both the va...

  9. Multiscale Analysis of Structurally-Graded Microstructures Using Molecular Dynamics, Discrete Dislocation Dynamics and Continuum Crystal Plasticity

    Science.gov (United States)

    Saether, Erik; Hochhalter, Jacob D.; Glaessgen, Edward H.; Mishin, Yuri

    2014-01-01

    A multiscale modeling methodology is developed for structurally-graded material microstructures. Molecular dynamic (MD) simulations are performed at the nanoscale to determine fundamental failure mechanisms and quantify material constitutive parameters. These parameters are used to calibrate material processes at the mesoscale using discrete dislocation dynamics (DD). Different grain boundary interactions with dislocations are analyzed using DD to predict grain-size dependent stress-strain behavior. These relationships are mapped into crystal plasticity (CP) parameters to develop a computationally efficient finite element-based DD/CP model for continuum-level simulations and complete the multiscale analysis by predicting the behavior of macroscopic physical specimens. The present analysis is focused on simulating the behavior of a graded microstructure in which grain sizes are on the order of nanometers in the exterior region and transition to larger, multi-micron size in the interior domain. This microstructural configuration has been shown to offer improved mechanical properties over homogeneous coarse-grained materials by increasing yield stress while maintaining ductility. Various mesoscopic polycrystal models of structurally-graded microstructures are generated, analyzed and used as a benchmark for comparison between multiscale DD/CP model and DD predictions. A final series of simulations utilize the DD/CP analysis method exclusively to study macroscopic models that cannot be analyzed by MD or DD methods alone due to the model size.

  10. A quantitative evaluation of the deformation texture predictions for aluminium alloys from crystal plasticity finite element method

    Science.gov (United States)

    Li, Saiyi; Van Houtte, Paul; Kalidindi, Surya R.

    2004-09-01

    Crystal plasticity finite element (CPFE) models are useful tools in modelling the anisotropic stress-strain responses in large deformation of polycrystalline metals. In this study, a CPFE model is applied to simulate the evolution of crystallographic textures during cold rolling of hot-rolled aluminium plates and during uniaxial tensile, uniaxial compression and simple shear tests of annealed aluminium sheets. The performance of the model is critically evaluated through quantitative comparisons of the simulated textures with those predicted by the full constraints (FC) Taylor model and the experimentally measured textures. It is shown that the CPFE model performs better than the FC Taylor model in all the cases. However, the quality of the texture predictions deteriorates with increasing strain values. The CPFE model gives better texture predictions in the moderately deformed tensile and compression samples (~20% strain), compared to the more heavily deformed simple shear (0.85-0.95 shear strain) and cold-rolled (40-98% thickness reduction) samples. It is also shown that the CPFE predictions for cold rolling can be improved with finer discretization, i.e. by assigning multiple elements per grain instead of one element per grain in the finite element model. The improvement is mainly reflected in an improved prediction of the copper component and, in some cases, an improved prediction of the brass component. Inspection of the local deformation gradients reveals that these texture changes can be attributed to the increase of shear relaxations in the RD-ND and RD-TD planes.

  11. Three-Dimensional Crystal Plasticity Finite Element Simulation of Hot Compressive Deformation Behaviors of 7075 Al Alloy

    Science.gov (United States)

    Li, Lei-Ting; Lin, Y. C.; Li, Ling; Shen, Lu-Ming; Wen, Dong-Xu

    2015-03-01

    Three-dimensional crystal plasticity finite element (CPFE) method is used to investigate the hot compressive deformation behaviors of 7075 aluminum alloy. Based on the grain morphology and crystallographic texture of 7075 aluminum alloy, the microstructure-based representative volume element (RVE) model was established by the pole figure inversion approach. In order to study the macroscopic stress-strain response and microstructural evolution, the CPFE simulations are performed on the established microstructure-based RVE model. It is found that the simulated stress-strain curves and deformation texture well agree with the measured results of 7075 aluminum alloy. With the increasing deformation degree, the remained initial weak Goss texture component tends to be strong and stable, which may result in the steady flow stress. The grain orientation and grain misorientation have significant effects on the deformation heterogeneity during hot compressive deformation. In the rolling-normal plane, the continuity of strain and misorientation can maintain across the low-angle grain boundaries, while the discontinuity of strain and misorientation is observed at the high-angle grain boundaries. The simulated results demonstrate that the developed CPFE model can well describe the hot compressive deformation behaviors of 7075 aluminum alloy under elevated temperatures.

  12. Forming limit prediction using a self-consistent crystal plasticity framework: a case study for body-centered cubic materials

    Science.gov (United States)

    Jeong, Youngung; Pham, Minh-Son; Iadicola, Mark; Creuziger, Adam; Foecke, Timothy

    2016-06-01

    A rate-dependent self-consistent crystal plasticity model was incorporated with the Marciniak-Kuczyński model in order to study the effects of anisotropy on the forming limits of BCC materials. The computational speed of the model was improved by a factor of 24 when running the simulations for several strain paths in parallel. This speed-up enabled a comprehensive investigation of the forming limits of various BCC textures, such as γ , σ , α , η and ɛ fibers and a uniform (random) texture. These simulations demonstrate that the crystallographic texture has significant (both positive and negative) effects on the resulting forming limit diagrams. For example, the γ fiber texture, which is often sought through thermo-mechanical processing due to a high r-value, had the highest forming limit in the balanced biaxial strain path but the lowest forming limit under the plane strain path among the textures under consideration. A systematic investigation based on the results produced by the current model, referred to as ‘VPSC-FLD’, suggests that the r-value does not serve as a good measure of forming limit strain. However, model predictions show a degree of correlation between the r-value and the forming limit stress.

  13. Atomic density functional and diagram of structures in the phase field crystal model

    Science.gov (United States)

    Ankudinov, V. E.; Galenko, P. K.; Kropotin, N. V.; Krivilyov, M. D.

    2016-02-01

    The phase field crystal model provides a continual description of the atomic density over the diffusion time of reactions. We consider a homogeneous structure (liquid) and a perfect periodic crystal, which are constructed from the one-mode approximation of the phase field crystal model. A diagram of 2D structures is constructed from the analytic solutions of the model using atomic density functionals. The diagram predicts equilibrium atomic configurations for transitions from the metastable state and includes the domains of existence of homogeneous, triangular, and striped structures corresponding to a liquid, a body-centered cubic crystal, and a longitudinal cross section of cylindrical tubes. The method developed here is employed for constructing the diagram for the homogeneous liquid phase and the body-centered iron lattice. The expression for the free energy is derived analytically from density functional theory. The specific features of approximating the phase field crystal model are compared with the approximations and conclusions of the weak crystallization and 2D melting theories.

  14. Modulated liquid-crystal phases induced by polarity: Twist-bend, splay-bend, and blue phases

    Science.gov (United States)

    Selinger, Jonathan; Shamid, Shaikh; Allender, David

    2014-03-01

    Nematic liquid crystals exhibit flexoelectric couplings between polar order and gradients in the director field. When the couplings become strong enough, the uniform nematic phase can become unstable to the formation of a modulated polar phase. The question is then: What is the structure of the modulated polar phase? Classic work by Meyer and further studies by Dozov predicted two possible structures, known as twist-bend and splay-bend. One of these predictions, the twist-bend phase, has recently been identified in experiments on bent-core liquid crystals. Here, we investigate modulated polar phases through a combination of Landau theory and lattice simulations. We find a range of possibilities, including the twist-bend and splay-bend phases as well as polar blue phases, with 2D or 3D modulations of the director field and the polar order. We compare these polar blue phases with chiral blue phases, and discuss opportunities for observing them experimentally. Supported by NSF DMR-1106014.

  15. Phase Equilibria and Crystal Growth for LiREF4 Scheelite Crystals

    OpenAIRE

    2009-01-01

    The scheelite type laser crystals LiREF4 melt congruently only for RE being one of the elements Er, Tm, Yb, Lu, or possibly Y, respectively. For RE = Eu, Gd, Tb, Dy, or Ho the corresponding scheelites undergo a peritectic melting under the formation of the corresponding rare earth fluoride. The melting behavior of LiREF4 mixed crystals with two or more RE is not yet known well. If RE is a mixture of Gd and Lu, Gd rich solid solutions melt peritectically under formation of (Gd,Lu)F3 and Lu ric...

  16. Differential modulation of motor cortical plasticity and excitability in early and late phases of human motor learning.

    Science.gov (United States)

    Rosenkranz, Karin; Kacar, Aleksandra; Rothwell, John C

    2007-10-31

    Different phases of motor skill learning appear to involve different physiological processes, with long-term potentiation (LTP) occurring at existing synapses in early and cortical reorganization involving synaptogenesis in later phases. Here, we test the evolution of skill learning-dependent changes in motor plasticity and excitability in six subjects trained to perform rapid thumb abductions over 5 d. Plasticity was examined using paired-associative stimulation (PAS) of the median nerve and motor cortex to induce LTP-like "PAS given with an interstimulus interval of 25 ms (PAS25)" or long-term depression (LTD)-like "PAS given with an interstimulus interval of 10 ms (PAS10)" plasticity. Excitability was tested by measuring recruitment of motor-evoked-potentials "input-output (IO) curve" and of short-latency intracortical inhibition (SICI curve), and sensorimotor organization (SMO). Task performance improved continuously over 5 d. After practice on day 1, the PAS25 effect reversed from facilitation to inhibition whereas the slope of the IO curve increased and the level of SICI decreased. These effects on IO curve and SICI were still present or even enhanced before the last practice on day 5, and were not changed by it. The effect of proprioceptive input from the trained muscle on SMO was also strengthened before practice on day 5. In contrast, PAS-induced plasticity was not influenced by motor practice on day 5, and had returned to prepractice values. The interference with PAS-induced plasticity suggests that the initial performance improvement relies on increasing the efficacy of existing synaptic connections. However, the long-lasting changes in the IO curve, SICI curve, and SMO suggest that continued practice enhances performance by changing Motor cortical organization. We hypothesize that new synaptic connections might have formed that allow LTP/LTD-susceptibility to be restored without reducing synaptic strength and performance skill.

  17. "Plastic" solar cells: self-assembly of bulk heterojunction nanomaterials by spontaneous phase separation.

    Science.gov (United States)

    Peet, Jeffrey; Heeger, Alan J; Bazan, Guillermo C

    2009-11-17

    As the global demand for low-cost renewable energy sources intensifies, interest in new routes for converting solar energy to electricity is rapidly increasing. Although photovoltaic cells have been commercially available for more than 50 years, only 0.1% of the total electricity generated in the United States comes directly from sunlight. The earliest commercial solar technology remains the basis for the most prevalent devices in current use, namely, highly-ordered crystalline, inorganic solar cells, commonly referred to as silicon cells. Another class of solar cells that has recently inspired significant academic and industrial excitement is the bulk heterojunction (BHJ) "plastic" solar cell. Research by a rapidly growing community of scientists across the globe is generating a steady stream of new insights into the fundamental physics, the materials design and synthesis, the film processing and morphology, and the device science and architecture of BHJ technology. Future progress in the fabrication of high-performance BHJ cells will depend on our ability to combine aspects of synthetic and physical chemistry, condensed matter physics, and materials science. In this Account, we use a combination of characterization tools to tie together recent advances in BHJ morphology characterization, device photophysics, and thin-film solution processing, illustrating how to identify the limiting factors in solar cell performance. We also highlight how new processing methods, which control both the BHJ phase separation and the internal order of the components, can be implemented to increase the power conversion efficiency (PCE). The failure of many innovative materials to achieve high performance in BHJ solar cell devices has been blamed on "poor morphology" without significant characterization of either the structure of the phase-separated morphology or the nature of the charge carrier recombination. We demonstrate how properly controlling the "nanomorphology", which is

  18. Quantitative Analysis of Bisphenol A Leached from Household Plastics by Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry (SPME-GC-MS)

    Science.gov (United States)

    Johnson, Bettie Obi; Burke, Fernanda M.; Harrison, Rebecca; Burdette, Samantha

    2012-01-01

    The measurement of trace levels of bisphenol A (BPA) leached out of household plastics using solid-phase microextraction (SPME) with gas chromatography-mass spectrometry (GC-MS) is reported here. BPA is an endocrine-disrupting compound used in the industrial manufacture of polycarbonate plastic bottles and epoxy resin can liners. This experiment…

  19. Quantitative Analysis of Bisphenol A Leached from Household Plastics by Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry (SPME-GC-MS)

    Science.gov (United States)

    Johnson, Bettie Obi; Burke, Fernanda M.; Harrison, Rebecca; Burdette, Samantha

    2012-01-01

    The measurement of trace levels of bisphenol A (BPA) leached out of household plastics using solid-phase microextraction (SPME) with gas chromatography-mass spectrometry (GC-MS) is reported here. BPA is an endocrine-disrupting compound used in the industrial manufacture of polycarbonate plastic bottles and epoxy resin can liners. This experiment…

  20. On the phase transformation of single-crystal 4H-SiC during nanoindentation

    Science.gov (United States)

    Matsumoto, Mitsuhiro; Huang, Hu; Harada, Hirofumi; Kakimoto, Koichi; Yan, Jiwang

    2017-07-01

    Microstructural changes of single-crystal 4H silicon carbide (SiC) induced by nanoindentation under various conditions were investigated. It was found that nanoindentation at different crystal orientations induced different Raman spectroscopic characteristics. Cross-sectional observation by transmission electron microscopy indicated that a very deep subsurface damage region was formed where dislocations occurring along the basal planes, crystal grains rotation and micro-cracks were observed. The microstructures of the damage regions were strongly affected by the nanoindentation conditions. Coupled analysis of lattice fringes and Raman spectra indicated that a phase transformation from 4H-SiC to 3C-SiC occurred during nanoindentation, which has never been reported before. Furthermore, the 4H to 3C phase transformation strongly depended on the indenter orientation with respect to the SiC crystal. These findings are meaningful for low-damage precision machining of SiC substrates.

  1. Hysteresis Loops and Phase Diagrams of the Spin-1 Ising Model in a Transverse Crystal Field

    Institute of Scientific and Technical Information of China (English)

    S. Bouhou; I. Essaoudi; A. Ainane; M. Saber; J. J. de Miguel; M. Kerouad1

    2012-01-01

    Within the framework of the effective-Geld theory with a probability distribution technique, which accounts for the self-spin correlation functions, the ferromagnetic spin-l Ising model with a transverse crystal field on honeycomb, square and simple cubic lattices is studied. We have investigated the effect of the transverse crystal field on the phase diagrams, magnetization, hysteresis loops and χz,h of the system. A number of interesting phenomena of the system are discussed.%Within the framework of the effective-field theory with a probability distribution technique,which accounts for the self-spin correlation functions,the ferromagnetic spin-1 Ising model with a transverse crystal field on honeycomb,square and simple cubic lattices is studied.We have investigated the effect of the transverse crystal field on the phase diagrams,magnetization,hysteresis loops and xz,h of the system.A number of interesting phenomena of the system are discussed.

  2. Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

    Directory of Open Access Journals (Sweden)

    George Jackson

    2013-08-01

    Full Text Available We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids.

  3. Introduction to Phase-Field Model and Its Applications in the Fields of Crystal Growth and Planetary Science

    Science.gov (United States)

    Miura, Hitoshi; Yokoyama, Etsuro; Tsukamoto, Katsuo

    2010-07-01

    The growth of crystal induces a change of ambient environment (temperature, concentration, etc.), and the environmental change gives some feedback to the growth of crystal. The interaction between the crystal growth and ambient environment is important to be taken into consideration, also in the crystallization process of cosmic crystals observed in chondritic meteorites. In this lecture, we will introduce the phase-field simulation, which is one of the powerful numerical methods to treat the crystal growth and diffusion fields (temperature, concentration, etc.) simultaneously. Participants can experience some phase-field simulations on their own laptop by using a newly developed Java program, which will be distributed at the school.

  4. Ultrasonic crystallization monitoring technique for simultaneous in-line measurement of liquid and solid phase

    Science.gov (United States)

    Stelzer, T.; Pertig, D.; Ulrich, J.

    2013-01-01

    The mean crystal size, the suspension density and the liquid concentration are the three most important process parameters to quantify the progress of industrial crystallization processes. It will be shown that these parameters can be in-line monitored simultaneously by means of an ultrasonic crystallization monitoring technique (UCM), which will be introduced here in a proof of concept. This process analytical technology (PAT) differs from the known ultrasonic attenuation spectroscopy (UAS). For the UCM the ultrasonic velocity and attenuation were correlated and related to characteristic events during a crystallization process measured at only one frequency (no spectra of frequencies as it is used for UAS). The results shown in this study prepare the ground to establish the UCM as a simple, less complex, robust, universal applicable, inexpensive and, therefore, a winning alternative PAT to monitor and control in-line the solid as well as the liquid phase in the industrial crystallization by means of only one measuring device with two sensors.

  5. Novel approach to protein crystallizations: Control of the phase behavior of aqueous solutions using microfluidics

    Science.gov (United States)

    Shim, Jung Uk

    A microfluidic device denoted the Phase Chip has been developed to exploit the permeation of water through poly(dimethylsiloxane) (PDMS) in order to vary the concentration of aqueous nanoliter volume microdrops stored in wells. The permeation of water in the Phase Chip is modeled using the diffusion equation and good agreement between experiment and theory is obtained. The phase diagram of a polymer/salt mixture is measured employing the Phase Chip and agrees well with the phase diagram obtained off-chip. The Phase Chip first creates drops of the polymer/salt mixture whose composition varies sequentially. Subsequently the drops are docked in storage wells and the concentration of each stored drop is controlled by varying the water activity of a reservoir that is separated from the drops by a thin layer of PDMS through which water, but not the solutes, permeates. The Phase Chip, incorporating a dialysis membrane on-chip, presents several advantages for protein crystallizations. First, protein crystallization is a non-equilibrium process so it makes sense to have dynamic control over the key thermodynamic variable; concentration. The Phase Chip, with its ability to reversibly control protein and precipitant concentrations, renders varying concentration as convenient as varying temperature. Second, by varying the water content of each drop we can explore many different crystallization conditions in the same drop. Finally, we have demonstrated that we can first formulate stable protein solutions, next induce nucleation and then grow large protein crystals. For these reasons, the Phase Chip promises to be a faster, better, and cheaper method for protein crystallization.

  6. Preparation of high-quality poly-Si films by a solid phase crystallizing method

    CERN Document Server

    Yao Ruo He

    2002-01-01

    A solid phase crystallizing method has been developed to grow a Si crystal at temperatures as low as 550 degree C. Using this method, a high-quality thin-film polycrystalline silicon (Poly-Si) was obtained. The largest grain size, examined with X-ray diffraction spectroscopy and scanning electron microscopy images of recrystallized samples, is approximately 1 mu m for substrate temperature at 300 degree C and annealed at 550 degree C for 3 hours

  7. A fast selenium derivatization strategy for crystallization and phasing of RNA structures

    OpenAIRE

    Olieric, Vincent; Rieder, Ulrike; Lang, Kathrin; Serganov, Alexander; Schulze-Briese, Clemens; Micura, Ronald; Dumas, Philippe; Ennifar, Eric

    2009-01-01

    Site-specific 2′-methylseleno RNA labeling is a promising tool for tackling the phase problem in RNA crystallography. We have developed an efficient strategy for crystallization and structure determination of RNA and RNA/protein complexes based on preliminary crystallization screening of 2′-OCH3-modified RNA sequences, prior to the replacement of 2′-OCH3 groups with their 2′-SeCH3 counterparts. The method exploits the similar crystallization properties of 2′-OCH3- and 2′-SeCH3-modified RNAs a...

  8. [Study on phase-matching of four-wave mixing spectrum in photonic crystal fiber].

    Science.gov (United States)

    Liu, Xiao-xu; Wang, Shu-tao; Zhao, Xing-tao; Chen, Shuang; Zhou, Gui-yao; Wu, Xi-jun; Li, Shu-guang; Hou, Lan-Tian

    2014-06-01

    In the present paper, the four-wave mixing principle of fiber was analyzed, and the high-gain phase-matching conditions were shown. The nonlinear coefficient and dispersion characteristics of photonic crystal fibers were calculated by multipole method. The phase mismatch characteristics of fibers with multiple zero-dispersion wavelengths were analyzed for the first time. The changing rules of phase matching wavelength with the pump wavelength and the pump power were obtained, and the phase matching curves were shown. The characteristics of phase matching wavelengths for different dispersion curves were analyzed. There are four new excitation wavelengths of four-wave mixing spectrum in two zero-dispersion wavelength photonic crystal fiers. Four-wave mixing spectroscopy of photonic crystal fibers with two zero-dispersion wavelengths was obtained in the experi-ent, which is consistent with the theoretical analysis, and verified the reliability of the phase matching theory. The fiber with multiple zero-dispersion wavelengths can create a ricbhphase-matching topology, excite more four-wave mixing wavelengths, ena-ling enhanced control over the spectral locations of the four-wave mixing and resonant-radiation bands emitted by solitons and short pulses. These provide theoretical guidance for photonic crystal fiber wavelength conversion and supercontinoum generation based on four-wave mixing.

  9. Orientational Phase Transition Around 274 K in C60 Single Crystal

    Institute of Scientific and Technical Information of China (English)

    徐亚伯; 何丕模; 杨宏顺; 郑萍; 余朝文; 陈兆甲; 张宣嘉; 李文铸

    1994-01-01

    The electrical conductivity of a C60 single crystal around 274 K and the specific heat of C60 crystals from 150 to 340 K have been measured.The delta-like specific heat peak at about 251 K related to the first-order phase transition has been reported.The activation energy change around 274 K and the lambda-like specific heat peak beginning at 270 K and ending at 310 K show that there is an orientational phase transition in fcc C60 crystals above 251 K.By taking the symmetry into consideration and further analyzing lambda-like specific heat peak and the activation energy change around 274 K,the conclusion has been reached that this new phase transition is an orientational structure transition from the merohedral twinning fcc to the orientationally disordered fcc.The temperature of free rotation of C60 molecules is about 281 K.

  10. Influence Cr on Crystallization and the Phase Transformations of the Bronze BA1044

    Directory of Open Access Journals (Sweden)

    B. P. Pisarek

    2007-07-01

    Full Text Available The investigations were introduced in the paper, method of thermal and derivative analysis (TDA, the process of crystallization and phase transformation in the solid state of the aluminium bronze CuA110Fe4Ni4 (BA1044 and with the addition 0.3% Cr. Two intermetallic phase were identified in the microstructure of the bronze BA1044: κFel - rich in Fe and Cu and κFe2 - rich in Fe, and in the microstructure of the bronze BA1044+0.3 % Cr only one phase κFel - rich in Fe, Cu and Cr. The presence of chrome in the bronze BA1044 reduce size the primary crystals of the phase β, reduces the dynamics of the processes of thermal phase transformation in the solid state and lengthens the time their of duration.

  11. Crystal Level Continuum Modeling of Phase Transformations: The (alpha) <--> (epsilon) Transformation in Iron

    Energy Technology Data Exchange (ETDEWEB)

    Barton, N R; Benson, D J; Becker, R; Bykov, Y; Caplan, M

    2004-10-18

    We present a crystal level model for thermo-mechanical deformation with phase transformation capabilities. The model is formulated to allow for large pressures (on the order of the elastic moduli) and makes use of a multiplicative decomposition of the deformation gradient. Elastic and thermal lattice distortions are combined into a single lattice stretch to allow the model to be used in conjunction with general equation of state relationships. Phase transformations change the mass fractions of the material constituents. The driving force for phase transformations includes terms arising from mechanical work, from the temperature dependent chemical free energy change on transformation, and from interaction energy among the constituents. Deformation results from both these phase transformations and elasto-viscoplastic deformation of the constituents themselves. Simulation results are given for the {alpha} to {epsilon} phase transformation in iron. Results include simulations of shock induced transformation in single crystals and of compression of polycrystals. Results are compared to available experimental data.

  12. Pressure-induced phase transformations in L-alanine crystals

    DEFF Research Database (Denmark)

    Olsen, J. Staun; Gerward, Leif; Freire, P.T.C.

    2008-01-01

    Raman scattering and synchrotron X-ray diffraction have been used to investigate the high-pressure behavior of L-alanine. This study has confirmed a structural phase transition observed by Raman scattering at 2.3 GPa and identified it as a change from orthorhombic to tetragonal structure. Another...... phase transformation from tetragonal to monoclinic structure has been observed at about 9 GPa. From the equation of state, the zero-pressure bulk modulus and its pressure derivative have been determined as (31.5 +/- 1.4) GPa and 4.4 +/- 0.4, respectively....

  13. On the crystal structure of Z-phase Cr(V,Nb)N

    DEFF Research Database (Denmark)

    Danielsen, Hilmar Kjartansson; Hald, John; Grumsen, Flemming Bjerg

    2006-01-01

    The Z-phase Cr(YNb)N particles in various 9 to 12 pct Cr creep-resistant steels were investigated with electron diffraction, energy dispersive spectroscopy (EDS), and electron energy loss spectroscopy(EELS). In addition to the well-known tetragonal crystal structure for Z phase, a cubic crystal s......(V,Nb)N particles could be of crucial importance to enable improvement of the long-term creep stability of 9 to 12 pct Cr martensitic steels.......The Z-phase Cr(YNb)N particles in various 9 to 12 pct Cr creep-resistant steels were investigated with electron diffraction, energy dispersive spectroscopy (EDS), and electron energy loss spectroscopy(EELS). In addition to the well-known tetragonal crystal structure for Z phase, a cubic crystal...... structure was identified for Cr(V,Nb)N and CrVN particles, but not for CrNbN. The tetragonal and cubic crystal structures were observed to coexist within the same particles, and the orientation relationship between the two lattices was determined. Understanding and controlling the nucleation of Cr...

  14. The neuropeptide F/nitric oxide pathway is essential for shaping locomotor plasticity underlying locust phase transition

    Science.gov (United States)

    Hou, Li; Yang, Pengcheng; Jiang, Feng; Liu, Qing; Wang, Xianhui; Kang, Le

    2017-01-01

    Behavioral plasticity is widespread in swarming animals, but little is known about its underlying neural and molecular mechanisms. Here, we report that a neuropeptide F (NPF)/nitric oxide (NO) pathway plays a critical role in the locomotor plasticity of swarming migratory locusts. The transcripts encoding two related neuropeptides, NPF1a and NPF2, show reduced levels during crowding, and the transcript levels of NPF1a and NPF2 receptors significantly increase during locust isolation. Both NPF1a and NPF2 have suppressive effects on phase-related locomotor activity. A key downstream mediator for both NPFs is nitric oxide synthase (NOS), which regulates phase-related locomotor activity by controlling NO synthesis in the locust brain. Mechanistically, NPF1a and NPF2 modify NOS activity by separately suppressing its phosphorylation and by lowering its transcript level, effects that are mediated by their respective receptors. Our results uncover a hierarchical neurochemical mechanism underlying behavioral plasticity in the swarming locust and provide insights into the NPF/NO axis. DOI: http://dx.doi.org/10.7554/eLife.22526.001 PMID:28346142

  15. Unique Reversible Crystal-to-Crystal Phase Transition – Structural and Functional Properties of Fused Ladder Thienoarenes

    KAUST Repository

    Abe, Yuichiro

    2017-08-15

    Donor-acceptor type molecules based on fused ladder thienoarenes, indacenodithiophene (IDT) and dithienocyclopenta-thienothiophene (DTCTT), coupled with benzothiadiazole, are prepared and their solid-state structures are investigated. They display a rich variety of solid phases ranging from amorphous glass states to crystalline states, upon changes in the central aromatic core and side group structures. Most notably, the DTCTT-based derivatives showed reversible crystal-to-crystal phase transitions in heating and cooling cycles. Unlike what has been seen in π−conjugated molecules variable temperature XRD revealed that structural change occurs continuously during the transition. A columnar self-assembled structure with slip-stacked π−π interaction is proposed to be involved in the solid-state. This research provides the evidence of unique structural behavior of the DTCTT-based molecules through the detailed structural analysis. This unique structural transition paves the way for these materials to have self-healing of crystal defects, leading to improved optoelectronic properties.

  16. Crystal structure of the commensurately modulated ζ phase of PAMC

    DEFF Research Database (Denmark)

    Harris, P.; Larsen, F.K.; Lebech, B.

    1994-01-01

    The commensurately modulated zeta low-temperature phase of bis(propylammonium) tetrachloromanganate(II), [NH3(C3H7)]2MnCl4, has been determined at 8 K. a = 7.437 (5), b = 7.082 (5), c = 13.096 (8) Angstrom, alpha = 105.59 (1)degrees. Superspace group P2(1)/b(0 beta 0)(1) over bar s, with beta = 1...... phase, indicating a 'lock-in' and phase shift between adjacent modulated layers. The modulation waves do not change much from the values of the epsilon phase, which confirms the lock-in of the modulation vector; only some components of the modulations of the propylammonium chains appear....../3, V = 664.4, Z = 2 D-x = 1.58 g cm(-3) Mo K alpha radiation, lambda = 0.71069 Angstrom, mu = 17.99 cm(-1) F(000) = 326, wR(F) = 0.064 for 1444 main reflections and wR(F) = 0.089 for 248 satellite reflections. The modulation vector flips and locks into a commensurate value compared with the epsilon...

  17. Low-temperature (˜180 °C) position-controlled lateral solid-phase crystallization of GeSn with laser-anneal seeding

    Science.gov (United States)

    Matsumura, Ryo; Chikita, Hironori; Kai, Yuki; Sadoh, Taizoh; Ikenoue, Hiroshi; Miyao, Masanobu

    2015-12-01

    To realize next-generation flexible thin-film devices, solid-phase crystallization (SPC) of amorphous germanium tin (GeSn) films on insulating substrates combined with seeds formed by laser annealing (LA) has been investigated. This technique enables the crystallization of GeSn at controlled positions at low temperature (˜180 °C) due to the determination of the starting points of crystallization by LA seeding and Sn-induced SPC enhancement. The GeSn crystals grown by SPC from LA seeds showed abnormal lateral profiles of substitutional Sn concentration. These lateral profiles are caused by the annealing time after crystallization being a function of distance from the LA seeds. This observation of a post-annealing effect also indicates that GeSn with a substitutional Sn concentration of up to ˜10% possesses high thermal stability. These results will facilitate the fabrication of next-generation thin-film devices on flexible plastic substrates with low softening temperatures (˜250 °C).

  18. Low symmetry tetrahedral nematic liquid crystal phases: Ambidextrous chirality and ambidextrous helicity.

    Science.gov (United States)

    Pleiner, Harald; Brand, Helmut R

    2014-02-01

    We discuss the symmetry properties as well as the dynamic behavior of various non-polar nematic liquid crystal phases with tetrahedral order. We concentrate on systems that show biaxial nematic order coexisting with octupolar (tetrahedral) order. Non-polar examples are phases with D2 and S4 symmetries, which can be characterized as biaxial nematics lacking inversion symmetry. It is this combination that allows for new features in the statics and dynamics of these phases. The D2-symmetric phase is chiral, even for achiral molecules, and shows ambidextrous chirality in all three preferred directions. The achiral S4-symmetric phase allows for ambidextrous helicity, similar to the higher-symmetric D2d-symmetric phase. Such phases are candidates for nematic phases made from banana-shaped molecules.

  19. Crystal Plasticity Model Validation Using Combined High-Energy Diffraction Microscopy Data for a Ti-7Al Specimen

    Science.gov (United States)

    Turner, Todd J.; Shade, Paul A.; Bernier, Joel V.; Li, Shiu Fai; Schuren, Jay C.; Kenesei, Peter; Suter, Robert M.; Almer, Jonathan

    2017-02-01

    High-Energy Diffraction Microscopy (HEDM) is a 3-d X-ray characterization method that is uniquely suited to measuring the evolving micro-mechanical state and microstructure of polycrystalline materials during in situ processing. The near-field and far-field configurations provide complementary information; orientation maps computed from the near-field measurements provide grain morphologies, while the high angular resolution of the far-field measurements provides intergranular strain tensors. The ability to measure these data during deformation in situ makes HEDM an ideal tool for validating micro-mechanical deformation models that make their predictions at the scale of individual grains. Crystal Plasticity Finite Element Models (CPFEM) are one such class of micro-mechanical models. While there have been extensive studies validating homogenized CPFEM response at a macroscopic level, a lack of detailed data measured at the level of the microstructure has hindered more stringent model validation efforts. We utilize an HEDM dataset from an alpha-titanium alloy (Ti-7Al), collected at the Advanced Photon Source, Argonne National Laboratory, under in situ tensile deformation. The initial microstructure of the central slab of the gage section, measured via near-field HEDM, is used to inform a CPFEM model. The predicted intergranular stresses for 39 internal grains are then directly compared to data from 4 far-field measurements taken between 4 and 80 pct of the macroscopic yield strength. The evolution of the elastic strain state from the CPFEM model and far-field HEDM measurements up to incipient yield are shown to be in good agreement, while residual stress at the individual grain level is found to influence the intergranular stress state even upon loading. Implications for application of such an integrated computational/experimental approach to phenomena such as fatigue are discussed.

  20. PHASE STRUCTURES AND TRANSITION BEHAVIORS OF A TRIPHENYLENE DISCOTIC LIQUID CRYSTAL

    Institute of Scientific and Technical Information of China (English)

    Kwang-Un Jeong; Alexander J. Jing; Bart Mansdorf; Matthew J. Graham; Yingfeng Tu; Frank W. Harris; Stephen Z. D. Cheng

    2007-01-01

    The phase behaviors and structures of a triphenylene-derived discotic liquid crystal (LC) hexa-n-octoxyl-triphenylene (C8HET) were studied using the combined techniques of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), selected area electron diffraction (SAED) and polarized light microscopy (PLM). Onedimensional (1D) powder WAXD results at different temperatures coupled with DSC and PLM observations revealed that the C8HET compound possessed an LC phase and three different crystalline (K3, K2 and K1) phases below the isotropic (Ⅰ)melt. The I (←→) LC phase transition was thermodynamically reversible and independent of the heating and cooling rates. The development and experimental observation of the three crystalline phases relied on different thermal histories. Among the three crystalline phases in C8HET, the K3 phase is the most stable phase, while the K2 and K1 phases are metastable. Note that the K1 phase only formed via a quenching process. On the basis of structure sensitive diffraction experiments such as 2D WAXD of oriented samples and SAED of single crystals, detailed structures and molecular packings of these four ordered phases were identified. The LC phase exhibited a hexagonal columnar phase with 2D lattice dimensions of a = b = 2.38 nm and γ= 120°. All the three crystalline phases possess monoclinic unit cells, yet the γ angle is not 90° in the cases of the K2 and the K3 phases, while in the case of the K1 phase the α angle is not 90°.

  1. Detection of an intermediate biaxial phase in the phase diagram of biaxial liquid crystals: Entropic sampling study

    Science.gov (United States)

    Kamala Latha, B.; Jose, Regina; Murthy, K. P. N.; Sastry, V. S. S.

    2014-05-01

    We investigate the phase sequence of biaxial liquid crystals, based on a general quadratic model Hamiltonian over the relevant parameter space, with a Monte Carlo simulation which constructs equilibrium ensembles of microstates, overcoming possible (free) energy barriers (combining entropic and frontier sampling techniques). The resulting phase diagram qualitatively differs from the universal phase diagram predicted earlier from mean-field theory (MFT), as well as the Monte Carlo simulations with the Metropolis algorithm. The direct isotropic-to-biaxial transition predicted by the MFT is replaced in certain regions of the space by the onset of an additional intermediate biaxial phase of very low order, leading to the sequence NB-NB1-I. This is due to inherent barriers to fluctuations of the components comprising the total energy, and may explain the difficulties in the experimental realization of these phases.

  2. Interface dynamics and crystal phase switching in GaAs nanowires

    Science.gov (United States)

    Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M.

    2016-03-01

    Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.

  3. Site occupation, phase stability, crystal and electronic structures of the doped S phase (Al2CuMg)

    Science.gov (United States)

    Gu, Jianglong; Gu, Huimin; Zhai, Yuchun; Ma, Peihua

    2016-07-01

    The S phase (Al2CuMg) is an important strengthening phase for the Al-Cu-Mg alloys, which are widely used in the aerospace and transportation industries. The commonly added alloying elements (Mn, Ti, Zr) and the impurity elements (Fe and Si) in the Al-Cu-Mg alloys are always found in the S phase. First-principles calculations based on the density functional theory (DFT) were used to investigate the influence of doping Mn, Ti, Zr, Fe and Si elements on the S phase. Key findings demonstrated that these elements prefer to occupy different atomic sites in the S phase. Ti and Zr improved the structural stability of the S phase. The bulk modulus of the Fe, Si, Ti and Zr doped S phases becomes larger than that of the pure S phase. Both the crystal and electronic structures of the S phase are affected by the dopants. The results of this study provide a better theoretical understanding of the S phase, providing guidance for improved composition design and performance optimization of Al-Cu-Mg alloys.

  4. CRYSTAL CHEMISTRY OF THREE-COMPONENT WHITE DWARFS AND NEUTRON STAR CRUSTS: PHASE STABILITY, PHASE STRATIFICATION, AND PHYSICAL PROPERTIES

    Energy Technology Data Exchange (ETDEWEB)

    Engstrom, T. A.; Yoder, N. C.; Crespi, V. H., E-mail: tae146@psu.edu, E-mail: ncy5007@psu.edu, E-mail: vhc2@psu.edu [Department of Physics, The Pennsylvania State University, University Park, PA 16802 (United States)

    2016-02-20

    A systematic search for multicomponent crystal structures is carried out for five different ternary systems of nuclei in a polarizable background of electrons, representative of accreted neutron star crusts and some white dwarfs. Candidate structures are “bred” by a genetic algorithm and optimized at constant pressure under the assumption of linear response (Thomas–Fermi) charge screening. Subsequent phase equilibria calculations reveal eight distinct crystal structures in the T = 0 bulk phase diagrams, five of which are complicated multinary structures not previously predicted in the context of compact object astrophysics. Frequent instances of geometrically similar but compositionally distinct phases give insight into structural preferences of systems with pairwise Yukawa interactions, including and extending to the regime of low-density colloidal suspensions made in a laboratory. As an application of these main results, we self-consistently couple the phase stability problem to the equations for a self-gravitating, hydrostatically stable white dwarf, with fixed overall composition. To our knowledge, this is the first attempt to incorporate complex multinary phases into the equilibrium phase-layering diagram and mass–radius-composition dependence, both of which are reported for He–C–O and C–O–Ne white dwarfs. Finite thickness interfacial phases (“interphases”) show up at the boundaries between single-component body-centered cubic (bcc) crystalline regions, some of which have lower lattice symmetry than cubic. A second application—quasi-static settling of heavy nuclei in white dwarfs—builds on our equilibrium phase-layering method. Tests of this nonequilibrium method reveal extra phases that play the role of transient host phases for the settling species.

  5. Chiral-induced self-assembly sphere phase liquid crystal with fast switching time

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Ji-Liang; Ni, Shui-Bin; Ping Chen, Chao; Lu, Jian-Gang, E-mail: lujg@sjtu.edu.cn; Su, Yikai [National Engineering Lab for TFT-LCD Materials and Technologies, Department of Electronic Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Wu, Dong-Qing [College of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Song, Xiao-Long; Chen, Chao-Yuan [The Jiangsu Hecheng Display Technology Co., Ltd., Nanjing 211300 (China); Shieh, Han-Ping D. [National Engineering Lab for TFT-LCD Materials and Technologies, Department of Electronic Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Department of Photonics and Display Institute, National Chiao Tung University, Hsinchu 300, Taiwan (China)

    2014-03-03

    A fluid self-assembly sphere phase (SP) of liquid crystal induced by chiral dopant is observed in a narrow temperature range between isotropic and blue phase or between isotropic and chiral nematic phase. The SP consists of three-dimensional twist spheres (3-DTSs) and disclinations among 3-DTSs. The temperature range of the SP has been broadened to more than 85 °C by stabilizing the disclinations with amorphous polymer chains. The electro-optical switching time of the polymer-stabilized SP is demonstrated in sub-millisecond with a low switching electric field of 4.4 V μm{sup −1}, which is of promising applications in displays, 3-D tunable photonic crystals, and phase modulators.

  6. Phase conjugator with two coherent beams in a BaTiO3: Ce crystal

    Institute of Scientific and Technical Information of China (English)

    武建劳; 谢平; 戴建华; 张洪钧

    2000-01-01

    A phase conjugator which includes two coherent beams that are incident upon one of a-faces of a BaTiO3: Ce crystal without internal reflection is performed experimentally. Based on the four-wave mixing, the mechanism of this conjugator is investigated numerically. in comparison with the cor-responding self-pumped phase conjugator, the phase-conjugate behavior of this conjugator is estab-lished much more quickly, its phase conjugate reflectivity is greater in some cases and the intensity threshold is lower by over two orders of magnitude. The configuration of this conjugator is easy to per-form because the output response exists over a wide range of angular and lateral positions of the two incident beams on the crystal.

  7. Phase separation in mixtures of thermotropic liquid crystals and flexible polymers

    Institute of Scientific and Technical Information of China (English)

    张红东; 林志群; 严栋; 杨玉良

    1997-01-01

    The spinodal equation and the concentration-induced anisotropic-isotropic transition equation of the mixtures of thermotropic liquid crystals and flexible polymers have been studied by using the molecular field theory The calculations of the phase diagrams of this system show that,besides the isotropic classic spinodal curve,there ex ists an anisotropic spinodal curve which has not been reported in literature.These two spinodal curves can be linked up by the concentration-induced anisotropic-isotropic transition line.In the various phase regions,demixing may take place due to different phase separation mechanisms.The phase equilibrium curve cannot always join the.spinodal curve at a critical point.These results are considered very meaningful for the understanding of the special properties of liquid crystal/polymer composites and very useful for controlling the morphology and the performance of PDLC materials

  8. Novel modulated Hexatic Phases in Symmetric Liquid Crystal Dimers

    OpenAIRE

    Date, R; Luckhurst, G.; Shuman, M.; Seddon, J

    1995-01-01

    Homologues of the dimeric α,ω-bis(4-n-alkylanilinebenzylidene-4'-oxy)alkanes (m.OnO.m) have been synthesised with spacer lengths n ranging from 9 to 12 methylene units and with terminal alkyl chain lengths m of 10, 12 and 14. Characterisation of these materials has been carried out by X-ray diffraction, differential scanning calorimetry and optical microscopy. In six of these compounds a novel modulated tilted hexatic phase, denoted S1, has been identified, in which the smectic layers have a ...

  9. Non-equilibrium phase transitions in a liquid crystal

    Science.gov (United States)

    Dan, K.; Roy, M.; Datta, A.

    2015-09-01

    The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min-1, consistent with a glass transition, a clear peak for β ≤ 5 K min-1 and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the

  10. Non-equilibrium phase transitions in a liquid crystal.

    Science.gov (United States)

    Dan, K; Roy, M; Datta, A

    2015-09-07

    The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min(-1), consistent with a glass transition, a clear peak for β ≤ 5 K min(-1) and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the

  11. Effects of shear flow on phase nucleation and crystallization

    Science.gov (United States)

    Mura, Federica; Zaccone, Alessio

    2016-04-01

    Classical nucleation theory offers a good framework for understanding the common features of new phase formation processes in metastable homogeneous media at rest. However, nucleation processes in liquids are ubiquitously affected by hydrodynamic flow, and there is no satisfactory understanding of whether shear promotes or slows down the nucleation process. We developed a classical nucleation theory for sheared systems starting from the molecular level of the Becker-Doering master kinetic equation and we analytically derived a closed-form expression for the nucleation rate. The theory accounts for the effect of flow-mediated transport of molecules to the nucleus of the new phase, as well as for the mechanical deformation imparted to the nucleus by the flow field. The competition between flow-induced molecular transport, which accelerates nucleation, and flow-induced nucleus straining, which lowers the nucleation rate by increasing the nucleation energy barrier, gives rise to a marked nonmonotonic dependence of the nucleation rate on the shear rate. The theory predicts an optimal shear rate at which the nucleation rate is one order of magnitude larger than in the absence of flow.

  12. Pulse shape discrimination characteristics of stilbene crystal, pure and 6Li loaded plastic scintillators for a high resolution coded-aperture neutron imager

    Science.gov (United States)

    Cieślak, M. J.; Gamage, K. A. A.; Glover, R.

    2017-07-01

    Pulse shape discrimination performances of single stilbene crystal, pure plastic and 6Li loaded plastic scintillators have been compared. Three pulse shape discrimination algorithms have been tested for each scintillator sample, assessing their quality of neutron/gamma separation. Additionally, the digital implementation feasibility of each algorithm in a real-time embedded system was evaluated. Considering the pixelated architecture of the coded-aperture imaging system, a reliable method of simultaneous multi-channel neutron/gamma discrimination was sought, accounting for the short data analysis window available for each individual channel. In this study, each scintillator sample was irradiated with a 252Cf neutron source and a bespoke digitiser system was used to collect the data allowing detailed offline examination of the sampled pulses. The figure-of-merit was utilised to compare the discrimination quality of the collected events with respect to various discrimination algorithms. Single stilbene crystal presents superior neutron/gamma separation performance when compared to the plastic scintillator samples.

  13. Synthesis, crystal structure and electronic structure of the binary phase Rh2Cd5

    Science.gov (United States)

    Koley, Biplab; Chatterjee, S.; Jana, Partha P.

    2017-02-01

    A new phase in the Rh-Cd binary system - Rh2Cd5 has been identified and characterized by single crystal X-ray diffraction and Energy dispersive X-ray analysis. The stoichiometric compound Rh2Cd5 crystallizes with a unit cell containing 14 atoms, in the orthorhombic space group Pbam (55). The crystal structure of Rh2Cd5 can be described as a defect form of the In3Pd5 structure with ordered vacancies, formed of two 2D atomic layers with the stacking sequence: ABAB. The A type layers consist of (3.6.3.6)-Kagomé nets of Cd atoms while the B type layers consist of (35) (37)- nets of both Cd and Rh atoms. The stability of this line phase is investigated by first principle electronic structure calculations on the model of ordered Rh2Cd5.

  14. Phase behavior of chromonic liquid crystal mixtures of Sunset Yellow and Disodium Cromoglycate

    Science.gov (United States)

    Yamaguchi, Akihiro; Smith, Gregory; Yi, Youngwoo; Xu, Charles; Biffi, Silvia; Serra, Francesca; Bellini, Tommaso; Clark, Noel

    2014-03-01

    Chromonic liquid crystals (CLCs) are formed when planar molecules dissolved in water stack into rod-like aggregates that can order as liquid crystals. Isotropic, nematic, and M-phases can be observed depending on the degree of molecular orientational and positional order by variation of the CLC concentration. We focused on mixtures of two well-known CLCs, Sunset Yellow, a food dye, and disodium cromoglycate (DSCG), an asthma medication. In order to study the phase behaviors of these mixtures, we observed their textures in glass cells and capillaries using polarized light microscopy. We report here a ternary phase diagram describing the complete phase behavior of the CLC mixtures. We observed a variety of phase behaviors depending on species ratio and concentration. In the isotropic phase, no clear phase separation of the two dyes was observed, while separation did occur in many nematic and M-phase combinations. We will also describe phase observations made using a light spectroscopy and bulk centrifugal partitioning. Grant support: NSF DMR 1207606 and NSF MRSEC DMR-0820579.

  15. Growth of Cd0.96Zn0.04Te single crystals by vapor phase gas transport method

    Directory of Open Access Journals (Sweden)

    S. H. Tabatabai Yazdi

    2006-03-01

    Full Text Available   Cd0.96Zn0.04Te crystals were grown using vapor phase gas transport method (VPGT. The results show that dendritic crystals with grain size up to 3.5 mm can be grown with this technique. X-ray diffraction and Laue back-reflection patterns show that dendritic crystals are single-phase, whose single crystal grains are randomly oriented with respect to the gas-transport axis. Electrical measurements, carried out using Van der Pauw method, show that the as-grown crystals have resistivity of about 104 Ω cm and n-type conductivity.

  16. Changes in the composition of ichthyoplankton assemblage and plastic debris in mangrove creeks relative to moon phases.

    Science.gov (United States)

    Lima, A R A; Barletta, M; Costa, M F; Ramos, J A A; Dantas, D V; Melo, P A M C; Justino, A K S; Ferreira, G V B

    2016-07-01

    Lunar influence on the distribution of fish larvae, zooplankton and plastic debris in mangrove creeks of the Goiana Estuary, Brazil, was studied over a lunar cycle. Cetengraulis edentulus, Anchovia clupeoides and Rhinosardinia bahiensis were the most abundant fish larvae (56·6%), independent of the moon phase. The full moon had a positive influence on the abundance of Gobionellus oceanicus, Cynoscion acoupa and Atherinella brasiliensis, and the new moon on Ulaema lefroyi. The full and new moons also influenced the number of zoeae and megalopae of Ucides cordatus, protozoeae and larvae of caridean shrimps, and the number of hard and soft plastic debris, both 5 mm. Micro and macroplastics were present in samples from all 12 creeks studied, at densities similar to the third most abundant taxon, R. bahiensis. Cetengraulis edentulus and R. bahiensis showed a strong positive correlation with the last quarter moon, when there was less zooplankton available in the creeks and higher abundance of microplastic threads. Anchovia clupeoides, Diapterus rhombeus, U. lefroyi and hard microplastics were positively associated with different moon phases, when calanoid copepods, Caridean larvae and zoeae of U. cordatus were highly available in the creeks. Cynoscion acoupa, G. oceanicus and A. brasiliensis were strongly associated with the full moon, when protozoeae of caridean shrimps and megalopae of U. cordatus were also highly available, as were hard and soft macroplastics, paint chips (moon phases influenced the distribution of fish larvae species, zooplankton and plastic debris by changing their compositions and abundances in the mangrove creeks of the Goiana Estuary when under the influence of different tidal current regimes.

  17. Staircase of crystal phases of hard-core bosons on the kagome lattice

    Science.gov (United States)

    Huerga, Daniel; Capponi, Sylvain; Dukelsky, Jorge; Ortiz, Gerardo

    2016-10-01

    We study the quantum phase diagram of a system of hard-core bosons on the kagome lattice with nearest-neighbor repulsive interactions, for arbitrary densities, by means of the hierarchical mean-field theory and exact diagonalization techniques. This system is isomorphic to the spin S =1 /2 XXZ model in presence of an external magnetic field, a paradigmatic example of frustrated quantum magnetism. In the nonfrustrated regime, we find two crystal phases at densities 1/3 and 2/3 that melt into a superfluid phase when increasing the hopping amplitude, in semiquantitative agreement with quantum Monte Carlo computations. In the frustrated regime and away from half-filling, we find a series of plateaux with densities commensurate with powers of 1/3. The broader density plateaux (at densities 1/3 and 2/3) are remnants of the classical degeneracy in the Ising limit. For densities near half-filling, this staircase of crystal phases melts into a superfluid, which displays finite chiral currents when computed with clusters having an odd number of sites. Both the staircase of crystal phases and the superfluid phase prevail in the noninteracting limit, suggesting that the lowest dispersionless single-particle band may be at the root of this phenomenon.

  18. Quasi-phase-matching bandwidth for second harmonic generation in crystals with a regular domain structure

    NARCIS (Netherlands)

    Dmitriev, VG; Yur'ev, YV

    1999-01-01

    The question of the quasi-phase-matching bandwidth for second harmonic generation in crystals with a regular domain structure is considered in terms of the approximation of a constant field of the fundamental-frequency radiation and in the nonlinear conversion regime.

  19. Liquid crystal multi-mode lenses and axicons based on electronic phase shift control.

    Science.gov (United States)

    Kirby, Andrew K; Hands, Philip J; Love, Gordon D

    2007-10-17

    We report on the principle of operation, construction and testing of a liquid crystal lens which is controlled by distributing voltages across the control electrodes, which are in turn controlled by adjusting the phase of the applied voltages. As well as (positive and negative) defocus, then lenses can be used to control tip/tilt, astigmatism, and to create variable axicons.

  20. Sub-millisecond, high stroke phase modulation using polymer network liquid crystals.

    Science.gov (United States)

    Love, Gordon D; Kirby, Andrew K; Ramsey, Robert A

    2010-03-29

    We describe the production of a high speed, and high stroke, phase modulator using a polymer network liquid crystal device. We present data showing fast response times (sub millisecond) in a device which can operate at visible wavelengths with a simple electrical addressing scheme.

  1. Fast photo-induced phase switching in organic conductor crystal; (EDO-TTF)2PF6

    Science.gov (United States)

    Chollet, Matthieu; Guerin, Laurent; Uchida, Naoki; Fukaya, Souichi; Ishikawa, Tadahiko; Koshihara, Shin-ya; Matsuda, Kazunari; Ota, Akira; Yamochi, Hideki; Saito, Gunzi

    Organic conductor (EDO-TTF) 2PF6 crystal shows metal (M)-insulator (I) transition at 280 K. Here, we report the occurrence of highly efficient photo-conversion from insulator to metal phase within a few pico-seconds.

  2. Continuous ferroelastic phase transition of a KBr:KCN mixed crystal

    DEFF Research Database (Denmark)

    Knorr, K.; Loidl, A.; Kjems, Jørgen

    1985-01-01

    The ferroelastic phase transition of (KBr)0.27(KCN)0.73 has been studied by X-ray diffraction, ultrasonics, and inelastic neutron scattering. It is the first example of a cubic crystal where the elastic shear constant C 44 softens completely corresponding to the m=2 universality class. C44...

  3. SAXS reveals the magnetic alignment pathway of the goethite columnar liquid crystal phase

    NARCIS (Netherlands)

    Leferink op Reinink, Anke B G M; van den Pol, Esther; Vroege, Gert Jan; Petukhov, Andrei V.

    2014-01-01

    The alignment of board-like colloidal goethite particles in the dense rectangular centred columnar liquid crystal phase in an external magnetic field is studied using small angle X-ray scattering (SAXS). Transient SAXS-patterns show broadening of the columnar reflections in specific directions. Whil

  4. Kinetics of the laser-induced solid phase crystallization of amorphous silicon-Time-resolved Raman spectroscopy and computer simulations

    Science.gov (United States)

    Očenášek, J.; Novák, P.; Prušáková, L.

    2017-01-01

    This study demonstrates that a laser-induced crystallization instrumented with Raman spectroscopy is, in general, an effective tool to study the thermally activated crystallization kinetics. It is shown, for the solid phase crystallization of an amorphous silicon thin film, that the integral intensity of Raman spectra corresponding to the crystalline phase grows linearly in the time-logarithmic scale. A mathematical model, which assumes random nucleation and crystal growth, was designed to simulate the crystallization process in the non-uniform temperature field induced by laser. The model is based on solving the Eikonal equation and the Arhenius temperature dependence of the crystal nucleation and the growth rate. These computer simulations successfully approximate the crystallization process kinetics and suggest that laser-induced crystallization is primarily thermally activated.

  5. Pronounced Plasticity Caused by Phase Separation and β-relaxation Synergistically in Zr-Cu-Al-Mo Bulk Metallic Glasses.

    Science.gov (United States)

    Wang, Tuo; Wang, Lu; Wang, Qinjia; Liu, Yanhui; Hui, Xidong

    2017-04-27

    Bulk metallic glasses (BMGs) are known to have extraordinary merits such as ultrahigh strength and dynamic toughness etc. but tied to the detrimental brittleness, which has become a critical issue to the engineering application and understanding the glass nature. In this article, we report a new class of Zr-Cu-Al-Mo BMGs with extraordinary plastic strain above 20%. "Work-hardening" effect after yielding in a wide range of plastic deformation process has been detected for this kind of BMGs. Compositional heterogeneity, which can be classified into ZrMo- and Cu-rich zones, was differentiated in this kind of BMG. Pronounced humps have been observed on the high frequency kinetic spectrum in Mo containing BMGs, which is the indicator of β-relaxation transition. The underlying mechanism for the excellent plastic deforming ability of this class of BMGs is ascribed to the synergistic effects of soft ZrMo-rich glass formed through phase separation and abundant flow units which related to β-relaxation.

  6. A phase-matchable nonlinear optical crystal 4-amino-5-mercapto-3-[1-(4-isobutylphenyl)ethyl]- 1,2,4-triazole: Synthesis, crystal growth and characterization

    Indian Academy of Sciences (India)

    K Naseema; Vijayalakshmi Rao; K V Sujith; Balakrishna Kalluraya

    2009-10-01

    In this paper, we report the synthesis, growth and characterization of a new organic NLO single crystal of 4-amino-5-mercapto-3-[1-(4-isobutylphenyl)ethyl]-1,2,4-triazole (AMIT). The title compound is synthesized and single crystals were grown by the slow evaporation technique at room temperature. The grown crystal was characterized by powder XRD, FTIR, UV–Vis. and microhardness studies. The thermal analysis of the crystal was carried out by TGA, DTA and DSC. From DSC, the melting point of the crystal is found to be 168°C. The scanning electron microscopy (SEM) provides information about the surface morphology of the crystal. The SHG efficiency has been estimated as 0.3 times that of KDP using Kurtz powder method and is found to be a phase-matchable NLO crystal.

  7. Dielectric properties and molecular motions of liquid crystal molecules in 4-(2-methylbytylphenyl 4-(4-octylphenylbenzoate liquid crystal having blue phase (CE8

    Directory of Open Access Journals (Sweden)

    Otowski W.

    2015-06-01

    Full Text Available Blue phase liquid crystals exhibit unique properties which are used in the new type of display. A blue-phase liquid crystal display was first presented commercially by Samsung in 2007. The blue-phase-three-color pixel display eliminates the need for color filters. This type of display uses blue-phase multi-component liquid crystal. Considering the one-component systems, it turns out that they are stable only in a very narrow range of temperatures between the isotropic and the chiral nematic phase (about 1 K. In 2005, a wide temperature range BP multi-component system was reported by researchers from the University of Cambridge. There are still several unsolved problems left. One of them is chemical stability and reliability. Therefore, the knowledge of molecular dynamics of blue phase liquid crystal is a prerequisite for understanding of blue-phase multi-component system. Understanding the molecular dynamics of a single component liquid-crystalline blue phase system can facilitate the solution of these problems. We present the molecular dynamics investigation of 4-(2-methylbytylphenyl 4-(4-octylphenylbenzoate (CE8, which may be a good candidate to form materials suitable for blue-phase liquid crystal displays.

  8. Dislocation-density-based modeling of the plastic behavior of 4H-SiC single crystals using the Alexander-Haasen model

    Science.gov (United States)

    Gao, B.; Kakimoto, K.

    2014-01-01

    To dynamically model the plastic deformation of 4H-SiC single crystals during physical vapor transport (PVT) growth, the Alexander-Haasen model, originally proposed for the elemental semiconductor, is extended into IV-IV compound semiconductors. By fitting the model parameters to the experimental data, we show that the Alexander-Haasen model can describe the plastic deformation of 4H-SiC single crystals if the activation of the carbon-core partial dislocation is modeled in the high-temperature region (above 1000 °C) and the silicon-core partial dislocation is modeled in the low-temperature region (below 1000 °C). We then apply the same model to the dynamical deformation process of a 4H-SiC single crystal during PVT growth. The time evolution of the dislocation density is shown, and the effects of the cooling time on the final dislocation density, residual stress and stacking faults are also examined.

  9. The construction, prediction and measurement of co-crystal ternary phase diagrams as a tool for solvent selection.

    Science.gov (United States)

    Holaň, Jan; Stěpánek, František; Billot, Pascal; Ridvan, Luděk

    2014-10-15

    Many active pharmaceutical ingredients (APIs) are poorly soluble and therefore poorly bioavailable. In recent years, the advances in crystal engineering have motivated the research in the design of pharmaceutical co-crystals. This study examines the combination of solvent selection and co-crystal ternary phase diagram prediction on the basis of solubility measurements into a single methodology that can be integrated into the pharmaceutical process development workflow. Ternary diagrams constructed from agomelatine citric acid co-crystal solubility data were compared with those obtained by modern calorimetric method called discontinuous isoperibolic thermal analysis (DITA). A suitable solvent for the co-crystallization process has been chosen on the basis of agomelatine citric acid co-crystal solubility, which is connected to the yield of the crystallization process. Furthermore, the quality of final crystals from crystallization experiments was evaluated.

  10. Visualization of membrane protein crystals in lipid cubic phase using X-ray imaging

    Energy Technology Data Exchange (ETDEWEB)

    Warren, Anna J. [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Armour, Wes [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Oxford e-Research Centre, 7 Keble Road, Oxford OX1 3QG (United Kingdom); Axford, Danny; Basham, Mark; Connolley, Thomas; Hall, David R. [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Horrell, Sam [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); University of Liverpool, Liverpool L69 3BX (United Kingdom); McAuley, Katherine E.; Mykhaylyk, Vitaliy; Wagner, Armin; Evans, Gwyndaf, E-mail: gwyndaf.evans@diamond.ac.uk [Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom)

    2013-07-01

    A comparison of X-ray diffraction and radiographic techniques for the location and characterization of protein crystals is demonstrated on membrane protein crystals mounted within lipid cubic phase material. The focus in macromolecular crystallography is moving towards even more challenging target proteins that often crystallize on much smaller scales and are frequently mounted in opaque or highly refractive materials. It is therefore essential that X-ray beamline technology develops in parallel to accommodate such difficult samples. In this paper, the use of X-ray microradiography and microtomography is reported as a tool for crystal visualization, location and characterization on the macromolecular crystallography beamlines at the Diamond Light Source. The technique is particularly useful for microcrystals and for crystals mounted in opaque materials such as lipid cubic phase. X-ray diffraction raster scanning can be used in combination with radiography to allow informed decision-making at the beamline prior to diffraction data collection. It is demonstrated that the X-ray dose required for a full tomography measurement is similar to that for a diffraction grid-scan, but for sample location and shape estimation alone just a few radiographic projections may be required.

  11. Extracting the temperature distribution on a phase-change memory cell during crystallization

    Science.gov (United States)

    Bakan, Gokhan; Gerislioglu, Burak; Dirisaglik, Faruk; Jurado, Zoila; Sullivan, Lindsay; Dana, Aykutlu; Lam, Chung; Gokirmak, Ali; Silva, Helena

    2016-10-01

    Phase-change memory (PCM) devices are enabled by amorphization- and crystallization-induced changes in the devices' electrical resistances. Amorphization is achieved by melting and quenching the active volume using short duration electrical pulses (˜ns). The crystallization (set) pulse duration, however, is much longer and depends on the cell temperature reached during the pulse. Hence, the temperature-dependent crystallization process of the phase-change materials at the device level has to be well characterized to achieve fast PCM operations. A main challenge is determining the cell temperature during crystallization. Here, we report extraction of the temperature distribution on a lateral PCM cell during a set pulse using measured voltage-current characteristics and thermal modelling. The effect of the thermal properties of materials on the extracted cell temperature is also studied, and a better cell design is proposed for more accurate temperature extraction. The demonstrated study provides promising results for characterization of the temperature-dependent crystallization process within a cell.

  12. Direct evidence of the molecular interaction propagation in the phase transition of liquid crystals

    Science.gov (United States)

    Katayama, Kenji; Sato, Takahiro; Kuwahara, Shota

    2016-09-01

    The molecular interaction sometimes propagates in a collective manner, reaching for a long distance on the order of millimeters. Such interactions have been well known in the field of strongly-correlated electron systems in a beautiful crystal interleaved by donor and acceptor layers, induced by photo-stimulus. The other examples can be found in liquid crystals (LCs), which could be found in many places in nature such as bio-membrane. Different from crystals, LCs features "softness", which enables it to be a curved structure such as a cell. In LCs, even a small molecular change would trigger the overall structural change by the propagation of the molecular interaction. Here we will show, for the first time, how long and how fast the molecular interaction propagates in LCs. The patterned phase transition was induced in a LC, causing the phase transition propagation in a controlled way and the propagation was measured with an time-resolved optical technique, called the transient grating. A LC sample doped with azobenzene was put into a thermally controlled LC cell. A grating pattern of a pulse light with 355 nm was impinged to the LC cell, and the light was absorbed by the dyes, releasing heat or photomechanical motion. We could observe the fringe spacing dependence on the phase transition response, which indicates that phase transition was delayed as the fringe spacing due to the delay by the phase transition propagation. This is the first direct evidence of the molecular interaction propagation of the LC molecules.

  13. Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles

    Science.gov (United States)

    Chen, Bin; Ten Brink, Gert H.; Palasantzas, George; Kooi, Bart J.

    2016-12-01

    Chalcogenide-based nanostructured phase-change materials (PCMs) are considered promising building blocks for non-volatile memory due to their high write and read speeds, high data-storage density, and low power consumption. Top-down fabrication of PCM nanoparticles (NPs), however, often results in damage and deterioration of their useful properties. Gas-phase condensation based on magnetron sputtering offers an attractive and straightforward solution to continuously down-scale the PCMs into sub-lithographic sizes. Here we unprecedentedly present the size dependence of crystallization for Ge2Sb2Te5 (GST) NPs, whose production is currently highly challenging for chemical synthesis or top-down fabrication. Both amorphous and crystalline NPs have been produced with excellent size and composition control with average diameters varying between 8 and 17 nm. The size-dependent crystallization of these NPs was carefully analyzed through in-situ heating in a transmission electron microscope, where the crystallization temperatures (Tc) decrease when the NPs become smaller. Moreover, methane incorporation has been observed as an effective method to enhance the amorphous phase stability of the NPs. This work therefore elucidates that GST NPs synthesized by gas-phase condensation with tailored properties are promising alternatives in designing phase-change memories constrained by optical lithography limitations.

  14. Liquid Crystal Phases of Molecular Bananas: Polarity and Chirality as Broken Symmetries

    Science.gov (United States)

    Clark, Noel

    2006-03-01

    The study of the interplay of chirality and polarity has been a particularly rich theme of soft matter science since Meyer's seminal discovery that tilted smectics of chiral molecules are macroscopically polar. This event, and the subsequent realization of polar domains and high-speed electro-optic switching in chiral smectics, engaged the liquid crystal community in a worldwide pursuit of novel smectics for applications, featured by the synthesis of more than 50,000 new liquid crystal compounds, and by a consequent broad diversification of the palette of liquid crystal phases and possibilities for supermolecular ordering. A current important activity in this scenario is the study of polar order in synthetically achiral molecules, for example, in molecular bananas, which, as their shape suggests, might be expected to organize in a polar way. Indeed they do, but beyond this, almost everything learned about them has been surprising, including their persistent tendency to exhibit chirality as a spontaneously broken symmetry. I will discuss some of these new phases and phenomena, including the discovery of fluid conglomerates (Pasteur's experiment in a fluid), triclinic fluid order, chiral twist grain boundary phases of achiral molecules, chirality flipping and field-induced deracemization, ferroelectric and antiferroelectric phases with supermolecular- scale polarization modulation, and chiral thermotropic sponge phases.

  15. Amelogenin Affects Brushite Crystal Morphology and Promotes Its Phase Transformation to Monetite

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Dongni; Ruan, Qichao; Tao, Jinhui; Lo, Jonathan; Nutt, Steven; Moradian-Oldak, Janet

    2016-09-07

    Amelogenin protein is involved in organized apatite crystallization during enamel formation. Brushite (CaHPO4·2H2O), which is one of the precursors for hydroxyapatite in in vitro mineralization, has been used for fabrication of biomaterials for hard tissue repair. In order to explore its potential application in biomimetic material synthesis, we studied the influence of amelogenin on brushite morphology and phase transformation to monetite. Our results show that amelogenin can adsorb onto surface of brushite, leading to the formation of layered structures on the (010) face. Amelogenin promoted the phase transformation of brushite into monetite (CaHPO4) in the dry state, presumably by interacting with crystalline water layers in brushite unit cell. Changes to the crystal morphology by amelogenin continued even after the phase transformation to monetite forming an organized nanotextured structure of nano-sticks resembling the bundle structure in enamel.

  16. Phase equilibria and crystal chemistry of rubidium niobates and rubidium tantalates

    Science.gov (United States)

    Minor, D. B.; Roth, R. S.; Parker, H. S.; Brower, W. S.

    1977-01-01

    The phase equilibria relations and crystal chemistry of portions of the Rb2O-Nb2O5 and Rb2O-Ta2O5 systems were investigated for structures potentially useful as ionic conductors. A hexagonal tungsten bronze-type (HTB) structure was found in both systems as well as three hexagonal phases with mixed HTB-pyrochlore type structures. Ion exchange experiments between various alkali ions are described for several phases. Unit cell dimensions and X-ray diffraction powder patterns are reported.

  17. Relationship between Multi-Phase Formation and Molecular Structure for Liquid Crystal System

    Institute of Scientific and Technical Information of China (English)

    LI Zhenxin; MA Heng; LI Shipu

    2005-01-01

    A mechanical model of liquid crystals ( LCs ) was used to explain the phase formation and thermal properties. The LC phases in the model are micro-machine systems consisting of an ensemble of molecular rotors, and some dynamic parameters in a semi-experiment molecular orbit method. A novel explanation on the multi-phase formation of LC system is obtained. It is found that the value of the critical rotational velocity is a key parameter for the characterization of each homologous series. The dipole moment of the molecules was also discussed.

  18. Liquid crystal terahertz phase shifters with functional indium-tin-oxide nanostructures for biasing and alignment

    Science.gov (United States)

    Yang, Chan-Shan; Tang, Tsung-Ta; Pan, Ru-Pin; Yu, Peichen; Pan, Ci-Ling

    2014-04-01

    Indium Tin Oxide (ITO) nanowhiskers (NWhs) obliquely evaporated by electron-beam glancing-angle deposition can serve simultaneously as transparent electrodes and alignment layer for liquid crystal (LC) devices in the terahertz (THz) frequency range. To demonstrate, we constructed a THz LC phase shifter with ITO NWhs. Phase shift exceeding π/2 at 1.0 THz was achieved in a ˜517 μm-thick cell. The phase shifter exhibits high transmittance (˜78%). The driving voltage required for quarter-wave operation is as low as 5.66 V (rms), compatible with complementary metal-oxide-semiconductor (CMOS) and thin-film transistor (TFT) technologies.

  19. On the theory of ternary melt crystallization with a non-linear phase diagram

    Science.gov (United States)

    Toropova, L. V.; Dubovoi, G. Yu; Alexandrov, D. V.

    2017-04-01

    The present study is concerned with a theoretical analysis of unidirectional solidification process of ternary melts in the presence of a phase transition (mushy) layer. A new analytical solution of heat and mass transfer equations describing the steady-state crystallization scenario is found with allowance for a non-linear liquidus equation. The model under consideration takes into account the presence of two phase transition layers, namely, the primary and cotectic mushy regions. We demonstrate that the phase diagram nonlinearity leads to substantial changes of analytical solutions.

  20. Beyond phthalates: Gas phase concentrations and modeled gas/particle distribution of modern plasticizers

    Energy Technology Data Exchange (ETDEWEB)

    Schossler, Patricia [Fraunhofer WKI, Department of Material Analysis and Indoor Chemistry, Bienroder Weg 54E, D-38108 Braunschweig (Germany); Institute of Environmental and Sustainable Chemistry, Technische Universitaet Braunschweig, Hagenring 30, D-38106 Braunschweig (Germany); Schripp, Tobias, E-mail: tobias.schripp@wki.fraunhofer.de [Fraunhofer WKI, Department of Material Analysis and Indoor Chemistry, Bienroder Weg 54E, D-38108 Braunschweig (Germany); Salthammer, Tunga [Fraunhofer WKI, Department of Material Analysis and Indoor Chemistry, Bienroder Weg 54E, D-38108 Braunschweig (Germany); Bahadir, Muefit [Institute of Environmental and Sustainable Chemistry, Technische Universitaet Braunschweig, Hagenring 30, D-38106 Braunschweig (Germany)

    2011-09-01

    The ongoing health debate about polymer plasticizers based on the esters of phthalic acid, especially di(2-ethylhexyl) phthalate (DEHP), has caused a trend towards using phthalates of lower volatility such as diisononyl phthalate (DINP) and towards other acid esters, such as adipates, terephthalates, citrates, etc. Probably the most important of these so-called 'alternative' plasticizers is diisononyl cyclohexane-1,2-dicarboxylate (DINCH). In the indoor environment, the continuously growing market share of this compound since its launch in 2002 is inter alia apparent from the increasing concentration of DINCH in settled house dust. From the epidemiological point of view there is considerable interest in identifying how semi-volatile organic compounds (SVOCs) distribute in the indoor environment, especially in air, airborne particles and sedimented house dust. This, however, requires reliable experimental concentration data for the different media and good measurements or estimates of their physical and chemical properties. This paper reports on air concentrations for DINP, DINCH, diisobutyl phthalate (DIBP), diisobutyl adipate (DIBA), diisobutyl succinate (DIBS) and diisobutyl glutarate (DIBG) from emission studies in the Field and Laboratory Emission Cell (FLEC). For DINP and DINCH it took about 50 days to reach the steady-state value: for four months no decay in the concentration could be observed. Moreover, vapor pressures p{sub 0} and octanol-air partitioning coefficients K{sub OA} were obtained for 37 phthalate and non-phthalate plasticizers from two different algorithms: EPI Suite and SPARC. It is shown that calculated gas/particle partition coefficients K{sub p} and fractions can widely differ due to the uncertainty in the predicted p{sub 0} and K{sub OA} values. For most of the investigated compounds reliable experimental vapor pressures are not available. Rough estimates can be obtained from the measured emission rate of the pure compound in a

  1. Investigation of crystallization and amorphization dynamics of phase-change thin films by subnanosecond laser pulses.

    Science.gov (United States)

    Kieu, Khanh; Narumi, Kenji; Mansuripur, Masud

    2006-10-20

    We report experimental results on amorphization and crystallization dynamics of reversible phase-change (PC) thin-film samples, GeSbTe and GeBiTe, for optical disk data storage. The investigation was conducted with subnanosecond laser pulses using a pump-and-probe configuration. Amorphization of the crystalline films could be achieved with a single subnanosecond laser pulse; the amorphization dynamics follow closely the temperature kinetics induced in the irradiated spot. As for crystallization of the samples initially in the amorphous state, a single subnanosecond pulse was found to be insufficient to fully crystallize the irradiated spot, but we could crystallize the PC film (in the area under the focused spot) by applying multiple short pulses. Our multipulse studies reveal that the GeSbTe crystallization is dominated by the growth of nuclei whose initial formation is slow but, once formed, their subsequent growth (under a sequence of subnanosecond pulses) happens quickly. In the case of GeBiTe samples, the crystalline nuclei appear to be present in the material initially, as they grow immediately upon illumination with laser pulses. Whereas our amorphous GeSbTe samples required approximately 200 pulses for full crystallization, for the GeBiTe samples approximately 15 pulses sufficed.

  2. Non-Resonant Magnetoelectric Energy Harvesting Utilizing Phase Transformation in Relaxor Ferroelectric Single Crystals

    Directory of Open Access Journals (Sweden)

    Peter Finkel

    2015-12-01

    Full Text Available Recent advances in phase transition transduction enabled the design of a non-resonant broadband mechanical energy harvester that is capable of delivering an energy density per cycle up to two orders of magnitude larger than resonant cantilever piezoelectric type generators. This was achieved in a [011] oriented and poled domain engineered relaxor ferroelectric single crystal, mechanically biased to a state just below the ferroelectric rhombohedral (FR-ferroelectric orthorhombic (FO phase transformation. Therefore, a small variation in an input parameter, e.g., electrical, mechanical, or thermal will generate a large output due to the significant polarization change associated with the transition. This idea was extended in the present work to design a non-resonant, multi-domain magnetoelectric composite hybrid harvester comprised of highly magnetostrictive alloy, [Fe81.4Ga18.6 (Galfenol or TbxDy1-xFe2 (Terfenol-D], and lead indium niobate–lead magnesium niobate–lead titanate (PIN-PMN-PT domain engineered relaxor ferroelectric single crystal. A small magnetic field applied to the coupled device causes the magnetostrictive element to expand, and the resulting stress forces the phase change in the relaxor ferroelectric single crystal. We have demonstrated high energy conversion in this magnetoelectric device by triggering the FR-FO transition in the single crystal by a small ac magnetic field in a broad frequency range that is important for multi-domain hybrid energy harvesting devices.

  3. Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Preidel, V., E-mail: veit.preidel@helmholtz-berlin.de; Amkreutz, D.; Haschke, J.; Wollgarten, M.; Rech, B.; Becker, C. [Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Division Renewable Energy, Kekuléstr. 5, 12489 Berlin (Germany)

    2015-06-14

    Liquid phase crystallized Si thin-film solar cells on nanoimprint textured glass substrates exhibiting two characteristic, but distinct different surface structures are presented. The impact of the substrate texture on light absorption, the structural Si material properties, and the resulting solar cell performance is analyzed. A pronounced periodic substrate texture with a vertical feature size of about 1 μm enables excellent light scattering and light trapping. However, it also gives rise to an enhanced Si crystal defect formation deteriorating the solar cell performance. In contrast, a random pattern with a low surface roughness of 45 nm allows for the growth of Si thin films being comparable to Si layers on planar reference substrates. Amorphous Si/crystalline Si heterojunction solar cells fabricated on the low-roughness texture exhibit a maximum open circuit voltage of 616 mV and internal quantum efficiency peak values exceeding 90%, resulting in an efficiency potential of 13.2%. This demonstrates that high quality crystalline Si thin films can be realized on nanoimprint patterned glass substrates by liquid phase crystallization inspiring the implementation of tailor-made nanophotonic light harvesting concepts into future liquid phase crystallized Si thin film solar cells on glass.

  4. Crystal growth and electronic structure of low-temperature phase SrMgF{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Atuchin, Victor V. [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Functional Electronics Laboratory, Tomsk State University, Tomsk 634050 (Russian Federation); Laboratory of Semiconductor and Dielectric Materials, Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Goloshumova, Alina A. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 630090 (Russian Federation); Isaenko, Ludmila I. [Laboratory of Semiconductor and Dielectric Materials, Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 630090 (Russian Federation); Jiang, Xingxing [BCCRD, Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Lobanov, Sergey I. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 630090 (Russian Federation); Zhang, Zhaoming [Australian Nuclear Science & Technology Organisation, Lucas Heights, NSW 2234 (Australia); Lin, Zheshuai, E-mail: zslin@mail.ipc.ac.cn [BCCRD, Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

    2016-04-15

    Using the vertical Bridgman method, the single crystal of low temperature phase SrMgF{sub 4} is obtained. The crystal is in a very good optical quality with the size of 10×7×5 mm{sup 3}. Detailed photoemission spectra of the element core levels are determined by a monochromatic AlKa (1486.6 eV) X-ray source. Moreover, the first-principles calculations are performed to investigate the electronic structure of SrMgF{sub 4}. A good agreement between experimental and calculated results is achieved. It is demonstrated that almost all the electronic orbitals are strongly localized and the hybridization with the others is very small, but the Mg–F bonds covalency is relatively stronger than that of Sr–F bonds. - Graphical abstract: Large size of low-temperature phase SrMgF{sub 4} crystal was obtained (right) and its electronic structure was investigated by X-ray photoelectron spectroscopy and first-principles calculation (left). - Highlights: • Large size single crystal of low-temperature phase SrMgF{sub 4} is obtained. • Electronic structure of SrMgF{sub 4} is measured by X-ray photoelectron spectroscopy. • Partial densities of states are determined by first-principles calculation. • Good agreement between experimental and calculated results is achieved. • Strong ionic characteristics of chemical bonds are exhibited in SrMgF{sub 4}.

  5. Molecular motion, dielectric response, and phase transition of charge-transfer crystals: acquired dynamic and dielectric properties of polar molecules in crystals.

    Science.gov (United States)

    Harada, Jun; Ohtani, Masaki; Takahashi, Yukihiro; Inabe, Tamotsu

    2015-04-08

    Molecules in crystals often suffer from severe limitations on their dynamic processes, especially on those involving large structural changes. Crystalline compounds, therefore, usually fail to realize their potential as dielectric materials even when they have large dipole moments. To enable polar molecules to undergo dynamic processes and to provide their crystals with dielectric properties, weakly bound charge-transfer (CT) complex crystals have been exploited as a molecular architecture where the constituent polar molecules have some freedom of dynamic processes, which contribute to the dielectric properties of the crystals. Several CT crystals of polar tetrabromophthalic anhydride (TBPA) molecules were prepared using TBPA as an electron acceptor and aromatic hydrocarbons, such as coronene and perylene, as electron donors. The crystal structures and dielectric properties of the CT crystals as well as the single-component crystal of TBPA were investigated at various temperatures. Molecular reorientation of TBPA molecules did not occur in the single-component crystal, and the crystal did not show a dielectric response due to orientational polarization. We have found that the CT crystal formation provides a simple and versatile method to develop molecular dielectrics, revealing that the molecular dynamics of the TBPA molecules and the dielectric property of their crystals were greatly changed in CT crystals. The TBPA molecules underwent rapid in-plane reorientations in their CT crystals, which exhibited marked dielectric responses arising from the molecular motion. An order-disorder phase transition was observed for one of the CT crystals, which resulted in an abrupt change in the dielectric constant at the transition temperature.

  6. Cross-phase-modulation-induced instability in photonic-crystal fibers.

    Science.gov (United States)

    Serebryannikov, E E; Konorov, S O; Ivanov, A A; Alfimov, M V; Scalora, M; Zheltikov, A M

    2005-08-01

    Cross-phase-modulation-induced instability is identified as a significant mechanism for efficient parametric four-wave-mixing frequency conversion in photonic-crystal fibers. Fundamental-wavelength femtosecond pulses of a Cr, forsterite laser are used in our experiments to transform the spectrum of copropagating second-harmonic pulses of the same laser in a photonic-crystal fiber. Efficient generation of sidebands shifted by more than 80 THz with respect to the central frequency of the second harmonic is observed in the output spectrum of the probe field.

  7. An energy-stable convex splitting for the phase-field crystal equation

    KAUST Repository

    Vignal, P.

    2015-10-01

    Abstract The phase-field crystal equation, a parabolic, sixth-order and nonlinear partial differential equation, has generated considerable interest as a possible solution to problems arising in molecular dynamics. Nonetheless, solving this equation is not a trivial task, as energy dissipation and mass conservation need to be verified for the numerical solution to be valid. This work addresses these issues, and proposes a novel algorithm that guarantees mass conservation, unconditional energy stability and second-order accuracy in time. Numerical results validating our proofs are presented, and two and three dimensional simulations involving crystal growth are shown, highlighting the robustness of the method. © 2015 Elsevier Ltd.

  8. The model of solid phase crystallization of amorphous silicon under elastic stress

    OpenAIRE

    2000-01-01

    Solid phase crystallization of an amorphous silicon (a-Si) film stressed by a Si3N4 cap was studied by laser Raman spectroscopy. The a-Si films were deposited on Si3N4 (50 nm)/Si(100) substrate by rf sputtering. The stress in an a-Si film was controlled by thickness of a Si3N4 cap layer. The Si3N4 films were also deposited by rf sputtering. It was observed that the crystallization was affected by the stress in a-Si films introduced by the Si3N4 cap layer. The study suggests that the elastic s...

  9. A study of the plasticity in the vortex matter across the second magnetization peak in a YBCO crystal via measurements of minor hysteresis loops

    Indian Academy of Sciences (India)

    D Pal; S Ramakrishnan; A K Grover; D Dasgupta; Bimal K Sarma

    2002-05-01

    Results of an investigation of the path dependence of the critical current density c due to the plastic deformation of the flux line lattice in a weakly pinned YBa2Cu3O7- (YBCO) crystal for $H||c$ are reported. The procedure of minor hysteresis loops has been used to explore the path dependence of c and the metastability effects. Contrary to the behavior observed in low c systems, in YBCO it is found that at low temperatures, the multivaluedness in c() could persist beyond the notional peak field p at which the anomalous variation in c() reaches its maximum value.

  10. Some effects of ice crystals on the FSSP measurements in mixed phase clouds

    Directory of Open Access Journals (Sweden)

    G. Febvre

    2012-10-01

    Full Text Available In this paper, we show that in mixed phase clouds, the presence of ice crystals may induce wrong FSSP 100 measurements interpretation especially in terms of particle size and subsequent bulk parameters. The presence of ice crystals is generally revealed by a bimodal feature of the particle size distribution (PSD. The combined measurements of the FSSP-100 and the Polar Nephelometer give a coherent description of the effect of the ice crystals on the FSSP-100 response. The FSSP-100 particle size distributions are characterized by a bimodal shape with a second mode peaked between 25 and 35 μm related to ice crystals. This feature is observed with the FSSP-100 at airspeed up to 200 m s−1 and with the FSSP-300 series. In order to assess the size calibration for clouds of ice crystals the response of the FSSP-100 probe has been numerically simulated using a light scattering model of randomly oriented hexagonal ice particles and assuming both smooth and rough crystal surfaces. The results suggest that the second mode, measured between 25 μm and 35 μm, does not necessarily represent true size responses but corresponds to bigger aspherical ice particles. According to simulation results, the sizing understatement would be neglected in the rough case but would be significant with the smooth case. Qualitatively, the Polar Nephelometer phase function suggests that the rough case is the more suitable to describe real crystals. Quantitatively, however, it is difficult to conclude. A review is made to explore different hypotheses explaining the occurrence of the second mode. However, previous cloud in situ measurements suggest that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is likely to be due to the shattering of large ice crystals on the probe inlet. This finding is supported by the rather good relationship between the concentration of particles larger than 20 μm (hypothesized to be ice shattered-fragments measured by the

  11. Solid-Phase Photocatalytic Degradation of Waste Plastics%固相光催化降解废弃塑料

    Institute of Scientific and Technical Information of China (English)

    杨昌军; 彭天右; 邓克俭; 昝菱

    2011-01-01

    White pollution has become a global environmental issue in recent years. Composite plastics embedding photocatalysts into ploymer matrix has excellent photocatalytic degradation activity. It could be degraded effectively in ambient air under sunlight exposure. So it is an eco-friendly disposal of polymer wastes, and provides a promising way to solve white pollution. In this paper, the latest research progress in solid-phase photocatalytic degradation of waste plastics is reviewed. The solid-phase photocatalytic activity of TiO2, ZnO, α-FeOOH and H3PW12O40, as well as the photocatalytic degradation mechanism of various composite plastics are introduced.Many new methods have been used to enhance the solid-phase photocatalytic degradation activity of composite plastics and the utilization efficiency of sunlight. For example, surface modifying photocatalyst by branched macromolecule is used to improve the dispersion of photocatalyst in polymer matrix, modifying photocatalyst by metal ion doping or dye sensitization is used to broaden the region of photoresponse and enhance the visible light activity of photocatalyst. At last, the potential application prospects for photodegradable composite plastics in the field of waste plastic treatment is discussed.%"白色污染"已成为目前普遍关注的一个全球性环保课题.将光催化剂掺入到塑料中制备出环境友好的可光降解复合塑料,利用其光催化活性可以使废弃塑料在太阳光的照射下发生有效降解,是解决"白色污染"问题的有效途径之一.本文综述了近年来固相光催化降解废弃塑料的研究进展,介绍了光催化剂TiO、ZnO、а-FeOOH和HPWO加对废弃塑料的固相光催化降解效率及各种复合塑料的光催化降解机理,阐述了对光催化剂进行表面改性可以改善其在聚合物中的分散性,以及对光催化剂进行修饰可以提高其对可见光的吸收,从而提高复合塑料的固相光催化降解活性及对

  12. Effects of gasket on coupled plastic flow and strain-induced phase transformations under high pressure and large torsion in a rotational diamond anvil cell

    Science.gov (United States)

    Feng, Biao; Levitas, Valery I.

    2016-01-01

    Combined plastic flow and strain-induced phase transformations (PTs) under high pressure in a sample within a gasket subjected to three dimensional compression and torsion in a rotational diamond anvil cell (RDAC) are studied using a finite element approach. The results are obtained for the weaker, equal-strength, and stronger high-pressure phases in comparison with low-pressure phases. It is found that, due to the strong gasket, the pressure in the sample is relatively homogenous and the geometry of the transformed zones is mostly determined by heterogeneity in plastic flow. For the equal-strength phases, the PT rate is higher than for the weaker and stronger high-pressure phases. For the weaker high-pressure phase, transformation softening induces material instability and leads to strain and PT localization. For the stronger high-pressure phase, the PT is suppressed by strain hardening during PT. The effect of the kinetic parameter k that scales the PT rate in the strain-controlled kinetic equation is also examined. In comparison with a traditional diamond anvil cell without torsion, the PT progress is much faster in RDAC under the same maximum pressure in the sample. Finally, the gasket size and strength effects are discussed. For a shorter and weaker gasket, faster plastic flow in radial and thickness directions leads to faster PT kinetics in comparison with a longer and stronger gasket. The rates of PT and plastic flows are not very sensitive to the modest change in a gasket thickness. Multiple experimental results are reproduced and interpreted. Obtained results allow one to design the desired pressure-plastic strain loading program in the experiments for searching new phases, reducing PT pressure by plastic shear, extracting kinetic properties from experiments with heterogeneous fields, and controlling homogeneity of all fields and kinetics of PTs.

  13. Crystallization kinetics of overlapping phases in Se70Te15Sb15 using isoconversional methods

    Directory of Open Access Journals (Sweden)

    M.A. Abdel-Rahim

    2015-04-01

    Full Text Available The crystallization kinetics of Se70Te15Sb15 chalcogenide glass was studied by Differential Scanning Calorimetry (DSC under non-isothermal conditions. This glass was found to have a double glass transition and double overlapped crystalline phases. The overlapped crystalline phases were successfully separated using the Gaussian fit model. The activation energy, Ec, and Avrami index, n, were determined by analyzing the data using the Matausita et. al. method. A strong heating rate depending on the activation energy for the two crystalline peaks was observed. The results indicated that the transformation from amorphous to crystalline phases is a complex process involving different mechanisms of nucleation and growth. The variation of activation energy with crystalline fraction was determined by Kissenger–Akahira–Sunose (KAS method. The obtained results of directly fitting the experimental DSC data to the calculated DSC curves indicated that the crystallization process of Se70Te15Sb15 glass cannot be satisfactorily described by the Johnson–Mehl–Avrami (JMA model. Simulation results indicated that the Sestak–Berggren (SB model is more suitable to describe the crystallization process for the studied glass. The crystalline phases for the two events were identified by using x-ray diffraction (XRD and scanning electron microscopy (SEM.

  14. Crystallization, X-ray diffraction analysis and SIRAS/molecular-replacenent phasing of three crystal forms of Anabaena sensory rhodopsin transducer

    Energy Technology Data Exchange (ETDEWEB)

    Vogeley, Lutz; Luecke, Hartmut, E-mail: hudel@uci.edu [University of California, Irvine (United States)

    2006-04-01

    Crystals of Anabaena sensory rhodopsin transducer, the transducer for the cyanobacterial photosensor Anabaena sensory rhodopsin, obtained in the space groups P4, C2 and P2{sub 1}2{sub 1}2{sub 1} diffract to 1.8, 2.1 and 2.0 Å, respectively. Phases for these crystal forms were obtained by SIRAS phasing using an iodide quick-soak derivative (P4) and molecular replacement (C2 and P2{sub 1}2{sub 1}2{sub 1}). Anabaena sensory rhodopsin transducer (ASRT) is a 14.7 kDa soluble signaling protein associated with the membrane-embedded light receptor Anabaena sensory rhodopsin (ASR) from Anabaena sp., a freshwater cyanobacterium. Crystals of ASRT were obtained in three different space groups, P4, C2 and P2{sub 1}2{sub 1}2{sub 1}, which diffract to 1.8, 2.1 and 2.0 Å, respectively. Phases for one of these crystal forms (P4) were obtained by SIRAS phasing using an iodide quick-soak derivative and a partial model was built. Phases for the remaining crystal forms were obtained by molecular replacement using the partial model from the P4 crystal form.

  15. Phase transitions and exchange interactions in the SmCr3(BO3)4 crystal

    Science.gov (United States)

    Dobretsova, E. A.; Boldyrev, K. N.; Popova, M. N.; Gavrilkin, S. Yu.; Mukhin, A. A.; Ivanov, V. Yu.; Mal'tsev, V. V.; Leonyuk, N. I.; Malkin, B. Z.

    2016-12-01

    Spectroscopic investigation and specific heat and magnetic susceptibility measurements of SmCr3(BO3)4 crystals were performed. The spectra of the Sm3+ and Cr3+ ions in samarium chromium borate were calculated and parameters of the exchange interactions between the nearest chromium ions, chromium and samarium ions were determined. Three phase transitions were observed at the temperatures T1 = 7.8 ± 0.5 K, T2 = 6.7 ± 0.5 K, and T3 = 4.3 ± 0.2 K, their nature is discussed. The crystal structures with different space symmetry groups R32 and C2/c were found to coexist in a SmCr3(BO3)4 single crystal.

  16. Phase-field simulations of faceted Ge/Si-crystal arrays, merging into a suspended film

    Science.gov (United States)

    Salvalaglio, Marco; Bergamaschini, Roberto; Backofen, Rainer; Voigt, Axel; Montalenti, Francesco; Miglio, Leo

    2017-01-01

    We simulate the morphological evolution of Ge microcrystals, grown out-of-equilibrium on deeply patterned Si substrates, as resulting from surface diffusion driven by the tendency toward the minimization of the surface energy. In particular, we report three-dimensional phase-field simulations accounting for the realistic surface energy anisotropy of Ge/Si crystals. In Salvalaglio et al. (2015) [10] it has been shown both by experiments and simulations that annealing of closely spaced crystals leads to a coalescence process with the formation of a suspended film. However, this was explained only by considering an isotropic surface energy. Here, we extend such a study by showing first the morphological changes of faceted isolated crystals. Then, the evolution of dense arrays is considered, describing their coalescence along with the evolution of facets. Combined with the previous results without anisotropy in the surface energy, this work allows us to confirm and assess the key features of the coalescence process.

  17. A fast selenium derivatization strategy for crystallization and phasing of RNA structures

    Science.gov (United States)

    Olieric, Vincent; Rieder, Ulrike; Lang, Kathrin; Serganov, Alexander; Schulze-Briese, Clemens; Micura, Ronald; Dumas, Philippe; Ennifar, Eric

    2009-01-01

    Site-specific 2′-methylseleno RNA labeling is a promising tool for tackling the phase problem in RNA crystallography. We have developed an efficient strategy for crystallization and structure determination of RNA and RNA/protein complexes based on preliminary crystallization screening of 2′-OCH3-modified RNA sequences, prior to the replacement of 2′-OCH3 groups with their 2′-SeCH3 counterparts. The method exploits the similar crystallization properties of 2′-OCH3- and 2′-SeCH3-modified RNAs and has been successfully validated for two test cases. In addition, our data show that 2′-SeCH3-modified RNA have an increased resistance to X-ray radiolysis in comparison with commonly used 5-halogen-modified RNA, which permits collection of experimental electron density maps of remarkable quality. PMID:19228585

  18. Predicting out-of-Equilibrium Phase Behavior in the Dynamic Self-Assembly of Colloidal Crystals

    Science.gov (United States)

    Swan, James; Sherman, Zachary

    Crystals self-assembled from colloidal particles are useful in an array of well demonstrated applications. During fabrication however, gelation and glassification often leave these materials arrested in defective or disordered metastable states. We show how time-dependent, pulsed interparticle interactions can avoid kinetic barriers and yield well-ordered crystalline domains for a suspension of hard, spherical colloidal particles interacting through short-range attractions. This dynamic self-assembly process is analogous to the flashing Brownian rachet. Although this is an inherently unsteady, out-of-equilibrium process, we can predict its outcome using appropriate time averages of equilibrium equations of state. The predicted phase behavior is tested and validated by examining the fluid/crystal coexistence of such dynamically self-assembling dispersions in Brownian dynamics simulations of sedimentation equilibrium and homogeneous nucleation. We also show that our dynamic self-assembly scheme offers control and tunability over the crystal growth kinetics and can even stabilize nonequilibrium structures.

  19. Photopeak detection by an InSb radiation detector made of liquid phase epitaxially grown crystals

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Yuki, E-mail: Y.Sato@nucleng.kyoto-u.ac.j [Graduate School of Engineering, Kyoto University, Sakyo, Kyoto 606-8501 (Japan); Morita, Yasunari; Harai, Tomoyuki; Kanno, Ikuo [Graduate School of Engineering, Kyoto University, Sakyo, Kyoto 606-8501 (Japan)

    2010-09-21

    We have fabricated a radiation detector using a p-type InSb crystal grown by liquid phase epitaxy (LPE). At temperatures below 100 K, the resistivity of the LPE crystal was over an order of magnitude higher than that of the commercial InSb crystal substrate. The resistance of the InSb detector is 680 k{Omega} at 4.2 K, which is one order of magnitude higher than that of detectors fabricated from commercial InSb wafers and, in an improvement over previous results, the energy resolution of {sup 241}Am alpha particles reaches 3%. In addition, we also observe the photopeak of gamma-rays emitted by {sup 133}Ba.

  20. The crystal structure of phase IV of poly(vinylidene fluoride)

    Science.gov (United States)

    Bachmann, M.; Gordon, W. L.; Weinhold, S.; Lando, J. B.

    1980-10-01

    The crystal structure of phase IV (polar α or δ phase) poly(vinylidene fluoride) was studied by x-ray diffraction. Oriented phase IV was obtained by orienting phase II (α phase) and then corona poling at approximately 2 MV/cm. The resulting material is a mixture of phases I, II, and IV. Infrared spectra indicate that phase IV has the same chain conformation (TGTG') as phase II. The reflections of phase IV can be indexed to an orthorhombic unit cell with lattice constants similar to the phase II lattice constants, a=0.496 nm, b=0.964 nm, and c (chain axis)=0.462 nm. There are two chains in this unit cell. The two chains pack with the chain dipole moments parallel. Three different ways of packing the chains were investigated: both chains up, one up and one down, and a statistical up-down packing. It was found that to within a 97% confidence level, the chains pack with a statistical up-down packing.

  1. Calorimetric and neutron scattering studies of plastically crystalline cyclooctanol

    Energy Technology Data Exchange (ETDEWEB)

    Yamamuro, Osamu [Department of Chemistry and Research Centre for Molecular Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Yamasaki, Hirotaka [Department of Chemistry and Research Centre for Molecular Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Madokoro, Yasushi [Department of Chemistry and Research Centre for Molecular Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Tsukushi, Itaru [Department of Physics, Chiba Institute of Technology, Narashino, Chiba 275-0023 (Japan); Matsuo, Takasuke [Department of Chemistry and Research Centre for Molecular Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

    2003-08-20

    The heat capacity of cyclooctanol was measured with an adiabatic calorimeter in the temperature range 5-340 K. Liquid cyclooctanol crystallized into crystal I, a plastic (orientationally disordered) phase. Crystal I was supercooled readily and underwent a glass transition at 160 K. Crystal II, obtained by annealing crystal I at about 200 K, also underwent a glass transition at 160 K, indicating that crystal II is also an orientationally disordered phase. On heating, crystal II transformed to crystal I at 261.7 K with a transition entropy of 8.06 J K{sup -1} mol{sup -1} and crystal I fused at 295.3 K with a fusion entropy of 7.00 J K{sup -1} mol{sup -1}. Neutron scattering of cyclooctanol was measured in the temperature range 20-335 K, energy range 0.1-20 meV and momentum transfer range 0.23-2.7 A{sup -1}. A clear boson peak was found around 2.5 meV in both orientational glasses of crystal I and II. Quasielastic scattering appeared at temperatures as low as the glass transition temperature. This may be due to a fast {beta} process which has been observed in most glass-forming liquids. The present results indicate that glass-forming plastic crystals are similar to glass-forming liquids in their dynamical properties in terahertz region.

  2. Phase transition, phase transition temperature and crystal structure of a new compound----Ca2PdWO6

    Institute of Scientific and Technical Information of China (English)

    傅正民; 李文秀

    1996-01-01

    A new compound Ca2PdWO6 has been synthesized by solid state sintering. The phase transition of this compound was investigated by means of differential thermal analysis (DTA), X-ray phase analysis, precise measurement of lattice parameters and other methods. It is discovered that the compound has a displacive phase transition of the first order at (806+5)C. The low temperature phase, a-Ca2PdWO6, belongs to orthorhombic system, with space group Pmm2. Its lattice parameters at room temperature are: a=0.79946nm, b=0.55404nm and c=0.58008nm. The measured density is Dm=6.26g/cm3, and each unit cell contains two formula weights. The high temperature phase, Ca2PdWO6, belongs to the cubic system, with space group fm3m and the lattice parameter is a = 0.810 3 nm at 860C; Z = 4. The calculated density is Dx=5.821g/cm3. The crystal structure of Ca2PdWO6 and Ca,PdWO6 was also determined by means of the X-ray polycrystal diffraction method. The factors influencing phase transition temperature are discussed in detail.

  3. Preliminary study of non-isothermal phase change phenomena in vertical Bridgman crystal growth

    Institute of Scientific and Technical Information of China (English)

    LIU Jie; LU WenQiang

    2007-01-01

    Axisymmetric dual reciprocity boundary element method (DRBEM) with augmented items is extended to simulate the heat and mass transfer problems in the vertical Bridgman method (VBM) crystal growth of HgCdTe and CdZnTe. Axial solute concentration redistribution of three regions numerically reappears, and the influence of the pulling rate of the ampoule on it is further studied. Secondly, one dimensional transient phase change phenomena is studied, and non-isothermal phase change phenomena is obtained from the initial transient region through the steady growth region to the final transient region. Thirdly, the two-dimensional axisymmetric phase change interface position, interfacial shape and the temperature field of the melt and the crystal are numerically captured under the condition to arrive at the steady state with zero pulling rate of the ampoule. Finally, the study of transient axisymmetric non-isothermal phase change phenomena is stressed and the results are compared with those in isothermal phase change. The influence of the pulling rate on non-isothermal phase change phenomena is revealed.

  4. Analytical Round Robin for Elastic-Plastic Analysis of Surface Cracked Plates: Phase I Results

    Science.gov (United States)

    Wells, D. N.; Allen, P. A.

    2012-01-01

    An analytical round robin for the elastic-plastic analysis of surface cracks in flat plates was conducted with 15 participants. Experimental results from a surface crack tension test in 2219-T8 aluminum plate provided the basis for the inter-laboratory study (ILS). The study proceeded in a blind fashion given that the analysis methodology was not specified to the participants, and key experimental results were withheld. This approach allowed the ILS to serve as a current measure of the state of the art for elastic-plastic fracture mechanics analysis. The analytical results and the associated methodologies were collected for comparison, and sources of variability were studied and isolated. The results of the study revealed that the J-integral analysis methodology using the domain integral method is robust, providing reliable J-integral values without being overly sensitive to modeling details. General modeling choices such as analysis code, model size (mesh density), crack tip meshing, or boundary conditions, were not found to be sources of significant variability. For analyses controlled only by far-field boundary conditions, the greatest source of variability in the J-integral assessment is introduced through the constitutive model. This variability can be substantially reduced by using crack mouth opening displacements to anchor the assessment. Conclusions provide recommendations for analysis standardization.

  5. Influences of Ice Crystal Number Concentrations and Habits on Arctic Mixed-Phase Cloud Dynamics

    Science.gov (United States)

    Komurcu, Muge

    2016-09-01

    Mixed-phase clouds are frequently present in the Arctic atmosphere, and strongly affect the surface energy budget. In this study, the influences of ice crystal number concentrations and crystal growth habits on the Arctic mixed-phase cloud microphysics and dynamics are investigated for internally and externally driven cloud systems using an eddy-resolving model. Separate simulations are performed with increasing ice concentrations and different ice crystal habits. It is found that the habit influence on cloud microphysics and dynamics is as pronounced as increasing the ice crystal concentrations for internally driven clouds and more dominant for externally driven clouds. Habit influence can lead to a 10 % reduction in surface incident longwave radiation flux. Sensitivity tests are performed to identify the interactions between processes affecting cloud dynamics that allow for persistent clouds (i.e., the radiative cooling at cloud top, ice precipitation stabilization at cloud-base). When cloud-base stabilization influences of ice precipitation are weak, cloud dynamics is more sensitive to radiative cooling. Additional sensitivity simulations are done with increasing surface latent and sensible heat fluxes to identify the influences of external forcing on cloud dynamics. It is found that the magnitude of cloud circulations for an externally driven cloud system with strong precipitation and weak surface fluxes is similar to a weakly precipitating, optically thick, internally driven cloud. For cloud systems with intense ice precipitation obtained through either increasing ice crystal concentrations or assuming ice crystal shapes that grow rapidly and fall fast, the cloud layer may collapse despite the moistening effect of surface fluxes.

  6. Determining Individual Phase Flow Properties in a Quench and Partitioning Steel with In Situ High-Energy X-Ray Diffraction and Multiphase Elasto-Plastic Self-Consistent Method

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Xiaohua; Choi, Kyoo Sil; Sun, Xin; Ren, Yang; Wang, Yangdong

    2016-02-26

    The micromechanical properties of the constituent phases were characterized for an advanced high strength steels (AHSS) produced by a quenching and partitioning (Q&P) process with in-situ tensile loading under Synchrotron-based high energy X-ray diffraction. The constituent phases present are retained austenite and three martensites (tempered, untempered and freshly formed martensites). For the material investigated, the 200 and 220 lattice strains of the retained austenite phase were calculated by examining the changes of the X-ray diffraction peak positions during deformation. The 200 and 211 lattice strains of the various martensitic phases with similar crystal structures were determined by separating their overlapped diffraction peaks. Apart from tempered and untempered martensite, the diffraction peaks of freshly formed martensite as a result of austenite to martensite transformation can also be able separated due to high initial austenite volume fraction. The phase stresses are first estimated with an empirical relationship through the X-ray diffraction elastic constants (XREC). A multi-phase elasto-plastic self constant model (EPSC) is next used for more accurate determination of the constitutive behaviors of the various phases by comparing the predicted lattice strain distributions and global stress-strain curves with the measured ones. The determined constitutive laws will be used for microstructure-based modeling for sheet formability of the Q&P AHSS steel.

  7. Stability of α-tocopherol in freeze-dried sugar-protein-oil emulsion solids as affected by water plasticization and sugar crystallization.

    Science.gov (United States)

    Zhou, Yankun; Roos, Yrjö H

    2012-08-01

    Water plasticization of sugar-protein encapsulants may cause structural changes and decrease the stability of encapsulated compounds during storage. The retention of α-tocopherol in freeze-dried lactose-milk protein-oil, lactose-soy protein-oil, trehalose-milk protein-oil, and trehalose-soy protein-oil systems at various water activities (a(w)) and in the presence of sugar crystallization was studied. Water sorption was determined gravimetrically. Glass transition and sugar crystallization were studied using differential scanning calorimetry and the retention of α-tocopherol spectrophotometrically. The loss of α-tocopherol followed lipid oxidation, but the greatest stability was found at 0 a(w) presumably because of α-tocopherol immobilization at interfaces and consequent reduction in antioxidant activity. A considerable loss of α-tocopherol coincided with sugar crystallization. The results showed that glassy matrices may protect encapsulated α-tocopherol; however, its role as an antioxidant at increasing aw accelerated its loss. Sugar crystallization excluded the oil-containing α-tocopherol from the protecting matrices and exposed it to surroundings, which decreased the stability of α-tocopherol.

  8. Crystallization of accessory phases in magmas by local saturation adjacent to phenocrysts

    Science.gov (United States)

    Bacon, C.R.

    1989-01-01

    Accessory minerals commonly occur attached to or included in the major crystalline phases of felsic and some intermediate igneous rocks. Apatite is particularly common as inclusions, but Fe-Ti oxides, pyrrhotite, zircon, monazite, chevkinite and xenotime are also known from silicic rocks. Accessories may nucleate near the host crystal/ liquid interface as a result of local saturation owing to formation of a differentiated chemical boundary layer in which accessory mineral solubility would be lower than in the surrounding liquid. Differentiation of this boundary layer would be greatest adjacent to ferromagnesian phenocrysts, especially Fe-Ti oxides; it is with oxides that accessories are most commonly associated in rocks. A boundary layer may develop if the crystal grows more rapidly than diffusion can transport incorporated and rejected elements to and from the phenocryst. Diffusion must dominate over convection as a mode of mass transfer near the advancing crystal/liquid interface in order for a boundary layer to exist. Accumulation of essential structural constituent elements of accessory minerals owing to their slow diffusion in evolved silicate melt also may force local saturation, but this is not a process that applies to all cases. Local saturation is an attractive mechanism for enhancing fractionation during crystallization differentiation. If accessory minerals attached to or included in phenocrysts formed because of local saturation, their host phenocrysts must have grown rapidly when accessories nucleated in comparison to lifetimes of magma reservoirs. Some inconsistencies remain in a local saturation origin for accessory phases that cannot be evaluated without additional information. ?? 1989.

  9. Comparison of measured and computed phase functions of individual tropospheric ice crystals

    Science.gov (United States)

    Stegmann, Patrick G.; Tropea, Cameron; Järvinen, Emma; Schnaiter, Martin

    2016-07-01

    Airplanes passing the incuda (lat. anvils) regions of tropical cumulonimbi-clouds are at risk of suffering an engine power-loss event and engine damage due to ice ingestion (Mason et al., 2006 [1]). Research in this field relies on optical measurement methods to characterize ice crystals; however the design and implementation of such methods presently suffer from the lack of reliable and efficient means of predicting the light scattering from ice crystals. The nascent discipline of direct measurement of phase functions of ice crystals in conjunction with particle imaging and forward modelling through geometrical optics derivative- and Transition matrix-codes for the first time allow us to obtain a deeper understanding of the optical properties of real tropospheric ice crystals. In this manuscript, a sample phase function obtained via the Particle Habit Imaging and Polar Scattering (PHIPS) probe during a measurement campaign in flight over Brazil will be compared to three different light scattering codes. This includes a newly developed first order geometrical optics code taking into account the influence of the Gaussian beam illumination used in the PHIPS device, as well as the reference ray tracing code of Macke and the T-matrix code of Kahnert.

  10. Orbital angular momentum light frequency conversion and interference with quasi-phase matching crystals

    CERN Document Server

    Zhou, Zhi-Yuan; Jiang, Yun-Kun; Li, Yan; Shi, Shuai; Wang, Xi-Shi; Shi, Bao-Sen; Guo, Guang-Can

    2014-01-01

    Light with helical phase structures, carrying quantized orbital angular momentum (OAM), has many applications in both classical and quantum optics, such as high-capacity optical communications and quantum information processing. Frequency conversion is a basic technique to expand the frequency range of fundamental light. The frequency conversion of OAM-carrying light gives rise to new physics and applications such as up-conversion detection of images and high dimensional OAM entanglements. Quasi-phase matching (QPM) nonlinear crystals are good candidates for frequency conversion, particularly for their high-valued effective nonlinear coefficients and no walk-off effect. Here we report the first experimental second-harmonic generation (SHG) of OAM light with a QPM crystal, where a UV light with OAM of 100 is generated. OAM conservation is verified using a specially designed interferometer. With a pump beam carrying an OAM superposition of opposite sign, we observed interesting interference phenomena in the SHG...

  11. Efficient broadband sum and difference frequency generation with a single chirped quasi-phase-matching crystal

    CERN Document Server

    Rangelov, Andon A

    2012-01-01

    We propose an efficient broadband frequency generation technique for two collinear optical parametric processes $\\omega_3=\\omega_1+\\omega_2$ and $\\omega_4=\\omega_1-\\omega_2$. It exploits chirped quasi-phase-matched gratings, which in the undepleted pump approximation regime perform population transfer that is analogous to adiabatic population transfer in a three-state ``vee'' quantum system. The energy of the input fields is transferred adiabatically either into $\\omega_3$ or $\\omega_4$ field, depending on which of the two phase matchings occurs first by the local modulation period in the crystal. One can switch the output between $\\omega_3$ and $\\omega_4$ by inverting the direction of the local modulation sweep, which corresponds to a rotation of the crystal by angle $\\pi$

  12. Experimental setup for investigating silicon solid phase crystallization at high temperatures.

    Science.gov (United States)

    Schmidt, Thomas; Gawlik, Annett; Schneidewind, Henrik; Ihring, Andreas; Andrä, Gudrun; Falk, Fritz

    2013-07-15

    An experimental setup is presented to measure and interpret the solid phase crystallization of amorphous silicon thin films on glass at very high temperatures of about 800 °C. Molybdenum-SiO(2)-silicon film stacks were irradiated by a diode laser with a well-shaped top hat profile. From the relevant thermal and optical parameters of the system the temperature evolution can be calculated accurately. A time evolution of the laser power was applied which leads to a temperature constant in time in the center of the sample. Such a process will allow the observation and interpretation of solid phase crystallization in terms of nucleation and growth in further work.

  13. Surface modes in "photonic cholesteric liquid crystal-phase plate-metal" structure.

    Science.gov (United States)

    Vetrov, S Ya; Pyatnov, M V; Timofeev, I V

    2014-05-01

    The light transmission spectrum has been calculated for a "cholesteric liquid crystal-phase plate-metal" structure. It is shown that the system can have an isolated waveguide surface mode with characteristics efficiently controllable by external fields acting on the cholesteric. The degree of localization of surface modes and the transmission coefficients have been found to differ considerably for the light of different polarizations.

  14. Optical trapping via guided resonance modes in a Slot-Suzuki-phase photonic crystal lattice.

    Science.gov (United States)

    Ma, Jing; Martínez, Luis Javier; Povinelli, Michelle L

    2012-03-12

    A novel photonic crystal lattice is proposed for trapping a two-dimensional array of particles. The lattice is created by introducing a rectangular slot in each unit cell of the Suzuki-Phase lattice to enhance the light confinement of guided resonance modes. Large quality factors on the order of 10⁵ are predicted in the lattice. A significant decrease of the optical power required for optical trapping can be achieved compared to our previous design.

  15. Berry Phase of Light under Bragg Reflection by Chiral Liquid-Crystal Media

    Science.gov (United States)

    Barboza, Raouf; Bortolozzo, Umberto; Clerc, Marcel G.; Residori, Stefania

    2016-07-01

    A Berry phase is revealed for circularly polarized light when it is Bragg reflected by a chiral liquid-crystal medium of the same handedness. By using a chiral nematic layer we demonstrate that if the input plane of the layer is rotated with respect to a fixed reference frame, a geometric phase effect occurs for the circularly polarized light reflected by the periodic helical structure of the medium. Theory and numerical simulations are supported by an experimental observation, disclosing novel applications in the field of optical manipulation and fundamental optical phenomena.

  16. Berry phase of light Bragg-reflected by chiral liquid crystal media

    CERN Document Server

    Barboza, Raouf; Residori, Stefania; Clerc, Marcel G

    2016-01-01

    Berry phase is revealed for circularly polarized light when it is Bragg-reflected by a chiral liquid crystal medium of the same handedness. By using a chiral nematic layer we demonstrate that if the input plane of the layer is rotated with respect to a fixed reference frame, then, a geometric phase effect occurs for the circularly polarized light reflected by the periodic helical structure of the medium. Theory and numerical simulations are supported by an experimental observation, disclosing novel applications in the field of optical manipulation and fundamental optical phenomena.

  17. Phase sensitivity to temperature of the guiding mode in polarization-maintaining photonic crystal fiber.

    Science.gov (United States)

    Song, Jingming; Sun, Kang; Li, Shuai; Cai, Wei

    2015-08-20

    The propagating phase changing of a polarization-maintaining photonic crystal fiber (PM-PCF) caused by temperature variation is theoretically studied, as well as compared with conventional PANDA fiber. As to verifying numerical analysis, a platform based on a Michelson interferometer for phase versus temperature measurement was built for both kinds of fiber. Experiments show that PM-PCF has similar temperature sensitivity with conventional polarization-maintaining fiber. With optimized PM-PCF design (thinner coating layer and coating material with smaller thermal expansion coefficient), the sensitivity could be further reduced to about 80% of the present level.

  18. Dynamical control and novel quantum phases in impurity doped linear ion crystals

    CERN Document Server

    Ivanov, Peter A; Singer, Kilian; Schmidt-Kaler, Ferdinand

    2010-01-01

    We explore the behavior of the phonon number distribution in an heterogeneous linear ion crystal. The presence of ion species with different masses changes dramatically the transverse energy spectrum, in such a way that two eigenfrequencies become non-analytic functions of the mass ratio in the form of a sharp cusp. This non-analyticity induces a quantum phase transition between condensed and conducting phase of the transverse local phonons. In order to continuously vary the mass ratio we adiabatically modify a locally applied laser field, exerting optical dipole forces which reduces the effective mass.

  19. Thick strings, the liquid crystal blue phase, and cosmological large-scale structure

    Science.gov (United States)

    Luo, Xiaochun; Schramm, David N.

    1992-01-01

    A phenomenological model based on the liquid crystal blue phase is proposed as a model for a late-time cosmological phase transition. Topological defects, in particular thick strings and/or domain walls, are presented as seeds for structure formation. It is shown that the observed large-scale structure, including quasi-periodic wall structure, can be well fitted in the model without violating the microwave background isotropy bound or the limits from induced gravitational waves and the millisecond pulsar timing. Furthermore, such late-time transitions can produce objects such as quasars at high redshifts. The model appears to work with either cold or hot dark matter.

  20. Phase diagram and enhanced electrical transport in KBr-NaBr mixed crystals

    Energy Technology Data Exchange (ETDEWEB)

    Manoravi, P. (Dept. of Physics, Indian Inst. of Tech., Kanpur (India)); Shahi, K. (Dept. of Physics, Indian Inst. of Tech., Kanpur (India) Material Science Program, Indian Inst. of Tech., Kanpur (India))

    1991-03-01

    Phase diagram and ionic conductivity of KBr-NaBr mixed crystals system have been studied over the entire composition and stable temperature range. A maximum conductivity enhancement by a factor of 25 with respect to pure KBr, and 8 with respect to pure NaBr, is obtained for the K{sub 0.5}Na{sub 0.5}Br solid solution at 500deg C. The conductivity values are found to follow the melting (solidus) temperature in a correlated manner. The minimum in the solidus curve of the phase diagram is observed between 43 and 72 mole% NaBr at 615deg C. (orig.).

  1. A 20MHz Low Phase-Noise 0.35μm CMOS Crystal Oscillator

    Institute of Scientific and Technical Information of China (English)

    GENG Jian-qiang; LAN Jia-long

    2005-01-01

    The design procedure of a CMOS process integrating Colpitts cr(ystal oscillator is described in detail by using the tools of Matlab and advanced design system (ADS). The small-signal analysis is performed both in the viewpoint of negative resistance and positive feedback. The analysis of condition for reliable start-up of oscillation and design guides for low phase noise is introduced. The measured phase noise is (172dBc/Hz@10 kHz and the power dissipation is 0.36 mW at power supply 3V.

  2. Fabrication and secondary-phase crystallization of rare-earth disilicate-silicon nitride ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Cinibulk, M.K.; Thomas, G. (Lawrence Berkeley Lab., CA (United States). Center for Advanced Materials); Johnson, S.M. (SRI International, Menlo Park, CA (United States). Materials Research Lab.)

    1992-08-01

    In this paper, the fabrication and intergranular-phase devitrification of silicon nitride densified with rare-earth (RE) oxide additives is investigated. The additions of the oxides of Sm, Gd, Dy, Er, and Yb, having high melting points and behaving similarly to Y[sub 2]O[sub 3], were compositionally controlled to tailor a microstructure with a crystalline secondary phase of RE[sub 2]Si[sub 2]O[sub 7]. The lanthanide oxides were found to be ass effective as Y[sub 2]O[sub 3] in densifying Si[sub 3]N[sub 4], resulting in identical microstructures and densities of 98-99% of theoretical density. The crystallization behavior of all six disilicates was similar, characterized by a limited nucleation and rapid growth mechanism resulting in large single crystals. Complete crystallization of the intergranular phase was obtained with the exception of a thin residual amorphous film which was observed at interfaces and believed to be rich in impurities, the cause of incomplete devitrification.

  3. Critical exponents for the cloud-crystal phase transition of charged particles in a Paul Trap

    CERN Document Server

    Weiss, D K; Blümel, R

    2015-01-01

    It is well known that charged particles stored in a Paul trap, one of the most versatile tools in atomic and molecular physics, may undergo a phase transition from a disordered cloud state to a geometrically well-ordered crystalline state (the Wigner crystal). In this paper we show that the average lifetime $\\bar\\tau_m$ of the metastable cloud state preceding the cloud $\\rightarrow$ crystal phase transition follows a powerlaw, $\\bar\\tau_m \\sim (\\gamma-\\gamma_c)^{-\\beta}$, $\\gamma>\\gamma_c$, where $\\gamma_c$ is the critical value of the damping constant $\\gamma$ at which the cloud $\\rightarrow$ crystal phase transition occurs. The critical exponent $\\beta$ depends on the trap control parameter $q$, but is independent of the number of particles $N$ stored in the trap and the trap control parameter $a$, which determines the shape (oblate, prolate, or spherical) of the cloud. For $q=0.15,0.20$, and $0.25$, we find $\\beta=1.20\\pm 0.03$, $\\beta=1.61\\pm 0.09$, and $\\beta=2.38\\pm 0.12$, respectively. In addition we f...

  4. Ground Based Retrievals of Small Ice Crystals and Water Phase in Arctic Cirrus

    Science.gov (United States)

    Mishra, Subhashree; Mitchell, David L.; DeSlover, Daniel

    2009-03-01

    The microphysical properties of cirrus clouds are uncertain due to the problem of ice particles shattering at the probe inlet upon sampling. To facilitate better estimation of small ice crystal concentrations in cirrus clouds, a new ground-based remote sensing technique has been used in combination with in situ aircraft measurements. Data from the Mixed-Phase Arctic Cloud Experiment (M-PACE), conducted at the north slope of Alaska (winter 2004), have been used to test a new method for retrieving the liquid water path (LWP) and ice water path (IWP) in mixed phase clouds. The framework of the retrieval algorithm consists of the modified anomalous diffraction approximation or MADA (for mixed phase cloud optical properties), a radar reflectivity-ice microphysics relationship and a temperature-dependent ice particle size distribution (PSD) scheme. Cloud thermal emission measurements made by the ground-based Atmospheric Emitted Radiance Interferometer (AERI) yield information on the total water path (TWP) while reflectivity measurements from the Millimeter Cloud Radar (MMCR) are used to derive the IWP. The AERI is also used to indicate the concentration of small ice crystals (DBeer's law absorption. While this is still a work in progress, the anticipated products from this AERI-radar retrieval scheme are the IWP, LWP, small-to-large ice crystal number concentration ratio and effective diameter for cirrus, as well as the ice particle number concentration for a given ice water content (IWC).

  5. Development of plastic elongation in nanocrystalline and amorphous Ni–W dual phase alloys by brushing technique

    Energy Technology Data Exchange (ETDEWEB)

    Nakayama, S., E-mail: 00sm.uk0806@gmail.com; Adachi, H., E-mail: adachi@eng.u-hyogo.ac.jp; Yamasaki, T., E-mail: yamasaki@eng.u-hyogo.ac.jp

    2015-09-15

    Highlights: • A novel agitation technique called the brushing technique is proposed. • A homogeneous material can be obtained with the brushing technique. • The brushed material exhibits large plastic elongation with work hardening. - Abstract: A novel agitation technique, referred to as the “brushing technique” is proposed to treat the surface of a Ni–W alloy film during electrodeposition. This technique was developed to directly remove hydrogen bubbles on the film surface and to apply Ni ions to the interfacial layer with the substrate. The intrinsic mechanical properties of the Ni–W electrodeposits are then evaluated with respect to application. High resolution transmission electron microscopy observations revealed that both treated and untreated films have nanocrystallites of approximately 5 nm in diameter and an amorphous phase. There was a compositional difference of about. 1.4 at% W between the face side and the reverse side of the film that was not subjected to the brushing technique, whereas this difference was absent in the film subjected to the brushing technique. In addition, the brushing technique reduced the surface roughness of the film and decreased the number of defects. As a result, a large plastic strain of about. 2.9% was observed with work hardening under tensile testing.

  6. Optimal design for hetero-associative memory: hippocampal CA1 phase response curve and spike-timing-dependent plasticity.

    Directory of Open Access Journals (Sweden)

    Ryota Miyata

    Full Text Available Recently reported experimental findings suggest that the hippocampal CA1 network stores spatio-temporal spike patterns and retrieves temporally reversed and spread-out patterns. In this paper, we explore the idea that the properties of the neural interactions and the synaptic plasticity rule in the CA1 network enable it to function as a hetero-associative memory recalling such reversed and spread-out spike patterns. In line with Lengyel's speculation (Lengyel et al., 2005, we firstly derive optimally designed spike-timing-dependent plasticity (STDP rules that are matched to neural interactions formalized in terms of phase response curves (PRCs for performing the hetero-associative memory function. By maximizing object functions formulated in terms of mutual information for evaluating memory retrieval performance, we search for STDP window functions that are optimal for retrieval of normal and doubly spread-out patterns under the constraint that the PRCs are those of CA1 pyramidal neurons. The system, which can retrieve normal and doubly spread-out patterns, can also retrieve reversed patterns with the same quality. Finally, we demonstrate that purposely designed STDP window functions qualitatively conform to typical ones found in CA1 pyramidal neurons.

  7. Constitutive Relations Analyses of Plastic Flow in Dual-Phase Steels to Elucidate Structure-Strength-Ductility Correlations

    Science.gov (United States)

    Saimoto, S.; Timokhina, I. B.; Pereloma, E. V.

    2017-07-01

    The structure-strength characterization is typically performed by correlating the structure with x-ray, electron, or atomic imaging devices to the bulk mechanical tensile parameters of yield stress and the plastic yielding response. The problem is that structure parameters embedded in the stress-strain data cannot be revealed without an analyzable constitutive relation. New functional slip-based constitutive formulation with precise digital fitting parameters can replicate the measured data with at least two loci. Thus, this study examines the possibility of identifying the mechanical response as a result of the various microstructure components. The key parameter, the mean slip distance, can be calibrated from the initial work-hardening slope at 0.2% strain from which all the fit parameters can be determined. In this process, a newly derived friction stress is defined to separate the yield phenomenon from the plastic strains beyond yield-point elongation. This methodology has been applied to dual-phase steel specimens that resulted in excellent predictive correlations with prior structure-strength characterization. Hence, the structure-strength-ductility changes resulting from processing conditions can be more precisely surmised from mechanical testing. Thus, a method to delineate the nanostructure evolution with deformation using mesoscopic mechanical parameters has been introduced.

  8. Phase transition, phase transition mechanism and crystal structure of a new compound-Ca2FeWO6

    Institute of Scientific and Technical Information of China (English)

    傅正民; 李文秀

    1995-01-01

    A new compound Ca2FeWO6 has been synthesized by solid state sintering. The phase transition of this compound was investigated by means of differential thermal analysis (DTA), X-ray powder diffraction and other methods. It is discovered that the compound has a displacive phase transition of the first order at (706±5)℃. The low temperature phase. α-Ca2FeWO6. belongs to orthorhombic system, with space group Pmm2. Its lattice parameters at room temperature are; a = 0.77051 nm, 6=0.54242nm and r = 0.551 08 nm, the measured density is Dm = 6.04g/cm3, and each unit cell contains two formula weight. The high temperature phase, β-Ca2FeWO6, belongs to the cubic system, with space group Fm3m and the lattice parameter is a = 0.780 8 nm at 750℃, z = 4. The calculated density is Dx = 5.802g/cm3, The crystal structures of α-Ca2FeWO6 and β-Ca2FeWO6 were also determined by means of the X-ray polycrystal diffraction method. The phase transition mechanism is expounded in detail.

  9. Phase sensitive properties and coherent manipulation of a photonic crystal microcavity.

    Science.gov (United States)

    Quiring, Wadim; Jonas, Björn; Förstner, Jens; Rai, Ashish K; Reuter, Dirk; Wieck, Andreas D; Zrenner, Artur

    2016-09-05

    We present phase sensitive cavity field measurements on photonic crystal microcavities. The experiments have been performed as autocorrelation measurements with ps double pulse laser excitation for resonant and detuned conditions. Measured E-field autocorrelation functions reveal a very strong detuning dependence of the phase shift between laser and cavity field and of the autocorrelation amplitude of the cavity field. The fully resolved phase information allows for a precise frequency discrimination and hence for a precise measurement of the detuning between laser and cavity. The behavior of the autocorrelation amplitude and phase and their detuning dependence can be fully described by an analytic model. Furthermore, coherent control of the cavity field is demonstrated by tailored laser excitation with phase and amplitude controlled pulses. The experimental proof and verification of the above described phenomena became possible by an electric detection scheme, which employs planar photonic crystal microcavity photo diodes with metallic Schottky contacts in the defect region of the resonator. The applied photo current detection was shown to work also efficiently at room temperature, which make electrically contacted microcavities attractive for real world applications.

  10. Stabilizing the spin vortex crystal phase in two-dimensional iron-based superconductors

    Science.gov (United States)

    O'Halloran, Joseph; Agterberg, D. F.; Chen, M. X.; Weinert, M.

    2017-02-01

    We present an investigation of the magnetic structure for iron-based superconductors (FeSCs) when inversion symmetry is broken, such as in substrate-supported monolayers or in the presence of a c -axis electric field. We perform group-, mean-field-, and density-functional-theoretic analyses on a model system of monolayer iron selenide (FeSe) on a strontium titanate [SrTiO3 (001)] substrate. Our group- and mean-field-theoretic calculations are more generally applicable to thin films of the rest of the 11 (e.g., FeSe) family of iron-based superconductors, as well as to thin films of the 111 (e.g., LiFeAs) and 1111 (e.g., LaOFeAs) families, as these all belong to the same space group. We find that in systems with a collinear antiferromagnetic phase in bulk, when inversion symmetry is broken, the transition is instead into a "spin vortex crystal" phase and that a further phase transition can occur at a lower temperature in some circumstances. The spin vortex crystal is a C4-symmetric magnetic phase which is related to this parent C2-symmetric collinear antiferromagnetic (stripe) phase which is ubiquitous among the iron-based superconductors.

  11. Phase-resolved pulse propagation through metallic photonic crystal slabs: plasmonic slow light.

    Science.gov (United States)

    Schönhardt, Anja; Nau, Dietmar; Bauer, Christina; Christ, André; Gräbeldinger, Hedi; Giessen, Harald

    2017-03-28

    We characterized the electromagnetic field of ultra-short laser pulses after propagation through metallic photonic crystal structures featuring photonic and plasmonic resonances. The complete pulse information, i.e. the envelope and phase of the electromagnetic field, was measured using the technique of cross-correlation frequency resolved optical gating. In good agreement, measurements and scattering matrix simulations show a dispersive behaviour of the spectral phase at the position of the resonances. Asymmetric Fano-type resonances go along with asymmetric phase characteristics. Furthermore, the spectral phase is used to calculate the dispersion of the sample and possible applications in dispersion compensation are investigated. Group refractive indices of 700 and 70 and group delay dispersion values of 90 000 fs(2) and 5000 fs(2) are achieved in transverse electric and transverse magnetic polarization, respectively. The behaviour of extinction and spectral phase can be understood from an intuitive model using the complex transmission amplitude. An associated depiction in the complex plane is a useful approach in this context. This method promises to be valuable also in photonic crystal and filter design, for example, with regards to the symmetrization of the resonances.This article is part of the themed issue 'New horizons for nanophotonics'. © 2017 The Author(s).

  12. Microscopic Theory of Blue Phases Ⅰ and Ⅱ of Liquid Crystal

    Institute of Scientific and Technical Information of China (English)

    LIU Jian-Jun; YANG Guo-Chen; SHEN Man

    2004-01-01

    The microscopic theory of the blue phases of chiral liquid crystal is proposed. Beginning with the potential between two molecules, by using the cell model of liquid, applying statistical physical method, the distribution function and the free energy of the system are obtained. By using variational approach and zero-order approximation, the differential equation that the order parameter tensor of the blue phase can satisfy is obtained. Then we change the differential equation to the eigenequation problem in quantum mechanics. Considering the symmetry of the blue phases,the order parameter tensors of blue phases Ⅰ and Ⅱ can be made up of the eigenvectors. Our results are the same as the results of Ginzberg-Landau's phenomenological theory. The parameters in the order parameter tensors that we calculate in the located system are close to the predecessors' results.

  13. Microscopic Theory of Blue Phases Ⅰ and Ⅱ of Liquid Crystal

    Institute of Scientific and Technical Information of China (English)

    LIUJian-Jun; YANGGuo-Chen; SHENMan

    2004-01-01

    The microscopic theory of the blue phases of chiral liquid crystal is proposed. Beginning with the potential between two molecules, by using the cell model of liquid, applying statistical physical method, the distribution function and the free energy of the system are obtained. By using variational approach and zero-order approximation, the differential equation that the order parameter tensor of the blue phase can satisfy is obtained. Then we change the differential equation to the eigenequation problem in quantum mechanics. Considering the symmetry of the blue phases, the order parameter tensors of blue phases Ⅰ and Ⅱ can be made up of the eigenvectors. Our results are the same as the results of Ginzberg-Landau's phenomenological theory. The parameters in the order parameter tensors that we calculate in the located system are close to the predecessors' results.

  14. A-site deficiency, phase purity and crystal structure in lanthanum strontium ferrite powders

    Energy Technology Data Exchange (ETDEWEB)

    Striker, T.; Ruud, J.A.; Gao, Y.; Heward, W.J. [GE Global Research Center, One Research Circle, Niskayuna, NY 12309 (United States); Steinbruchel, C. [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States)

    2007-07-31

    Lanthanum strontium ferrite (LSF) powders of average composition of (La{sub 1-x'} Sr{sub x'}){sub y'}FeO{sub 3+{delta}}, were fabricated over a range of average strontium composition between 0.2 {<=} x' {<=} 0.5 and average A-site occupancy between 0.8 {<=} y' {<=} 1.0. Samples that were originally determined to be perovskite phase pure using X-ray diffraction with CuK{sub {alpha}} radiation were found to have significant amounts of non-perovskite phases when evaluated using high-energy synchrotron radiation. As-fabricated samples with nominal A-site deficiency, y' < 1, contained a hexaferrite phase. When treated at 955 C in pO{sub 2} = 10{sup -} {sup 10} atm, those samples contained magnetite. The actual composition of the perovskite phase was corrected to account for the presence of the second phases through mass balance calculations. As a result, the actual A-site deficiency of the perovskite phase was much lower than the average value of the bulk powder. For as-fabricated powders with x' < 0.4, it was determined that the A-site deficient LSF perovskite phases were metastable. At equilibrium, a mixture of A-site stoichiometric perovskite and hexaferrite phases was present. The refined perovskite crystal structures and unit cell volumes were consistent with literature trends. (author)

  15. Microstructure and Phase Stability of Single Crystal NiAl Alloyed with Hf and Zr

    Science.gov (United States)

    Locci, I. E.; Dickerson, R. M.; Garg, A.; Noebe, R. D.; Whittenberger, J. D.; Nathal, M. V.; Darolia, R.

    1996-01-01

    Six near stoichiometric, NiAl single-crystal alloys, with 0.05-1.5 at.% of Hf and Zr additions plus Si impurities, were microstructurally analyzed in the as-cast, homogenized, and aged conditions. Hafnium-rich interdendritic regions, containing the Heusler phase (Ni2AlHf), were found in all the as-cast alloys containing Hf. Homogenization heat treatments partially reduced these interdendritic segregated regions. Transmission electron microscopy (TEM) observations of the as-cast and homogenized microstructures revealed the presence of a high density of fine Hf (or Zr) and Si-rich precipitates. These were identified as G-phase, Nil6X6Si7, or as an orthorhombic NiXSi phase, where X is Hf or Zr. Under these conditions the expected Heusler phase (beta') was almost completely absent. The Si responsible for the formation of the G and NiHfSi phases is the result of molten metal reacting with the Si-containing crucible used during the casting process. Varying the cooling rates after homogenization resulted in the refinement or complete suppression of the G and NiHfSi phases. In some of the alloys studied, long-term aging heat treatments resulted in the formation of Heusler precipitates, which were more stable at the aging temperature and coarsened at the expense of the G-phase. In other alloys, long-term aging resulted in the formation of the NiXSi phase. The stability of the Heusler or NiXSi phases can be traced to the reactive element (Hf or Zr) to silicon ratio. If the ratio is high, then the Heusler phase appears stable after long time aging. If the ratio is low, then the NiHfSi phase appears to be the stable phase.

  16. An Experimental Study on the Thermal Performance of Phase-Change Material and Wood-Plastic Composites for Building Roofs

    Directory of Open Access Journals (Sweden)

    Min Hee Chung

    2017-02-01

    Full Text Available We assessed the usefulness of phase-change material (PCM-based thermal plates fabricated from wood-plastic composites (WPCs in mitigating the urban heat island effect. The thermal performance of plates containing PCMs with two different melting temperatures and with two different albedo levels was evaluated. The results showed that the PCM with a melting temperature of 44 °C maintained lower surface and inner temperatures than the PCM with a melting temperature of 25 °C. Moreover, a higher surface albedo resulted in a lower surface temperature. However, the thermal performance of PCMs with different melting temperatures but the same surface albedo did not differ. Using PCM-based materials in roof finishing materials can reduce surface temperatures and improve thermal comfort.

  17. Determining Individual Phase Flow Properties in a Quench and Partitioning Steel with In Situ High-Energy X-Ray Diffraction and Multiphase Elasto-Plastic Self-Consistent Method

    Science.gov (United States)

    Hu, Xiaohua; Choi, Kyoo Sil; Sun, Xin; Ren, Yang; Wang, Yangdong

    2016-12-01

    The micromechanical properties of the constituent phases were characterized for advanced high-strength steels (AHSS) produced by a quenching and partitioning (Q&P) process with in situ tensile loading under synchrotron-based, high-energy X-ray diffraction. The constituent phases present are retained austenite and three martensites (tempered, untampered, and freshly formed martensites). For the material investigated, the 200 and 220 lattice strains of the retained austenite phase were calculated by examining the changes of the X-ray diffraction peak positions during deformation. The 200 and 211 lattice strains of the various martensitic phases with similar crystal structures were determined by separating their overlapped diffraction peaks. Apart from tempered and untempered martensite, the diffraction peaks of freshly formed martensite as a result of austenite-to-martensite transformation can also be separated due to a high initial austenite volume fraction. The phase stresses are first estimated with an empirical relationship through the X-ray diffraction elastic constants. A multiphase elasto-plastic self-consistent model is next used for more accurate determination of the constitutive behaviors of the various phases by comparing the predicted lattice strain distributions and global stress-strain curves with the measured ones. The determined constitutive laws will be used for microstructure-based modeling for sheet formability of the Q&P AHSS steel.

  18. Polymer-stabilized blue phase liquid crystal display with slanted wall-shaped electrodes

    Institute of Scientific and Technical Information of China (English)

    Feng Zhou; Qionghua Wang; Di Wu; Jianpeng Cui

    2012-01-01

    A polymer-stabilized blue phase liquid crystal display (BPLCD) with slanted wall-shaped electrodes is proposed. Compared with the traditional BPLCD with wall-shaped electrodes, the electrodes of the proposed BPLCD are slightly angled to obtain phase retardation in the entire cell even at the position of electrodes. The proposed BPLCD demonstrates a relatively higher average transmittance and overall brightness than the traditional BPLCD.%A polymer-stabilized blue phase liquid crystal display (BPLCD) with slanted wall-shaped electrodes is proposed.Compared with the traditional BPLCD with wall-shaped electrodes,the electrodes of the proposed BPLCD are slightly angled to obtain phase retardation in the entire cell even at the position of electrodes.The proposed BPLCD demonstrates a relatively higher average transmittance and overall brightness than the traditional BPLCD.Owing to the continuous improvement in image quality of liquid crystal displays (LCDs),they have been widely employed in desktop monitors,TVs,and mobile displays at present[1-5].With the development of LCDs the polymer-stabilized blue phase LCDs (BPLCDs)[6-11]can replace the conventional LCDs and become the nextgeneration display technology.The polymer-stabilized BPLCDs have numerous attractive features,such as submillisecond gray-to-gray response time,alignmentlayer-free process optically isotropic dark state and cell gap insensitivity[12-14].Because of these advantages,the fabrication processes of the BPLCDs are simplified,motion-image blurs are reduced,and color-sequential displays using RGB LEDs are enabled.

  19. Influence of downsizing of zeolite crystals on the orthorhombic ↔ monoclinic phase transition in pure silica MFI-type

    Science.gov (United States)

    Kabalan, Ihab; Michelin, Laure; Rigolet, Séverinne; Marichal, Claire; Daou, T. Jean; Lebeau, Bénédicte; Paillaud, Jean-Louis

    2016-08-01

    The impact of crystal size on the transition orthorhombic ↔ monoclinic phase in MFI-type purely silica zeolites is investigated between 293 and 473 K using 29Si MAS NMR and powder X-ray diffraction. Three silicalite-1 zeolites are synthesized: a material constituted of micron-sized crystals, pseudospherical nanometer-sized crystals and hierarchical porous zeolites with a mesoporous network created by the use of a gemini-type diquaternary ammonium surfactant giving nanosheet zeolites. Our results show for the first time that the orthorhombic ↔ monoclinic phase transition already known for micron-sized particles also occurs in nanometer-sized zeolite crystals whereas our data suggest that the extreme downsizing of the zeolite crystal to one unit cell in thickness leads to an extinction of the phase transition.

  20. Phase transitions in quantum crystals : on growth of magnetically ordered 3He and a search for supersolid 4He

    NARCIS (Netherlands)

    Bueno, Juan

    2007-01-01

    Due to its rich magnetic phase diagram and its superfluidity, 3He is a very interesting system if magnetic effects on the crystal growth mechanisms want to be studied. Solid 3He orders magnetically into the U2D2 phase (an antiferromagnetic phase with two planes of spins pointing up and two planes o

  1. Novelty-Induced Phase-Locked Firing to Slow Gamma Oscillations in the Hippocampus: Requirement of Synaptic Plasticity.

    Science.gov (United States)

    Kitanishi, Takuma; Ujita, Sakiko; Fallahnezhad, Mehdi; Kitanishi, Naomi; Ikegaya, Yuji; Tashiro, Ayumu

    2015-06-03

    Temporally precise neuronal firing phase-locked to gamma oscillations is thought to mediate the dynamic interaction of neuronal populations, which is essential for information processing underlying higher-order functions such as learning and memory. However, the cellular mechanisms determining phase locking remain unclear. By devising a virus-mediated approach to perform multi-tetrode recording from genetically manipulated neurons, we demonstrated that synaptic plasticity dependent on the GluR1 subunit of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionate) receptor mediates two dynamic changes in neuronal firing in the hippocampal CA1 area during novel experiences: the establishment of phase-locked firing to slow gamma oscillations and the rapid formation of the spatial firing pattern of place cells. The results suggest a series of events potentially underlying the acquisition of new spatial information: slow gamma oscillations, originating from the CA3 area, induce the two GluR1-dependent changes of CA1 neuronal firing, which in turn determine information flow in the hippocampal-entorhinal system.

  2. Photo-Induced Phase Transitions to Liquid Crystal Phases: Influence of the Chain Length from C8E4 to C14E4

    Directory of Open Access Journals (Sweden)

    Simone Techert

    2009-09-01

    Full Text Available Photo-induced phase transitions are characterized by the transformation from phase A to phase B through the absorption of photons. We have investigated the mechanism of the photo-induced phase transitions of four different ternary systems CiE4/alkane (i with n = 8, 10, 12, 14; cyclohexane/H2O. We were interested in understanding the effect of chain length increase on the dynamics of transformation from the microemulsion phase to the liquid crystal phase. Applying light pump (pulse/x-ray probe (pulse techniques, we could demonstrate that entropy and diffusion control are the driving forces for the kind of phase transition investigated.

  3. Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions

    Science.gov (United States)

    Honorato Rios, Camila; Kuhnhold, Anja; Bruckner, Johanna; Dannert, Rick; Schilling, Tanja; Lagerwall, Jan

    2016-05-01

    The cholesteric liquid crystal self-assembly of water-suspended cellulose nanocrystal (CNC) into a helical arrangement was observed already more than 20 years ago and the phenomenon was used to produce iridescent solid films by evaporating the solvent or via sol-gel processing. Yet it remains challenging to produce optically uniform films and to control the pitch reproducibly, reflecting the complexity of the three-stage drying process that is followed in preparing the films. An equilibrium liquid crystal phase formation stage is followed by a non-equilibrium kinetic arrest, which in turn is followed by structural collapse as the remaining solvent is evaporated. Here we focus on the first of these stages, combining a set of systematic rheology and polarizing optics experiments with computer simulations to establish a detailed phase diagram of aqueous CNC suspensions with two different values of the surface charge, up to the concentration where kinetic arrest sets in. We also study the effect of varying ionic strength of the solvent. Within the cholesteric phase regime, we measure the equilibrium helical pitch as a function of the same parameters. We report a hitherto unnoticed change in character of the isotropic-cholesteric transition at increasing ionic strength, with a continuous weakening of the first-order character up to the point where phase coexistence is difficult to detect macroscopically due to substantial critical fluctuations.

  4. Phase singularities in 3D plasmonic crystal metamaterials for ultra-sensitive biosensing

    Science.gov (United States)

    Danilov, Artem; Aristov, Andrey I.; Manousidaki, Maria; Terzaki, Konstantina; Fotakis, Costas; Farsari, Maria; Kabashin, Andrei V.

    2017-02-01

    Plasmonic biosensors form the core label-free technology for studies of biomolecular interactions, but they still need a drastic improvement of sensitivity and novel nano-architectural implementations to match modern trends of nanobiotechnology. Here, we consider the generation of resonances in light reflected from 3D woodpile plasmonic crystal metamaterials fabricated by Direct Laser Writing by Multi-Photon Polymerization, followed by silver electroless plating. We show that the generation of these resonances is accompanied by the appearance of singularities of phase of reflected light and examine the response of phase characteristics to refractive index variations inside the metamaterial matrix. The recorded phase sensitivity (3*104 deg. of phase shift per RIU change) outperforms most plasmonic counterparts and is attributed to particular conditions of plasmon excitation in 3D plasmonic crystal geometry. Combined with a large surface for biomolecular immobilizations offered by the 3D woodpile matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology.

  5. Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions

    Directory of Open Access Journals (Sweden)

    Camila eHonorato Rios

    2016-05-01

    Full Text Available The cholesteric liquid crystal self-assembly of water-suspended cellulose nanocrystal (CNC into a helical arrangement was observed already more than 20 years ago and the phenomenon was used to produce iridescent solid films by evaporating the solvent or via sol-gel processing. Yet it remains challenging to produce optically uniform films and to control the pitch reproducibly, reflecting the complexity of the three-stage drying process that is followed in preparing the films. An equilibrium liquid crystal phase formation stage is followed by a non-equilibrium kinetic arrest, which in turn is followed by structural collapse as the remaining solvent is evaporated. Here we focus on the first of these stages, combining a set of systematic rheology and polarizing optics experiments with computer simulations to establish a detailed phase diagram of aqueous CNC suspensions with two different values of the surface charge, up to the concentration where kinetic arrest sets in. We also study the effect of varying ionic strength of the solvent. Within the cholesteric phase regime, we measure the equilibrium helical pitch as a function of the same parameters. We report a hitherto unnoticed change in character of the isotropic-cholesteric transition at increasing ionic strength, with a continuous weakening of the first-order character up to the point where phase coexistence is difficult to detect macroscopically due to substantial critical fluctuations.

  6. Effects of Alloying Elements on the Concentration Profile of Equilibrium Phases in Transformation Induced Plasticity Steel

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    With the two sublattices model, equilibrium compositions of ferrite (α) and austenite (γ) phases, as well as thevolume percent of austenite (γ) in different TRIP steels are calculated. Concentration profiles of carbon, manganese,aluminum and silicon in these steels are also estimated under the lattice fixed frame of reference so as to identifyif the equilibrium state is obtained. Through the comparison between the profiles after different time diffusion, thedistribution of elements in phases is exhibited and the complex effect due to the mutual interaction of the elementson diffusion is discussed.

  7. Epitaxial growth of three dimensionally structured III-V photonic crystal via hydride vapor phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Qiye; Kim, Honggyu; Zhang, Runyu; Zuo, Jianmin; Braun, Paul V., E-mail: pbraun@illinois.edu [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Sardela, Mauro [Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Balaji, Manavaimaran; Lourdudoss, Sebastian; Sun, Yan-Ting [Laboratory of Semiconductor Materials, Department of Materials and Nano Physics, Royal Institute of Technology (KTH), Electrum 229, 164 40 Kista (Sweden)

    2015-12-14

    Three-dimensional (3D) photonic crystals are one class of materials where epitaxy, and the resultant attractive electronic properties, would enable new functionalities for optoelectronic devices. Here we utilize self-assembled colloidal templates to fabricate epitaxially grown single crystal 3D mesostructured Ga{sub x}In{sub 1−x}P (GaInP) semiconductor photonic crystals using hydride vapor phase epitaxy (HVPE). The epitaxial relationship between the 3D GaInP and the substrate is preserved during the growth through the complex geometry of the template as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy. XRD reciprocal space mapping of the 3D epitaxial layer further demonstrates the film to be nearly fully relaxed with a negligible strain gradient. Fourier transform infrared spectroscopy reflection measurement indicates the optical properties of the photonic crystal which agree with finite difference time domain simulations. This work extends the scope of the very few known methods for the fabrication of epitaxial III-V 3D mesostructured materials to the well-developed HVPE technique.

  8. Liquid crystalline phase as a probe for crystal engineering of lactose: carrier for pulmonary drug delivery.

    Science.gov (United States)

    Patil, Sharvil S; Mahadik, Kakasaheb R; Paradkar, Anant R

    2015-02-20

    The current work was undertaken to assess suitability of liquid crystalline phase for engineering of lactose crystals and their utility as a carrier in dry powder inhalation formulations. Saturated lactose solution was poured in molten glyceryl monooleate which subsequently transformed into gel. The gel microstructure was analyzed by PPL microscopy and SAXS. Lactose particles recovered from gels after 48 h were analyzed for polymorphism using techniques such as FTIR, XRD, DSC and TGA. Particle size, morphology and aerosolisation properties of prepared lactose were analyzed using Anderson cascade impactor. In situ seeding followed by growth of lactose crystals took place in gels with cubic microstructure as revealed by PPL microscopy and SAXS. Elongated (size ∼ 71 μm) lactose particles with smooth surface containing mixture of α and β-lactose was recovered from gel, however percentage of α-lactose was more as compared to β-lactose. The aerosolisation parameters such as RD, ED, %FPF and % recovery of lactose recovered from gel (LPL) were found to be comparable to Respitose® ML001. Thus LC phase (cubic) can be used for engineering of lactose crystals so as to obtain particles with smooth surface, high elongation ratio and further they can be used as carrier in DPI formulations.

  9. Liquid phase crystallized silicon on glass: Technology, material quality and back contacted heterojunction solar cells

    Science.gov (United States)

    Haschke, Jan; Amkreutz, Daniel; Rech, Bernd

    2016-04-01

    Liquid phase crystallization has emerged as a novel approach to grow large grained polycrystalline silicon films on glass with high electronic quality. In recent years a lot of effort was conducted by different groups to determine and optimize suitable interlayer materials, enhance the crystallographic quality or to improve post crystallization treatments. In this paper, we give an overview on liquid phase crystallization and describe the necessary process steps and discuss their influence on the absorber properties. Available line sources are compared and different interlayer configurations are presented. Furthermore, we present one-dimensional numerical simulations of a rear junction device, considering silicon absorber thicknesses between 1 and 500 µm. We vary the front surface recombination velocity as well as doping density and minority carrier lifetime in the absorber. The simulations suggest that a higher absorber doping density is beneficial for layer thicknesses below 20 µm or when the minority carrier lifetime is short. Finally, we discuss possible routes for device optimization and propose a hybride cell structure to circumvent current limitations in device design.

  10. Pressure-induced phase transitions in organic molecular crystals: a combination of x-ray single-crystal and powder diffraction, raman and IR-spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Boldyreva, E V; Goryainov, S V; Seryotkin, Y V; Kolesnik, E N; Shakhtshneider, T P; Ivashevskaya, S N; Drebushchak, T N [Research and Education Center ' Molecular Design and Ecologically Safe Technologies' , REC-008, Novosibirsk State University (Russian Federation); Sowa, H [Goettingen University (Germany); Ahsbahs, H; Chernyshev, V V [Marburg University (Germany); Dmitriev, V P [Swiss-Norwegian Beamline ESRF, Grenoble (France)], E-mail: boldyrev@nsu.ru

    2008-07-15

    The contribution summarizes the results of recent studies of phase transitions induced by high pressure in a number of molecular organic crystals, such as polymorphs of paracetamol, chlorpropamide, polymorphs of glycine, L- and DL-serine, {beta}-alanine. The main attention is paid to the following topics: (1) Reversible / irreversible transformations; (2) Different behavior of single crystals / powders; (3) The role of pressure-transmitting liquid; (4) The role of the kinetic factors: phase transitions on decompression, or after a long storage at a selected pressure; (5) Isosymmetric phase transitions; (6) The role of the changes in the hydrogen bond networks / intramolecular conformational changes in the phase transitions; (7) Superstructures / nanostructures formed as a result of pressure-induced phase transitions.

  11. High-energy Few-cycle Pulses Directly Generated from Strongly Phase-mismatched Lithium Niobate Crystal

    DEFF Research Database (Denmark)

    Zhou, Binbin; Chong, A.; Wise, F.W.;

    2012-01-01

    We show that effective soliton compression can be realized in strongly phase-mismatched quadratic media. Sub-15 fs pulses are experimentally generated directly from 10-mm-long bulk lithium niobate crystal by 120-fs input pulses at 1300 nm.......We show that effective soliton compression can be realized in strongly phase-mismatched quadratic media. Sub-15 fs pulses are experimentally generated directly from 10-mm-long bulk lithium niobate crystal by 120-fs input pulses at 1300 nm....

  12. On the relationship between Bloch modes and phase-related refractive index of photonic crystals.

    Science.gov (United States)

    Sun, Guilin; Kirk, Andrew G

    2007-10-01

    It has previously been shown that the phase-related refractive index is positive in photonic crystals that display negative refraction at higher bands. We hypothesize that the phase velocity is governed by a wave that can be related to the dominant Bloch mode. This dominant wave can be identified from an approximate solution of Maxwell Equations using a homogeneously averaged dielectric constant and the dominant wavevector is related to the fundamental wavevector and the reciprocal lattice vectors. We validate this hypothesis by numerical Fourier decomposition of the field in the entire simulation domain. It confirms that for negative refraction at higher bands, the phase-related refractive index is indeed positive and differs significantly from the negative value of effective refractive index calculated from the band structure.

  13. Atomistic simulation of fcc-bcc phase transition in single crystal A1 under uniform compression

    Institute of Scientific and Technical Information of China (English)

    Li Li; Shao Jian-Li; Li Yan-Fang; Duan Su-Qing; [ Liang Jiu-Qing

    2012-01-01

    By molecular dynamics simulations employing an embedded atom model potential,we investigate the fcc-to-bcc phase transition in single crystal Al,caused by uniform compression.Results show that the fec structure is unstable when the pressure is over 250 GPa,in reasonable agreement with the calculated value through the density functional theory.The morphology evolution of the structural transition and the corresponding transition mechanism are analysed in detail.The bec (011) planes are transited from the fcc (11(1)) plane and the (1(1)1) plane.We suggest that the transition mechanism consists mainly of compression,shear,slid and rotation of the lattice.In addition,our radial distribution function analysis explicitly indicates the phase transition of A1 from fcc phase to bcc structure.

  14. Phase relations and crystal structures in the system Ta-V-Ge.

    Science.gov (United States)

    Khan, Atta U; Bursik, J; Rogl, P

    2012-05-28

    Phase equilibria have been derived for the isothermal section of the Ta-V-Ge system at 1500 °C (for concentrations phases have been identified within the isothermal section, out of which three were characterized by Rietveld refinement of X-ray powder diffraction data. τ(1)-(Ta(1-x)V(x))(5)Ge(3) (0.21 ≤ x ≤ 0.63) adopts the Mn(5)Si(3)-type and τ(2)-Ta(Ta(x)V(1-x-y)Ge(y))(2), x = 0.02, y = 0.12 was found to be a MgZn(2)-type Laves phase. Detailed transmission electron microscopy (TEM) in several crystallographic directions confirmed lattice parameters and crystal symmetry of this phase and rejected the presence of any superstructure. τ(3)-Ta(9-x+y)V(4+x-y-z)Ge(1+z), x = 0.32, y = 0.51, z = 0.98 crystallizes with the Nb(9)Co(4)Ge-type, whereas the structure of τ(4) is not yet known. Although a MgCu(2)-type cubic Laves phase is not present in the Ta-V binary at this temperature, additions of Ge stabilize this phase in the ternary system: C15-Ta(Ta(x)V(1-x-y)Ge(y))(2), x = 0.04, y = 0.05. V(11)Ge(8) (Cr(11)Ge(8) type) shows a large solubility up to (Ta(x)V(1-x))(11)Ge(8), x = 0.64 at 1500 °C.

  15. Effects of ice crystals on the FSSP measurements in mixed phase clouds

    Directory of Open Access Journals (Sweden)

    G. Febvre

    2012-03-01

    Full Text Available In this paper, we show that in mixed phase clouds FSSP-100 measurements may be contaminated by ice crystals, inducing wrong interpretation of particle size and subsequent bulk parameters. This contamination is generally revealed by a bimodal feature of the particle size distribution; in other words, in mixed phase clouds bimodal features could be an indication of the presence of ice particles. The combined measurements of the FSSP-100 and the Polar Nephelometer give a coherent description of the effect of the ice crystals on the FSSP-100 response. The FSSP-100 particle size distributions are characterized by a bimodal shape with a second mode peaked between 25 and 35 μm related to ice crystals. This feature is observed with the FSSP-100 at airspeed up to 200 m s−1 and with the FSSP-300 series. In order to assess the size calibration for clouds of ice crystals the response of the FSSP-100 probe has been numerically simulated using a light scattering model of randomly oriented hexagonal ice particles and assuming both smooth and rough crystal surfaces. The results suggest that the second mode measured between 25 μm and 35 μm, does not necessarily represent true size responses but likely corresponds to bigger aspherical ice particles. According to simulation results, the sizing understatement would be neglected in the rough case but would be major with the smooth case. Qualitatively, the Polar Nephelometer phase function suggests that the rough case is the more suitable to describe real crystals. Quantitatively, however, it is difficult to conclude. Previous cloud in situ measurements suggest that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is likely to be due to the shattering of large ice crystals on the probe tips. This finding is supported by the rather good relationship between the concentration of particles larger than 20 μm (hypothesized to be ice shattered-fragments measured by the FSSP and the

  16. Phase diagram for the transition from photonic crystals to dielectric metamaterials.

    Science.gov (United States)

    Rybin, Mikhail V; Filonov, Dmitry S; Samusev, Kirill B; Belov, Pavel A; Kivshar, Yuri S; Limonov, Mikhail F

    2015-12-02

    Photonic crystals and dielectric metamaterials represent two different classes of artificial media but are often composed of similar structural elements. The question is how to distinguish these two types of periodic structures when their parameters, such as permittivity and lattice constant, vary continuously. Here we discuss transition between photonic crystals and dielectric metamaterials and introduce the concept of a phase diagram, based on the physics of Mie and Bragg resonances. We show that a periodic photonic structure transforms into a metamaterial when the Mie gap opens up below the lowest Bragg bandgap where the homogenization approach can be justified and the effective permeability becomes negative. Our theoretical approach is confirmed by microwave experiments for a metacrystal composed of tubes filled with heated water. This analysis yields deep insight into the properties of periodic structures, and provides a useful tool for designing different classes of electromagnetic materials with variable parameters.

  17. Phase diagram for the transition from photonic crystals to dielectric metamaterials

    Science.gov (United States)

    Rybin, Mikhail V.; Filonov, Dmitry S.; Samusev, Kirill B.; Belov, Pavel A.; Kivshar, Yuri S.; Limonov, Mikhail F.

    2015-01-01

    Photonic crystals and dielectric metamaterials represent two different classes of artificial media but are often composed of similar structural elements. The question is how to distinguish these two types of periodic structures when their parameters, such as permittivity and lattice constant, vary continuously. Here we discuss transition between photonic crystals and dielectric metamaterials and introduce the concept of a phase diagram, based on the physics of Mie and Bragg resonances. We show that a periodic photonic structure transforms into a metamaterial when the Mie gap opens up below the lowest Bragg bandgap where the homogenization approach can be justified and the effective permeability becomes negative. Our theoretical approach is confirmed by microwave experiments for a metacrystal composed of tubes filled with heated water. This analysis yields deep insight into the properties of periodic structures, and provides a useful tool for designing different classes of electromagnetic materials with variable parameters. PMID:26626302

  18. A New, More Stable Polymorphic Form of Otilonium Bromide: Solubility, Crystal Structure, and Phase Transformation.

    Science.gov (United States)

    Vega, Daniel R; Halac, Emilia; Segovia, Luciano; Baggio, Ricardo

    2016-10-01

    A new polymorphic form of otilonium bromide is presented (Form I), and a thorough analysis of its crystal and molecular structure is performed. The compound suffers a temperature-driven first-order phase transition at about 396 K, which transforms it into the polymorph reported by Dapporto P and Sega A (Acta Cryst. 1986;C42:474-478) (Form II). Through thermal analysis and solubility experiments the relative stability of both crystal modifications were determined, confirming that at room temperature this new Form I is the more stable one, Form II existing just in a metastable state. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  19. Nanomechanical responses of intermetallic phase at the solder joint interface - Crystal orientation and metallurgical effects

    Energy Technology Data Exchange (ETDEWEB)

    Song, Jenn-Ming, E-mail: samsong@nchu.edu.tw [Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan (China); Huang, Bo-Ron [Department of Materials Science and Engineering, National Dong Hwa University, Hualien 974, Taiwan (China); Liu, Cheng-Yi [Department of Chemical and Materials Engineering, National Central University, Taoyuan 320, Taiwan (China); Lai, Yi-Shao; Chiu, Ying-Ta [Central Labs, Advanced Semiconductor Engineering, Inc., Kaohsiung 811, Taiwan (China); Huang, Tzu-Wen [Laboratory for High Performance Ceramics, EMPA, Swiss Federal Laboratories for Materials Science and Technology (Switzerland)

    2012-02-01

    Highlights: Black-Right-Pointing-Pointer Textural and alloying effects on mechanical behavior of Cu{sub 6}Sn{sub 5} are explored. Black-Right-Pointing-Pointer Orientation dependence on elastic behavior of Cu{sub 6}Sn{sub 5} is verified and explained. Black-Right-Pointing-Pointer Allotropic transition and plastic ability for Cu{sub 6}Sn{sub 5} are linked. Black-Right-Pointing-Pointer How alloying affects the hexagonal to monoclinic transition of Cu{sub 6}Sn{sub 5} is proposed. - Abstract: In this study, the relationships between crystal structures, metallurgical effects, and mechanical properties of the most common intermetallic compound formed at the interface of solder joints, Cu{sub 6}Sn{sub 5}, were investigated using nanoindentation. Experimental results show that the (112{sup Macron }0) oriented hexagonal Cu{sub 6}Sn{sub 5} exhibited anisotropic mechanical behavior compared to those with random growth directions. The closest atomic packing density of the (112{sup Macron }0) plane in hexagonal Cu{sub 6}Sn{sub 5} resulted in higher hardness and notably, greater stiffness. Subjected to long time aging at 150 Degree-Sign C, hexagonal Cu{sub 6}Sn{sub 5} was transformed into the equilibrium monoclinic structure, resulting in a reduced modulus and thus inferior ability for plasticity. Alloying of Ni, Mn and rare earth elements (La and Ce) had various contributions to the allotropic transition and thus nanoindentation responses. It was found that the differences in atomic radius between the solute elements and Cu affected the kinetics of the allotropic transformation and also the mechanical performance of Cu{sub 6}Sn{sub 5}. There exists a critical value for the modulus/hardness ratio (E/H) of about 17.3-17.5, below which the indent morphology showed a brittle characteristic.

  20. Method to measure the phase modulation characteristics of a liquid crystal spatial light modulator.

    Science.gov (United States)

    Wu, Yunlong; Nie, Jinsong; Shao, Li

    2016-11-01

    The universal liquid crystal spatial light modulator (LC-SLM) is widely used in many aspects of optical studies. The working principles and applications of LC-SLM were introduced briefly. The traditional Twyman-Green interference method, which was used to measure the phase modulation characteristics of a liquid spatial light modulator, had some obvious disadvantages in practice. To avoid these issues, the traditional Twyman-Green interference method was improved. Also, a new method to process interference fringes and measure the shift distances and cycles automatically by computers was proposed. The phase modulation characteristics of P512-1064 LC-SLM produced by the Meadowlark Company were measured to verify the validity of the newly proposed method. In addition, in order to compensate and correct the nonlinear characteristics of the phase modulation curve, three universal inverse interpolation methods were utilized. The root mean squared error and residual sum of squares between the calibrated phase modulation curve and the ideal phase modulation curve were reduced obviously by taking advantage of the inverse interpolation methods. Subsequently, the method of shape-preserving subsection cubic interpolation had acquired the best performance with high computation efficiency. Experiments have been performed to verify the validity of the interpolation method. The experimental results showed that the phase modulation characteristics of LC-LSM could be acquired and calibrated automatically with convenience and high efficiency by utilizing the newly proposed processing method.

  1. Local structure, composition, and crystallization mechanism of a model two-phase "composite nanoglass"

    Science.gov (United States)

    Chattopadhyay, Soma; Kelly, S. D.; Shibata, Tomohiro; Balasubramanian, M.; Srinivasan, S. G.; Du, Jincheng; Banerjee, Rajarshi; Ayyub, Pushan

    2016-02-01

    We report a detailed study of the local composition and structure of a model, bi-phasic nanoglass with nominal stoichiometry Cu55Nb45. Three dimensional atom probe data suggest a nanoscale-phase-separated glassy structure having well defined Cu-rich and Nb-rich regions with a characteristic length scale of ≈3 nm. However, extended x-ray absorption fine structure analysis indicates subtle differences in the local environments of Cu and Nb. While the Cu atoms displayed a strong tendency to cluster and negligible structural order beyond the first coordination shell, the Nb atoms had a larger fraction of unlike neighbors (higher chemical order) and a distinctly better-ordered structural environment (higher topological order). This provides the first experimental indication that metallic glass formation may occur due to frustration arising from the competition between chemical ordering and clustering. These observations are complemented by classical as well as ab initio molecular dynamics simulations. Our study indicates that these nanoscale phase-separated glasses are quite distinct from the single phase nanoglasses (studied by Gleiter and others) in the following three respects: (i) they contain at least two structurally and compositionally distinct, nanodispersed, glassy phases, (ii) these phases are separated by comparatively sharp inter-phase boundaries, and (iii) thermally induced crystallization occurs via a complex, multi-step mechanism. Such materials, therefore, appear to constitute a new class of disordered systems that may be called a composite nanoglass.

  2. Local structure, composition, and crystallization mechanism of a model two-phase “composite nanoglass”

    Energy Technology Data Exchange (ETDEWEB)

    Chattopadhyay, Soma; Shibata, Tomohiro [CSRRI-IIT, MRCAT, Sector 10, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Kelly, S. D. [EXAFS Analysis, Bolingbrook, Illinois 60440 (United States); Balasubramanian, M. [Sector 20 XOR, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Srinivasan, S. G.; Du, Jincheng; Banerjee, Rajarshi [Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203-5017 (United States); Ayyub, Pushan, E-mail: pushan@tifr.res.in [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005 (India)

    2016-02-14

    We report a detailed study of the local composition and structure of a model, bi-phasic nanoglass with nominal stoichiometry Cu{sub 55}Nb{sub 45}. Three dimensional atom probe data suggest a nanoscale-phase-separated glassy structure having well defined Cu-rich and Nb-rich regions with a characteristic length scale of ≈3 nm. However, extended x-ray absorption fine structure analysis indicates subtle differences in the local environments of Cu and Nb. While the Cu atoms displayed a strong tendency to cluster and negligible structural order beyond the first coordination shell, the Nb atoms had a larger fraction of unlike neighbors (higher chemical order) and a distinctly better-ordered structural environment (higher topological order). This provides the first experimental indication that metallic glass formation may occur due to frustration arising from the competition between chemical ordering and clustering. These observations are complemented by classical as well as ab initio molecular dynamics simulations. Our study indicates that these nanoscale phase-separated glasses are quite distinct from the single phase nanoglasses (studied by Gleiter and others) in the following three respects: (i) they contain at least two structurally and compositionally distinct, nanodispersed, glassy phases, (ii) these phases are separated by comparatively sharp inter-phase boundaries, and (iii) thermally induced crystallization occurs via a complex, multi-step mechanism. Such materials, therefore, appear to constitute a new class of disordered systems that may be called a composite nanoglass.

  3. Salts and Co-crystals of Theobromine and their phase transformations in water

    Indian Academy of Sciences (India)

    Palash Sanphui; Ashwini Nangia

    2014-09-01

    Theobromine, a xanthine derivative analogous to caffeine and theophylline, is an effective central nervous system stimulant. It has lower aqueous solubility than caffeine and theophylline. Salts of theobromine with hydrochloric acid, phosphoric acid, methanesulfonic acid, benzenesulfonic acid and -toluenesulfonic acid were prepared using liquid-assisted grinding (LAG). Proton transfer from the strong acid to the weak base imidazole N resulted in N+-H…O− hydrogen-bonded supramolecular assemblies of theobromine salts. The mesylate salt is polymorphic with amide N-H…O dimer and catemer synthons for the theobromine cations. A variable stoichiometry for phosphate salts (1:3 and 1:2.5) were observed with the latter being more stable. All new salts were characterized by FT-IR, PXRD, DSC and finally single crystal X-ray diffraction. In terms of stability, these salts transformed to theobromine within 1 h of dissolution in water. Remarkably, the besylate and tosylate salts are 88 and 58 times more soluble than theobromine, but they dissociated within 1 h. In contrast, theobromine co-crystals with gallic acid, anthranilic acid and 5-chlorosalicylic acid were found to be stable for more than 24 h in the aqueous slurry conditions, except malonic co-crystal which transformed to theobrominewithin 1 h.Water mediated phase transformation of theobromine salts and co-crystalmay be due to the incongruency (high solubility difference) between the components. These results suggest that even though traditional salts are highly soluble compared to co-crystals, co-crystals can be superior in terms of stability.

  4. Crystallization and microstructures of Y–Si–Al–O–N glass–ceramics containing main crystal phase Y3Al5O12

    Indian Academy of Sciences (India)

    Xiuying Li; Anxian Lu

    2011-07-01

    A glass with the nominal composition of 28Y48Si24Al83O17N (in equal percentage) was chosen as parent glass in this paper to prepare Y3Al5O12-based glass–ceramics. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to assess the crystallization process of the parent glass. YAG as the only crystalline phase appears in all glass–ceramics produced under 1250°C. A small amount of O′-Sialon secondary phase starts to precipitate from parent glass samples as heat treatment temperature increases to 1250°C. Grain size of the dendrite crystal which corresponds to YAG phase increases and the dendrite branches get thickened as heat treatment temperature increases. Moreover, grain size of YAG phase resulting from two-stage heat treatment is much smaller than that of YAG phase obtained by one-stage heat treatment. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass–ceramics and for heat treatments of YAG/-SiAlON materials.

  5. A transcription-dependent increase in miniature EPSC frequency accompanies late-phase plasticity in cultured hippocampal neurons

    Directory of Open Access Journals (Sweden)

    Hofmann Frank

    2009-09-01

    Full Text Available Abstract Background The magnitude and longevity of synaptic activity-induced changes in synaptic efficacy is quantified by measuring evoked responses whose potentiation requires gene transcription to persist for more than 2-3 hours. While miniature EPSCs (mEPSCs are also increased in amplitude and/or frequency during long-term potentiation (LTP, it is not known how long such changes persist or whether gene transcription is required. Results We use whole-cell patch clamp recordings from dissociated hippocampal cultures to characterise for the first time the persistence and transcription dependency of mEPSC upregulation during synaptic potentiation. The persistence of recurrent action potential bursting in these cultures is transcription-, translation- and NMDA receptor-dependent thus providing an accessible model for long-lasting plasticity. Blockade of GABAA-receptors with bicuculline for 15 minutes induced action potential bursting in all neurons and was maintained in 50-60% of neurons for more than 6 hours. Throughout this period, the frequency but neither the amplitude of mEPSCs nor whole-cell AMPA currents was markedly increased. The transcription blocker actinomycin D abrogated, within 2 hours of burst induction, both action potential bursting and the increase in mEPSCs. Reversible blockade of action potentials during, but not after this 2 hour transcription period suppressed the increase in mEPSC frequency and the recovery of burst activity at a time point 6 hours after induction. Conclusion These results indicate that increased mEPSC frequency persists well beyond the 2 hour transcription-independent phase of plasticity in this model. This long-lasting mEPSC upregulation is transcription-dependent and requires ongoing action potential activity during the initial 2 hour period but not thereafter. Thus mEPSC upregulation may underlie the long term, transcription-dependent persistence of action potential bursting. This provides mechanistic

  6. Structure of Plastic Crystalline Succinonitrile: High-Resolution in situ Powder Diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Hore, S.; Dinnebier, R; Wen, W; Hanson, J; Maier, J

    2009-01-01

    The temperature dependent (150-290 K) crystal structure of the low-temperature -phase, and high temperature -phase, of succinonitrile has been determined by high resolution in situ powder diffraction. The -phase has a monoclinic unit cell that contains four gauche molecules and belongs to the P21/a space group. The crystal undergoes a reversible first-order phase transition at 233 K into the high temperature -phase. The lattice parameters increase with temperature and the phase transition leads to an abrupt 6.7 % increase in volume. The -phase crystallizes into a bcc-structure that belongs to the space group. The high temperature phase; however, is a highly disordered plastic crystal at room temperature that contains both gauche and trans molecules. The non-linearity in the overall isotropic temperature-factor indicates other possible phase transitions in the temperature range of 233-250 K

  7. Photo polymerization-induced vertical phase separation and homeotropic alignment in liquid crystal and polymer mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Hyo [Samsung Advanced Institute of Technology, Yongin (Korea, Republic of); Joo, Sangwoo; Kang, Daeseung [Soongsil Univ., Seoul (Korea, Republic of)

    2012-04-15

    We presented a novel method for the homeotropic alignment of LC by using the irradiation of UV light on the LC/NOA65 mixture cell, in which the photo-initiated-polymerization-induced phase separation lowers the surface energy. When the amount of polymer content is sufficiently small, the gravel and network patterns were formed at the substrates via the vertical phase separation. We found that surface roughness plays an important role in the formation of the homeotropic alignment of LC. We also observed the alignment transition of the cells by varying the mixing ratio of LC/NOA65 or the UV radiation time. Furthermore, the present proposed method has great potential for application in display devices. For decades, studies on the alignment of liquid crystal (LC) molecules have been of significant interest due to their immediate applications for display devices and the intriguing physiochemical properties they exhibit at the surface of mixtures. Usually, homeotropic (or vertical) alignment, in which the long axes of the LC molecules are oriented in a direction perpendicular to the surface, is achieved by using surfactants such as lecithin, silanes or polyimide. Recently homeotropic alignment of liquid crystal molecules was achieved by irradiating photosensitive polymers, by doping nanoparticles into LC, by utilizing nano/micro patterns, or by incorporating self-assembled monolayers (SAMs). However, a clear understanding about the alignment mechanism is still elusive. In this paper, we report a novel method for homeotropic alignment of LC by utilizing the phase separation of LC/polymer mixtures.

  8. High-Pressure High-Temperature Phase Diagram of the Organic Crystal Paracetamol

    Science.gov (United States)

    Smith, Spencer; Montgomery, Jeffrey; Vohra, Yogesh

    High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped diamond as heating anvil. The HPHT data obtained from boron-doped diamond heater is cross-checked with data obtained using a standard block heater diamond anvil cell. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in a number of different experiments. Solid state phase transitions from monoclinic Form I --> orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II --> unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. Our previous angle dispersive x-ray diffraction studies at the Advanced Photon Source has confirmed the existence of two unknown crystal structures Form IV and Form V of paracetamol at high pressure and ambient temperature. The phase transformation from Form II to Form IV occurs at ~8.5 GPa and from Form IV to Form V occurs at ~11 GPa at ambient temperature. Our new data is combined with the previous ambient temperature high-pressure Raman and X- ray diffraction data to create the first HPHT phase diagram of paracetamol. Doe-NNSA Carnegie DOE Alliance Center (CDAC) under Grant Number DE-NA0002006.

  9. 149.8 nm, the shortest wavelength generated by phase matching in nonlinear crystals

    Science.gov (United States)

    Nakazato, Tomoharu; Ito, Isao; Kobayashi, Yohei; Wang, Xiaoyang; Chen, Chuangtian; Watanabe, Shuntaro

    2017-02-01

    Narrow band light sources in the vacuum ultraviolet (VUV) region are attractive for photo lithography and high resolution photoelectron spectroscopy. Phase matching is essential to generate high power VUV lights by using a narrow band, low peak intensity and nanosecond pump source. In this research, sum frequency mixing has been demonstrated below 150 nm in KBe2BO3F2 by using the fundamental with its fourth harmonic of a 6 kHz Ti:sapphire laser. The laser system we have developed in this research, consists of a Ti:sapphire laser system and a frequency conversion stage. We generated 149.8-nm radiation, which is the shortest wavelength ever obtained to our knowledge by phase matching in nonlinear crystals. The fifth harmonic output powers were 3.6 μW at 149.8 nm and 110 μW at 154.0 nm, respectively. The phase matching angles measured from 149.8 nm to 158.1 nm are larger by 3-4 degrees than those expected from the existing Sellmeier equation. The optical transmission spectra of some KBBF crystals were measured by the spectrophotometer. The transmittance near the absorption edge supports the generation of coherent radiation below 150 nm. The improvement of a prism-coupled device contributed to the generation of coherent radiation below 150 nm. Another reason for the present break through to the shorter wavelength is the use of the short pulse driving source compared with our previous research.

  10. EPR spectroscopic studies of the process of interaction in a system of liquid phase of the plastic coal mass and thermally unstable carbon filler

    Energy Technology Data Exchange (ETDEWEB)

    Ikonomopulo, V.P.

    1983-01-01

    In conection with discovering the mechanism of coke formation, possible reactions of transient products of thermodestruction in liquid phase-thermally unstable carbon filler systems are studied. The investigations demonstrated that the liquid-phase transient products of one component of the mixture accelerated the process of plastification of solid transient products, and this in turn facilitated the development of the formation of ordered paramagnetic structures. The influence of non-plasticizing thermostable carbon fillers on the thermochemical conversions of liquid phase materials is similar to that of thermostable carbon fillers. A vapor-gas medium is the possible channel of reaction in a liquid phase-solid transient product system. (8 refs.)

  11. Non-isothermal crystallization kinetics and phase transformation of Bi2O3-SiO2 glass-ceramics

    Directory of Open Access Journals (Sweden)

    Guo H.W.

    2011-01-01

    Full Text Available The Bi2O3-SiO2 (BS glass-ceramics were prepared by melt-quench technique, and the crystallization kinetics and phase transformation behavior were investigated in accordance with Kissinger and Johson-Mehl-Avrami equation, DSC, XRD and SEM. The results show that in the heat treatment process (or termed as re-crystallizing process Bi2SiO5 and Bi4Si3O12 crystals were found consequently. Respectively, the crystallization activation energies of the two crystals are Ep1=14.8kJ/mol and Ep2=34.1kJ/mol. And the average crystallization index of n1=1.73 and n2=1.38 suggested volume nucleation, one-dimensional growth and surface nucleation, one-dimensional growth from surface to the inside respectively. The meta-stable needle-like Bi2SiO5 crystals are easily to be transformed into stable prismatic Bi4Si3O12 crystals. By quenching the melt and hold in 850°C for 1h, the homogenous single Bi4Si3O12 crystals were found in the polycrystalline phase of the BS glassceramics system.

  12. Impact of polymers on the crystallization and phase transition kinetics of amorphous nifedipine during dissolution in aqueous media.

    Science.gov (United States)

    Raina, Shweta A; Alonzo, David E; Zhang, Geoff G Z; Gao, Yi; Taylor, Lynne S

    2014-10-06

    The commercial and clinical success of amorphous solid dispersions (ASD) in overcoming the low bioavailability of poorly soluble molecules has generated momentum among pharmaceutical scientists to advance the fundamental understanding of these complex systems. A major limitation of these formulations stems from the propensity of amorphous solids to crystallize upon exposure to aqueous media. This study was specifically focused on developing analytical techniques to evaluate the impact of polymers on the crystallization behavior during dissolution, which is critical in designing effective amorphous formulations. In the study, the crystallization and polymorphic conversions of a model compound, nifedipine, were explored in the absence and presence of polyvinylpyrrolidone (PVP), hydroxypropylmethyl cellulose (HPMC), and HPMC-acetate succinate (HPMC-AS). A combination of analytical approaches including Raman spectroscopy, polarized light microscopy, and chemometric techniques such as multivariate curve resolution (MCR) were used to evaluate the kinetics of crystallization and polymorphic transitions as well as to identify the primary route of crystallization, i.e., whether crystallization took place in the dissolving solid matrix or from the supersaturated solutions generated during dissolution. Pure amorphous nifedipine, when exposed to aqueous media, was found to crystallize rapidly from the amorphous matrix, even when polymers were present in the dissolution medium. Matrix crystallization was avoided when amorphous solid dispersions were prepared, however, crystallization from the solution phase was rapid. MCR was found to be an excellent data processing technique to deconvolute the complex phase transition behavior of nifedipine.

  13. Magnetic field response of NaCl:Eu crystal plasticity due to spin-dependent Eu2+ aggregation

    Science.gov (United States)

    Morgunov, R. B.; Buchachenko, A. L.

    2010-07-01

    Magnetic field impulse (7 T amplitude 10 ms duration) was found to affect microhardness of NaCl:Eu crystals at room temperature. Dimers (pairs of Eu2+ paramagnetic ions) were shown to be responsible for the crystal softening induced by magnetic field. Theoretical treatment of the magnetoplastic effect based on the spin dependence of processes resulting in transformation of the dimers in crystals is developed and applied to the description of the long-term magnetic memory. Activation energies of the dimer formation, E1=0.23±0.04eV and decomposition, E2=0.33±0.06eV were extracted from thermoactivation analysis of magnetic field controlled Eu2+ aggregation in 77-473 K temperature range.

  14. Effect of Hafnium and Zirconium to Glass Forming Ability, Thermal Stability, Plasticity Deformation and Crystallization of Ni-Free Pentabasic Ti-Based Bulk Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Oak J.J.

    2017-06-01

    Full Text Available The newly designed Ti-based bulk metallic glass (BMG in which case of fracture behavior was observed 1990MPa to compressive strength with a wide plastic deformation around 7% after process of elastic deformation. This phenomenon can be compared with those of Ti-based alloys and other Ti-based BMGs and indicates high potential to be applied in use. It was evaluated the Ti-based BMG for thermal stability that the reduced glass parameters, ΔTx, Trg and γ, are 79K, 0.50 and 0.38, respectively. In addition, it reveals high activation energies for crystallization in which are estimated to Ex1 = 291.77 ±9.71 kJ/mol, Ex2 = 588.77 ±28.88 kJ/mol and Ex3 = 330.26 ±3.61 kJ/mol on kissinger plotting in this study.

  15. Study of 3-D stress development in parent and twin pairs of a hexagonal close-packed polycrystal: Part II - Crystal plasticity finite element modeling

    DEFF Research Database (Denmark)

    Abdolvand, Hamidreza; Majkut, Marta; Oddershede, Jette

    2015-01-01

    -of-mass positions and volumes as measured by three-dimensional X-ray diffraction (3DXRD) microscopy. The constructed microstructure is meshed with different element densities and for different numbers of grains. Then a selected group of twin and parent pairs are studied. It is shown that the measured average stress...... each grain, stresses in the parent and twin are quite different if they are plotted in the global coordinate system. However, if the stress tensor is rotated into the local coordinate system of the twin habit plane, all the stress components averaged over the presented population are close, except......Stress heterogeneity within each individual grain of polycrystalline Zircaloy-2 is studied using a crystal plasticity finite element (CPFE) model. For this purpose, the weighted Voronoi tessellation method is used to construct 3D geometries of more than 2600 grains based on their center...

  16. Gas phase acetic acid and its qualitative effects on snow crystal morphology and the quasi-liquid layer

    Directory of Open Access Journals (Sweden)

    T. N. Knepp

    2009-10-01

    Full Text Available A chamber was constructed within which snow crystals were grown on a string at various temperatures, relative humidities, and acetic acid gas phase mole fractions. The temperature, relative humidity, and acid mole fraction were measured for the first time at the point of crystal growth. Snow crystal morphological transition temperature shifts were recorded as a function of acid mole fraction, and interpreted according to the calculated acid concentration in the crystal's quasi-liquid layer, which is believed to have increased in thickness as a function of acid mole fraction, thereby affecting the crystal's morphology consistent with the hypothesis of Kuroda and Lacmann. Deficiencies in the understanding of the quasi-liquid layer and its role in determining snow crystal morphology are briefly discussed.

  17. Effect of plastic deformation on the optical and electrical properties in Cd0.96Zn0.04Te single crystals

    Science.gov (United States)

    Lmai, F.; Moubah, R.; Amiri, A. El.; Boudali, A.; Hlil, E. K.; Lassri, H.

    2017-01-01

    Using UV-visible, photoluminescence, electrical measurements and ab-initio calculations, we study the effect of introduced dislocations on the optical and electrical properties in Cd0.96Zn0.04Te crystals. To generate dislocations, a plastic deformation on the Cd(111) and Te (1 bar 1 bar 1 bar) faces was induced. It is shown that the plastic deformation results in: i) a decrease in Zn concentration in the deformed regions, which is higher on the Cd face, ii) decrease in the band gap energy, iii) an increase of acceptor concentration, and iv) the leakage current is higher on the Te face. Calculation of barrier height has led to identify the dominant defect, which is the complex Cd vacancies, acceptor center [VCd, ACd] on the Cd face and VTe on the Te side, respectively. Electronic structure calculations based on full potential linearized augmented plane waves (FPLAPW) method were performed as well and have shown that the optical band gap energy decrease upon deformation can be understood by the decrease in Zn content in the deformed regions.

  18. Theoretical and Experimental Demonstration on Grating Lobes of Liquid Crystal Optical Phased Array

    Directory of Open Access Journals (Sweden)

    Xiangru Wang

    2016-01-01

    Full Text Available High deflection efficiency is one of the urgent requirements for practical liquid crystal optical phased array (LC-OPA. In this paper, we demonstrate that high order grating lobes induced from fringe effect are the most important issue to reduce occupation of main lobe. A novel theoretical model is developed to analyze the feature of grating lobes when the device of LC-OPA is working on the scheme of variable period grating (VPG or variable blazing grating (VBG. Subsequently, our experiments present the relevant results showing a good agreement with the theoretical analysis.

  19. Linearly first- and second-order, unconditionally energy stable schemes for the phase field crystal model

    Science.gov (United States)

    Yang, Xiaofeng; Han, Daozhi

    2017-02-01

    In this paper, we develop a series of linear, unconditionally energy stable numerical schemes for solving the classical phase field crystal model. The temporal discretizations are based on the first order Euler method, the second order backward differentiation formulas (BDF2) and the second order Crank-Nicolson method, respectively. The schemes lead to linear elliptic equations to be solved at each time step, and the induced linear systems are symmetric positive definite. We prove that all three schemes are unconditionally energy stable rigorously. Various classical numerical experiments in 2D and 3D are performed to validate the accuracy and efficiency of the proposed schemes.

  20. Theoretical modeling on the laser induced effect of liquid crystal optical phased beam steering

    Science.gov (United States)

    He, Xiaoxian; Wang, Xiangru; Wu, Liang; Tan, Qinggui; Li, Man; Shang, Jiyang; Wu, Shuanghong; Huang, Ziqiang

    2017-01-01

    Non-mechanical laser beam steering has been reported previously in liquid crystal array devices. To be one of the most promising candidates to be practical non-mechanical laser deflector, its laser induced effect still has few theoretical model. In this paper, we propose a theoretical model to analyze this laser induced effect of LC-OPA to evaluate the deterioration on phased beam steering. The model has three parts: laser induced thermal distribution; temperature dependence of material parameters and beam steering deterioration. After these three steps, the far field of laser beam is obtained to demonstrate the steering performance with the respect to the incident laser beam power and beam waist.

  1. Enhanced optical tuning of modified-geometry resonators clad in blue phase liquid crystals.

    Science.gov (United States)

    Ptasinski, Joanna; Khoo, Iam-Choon; Fainman, Yeshaiahu

    2014-09-15

    Active optical tuning of silicon racetrack resonators clad in dye-doped blue phase liquid crystals (BPLCs) is experimentally demonstrated. An adiabatic racetrack resonator geometry that allows for enhanced tuning is presented and analyzed. The resonance shift of an unmodified geometry racetrack is Δλ=0.7 nm, while an adiabatic racetrack achieves a Δλ=1.23 nm resonance shift because of a greater mode overlap with the cladding. The calculated refractive index change of the BPLC is Δn=0.0041 for both geometries.

  2. Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

    OpenAIRE

    Zhang, Zichen; You, Zheng; Chu, DaPing

    2014-01-01

    This is the final version. It has been published by NPG in Light: Science & Applications here: http://www.nature.com/lsa/journal/v3/n10/full/lsa201494a.html. This paper describes the fundamentals of phase-only liquid crystal on silicon (LCOS) technology, which have not been previously discussed in detail. This technology is widely utilized in high efficiency applications for real-time holography and diffractive optics. The paper begins with a brief introduction on the developmental traject...

  3. Observation of blue phase in chiral nematic liquid crystal and its stabilization by silica nanoparticles

    Science.gov (United States)

    Singh, Arshdeep; Malik, Praveen; Jayoti, Divya

    2016-01-01

    In the present work, we report the blue phase (BP) in a binary mixture of cholesteryl nonanoate (CN) and N-(4-ethoxybenzylidene)-4-butylaniline (EBBA). The mixture exhibits BP over a temperature range of 2.3 K at optimum composition (50:50) of liquid crystals (LCs). The effect of silica nanoparticles (SNPs) doping on thermal stability of BPs has also been demonstrated and nearly 6 K wide BP temperature range was achieved at 0.5 wt.% of SNPs. A porous type texture was also observed during the BP formation process in the doped samples.

  4. Ligand mediated synthesis of AgInSe{sub 2} nanoparticles with tetragonal/orthorhombic crystal phases

    Energy Technology Data Exchange (ETDEWEB)

    Abazovic, Nadica D., E-mail: kiki@vinca.rs; Comor, Mirjana I.; Mitric, Miodrag N. [University of Belgrade, Vinca Institute of Nuclear Sciences (Serbia); Piscopiello, Emanuela [ENEA, Department of Advanced Physics Technology and New Materials (FIM) (Italy); Radetic, Tamara [Lawrence Berkeley National Laboratory (United States); Jankovic, Ivana A.; Nedeljkovic, Jovan M. [University of Belgrade, Vinca Institute of Nuclear Sciences (Serbia)

    2012-03-15

    Nanosized AgInSe{sub 2} particles (d {approx} 7-25 nm) were synthesized using colloidal chemistry method at 270 Degree-Sign C. As solvents/surface ligands 1-octadecene, trioctylphosphine, and oleylamine were used. It was shown that choice of ligand has crucial impact not only on final crystal phase of nanoparticles, but also at mechanism of crystal growth. X-ray diffraction and TEM/HRTEM techniques were used to identify obtained crystal phases and to measure average size and shape of nanoparticles. UV/Vis data were used to estimate band-gap energies of obtained samples. It was shown that presented routes can provide synthesis of nanoparticles with desired crystal phase (tetragonal and/or orthorhombic), with band-gap energies in the range from 1.25 to 1.53 eV.

  5. Molecular simulation of homogeneous crystal nucleation of AB2 solid phase from a binary hard sphere mixture

    Science.gov (United States)

    Bommineni, Praveen Kumar; Punnathanam, Sudeep N.

    2017-08-01

    Co-crystal formation from fluid-mixtures is quite common in a large number of systems. The simplest systems that show co-crystal (also called substitutionally ordered solids) formation are binary hard sphere mixtures. In this work, we study the nucleation of AB2 type solid compounds using Monte Carlo molecular simulations in binary hard sphere mixtures with the size ratio of 0.55. The conditions chosen for the study lie in the region where nucleation of an AB2 type solid competes with that of a pure A solid with a face-centered-cubic structure. The fluid phase composition is kept equal to that of the AB2 type solid. The nucleation free-energy barriers are computed using the seeding technique of Sanz et al. [J. Am. Chem. Soc. 135, 15008 (2013)]. Our simulation results show that the nucleation of the AB2 type solid is favored even under conditions where the pure A solid is more stable. This is primarily due to the similarity in the composition of the fluid phase and the AB2 type solid which in turn leads to much lower interfacial tension between the crystal nucleus and the fluid phase. This system is an example of how the fluid phase composition affects the structure of the nucleating solid phase during crystallization and has relevance to crystal polymorphism during crystallization processes.

  6. A raman study of hydrostatic pressure induced phase transitions in Rb2KInF6 crystals

    Science.gov (United States)

    Vtyurin, A. N.; Krylov, A. S.; Goryainov, S. V.; Krylova, S. N.; Oreshonkov, A. S.; Voronov, V. N.

    2012-05-01

    The Raman spectra of the elpasolite (Rb2KInF6) crystal have been studied in the pressure range from 0 to 5.3 GPa at a temperature of 295 K. A phase transition at a pressure of approximately 0.9 GPa has been found. An analysis of the variations in the spectral parameters has led to the conclusion that the phase transition to a distorted phase is accompanied by the doubling of the volume of the primitive cell of the initial cubic phase. Numerical calculations of the lattice dynamics in the Rb2KInF6 crystal have been performed. The numerical simulation has established that the phase transition at a pressure of 0.9 GPa is associated with condensation of the F lg mode. A probable high-pressure phase is the phase with space group C2/ m.

  7. Label-free protein sensing by employing blue phase liquid crystal.

    Science.gov (United States)

    Lee, Mon-Juan; Chang, Chung-Huan; Lee, Wei

    2017-03-01

    Blue phases (BPs) are mesophases existing between the isotropic and chiral nematic phases of liquid crystals (LCs). In recent years, blue phase LCs (BPLCs) have been extensively studied in the field of LC science and display technology. However, the application of BPLCs in biosensing has not been explored. In this study, a BPLC-based biosensing technology was developed for the detection and quantitation of bovine serum albumin (BSA). The sensing platform was constructed by assembling an empty cell with two glass slides coated with homeotropic alignment layers and with immobilized BSA atop. The LC cells were heated to isotropic phase and then allowed to cool down to and maintained at distinct BP temperatures for spectral measurements and texture observations. At BSA concentrations below 10(-6) g/ml, we observed that the Bragg reflection wavelength blue-shifted with increasing concentration of BSA, suggesting that the BP is a potentially sensitive medium in the detection and quantitation of biomolecules. By using the BPLC at 37 °C and the same polymorphic material in the smectic A phase at 20 °C, two linear correlations were established for logarithmic BSA concentrations ranging from 10(-9) to 10(-6) g/ml and from 10(-6) to 10(-3) g/ml. Our results demonstrate the potential of BPLCs in biosensing and quantitative analysis of biomolecules.

  8. A Conceptual Model for Shear-Induced Phase Behavior in Crystallizing Cocoa Butter

    Energy Technology Data Exchange (ETDEWEB)

    Mazzanti,G.; Guthrie, S.; Marangoni, A.; Idziak, S.

    2007-01-01

    We propose a conceptual model to explain the quantitative data from synchrotron X-ray diffraction experiments on the shear-induced phase behavior of cocoa butter, the main structural component of chocolate. We captured two-dimensional diffraction patterns from cocoa butter at crystallization temperatures of 17.5, 20.0, and 22.5 {sup o}C under shear rates from 45 to 1440 s{sup -1} and under static conditions. From the simultaneous analysis of the integrated intensity, correlation length, lamellar thickness, and crystalline orientation, we postulate a conceptual model to provide an explanation for the distribution of phases II, IV, V, and X and the kinetics of the process. As previously proposed in the literature, we assume that the crystallites grow layer upon layer of slightly different composition. The shear rate and temperature applied define these compositions. Simultaneously, the shear and temperature define the crystalline interface area available for secondary nucleation by promoting segregation and affecting the size distribution of the crystallites. The combination of these factors (composition, area, and size distribution) favors dramatically the early onset of phase V under shear and determines the proportions of phases II, IV, V, and X after the transition. The experimental observations, the methodology used, and the proposed explanation are of fundamental and industrial interest, since the structural properties of crystalline networks are determined by their microstructure and polymorphic crystalline state. Different proportions of the phases will thus result in different characteristics of the final material.

  9. Phase field crystal modelling of the order-to-disordered atomistic structure transition of metallic glasses

    Science.gov (United States)

    Zhang, W.; Mi, J.

    2016-03-01

    Bulk metallic glass composites are a new class of metallic alloy systems that have very high tensile strength, ductility and fracture toughness. This unique combination of mechanical properties is largely determined by the presence of crystalline phases uniformly distributed within the glassy matrix. However, there have been very limited reports on how the crystalline phases are nucleated in the super-cooled liquid and their growth dynamics, especially lack of information on the order-to-disordered atomistic structure transition across the crystalline-amorphous interface. In this paper, we use phase field crystal (PFC) method to study the nucleation and growth of the crystalline phases and the glass formation of the super cooled liquid of a binary alloy. The study is focused on understanding the order-to-disordered transition of atomistic configuration across the interface between the crystalline phases and amorphous matrix of different chemical compositions at different thermal conditions. The capability of using PFC to simulate the order-to-disorder atomistic transition in the bulk material or across the interface is discussed in details.

  10. The Strengthening Effect of Phase Boundaries in a Severely Plastically Deformed Ti-Al Composite Wire

    Directory of Open Access Journals (Sweden)

    Tom Marr

    2014-02-01

    Full Text Available An accumulative swaging and bundling technique is used to prepare composite wires made of Ti and an Al alloy. These wires show reasonable higher yield stresses than expected from the pure material flow curves. The additional strengthening in the composite is analyzed using nanoindentation measurements, tensile testings and investigations of the microstructure. In addition, these properties are analyzed in relation to the fracture surface of the mechanically tested wires. Additional strengthening due to the presence of phase boundaries could be verified. Indications for residual stresses are found that cause a global hardness gradient from the center to the wire rim. Finally, the yield stress of the wires are calculated based on local hardness measurements.

  11. Effect of poling on dielectric anomalies at phase transitions for lead magnesium niobate-lead titanate crystals in the morphotropic phase boundary region

    Science.gov (United States)

    Sehirlioglu, Alp; Payne, David A.; Han, Pengdi

    2006-03-01

    Dielectric measurements are reported as a function of temperature for phase transformations in the lead magnesium niobate-lead titanate system (PMN-PT). Data are given for single crystal specimens in the morphotropic phase boundary (MPB) region. Transition temperatures were determined from dielectric loss data. The characteristics for both poled and unpoled crystals are compared. Values of dielectric constant were found to increase after poling at room temperature, and an anomaly was induced at the lower-temperature transition. Details are reported for these properties depending upon composition within the MPB region. At room temperature, the poled crystals had high values for dielectric constant (e.g., 5000-15 000), piezoelectric coefficient (e.g., 1000-4000 pC/N), and electromechanical coupling factor (e.g., >0.9). The temperature dependence of dielectric properties is treated in terms of competing phases at transformations, with a change from continuous to discontinuous behavior with increasing PT content towards the MPB. The effect of poling on the induction of the tetragonal (T) phase, with a lowering of the low temperature to tetragonal (LT-->T) phase transformation temperature, is discussed. Piezoelectric crystals with the highest depoling temperature were farthest away from the MPB in the MPB region. This information should be useful for the application of PMN-PT piezoelectric crystals.

  12. Visualization of membrane protein crystals in lipid cubic phase using X-ray imaging.

    Science.gov (United States)

    Warren, Anna J; Armour, Wes; Axford, Danny; Basham, Mark; Connolley, Thomas; Hall, David R; Horrell, Sam; McAuley, Katherine E; Mykhaylyk, Vitaliy; Wagner, Armin; Evans, Gwyndaf

    2013-07-01

    The focus in macromolecular crystallography is moving towards even more challenging target proteins that often crystallize on much smaller scales and are frequently mounted in opaque or highly refractive materials. It is therefore essential that X-ray beamline technology develops in parallel to accommodate such difficult samples. In this paper, the use of X-ray microradiography and microtomography is reported as a tool for crystal visualization, location and characterization on the macromolecular crystallography beamlines at the Diamond Light Source. The technique is particularly useful for microcrystals and for crystals mounted in opaque materials such as lipid cubic phase. X-ray diffraction raster scanning can be used in combination with radiography to allow informed decision-making at the beamline prior to diffraction data collection. It is demonstrated that the X-ray dose required for a full tomography measurement is similar to that for a diffraction grid-scan, but for sample location and shape estimation alone just a few radiographic projections may be required.

  13. Polymer Wall Formation Using Liquid-Crystal/Polymer Phase Separation Induced on Patterned Polyimide Films

    Science.gov (United States)

    Murashige, Takeshi; Fujikake, Hideo; Sato, Hiroto; Kikuchi, Hiroshi; Kurita, Taiichiro; Sato, Fumio

    2004-12-01

    We could form lattice-shaped polymer walls in a liquid crystal (LC) layer through the thermal phase separation of an LC/polystyrene solution between substrates with polyimide films etched by short-wavelength ultraviolet irradiation using a photomask. The LC wetting difference between the polyimide and substrate surfaces caused the coalescence of growing LC droplets on patterned polyimide films with the progress of phase separation. Consequently, polymer walls were formed on substrate surface areas without polyimide films. The shape of the polymer wall formed became sharp with the use of rubbed polyimide films because the nucleation of growing LC droplets concentrated on the patterned polyimide films. It is thought that the increase in the alignment order of LC molecules in the solution near the rubbed polyimide films promotes the formation of LC molecular aggregation, which becomes the growth nuclei of LC droplets.

  14. Light Diffraction of Aligned Polymer Fibers Periodically Dispersed by Phase Separation of Liquid Crystal and Polymer

    Science.gov (United States)

    Murashige, Takeshi; Fujikake, Hideo; Sato, Hiroto; Kikuchi, Hiroshi; Kurita, Taiichiro; Sato, Fumio

    2004-12-01

    We have confirmed light diffraction of aligned polymer fibers obtained by a phase separation of an anisotropic-phase solution of liquid crystal and polymer. He—Ne laser light passing through the polymer fibers was scattered in the axis vertical to the fibers, and had two peaks of light intensity symmetrical to the center of the transmitting laser spot. The two peaks were found to be caused by light diffraction due to the periodic polymer-fiber dispersion because the peaks corresponded to values calculated by intervals between the fibers. The periodical fiber networks are considered to be formed by anisotropic spinodal decomposition. This effect can be used to measure the dispersion order of the polymer fibers.

  15. Magnetic, magnetocaloric and magnetoresistive properties of cubic Laves phase HoAl2 single crystal.

    Science.gov (United States)

    Patra, M; Majumdar, S; Giri, S; Xiao, Y; Chatterji, T

    2014-01-29

    We report the magnetization (M) and magnetoresistance (MR) results of HoAl2 single crystals oriented along the ⟨100⟩ and ⟨110⟩ directions. Although HoAl2 has cubic Laves phase structure, a large anisotropy is observed in M and MR below the Curie temperature (TC). A satisfactory correlation between magnetic entropy change (ΔSM) and MR could be established along ⟨110⟩ and also ⟨100⟩, except for the temperature (T) region around which spin reorientation takes place. Large inverse magnetocaloric effect is observed at low T, which is associated with the spin reorientation process in the ⟨100⟩ direction. A theoretical model based on the Landau theory of phase transition can describe the T-variation of -ΔSM for T > TC.

  16. First and second order operator splitting methods for the phase field crystal equation

    Science.gov (United States)

    Lee, Hyun Geun; Shin, Jaemin; Lee, June-Yub

    2015-10-01

    In this paper, we present operator splitting methods for solving the phase field crystal equation which is a model for the microstructural evolution of two-phase systems on atomic length and diffusive time scales. A core idea of the methods is to decompose the original equation into linear and nonlinear subequations, in which the linear subequation has a closed-form solution in the Fourier space. We apply a nonlinear Newton-type iterative method to solve the nonlinear subequation at the implicit time level and thus a considerably large time step can be used. By combining these subequations, we achieve the first- and second-order accuracy in time. We present numerical experiments to show the accuracy and efficiency of the proposed methods.

  17. First and second order operator splitting methods for the phase field crystal equation

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyun Geun; Shin, Jaemin [Institute of Mathematical Sciences, Ewha Womans University, Seoul 120-750 (Korea, Republic of); Lee, June-Yub, E-mail: jyllee@ewha.ac.kr [Department of Mathematics, Ewha Womans University, Seoul 120-750 (Korea, Republic of)

    2015-10-15

    In this paper, we present operator splitting methods for solving the phase field crystal equation which is a model for the microstructural evolution of two-phase systems on atomic length and diffusive time scales. A core idea of the methods is to decompose the original equation into linear and nonlinear subequations, in which the linear subequation has a closed-form solution in the Fourier space. We apply a nonlinear Newton-type iterative method to solve the nonlinear subequation at the implicit time level and thus a considerably large time step can be used. By combining these subequations, we achieve the first- and second-order accuracy in time. We present numerical experiments to show the accuracy and efficiency of the proposed methods.

  18. Long-wavelength properties of phase-field-crystal models with second-order dynamics

    Science.gov (United States)

    Heinonen, V.; Achim, C. V.; Ala-Nissila, T.

    2016-05-01

    The phase-field-crystal (PFC) approach extends the notion of phase-field models by describing the topology of the microscopic structure of a crystalline material. One of the consequences is that local variation of the interatomic distance creates an elastic excitation. The dynamics of these excitations poses a challenge: pure diffusive dynamics cannot describe relaxation of elastic stresses that happen through phonon emission. To this end, several different models with fast dynamics have been proposed. In this article we use the amplitude expansion of the PFC model to compare the recently proposed hydrodynamic PFC amplitude model with two simpler models with fast dynamics. We compare these different models analytically and numerically. The results suggest that in order to have proper relaxation of elastic excitations, the full hydrodynamical description of the PFC amplitudes is required.

  19. Graphene oxide liquid crystals: synthesis, phase transition, rheological property, and applications in optoelectronics and display

    Science.gov (United States)

    Lin, Feng; Tong, Xin; Wang, Yanan; Bao, Jiming; Wang, Zhiming M.

    2015-11-01

    Graphene oxide (GO) liquid crystals (LCs) are macroscopically ordered GO flakes dispersed in water or polar organic solvents. Since the first report in 2011, GO LCs have attracted considerable attention for their basic properties and potential device applications. In this review, we summarize recent developments and present a comprehensive understanding of GO LCs via many aspects ranging from the exfoliation of GO flakes from graphite, to phases and phase transitions under various conditions, the orientational responses of GO under external magnetic and electric fields, and finally Kerr effect and display applications. The emphasis is placed on the unique and basic properties of GO and their ordered assembly. We will also discuss challenges and issues that need to be overcome in order to gain a more fundamental understanding and exploit full device potentials of GO LCs.

  20. High-pressure high-temperature phase diagram of organic crystal paracetamol

    Science.gov (United States)

    Smith, Spencer J.; Montgomery, Jeffrey M.; Vohra, Yogesh K.

    2016-01-01

    High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped heating diamond anvil. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in five different experiments. Solid state phase transitions from monoclinic Form I  →  orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II  →  unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. This new data is combined with previous ambient temperature high-pressure Raman and x-ray diffraction data to create the first HPHT phase diagram of paracetamol.

  1. Liquid Crystal Phase Transition driven three-dimensional Quantum Dot Organization

    Science.gov (United States)

    Rodarte, Andrea L.; Pandolfi, R. J.; Ghosh, S.; Hirst, L. S.

    2013-03-01

    We use a nematic liquid crystal (LC) to create organized assemblies of CdSe/ZnS core/shell quantum dots (QDs). At the isotropic-nematic LC phase transition, ordered domains of nematic LC expel the majority of dispersed QDs into the isotropic domains. The final LC phase produces a series of three dimensional columnar QD assemblies that are situated at defect points in the LC volume. Within each assembly the QD emission is spectrally-red-shifted due to resonant energy transfer. We use this spectral shift as a measure of the inter-dot separation and find that the QDs are packed uniformly in these assemblies over distances of microns between the glass plates of a standard LC cell. In addition, because the QD clusters form at defects, we can deterministically control the location of the assemblies by seeding the LC cell with defect nucleation points. Funding provided by NSF, UC MERI and UC MEXUS.

  2. Low voltage transflective blue-phase liquid crystal display with a non-uniform etching substrate

    Science.gov (United States)

    Wang, Jian; Mao, Jiang-Lin; Fan, Hao-Xiang; Wang, Qiong-Hua

    2016-09-01

    A transflective polymer-stabilized blue-phase liquid crystal display (BP-LCD) with a non-uniform etching substrate is proposed. In-plane switching (IPS) electrodes on the bottom substrate are put on the different gaps, and the bottom substrate between the electrodes is etched into different depths in transmissive (T) and reflective (R) regions. This structure can balance the optical phase retardation in the two regions and is helpful to achieve well-matched voltag-dependent transmittance and reflectance curves. This transflective display has high optical efficiency, a wide viewing angle, and low operating voltage (approximately 6 V). Project supported by the National Natural Science Foundation of China (Grant Nos. 61535007 and 61320106015) and the National Basic Research Program of China (Grant No. 2013CB328802).

  3. A magnetic glassy phase in Fe(1+y)Se(x)Te(1-x) single crystals.

    Science.gov (United States)

    Lamura, G; Shiroka, T; Bonfà, P; Sanna, S; Bernardini, F; De Renzi, R; Viennois, R; Giannini, E; Piriou, A; Emery, N; Cimberle, M R; Putti, M

    2013-04-17

    The evolution of magnetic order in Fe1+ySexTe1-x crystals as a function of Se content was investigated by means of ac/dc magnetometry and muon-spin spectroscopy. Experimental results and self-consistent density functional theory calculations both indicate that muons are implanted in vacant iron-excess sites, where they probe a local field mainly of dipolar origin, resulting from an antiferromagnetic (AFM) bicollinear arrangement of iron spins. This long-range AFM phase becomes progressively disordered with increasing Se content. At the same time all the tested samples manifest a marked glassy character that vanishes for high Se contents. The presence of local electronic/compositional inhomogeneities most likely favours the growth of clusters whose magnetic moment 'freezes' at low temperature. This glassy magnetic phase justifies both the coherent muon precession seen at short times in the asymmetry data, as well as the glassy behaviour evidenced by both dc and ac magnetometry.

  4. A low-phase-noise digitally controlled crystal oscillator for DVB TV tuners

    Energy Technology Data Exchange (ETDEWEB)

    Zhao Wei; Lu Lei; Tang Zhangwen, E-mail: zwtang@fudan.edu.c [State Key Laboratory of ASIC and System, Fudan University, Shanghai 201203 (China)

    2010-07-15

    This paper presents a 25-MHz fully-integrated digitally controlled crystal oscillator (DCXO) with automatic amplitude control (AAC). The DCXO is based on Colpitts topology for one-pin solution. The AAC circuit is introduced to optimize the phase noise performance. The automatic frequency control is realized by a 10-bit thermometer-code segmental tapered MOS capacitor array, ensuring a {approx} 35 ppm tuning range and {approx} 0.04 ppm frequency step. The measured phase noise results are -139 dBc/Hz at 1 kHz and -151 dBc/Hz at 10 kHz frequency offset, respectively. The chip consumes 1 mA at 1.8V supply and occupies 0.4 mm{sup 2} in a 0.18-{mu}m CMOS process.

  5. A low-phase-noise digitally controlled crystal oscillator for DVB TV tuners

    Science.gov (United States)

    Wei, Zhao; Lei, Lu; Zhangwen, Tang

    2010-07-01

    This paper presents a 25-MHz fully-integrated digitally controlled crystal oscillator (DCXO) with automatic amplitude control (AAC). The DCXO is based on Colpitts topology for one-pin solution. The AAC circuit is introduced to optimize the phase noise performance. The automatic frequency control is realized by a 10-bit thermometer-code segmental tapered MOS capacitor array, ensuring a ~ 35 ppm tuning range and ~ 0.04 ppm frequency step. The measured phase noise results are -139 dBc/Hz at 1 kHz and -151 dBc/Hz at 10 kHz frequency offset, respectively. The chip consumes 1 mA at 1.8V supply and occupies 0.4 mm2 in a 0.18-μm CMOS process.

  6. Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase

    Science.gov (United States)

    Saito, Shohei; Nobusue, Shunpei; Tsuzaka, Eri; Yuan, Chunxue; Mori, Chigusa; Hara, Mitsuo; Seki, Takahiro; Camacho, Cristopher; Irle, Stephan; Yamaguchi, Shigehiro

    2016-07-01

    Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of sufficient bonding strength and its rapid disappearance by photoirradiation. Here we report a dynamic molecular LC material that meets these requirements. Columnar-stacked V-shaped carbon frameworks display sufficient bonding strength even during heating conditions, while its bonding ability is immediately lost by a light-induced self-melting function. The light-melt adhesive is reusable and its fluorescence colour reversibly changes during the cycle, visualizing the bonding/nonbonding phases of the adhesive.

  7. Threshold for plasma phase transition of aluminum single crystal induced by hypervelocity impact

    Energy Technology Data Exchange (ETDEWEB)

    Ju, Yuanyuan; Zhang, Qingming, E-mail: qmzhang@bit.edu.cn [State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081 (China)

    2015-12-15

    Molecular dynamics method is used to study the threshold for plasma phase transition of aluminum single crystal induced by hypervelocity impact. Two effective simulation methods, piston-driven method and multi-scale shock technique, are used to simulate the shock wave. The simulation results from the two methods agree well with the experimental data, indicating that the shock wave velocity is linearly dependent on the particle velocity. The atom is considered to be ionized if the increase of its internal energy is larger than the first ionization energy. The critical impact velocity for plasma phase transition is about 13.0 km/s, corresponding to the threshold of pressure and temperature which is about 220 GPa and 11.0 × 10{sup 3 }K on the shock Hugoniot, respectively.

  8. Unraveling Crystal Growth in GeSb Phase-Change Films in between the Glass-Transition and Melting Temperatures

    NARCIS (Netherlands)

    Eising, Gert; Van Damme, Tobias; Kooi, Bart J.

    2014-01-01

    The study of crystal growth in phase-change thin films is of crucial importance to improve our understanding of the extraordinary phase transformation kinetics of these materials excellently suited for data storage applications. Here, we developed and used a new method, based on isothermal heating u

  9. Utilization of a liquid crystal spatial light modulator in a gray scale detour phase method for Fourier holograms.

    Science.gov (United States)

    Makey, Ghaith; El-Daher, Moustafa Sayem; Al-Shufi, Kanj

    2012-11-10

    This paper introduces a new modification for the well-known binary detour phase method, which is largely used to represent Fourier holograms; the modification utilizes gray scale level control provided by a liquid crystal spatial light modulator to improve the traditional binary detour phase. Results are shown by both simulation and experiment.

  10. Potassium doped barium bismuthates coexisting near the tetra (ortho) and cubic phases boundary: crystal growth and properties

    Energy Technology Data Exchange (ETDEWEB)

    Barilo, S.N. [Institute of Solid State and Semiconductors Physics, Minsk 220072 (Belarus). E-mail: bars at ifttp.bas-net.by; Shiryaev, S.V.; Soldatov, A.G.; Smirnova, T.V.; Gatalskaya, V.I. [Institute of Solid State and Semiconductors Physics, Minsk 220072 (Belarus); Reichardt, W. [Foschungszentrum Karlsruhe, INFP, 3640-76021, Karlsruhe (Germany); Braden, M. [Laboratoire Leon Brillouin, CE-Saclay, CEA, Cedex 91191, Gif sur Yvette (France); Szymczak, H.; Szymczak, R.; Baran, M. [Institute of Physics, PL02-668, Warsaw (Poland)

    2000-08-01

    We report on the seeded growth of large (up to 2 cm{sup 3}) single crystals of the cubic and orthorhombic phases of Ba{sub 1-x}K{sub x}BiO{sub 3}. The shape of the crystals varies with potassium content from a cube to a cube-octahedron shape at x{approx}0.2. The flux saturated by Bi{sub 2}O{sub 3} alone with an anode potential of +740 mV were selected to grow cubic Ba{sub 1-x}K{sub x}BiO{sub 3} crystals with x 0.67, T{sub c}{approx}4.5 K. We found that a new cubic phase (x = 0.51, a = 4.266 A) of crystals could be grown under +970 mV potential and reduced Bi{sub 2}O{sub 3} content in the flux. The crystals grown at {approx}250 deg. C acquired a cube-octahedron shape. In turn, crystals of the tetragonal Ba{sub 1.7}K{sub 1.3}Bi{sub 2}O{sub 7} phase (a = 4.25 A, c = 21.91 A) up to several mm{sup 3} in size were grown at the same temperature but lower potential and higher Bi{sub 2O}3 concentration in the flux. Surprisingly the crystals exhibited a weak superconductor-like magnetization. (author)

  11. 5 × 5 cm2 silicon photonic crystal slabs on glass and plastic foil exhibiting broadband absorption and high-intensity near-fields

    Science.gov (United States)

    Becker, C.; Wyss, P.; Eisenhauer, D.; Probst, J.; Preidel, V.; Hammerschmidt, M.; Burger, S.

    2014-07-01

    Crystalline silicon photonic crystal slabs are widely used in various photonics applications. So far, the commercial success of such structures is still limited owing to the lack of cost-effective fabrication processes enabling large nanopatterned areas (>> 1 cm2). We present a simple method for producing crystalline silicon nanohole arrays of up to 5 × 5 cm2 size with lattice pitches between 600 and 1000 nm on glass and flexible plastic substrates. Exclusively up-scalable, fast fabrication processes are applied such as nanoimprint-lithography and silicon evaporation. The broadband light trapping efficiency of the arrays is among the best values reported for large-area experimental crystalline silicon nanostructures. Further, measured photonic crystal resonance modes are in good accordance with light scattering simulations predicting strong near-field intensity enhancements greater than 500. Hence, the large-area silicon nanohole arrays might become a promising platform for ultrathin solar cells on lightweight substrates, high-sensitive optical biosensors, and nonlinear optics.

  12. 5 × 5 cm² silicon photonic crystal slabs on glass and plastic foil exhibiting broadband absorption and high-intensity near-fields.

    Science.gov (United States)

    Becker, C; Wyss, P; Eisenhauer, D; Probst, J; Preidel, V; Hammerschmidt, M; Burger, S

    2014-07-30

    Crystalline silicon photonic crystal slabs are widely used in various photonics applications. So far, the commercial success of such structures is still limited owing to the lack of cost-effective fabrication processes enabling large nanopatterned areas (≫ 1 cm(2)). We present a simple method for producing crystalline silicon nanohole arrays of up to 5 × 5 cm(2) size with lattice pitches between 600 and 1000 nm on glass and flexible plastic substrates. Exclusively up-scalable, fast fabrication processes are applied such as nanoimprint-lithography and silicon evaporation. The broadband light trapping efficiency of the arrays is among the best values reported for large-area experimental crystalline silicon nanostructures. Further, measured photonic crystal resonance modes are in good accordance with light scattering simulations predicting strong near-field intensity enhancements greater than 500. Hence, the large-area silicon nanohole arrays might become a promising platform for ultrathin solar cells on lightweight substrates, high-sensitive optical biosensors, and nonlinear optics.

  13. A Phase Field Technique for Modeling and Predicting Flow Induced Crystallization Morphology of Semi-Crystalline Polymers

    Directory of Open Access Journals (Sweden)

    Xiaodong Wang

    2016-06-01

    Full Text Available Flow induced crystallization of semi-crystalline polymers is an important issue in polymer science and engineering because the changes in morphology strongly affect the properties of polymer materials. In this study, a phase field technique considering polymer characteristics was established for modeling and predicting the resulting morphologies. The considered crystallization process can be divided into two stages, which are nucleation upon the flow induced structures and subsequent crystal growth after the cessation of flow. Accordingly, the proposed technique consists of two parts which are a flow induced nucleation model based on the calculated information of molecular orientation and stretch, and a phase field crystal growth model upon the oriented nuclei. Two-dimensional simulations are carried out to predict the crystallization morphology of isotactic polystyrene under an injection molding process. The results of these simulations demonstrate that flow affects crystallization morphology mainly by producing oriented nuclei. Specifically, the typical skin-core structures along the thickness direction can be successfully predicted. More importantly, the results reveal that flow plays a dominant part in generating oriented crystal morphologies compared to other parameters, such as anisotropy strength, crystallization temperature, and physical noise.

  14. Crystal structure and thermochemical properties of bis(1-octylammonium) tetrachlorochromate phase change materials

    Institute of Scientific and Technical Information of China (English)

    Lu Dong-Fei; Di You-Ying; He Dong-Hua

    2012-01-01

    A new crystalline complex (C8H17NH3)2CdCl4 (s) (abbreviated as CsCd(s)) is synthesized by liquid phase reaction.The crystal structure and composition of the complex are determined by single crystal X-ray diffraction,chemical analysis,and elementary analysis.It is triclinic,the space group is P-1 and Z =2.The lattice potential energy of the title complex is calculated to be UpoT (CsCd(s))=978.83 kJ.mol-1 from crystallographic data.Low-temperature heat capacities of the complex are measured by using a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K.The temperature,molar enthalpy,and entropy of the phase transition for the complex are determined to be 307.3±0.15 K,10.15±0.23 kJ.mol-1 and 33.05±0.78 J.K-1.mo1-1 respectively for the endothermic peak.Two polynomial equations of the heat capacities each as a function of temperature are fitted by using the leastsquare method.Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.

  15. Partially transformed relaxor ferroelectric single crystals with distributed phase transformation behavior

    Science.gov (United States)

    Gallagher, John A.

    2015-11-01

    Relaxor ferroelectric single crystals such as PMN-PT and PIN-PMN-PT undergo field driven phase transformations when electrically or mechanically loaded in crystallographic directions that provide a positive driving force for the transformation. The observed behavior in certain compositions is a phase transformation distributed over a range of fields without a distinct forward or reverse coercive field. This work focuses on the material behavior that is observed when the crystals are loaded sufficiently to drive a partial transformation and then unloaded, as might occur when driving a transducer to achieve high power levels. Distributed transformations have been modeled using a normal distribution of transformation thresholds. A set of experiments was conducted to characterize the hysteresis loops that occur with the partial transformations. In this work the normal distribution model is extended to include the partial transformations that occur when the field is reversed before the transformation is complete. The resulting hysteresis loops produced by the model are in good agreement with the experimental results.

  16. Detecting, visualizing, and measuring gold nanoparticle chirality using helical pitch measurements in nematic liquid crystal phases.

    Science.gov (United States)

    Sharma, Anshul; Mori, Taizo; Lee, Huey-Charn; Worden, Matthew; Bidwell, Eric; Hegmann, Torsten

    2014-12-23

    Chirality at the nanoscale, or more precisely, the chirality or chiroptical effects of chiral ligand-capped metal nanoparticles (NPs) is an intriguing and rapidly evolving field in nanomaterial research with promising applications in catalysis, metamaterials, and chiral sensing. The aim of this work was to seek out a system that not only allows the detection and understanding of NP chirality but also permits visualization of the extent of chirality transfer to a surrounding medium. The nematic liquid crystal phase is an ideal candidate, displaying characteristic defect texture changes upon doping with chiral additives. To test this, we synthesized chiral cholesterol-capped gold NPs and prepared well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism spectropolarimetry and polarized light optical microscopy revealed that all three gold NPs induce chiral nematic phases, and that those synthesized in the presence of a chiral bias (disulfide) are more powerful chiral inducers than those where the NP was formed in the absence of a chiral bias (prepared by conjugation of a chiral silane to preformed NPs). Helical pitch data here visually show a clear dependence on the NP size and the number of chiral ligands bound to the NP surface, thereby supporting earlier experimental and theoretical data that smaller metal NPs made in the presence of a chiral bias are stronger chiral inducers.

  17. A fundamental measure density functional for fluid and crystal phases of the Asakura-Oosawa model

    Science.gov (United States)

    Mortazavifar, Mostafa; Oettel, Martin

    2016-06-01

    We investigate a density functional for the Asakura-Oosawa model of colloid-polymer mixtures, describing both fluid and crystal phases. It is derived by linearizing the two-component fundamental-measure hard sphere tensor functional in the second (polymer) component. We discuss the formulation of an effective density functional for colloids only. For small polymer-colloid size ratios the effective, polymer-induced potential between colloids is short-range attractive and of two-body form but we show that the effective density functional is not equivalent to standard mean-field approaches where attractions are taken into account by terms second order in the colloid density. We calculate numerically free energies and phase diagrams in good agreement with available simulations, furthermore we discuss the colloid and polymer distributions in the crystal and determine equilibrium vacancy concentrations. Numerical results reveal a fairly strong sensitivity to the specific type of underlying fundamental measure hard sphere functional which could aid further development of fundamental measure theory.

  18. Plastic Surgery

    Science.gov (United States)

    ... Surgery? A Week of Healthy Breakfasts Shyness Plastic Surgery KidsHealth > For Teens > Plastic Surgery Print A A ... forehead lightened with a laser? What Is Plastic Surgery? Just because the name includes the word "plastic" ...

  19. Rich magnetoelectric phase diagrams of multiferroic single-crystal α -NaFeO2

    Science.gov (United States)

    Terada, Noriki; Ikedo, Yuta; Sato, Hirohiko; Khalyavin, Dmitry D.; Manuel, Pascal; Miyake, Atsushi; Matsuo, Akira; Tokunaga, Masashi; Kindo, Koichi

    2017-07-01

    The magnetic and dielectric properties of the multiferroic triangular lattice magnet compound α -NaFeO2 were studied by magnetization, specific heat, dielectric permittivity, and pyroelectric current measurements and by neutron diffraction experiments using single crystals grown by a hydrothermal synthesis method. This work produced magnetic field (in the monoclinic a b -plane, Ba b, and along the c*-axis, Bc) versus temperature magnetic phase diagrams, including five and six magnetically ordered phases in Ba b and along Bc, respectively. In zero magnetic field, two spin-density-wave orderings with different k vectors—(0 ,q ,1/2 ) in phase I and (qa,qb,qc ) in phase II—appeared at T =9.5 and 8.25 K, respectively. Below T =5 K, a commensurate order with k =(0.5 ,0 ,0.5 ) was stabilized as the ground state in phase III. Both Ba b≥3 T and Bc≥5 T were found to induce ferroelectric phases at the lowest temperature (2 K), with an electric polarization that was not confined to any highly symmetric directions in phases IVa b (3.3 ≤Ba b≤8.5 T), Va b (8.5 ≤Ba b≤13.6 T), IVc (5.0 ≤Bc≤8.5 T), and Vc (8.5 ≤Bc≤13.5 T). In phase VIc, within a narrow temperature region in Bc, the polarization was confined to the a b plane. For each of the ferroelectric phases, the k vector was (qa,qb,qc ), and noncollinear structures were identified, including a general spiral in IVa b an a b cycloid in IVc and Vc, and a proper screw in VIc, along with a triclinic 11' magnetic point group allowing polarization in the general direction. Comparing the polarization direction to the magnetic structures in the ferroelectric phases, we conclude that the extended inverse Dzyaloshinskii-Moriya mechanism expressed by the orthogonal components p1∝ri j×(Si×Sj) and p2∝Si×Sj can explain the polarization directions. Based on calculations incorporating exchange interactions up to fourth-nearest-neighbor (NN) couplings, we infer that competition among antiferromagnetic second NN

  20. Multiple-beams Mutually Pumped Phase Conjugation Generated by a Bridge Phase Conjugator in Photorefractive Ba1 - xSrxTi03 Crystal

    Institute of Scientific and Technical Information of China (English)

    QIU Yishen; LU Tuansun; HUANG Wenchai; ZHENG Zhiqiang; ZHUANG Jian; TANG Dingyuan

    2000-01-01

    A new method generating multiple-beams mutually pumped phase conjugation (MMPPC) in a photorefractive Bat- xSrxTiO3 crystal is demonstrated, in which a pumping beam is incident upon a-face of the crystal and two signal beams are introduced into + c face of the crystal with the almost same incident angle and position. The time evolution of the phase conjugations from signal beams and the dependence of phase-conjugate reflectivities on the input-beam intensity ratios are presented. Also, the amplitude coupled-wave equations based on the model of two interaction reigns is derived. The results obtained by numerical calculation of the corresponding coupled-wave equations show qualitative agreement with the experimental results.