WorldWideScience

Sample records for crystal lattice vibrations

  1. [Lattice vibration of Sr3TaGa3Si2O14 single crystal].

    Science.gov (United States)

    Yang, Hong; Lu, Gui-Wu; Yu, Ying-Hui; Li, Ying-Feng; Wang, Zeng-Mei

    2008-03-01

    Based on the space group theory, the normal vibration modes of Sr3 TaGa3Si2O14 (STGS) single crystal were predicted, and the Raman scattering intensities of non-polar and polar modes were calculated. The Raman spectrum of STGS crystal was measured, and lattice vibration modes of STGS crystal were assigned. For symmetry species A1, six typical Raman-active optical modes have been recorded at 126, 245, 557, 604, 896 and 991 cm(-1), respectively. It is easy to assign the mode of 126 cm(-1) as the relative translation between SiO4, Sr and the TaO6. The mode 245 cm(-1) corresponds to the twisting vibration of SiO4 correlating with the Sr-TaO6-Sr stretching vibration. The mode 557 cm(-1) was assigned as the O-Ta-O stretching vibration, while the mode 604 cm(-1) as the O-Ga-O stretching vibration. The band at 896 cm(-1) in the Raman spectrum was assigned to be the O-Si-O stretching vibration of the two SiO4 tetrahedra in the primitive cell of STGS single crystal. Meanwhile, the band at 991 cm(-1) in the Raman spectrum was assigned to be the Si-O stretching vibration of the two SiO4 tetrahedra in the primitive cell of STGS single crystal. The layer structure of STGS crystal was identified by both theory study and Raman spectroscopy experiment results. The small anisotropy and piezoelectric modulus of STGS crystal were ascribed to the weak distortion of decahedral unit.

  2. High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4.

    Science.gov (United States)

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Gomis, Oscar; Achary, S Nagabhusan; Popescu, Catalin; Patwe, Sadeque J; Tyagi, Avesh K

    2016-05-16

    The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations.

  3. Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice

    Energy Technology Data Exchange (ETDEWEB)

    Zhukova, Elena S., E-mail: zhukovaelenka@gmail.com; Gorshunov, Boris P. [Moscow Institute of Physics and Technology, 9 Institutskiy per., 141700 Dolgoprudny, Moscow Region (Russian Federation); 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany); A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilova Street 38, 119991 Moscow (Russian Federation); Torgashev, Victor I. [Faculty of Physics, Southern Federal University, 5 Zorge St., 344090 Rostov-on-Don (Russian Federation); Lebedev, Vladimir V. [Moscow Institute of Physics and Technology, 9 Institutskiy per., 141700 Dolgoprudny, Moscow Region (Russian Federation); Landau Institute for Theoretical Physics, Russian Academy of Sciences, Akademika Semenova av., 1-A, 142432 Chernogolovka, Moscow Region (Russian Federation); Shakurov, Gil' man S. [Kazan Physical-Technical Institute, Russian Academy of Sciences, 10/7 Sibirsky Trakt, 420029 Kazan (Russian Federation); Kremer, Reinhard K. [Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Pestrjakov, Efim V. [Institute of Laser Physics, Russian Academy of Sciences, 13/3 Ac. Lavrentyev' s Prosp., 630090 Novosibirsk (Russian Federation); Thomas, Victor G.; Fursenko, Dimitry A. [Institute of Geology and Mineralogy, Russian Academy of Sciences, 3 Ac. Koptyug' s Prosp., 630090 Novosibirsk (Russian Federation); Prokhorov, Anatoly S. [Moscow Institute of Physics and Technology, 9 Institutskiy per., 141700 Dolgoprudny, Moscow Region (Russian Federation); A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilova Street 38, 119991 Moscow (Russian Federation); Dressel, Martin [1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany)

    2014-06-14

    Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be{sub 3}Al{sub 2}Si{sub 6}O{sub 18}, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ε{sup ′}(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm{sup −1}, at temperatures 5–300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ε{sup ′}(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν{sub 1}, ν{sub 2}, and ν{sub 3} of the H{sub 2}O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm{sup −1} reveal a rich set of highly anisotropic features in the low-energy response of H{sub 2}O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ∼90 cm{sup −1} and ∼160 cm{sup −1}, several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400–500 cm{sup −1}) and translational (150–200 cm{sup −1}) vibrations of water-I molecule that is weakly coupled to the nano-cavity “walls.” A model is presented that explains the “fine structure” of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential

  4. Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice.

    Science.gov (United States)

    Zhukova, Elena S; Torgashev, Victor I; Gorshunov, Boris P; Lebedev, Vladimir V; Shakurov, Gil'man S; Kremer, Reinhard K; Pestrjakov, Efim V; Thomas, Victor G; Fursenko, Dimitry A; Prokhorov, Anatoly S; Dressel, Martin

    2014-06-14

    Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be3Al2Si6O18, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ɛ'(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm(-1), at temperatures 5-300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ɛ'(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν1, ν2, and ν3 of the H2O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm(-1) reveal a rich set of highly anisotropic features in the low-energy response of H2O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ~90 cm(-1) and ~160 cm(-1), several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400-500 cm(-1)) and translational (150-200 cm(-1)) vibrations of water-I molecule that is weakly coupled to the nano-cavity "walls." A model is presented that explains the "fine structure" of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential relief felt by a molecule within the cavity.

  5. Lattice Vibrations in Chlorobenzenes:

    DEFF Research Database (Denmark)

    Reynolds, P. A.; Kjems, Jørgen; White, J. W.

    1974-01-01

    Lattice vibrational dispersion curves for the ``intermolecular'' modes in the triclinic, one molecule per unit cell β phase of p‐C6D4Cl2 and p‐C6H4Cl2 have been obtained by inelastic neutron scattering. The deuterated sample was investigated at 295 and at 90°K and a linear extrapolation to 0°K...... by consideration of electrostatic forces or by further anisotropy in the dispersion forces not described in the atom‐atom model. Anharmonic effects are shown to be large, but the dominant features in the temperature variation of frequencies are describable by a quasiharmonic model....

  6. Lattice and Molecular Vibrations in Single Crystal I2 at 77 K by Inelastic Neutron Scattering

    DEFF Research Database (Denmark)

    Smith, H. G.; Nielsen, Mourits; Clark, C. B.

    1975-01-01

    Phonon dispersion curves of single crystal iodine at 77 K have been measured by one-phonon coherent inelastic neutron scattering techniques. The data are analysed in terms of two Buckingham-six intermolecular potentials; one to represent the shortest intermolecular interaction (3.5 Å) and the oth...... to represent the more distant interactions. Moderate agreement is obtained between the observed and calculated frequencies, but it also oappears necessary to treat the second-nearest-neighbor interaction (3.97 Å) separately from the van der Waals interactions (distances ⩾ 4.2 Å).......Phonon dispersion curves of single crystal iodine at 77 K have been measured by one-phonon coherent inelastic neutron scattering techniques. The data are analysed in terms of two Buckingham-six intermolecular potentials; one to represent the shortest intermolecular interaction (3.5 Å) and the other...

  7. Phonon-enhanced crystal growth and lattice healing

    Science.gov (United States)

    Buonassisi, Anthony; Bertoni, Mariana; Newman, Bonna

    2013-05-28

    A system for modifying dislocation distributions in semiconductor materials is provided. The system includes one or more vibrational sources for producing at least one excitation of vibrational mode having phonon frequencies so as to enhance dislocation motion through a crystal lattice.

  8. An Intermolecular Vibration Model for Lattice Ice

    Directory of Open Access Journals (Sweden)

    Quinn M. Brewster

    2010-06-01

    Full Text Available Lattice ice with tetrahedral arrangement is studied using a modified Einstein’s model that incorporates the hindered translational and rotational vibration bands into a harmonic oscillation system. The fundamental frequencies for hindered translational and rotational vibrations are assigned based on the intermolecular vibration bands as well as thermodynamic properties from existing experimental data. Analytical forms for thermodynamic properties are available for the modified model, with three hindered translational bands at (65, 229, 229 cm-1 and three effective hindered rotational bands at 560 cm-1. The derived results are good for temperatures higher than 30 K. To improve the model below 30 K, Lorentzian broadening correction is added. This simple model helps unveil the physical picture of ice lattice vibration behavior.

  9. Thermodynamic properties of the magnetized Coulomb crystal lattices

    Science.gov (United States)

    Kozhberov, A. A.

    2016-08-01

    It is thought that Coulomb crystals of ions with hexagonal close-packed lattice may form in the crust of strongly-magnetized neutron stars (magnetars). In this work we are trying to verify this prediction assuming that the direction of the magnetic field corresponds to the minimum of the zero-point energy. We also continue a detailed study of vibration modes and thermodynamic properties of magnetized Coulomb crystals in a wide range of temperatures and magnetic fields. It is demonstrated that the total Helmholtz free energy of the body-centered cubic Coulomb crystal is always lower than that of the Coulomb crystal with hexagonal close-packed or face-centered cubic lattice, which casts doubt on the hypothesis above.

  10. Instability of vibrational modes in hexagonal lattice

    Science.gov (United States)

    Korznikova, Elena A.; Bachurin, Dmitry V.; Fomin, Sergey Yu.; Chetverikov, Alexander P.; Dmitriev, Sergey V.

    2017-02-01

    The phenomenon of modulational instability is investigated for all four delocalized short-wave vibrational modes recently found for the two-dimensional hexagonal lattice with the help of a group-theoretic approach. The polynomial pair potential with hard-type quartic nonlinearity ( β-FPU potential with β > 0) is used to describe interactions between atoms. As expected for the hard-type anharmonic interactions, for all four modes the frequency is found to increase with the amplitude. Frequency of the modes I and III bifurcates from the upper edge of the phonon spectrum, while that of the modes II and IV increases from inside the spectrum. It is also shown that the considered model supports spatially localized vibrational mode called discrete breather (DB) or intrinsic localized mode. DB frequency increases with the amplitude above the phonon spectrum. Two different scenarios of the mode decay were revealed. In the first scenario (for modes I and III), development of the modulational instability leads to a formation of long-lived DBs that radiate their energy slowly until thermal equilibrium is reached. In the second scenario (for modes II and IV) a transition to thermal oscillations of atoms is observed with no formation of DBs.

  11. Low-Frequency Vibrational Modes of Poly(glycolic acid) and Thermal Expansion of Crystal Lattice Assigned On the Basis of DFT-Spectral Simulation Aided with a Fragment Method.

    Science.gov (United States)

    Yamamoto, Shigeki; Miyada, Mai; Sato, Harumi; Hoshina, Hiromichi; Ozaki, Yukihiro

    2017-02-09

    Low-frequency vibrational modes of lamellar crystalline poly(glycolic acid) (PGA) were measured on Raman and far-infrared (FIR) spectra. Among the observed bands, an FIR band at ∼70 cm(-1) and a Raman band at 125 cm(-1) showed a gradual lower-frequency shift with increasing temperature from 20 °C to the melting point at ∼230 °C. Their polarization direction was perpendicular to the chain axis of PGA. Both spectra were quantum-mechanically simulated with the aid of a fragment method, the Cartesian-coordinate tensor transfer, which enabled an explicit consideration of molecular interactions between two adjacent polymer chains. Good agreement was achieved between the experiment and theory in both spectra. The temperature-sensitive bands at ∼70 cm(-1) in FIR and at 125 cm(-1) in Raman comprise the out-of-plane C═O bending motion. The temperature-dependent shifts of the low-frequency bands were successfully simulated by the DFT-spectral calculation, exploring that the main origin of the shifts is the thermal expansion of the crystal lattice. This result indicates that the thermally shifted bands may be used as an indicator of the lattice expansion of PGA. Possible changes in intermolecular interactions of PGA under temperature rising were ascribed on the basis of natural bond orbital theory. The steric repulsion between the carbonyl O atom in one chain and the H-C bond in the adjacent chain will be a dominant interaction in the lattice-expanding process, which would cause the observed thermal shifts of the bending modes. Comparisons of the spectral assignment for PGA obtained in this study and that for poly-(R)-3-hydroxybutyrate (PHB) reported by us suggest that crystalline polyesters give vibrational modes composed of out-of-plane bending motion of C═O groups between ∼70 and ∼125 cm(-1), the modes of which are sensitive to the thermal expansion of crystal lattice and its concomitant changes in their intermolecular interactions.

  12. Lattice vibrations of the icosahedral solid. alpha. -boron

    Energy Technology Data Exchange (ETDEWEB)

    Beckel, C.L.; Yousaf, M.; Fuka, M.Z.; Raja, S.Y.; Lu, N. (Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico (USA))

    1991-08-01

    Crystalline {alpha}-boron consists of B{sub 12} icosahedra in a rhombohedral lattice of {ital R}{bar 3}{ital m} space-group symmetry. We here carry out a classical force-field analysis of the lattice vibrations. The {bold q}={bold 0} Brillouin-zone vibrations are treated as those of a {ital D}{sub 3{ital d}}-point-group-symmetry B{sub 12} cluster perturbed by intericosahedral crystalline forces; valence-force constants are fitted to account for Raman and ir spectral data. Two-centered intericosahedral bonds are found to be twice as strong as intraicosahedral bonds, while three-centered crystalline bonds are almost as strong as those within a B{sub 12} unit. The highest-frequency Raman line arises from the breathing mode, strongly perturbed by the two-centered interactions. The lowest-observed-frequency Raman line is attributed to B{sub 12} libration. As crystal-force-field strengths are turned up, noncrossing of frequencies is encountered; we, therefore, correlate {alpha}-crystal modes with {ital I}{sub {ital h}} regular-icosahedral and {ital D}{sub 3{ital d}} B{sub 12}-cluster modes through eigenvector expansions. Useful classical predictions are made of ir intensities for wave vector {bold q}={bold 0} modes by considering adjacent bond stretching; a prediction of Raman intensities in terms of bond polarizabilities appears to be of very limited value. The phonon analysis is extended from the Brillouin-zone center to the edges by introducing phase-angle differences along two distinct (one {ital C}{sub 3} and one {ital C}{sub 2}) rotational-symmetry axes. The acoustical-branch wave speeds are predicted to be 1.1{times}10{sup 6} and 0.38{times}10{sup 6} cm/sec for the {ital c}-direction longitudinal and transverse components, respectively.

  13. Theoretical and Experimental Study of the Crystal Structures, Lattice Vibrations, and Band Structures of Monazite-Type PbCrO4, PbSeO4, SrCrO4, and SrSeO4.

    Science.gov (United States)

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Proctor, John E; Sapiña, Fernando; Bettinelli, Marco

    2015-08-03

    The crystal structures, lattice vibrations, and electronic band structures of PbCrO4, PbSeO4, SrCrO4, and SrSeO4 were studied by ab initio calculations, Raman spectroscopy, X-ray diffraction, and optical-absorption measurements. Calculations properly describe the crystal structures of the four compounds, which are isomorphic to the monazite structure and were confirmed by X-ray diffraction. Information is also obtained on the Raman- and IR-active phonons, with all of the vibrational modes assigned. In addition, the band structures and electronic densities of states of the four compounds were determined. All are indirect-gap semiconductors. In particular, chromates are found to have band gaps smaller than 2.5 eV and selenates higher than 4.3 eV. In the chromates (selenates), the upper part of the valence band is dominated by O 2p states and the lower part of the conduction band is composed primarily of electronic states associated with the Cr 3d and O 2p (Se 4s and O 2p) states. Calculations also show that the band gap of PbCrO4 (PbSeO4) is smaller than the band gap of SrCrO4 (SrSeO4). This phenomenon is caused by Pb states, which, to some extent, also contribute to the top of the valence band and the bottom of the conduction band. The agreement between experiments and calculations is quite good; however, the band gaps are underestimated by calculations, with the exception of the bang gap of SrCrO4, for which theory and calculations agree. Calculations also provide predictions of the bulk modulus of the studied compounds.

  14. Vibrational Properties of a Two-Dimensional Silica Kagome Lattice.

    Science.gov (United States)

    Björkman, Torbjörn; Skakalova, Viera; Kurasch, Simon; Kaiser, Ute; Meyer, Jannik C; Smet, Jurgen H; Krasheninnikov, Arkady V

    2016-12-27

    Kagome lattices are structures possessing fascinating magnetic and vibrational properties, but in spite of a large body of theoretical work, experimental realizations and investigations of their dynamics are scarce. Using a combination of Raman spectroscopy and density functional theory calculations, we study the vibrational properties of two-dimensional silica (2D-SiO2), which has a kagome lattice structure. We identify the signatures of crystalline and amorphous 2D-SiO2 structures in Raman spectra and show that, at finite temperatures, the stability of 2D-SiO2 lattice is strongly influenced by phonon-phonon interaction. Our results not only provide insights into the vibrational properties of 2D-SiO2 and kagome lattices in general but also suggest a quick nondestructive method to detect 2D-SiO2.

  15. Evidence of Ultrafast Charge Transfer Driven by Coherent Lattice Vibrations.

    Science.gov (United States)

    Rury, Aaron S; Sorenson, Shayne A; Dawlaty, Jahan M

    2017-01-05

    We report evidence that intermolecular vibrations coherently drive charge transfer between the sites of a material on ultrafast time scales. Following a nonresonant stimulated Raman pump pulse that excites the organic material quinhydrone, we observe the initial appearance of oscillations due to intermolecular lattice vibrations and then the delayed appearance of a higher-frequency oscillation that we assign to a totally symmetric intramolecular vibration. We use the coherent dynamics of the transient reflectivity signal to propose that coherence transfer drives excitation of this intramolecular vibration. Furthermore, we conclude that the dynamical frequency shift of the intramolecular vibration reports the formation of a quasi-stable charge-separated state on ultrafast time scales. We calculate model dynamics using the extended Hubbard Hamiltonian to explain coherence transfer due to vibrationally driven charge transfer. These results demonstrate that the coherent excitation of low-frequency vibrations can drive charge transfer in the solid state and control material properties.

  16. Lattice effects in YVO3 single crystal

    NARCIS (Netherlands)

    Marquina, C; Sikora, M; Ibarra, MR; Nugroho, AA; Palstra, TTM

    2005-01-01

    In this paper we report on the lattice effects in the Mott insulator yttrium orthovanadate (YVO3). Linear thermal expansion and magnetostriction experiments have been performed on a single crystal, in the temperature range from 5 K to room temperature. The YVO3 orders antiferromagnetically at T-N =

  17. Lattice vibrations of icosahedral boron-rich solids

    Energy Technology Data Exchange (ETDEWEB)

    Beckel, C.L.; Yousaf, M. (The University of New Mexico, Albuquerque, New Mexico 87131 (United States))

    1991-07-01

    The rhombohedral lattices for {alpha}-boron, boron arsenide, and boron phosphide are each of D{sub 3d} symmetry and have bases that include B{sub 12} icosahedra. Boron carbide with B{sub 4}C stoichiometry has near-D{sub 3d} symmetry and is almost certainly composed of B{sub 11}C icosahedra and C-B-C chains. Comparable classical force field models are applied to each of these crystals to correlate q=0 phonon structure with experimental Raman and IR spectra. We here describe our methods and contrast interaction strengths for different materials. Vibrations are correlated in the different crystals through normal mode eigenvector expansions. Acoustic wave velocities from Brillouin zone dispersion curves in two distinct symmetry-axis directions are presented and contrasted for {alpha}-boron and B{sub 12}As{sub 2}. The origin of lines with anomalous polarization and width in {alpha}-boron, B{sub 12}As{sub 2}, and B{sub 12}P{sub 2} is considered.

  18. Vibrational relaxation and vibrational cooling in low temperature molecular crystals

    Science.gov (United States)

    Hill, Jeffrey R.; Chronister, Eric L.; Chang, Ta-Chau; Kim, Hackjin; Postlewaite, Jay C.; Dlott, Dana D.

    1988-01-01

    The processes of vibrational relaxation (VR) and vibrational cooling (VC) are investigated in low temperature crystals of complex molecules, specifically benzene, naphthalene, anthracene, and durene. In the VR process, a vibration is deexcited, while VC consists of many sequential and parallel VR steps which return the crystal to thermal equilibrium. A theoretical model is developed which relates the VR rate to the excess vibrational energy, the molecular structure, and the crystal structure. Specific relations are derived for the vibrational lifetime T1 in each of three regimes of excess vibrational energy. The regimes are the following: Low frequency regime I where VR occurs by emission of two phonons, intermediate frequency regime II where VR occurs by emission of one phonon and one vibration, and high frequency regime III where VR occurs by evolution into a dense bath of vibrational combinations. The VR rate in each regime depends on a particular multiphonon density of states and a few averaged anharmonic coefficients. The appropriate densities of states are calculated from spectroscopic data, and together with available VR data and new infrared and ps Raman data, the values of the anharmonic coefficients are determined for each material. The relationship between these parameters and the material properties is discussed. We then describe VC in a master equation formalism. The transition rate matrix for naphthalene is found using the empirically determined parameters of the above model, and the time dependent redistribution in each mode is calculated.

  19. Parametric Vibration and Vibration Reduction of Cables in Cable-stayed Space Latticed Structure

    Institute of Scientific and Technical Information of China (English)

    BAO Yan; ZHOU Dai; LIU Jie

    2008-01-01

    Mechanical model and vibration equation of a cable in cable-stayed sparse latticed structure (CSLS) under external axial excitation were founded. Determination of the mass lumps and natural frequencies supplied by the space latticed structure (SLS) was analyzed. Multiple scales method (MSM) was introduced to analyze the characteristics of cable's parametric vibration, and the precise time-integration method (PTIM) was used to solve vibration equation. The vibration behavior of a cable is closely relative to the frequency ratio of the cable and SLS. The cable's parametric vibration caused by the external axial excitation easily occurs if the frequency ratio of the cable and SLS is in a certain range, and the cable's vibration amplitude varies greatly even if the initial disturbance supplied by SLS changes a little. Furthermore, the mechanical model and vibration equation of the composite cable system consisting of main cables and assistant cables were studied. The parametric analysis such as the pre-tension level and arrangement of the assistant cables was carried out. Due to the assistant cables, the single-cable vibration mode can be transferred to the global vibration mode, and the stiffness and damping of the cable system are enhanced. The natural frequencies of the composite cable system with the curve line arrangement of assistant cables are higher than those with the straight-line arrangement and the former is more effective than the latter on the cable's vibration suppression.

  20. Lattice vibration frequencies in Raman spectra of manganese and rhenium decacarbonyls

    Energy Technology Data Exchange (ETDEWEB)

    Volkov, V.E.; Danilov, I.Yu.; Zhidkov, L.L.; Kovalev, Yu.G.; Ioganson, A.A. (AN SSSR, Krasnoyarsk. Inst. Khimii i Khimicheskoj Tekhnologii)

    1983-06-01

    Raman spectra (RS) in the 170-10 cm/sup -1/ region of Mn/sub 2/(CO)/sub 10/, Re/sub 2/(CO)/sub 10/ polycrystal samples and their mixed crystals with different component percentage were obtained in the 296-123 K range. Investigations at low temperatures enabled to obtain most complete spectra in the given region. The spectra were separated to intramolecular and lattice ones on the basis of both comparing the spectra of pure components with those of mixed crystals, and studying the temperature behaviour of frequencies in the spectra. It was established that frequencies, placed below 60 cm/sup -1/ as well as in the region of 130-150 cm/sup -1/ in the spectra of manganese- and rhenium decacarbonyls are determined by the lattice vibrations of molecules in crystals.

  1. Lattice Metamaterials with Mechanically Tunable Poisson's Ratio for Vibration Control

    Science.gov (United States)

    Chen, Yanyu; Li, Tiantian; Scarpa, Fabrizio; Wang, Lifeng

    2017-02-01

    Metamaterials with artificially designed architectures are increasingly considered as new paradigmatic material systems with unusual physical properties. Here, we report a class of architected lattice metamaterials with mechanically tunable negative Poisson's ratios and vibration-mitigation capability. The proposed lattice metamaterials are built by replacing regular straight beams with sinusoidally shaped ones, which are highly stretchable under uniaxial tension. Our experimental and numerical results indicate that the proposed lattices exhibit extreme Poisson's-ratio variations between -0.7 and 0.5 over large tensile deformations up to 50%. This large variation of Poisson's-ratio values is attributed to the deformation pattern switching from bending to stretching within the sinusoidally shaped beams. The interplay between the multiscale (ligament and cell) architecture and wave propagation also enables remarkable broadband vibration-mitigation capability of the lattice metamaterials, which can be dynamically tuned by an external mechanical stimulus. The material design strategy provides insights into the development of classes of architected metamaterials with potential applications including energy absorption, tunable acoustics, vibration control, responsive devices, soft robotics, and stretchable electronics.

  2. Invariant patterns in crystal lattices: Implications for protein folding algorithms

    Energy Technology Data Exchange (ETDEWEB)

    HART,WILLIAM E.; ISTRAIL,SORIN

    2000-06-01

    Crystal lattices are infinite periodic graphs that occur naturally in a variety of geometries and which are of fundamental importance in polymer science. Discrete models of protein folding use crystal lattices to define the space of protein conformations. Because various crystal lattices provide discretizations of the same physical phenomenon, it is reasonable to expect that there will exist invariants across lattices related to fundamental properties of the protein folding process. This paper considers whether performance-guaranteed approximability is such an invariant for HP lattice models. The authors define a master approximation algorithm that has provable performance guarantees provided that a specific sublattice exists within a given lattice. They describe a broad class of crystal lattices that are approximable, which further suggests that approximability is a general property of HP lattice models.

  3. First-principles theories for anharmonic lattice vibrations.

    Science.gov (United States)

    Hirata, So; Keçeli, Murat; Yagi, Kiyoshi

    2010-07-21

    Size-extensive generalizations of the vibrational self-consistent field (VSCF), vibrational Moller-Plesset perturbation (VMP), and vibrational coupled-cluster (VCC) methods are made to anharmonic lattice vibrations of extended periodic systems on the basis of a quartic force field (QFF) in delocalized normal coordinates. Copious terms in the formalisms of VSCF that have nonphysical size dependence are identified algebraically and eliminated, leading to compact and strictly size-extensive equations. This "quartic" VSCF method (qVSCF) thus defined has no contributions from cubic force constants and alters only the transition energies of the underlying harmonic-oscillator reference from a subset of quartic force constants. It also provides a way to evaluate an anharmonic correction to the lattice structure due to cubic force constants of a certain type. The second-order VMP and VCC methods in the QFF based on the qVSCF reference are shown to account for anharmonic effects due to all cubic and quartic force constants in a size-extensive fashion. These methods can be readily extended to a higher-order truncated Taylor expansion of a potential energy surface in normal coordinates. An algebraic proof of the lack of size-extensivity in the vibrational configuration-interaction method is also presented.

  4. The normal modes of lattice vibrations of ice XI

    Science.gov (United States)

    Zhang, Peng; Wang, Zhe; Lu, Ying-Bo; Ding, Zheng-Wen

    2016-07-01

    The vibrational spectrum of ice XI at thermal wavelengths using the CASTEP code, a first-principles simulation method, is investigated. A dual-track approach is constructed to verify the validity for the computational phonon spectrum: collate the simulated spectrum with inelastic neutron scattering experiments and assign the photon scattering peaks according to the calculated normal vibration frequencies. The 33 optical normal vibrations at the Brillouin center are illustrated definitely from the ab initio outcomes. The depolarizing field effect of the hydrogen bond vibrations at frequencies of 229 cm‑1 and 310 cm‑1 is found to agree well with the LST relationship. It is a convincing evidence to manifest the LO-TO splitting of hydrogen bonds in ice crystal. We attribute the two hydrogen bond peaks to the depolarization effect and apply this viewpoint to ordinary ice phase, ice Ih, which is difficult to analyse their vibration modes due to proton disorder.

  5. Coulomb crystals in the harmonic lattice approximation

    CERN Document Server

    Baiko, D A; De Witt, H E; Slattery, W L

    2000-01-01

    The dynamic structure factor ${\\tilde S}({\\bf k},\\omega)$ and the two-particle distribution function $g({\\bf r},t)$ of ions in a Coulomb crystal are obtained in a closed analytic form using the harmonic lattice (HL) approximation which takes into account all processes of multi-phonon excitation and absorption. The static radial two-particle distribution function $g(r)$ is calculated for classical ($T \\gtrsim \\hbar \\omega_p$, where $\\omega_p$ is the ion plasma frequency) and quantum ($T \\ll \\hbar \\omega_p$) body-centered cubic (bcc) crystals. The results for the classical crystal are in a very good agreement with extensive Monte Carlo (MC) calculations at $1.5 \\lesssim r/a calculated for classical and quantum bcc and face-centered cubic crystals, and anharmonic corrections are discussed. The inelastic part of the HL static structure factor $S''(k)$, averaged over orientations of wave-vector {\\bf k}, is shown to contain pronounced singularities at Bragg diffraction positions. The type of the singularities is di...

  6. Photonic band gap of 2D complex lattice photonic crystal

    Institute of Scientific and Technical Information of China (English)

    GUAN Chun-ying; YUAN Li-bo

    2009-01-01

    It is of great significance to present a photonic crystal lattice structure with a wide photonic bandgap. A two-dimension complex lattice photonic crystal is proposed. The photonic crystal is composed of complex lattices with triangular structure, and each single cell is surrounded by six scatterers in an hexagon. The photonic band gaps are calculated based on the plane wave expansion (PWE) method. The results indicate that the photonic crystal has tunable large TM polarization band gap, and a gap-midgap ratio of up to 45.6%.

  7. Angular vibrations of cryogenically cooled double-crystal monochromators.

    Science.gov (United States)

    Sergueev, I; Döhrmann, R; Horbach, J; Heuer, J

    2016-09-01

    The effect of angular vibrations of the crystals in cryogenically cooled monochromators on the beam performance has been studied theoretically and experimentally. A simple relation between amplitude of the vibrations and size of the focused beam is developed. It is shown that the double-crystal monochromator vibrations affect not only the image size but also the image position along the optical axis. Several methods to measure vibrations with the X-ray beam are explained and analyzed. The methods have been applied to systematically study angular crystal vibrations at monochromators installed at the PETRA III light source. Characteristic values of the amplitudes of angular vibrations for different monochromators are presented.

  8. A lattice vibrational model using vibrational density of states for constructing thermodynamic databases (Invited)

    Science.gov (United States)

    Jacobs, M. H.; Van Den Berg, A. P.

    2013-12-01

    Thermodynamic databases are indispensable tools in materials science and mineral physics to derive thermodynamic properties in regions of pressure-temperature-composition space for which experimental data are not available or scant. Because the amount of phases and substances in a database is arbitrarily large, thermodynamic formalisms coupled to these databases are often kept as simple as possible to sustain computational efficiency. Although formalisms based on parameterizations of 1 bar thermodynamic data, commonly used in Calphad methodology, meet this requirement, physically unrealistic behavior in properties hamper the application in the pressure regime prevailing in the Earth's lower mantle. The application becomes especially cumbersome when they are applied to planetary mantles of massive super earth exoplanets or in the development of pressure scales, where Hugoniot data at extreme conditions are involved. Methods based on the Mie-Grüneisen-Debye formalism have the advantage that physically unrealistic behavior in thermodynamic properties is absent, but due to the simple construction of the vibrational density of states (VDoS), they lack engineering precision in the low-pressure regime, especially at 1 bar pressure, hampering application of databases incorporating such formalism to industrial processes. To obtain a method that is generally applicable in the complete stability range of a material, we developed a method based on an alternative use of Kieffer's lattice vibrational formalism. The method requires experimental data to constrain the model parameters and is therefore semi-empirical. It has the advantage that microscopic properties for substances, such as the VDoS, Grüneisen parameters and electronic and static lattice properties resulting from present-day ab-initio methods can be incorporated to constrain a thermodynamic analysis of experimental data. It produces results free from physically unrealistic behavior at high pressure and temperature

  9. Enhancement of polymer dye lasers by multifunctional photonic crystal lattice

    DEFF Research Database (Denmark)

    Christiansen, Mads Brøkner; Xiao, Sanshui; Mortensen, Asger

    2009-01-01

    The light output of dye doped hybrid polymer band-edge lasers is increased more than 100 times by using a rectangular lattice photonic crystal, which provides both feedback and couples more pump light into the laser.......The light output of dye doped hybrid polymer band-edge lasers is increased more than 100 times by using a rectangular lattice photonic crystal, which provides both feedback and couples more pump light into the laser....

  10. Crystal lattice optimization and new forms of silicon

    Science.gov (United States)

    Stucke, David P.

    In Chapter 1 a basic outline of the two main methods used in this thesis is given. A genetic algorithm optimization method based on the concept of natural selection is given. The important factors to consider in creating an effective genetic algorithm search are described. I then give a brief overview of Density Functional Theory (DFT) which is the technique most commonly used to do ab-inito calculations on solid-state systems. The basis for its formulation along with how it is applied to a practical system with some approximations is discussed. In Chapter 2 a description of a genetic search algorithm for optimizing the crystal structure of an infinite crystal is given. This method is applied to a system of colloidal spheres, where the packing density is the figure of merit for structure selection. Our examination of self-assembled multi-component crystals of nanoparticles predicts several new structures with stoichiometries of AB (fused spheres), ABC2, ABC 3, ABC4 and AB2 C2. These new structures have hierarchical layered or linear arrangements that could be useful for functional self-assembled systems. For example, the fused-sphere binary crystal assembles with zig-zag rows of parallel nanowires. The genetic search suceeds while a comparable stochastic algorithm fails to find any structures better than the well-known unary or binary phase-separated systems. Here we describe the algorithm and the results it produces: several new classes of binary and ternary crystals of spherical nanoparticles, including a family of layered perovskite-like systems and an unusual three-dimensional array of parallel zig-zag nanowires. In Chapter 3, We discuss the possibility of constructing new forms of silicon by building in multiple bonds consistent with molecules that have been produced experimentally. We find a dilated diamond crystal lattice containing a silicon-silicon triple bond that is metastable. This structure has very soft vibrational modes that are common in similar

  11. Optical spectra and lattice dynamics of molecular crystals

    CERN Document Server

    Zhizhin, GN

    1995-01-01

    The current volume is a single topic volume on the optical spectra and lattice dynamics of molecular crystals. The book is divided into two parts. Part I covers both the theoretical and experimental investigations of organic crystals. Part II deals with the investigation of the structure, phase transitions and reorientational motion of molecules in organic crystals. In addition appendices are given which provide the parameters for the calculation of the lattice dynamics of molecular crystals, procedures for the calculation of frequency eigenvectors of utilizing computers, and the frequencies and eigenvectors of lattice modes for several organic crystals. Quite a large amount of Russian literature is cited, some of which has previously not been available to scientists in the West.

  12. Comparison of High Temperature Crystal Lattice and Bulk Thermal Expansion Measurements of LGT Single Crystal

    Energy Technology Data Exchange (ETDEWEB)

    Beaucage, Timothy R [University of Maine; Beenfeldt, Eric P [University of Maine; Speakman, Scott A [ORNL; Porter, Wallace D [ORNL; Payzant, E Andrew [ORNL; Pereira da Cunha, Mauricio [University of Maine

    2006-01-01

    Among the langasite family of crystals (LGX), the three most popular materials are langasite (LGS, La3Ga5SiO14), langatate (LGT, La3Ga5.5Ta0.5O14) and langanite (LGN, La3Ga5.5Nb0.5O14). The LGX crystals have received significant attention for acoustic wave (AW) device applications due to several properties, which include: (1) piezoelectric constants about two and a half times those of quartz, thus allowing the design of larger bandwidth filters; (2) existence of temperature compensated orientations; (3) high density, with potential for reduced vibration and acceleration sensitivity; and (4) possibility of operation at high temperatures, since the LGX crystals do not present phase changes up to their melting point above 1400degC. The LGX crystals' capability to operate at elevated temperatures calls for an investigation on the growth quality and the consistency of these materials' properties at high temperature. One of the fundamental crystal properties is the thermal expansion coefficients in the entire temperature range where the material is operational. This work focuses on the measurement of the LGT thermal expansion coefficients from room temperature (25degC) to 1200degC. Two methods of extracting the thermal expansion coefficients have been used and compared: (a) dual push-rod dilatometry, which provides the bulk expansion; and (b) x-ray powder diffraction, which provides the lattice expansion. Both methods were performed over the entire temperature range and considered multiple samples taken from <001> Czochralski grown LGT material. The thermal coefficients of expansion were extracted by approximating each expansion data set to a third order polynomial fit over three temperature ranges reported in this work: 25degC to 400degC, 400degC to 900degC, 900degC to 1200degC. An accuracy of fit better than 35ppm for the bulk expansion and better than 10ppm for the lattice expansion have been obtained with the aforementioned polynomial fitting. The

  13. Structure and lattice dynamics of rare-earth ferroborate crystals: Ab initio calculation

    Science.gov (United States)

    Chernyshev, V. A.; Nikiforov, A. E.; Petrov, V. P.; Serdtsev, A. V.; Kashchenko, M. A.; Klimin, S. A.

    2016-08-01

    The ab initio calculation of the crystal structure and the phonon spectrum of crystals RFe3(BO3)4 ( R = Pr, Nd, Sm) has been performed in the framework of the density functional theory. The ion coordinates in the unit cell, the lattice parameters, the frequencies and the types of fundamental vibrations, and also the intensities of lines in the Raman spectrum and infrared reflection spectra have been found. The elastic constants of the crystals have been calculated. For low-frequency A 2 mode in PrFe3(BO3)4, a "seed" vibration frequency that strongly interacts with the electronic excitation on a praseodymium ion was found. The calculation results satisfactory agree with the experimental data.

  14. Vibrational spectra of pilocarpine hydrochloride crystals

    Energy Technology Data Exchange (ETDEWEB)

    Bento, R.R.F. [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Inst. de Fisica; Freire, P.T.C. [Universidade Federal do Ceara (UFC), Fortaleza, CE (Brazil). Dept. de Fisica]. E-mail: tarso@fisica.ufc.br; Teixeira, A.M.R.; Silva, J.H. [Universidade Regional do Cariri, Crato, CE (Brazil). Dept. Ciencias Fisicas e Biologicas; Lima Junior, J.A. [Universidade Estadual do Ceara (UECE), Limoeiro do Norte, CE (Brazil); Oliveira, M.C.F. de; Andrade-Neto, M. [Universidade Federal do Ceara (UFC), Fortaleza, CE (Brazil). Dept. de Quimica Organica e Inorganica; Romero, N.R. [Universidade Federal do Ceara (UFC), Fortaleza, CE (Brazil). Dept. de Farmacia; Pontes, F.M. [Universidade Estadual Paulista, Bauru, SP (Brazil). Faculdade de Ciencias

    2009-03-15

    Pilocarpine is a natural substance with potential application in the treatment of several diseases. In this work Fourier Transform (FT)-Raman spectrum and the Fourier Transform infra red (FT-IR) spectrum of pilocarpine hydrochloride C{sub 11} H{sub 17} N{sub 2} O{sup +}{sub 2} .Cl{sup -1} were investigated at 300 K. Vibrational wavenumber and wave vector have been predicted using density functional theory (B3LYP) calculations with the 6-31 G(d,p) basis set. A comparison with experiment allowed to assign most of the normal modes of the crystal. (author)

  15. A novel lattice energy calculation technique for simple inorganic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Kaya, Cemal [Department of Chemistry, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Kaya, Savaş, E-mail: savaskaya@cumhuriyet.edu.tr [Department of Chemistry, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Banerjee, Priyabrata [Surface Engineering and Tribology Group, CSIR-Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur 713209 (India)

    2017-01-01

    In this pure theoretical study, a hitherto unexplored equation based on Shannon radii of the ions forming that crystal and chemical hardness of any crystal to calculate the lattice energies of simple inorganic ionic crystals has been presented. To prove the credibility of this equation, the results of the equation have been compared with experimental outcome obtained from Born-Fajans-Haber- cycle which is fundamentally enthalpy-based thermochemical cycle and prevalent theoretical approaches proposed for the calculation of lattice energies of ionic compounds. The results obtained and the comparisons made have demonstrated that the new equation is more useful compared to other theoretical approaches and allows to exceptionally accurate calculation of lattice energies of inorganic ionic crystals without doing any complex calculations.

  16. A novel lattice energy calculation technique for simple inorganic crystals

    Science.gov (United States)

    Kaya, Cemal; Kaya, Savaş; Banerjee, Priyabrata

    2017-01-01

    In this pure theoretical study, a hitherto unexplored equation based on Shannon radii of the ions forming that crystal and chemical hardness of any crystal to calculate the lattice energies of simple inorganic ionic crystals has been presented. To prove the credibility of this equation, the results of the equation have been compared with experimental outcome obtained from Born-Fajans-Haber- cycle which is fundamentally enthalpy-based thermochemical cycle and prevalent theoretical approaches proposed for the calculation of lattice energies of ionic compounds. The results obtained and the comparisons made have demonstrated that the new equation is more useful compared to other theoretical approaches and allows to exceptionally accurate calculation of lattice energies of inorganic ionic crystals without doing any complex calculations.

  17. Vibration band-gap properties of three-dimensional Kagome lattices using the spectral element method

    Science.gov (United States)

    Wu, Zhi-Jing; Li, Feng-Ming; Zhang, Chuanzeng

    2015-04-01

    The spectral element method (SEM) is extended to investigate the vibration band-gap properties of three-dimensional (3D) Kagome lattices. The dynamic stiffness matrix of the 3D element which contains bending, tensional and torsional components is derived. The spectral equations of motion of the whole 3D Kagome lattice are then established. Comparing with frequency-domain solutions calculated by the finite element method (FEM), the accuracy and the feasibility of the SEM solutions are verified. It can be shown that the SEM is suitable for analyzing the vibration band-gap properties. Due to the band-gap characteristics, the periodic 3D Kagome lattice has the performance of vibration isolation. The influences of the structural and material parameters on the vibration band-gaps are discussed and a new type of 3D Kagome lattice is designed to obtain the improved vibration isolation capability.

  18. The lattice parameter of highly pure silicon single crystals

    Science.gov (United States)

    Becker, P.; Scyfried, P.; Siegert, H.

    1982-08-01

    From crystal to crystal comparison, the d 220 lattice spacing in PERFX and WASO silicon crystals used in the only two existing absolute measurements have been found to be equal within ±2×10-7 d 220. This demonstrates that generic variabilities of the two crystals account only for a small part of the 1.8×10-6 d 220 difference in the two absolute measurements. In a new series of 336 single measurements, our d 220 value reported recently has been confirmed within ±2×10-8 d 220. From these results we derive the following lattice parameter for highly pure silicon single crystals: a 0=(543 102.018±0.034) fm (at 22.5°C, in vacuum).

  19. Photonic Crystal Waveguides in Triangular Lattice of Nanopillars

    DEFF Research Database (Denmark)

    Chigrin, Dmitry N.; Lavrinenko, Andrei

    2004-01-01

    Photonic nanopillars waveguides have been analysed. Dielectric nanopillars are arranged in such way that they from a tringular lattice of 2D photonic crystal. Dispersion of the modes depends on the direction of the triangular lattice, Ã-J or Ã-X, in which nanopillars arrays are extended. Light....... Transmission spectra calculated by FDTD method completely reflect peculiarities of modes dispersion, showing up to 80% transmission for a realistic SOI nanopillar structure....

  20. Influence of lattice vibrations on luminescence and transfer of excitons in WS2 monolayer semiconductors

    Science.gov (United States)

    Wang, X. H.; Su, Z. C.; Ning, J. Q.; Wang, M. Z.; Xu, S. J.; Han, S.; Jia, F.; Zhu, D. L.; Lu, Y. M.

    2016-11-01

    Monolayers of transition metal dichalcogenides (TMDs) have been recently demonstrated to be a new family of direct bandgap semiconductors exhibiting extraordinary excitonic effects and high-efficiency luminescence. Here we present a micro-photoluminescence (PL) study on temperature dependent luminescence of excitons from an exfoliated WS2 monolayer. It is found that lattice vibrations (i.e. phonons) have a profound influence on the excitonic luminescence of the WS2 monolayer in several aspects including the spectral peak shift, lineshape broadening, transfer, and even formation entropy of excitons. Our study not only leads to the determination of the fundamental excitonic bandgap: {{E}\\text{g}}=2.061~ eV at T=0 \\text{K} , but also reveals that 120 K is a ‘turning’ temperature for the competition and formation entropy of free excitons and defect-bound excitons in the studied 2D WS2 crystals.

  1. Vibration-assisted machining of single crystal

    Science.gov (United States)

    Zahedi, S. A.; Roy, A.; Silberschmidt, V. V.

    2013-07-01

    Vibration-assisted machining offers a solution to expanding needs for improved machining, especially where accuracy and precision are of importance, such as in micromachining of single crystals of metals and alloys. Crystallographic anisotropy plays a crucial role in determining on overall response to machining. In this study, we intend to address the matter of ultra-precision machining of material at the micron scale using computational modelling. A hybrid modelling approach is implemented that combines two discrete schemes: smoothed particle hydrodynamics and continuum finite elements. The model is implemented in a commercial software ABAQUS/Explicit employing a user-defined subroutine (VUMAT) and used to elucidate the effect of crystallographic anisotropy on a response of face centred cubic (f.c.c.) metals to machining.

  2. Photographic appraisal of crystal lattice growth technique

    Directory of Open Access Journals (Sweden)

    Kapoor D

    2005-01-01

    Full Text Available Concept of creating mechanical retention for bonding through crystal growth has been successfully achieved in the present study. By using polyacrylic acid, sulphated with sulphuric acid as etchant, abundant crystal growth was demonstrated. Keeping in view the obvious benefits of crystal growth technique, the present SEM study was aimed to observe and compare the changes brought about by different etching agents (phosphoric acid, polyacrylic acid and polyacrylic acid sulphated and to evaluate their advantages and disadvantages in an attempt to reduce iatrogenic trauma caused due to surface enamel alteration. Control and experimental groups were made of 24 and 30 premolars, respectively, for scanning electron microscopic appraisal of normal unetched and etched enamel surface and fracture site and finished surface evaluation. When compared with conventional phosphoric acid and weaker polyacrylic acid, investigations indicated that crystal growth treatment on enamel surface caused minimal iatrogenic trauma and surface alteration were restored to the original untreated condition to a large extent.

  3. Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics

    Science.gov (United States)

    Davis, Bruce L.; Hussein, Mahmoud I.

    2011-12-01

    The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell) and the phononic crystal lattice (defined by a supercell) contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicity levels. Here we demonstrate the utility of using supercell lattice dynamics to investigate the thermal transport behavior of three-dimensional nanoscale phononic crystals formed from silicon and cubic voids of vacuum. The periodicity of the voids follows a simple cubic arrangement with a lattice constant that is around an order of magnitude larger than that of the bulk crystalline silicon primitive cell. We consider an atomic-scale supercell which incorporates all the details of the silicon atomic locations and the void geometry. For this supercell, we compute the phonon band structure and subsequently predict the thermal conductivity following the Callaway-Holland model. Our findings dictate that for an analysis based on supercell lattice dynamics to be representative of the properties of the underlying lattice model, a minimum supercell size is needed along with a minimum wave vector sampling resolution. Below these minimum values, a thermal conductivity prediction of a bulk material based on a supercell will not adequately recover the value obtained based on a primitive cell. Furthermore, our results show that for the relatively small voids and void spacings we consider (where boundary scattering is dominant), dispersion at the phononic crystal unit cell level plays a noticeable role in determining the thermal conductivity.

  4. Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics

    Directory of Open Access Journals (Sweden)

    Bruce L. Davis

    2011-12-01

    Full Text Available The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell and the phononic crystal lattice (defined by a supercell contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicity levels. Here we demonstrate the utility of using supercell lattice dynamics to investigate the thermal transport behavior of three-dimensional nanoscale phononic crystals formed from silicon and cubic voids of vacuum. The periodicity of the voids follows a simple cubic arrangement with a lattice constant that is around an order of magnitude larger than that of the bulk crystalline silicon primitive cell. We consider an atomic-scale supercell which incorporates all the details of the silicon atomic locations and the void geometry. For this supercell, we compute the phonon band structure and subsequently predict the thermal conductivity following the Callaway-Holland model. Our findings dictate that for an analysis based on supercell lattice dynamics to be representative of the properties of the underlying lattice model, a minimum supercell size is needed along with a minimum wave vector sampling resolution. Below these minimum values, a thermal conductivity prediction of a bulk material based on a supercell will not adequately recover the value obtained based on a primitive cell. Furthermore, our results show that for the relatively small voids and void spacings we consider (where boundary scattering is dominant, dispersion at the phononic crystal unit cell level plays a noticeable role in determining the thermal conductivity.

  5. Acoustic vibration modes and electron-lattice coupling in self-assembled silver nanocolumns.

    Science.gov (United States)

    Burgin, J; Langot, P; Arbouet, A; Margueritat, J; Gonzalo, J; Afonso, C N; Vallée, F; Mlayah, A; Rossell, M D; Van Tendeloo, G

    2008-05-01

    Using ultrafast spectroscopy, we investigated electron-lattice coupling and acoustic vibrations in self-assembled silver nanocolumns embedded in an amorphous Al2O3 matrix. The measured electron-lattice energy exchange time is smaller in the nanocolumns than in bulk silver, with a value very close to that of isolated nanospheres with comparable surface to volume ratio. Two vibration modes were detected and ascribed to the breathing and extensional mode of the nanocolumns, in agreement with numerical simulations.

  6. Vibrational energy transfer in shocked molecular crystals.

    Science.gov (United States)

    Hooper, Joe

    2010-01-07

    We consider the process of establishing thermal equilibrium behind an ideal shock front in molecular crystals and its possible role in initiating chemical reaction at high shock pressures. A new theory of equilibration via multiphonon energy transfer is developed to treat the scattering of shock-induced phonons into internal molecular vibrations. Simple analytic forms are derived for the change in this energy transfer at different Hugoniot end states following shock compression. The total time required for thermal equilibration is found to be an order of magnitude or faster than proposed in previous work; in materials representative of explosive molecular crystals, equilibration is predicted to occur within a few picoseconds following the passage of an ideal shock wave. Recent molecular dynamics calculations are consistent with these time scales. The possibility of defect-induced temperature localization due purely to nonequilibrium phonon processes is studied by means of a simple model of the strain field around an inhomogeneity. The specific case of immobile straight dislocations is studied, and a region of enhanced energy transfer on the order of 5 nm is found. Due to the rapid establishment of thermal equilibrium, these regions are unrelated to the shock sensitivity of a material but may allow temperature localization at high shock pressures. Results also suggest that if any decomposition due to molecular collisions is occurring within the shock front itself, these collisions are not enhanced by any nonequilibrium thermal state.

  7. The characters of nonlinear vibration in the two-dimensional discrete monoatomic lattice

    Institute of Scientific and Technical Information of China (English)

    XU Quan; TIAN Qiang

    2005-01-01

    The two-dimensional discrete monoatomic lattice is analyzed. Taking nearest-neighbor interaction into account, the characters of the nonlinear vibration in two-dimensional discrete monoatomic lattice are described by the two-dimensional cubic nonlinear Schrodinger equation. Considering the quartic nonlinear potential, the two-dimensional discrete-soliton trains and the solutions perturbed by the neck mode are presented.

  8. Study on the vibration band gap and vibration attenuation property of phononic crystals

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Phononic crystals (PCs) are functional materials with periodic structures and elas- tic wave (vibration) band gaps, where propagation of vibrations with frequencies within band gaps is forbidden. PCs with finite periods can restrain the propagation of vibrations with frequencies in band gaps and thus has vibration attenuation property. Worldwide, many institutions and researchers are engaged in the re- search of PCs, however, studies on the vibration attenuation property of PCs are still limited. In this paper, we report our study of band gaps and vibration attenua- tion properties of 1) a simplified PC—periodic mass-spring structures, 2) longitu- dinal vibration of one-dimensional (1D-), 2D-, 3D-PCs, and 3) the flexural vibration of 1D- and 2D-PCs. These studies provide a foundation for the applications of PCs in vibration attenuation.

  9. Study on the vibration band gap and vibration attenuation property of phononic crystals

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Phononic crystals (PCs) are functional materials with periodic structures and elastic wave (vibration) band gaps, where propagation of vibrations with frequencies within band gaps is forbidden. PCs with finite periods can restrain the propagation of vibrations with frequencies in band gaps and thus has vibration attenuation property. Worldwide, many institutions and researchers are engaged in the research of PCs, however, studies on the vibration attenuation property of PCs are still limited. In this paper, we report our study of band gaps and vibration attenuation properties of 1) a simplified PC-periodic mass-spring structures, 2) longitudinal vibration of one-dimensional (1D-), 2D-, 3D-PCs, and 3) the flexural vibration of 1D- and 2D-PCs. These studies provide a foundation for the applications of PCs in vibration attenuation.

  10. Lattice variation and thermal parameters of gel grown KDP crystals added with some ammonium compounds

    Indian Academy of Sciences (India)

    T H Freeda; C Mahadevan

    2001-10-01

    Pure and impurity added (with NH4Cl, NH4NO3, NH4H2PO4, and (NH4)2SO4) KDP single crystals were grown by the gel method using silica gels. X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye–Waller factor, mean-square amplitude of vibration, Debye temperature and Debye frequency. The thermal parameters do not vary in a particular order with respect to impurity concentration. The results obtained are reported and discussed.

  11. 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.

  12. Optical vibration modes and electron-phonon interaction in ternary mixed crystals of polar semiconductors

    Institute of Scientific and Technical Information of China (English)

    Liang Xi-Xia; Ban Shi-Liang

    2004-01-01

    @@ Optical vibrations of the lattice and the electron-phonon interaction in polar ternary mixed crystals are studied in the framework of the continuum model of Born and Huang and the random-element-isodisplacement model. A normal-coordinate system to describe the optical vibration in ternary mixed crystals is correctly adopted to derive a new Frohlich-like Hamiltonian for the electron-phonon interaction including the unit-cell volume variation influence.The numerical results for the phonon modes, the electron-phonon coupling constants and the polaronic energies for several typical materials are obtained. It is verified that the nonlinearity of the electron-phonon coupling effects with the composition is essential and the unit-cell volume effects cannot be neglected for most ternary mixed crystals.

  13. Common Misconceptions about the Dynamical Theory of Crystal Lattices: Cauchy Relations, Lattice Potentials and Infinite Crystals

    Science.gov (United States)

    Elcoro, Luis; Etxebarria, Jesus

    2011-01-01

    The requirement of rotational invariance for lattice potential energies is investigated. Starting from this condition, it is shown that the Cauchy relations for the elastic constants are fulfilled if the lattice potential is built from pair interactions or when the first-neighbour approximation is adopted. This is seldom recognized in widely used…

  14. Study on vibrational modes by group theory and infrared spectra by D FT for calcite crystal

    Institute of Scientific and Technical Information of China (English)

    Danhua Lou; Fengjiu Sun; Lijuan Li

    2007-01-01

    The factor group symmetry analysis (FSA) method and position symmetry analysis (PSA) method are used to analyze the vibrational modes of calcite (CaCO3) crystal, respectively. With the activated results of infrared and Raman spectra presented, strong points of each method are concluded. The infrared spectra are studied by using dynamics calculations based on density-functional theory (DFT) with the supercell model of calcite crystal. The frequencies of 27 normal modes are achieved, which are consistent with that by the group symmetry analysis very well, and fit with the experimental results better than the lattice dynamical methods.

  15. Cubic to tetragonal crystal lattice reconstruction during ordering or decomposition

    Energy Technology Data Exchange (ETDEWEB)

    Cheong, Byung-kl [Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering

    1992-09-01

    This thesis studied thermodynamic stability and morphology of product phases in diffusional phase transformations involving cubic-to-tetragonal crystal lattice reconstructions. Two different kinds of diffusional transformations were examined: L1{sub 0} ordering (fcc to fct lattice change) and decomposition of off-stoichiometric B2 ordering alloys accompanying bcc to fcc Bain transformation. In the first case, Fe-45 at.% Pd alloys were studied by TEM; in the second, the Bain strain relaxation during decomposition of hyper-eutectoid Cu-9.04 wt% Be alloy was studied. CuAu and InMg were also studied.

  16. Vibrational relaxation of guest and host in mixed molecular crystals

    Science.gov (United States)

    Hill, Jeffrey R.; Chronister, Eric L.; Chang, Ta-Chau; Kim, Hackjin; Postlewaite, Jay C.; Dlott, Dana D.

    1988-02-01

    Vibrational relaxation (VR) of dilute impurity molecules (naphthalene, anthracene) in crystalline host matrices (durene, naphthalene) is studied with the ps photon echo technique. The results obtained by echoes on vibrations in the electronically excited state are compared to previous ps time delayed coherent Raman studies of ground state vibrations of the pure host matrix. The relaxation channels for guest and host, and the effects of molecular and crystal structure on VR rates are determined.

  17. Lattice Boltzmann Simulation of the Cross Flow Over a Cantilevered and Longitudinally Vibrating Circular Cylinder

    Institute of Scientific and Technical Information of China (English)

    XIA Yong; LU De-Tang; LIU Yang; XU You-Sheng

    2009-01-01

    The multiple-relaxation-time lattice Boltzmann method (MRT-LBM) is implemented to numerically simulate the cross flow over a longitudinal vibrating circular cylinder.This research is carried out on a three-dimensional (3D) finite cantilevered cylinder to investigate the effect of forced vibration on the wake characteristics and the 319 effect of a cantilevered cylinder.To meet the accuracy of this method,the present calculation is carried out at a low Reynolds number Re = 100,as well as to make the vibration obvious,we make the vibration strong enough.The calculation results indicate that the vibration has significant influence on the wake characteristics. When the vibrating is big enough,our early works show that the 2D vortex shedding would be locked up by vibration.Contrarily,this phenomenon would not appear in the present 313 case because of the end effect of the cantilevered cylinder.

  18. The Characteristics of the Shear-Vibrating Quartz Crystal Resonator

    Institute of Scientific and Technical Information of China (English)

    Wenjie Tian; Lingling Liu; Junling Lu; Fuxue Zhang

    2006-01-01

    According to the piezoelectric equation and the vibration theory of the quartz crystal, the relations between the vibrating frequency and structural parameters under the thickness-shear-vibration of AT-cut quartz crystal have been studied.The frequency conditions under which quartz crystal resonator formed stationary wave inside the electrode district and the transmission characteristics of wave outside the electrode district have also been discussed. A quartz crystal resonator was developed based on this analysis. The experiment showed that the force-sensing characteristics were independent of the fixation of the crystal edge. The detecting distinguish ability was up to 0.001 °, and the short-term frequency stability was up to 1.38x 10-10/min.

  19. Lattice dynamics of KxRhO2 single crystals

    Directory of Open Access Journals (Sweden)

    Bin-Bin Zhang

    2015-08-01

    Full Text Available A series of crystals KxRhO2 (x = 0.72, 0.63, 0.55, 0.39, and 0.24 have been synthesized and their vibrational properties have been studied by first principles calculations, Raman spectroscopy, and inelastic neutron scattering. The measured vibrational spectra of KxRhO2 for x = 0.72 and 0.63 are consistent with the theoretical prediction for the stoichiometric KRhO2. For samples with x = 0.55, 0.39 and 0.24, extra vibrational modes have been observed and they are believed to be due to the symmetry reduction and the loss of translational symmetry induced by K disorder. The good agreement was found for the phonon density of states among the Raman spectroscopic observations, inelastic neutron scattering and the first principles calculations, as an evidence for the generation of structure disorder by K deficiency.

  20. Lattice variation and thermal parameters of NiMg1–SO4 7H2O single crystals

    Indian Academy of Sciences (India)

    M Theivanayagom; C Mahadevan

    2001-10-01

    NiMg1–SO4.7H2O single crystals were grown by the slow evaporation method from aqueous solutions. Density was measured by the floatation method. X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye–Waller factor, mean-square amplitude of vibration and Debye temperature. Lattice volumes approximately obey a relation similar to Retger’s rule. Values of thermal parameters do not follow any particular order with composition. The results obtained are reported.

  1. Coefficient of crystal lattice matching as a parameter of substrate - crystal structure compatibility in silumins

    Directory of Open Access Journals (Sweden)

    J. Piątkowski

    2009-07-01

    Full Text Available Adding high-melting point elements (Mo, Nb, Ni, Ti, W to complex silumins results in hardening of the latter ones, owing to the formation of new intermetallic phases of the AlxMey type, with refinement of dendrites in α solution and crystals in β phase. The hardening is also due to the effect of various inoculants. An addition of the inoculant is expected to form substrates, the crystal lattice of which, or some (privileged lattice planes and interatomic spaces should bear a strong resemblance to the crystal nucleus. To verify this statement, using binary phase equilibria systems, the coefficient of crystal lattice matching, being one of the measures of the crystallographic similarity, was calculated. A compatibility of this parameter (up to 20% may decide about the structure compatibility between the substrate and crystal which, in turn, is responsible for the effectiveness of alloy modification. Investigations have proved that, given the temperature range of their formation, the density, the lattice type, and the lattice parameter, some intermetallic phases of the AlxMey type can act as substrates for the crystallisation of aluminium and silicon, and some of the silumin hardening phases.

  2. Vibrational stability of a cryocooled horizontal double-crystal monochromator

    Science.gov (United States)

    Kristiansen, Paw; Johansson, Ulf; Ursby, Thomas; Jensen, Brian Norsk

    2016-01-01

    The vibrational stability of a horizontally deflecting double-crystal monochromator (HDCM) is investigated. Inherently a HDCM will preserve the vertical beam stability better than a ‘normal’ vertical double-crystal monochromator as the vibrations of a HDCM will almost exclusively affect the horizontal stability. Here both the relative pitch vibration between the first and second crystal and the absolute pitch vibration of the second crystal are measured. All reported measurements are obtained under active cooling by means of flowing liquid nitrogen (LN2). It is found that it is favorable to circulate the LN2 at high pressures and low flow rates (up to 5.9 bar and down to 3 l min−1 is tested) to attain low vibrations. An absolute pitch stability of the second crystal of 18 nrad RMS, 2–2500 Hz, and a relative pitch stability between the two crystals of 25 nrad RMS, 1–2500 Hz, is obtained under cryocooling conditions that allow for 1516 W to be adsorbed by the LN2 before it vaporizes. PMID:27577758

  3. NONLINEARLY VIBRATIONAL ENERGY-SPECTRA OF MOLECULAR CRYSTALS

    Institute of Scientific and Technical Information of China (English)

    PANG XIAO-FENG; CHEN XIANG-RONG

    2000-01-01

    The nonlinear quantum vibrational energy spectra of amide-I in the molecular crystals acetanilide are calculatedby using the discrete nonlinear Schrodinger equation appropriate to this kind of crystals. The numerical results obtainedby this method are in good agreement with the experimental values. Meanwhile, the energy levels at high excited stateshave also been obtained for the acetanilide, which is helpful in researching the Raman scattering and infrared absorptionproperties of the this kind of crystals.

  4. Vibration-dependent Crystal Form of Isotactic Polypropylene under Nonisothermal Crystallization

    Institute of Scientific and Technical Information of China (English)

    SHANGGUAN Yong-gang; TONG Li-fang; PENG Mao; ZHENG Qiang

    2004-01-01

    A study concerning the effect of vibration on the crystal structure and morphology for isotactic polypropylene(iPP) was conducted. The crystallite size, crystal structure and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry(DSC) and wideangle X-ray diffraction(WAXD). The results reveal that the crystallinity of the vibrated samples decreases at a high cooling rate, but it remains constant at a low cooling rate because of the chain relaxation of iPP. It has been found that vibration obviously increases the content of β-form of crystal phase and the amount of β-crystal mainly depends on the vibration amplitude.

  5. Molecular dynamics simulation of triclinic lysozyme in a crystal lattice.

    Science.gov (United States)

    Janowski, Pawel A; Liu, Chunmei; Deckman, Jason; Case, David A

    2016-01-01

    Molecular dynamics simulations of crystals can enlighten interpretation of experimental X-ray crystallography data and elucidate structural dynamics and heterogeneity in biomolecular crystals. Furthermore, because of the direct comparison against experimental data, they can inform assessment of molecular dynamics methods and force fields. We present microsecond scale results for triclinic hen egg-white lysozyme in a supercell consisting of 12 independent unit cells using four contemporary force fields (Amber ff99SB, ff14ipq, ff14SB, and CHARMM 36) in crystalline and solvated states (for ff14SB only). We find the crystal simulations consistent across multiple runs of the same force field and robust to various solvent equilibration schemes. However, convergence is slow compared with solvent simulations. All the tested force fields reproduce experimental structural and dynamic properties well, but Amber ff14SB maintains structure and reproduces fluctuations closest to the experimental model: its average backbone structure differs from the deposited structure by 0.37Å; by contrast, the average backbone structure in solution differs from the deposited by 0.65Å. All the simulations are affected by a small progressive deterioration of the crystal lattice, presumably due to imperfect modeling of hydrogen bonding and other crystal contact interactions; this artifact is smallest in ff14SB, with average lattice positions deviating by 0.20Å from ideal. Side-chain disorder is surprisingly low with fewer than 30% of the nonglycine or alanine residues exhibiting significantly populated alternate rotamers. Our results provide helpful insight into the methodology of biomolecular crystal simulations and indicate directions for future work to obtain more accurate energy models for molecular dynamics.

  6. Aqueous solubility prediction: do crystal lattice interactions help?

    Science.gov (United States)

    Salahinejad, Maryam; Le, Tu C; Winkler, David A

    2013-07-01

    Aqueous solubility is a very important physical property of small molecule drugs and drug candidates but also one of the most difficult to predict accurately. Aqueous solubility plays a major role in drug delivery and pharmacokinetics. It is believed that crystal lattice interactions are important in solubility and that including them in solubility models should improve the accuracy of the models. We used calculated values for lattice energy and sublimation enthalpy of organic molecules as descriptors to determine whether these would improve the accuracy of the aqueous solubility models. Multiple linear regression employing an expectation maximization algorithm and a sparse prior (MLREM) method and a nonlinear Bayesian regularized artificial neural network with a Laplacian prior (BRANNLP) were used to derive optimal predictive models of aqueous solubility of a large and highly diverse data set of 4558 organic compounds over a normal ambient temperature range of 20-30 °C (293-303 K). A randomly selected test set and compounds from a solubility challenge were used to estimate the predictive ability of the models. The BRANNLP method showed the best statistical results with squared correlation coefficients of 0.90 and standard errors of 0.645-0.665 log(S) for training and test sets. Surprisingly, including descriptors that captured crystal lattice interactions did not significantly improve the quality of these aqueous solubility models.

  7. Thermodynamics of sublimation, crystal lattice energies, and crystal structures of racemates and enantiomers: (+)- and (+/-)-ibuprofen.

    Science.gov (United States)

    Perlovich, German L; Kurkov, Sergey V; Hansen, Lars Kr; Bauer-Brandl, Annette

    2004-03-01

    Thermodynamic differences between ibuprofen (IBP) racemate and the (+)-enantiomer were studied by X-ray diffraction, thermoanalysis, and crystal energy calculations. The thermodynamic functions of sublimation (as a measure of crystal lattice energy) were obtained by the transpiration method. The sublimation enthalpies (DeltaH(sub)) of (+/-)-IBP and (+)-IBP are 115.8 +/- 0.6 and 107.4 +/- 0.5 kJ. mol(-1), respectively. Using the temperature dependency of the saturated vapor pressure, the relative fractions of enthalpy and entropy of the sublimation process were calculated, and the sublimation process for both the racemate and the enantiomer was found to be enthalpy driven (62%). Two different force fields, Mayo et al. (M) and Gavezzotti (G), were used for comparative analysis of crystal lattice energies. Both force fields revealed that the van der Waals term contributes more to the packing energy in (+)-IBP than in (+/-)-IBP. The hydrogen bonding energy, however, contributes at 29.7 and 32.3% to the total crystal lattice energy in (+)-IBP and (+/-)-IBP (M), respectively. Furthermore, different structure fragments of the IBP molecule were analyzed with respect to their contribution to nonbonded van der Waals interactions. The effect of the C-H distance on the van der Waals term of the crystal lattice energy was also studied.

  8. Large-lattice-parameter perovskite single-crystal substrates

    Science.gov (United States)

    Uecker, Reinhard; Bertram, Rainer; Brützam, Mario; Galazka, Zbigniew; Gesing, Thorsten M.; Guguschev, Christo; Klimm, Detlef; Klupsch, Michael; Kwasniewski, Albert; Schlom, Darrell G.

    2017-01-01

    The pseudobinary system LaLuO3-LaScO3 was explored in hopes of discovering new perovskite-type substrates with pseudocubic lattice parameters above 4 Å. A complete solid solution of the type (LaLuO3)1-x(LaScO3)x forms between the end members LaLuO3 and LaScO3, enabling large single crystals of (LaLuO3)1-x(LaScO3)x to be grown from the melt. A single crystal with x≈0.34 was demonstrated. Considering the maximum thermal load of the iridium crucibles appropriate for Czochralski growth of this solid solution, the theoretically maximum achievable x-value is 0.67. Based on the phase diagram determined, it is anticipated that single crystals with pseudocubic lattice constants between 4.09 and 4.18 Å can be grown in this system by the Czochralski method.

  9. Photomechanical vibration of thin crystals of polar semiconductors

    Science.gov (United States)

    Lagowski, J.; Gatos, H. C.

    1974-01-01

    It was found that thin crystals of polar (non-centrosymmetric) semiconductors constitute a new type of photosensitive system in which incident illumination is converted into mechanical energy: thus, illumination-induced elastic deformation (bending) was observed on thin (00.1) CdS and (111) GaAs crystals; furthermore, by employing chopped light the crystals were excited to their resonant vibration (photomechanical vibration); the dependence of the amplitude of this vibration on the energy of the incident radiation was found to be similar to the dependence of the surface photovoltage on the energy of the incident radiation (surface photovoltage spectrum). The present findings are consistent with a model based on light-induced modulation of the piezoelectric surface stresses.

  10. Numerical Studies of Localized Vibrating Structures in Nonlinear Lattices

    Science.gov (United States)

    1991-03-01

    lattice, from Denardo [19901. 11 strings which supported adjacent elements , and was assumed to be approximately linear. For our purposes, we will assume a...City, State, and ZIP Code) 10 SOURCE OF FUNDING NUMBERS PROGRAM PROJECT TASK WORK UNIT ELEMENT NO NO NO ACCESSION NO 11 TITLE (Include Security...art in cosmology , particle physics, condensed matter physics, and hydrodynamics, to name but a few. Most of the soliton work performed to date has

  11. Optimization of chiral lattice based metastructures for broadband vibration suppression using genetic algorithms

    Science.gov (United States)

    Abdeljaber, Osama; Avci, Onur; Inman, Daniel J.

    2016-05-01

    One of the major challenges in civil, mechanical, and aerospace engineering is to develop vibration suppression systems with high efficiency and low cost. Recent studies have shown that high damping performance at broadband frequencies can be achieved by incorporating periodic inserts with tunable dynamic properties as internal resonators in structural systems. Structures featuring these kinds of inserts are referred to as metamaterials inspired structures or metastructures. Chiral lattice inserts exhibit unique characteristics such as frequency bandgaps which can be tuned by varying the parameters that define the lattice topology. Recent analytical and experimental investigations have shown that broadband vibration attenuation can be achieved by including chiral lattices as internal resonators in beam-like structures. However, these studies have suggested that the performance of chiral lattice inserts can be maximized by utilizing an efficient optimization technique to obtain the optimal topology of the inserted lattice. In this study, an automated optimization procedure based on a genetic algorithm is applied to obtain the optimal set of parameters that will result in chiral lattice inserts tuned properly to reduce the global vibration levels of a finite-sized beam. Genetic algorithms are considered in this study due to their capability of dealing with complex and insufficiently understood optimization problems. In the optimization process, the basic parameters that govern the geometry of periodic chiral lattices including the number of circular nodes, the thickness of the ligaments, and the characteristic angle are considered. Additionally, a new set of parameters is introduced to enable the optimization process to explore non-periodic chiral designs. Numerical simulations are carried out to demonstrate the efficiency of the optimization process.

  12. Molecular modeling study of chiral drug crystals: lattice energy calculations.

    Science.gov (United States)

    Li, Z J; Ojala, W H; Grant, D J

    2001-10-01

    The lattice energies of a number of chiral drugs with known crystal structures were calculated using Dreiding II force field. The lattice energies, including van der Waals, Coulombic, and hydrogen-bonding energies, of homochiral and racemic crystals of some ephedrine derivatives and of several other chiral drugs, are compared. The calculated energies are correlated with experimental data to probe the underlying intermolecular forces responsible for the formation of racemic species, racemic conglomerates, or racemic compounds, termed chiral discrimination. Comparison of the calculated energies among ephedrine derivatives reveals that a greater Coulombic energy corresponds to a higher melting temperature, while a greater van der Waals energy corresponds to a larger enthalpy of fusion. For seven pairs of homochiral and racemic compounds, correlation of the differences between the two forms in the calculated energies and experimental enthalpy of fusion suggests that the van der Waals interactions play a key role in the chiral discrimination in the crystalline state. For salts of the chiral drugs, the counter ions diminish chiral discrimination by increasing the Coulombic interactions. This result may explain why salt forms favor the formation of racemic conglomerates, thereby facilitating the resolution of racemates.

  13. Chaotic phenomena of charged particles in crystal lattices.

    Science.gov (United States)

    Desalvo, Agostino; Giannerini, Simone; Rosa, Rodolfo

    2006-06-01

    In this article, we have applied the methods of chaos theory to channeling phenomena of positive charged particles in crystal lattices. In particular, we studied the transition between two ordered types of motion; i.e., motion parallel to a crystal axis (axial channeling) and to a crystal plane (planar channeling), respectively. The transition between these two regimes turns out to occur through an angular range in which the particle motion is highly disordered and the region of phase space spanned by the particle is much larger than the one swept in the two ordered motions. We have evaluated the maximum Lyapunov exponent with the method put forward by Rosenstein et al. [Physica D 65, 117 (1993)] and by Kantz [Phys. Lett. A 185, 77 (1994)]. Moreover, we estimated the correlation dimension by using the Grassberger-Procaccia method. We found that at the transition the system exhibits a very complex behavior showing an exponential divergence of the trajectories corresponding to a positive Lyapunov exponent and a noninteger value of the correlation dimension. These results turn out to be linked to a physical interpretation. The Lyapunov exponents are in agreement with the model by Akhiezer et al. [Phys. Rep. 203, 289 (1991)], based on the equivalence between the ion motion along the crystal plane described as a "string of strings" and the "kicked" rotator. The nonintegral value of the correlation dimension can be explained by the nonconservation of transverse energy at the transition.

  14. Vibrational Spectroscopy and Phonon-Related Properties of the L-Aspartic Acid Anhydrous Monoclinic Crystal.

    Science.gov (United States)

    Silva, A M; Costa, S N; Sales, F A M; Freire, V N; Bezerra, E M; Santos, R P; Fulco, U L; Albuquerque, E L; Caetano, E W S

    2015-12-10

    The infrared absorption and Raman scattering spectra of the monoclinic P21 l-aspartic acid anhydrous crystal were recorded and interpreted with the help of density functional theory (DFT) calculations. The effect of dispersive forces was taken into account, and the optimized unit cells allowed us to obtain the vibrational normal modes. The computed data exhibits good agreement with the measurements for low wavenumbers, allowing for a very good assignment of the infrared and Raman spectral features. The vibrational spectra of the two lowest energy conformers of the l-aspartic molecule were also evaluated using the hybrid B3LYP functional for the sake of comparison, showing that the molecular calculations give a limited description of the measured IR and Raman spectra of the l-aspartic acid crystal for wavenumbers below 1000 cm(-1). The results obtained reinforce the need to use solid-state calculations to describe the vibrational properties of molecular crystals instead of calculations for a single isolated molecule picture even for wavenumbers beyond the range usually associated with lattice modes (200 cm(-1) < ω < 1000 cm(-1)).

  15. Temperature dependence of lattice vibrations and analysis of specific heat in graphite. Cooperative research

    Energy Technology Data Exchange (ETDEWEB)

    Nihira, Takeshi; Iwata, Tadao; Iwase, Akihiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2001-11-01

    The semi-continuum model of lattice vibrations of graphite proposed by Komatsu and Nagamiya is the only one that has succeeded in expressing analytically the dispersion relation of lattice vibrations. The expressions of the dispersion relation contain the interlayer spacing, c, and the elastic constants, C{sub 11}, C{sub 12}, C{sub 13}, C{sub 33}, C{sub 44} and {kappa}, as parameters, where c{rho}{kappa}{sup 2} is the bending elastic constants of a graphite layer and {rho} is the density. We improve the semi-continuum model by taking these parameters as a function of temperature. For the parameters except {kappa}, we use the experimental data already known and the relations derived from them. {kappa} is derived as a function of temperature by fitting the calculated specific heat to the experimental one. The improved semi-continuum model can explain the specific heat well in the temperature range below 360 K and be reliably used there for the analysis of thermal conductivity, etc.. {kappa} decreases largely with temperature increasing, which means that there occurs the softening of the out-of-plane vibration. The second derivative of the experimental specific heat curve with respect to temperature gives information on the frequency distribution of lattice vibrations. From the analysis of the low-temperature specific heat, the value of C{sub 44} at room temperature is determined to be 0.415 x 10{sup 11} dyn/cm{sup 2}. (author)

  16. Terahertz Vibrations and Hydrogen-Bonded Networks in Crystals

    Directory of Open Access Journals (Sweden)

    Masae Takahashi

    2014-03-01

    Full Text Available The development of terahertz technology in the last few decades has made it possible to obtain a clear terahertz (THz spectrum. THz vibrations clearly show the formation of weak bonds in crystals. The simultaneous progress in the code of first-principles calculations treating noncovalent interactions has established the position of THz spectroscopy as a powerful tool for detecting the weak bonding in crystals. In this review, we are going to introduce, briefly, the contribution of weak bonds in the construction of molecular crystals first, and then, we will review THz spectroscopy as a powerful tool for detecting the formation of weak bonds and will show the significant contribution of advanced computational codes in treating noncovalent interactions. From the second section, following the Introduction, to the seventh section, before the conclusions, we describe: (1 the crystal packing forces, the hydrogen-bonded networks and their contribution to the construction of organic crystals; (2 the THz vibrations observed in hydrogen-bonded molecules; (3 the computational methods for analyzing the THz vibrations of hydrogen-bonded molecules; (4 the dispersion correction and anharmonicity incorporated into the first-principles calculations and their effect on the peak assignment of the THz spectrum (5 the temperature dependence; and (6 the polarization dependence of the THz spectrum.

  17. Vibrational mechanics in an optical lattice: controlling transport via potential renormalization.

    Science.gov (United States)

    Wickenbrock, A; Holz, P C; Wahab, N A Abdul; Phoonthong, P; Cubero, D; Renzoni, F

    2012-01-13

    We demonstrate theoretically and experimentally the phenomenon of vibrational resonance in a periodic potential, using cold atoms in an optical lattice as a model system. A high-frequency (HF) drive, with a frequency much larger than any characteristic frequency of the system, is applied by phase modulating one of the lattice beams. We show that the HF drive leads to the renormalization of the potential. We used transport measurements as a probe of the potential renormalization. The very same experiments also demonstrate that transport can be controlled by the HF drive via potential renormalization.

  18. Differences of Band Gap Characteristics of Square and Triangular Lattice Photonic Crystals in Terahertz Range

    Institute of Scientific and Technical Information of China (English)

    Jie Zha; Zhi-Yong Zhong; Huai-Wu Zhang; Qi-Ye Wen; Yuan-Xun Li

    2009-01-01

    Band gap characteristics of the photonic crystals in terahertz range with square lattice and triangular lattice of GaAs cylinders are comparatively studied by means of plane wave method (PWM). The influence of the radius on the band gap width is analyzed and the critical values where the band gap appears are put forward. The results show that themaximum band gap width of photonic crystal with triangular lattice of GaAs cylinders is much wider than that of photonic crystal with square lattice. The research provides a theoretic basis for the development of terahertz (THz) devices.

  19. Compact triplexer in two-dimensional hexagonal lattice photonic crystals

    Institute of Scientific and Technical Information of China (English)

    Hongliang Ren; Jianping Ma; Hao Wen; Yali Qin; Zhefu Wu; Weisheng Hu; Chun Jiang; Yaohui Jin

    2011-01-01

    We design a contpact triplexer based on two-dimensional (2D) hexagonal lattice photonic crystals (PCs). A folded directional coupler (FDC) is introduced in the triplexer beside the point-defect micro-cavities and line-defect waveguides. Because of the reflection feedback of the FDC, high channel drop efficiency can be realized and a compact size with the order of micrometers can be maintained. The proposed device is analyzed using the plane wave expansion method, and its transmission characteristics are calculated using the finites-difference time-domain method. The footprint of the triplexer is about 12× 9 μm, and its extinction ratios are less than -20 dB for 1310 nm, approximately -20 dB for 1490 nm, and under -4O dB for 1550 nm, making it a potentially essential device ii future fiber-to-the-home networks.%@@ We design a compact triplexer based on two-dimensional (2D) hexagonal lattice photonic crystals (PCs).A folded directional coupler (FDC) is introduced in the triplexer beside the point-defect micro-cavities and line-defect waveguides.Because of the reflection feedback of the FDC, high channel drop efficiency can be realized and a compact size with the order of micrometers can be maintained.The proposed device is analyzed using the plane wave expansion method, and its transmission characteristics are calculated using the finite-difference time-domain method.The footprint of the triplexer is about 12×9 μm, and its extinction ratios are less than -20 dB for 1310 nm, approximately -20 dB for 1490 nm, and under -40 dB for 1550 nm, making it a potentially essential device in future fiber-to-the-home networks.

  20. Photonic band structures of two-dimensional photonic crystals with deformed lattices

    Institute of Scientific and Technical Information of China (English)

    Cai Xiang-Hua; Zheng Wan-Hua; Ma Xiao-Tao; Ren Gang; Xia Jian-Bai

    2005-01-01

    Using the plane-wave expansion method, we have calculated and analysed the changes of photonic band structures arising from two kinds of deformed lattices, including the stretching and shrinking of lattices. The square lattice with square air holes and the triangular lattice with circular air holes are both studied. Calculated results show that the change of lattice size in some special ranges can enlarge the band gap, which depends strongly on the filling factor of air holes in photonic crystals; and besides, the asymmetric band edges will appear with the broken symmetry of lattices.

  1. 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.

  2. Coordinate-Invariant Lyddane-Sachs-Teller Relationship for Polar Vibrations in Materials with Monoclinic and Triclinic Crystal Systems.

    Science.gov (United States)

    Schubert, Mathias

    2016-11-18

    A coordinate-invariant generalization of the Lyddane-Sachs-Teller relation is presented for polar vibrations in materials with monoclinic and triclinic crystal systems. The generalization is derived from an eigendielectric displacement vector summation approach, which is equivalent to the microscopic Born-Huang description of polar lattice vibrations in the harmonic approximation. An expression for a general oscillator strength is also described for materials with monoclinic and triclinic crystal systems. A generalized factorized form of the dielectric response characteristic for monoclinic and triclinic materials is proposed. The generalized Lyddane-Sachs-Teller relation is found valid for monoclinic β-Ga_{2}O_{3}, where accurate experimental data became available recently from a comprehensive generalized ellipsometry investigation [Phys. Rev. B 93, 125209 (2016)]. Data for triclinic crystal systems can be measured by generalized ellipsometry as well, and are anticipated to become available soon and results can be compared with the generalized relations presented here.

  3. Three-sublattice skyrmion crystal in the antiferromagnetic triangular lattice

    Science.gov (United States)

    Rosales, H. D.; Cabra, D. C.; Pujol, Pierre

    2015-12-01

    The frustrated classical antiferromagnetic Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied under a magnetic field by means of semiclassical calculations and large-scale Monte Carlo simulations. We show that even a small DM interaction induces the formation of an antiferromagnetic skyrmion crystal (AF-SkX) state. Unlike what is observed in ferromagnetic materials, we show that the AF-SkX state consists of three interpenetrating skyrmion crystals (one by sublattice), and most importantly, the AF-SkX state seems to survive in the limit of zero temperature. To characterize the phase diagram we compute the average of the topological order parameter which can be associated with the number of topological charges or skyrmions. As the magnetic field increases this parameter presents a clear jump, indicating a discontinuous transition from a spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the spin structure factor. For higher fields, a second (probably continuous) transition occurs into a featureless paramagnetic phase.

  4. Electronic and vibrational spectra of some rare earth trifluoromethanesulfonates crystals

    Science.gov (United States)

    Paul, P.; Ghosh, M.; Neogy, D.; Mallick, P. K.

    2011-01-01

    The Raman and infrared spectra of some rare earth (dysprosium and terbium) trifluoromethanesulfonates crystals have been analyzed. Different vibrational frequencies of trifluoromethanesulfonate ions (CF 3SO 3-) are identified and assigned to different vibrations of the SO 3 and CF 3 groups. Electronic transitions of R 3+ ions (R = Dy, Tb) in these salts have been assigned to transitions from the ground to different energy levels of the ground multiplet. The electronic energy levels of the rare earth ions are also determined theoretically with the help of single electron crystal field theory. They are found to yield results not only in good agreement with the observed spectral data but also in good conformity with those obtained previously from magnetic measurements.

  5. Quadrupole lattice resonances in plasmonic crystal excited by cylindrical vector beams

    Science.gov (United States)

    Sakai, Kyosuke; Nomura, Kensuke; Yamamoto, Takeaki; Omura, Tatsuya; Sasaki, Keiji

    2016-10-01

    We report a scheme to exploit low radiative loss plasmonic resonance by combining a dark (subradiant) mode and a lattice resonance. We theoretically demonstrate that such dark-mode lattice resonances in periodic arrays of nanodisks or plasmonic crystals can be excited by vertically incident light beams. We investigate the excitation of lattice resonances in a finite sized, square-lattice plasmonic crystal by two types of cylindrical vector beams and a linearly polarized Gaussian beam. Quadrupole lattice resonances are excited by all three beams, and the largest peak intensity is obtained by using a specific type of cylindrical vector beam. Because of their lower radiative losses with many hotspots, the quadrupole lattice resonances in plasmonic crystal may pave the way for photonic research and applications that require strong light-matter interactions.

  6. A new approach for modelling lattice energy in finite crystal domains

    Science.gov (United States)

    Bilotsky, Y.; Gasik, M.

    2015-09-01

    Evaluation of internal energy in a crystal lattice requires precise calculation of lattice sums. Such evaluation is a problem in the case of small (nano) particles because the traditional methods are usually effective only for infinite lattices and are adapted to certain specific potentials. In this work, a new method has been developed for calculation of lattice energy. The method is a generalisation of conventional geometric probability techniques for arbitrary fixed lattices in a finite crystal domain. In our model, the lattice energy for wide range of two- body central interaction potentials (including long-range Coulomb potential) has been constructed using absolutely convergent sums. No artificial cut-off potential or periodical extension of the domain (which usually involved for such calculations) have been made for calculation of the lattice energy under this approach. To exemplify the applications of these techniques, the energy of Coulomb potential has been plotted as the function of the domain size.

  7. DFT study of the molecular and crystal structure and vibrational analysis of cisplatin

    Science.gov (United States)

    Georgieva, I.; Trendafilova, N.; Dodoff, N.; Kovacheva, D.

    2017-04-01

    DFT and periodic-DFT (PAW-PBE method, code VASP) calculations have been performed to study the structural and vibrational characteristics of cis-diamminedichloroplatinum(II) (cisplatin) at molecular and outside molecular level. To estimate the effect of the intermolecular interactions in crystal on the structural and vibrational properties of cisplatin, three theoretical models are considered in the present study: monomer (isolated molecule), hydrogen bonded dimer and periodic solid state structures. The work focused on the role of the theoretical models for correct modeling and prediction of geometrical and vibrational parameters of cisplatin. It has been found that the elaborate three-dimensional intermolecular hydrogen bonding network in the crystalline cisplatin significantly influences the structural and vibrational pattern of cisplatin and therefore the isolated cisplatin molecule is not the correct computational model regardless of the theoretical level used. To account for the whole intermolecular hydrogen bonding network in direction of both a and c axis and for more reliable calculations of structural and vibrational parameters periodic DFT calculations were carried out in the full crystalline periodic environment with the known lattice parameters for each cisplatin polymorph phase. The model calculations performed both at molecular level and for the periodic structures of alpha and beta cisplatin polymorph forms revealed the decisive role of the extended theoretical model for reliable prediction of the structural and vibrational characteristics of cisplatin. The powder diffraction pattern and the calculated IR and Raman spectra predicted beta polymorph form of our cisplatin sample freshly synthesized for the purposes of the present study using the Dhara's method. The various rotamers realized in the polymorph forms of cisplatin were explained by the low population of the large number of rotamers in solution as well as with the high rotamer

  8. First Principles Calculation of Terahertz Vibrational Modes of a Disaccharide Monohydrate Crystal of Lactose

    Science.gov (United States)

    Saito, Shigeki; Inerbaev, Talgat M.; Mizuseki, Hiroshi; Igarashi, Nobuaki; Note, Ryunosuke; Kawazoe, Yoshiyuki

    2006-11-01

    First-principles calculations of the crystalline vibrations of a lactose monohydrate crystal in the terahertz (THz) region were performed using periodic density functional theory calculations. The calculated vibrational modes in the THz region were derived from group motions with different sizes: molecules of lactose and crystal water, pyranose rings, and intramolecular frames. The intermolecular modes with large vibrational amplitude of lactose of 17.5-100.6 cm-1 and of crystal-water of 136.1-237.7 cm-1 were clearly separated. This article especially refers to the intermolecular vibrational modes of crystal water with the THz absorption, which provide detectable spectral features of hydrated crystals.

  9. Effects of protein engineering and rational mutagenesis on crystal lattice of single chain antibody fragments.

    Science.gov (United States)

    Kalyoncu, Sibel; Hyun, Jeongmin; Pai, Jennifer C; Johnson, Jennifer L; Entzminger, Kevin; Jain, Avni; Heaner, David P; Morales, Ivan A; Truskett, Thomas M; Maynard, Jennifer A; Lieberman, Raquel L

    2014-09-01

    Protein crystallization is dependent upon, and sensitive to, the intermolecular contacts that assist in ordering proteins into a three-dimensional lattice. Here we used protein engineering and mutagenesis to affect the crystallization of single chain antibody fragments (scFvs) that recognize the EE epitope (EYMPME) with high affinity. These hypercrystallizable scFvs are under development to assist difficult proteins, such as membrane proteins, in forming crystals, by acting as crystallization chaperones. Guided by analyses of intermolecular crystal lattice contacts, two second-generation anti-EE scFvs were produced, which bind to proteins with installed EE tags. Surprisingly, although noncomplementarity determining region (CDR) lattice residues from the parent scFv framework remained unchanged through the processes of protein engineering and rational design, crystal lattices of the derivative scFvs differ. Comparison of energy calculations and the experimentally-determined lattice interactions for this basis set provides insight into the complexity of the forces driving crystal lattice choice and demonstrates the availability of multiple well-ordered surface features in our scFvs capable of forming versatile crystal contacts.

  10. Free vibration analysis of simply supported sandwich beams with lattice truss core

    Energy Technology Data Exchange (ETDEWEB)

    Lou, Jia, E-mail: jiajia_smile@163.com [Center for Composite Materials and Structures, Harbin Institute of Technology, P.O. Box 3011, Science Park of HIT, No. 2 Yi-Kuang Street, Harbin 150080 (China); Ma, Li, E-mail: mali@hit.edu.cn [Center for Composite Materials and Structures, Harbin Institute of Technology, P.O. Box 3011, Science Park of HIT, No. 2 Yi-Kuang Street, Harbin 150080 (China); Wu, Lin-Zhi, E-mail: wlz@hit.edu.cn [Center for Composite Materials and Structures, Harbin Institute of Technology, P.O. Box 3011, Science Park of HIT, No. 2 Yi-Kuang Street, Harbin 150080 (China)

    2012-11-20

    Free vibration of AISI 304 stainless steel sandwich beams with pyramidal truss core is investigated in the present paper. The lattice truss core is transformed to a continuous homogeneous material. Considering the deformation characteristics of the sandwich beam, the following assumptions are made: (1) the thickness of the sandwich beam remains constant during deformation; (2) for the thin face sheets, only bending deformation is considered, neglecting the effect of transverse shear deformation; (3) for the core, only shear deformation is considered as the core is too weak to provide a significant contribution to the bending stiffness of the sandwich beam. The shear stress is assumed to be constant along the thickness of the core. The governing equation of free vibration is derived from Hamilton's principle, and the natural frequencies are calculated under simply supported boundary conditions. Finally, numerical simulation is carried out to get the mode shapes and natural frequencies. Our results show that the theoretical solutions agree well with the numerical results. It indicates the present method would be useful for free vibration analysis of sandwich beams with lattice truss core.

  11. Two dimentional lattice vibrations from direct product representations of symmetry groups

    Directory of Open Access Journals (Sweden)

    J. N. Boyd

    1983-01-01

    two dimensional crystals. First, the Born cyclic condition is applied to a double chain composed of coupled linear lattices to obtain a cylindrical arrangement. Then the quadratic Lagrangian function for the system is written in matrix notation. The Lagrangian is diagonalized to yield the natural frequencies of the system. The transformation to achieve the diagonalization was obtained from group theorectic considerations. Next, the techniques developed for the double chain are applied to a square lattice. The square lattice is transformed into the toroidal Ising model. The direct product nature of the symmetry group of the torus reveals the transformation to diagonalize the Lagrangian for the Ising model, and the natural frequencies for the principal directions in the model are obtained in closed form.

  12. Vibration-rotation-translation spectrum of molecular hydrogen in fullerite lattices around 80 K

    Science.gov (United States)

    Herman, Roger M.; Lewis, John Courtenay

    2009-05-01

    Calculations are presented for the fundamental vibration-rotation spectrum of H2 in fcc C60 (fullerite) lattices near 80 K using the approach and the parameters used by Herman and Lewis [Phys. Rev. B 73 (2006) 155408; in: E. Oks, M. Pindzola (Eds.) Spectral Line Shapes, AIP Conference Proceedings, No. 874, American Institute of Physics, 2006, pp. 162-176 (Proceedings of the 18th ICSLS)] at 293 K. Good agreement is found with recent DRIFT spectra of FitzGerald et al. [Personal communication, 2006]. It is argued that our approach cannot be extended to the 10 K spectrum without significant modification.

  13. Descriptors for predicting the lattice constant of body centered cubic crystal

    Science.gov (United States)

    Takahashi, Keisuke; Takahashi, Lauren; Baran, Jakub D.; Tanaka, Yuzuru

    2017-05-01

    The prediction of the lattice constant of binary body centered cubic crystals is performed in terms of first principle calculations and machine learning. In particular, 1541 binary body centered cubic crystals are calculated using density functional theory. Results from first principle calculations, corresponding information from periodic table, and mathematically tailored data are stored as a dataset. Data mining reveals seven descriptors which are key to determining the lattice constant where the contribution of descriptors is also discussed and visualized. Support vector regression (SVR) technique is implemented to train the data where the predicted lattice constants have the mean score of 83.6% accuracy via cross-validation and maximum error of 4% when compared to experimentally determined lattice constants. In addition, trained SVR is successful in predicting material combinations from a desired lattice constant. Thus, a set of descriptors for determining the lattice constant is identified and can be used as a base descriptor for lattice constants of further complex crystals. This would allow for the acceleration of the search for lattice constants of desired atomic compositions as well as the prediction of new materials based on a specified lattice constant.

  14. Extremely Low Loss THz Guidance Using Kagome Lattice Porous Core Photonic Crystal Fiber

    DEFF Research Database (Denmark)

    Hossain, Anwar; Hasanuzzaman, G.K.M.; Habib, Selim;

    2015-01-01

    A novel porous core Kagome lattice photonic crystal fiber is proposed for extremely low loss THz waves guiding. It has been reported that 82.5% of bulk effective material loss of Topas can be reduced......A novel porous core Kagome lattice photonic crystal fiber is proposed for extremely low loss THz waves guiding. It has been reported that 82.5% of bulk effective material loss of Topas can be reduced...

  15. Optical properties, lattice dynamics, and structural phase transition in hexagonal 2 H -BaMn O3 single crystals

    Science.gov (United States)

    Stanislavchuk, T. N.; Litvinchuk, A. P.; Hu, Rongwei; Jeon, Young Hun; Ji, Sung Dae; Cheong, S.-W.; Sirenko, A. A.

    2015-10-01

    Optical properties and lattice dynamics of hexagonal 2 H -BaMn O3 single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be Eg=3.2 eV . At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-active phonons; two of them are polarized along the c axis and four are polarized within the a-b plane. Seven phonon modes are identified in the Raman scattering experiments. Group theoretical mode analysis and complementary density functional theory lattice dynamics calculations are consistent with the 2 H -BaMn O3 structure belonging to the polar P 63m c space group at room temperature. All observed vibrational modes are assigned to specific eigenmodes of the lattice. The neutron diffraction measurements reveal a structural phase transition upon cooling below TC=130 ±5 K , which is accompanied by a lattice symmetry change from P 63m c to P 63c m . Simultaneously, at temperatures below TC several additional IR- and Raman-active modes are detected in experimental spectra. This confirms the occurrence of a structural transition, which is possibly associated with the appearance of electrical polarization along the c axis and a previously known tripling of the primitive cell volume at low temperatures.

  16. Raman electron spin-lattice relaxation with the Debye-type and with real phonon spectra in crystals.

    Science.gov (United States)

    Hoffmann, Stanislaw K; Lijewski, Stefan

    2013-02-01

    Electron spin-lattice relaxation temperature dependence was measured for Ti(2+) (S=1) and for Cu(2+) (S=1/2) ions in SrF(2) single crystal by electron spin echo method in temperature range 4-109K. The spin relaxation was governed by the two-phonon Raman processes. The relaxation theory is outlined and presented in a form suitable for applying with real phonon spectra. The experimental relaxation results were described using Debye-type phonon spectrum and the real phonon spectrum of SrF(2) crystal. The Debye approximation does not fit well the results for SrF(2) both at low and at high temperature. The relaxation rate is faster than that predicted by Debye-type phonon spectrum at low temperatures where excess of lattice vibrations over the Debye model exists but is slower at higher temperatures (above 50K) where density of phonon states continuously decreases when approaching to the maximal acoustic phonon frequency. The expected deviation from Debye approximation was analyzed also for Cu(2+) in NaCl and MgSiO(3) crystals for which phonon spectra are available. The fitting with the real phonon spectrum allowed us to calculate spin-phonon coupling parameter as 267 cm(-1) for Ti(2+) and 1285 cm(-1) for Cu(2+) in SrF(2).

  17. Direct calculation of the lattice Green function with arbitrary interactions for general crystals.

    Science.gov (United States)

    Yasi, Joseph A; Trinkle, Dallas R

    2012-06-01

    Efficient computation of lattice defect geometries such as point defects, dislocations, disconnections, grain boundaries, interfaces, and free surfaces requires accurate coupling of displacements near the defect to the long-range elastic strain. Flexible boundary condition methods embed a defect in infinite harmonic bulk through the lattice Green function. We demonstrate an efficient and accurate calculation of the lattice Green function from the force-constant matrix for general crystals with an arbitrary basis by extending a method for Bravais lattices. New terms appear due to the presence of optical modes and the possible loss of inversion symmetry. By separately treating poles and discontinuities in reciprocal space, numerical accuracy is controlled at all distances. We compute the lattice Green function for a two-dimensional model with broken symmetry to elucidate the role of different coupling terms. The algorithm is generally applicable in two and three dimensions to crystals with arbitrary number of atoms in the unit cell, symmetry, and interactions.

  18. Anharmonicity of lattice vibrations induced by charged nickel additions in A sup 2 B sup 6 semiconductors

    CERN Document Server

    Sokolov, V I; Shirokov, E A; Kislov, A N

    2002-01-01

    Paper presents the results of investigations into lattice vibrations induced by nickel impurities charged negatively as to the lattice in ZnSe:Ni, ZnO:Ni, ZnS:Ni, CdS:Ni semiconductors. To investigate into vibrations one applies a sensitive technique of field exciton-oscillation spectroscopy. One observes experimentally oscillating reiterations of the impurity exciton head line including the intensive peaks of combined repetitions up to the 8-th order. The experimental results are discussed on the basis of the model estimations of oscillations of a lattice with a charged impurity centre, as well as, on the ground of calculations for oscillations of monoatomic chain with high anharmonicity. Charged impurity centres are shown to induce new oscillations of lattice - impurity anharmonic modes

  19. Multimodal coupling of periodic lattices and application to rod vibration damping with a piezoelectric network

    Science.gov (United States)

    Lossouarn, B.; Aucejo, M.; Deü, J.-F.

    2015-04-01

    An elastic lattice of point masses can be a suitable representation of a continuous rod for the study of longitudinal wave propagation. By extrapolating the classical tuned mass damping strategy, a multimodal tuned mass damper is introduced from the coupling of two lattices having the same modal properties. The aim of the study is then to implement this multimodal control on a rod coupled to an electrical network. The electromechanical analogy applied to a lattice gives the required network, and the energy conversion is performed with piezoelectric patches. The coupled problem is modeled by a novel semi-continuous transfer matrix formulation, which is experimentally validated by a setup involving a rod equipped with 20 pairs of piezoelectric patches. The broadband efficiency of the multimodal control is also experimentally proved with vibration reductions up to 25 dB on the four first resonances of the rod. Finally, the practical interest of the network is pointed out, as it limits the required inductance. This is confirmed by the present purely passive setup that only involves standard low value inductors.

  20. Self-collimated waveguide bends and partial bandgap reflection of photonic crystals with parallelogram lattice.

    Science.gov (United States)

    Gao, Dingshan; Zhou, Zhiping; Citrin, David S

    2008-03-01

    The photonic crystal structure with parallelogram lattice, capable of bending a self-collimated wave with free angles and partial bandgap reflection, is presented. The equifrequency contours show that the direction of the collimation wave can be turned by tuning the angle between the two basic vectors of the lattice. Acute, right, and obtuse angles of collimating waveguide bends have been realized by arc lattices of parallelogram photonic crystals. Moreover, partial bandgap reflection of the parallelogram lattice photonic crystals is validated from the equifrequency contours and the projected band structures. A waveguide taper based on this partial bandgap reflection is also designed and proved to have above 85% transmittance over a very wide operating bandwidth of 180 nm.

  1. Understanding the role of vibrations, exact exchange, and many-body van der Waals interactions in the cohesive properties of molecular crystals

    Science.gov (United States)

    Reilly, Anthony M.; Tkatchenko, Alexandre

    2013-07-01

    The development and application of computational methods for studying molecular crystals, particularly density-functional theory (DFT), is a large and ever-growing field, driven by their numerous applications. Here we expand on our recent study of the importance of many-body van der Waals interactions in molecular crystals [A. M. Reilly and A. Tkatchenko, J. Phys. Chem. Lett. 4, 1028 (2013), 10.1021/jz400226x], with a larger database of 23 molecular crystals. Particular attention has been paid to the role of the vibrational contributions that are required to compare experiment sublimation enthalpies with calculated lattice energies, employing both phonon calculations and experimental heat-capacity data to provide harmonic and anharmonic estimates of the vibrational contributions. Exact exchange, which is rarely considered in DFT studies of molecular crystals, is shown to have a significant contribution to lattice energies, systematically improving agreement between theory and experiment. When the vibrational and exact-exchange contributions are coupled with a many-body approach to dispersion, DFT yields a mean absolute error (3.92 kJ/mol) within the coveted "chemical accuracy" target (4.2 kJ/mol). The role of many-body dispersion for structures has also been investigated for a subset of the database, showing good performance compared to X-ray and neutron diffraction crystal structures. The results show that the approach employed here can reach the demanding accuracy of crystal-structure prediction and organic material design with minimal empiricism.

  2. Oxygen plasma etching-induced crystalline lattice transformation of colloidal photonic crystals.

    Science.gov (United States)

    Ding, Tao; Wang, Fei; Song, Kai; Yang, Guoqiang; Tung, Chen-Ho

    2010-12-15

    This communication describes the transformation of a colloidal crystalline lattice that was realized via oxygen plasma etching of colloidal crystals made of SiO2@PMMA core-shell microspheres. The plasma etching of the colloidal crystals proceeded nonuniformly from the top to the bottom of the colloidal crystals. The PMMA shell was etched away by the oxygen plasma in a layer-by-layer manner, and the silica core was drawn into the pit formed by the neighboring spheres in the layer below. Consequently, the crystalline lattice was transformed while the order was maintained. Scanning electron microscopy images and reflection spectra further confirmed the change in the crystalline structures. Colloidal crystals with sc and bcc lattices can be fabricated if the ratio of the polymer shell thickness to the silica core diameter is equal to certain values. More importantly, this approach may be applicable to the fabrication of various assembly structures with different inorganic particles.

  3. Low temperature vibrational spectra, lattice dynamics, and phase transitions in some potassium hexahalometallates: K2[XY6] with X=Sn or Te and Y=Cl or Br

    DEFF Research Database (Denmark)

    Chodos, Steven L.; Berg, Rolf W.

    1979-01-01

    This paper deals with the observation and identification of phonon frequencies resulting from the low temperature phase transitions in K2XY6 crystals. By means of a simple lattice dynamical model, the vibrational Raman and IR data available in the literature and obtained here have been analyzed....... The model used is an extension of one previously used to explain the vibronic spectra of several related compounds. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  4. Raman spectrum of plutonium dioxide: Vibrational and crystal field modes

    Science.gov (United States)

    Naji, M.; Magnani, N.; Bonales, L. J.; Mastromarino, S.; Colle, J.-Y.; Cobos, J.; Manara, D.

    2017-03-01

    The Raman spectrum of plutonium dioxide is studied both experimentally and theoretically. Particular attention has been devoted to the identification of high-energy modes at 2110 and 2620 c m-1 , whose attribution has so far been controversial. The temperature dependence of both modes suggests an electronic origin for them. Original crystal field (CF) calculations reported in this work show that these two modes can be respectively assigned to the Γ1→Γ5 and Γ1→Γ3 CF transitions within the I54 manifold. These two modes, together with the only vibrational line foreseen by the group theory for the F m -3 m Pu O2 symmetry—the T2 gPu -O stretching mode observed at 478 c m-1 —can thus be used as a Raman fingerprint of fcc plutonium dioxide.

  5. Semiclassical treatments for small-molecule dynamics in low-temperature crystals using fixed and adiabatic vibrational bases

    Science.gov (United States)

    Chapman, Craig T.; Cina, Jeffrey A.

    2007-09-01

    Time-resolved coherent nonlinear optical experiments on small molecules in low-temperature host crystals are exposing valuable information on quantum mechanical dynamics in condensed media. We make use of generic features of these systems to frame two simple, comprehensive theories that will enable the efficient calculations of their ultrafast spectroscopic signals and support their interpretation in terms of the underlying chemical dynamics. Without resorting to a simple harmonic analysis, both treatments rely on the identification of normal coordinates to unambiguously partition the well-structured guest-host complex into a system and a bath. Both approaches expand the overall wave function as a sum of product states between fully anharmonic vibrational basis states for the system and approximate Gaussian wave packets for the bath degrees of freedom. The theories exploit the fact that ultrafast experiments typically drive large-amplitude motion in a few intermolecular degrees of freedom of higher frequency than the crystal phonons, while these intramolecular vibrations indirectly induce smaller-amplitude—but still perhaps coherent—motion among the lattice modes. The equations of motion for the time-dependent parameters of the bath wave packets are fairly compact in a fixed vibrational basis/Gaussian bath (FVB/GB) approach. An alternative adiabatic vibrational basis/Gaussian bath (AVB/GB) treatment leads to more complicated equations of motion involving adiabatic and nonadiabatic vector potentials. Computational demands for propagation of the parameter equations of motion appear quite manageable for tens or hundreds of atoms and scale similarly with system size in the two cases. Because of the time-scale separation between intermolecular and lattice vibrations, the AVB/GB theory may in some instances require fewer vibrational basis states than the FVB/GB approach. Either framework should enable practical first-principles calculations of nonlinear optical

  6. Two-Dimensional Anharmonic Crystal Lattices: Solitons, Solectrons, and Electric Conduction

    OpenAIRE

    Velarde, Manuel G.; Ebeling, Werner; Chetverikov, Alexander P.

    2011-01-01

    Reported here are salient features of soliton-mediated electron transport in anharmonic crystal lattices.After recalling how an electron-soliton bound state (solectron) can be formed we comment on consequences like electron surfing on a sound wave and balistic transport, possible percolation in 2d lattices, and a novel form of electron pairing with strongly correlated electrons both in real space and momentum space.

  7. Tuning of band gaps for a two-dimensional piezoelectric phononic crystal with a rectangular lattice

    Institute of Scientific and Technical Information of China (English)

    Yize Wang; Fengming Li; Yuesheng Wang; Kikuo Kishimoto; Wenhu Huang

    2009-01-01

    In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic-electric coupling. The gener-alized eigenvalue equation is obtained by the relation of the mechanic and electric fields as well as the Bloch-Floquet the-orem. The band structures of both the in-plane and anti-plane modes are calculated for a rectangular lattice by the plane-wave expansion method. The effects of the lattice constant ratio and the piezoelectricity with different filling fractions are analyzed. The results show that the largest gap width is not always obtained for a square lattice. In some situations, a rectangular lattice may generate larger gaps. The band gap characteristics are influenced obviously by the piezoelectric-ity with the larger lattice constant ratios and the filling frac-tions.

  8. Crystal lattice properties fully determine short-range interaction parameters for alkali and halide ions

    CERN Document Server

    Mao, Albert H; 10.1063/1.4742068

    2012-01-01

    Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-d...

  9. Growth, vibrational and luminescence analysis of monoclinic KGd(1-x)Prx(WO4)2 (x=0.005, 0.02, 0.05) single crystals

    Science.gov (United States)

    Thangaraju, D.; Moorthy Babu, S.; Durairajan, A.; Balaji, D.; Samuel, P.; Hayakawa, Y.

    2013-01-01

    Growth of pure KGW, 0.5, 2 and 5 wt% Pr3+ doped KGd(WO4)2 single crystals were carried out using top seeded solution growth (TSSG) method with K2WO4 as flux. Growth parameters that include the cooling rate and pulling rate were modified to achieve transparent doped crystals to that of pure crystals. Optically polished samples were used for optical and structural studies. Structure of grown crystals was confirmed and lattice parameter values were calculated using single crystal X-ray diffractometer. Both pure and doped crystals belong to the monoclinic phase with C2/c space group. When compared to pure matrix of KGW, some notable changes were observed in the lattice parameter values of doped crystals. It may be due to the ionic radii mismatch of replacing praseodymium ion in the place of gadolinium ion. Absorption and emission measurements were carried out for the 2 mm thick polished samples. The doped samples show a very good transparency with an intense absorption band around the blue region of the spectrum with additional absorption peaks in the IR region as well. Strong red emission was observed in the emission spectrum. The energy levels and their corresponding transitions were figured out in Pr3+ ions inside the matrix. Emission characteristics were compared for different dopant concentration. Raman spectra reveal the intense tungstate vibrational modes in the higher frequency region. Comparison of pure and doped samples reveal that there is no significant change in vibrational modes at higher doping concentration.

  10. Vibrational properties of Ca{sub 3}Sc{sub 2}Ge{sub 3}O{sub 12}, a garnet host crystal for laser applications

    Energy Technology Data Exchange (ETDEWEB)

    Cavalli, Enrico [Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica e Chimica Fisica, Universita di Parma, Parma (Italy)]. E-mail: cavalli@ipruniv.cce.unipr.it; Zannoni, Ester [Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica e Chimica Fisica, Universita di Parma, Parma (Italy); Bettinelli, Marco; Speghini, Adolfo [Dipartimento Scientifico e Tecnologico, Universita di Verona Ca Vignal, Verona (Italy); Tonelli, Mauro; Toncelli, Alessandra [INFM, Pisa (Italy); Dipartimento di Fisica, Universita di Pisa, Pisa (Italy)

    2000-05-29

    The IR and the Raman spectra of the Ca{sub 3}Sc{sub 2}Ge{sub 3}O{sub 12} (CaSGG) garnet crystal have been measured and discussed in terms of internal and external modes of the tetrahedral GeO{sup 4-}{sub 4} moiety. Some important aspects of the electronic spectroscopy of these materials activated with luminescent ions, i.e. the multiphonon relaxation of the excited states and the vibrational structure of the optical bands, have been taken into consideration, and correspondences with the vibrational properties of the host lattice have been presented. (author)

  11. FORMATION (DECOMPOSITION) ENTHALPY CALCULATIONS FOR CRYSTAL LATTICES OF ALKALINE-EARTH FLUORIDES

    OpenAIRE

    Gruba, O.; Germanyuk, N.; Ryabukhin, A.

    2015-01-01

    A series of calculations of structural and thermochemical properties has been carried out for the alkaline-earth fluorides. The calculations have been carried out using the modified model of effective ionic radii and the model of enthalpy calculation for the crystal lattice. The results of the calculations are in accordance with the known experimental data within confidence intervals.

  12. Light source design using Kagome-lattice hollow core photonic crystal fibers

    Science.gov (United States)

    Hossain, Md. Anwar; Namihira, Yoshinori

    2014-09-01

    Supercontinuum (SC) light source is designed using high pressure Xe-filled hollow core Kagome-lattice photonic crystal fiber. Using finite element method with perfectly matched layer, SC spectra in normal chromatic dispersion region have been generated using picosecond optical pulses from relatively less expensive laser sources.

  13. Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC)

    Indian Academy of Sciences (India)

    K S Upadhyaya; Ajay Kumar Singh; Atul Pandey; S N Pathak; A K Singh

    2005-02-01

    Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC) have been presented by including the effects of free-carrier doping and three-body interactions in the rigid shell model. The short-range overlap repulsion is operative up to the second neighbour ions. An excellent agreement has been obtained between theory and experiment for their phonon dispersion curves and Debye temperature variations. It is concluded that the contributions of free-carrier doping and three-body interactions are essential for the description of the lattice dynamics of these carbides.

  14. First principles computation of lattice energies of organic solids: the benzene crystal.

    Science.gov (United States)

    Ringer, Ashley L; Sherrill, C David

    2008-01-01

    We provide a first-principles methodology to obtain converged results for the lattice energy of crystals of small, neutral organic molecules. In particular, we determine the lattice energy of crystalline benzene using an additive system based on the individual interaction energies of benzene dimers. Enthalpy corrections are estimated so that the lattice energy can be directly compared to the experimentally determined sublimation energy. Our best estimate of the sublimation energy is 49.4 kJ mol(-1), just over the typical experimentally reported values of 43-47 kJ mol(-1). Our results underscore the necessity of using highly correlated electronic structure methods to determine thermodynamic properties within chemical accuracy. The first coordination sphere contributes about 90 % of the total lattice energy, and the second coordination sphere contributes the remaining 10 %. Three-body interactions are determined to be negligible.

  15. Holographic Fabrication of Designed Functional Defect Lines in Photonic Crystal Lattice Using a Spatial Light Modulator

    Directory of Open Access Journals (Sweden)

    Jeffrey Lutkenhaus

    2016-04-01

    Full Text Available We report the holographic fabrication of designed defect lines in photonic crystal lattices through phase engineering using a spatial light modulator (SLM. The diffracted beams from the SLM not only carry the defect’s content but also the defect related phase-shifting information. The phase-shifting induced lattice shifting in photonic lattices around the defects in three-beam interference is less than the one produced by five-beam interference due to the alternating shifting in lattice in three beam interference. By designing the defect line at a 45 degree orientation and using three-beam interference, the defect orientation can be aligned with the background photonic lattice, and the shifting is only in one side of the defect line, in agreement with the theory. Finally, a new design for the integration of functional defect lines in a background phase pattern reduces the relative phase shift of the defect and utilizes the different diffraction efficiency between the defect line and background phase pattern. We demonstrate that the desired and functional defect lattice can be registered into the background lattice through the direct imaging of designed phase patterns.

  16. Hybrid density functional study on lattice vibration, thermodynamic properties, and chemical bonding of plutonium monocarbide

    Science.gov (United States)

    Rong, Yang; Bin, Tang; Tao, Gao; BingYun, Ao

    2016-06-01

    Hybrid density functional theory is employed to systematically investigate the structural, magnetic, vibrational, thermodynamic properties of plutonium monocarbide (PuC and PuC0.75). For comparison, the results obtained by DFT, DFT + U are also given. For PuC and PuC0.75, Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic (AFM) structure. The calculated phonon spectra suggest that PuC and PuC0.75 are dynamically stable. Values of the Helmholtz free energy ΔF, internal energy ΔE, entropy S, and constant-volume specific heat C v of PuC and PuC0.75 are given. The results are in good agreement with available experimental or theoretical data. As for the chemical bonding nature, the difference charge densities, the partial densities of states and the Bader charge analysis suggest that the Pu-C bonds of PuC and PuC0.75 have a mixture of covalent character and ionic character. The effect of carbon vacancy on the chemical bonding is also discussed in detail. We expect that our study can provide some useful reference for further experimental research on the phonon density of states, thermodynamic properties of the plutonium monocarbide. Project supported by the National Natural Science Foundation of China (Grant Nos. 21371160 and 21401173).

  17. Lattice Dynamic of Ag8SnSe6 Crystal

    Directory of Open Access Journals (Sweden)

    I.V. Semkiv

    2016-10-01

    Full Text Available The synthesis and structure properties of Ag8SnSe6 argyrodite are described. Argyrodite belongs to the orthorhombic space group Pmn21 with 15 atoms per primitive cell. Classification of the main phonon modes of crystal carried out. First-principles phonon-dispersion curves for argyrodite Ag8SnSe6 are calculated. Peak position in Raman spectra and IR-spectra was clarified.

  18. Numerical Research of Materials Crystal Lattice Parameters Based on Rare-Earth Metals

    Directory of Open Access Journals (Sweden)

    Obkhodsky Artem

    2017-01-01

    Full Text Available Geometrical parameters (coordinates and angles of CeO2 crystal lattice by molecular dynamics method are calculated. Calculated parameters of crystal lattice are applied for definition the energy band structure via Hartree-Fock method in an approximation to CO LCAO (crystal orbitals as linear combination of atomic orbitals and using the model of cyclic cluster. Calculated minimum energy band p-d is within the value range of experimental data. Valence band maximum is 4.2 while minimum energy band p-d width is 2.8 eV Quantum-chemical calculations are accelerated by Schwarz inequality and direct inversion method in iterative subspace. The obtained mathematical model is implemented into software package for calculating material properties.

  19. Analysis of band gap of non-bravais lattice photonic crystal fiber

    Institute of Scientific and Technical Information of China (English)

    Yichao MA; Heming CHEN

    2009-01-01

    This article designs a novel type ofnon-bravais lattice photonic crystal fiber. To form the nesting complexperiod with positive and negative refractive index materials respectively, a cylinder with the same radius and negative refractive index is introduced into the center of each lattice unit cell in the traditional square lattice air-holes photonic crystal fiber. The photonic band-gap of the photonic crystal fiber is calculated numerically by the plane wave expansion method. The result shows that compared with the traditional square photonic band-gap fiber (PBGF),when R/A is 0.35, the refractive index of the substrate, airhole, and medium-column are 1.30, 1.0, and -1.0,respectively. This new PBGF can transmit signal by the photonic band-gap effect. When the lattice constant Λvaries from 1.5 μm to 3.0 μm, the range of the wavelength ranges from 880 nm to 2300 nm.

  20. Theory of the lattice dynamics of model crystals containing screw dislocations

    Energy Technology Data Exchange (ETDEWEB)

    Glass, N. E.

    1976-08-01

    A theoretical study of the lattice dynamics of a simple cubic model-crystal is made. The perturbation matrix of a single screw dislocation is determined and is used with the perfect lattice Green function to find four secular equations for the frequencies altered by the dislocation. The solutions yield, depending on the model parameters, up to four separate bands of optic localized-modes across the Brillouin zone. No shifts in the perfect lattice acoustical bands are found. The frequencies of the dislocation-induced localized modes are well separated from the frequencies of the perfect lattice modes and should present no difficulty in being distinguished experimentally. The Green function of the lattice containing many parallel screw dislocations is determined by following the method in use for point defects. With this imperfect-lattice Green function, the neutron cross-section for coherent one-phonon inelastic scattering by the dislocation localized-modes is obtained. Using model parameters corresponding to simple metals, the numerical evaluation yields cross-sections on the borderline of present capabilities for experimental detection and indicates the desirability of an experimental test-search. The most important parameter is found to be the ratio of the longitudinal (lambda) to the transverse (..mu..) force constants. As lambda:..mu.. increases, the localized-mode branches separate, the many-dislocation effects become noticeable, and the cross-section for inelastic scattering by the localized-modes rises. Crystals undergoing transverse mode softening, in which lambda:..mu.. grows as ..mu.. tends toward zero, may be useful in the experimental detection of dislocation-induced lattice modes.

  1. Studies on Crystal Growth, Vibrational, Electronic Properties of Nonlinear Optical Crystal: Triglycine Phosphate

    Science.gov (United States)

    Meera, M. R.; Dipuna Das, C. N.; Bena Jothy, V.; Rayar, S. L.

    2016-10-01

    Nonlinear optics is a topic of much current interest that exhibits a great diversity. This is due to the technological potentials of certain nonlinear optical effects for photonic based technologies. Many NLO crystals grown by mixing amino acids with various organic and inorganic acids have been reported in the literature. Hence, glycine mixed semi-organic material will be of special interest as a fundamental building block to develop many complex crystals with improved NLO properties. In this context, the present work it is attempted to grow NLO active Triglycine phosphate [(NH2CH2COOH)3H3PO4](TGP) crystal from aqueous solution at room temperature by slow evaporation method. The geometry, intermolecular hydrogen bonding and harmonic vibrational wavenumbers of TGP was investigated with the help of B3LYP density functional theory (DFT) methods. Natural Bond Orbital (NBO) analysis confirms the occurrence of strong intermolecular N-H...O hydrogen bond. Second harmonic frequency generation was examined by Kurtz and Perry powder test. Theoretical first order hyperpolarizability value was calculated.

  2. Crystal engineering on industrial diaryl pigments using lattice energy minimizations and X-ray powder diffraction.

    Science.gov (United States)

    Schmidt, Martin U; Dinnebier, Robert E; Kalkhof, Holger

    2007-08-23

    Diaryl azo pigments play an important role as yellow pigments for printing inks, with an annual pigment production of more than 50,000 t. The crystal structures of Pigment Yellow 12 (PY12), Pigment Yellow 13 (PY13), Pigment Yellow 14 (PY14), and Pigment Yellow 83 (PY83) were determined from X-ray powder data using lattice energy minimizations and subsequent Rietveld refinements. Details of the lattice energy minimization procedure and of the development of a torsion potential for the biphenyl fragment are given. The Rietveld refinements were carried out using rigid bodies, or constraints. It was also possible to refine all atomic positions individually without any constraint or restraint, even for PY12 having 44 independent non-hydrogen atoms per asymmetric unit. For PY14 (23 independent non-hydrogen atoms), additionally all atomic isotropic temperature factors could be refined individually. PY12 crystallized in a herringbone arrangement with twisted biaryl fragments. PY13 and PY14 formed a layer structure of planar molecules. PY83 showed a herringbone structure with planar molecules. According to quantum mechanical calculations, the twisting of the biaryl fragment results in a lower color strength of the pigments, whereas changes in the substitution pattern have almost no influence on the color strength of a single molecule. Hence, the experimentally observed lower color strength of PY12 in comparison with that of PY13 and PY83 can be explained as a pure packing effect. Further lattice energy calculations explained that the four investigated pigments crystallize in three different structures because these structures are the energetically most favorable ones for each compound. For example, for PY13, PY14, or PY83, a PY12-analogous crystal structure would lead to considerably poorer lattice energies and lower densities. In contrast, lattice energy calculations revealed that PY12 could adopt a PY13-type structure with only slightly poorer energy. This structure was

  3. Crystal Engineering on Industrial Diaryl Pigments Using Lattice Energy Minimizations and X-ray Powder Diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt,M.; Dinnebier, R.; Kalkhof, H.

    2007-01-01

    Diaryl azo pigments play an important role as yellow pigments for printing inks, with an annual pigment production of more than 50,000 t. The crystal structures of Pigment Yellow 12 (PY12), Pigment Yellow 13 (PY13), Pigment Yellow 14 (PY14), and Pigment Yellow 83 (PY83) were determined from X-ray powder data using lattice energy minimizations and subsequent Rietveld refinements. Details of the lattice energy minimization procedure and of the development of a torsion potential for the biphenyl fragment are given. The Rietveld refinements were carried out using rigid bodies, or constraints. It was also possible to refine all atomic positions individually without any constraint or restraint, even for PY12 having 44 independent non-hydrogen atoms per asymmetric unit. For PY14 (23 independent non-hydrogen atoms), additionally all atomic isotropic temperature factors could be refined individually. PY12 crystallized in a herringbone arrangement with twisted biaryl fragments. PY13 and PY14 formed a layer structure of planar molecules. PY83 showed a herringbone structure with planar molecules. According to quantum mechanical calculations, the twisting of the biaryl fragment results in a lower color strength of the pigments, whereas changes in the substitution pattern have almost no influence on the color strength of a single molecule. Hence, the experimentally observed lower color strength of PY12 in comparison with that of PY13 and PY83 can be explained as a pure packing effect. Further lattice energy calculations explained that the four investigated pigments crystallize in three different structures because these structures are the energetically most favorable ones for each compound. For example, for PY13, PY14, or PY83, a PY12-analogous crystal structure would lead to considerably poorer lattice energies and lower densities. In contrast, lattice energy calculations revealed that PY12 could adopt a PY13-type structure with only slightly poorer energy. This structure was

  4. Photonic Bandgap Properties of Atom-lattice Photonic Crystals in Polymer

    Institute of Scientific and Technical Information of China (English)

    REN Lin; WANG Dian; SUN Gui-ting; NIU Li-gang; YANG Han; SONG Jun-feng

    2011-01-01

    The present paper covers the various photonic crystals(PhCs) structures mimicking real atom-lattice structures in electronic crystals by using the femtosecond laser-induced two-photon photopolymerization of SU-8 resin. The bandgap properties were investigated by varying the crystal orientations in <111>, <110> and <100> of diamond-lattice PhCs. lhe photonic stop gaps were present at λ=3.88 μm in <111> direction, λ=4.01 μtm in <110> direction and λ=5.30 μm in <100> direction, respectively. In addition, defects were introduced in graphite-lattice PhCs and the strong localization of photons in this structure with defects at λ=5 μm was achieved. All the above work shows the powerful capability of femtosecond laser fabrication in manufacturing various complicated threedimensional photonic crystals and of controlling photons by inducing defects in the PhCs samples.

  5. Structure determination of the 1918 H1N1 neuraminidase from a crystal with lattice-translocation defects

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xueyong [Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States); Xu, Xiaojin [Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States); Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU (United Kingdom); Wilson, Ian A., E-mail: wilson@scripps.edu [Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States); The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States)

    2008-08-01

    The structure of the 1918 H1N1 neuraminidase was determined to 1.65 Å from crystals with a lattice-translocation defect using uncorrected, as well as corrected, diffraction data. Few examples of macromolecular crystals containing lattice-translocation defects have been published in the literature. Lattice translocation and twinning are believed to be two common but different crystal-growth anomalies. While the successful use of twinned data for structure determination has become relatively routine in recent years, structure determination of crystals with lattice-translocation defects has not often been reported. To date, only four protein crystal structures containing such a crystal defect have been determined, using corrected, but not uncorrected, intensity data. In this report, the crystallization, structure determination and refinement of N1 neuraminidase derived from the 1918 H1N1 influenza virus (18NA) at 1.65 Å resolution are described. The crystal was indexed in space group C222{sub 1}, with unit-cell parameters a = 117.7, b = 138.5, c = 117.9 Å, and the structure was solved by molecular replacement. The lattice-translocation vector in the 18NA crystal was (0, 1/2, 1/2) or its equivalent vector (1/2, 0, 1/2) owing to the C lattice symmetry. Owing to this special lattice-translocation vector in space group C222{sub 1}, structure refinement could be achieved in two different ways: using corrected or uncorrected diffraction data. In the refinement with uncorrected data, a composite model was built to represent the molecules in the translated and untranslated layers, respectively. This composite structure model provided a unique example to examine how the molecules were arranged in the two lattice domains resulting from lattice-translocation defects.

  6. Influence of controlling vibrations on heat transfer in floating zone crystal growth*

    Science.gov (United States)

    Fedyushkin, A. I.

    The crystal growth processes of monocrystals are strongly vibrational sensitive systems and in particular it concerns to a floating zone method as presence of a free surface and two fronts of crystallization and melting that aggravate it The given work is devoted to numerical investigations of the influence of controlling vibrations on heat transfer during crystal growth by floating zone technique Normal and weightless environment conditions are considered Mathematical simulation is performed on the numerical solutions of basis unsteady Navier-Stokes equations for incompressible fluid flows and energy equation 2D axisymmetric geometry was used in model Marangoni convection and radiation condition on the curvature free surface were taken in account The calculations of the shape of a free surface of a liquid zone and influences on it of a corner of wetting force of weight and size of factor of a superficial tension are carried out The simulations of convective heat transfer for real curvature free surface of a liquid zone with and without the taking into account of the following factors parameters of radiation rotations natural and Marangoni convection and vibrations are carried out The given calculations are carried out for semiconductors melts with Prandtl number Pr 1 and for oxides Pr 1 The influence of vibrations of a crystal on melt flow and on the wide of dynamic and thermal boundary layers at melt-crystal interface is studied The action of vibrations on an enhancement of heat fluxes at the melt crystal interface is shown

  7. A novel optical beam splitter based on photonic crystal with hybrid lattices

    Institute of Scientific and Technical Information of China (English)

    Zhu Qing-Yi; Fu Yong-Qi; Hu De-Qing; Zhang Zhi-Min

    2012-01-01

    A novel optical beam splitter constructed on the basis of photonic crystal (PC) with hybrid lattices is proposed in this paper.The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams.Triangular-lattice graded-index PCs are combined for focusing each branch.Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design.The waveguide is unnecessary in the design.Thus the device has functions of both splitting and focusing beams.Size of the divided beam at site of full-width at half-maximum is of the order of λ/2.The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process.

  8. Self-assembly of kagome lattices, entangled webs and linear fibers with vibrating patchy particles in two dimensions.

    Science.gov (United States)

    Chapela, Gustavo A; Guzmán, Orlando; Martínez-González, José Adrián; Díaz-Leyva, Pedro; Quintana-H, Jacqueline

    2014-12-07

    A vibrating version of patchy particles in two dimensions is introduced to study self-assembly of kagome lattices, disordered networks of looping structures, and linear arrays. Discontinuous molecular dynamics simulations in the canonical ensemble are used to characterize the molecular architectures and thermodynamic conditions that result in each of those morphologies, as well as the time evolution of lattice formation. Several versions of the new model are tested and analysed in terms of their ability to produce kagome lattices. Due to molecular flexibility, particles with just attractive sites adopt a polarized-like configuration and assemble into linear arrays. Particles with additional repulsive sites are able to form kagome lattices, but at low temperature connect as entangled webs. Abundance of hexagonal motifs, required for the kagome lattice, is promoted even for very small repulsive sites but hindered when the attractive range is large. Differences in behavior between the new flexible model and previous ones based on rigid bodies offer opportunities to test and develop theories about the relative stability, kinetics of formation and mechanical response of the observed morphologies.

  9. Slow light with large group index - bandwidth product in lattice-shifted photonic crystal waveguides

    Science.gov (United States)

    Tang, Jian; Li, Wenhui; Wu, Jun; Xu, Zhonghui

    2016-10-01

    This study presents a systematic optimization procedure to generate slow light with large group index, wideband, and low dispersion in an lattice-shifted photonic crystal waveguide. The waveguide is based on triangular lattice photonic crystal imposed by selectively altering the locations of the holes adjacent to the line defect. Under a constant group index criterion of ± 10% variation, when group indices are nearly constants of 24, 33, 46, 57, and 66, their corresponding bandwidths of flat band reach 24.2, 17.6, 12.8, 10.1 and 8.6 nm around 1550 nm, respectively. A nearly constant large group index - bandwidth product (GBP) of 0.37 is achieved for all cases. Low dispersion slow light propagation is confirmed by studying the relative temporal pulse-width spreading with the 2-D finite-difference time-domain method.

  10. Resonant tunneling effect in one-dimensional twinned lattice photonic crystal under total reflection conditions

    Science.gov (United States)

    Feng, Xi; Li, Hu; Yuxia, Tang

    2016-07-01

    Under total reflection conditions, it typically seems as though light waves will be reflected completely on the interface; in actuality, the waves can penetrate the medium as evanescent waves. In this paper, we present a twinned lattice photonic crystal with a unit cell composed of AB layers and their mirror. We assume that the refractive index n 0 of the input and output end is equal to n B and larger than n A . We first demonstrate the dependence of band structure on the incidence angle and normalized wavelength, in which the resonant tunneling bands are exposed. We then draw a comparison of bands between ABBA and AB. To conclude, we discuss the resonant tunneling effect in the twinned lattice photonic crystal under the total reflection conditions. As incidence angle increases, the resonant tunneling band ultimately vanishes completely.

  11. Light confinement at a Dirac point in honeycomb-like lattice photonic crystal

    Science.gov (United States)

    Mao, Qiuping; Xie, Kang; Hu, Lei; Li, Qian; Zhang, Wei; Jiang, Haiming; Hu, Zhijia; Wang, Erlei

    2017-02-01

    Optical waveguides and cavities are important components among modern optical devices. Traditional optical cavities rely on total internal reflection or photonic bandgaps to achieve field confinement. Recently, a new type of trapped mode, the Dirac mode, has been reported to occur in triangular or honeycomb lattice photonic crystal. This novel localized mode is attribute to neither of the traditional light-guiding mechanisms and owns different characteristics. Here we report the discovery of the Dirac mode in honeycomb-like photonic crystal lattice. The Dirac mode occurs at a Dirac frequency, which is beyond the complete photonic bandgaps. It has a different algebraic-decay feature. Our discovery extends applicability of the Dirac mode in designing for optical devices.

  12. Extraordinary lateral beaming of sound from a square-lattice phononic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Xiaoxue; Qiu, Chunyin; He, Hailong; Peng, Shasha; Ke, Manzhu [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Liu, Zhengyou, E-mail: zyliu@whu.edu.cn [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Institute for Advanced Studies, Wuhan University, Wuhan 430072 (China)

    2017-03-03

    Highlights: • An extraordinary lateral beaming phenomenon is observed in a finite phononic crystal made of square lattice. • The phenomenon can be explained by the equivalence of the states located around the four corners of the first Brillouin zone. • The lateral beaming behavior enables a simple design of acoustic beam splitters. • In some sense, the phenomenon can be described by a near zero refractive index. - Abstract: This work revisits the sound transmission through a finite phononic crystal of square lattice. In addition to a direct, ordinary transmission through the sample, an extraordinary lateral beaming effect is also observed. The phenomenon stems from the equivalence of the states located around the four corners of the first Brillouin zone. The experimental result agrees well with the theoretical prediction. The lateral beaming behavior enables a simple design for realizing acoustic beam splitters.

  13. Theory of vibrational cooling in molecular crystals: Application to crystalline naphthalene

    Science.gov (United States)

    Hill, Jeffrey R.; Dlott, Dana D.

    1988-07-01

    The process of vibrational cooling (VC) is theoretically investigated in the molecular crystal naphthalene. Specificially we consider the process where a highly excited vibration cools by emitting lower energy vibrations (vibrational relaxation, or VR) and phonons. We also consider the subsequent cooling of emitted optic phonons by emission of acoustic phonons. Using previously determined vibrational lifetimes [J. R. Hill et al., J. Chem. Phys. 88, 949 (1988)], a consistent transition rate matrix is obtained which describes VR of all vibrations and optic phonons at all temperatures. Then a Master equation is solved numerically to obtain the time dependent vibrational populations of all states following impulse excitation of a high frequency vibration. These results are compared to a previously derived analytic model for VC in molecular crystals [J. R. Hill and D. D. Dlott, J. Chem. Phys. 89, 830 (1988)]. In that theory, which is shown to be in good agreement with the naphthalene calculation, the excess vibrational excitation moves to lower energy states and broadens as time increases. The motion toward lower energy states is described by a temperature independent ``vibrational velocity'' (emitted energy per unit time). In naphthalene, the vibrational velocity is V0 ≊9 cm-1 /ps. The VC process occurs on a time scale as much as an order of magnitude longer than an individual VR step. Although VR is highly temperature dependent, VC is not. The VC calculations are used to predict the decay from the initial state, the time dependent populations of transient vibrational excitations, and the return to the vibrationless ground state. All these quantities are directly related to experimental observables such as incoherent anti-Stokes Raman scattering and hot luminescence.

  14. Crystal growth and comparison of vibrational and thermal properties of semi-organic nonlinear optical materials

    Indian Academy of Sciences (India)

    S Gunasekaran; G Anand; R Arun Balaji; J Dhanalakshmi; S Kumaresan

    2010-10-01

    Single crystals of urea thiourea mercuric sulphate (UTHS) and urea thiourea mercuric chloride (UTHC), semi-organic nonlinear optical materials, were grown by low-temperature solution growth technique by slow evaporation method using water as the solvent. Good quality single crystals were grown within three weeks. The nonlinear nature of the crystals was confirmed by SHG test. The UV–Vis spectrum showed the transmitting ability of the crystals in the entire visible region. FTIR spectrum was recorded and vibrational assignments were made. The degree of dopant inclusion was ascertained by AAS. The TGA–DTA studies showed the thermal properties of the crystals.

  15. Tuning negative refractive collimation beam by square lattice sonic crystal with concave incident surface

    Directory of Open Access Journals (Sweden)

    F. Shen

    2016-02-01

    Full Text Available Negative refractive collimation beam at the low frequency region is achieved in a square lattice sonic crystal with the small magnitude of effective refractive index. A simple tuning approach for such acoustic beam is also proposed by attaching an additional concave surface of incidence to the crystal slab. This can increase the propagation distance of collimation beam, enhance or suppress the beam intensity. The proposed approach is rather general and applicable to other acoustic materials as long as their effective index can be retrieved. Moreover, the results can be applied to wavefront manipulation and transmission enhancement.

  16. Colloidal nanoparticles trapped by liquid-crystal defect lines: A lattice Monte Carlo simulation

    Science.gov (United States)

    Jose, Regina; Skačej, Gregor; Sastry, V. S. S.; Žumer, Slobodan

    2014-09-01

    Lattice-based Monte Carlo simulations are performed to study a confined liquid crystal system with a topological disclination line entangling a colloidal nanoparticle. In our microscopic study the disclination line is stretched by moving the colloid, as in laser tweezing experiments, which results in a restoring force attempting to minimize the disclination length. From constant-force simulations we extract the corresponding disclination line tension, estimated as ˜50 pN, and observe its decrease with increasing temperature.

  17. Square-lattice large-pitch hollow-core photonic crystal fiber

    DEFF Research Database (Denmark)

    Couny, F.; Roberts, John; Birks, T.A.;

    2008-01-01

    We report on the design, fabrication and characterization of silica square-lattice hollow core photonic crystal fibers optimized for low loss guidance over an extended frequency range in the mid-IR region of the optical spectrum. The fiber's linear optical properties include an ultra-low group...... velocity dispersion and a polarization cross-coupling as low as -13.4dB over 10m of fiber....

  18. Crystal structure of human CRMP-4: correction of intensities for lattice-translocation disorder

    Energy Technology Data Exchange (ETDEWEB)

    Ponnusamy, Rajesh [Universidade Nova de Lisboa, Avenida da República, EAN, 2781-901 Oeiras (Portugal); Lebedev, Andrey A. [Research Complex at Harwell, STFC Rutherford Appleton Laboratory, Didcot OX11 0FA (United Kingdom); Pahlow, Steffen [University of Hamburg, Ohnhorststrasse 18, 22609 Hamburg (Germany); Lohkamp, Bernhard, E-mail: bernhard.lohkamp@ki.se [Karolinska Institutet, Tomtebodavägen 6, 4tr, 17177 Stockholm (Sweden); Universidade Nova de Lisboa, Avenida da República, EAN, 2781-901 Oeiras (Portugal)

    2014-06-01

    Crystals of human CRMP-4 showed severe lattice-translocation disorder. Intensities were demodulated using the so-called lattice-alignment method and a new more general method with simplified parameterization, and the structure is presented. Collapsin response mediator proteins (CRMPs) are cytosolic phosphoproteins that are mainly involved in neuronal cell development. In humans, the CRMP family comprises five members. Here, crystal structures of human CRMP-4 in a truncated and a full-length version are presented. The latter was determined from two types of crystals, which were either twinned or partially disordered. The crystal disorder was coupled with translational NCS in ordered domains and manifested itself with a rather sophisticated modulation of intensities. The data were demodulated using either the two-lattice treatment of lattice-translocation effects or a novel method in which demodulation was achieved by independent scaling of several groups of intensities. This iterative protocol does not rely on any particular parameterization of the modulation coefficients, but uses the current refined structure as a reference. The best results in terms of R factors and map correlation coefficients were obtained using this new method. The determined structures of CRMP-4 are similar to those of other CRMPs. Structural comparison allowed the confirmation of known residues, as well as the identification of new residues, that are important for the homo- and hetero-oligomerization of these proteins, which are critical to nerve-cell development. The structures provide further insight into the effects of medically relevant mutations of the DPYSL-3 gene encoding CRMP-4 and the putative enzymatic activities of CRMPs.

  19. Wavelets centered on a knot sequence: piecewise polynomial wavelets on a quasi-crystal lattice

    CERN Document Server

    Atkinson, Bruce W; Geronimo, Jeffrey S; Hardin, Douglas P

    2011-01-01

    We develop a general notion of orthogonal wavelets `centered' on an irregular knot sequence. We present two families of orthogonal wavelets that are continuous and piecewise polynomial. As an application, we construct continuous, piecewise quadratic, orthogonal wavelet bases on the quasi-crystal lattice consisting of the $\\tau$-integers where $\\tau$ is the golden-mean. The resulting spaces then generate a multiresolution analysis of $L^2(\\mathbf{R})$ with scaling factor $\\tau$.

  20. Controlling the focusing properties of a triangular-lattice metallic photonic-crystal slab

    Institute of Scientific and Technical Information of China (English)

    Feng Shuai; Wang Yi-Quan; Li Zhi-Yuan; Cheng Bing-Ying; Zhang Dao-Zhong

    2007-01-01

    This paper studies the focusing properties of a two-dimensional photonic crystal (PC) slab consisting of a triangular lattice of metallic cylinders immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the PC slab, it finds that both the image distance and image quality can be controlled by simply adjusting the refractive index of the background material.

  1. Formation of Bragg Band Gaps in Anisotropic Phononic Crystals Analyzed With the Empty Lattice Model

    Directory of Open Access Journals (Sweden)

    Yan-Feng Wang

    2016-05-01

    Full Text Available Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowest intersections coincide with boundaries of the first Brillouin zone. However, if a phononic crystal contains elastically anisotropic materials, its overall symmetry is not dictated solely by the lattice symmetry. We construct an empty lattice model for phononic crystals made of isotropic and anisotropic materials, based on their slowness curves. We find that, in the anisotropic case, avoided crossings generally do not appear at the boundaries of traditionally defined Brillouin zones. Furthermore, the Bragg “planes” which give rise to phononic band gaps, are generally not flat planes but curved surfaces. The same is found to be the case for avoided crossings between shear (transverse and longitudinal bands in the isotropic case.

  2. Structure Determination of the 1918 H1N1 Neuraminidase From a Crystal With Lattice-Translocation Defects

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, X.; Xu, X.; Wilson, I.A.

    2009-05-28

    Few examples of macromolecular crystals containing lattice-translocation defects have been published in the literature. Lattice translocation and twinning are believed to be two common but different crystal-growth anomalies. While the successful use of twinned data for structure determination has become relatively routine in recent years, structure determination of crystals with lattice-translocation defects has not often been reported. To date, only four protein crystal structures containing such a crystal defect have been determined, using corrected, but not uncorrected, intensity data. In this report, the crystallization, structure determination and refinement of N1 neuraminidase derived from the 1918 H1N1 influenza virus (18NA) at 1.65 {angstrom} resolution are described. The crystal was indexed in space group C222{sub 1}, with unit-cell parameters a = 117.7, b = 138.5, c = 117.9 {angstrom}, and the structure was solved by molecular replacement. The lattice-translocation vector in the 18NA crystal was (0, 1/2, 1/2) or its equivalent vector (1/2, 0, 1/2) owing to the C lattice symmetry. Owing to this special lattice-translocation vector in space group C222{sub 1}, structure refinement could be achieved in two different ways: using corrected or uncorrected diffraction data. In the refinement with uncorrected data, a composite model was built to represent the molecules in the translated and untranslated layers, respectively. This composite structure model provided a unique example to examine how the molecules were arranged in the two lattice domains resulting from lattice-translocation defects.

  3. Thermodynamic properties of water in the lattice gas model with consideration of the vibrational motions of molecules

    Science.gov (United States)

    Titov, S. V.; Tovbin, Yu. K.

    2016-11-01

    A molecular model developed earlier for a polar fluid within the lattice gas model is supplemented by considering the vibrational motions of molecules using water as an example. A combination of point dipole and Lennard-Jones potentials from SPC parametrization is chosen as the force field model for the molecule. The main thermodynamic properties of liquid water (density, internal energy, and entropy) are studied as functions of temperature. There is qualitative agreement between the calculation results and the experimental data. Ways of refining the molecular theory are discussed.

  4. Influence of the lattice mismatch on the lattice vibration modes for InAs/GaSb superlattices

    Science.gov (United States)

    Aslan, Bulent; Korkmaz, Melih

    2016-01-01

    Raman scattering study on a group of InAs/GaSb superlattice (SL) samples where the strain is systematically changed from tensile to compressive regime is presented. The effect of the lattice mismatch between the substrate and the epitaxially grown SL layers on particularly the InSb-like interface phonon frequencies is revealed in the backscattering geometry. The higher order folded longitudinal acoustic (FLA) phonon modes are also observed for samples having different superlattice periodicity. An ideality factor is incorporated into the model used for predicting the FLA phonon frequencies to simply express the deviation in the average acoustic velocity in the SL from the one in the homogeneous medium with abrupt transition in the interfaces.

  5. Vibrational spectroscopy and dynamics of W(CO)6 in solid methane as a probe of lattice properties

    Science.gov (United States)

    Thon, Raphael; Chin, Wutharath; Chamma, Didier; Galaup, Jean-Pierre; Ouvrard, Aimeric; Bourguignon, Bernard; Crépin, Claudine

    2016-12-01

    Methane solids present more than one accessible crystalline phase at low temperature at zero pressure. We trap W(CO)6 in CH4 and CD4 matrices between 8 and 35 K to probe the interaction between an impurity and its surrounding molecular solid under various physical conditions. Linear and nonlinear vibrational spectroscopies of W(CO)6 highlight different kinds of interaction and reveal new and remarkable signatures of the phase transition of methane. The structures in the absorption band of the antisymmetric CO stretching mode exhibit a clear modification at the transition between phase II and phase I in CH4 and motional narrowing is observed upon temperature increase. The vibrational dynamics of this mode is probed in stimulated photon echo experiments performed with a femtosecond IR laser. A short component around 10 ps is detected in the population relaxation lifetime in the high temperature phase of solid CH4 (phase I) and disappears at lower temperatures (phase II) where the vibrational lifetime is in the hundreds of ps. The analysis of the nonlinear time-resolved results suggests that the short component comes from a fast energy transfer between the vibrational excitation of the guest and the lattice in specific families of sites. Such fast transfers are observed in the case of W(CO)6 trapped in CD4 because of an energy overlap of the excitation of W(CO)6 and a lattice vibron. In solid CH4, even when these V-V transfers are not efficient, pure dephasing processes due to the molecular nature of the host occur: they are temperature dependent without a clear modification at the phase transition.

  6. Helium and neon diffusion in pure hematite (α-Fe2O3) crystal lattice

    Science.gov (United States)

    Balout, Hilal; Roques, Jérôme; Gautheron, Cécile; Tassan-Got, Laurent

    2016-04-01

    Hematite (α-Fe2O3) has the corundum-type structure and is relatively present on Earth and Mars surface associated to ore mineral precipitation or as a weathering phase. He and Ne retention in such mineral has been intensively investigated experimentally because of the potential use of (U-Th-Sm)/(He-Ne) chronometer and thermochronometer. Therefore, the He/Ne diffusion in hematite crystal is an important issue for the interpretation of (U-Th)/(He-Ne) thermochronometric ages. For this purpose an accurate investigation of helium and neon diffusion in hematite crystal lattice has been achieved by computational multi-scale approach. Different insertion sites and diffusion pathways are first characterized where the spin polarized density functional theory (sp-DFT) approach coupled to the nudged elastic band (NEB) method is used to determine the migration energies between the insertion sites. Then, a statistical method, based on transition state theory (TST), is used to compute the jump probability between sites. The previous results are used as input data in a 3D random walk simulation, which permits to determine the effective activation energy and diffusion coefficient. Using the He/Ne diffusion coefficients, the closure temperature Tc has been calculated. For typical grain size of 100 microns, Tc will be of 116° C and 297° C for He and Ne atoms, respectively. These results Show that He and Ne atoms are highly retained in the crystal lattice at surface temperature. The obtained diffusion coefficients confirm that He/Ne retentively power in hematite lattice is very important, allowing a large range of different geological applications such the measurement of hematite crystallization ages on Earth and Mars.

  7. On anisotropy function in crystal growth simulations using Lattice Boltzmann equation

    CERN Document Server

    Younsi, Amina

    2016-01-01

    In this paper, we present the ability of the Lattice Boltzmann (LB) equation, usually applied to simulate fluid flows, to simulate various shapes of crystals. Crystal growth is modeled with a phase-field model for a pure substance, numerically solved with a LB method in 2D and 3D. This study focuses on the anisotropy function that is responsible for the anisotropic surface tension between the solid phase and the liquid phase. The anisotropy function involves the unit normal vectors of the interface, defined by gradients of phase-field. Those gradients have to be consistent with the underlying lattice of the LB method in order to avoid unwanted effects of numerical anisotropy. Isotropy of the solution is obtained when the directional derivatives method, specific for each lattice, is applied for computing the gradient terms. With the central finite differences method, the phase-field does not match with its rotation and the solution is not any more isotropic. Next, the method is applied to simulate simultaneous...

  8. CCSD(T)/CBS fragment-based calculations of lattice energy of molecular crystals

    Science.gov (United States)

    Červinka, Ctirad; Fulem, Michal; Růžička, Květoslav

    2016-02-01

    A comparative study of the lattice energy calculations for a data set of 25 molecular crystals is performed using an additive scheme based on the individual energies of up to four-body interactions calculated using the coupled clusters with iterative treatment of single and double excitations and perturbative triples correction (CCSD(T)) with an estimated complete basis set (CBS) description. The CCSD(T)/CBS values on lattice energies are used to estimate sublimation enthalpies which are compared with critically assessed and thermodynamically consistent experimental values. The average absolute percentage deviation of calculated sublimation enthalpies from experimental values amounts to 13% (corresponding to 4.8 kJ mol-1 on absolute scale) with unbiased distribution of positive to negative deviations. As pair interaction energies present a dominant contribution to the lattice energy and CCSD(T)/CBS calculations still remain computationally costly, benchmark calculations of pair interaction energies defined by crystal parameters involving 17 levels of theory, including recently developed methods with local and explicit treatment of electronic correlation, such as LCC and LCC-F12, are also presented. Locally and explicitly correlated methods are found to be computationally effective and reliable methods enabling the application of fragment-based methods for larger systems.

  9. Optical induction of Bessel-like lattices in methyl-red doped liquid crystal cells

    Science.gov (United States)

    Mantashyan, Paytsar; Drampyan, Rafael; Beeckman, Jeroen; Willekens, Oliver; Neyts, Kristiaan

    2015-03-01

    The optical induction of annular photonic lattices by a traveling Bessel beam has been investigated in Methyl-red (MR) doped nematic liquid crystal (LC). Non-diffracting Bessel beams were formed by an axicon. The induced Bessel-like lattice had a ~15 μm period in the radial direction. The lattice was tested by measuring the forward diffracted power of the recording Bessel beam. The dependency on the angle between the polarization of the laser beam and the director of the LC and on the axial position of the LC cell had been investigated. A diffraction efficiency of 14% had been obtained. Investigations have been performed for different MR dye doping concentrations. An erasure time of the lattice of 60 s has been determined by a 532 nm probe Gaussian beam of 2 mW in a LC cell with MR dye concentration of 1.15 wt%. The induced periodically varying refractive index in the LC medium is analogous to microstructured fibers and allows the study of light localization and soliton behavior in highly nonlinear waveguide arrays.

  10. Acoustic vibrations contribute to the diffuse scatter produced by ribosome crystals

    Energy Technology Data Exchange (ETDEWEB)

    Polikanov, Yury S.; Moore, Peter B.

    2015-09-26

    The diffuse scattering pattern produced by frozen crystals of the 70S ribosome fromThermus thermophilusis as highly structured as it would be if it resulted entirely from domain-scale motions within these particles. However, the qualitative properties of the scattering pattern suggest that acoustic displacements of the crystal lattice make a major contribution to it.

  11. Capturing the crystal: prediction of enthalpy of sublimation, crystal lattice energy, and melting points of organic compounds.

    Science.gov (United States)

    Salahinejad, Maryam; Le, Tu C; Winkler, David A

    2013-01-28

    Accurate computational prediction of melting points and aqueous solubilities of organic compounds would be very useful but is notoriously difficult. Predicting the lattice energies of compounds is key to understanding and predicting their melting behavior and ultimately their solubility behavior. We report robust, predictive, quantitative structure-property relationship (QSPR) models for enthalpies of sublimation, crystal lattice energies, and melting points for a very large and structurally diverse set of small organic compounds. Sparse Bayesian feature selection and machine learning methods were employed to select the most relevant molecular descriptors for the model and to generate parsimonious quantitative models. The final enthalpy of sublimation model is a four-parameter multilinear equation that has an r(2) value of 0.96 and an average absolute error of 7.9 ± 0.3 kJ.mol(-1). The melting point model can predict this property with a standard error of 45° ± 1 K and r(2) value of 0.79. Given the size and diversity of the training data, these conceptually transparent and accurate models can be used to predict sublimation enthalpy, lattice energy, and melting points of organic compounds in general.

  12. Manifestation of Crystal Lattice Distortions in the IR Reflection Spectra of Abrasion-Treated ZnSe Ceramics

    Science.gov (United States)

    Sitnikova, V. E.; Dunaev, A. A.; Mamalimov, R. I.; Pakhomov, P. M.; Khizhnyak, S. D.; Chmel, A. E.

    2017-07-01

    The Fourier IR reflection spectra of ZnSe ceramics prepared by hot pressing (HP), physical vapor deposition (PVD), and PVD combined with hot isostatic pressing (HIP) are presented. The optical constants of polished and dry-ground specimens were used for comparison. The grinding treatment simulated the erosion of the outer surface of optical elements made of zinc selenide under the influence of solid dust particles and deposits. In the polished specimens residual stresses showed up in the IR reflection spectra of the ZnSePVD and ZnSeHIP ceramics, which had well-defined orientation of grains, but were not present in the spectra of the ZnSeHIP ceramics as a result of mutual compensation of the stresses in the randomly oriented grains of the material. The stresses, which appeared as a shift of the absorption bands calculated by the Kramers-Kronig method, increased significantly after abrasive treatment of the specimens. For all the treated ceramics the intensity of the absorption bands resulting from the anharmonicity of the vibrations in the distorted crystal lattice increased by several times. The last effect also depends on the production prehistory of the ceramics.

  13. Lattice Boltzmann Simulation of Kinetic Isotope Effect During Snow Crystal Formation

    Science.gov (United States)

    Lu, G.; Depaolo, D. J.; Kang, Q.; Zhang, D.

    2007-12-01

    The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically-symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over- saturation, determines crystal morphology, there are no quantitative models that relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be direct relationships between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D lattice Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. Crystal growth patterns can be varied between random growth and deterministic growth (along the maximum concentration gradient for example). The input parameters needed are the isotope- dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the condensation coefficient for ice is uncertain. The ratio D/k is a length (order 1 micron) that determines the minimum scale of dendritic growth features

  14. Surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber

    Science.gov (United States)

    Bing, Pibin; Li, Zhongyang; Yuan, Sheng; Yao, Jianquan; Lu, Ying

    2016-04-01

    A surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber has been designed and simulated by finite element method. The square-lattice airholes are first coated with a calcium fluoride layer to provide mode confinement, then a nanoscale gold layer is deposited to excite the plasmon mode, and finally, the sample is infiltrated into the holes. The numerical results reveal that the resonance properties are easily affected by many parameters. The refractive index resolution of corresponding sensor can reach 4.3 × 10-6 RIU when the optimum parameters are set as the radius of curvature of the airhole r = 2 μm, the thickness of the core struts c = 200 nm, the auxiliary dielectric layer s = 1 μm, and the gold film d = 40 nm. In addition, the effective area and nonlinear coefficient are calculated.

  15. 2D photonic crystals on the Archimedean lattices (tribute to Johannes Kepler (1571 1630))

    Science.gov (United States)

    Gajić, R.; class="cross-out">D. Jovanović,

    2008-03-01

    Results of our research on 2D Archemedean lattice photonic crystals are presented. This involves the calculations of the band structures, band-gap maps, equifrequency contours and FDTD simulations of electromagnetic propagation through the structures as well as an experimental verification of negative refraction at microwaves. The band-gap dependence on dielectric contrast is established both for dielectric rods in air and air-holes in dielectric materials. A special emphasis is placed on possibilities of negative refraction and left-handedness in these structures. Together with the familiar Archimedean lattices like square, triangular, honeycomb and Kagome' ones, we consider also, the less known, (3 2, 4, 3, 4) (ladybug) and (3, 4, 6, 4) (honeycomb-ring) structures.

  16. An improvement of the lattice theory of dislocation for a two-dimensional triangular crystal

    Institute of Scientific and Technical Information of China (English)

    Wang Shao-Feng

    2005-01-01

    The structure of dislocation in a two-dimensional triangular crystal has been studied theoretically on the basis of atomic interaction and lattice statics. The theory presented in this paper is an improvement to that published previously.Within a reasonable interaction approximation, a new dislocation equation is obtained, which remedies a fault existing in the lattice theory of dislocation. A better simplification of non-diagonal terms of the kernel is given. The solution of the new dislocation equation asymptotically becomes the same as that obtained in the elastic theory, and agrees with experimental data. It is found that the solution is formally identical with that proposed phenomenologically by Foreman et al, where the parameter can be chosen freely, but cannot uniquely determined from theory. Indeed, if the parameter in the expression of the solution is selected suitably, the expression can be well applied to describe the fine structure of the dislocation.

  17. Dynamics of a Bose-Einstein condensate in a horizontally vibrating shallow optical lattice

    Science.gov (United States)

    Valizadeh, A.; Jahanbani, Kh.; Kolahchi, M. R.

    2010-02-01

    We consider a solitonic solution of the self-attractive Bose-Einstein condensate in a one-dimensional external potential of a shallow optical lattice with large periodicity when the lattice is horizontally shaken. We investigate the dynamics of the bright soliton through the properties of the fixed points. The special type of bifurcation results in a simple criterion for the stability of the fixed points depending only on the amplitude of the shaking lattice. Because of the similarity of the equations with those of an ac-driven Josephson junction, some results may find applications in other branches of physics.

  18. New Crystal-Growth Methods for Producing Lattice-Matched Substrates for High-Temperature Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Boatner, L.A.

    2008-06-24

    This effort addressed the technical problem of identifying and growing, on a commercial scale, suitable single-crystal substrates for the subsequent deposition of epitaxial thin films of high temperature semiconductors such as GaN/AlN. The lack of suitable lattice-matched substrate materials was one of the major problem areas in the development of semiconducting devices for use at elevated temperatures as well as practical opto-electronic devices based on Al- and GaN technology. Such lattice-matched substrates are necessary in order to reduce or eliminate high concentrations of defects and dislocations in GaN/AlN and related epitaxial thin films. This effort concentrated, in particular, on the growth of single crystals of ZnO for substrate applications and it built on previous ORNL experience in the chemical vapor transport growth of large single crystals of zinc oxide. This combined expertise in the substrate growth area was further complemented by the ability of G. Eres and his collaborators to deposit thin films of GaN on the subject substrates and the overall ORNL capability for characterizing the quality of such films. The research effort consisted of research on the growth of two candidate substrate materials in conjunction with concurrent research on the growth and characterization of GaN films, i.e. the effort combined bulk crystal growth capabilities in the area of substrate production at both ORNL and the industrial partner, Commercial Crystal Growth Laboratories (CCL), Naples, Florida, with the novel thin-film deposition techniques previously developed in the ORNL SSD.

  19. QSPR modeling mineral crystal lattice energy by optimal descriptors of the graph of atomic orbitals

    Science.gov (United States)

    Toropova, A. P.; Toropov, A. A.; Maksudov, S. Kh.

    2006-09-01

    Models of the crystal lattice of minerals of general formula of A mC n: m, n = 1,2: A = Li, K, Na, Mg, Ca, Mn, Cu, Zn, Sr, Cd, Ba, Hg, Pb, Cs, and Rb ; C = Be, O, F, S, Cl, Br, and I; as a mathematical function of their structure have been constructed. Two elucidations of molecular structure have been used: molecular graph (vertexes are atoms, i.e., Li, Na, K, etc.) and graph of atomic orbitals, GAO (vertexes are atomic orbitals, i.e., 1s 2, 2p 5, 3d 10, etc). Statistical characteristics of the GAO-based models are better.

  20. Electron microscopic investigation of crystal lattice bending-torsion and internal stresses in deformed polycrystalline alloys

    Energy Technology Data Exchange (ETDEWEB)

    Koneva, N. A., E-mail: koneva@tsuab.ru; Kozlov, E. V. [Tomsk State University of Architecture and Building, 634003, Tomsk, Solyanaya Sq., 2 (Russian Federation)

    2016-01-15

    Generalization of the results of electron microscopy investigations of the crystal lattice bending-torsion (χ) and the internal stresses (IS) was conducted. The deformed polycrystalline alloys and steels were investigated. The sources of χ and IS origin were established. The regularities of their change with the distance from the sources and the evolution with deformation were revealed. The contribution of IS into the deformation resistance was determined. The nature of formation of two sequences of dislocation substructure transformations during deformation of alloys was established.

  1. Anisotropic crystal of the δ-BiB3O6 investigated by vibrational spectroscopy

    Science.gov (United States)

    Strikina, E. A.; Krylov, A. S.; Oreshonkov, A. S.; Vtyurin, A. N.; Maximova, A.

    2016-11-01

    The vibrational spectroscopy has been applied to investigate the structure the BiB3O6 (BIBO) crystal. Based on the experimental results, the total set of phonons mode of the polarized Raman spectra was proposed. To verify the obtained experimental data have been performed theoretical calculation in software package LADY.

  2. Discrete Element Method Numerical Modelling on Crystallization of Smooth Hard Spheres under Mechanical Vibration

    Institute of Scientific and Technical Information of China (English)

    AN Xi-Zhong

    2007-01-01

    The crystallization, corresponding to the fcc structure (with packing density p ≈ 0.74), of smooth equal hard spheres under batch-wised feeding and three-dimensional interval vibration is numerically obtained by using the discrete element method. The numerical experiment shows that the ordered packing can be realized by proper control of the dynamic parameters such as batch of each feeding § and vibration amplitude A. The radial distribution function and force network are used to characterize the ordered structure. The defect formed during vibrated packing is characterized as well The results in our work fill the gap of getting packing density between random close packing and fcc packing in phase diagram which provides an effective way of theoretically investigating the complex process and mechanism of hard sphere crystallization and its dynamics.

  3. Efficiency of various lattices from hard ball to soft ball: theoretical study of thermodynamic properties of dendrimer liquid crystal from atomistic simulation.

    Science.gov (United States)

    Li, Youyong; Lin, Shiang-Tai; Goddard, William A

    2004-02-18

    Self-assembled supramolecular organic liquid crystal structures at nanoscale have potential applications in molecular electronics, photonics, and porous nanomaterials. Most of these structures are formed by aggregation of soft spherical supramolecules, which have soft coronas and overlap each other in the packing process. Our main focus here is to study the possible packing mechanisms via molecular dynamics simulations at the atomistic level. We consider the relative stability of various lattices packed by the soft dendrimer balls, first synthesized and characterized by Percec et al. (J. Am. Chem. Soc. 1997, 119, 1539) with different packing methods. The dendrons, which form the soft dendrimer balls, have the character of a hard aromatic region from the point of the cone to the edge with C(12) alkane "hair". After the dendrons pack into a sphere, the core of the sphere has the hard aromatic groups, while the surface is covered with the C(12) alkane "hair". In our studies, we propose three ways to organize the hair on the balls, Smooth/Valentino balls, Sticky/Einstein balls, and Asymmetric/Punk balls, which lead to three different packing mechanisms, Slippery, Sticky, and Anisotropic, respectively. We carry out a series of molecular dynamics (MD) studies on three plausible crystal structures (A15, FCC, and BCC) as a function of density and analyze the MD based on the vibrational density of state (DoS) method to extract the enthalpy, entropy, and free energies of these systems. We find that anisotropic packed A15 is favored over FCC, BCC lattices. Our predicted X-ray intensities of the best structures are in excellent agreement with experiment. "Anisotropic ball packing" proposed here plays an intermediate role between the enthalpy-favored "disk packing" and entropy-favored "isotropic ball packing", which explains the phase transitions at different temperatures. Free energies of various lattices at different densities are essentially the same, indicating that the

  4. Numerical investigation of flows in Czochralski crystal growth by an axisymmetric lattice Boltzmann method

    CERN Document Server

    Peng, Y; Chew, Y T; Qiu, J

    2003-01-01

    An alternative new method called lattice Boltzmann method (LBM) is applied in this work to simulate the flows in Czochralski crystal growth, which is one of the widely used prototypical systems for melt-crystal growth. The standard LBM can only be used in Cartesian coordinate system and we extend it to be applicable to this axisymmetric thermal flow problem, avoiding the use of three-dimensional LBM on Cartesian coordinate system. The extension is based on the following idea. By inserting position and time dependent source terms into the evolution equation of standard LBM, the continuity and NS equations on the cylindrical coordinate system can be recovered. Our extension is validated by its application to the benchmark problem suggested by Wheeler .

  5. Crystal field-phonon coupling in the Kondo lattice CeCu2

    Science.gov (United States)

    Witte, U.; Kramp, S.; Braden, M.; Svoboda, P.; Loewenhaupt, M.

    CeCu2 is a Kondo lattice and shows antiferromagnetic order below 3.5K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons.

  6. Crystal field-phonon coupling in the Kondo lattice CeCu{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Witte, U. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany); HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Kramp, S. [HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Braden, M. [LLB Saclay, 91191 Gif-Sur-Yvette Cedex (France); Svoboda, P. [Charles University, 12116 Praha (Czech Republic); Loewenhaupt, M. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany)

    2002-07-01

    CeCu{sub 2} is a Kondo lattice and shows antiferromagnetic order below 3.5 K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150 K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons. (orig.)

  7. Measurement of the \\{220\\} lattice-plane spacing of a $^{28}$Si crystal

    CERN Document Server

    Massa, Enrico; Kuetgens, Ulrich; Ferroglio, Luca

    2010-01-01

    The spacing of the \\{220\\} lattice planes of a $^{28}$Si crystal was measured by combined x-ray and optical interferometry to a $3.5\\times 10^{-9}$ relative accuracy. The result is $d_{220}=(192014712.67 \\pm 0.67)$ am, at 20.0 $^\\circ$C and 0 Pa. This value is greater by $(1.9464 \\pm 0.0067)\\times 10^{-9} d_{220}$ than the spacing in natural Si, a difference which confirms quantum mechanics calculations. Subsequently, this crystal has been used to determine the Avogadro constant by counting the Si atoms, a key step towards a realization of the mass unit based on a conventional value of the Planck or the Avogadro constants.

  8. Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds

    Science.gov (United States)

    Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

    2006-12-01

    The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number

  9. Li2MoO4 crystal growth from solution activated by low-frequency vibrations

    Science.gov (United States)

    Barinova, Olga; Sadovskiy, Andrey; Ermochenkov, Ivan; Kirsanova, Svetlana; Sukhanova, Ekaterina; Kostikov, Vladimir; Belov, Stanislav; Mozhevitina, Elena; Khomyakov, Andrew; Kuchuk, Zhanna; Zharikov, Eugeny; Avetissov, Igor

    2017-01-01

    The possibility of Li2MoO4 crystal growth from aqueous solutions activated by axial vibrational control (AVC) technique was investigated. It was found out that a low-frequency mechanical activation of the solution led to an increase of Li2MoO4 equilibrium solubility in aqueous solution for 11 rel% in the 25-29 °C temperature range. The changes in solution structure were analyzed in situ by Raman study of the solution. The AVC activation of solution resulted in a re-faceting of growing crystals, a smoothing of a face surface morphology and reduction of water content in the crystal.

  10. Modelling of acoustic waves propagating in nesting Fibonacci super-lattice phononic crystal

    Science.gov (United States)

    Zhao, Min; Qi, Hai-Feng; Xu, Jia-Hui; Xie, Ya-Zhuo; Zhang, Xing-Gan; Gao, Jian

    2014-07-01

    Herein, we report construction of one kind of nesting-Fibonacci-super-lattice phononic crystal, in which the super-lattice cell is a well-defined Fibonacci generation sequence. We present a comparative study on band-gap structures of acoustic waves propagating in one-dimensional, nesting Fibonacci-periodic structure and simple-periodic structure. We find that there are more band gaps in nesting Fibonacci super-lattice models, and that they present behavior different from the split-up of band gaps with different generation numbers. With the increase of generation number, more band gaps split and occur. Additionally, when generation number becomes larger, Bragg scattering becomes more significant: the characteristic curves become flatter and band gaps become wider. Furthermore, we study the effect of various parameters such as density, thickness and defects on band-gap structures. Our work is significant both for understanding the intrinsic physical properties of nesting Fibonacci sequences and for providing flexible choices to meet real engineering requirements.

  11. Coherent lattice dynamics in opaque crystals: Testing the adequacy of two-tensor model

    Science.gov (United States)

    Misochko, O. V.; Lebedev, M. V.

    2016-11-01

    We report the ultrafast pump-probe study of B i2T e3 , Sb, Bi, and Te aimed to check the two-tensor model predictions for the creation of lattice coherence. The dependence of coherent ultrafast response on phonon frequency was measured for topological insulator B i2T e3 , the spectrum of which possesses two fully symmetric phonons. The effect of the pump pulse duration and power on the magnitude of coherent amplitude was evaluated in the model opaque crystals, such as two semimetals, bismuth and antimony, and semiconducting tellurium. In our analysis of the pump-probe data, we separated the transient total reflectivity into the sum of two contributions: one due to the photogenerated carriers and the second due to the coherent phonons. All fully symmetric phonons exhibit a cosinelike dependence and grow linearly with increasing average pump power provided the pulse duration remains unchanged. Varying the pump pulse duration, we observed a monotonic decrease of coherent amplitude for longer pulses, whereas the electronic contribution was almost unchanged. This lack of the correlation between the carriers and the coherent amplitude was further supported by coherent control experiments on Te. Based on the comparison of theoretical predictions with experimental observations, we conjecture that the lattice coherence creation in opaque crystals can be linked to a Raman-like process.

  12. Nucleation in a Potts lattice gas model of crystallization from solution

    Science.gov (United States)

    Duff, Nathan; Peters, Baron

    2009-11-01

    Nucleation from solution is important in many pharmaceutical crystallization, biomineralization, material synthesis, and self-assembly processes. Simulation methodology has progressed rapidly for studies of nucleation in pure component and implicit solvent systems; however little progress has been made in the simulation of explicit solvent systems. The impasse stems from the inability of rare events simulation methodology to be combined with simulation techniques which maintain a constant chemical potential driving force (supersaturation) for nucleation. We present a Potts lattice gas (PLG) to aid in the development of new simulation strategies for nucleation from solution. The PLG captures common crystallization phase diagram features such as a eutectic point and solute/solvent melting points. Simulations of the PLG below the bulk solute melting temperature reveal a competition between amorphous and crystalline nuclei. As the temperature is increased toward the bulk melting temperature, the nucleation pathway changes from a one step crystalline nucleation pathway to a two step pathway, where an amorphous nucleus forms and then crystallizes. We explain these results in terms of classical nucleation theory with different size-dependant chemical potentials for the amorphous and crystalline nucleation pathways. The two step pathway may be particularly important when crystallization is favored only at postcritical sizes.

  13. Nucleation in a Potts lattice gas model of crystallization from solution.

    Science.gov (United States)

    Duff, Nathan; Peters, Baron

    2009-11-14

    Nucleation from solution is important in many pharmaceutical crystallization, biomineralization, material synthesis, and self-assembly processes. Simulation methodology has progressed rapidly for studies of nucleation in pure component and implicit solvent systems; however little progress has been made in the simulation of explicit solvent systems. The impasse stems from the inability of rare events simulation methodology to be combined with simulation techniques which maintain a constant chemical potential driving force (supersaturation) for nucleation. We present a Potts lattice gas (PLG) to aid in the development of new simulation strategies for nucleation from solution. The PLG captures common crystallization phase diagram features such as a eutectic point and solute/solvent melting points. Simulations of the PLG below the bulk solute melting temperature reveal a competition between amorphous and crystalline nuclei. As the temperature is increased toward the bulk melting temperature, the nucleation pathway changes from a one step crystalline nucleation pathway to a two step pathway, where an amorphous nucleus forms and then crystallizes. We explain these results in terms of classical nucleation theory with different size-dependant chemical potentials for the amorphous and crystalline nucleation pathways. The two step pathway may be particularly important when crystallization is favored only at postcritical sizes.

  14. Lattice dynamics of K{sub x}RhO{sub 2} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Bin-Bin; Dong, Song-Tao; Lv, Yangyang; Yao, Shuhua, E-mail: shyao@nju.edu.cn; Zhang, Shan-Tao; Gu, Zheng-Bin; Zhou, Jian, E-mail: zhoujian@nju.edu.cn; Chen, Yan-Feng [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Zhang, NaNa [College of Chemistry & Chemical and Environmental Engineering, Weifang University, Weifang, 261061 (China); Chen, Y. B. [National Laboratory of Solid State Microstructure and Department of Physics, Nanjing University, Nanjing 210093 (China); Guedes, Ilde [Departamento de Física, Universidade Federal do Ceará, Campus do Pici, CP 6030, Fortaleza CE 60455-760 (Brazil); Yu, Dehong [Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234 (Australia)

    2015-08-15

    A series of crystals K{sub x}RhO{sub 2} (x = 0.72, 0.63, 0.55, 0.39, and 0.24) have been synthesized and their vibrational properties have been studied by first principles calculations, Raman spectroscopy, and inelastic neutron scattering. The measured vibrational spectra of K{sub x}RhO{sub 2} for x = 0.72 and 0.63 are consistent with the theoretical prediction for the stoichiometric KRhO{sub 2}. For samples with x = 0.55, 0.39 and 0.24, extra vibrational modes have been observed and they are believed to be due to the symmetry reduction and the loss of translational symmetry induced by K disorder. The good agreement was found for the phonon density of states among the Raman spectroscopic observations, inelastic neutron scattering and the first principles calculations, as an evidence for the generation of structure disorder by K deficiency.

  15. A far-infrared study of the lattice vibrations of nickelous iodide and cobaltous iodide.

    NARCIS (Netherlands)

    Kuindersma, S. R.

    1981-01-01

    The anisotropy in the lattice dynamics of NiI2 and CoI2 was studied by polarized far-IR-reflection spectroscopy at 4.2-300 K. The static and high-frequency dielec. consts., the frequencies of the transverse and longitudinal optical modes, and the damping consts. were detd. The anisotropy arises from

  16. A Simple Method for the Calculation of Lattice Energies of Inorganic Ionic Crystals Based on the Chemical Hardness.

    Science.gov (United States)

    Kaya, Savaş; Kaya, Cemal

    2015-09-08

    This paper presents a new technique for estimation of lattice energies of inorganic ionic compounds using a simple formula. This new method demonstrates the relationship between chemical hardness and lattice energies of ionic compounds. Here chemical hardness values of ionic compounds are calculated via our molecular hardness equation. The results obtained using the present method and comparisons made by considering experimental data and the results from other theoretical methods in the literature showed that the new method allows easy evaluation of lattice energies of inorganic ionic crystals without the need for ab initio calculations and complex calculations.

  17. Absolute band gaps of a two-dimensional triangular-lattice dielectric photonic crystal with different shapes

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Absolute band gaps of a two-dimensional triangular-lattice photonic crystal are calculated with the finite-difference time-domain method in this paper.Through calculating the photonic band structures of the triangular-lattice photonic crystal consisting of Ge rods immersed in air with different shapes,it is found that a large absolute band gap of 0.098 (2c/a) can be obtained for the structures with hollow triangular Ge rods immersed in air,corresponding to 19.8% of the middle frequency.The influence of the different factors on the width of the absolute band gaps is also discussed.

  18. Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

    Science.gov (United States)

    Sedao, Xxx; Maurice, Claire; Garrelie, Florence; Colombier, Jean-Philippe; Reynaud, Stéphanie; Quey, Romain; Pigeon, Florent

    2014-04-01

    The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

  19. Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

    Energy Technology Data Exchange (ETDEWEB)

    Sedao, Xxx; Garrelie, Florence, E-mail: florence.garrelie@univ-st-etienne.fr; Colombier, Jean-Philippe; Reynaud, Stéphanie; Pigeon, Florent [Université de Lyon, CNRS, UMR5516, Laboratoire Hubert Curien, Université de Saint Etienne, Jean Monnet, F-42023 Saint-Etienne (France); Maurice, Claire; Quey, Romain [Ecole Nationale Supérieure des Mines de Saint-Etienne, CNRS, UMR5307, Laboratoire Georges Friedel, F-42023 Saint-Etienne (France)

    2014-04-28

    The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

  20. Structural, electronic and vibrational properties of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) crystal

    Science.gov (United States)

    Colle, Renato; Grosso, Giuseppe; Cassinese, Antonio; Centore, Roberto

    2013-09-01

    We present a theoretical and experimental investigation of the crystalline structure of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) that has been deduced combining experimental XRD data, obtained from powders, with global-optimization algorithms which allow to identify Bravais lattice, primitive cell parameters, and space group of the crystal. The XRD spectrum calculated for the proposed crystalline structure very well reproduces the measured XRD data. Our results suggest the triclinic lattice structure of spatial groups Poverline{1} and P1, respectively, for the crystalline PDI-FCN2-1,7 and PDI-FCN2-1,6 isomers. In both cases, the primitive cell contains a single molecule. On the proposed crystalline structures, KS-DFT cell energy calculations, including van der Waals interactions, have been performed to assign the minimum energy geometrical structure and orientation of the molecule inside the corresponding primitive cell. These calculations evidence the molecular packing that characterizes the strong anisotropy of the PDI-FCN2 crystal. Electronic band-structures calculated for both isomers within the Kohn-Sham density-functional theory indicate that the crystalline Poverline{1} structure is an indirect gap semiconductor, while the P1 structure is a direct gap semiconductor. The electronic band structure calculations on the optimized crystal geometries highlight strong anisotropy in the dispersion curves E(k), which roots at the molecular packing in the crystal. Finally, the vibrational spectrum of both crystalline isomers has been calculated in the harmonic approximation and the dominant vibrational frequencies have been associated to collective motions of selected atoms in the molecules.

  1. Structural, electronic and vibrational properties of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) crystal.

    Science.gov (United States)

    Colle, Renato; Grosso, Giuseppe; Cassinese, Antonio; Centore, Roberto

    2013-09-21

    We present a theoretical and experimental investigation of the crystalline structure of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) that has been deduced combining experimental XRD data, obtained from powders, with global-optimization algorithms which allow to identify Bravais lattice, primitive cell parameters, and space group of the crystal. The XRD spectrum calculated for the proposed crystalline structure very well reproduces the measured XRD data. Our results suggest the triclinic lattice structure of spatial groups P1 and P1, respectively, for the crystalline PDI-FCN2-1,7 and PDI-FCN2-1,6 isomers. In both cases, the primitive cell contains a single molecule. On the proposed crystalline structures, KS-DFT cell energy calculations, including van der Waals interactions, have been performed to assign the minimum energy geometrical structure and orientation of the molecule inside the corresponding primitive cell. These calculations evidence the molecular packing that characterizes the strong anisotropy of the PDI-FCN2 crystal. Electronic band-structures calculated for both isomers within the Kohn-Sham density-functional theory indicate that the crystalline P1 structure is an indirect gap semiconductor, while the P1 structure is a direct gap semiconductor. The electronic band structure calculations on the optimized crystal geometries highlight strong anisotropy in the dispersion curves E(k), which roots at the molecular packing in the crystal. Finally, the vibrational spectrum of both crystalline isomers has been calculated in the harmonic approximation and the dominant vibrational frequencies have been associated to collective motions of selected atoms in the molecules.

  2. Slow light engineering in polyatomic photonic crystal waveguides based on square lattice

    Science.gov (United States)

    Wang, Daobin; Zhang, Jie; Yuan, Lihua; Lei, Jingli; Chen, Sai; Han, Jiawei; Hou, Shanglin

    2011-12-01

    In this paper, the slow light properties of the polyatomic Photonic Crystal (PhC) which has multiple different air holes in each primitive cell are investigated. A slow light waveguide with "U-type" group index-frequency curve, which results in nearly constant group index over large bandwidth, is achieved using this new photonic crystal geometry based on the square lattice. Also, the radius and position of the innermost rows of small air holes have been modified to investigate the feasibility of controlling the dispersion relation by subtle structural modification. Numerical results demonstrate that decreasing the group velocity effectively and meanwhile maintaining a large Normalized Delay-Bandwidth Product ( NDBP) can be achieved by only modifying the radius of the innermost rows of small air holes. Shifting the innermost rows of small air holes toward the waveguide core is highly beneficial to enlarge the slow light bandwidth, but it contributes nothing to the promotion of NDBP. Our results provide important theoretical basis for the potential application offered by the polyatomic photonic crystal in future optical networks.

  3. TAILORING OF FLATTENED DISPERSION IN TRIANGULAR-LATTICE PHOTONIC CRYSTAL FIBER

    Directory of Open Access Journals (Sweden)

    Sandhir Kumar Singh

    2011-12-01

    Full Text Available The interest of researchers and engineers in several laboratories, since the1980s, has been attracted by the ability to structure materials on the scale of the optical wavelength, a fraction of micrometers or less, in order to develop new optical medium, known as photonic crystals . Photonic crystals rely on a regular morphological microstructure of air-holes, incorporated into the material, which radically alters its optical properties. In Photonic Crystal Fiber (PCF it is possible to realize flat dispersion over a wide wavelength range that cannot be realized with a conventional single-mode fiber. In PCFs, the dispersion can be controlled and tailored with unprecedented freedom. In fact, due to the high refractive index difference between silica and air, and to the flexibility of changing air-hole sizes and patterns, the waveguide contribution to the dispersion parameter can be significantly changed, thus obtaining unusual position of the zero dispersion wavelength, as well as particular values of the dispersion curve slope. In particular, by manipulating the air- hole radius or the lattice period of the micro structured cladding, it is possible to control the zero-dispersion wavelength, which can be tuned over a very wide range, or the dispersion curves, which can be engineered to be ultra flattened. In this paper the geometric parameters of triangular PCF have been properly changed to optimize the dispersion compensation over a wide wavelength range.

  4. 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.

  5. Lattice site specific diffusion properties for substitutional and interstitial impurity atoms in ZnO crystals

    Science.gov (United States)

    Yaqoob, Faisal; Huang, Mengbing

    2016-09-01

    Fundamental understanding of impurity diffusion in crystals remains a challenge due to lack of experimental capabilities for measuring the diffusion properties of atoms according to their substitutional and interstitial lattice locations. With examples of indium and silver in ZnO crystals, we demonstrate an ion beam based method to experimentally determine the energetics and entropy changes in diffusion of substitutional and interstitial impurity atoms. While the interstitial Ag diffuses much faster than the substitutional Ag, as normally expected, the interstitial In migrates slower than the substitutional In, which is attributed to a large negative entropy change (˜-10 kB), possibly caused by the large atomic size of In. The activation energy and the diffusivity pre-exponential factor for the interstitial Ag are significantly enhanced, being more than a factor of two and ˜13 orders of magnitude, respectively, relative to the case for the interstitial In. This implies two different diffusion mechanisms between these two types of interstitial atoms in ZnO crystals: the direct interstitial diffusion mechanism for the interstitial In and the kick-out diffusion mechanism for the interstitial Ag. In addition, the activation energies and the diffusivity prefactors follow the Meyer-Neldel relationship with an excitation energy of ˜92 meV.

  6. Superconductivity in LiOHFeS single crystals with a shrunk c-axis lattice constant

    Science.gov (United States)

    Lin, Hai; Kang, RuiZhe; Kong, Lu; Zhu, XiYu; Wen, Hai-Hu

    2017-02-01

    By using a hydrothermal ion-exchange method, we have successfully grown superconducting crystals of LiOHFeS with T c of about 2.8 K. Being different from the sister sample (Li1- x Fe x )OHFeSe, the energy dispersion spectrum analysis on LiOHFeS shows that the Fe/S ratio is very close to 1:1, suggesting an almost charge neutrality and less electron doping in the FeS planes of the system. Comparing with the non superconducting LiOHFeS crystal, each peak of the X-ray diffraction pattern of the superconducting crystal splits into two, and the diffraction peaks locating at lower reflection angles are consistent with that of non-superconducting ones. The rest set of diffraction peaks with higher reflection angles is corresponding to the superconducting phase, suggesting that the superconducting phase may has a shrunk c-axis lattice constant. Magnetization measurements indicate that the magnetic shielding due to superconductivity can be quite high under a weak magnetic field. The resistivity measurements under various magnetic fields show that the upper critical field is quite low, which is similar to the tetragonal FeS superconductor.

  7. Lattice vibrations boost demagnetization entropy in a shape-memory alloy

    Science.gov (United States)

    Stonaha, P. J.; Manley, M. E.; Bruno, N. M.; Karaman, I.; Arroyave, R.; Singh, N.; Abernathy, D. L.; Chi, S.

    2015-10-01

    Magnetocaloric (MC) materials present an avenue for chemical-free, solid-state refrigeration through cooling via adiabatic demagnetization. We have used inelastic neutron scattering to measure the lattice dynamics in the MC material N i45C o5M n36.6I n13.4 . Upon heating across the Curie temperature (TC) , the material exhibits an anomalous increase in phonon entropy of 0.22 ±0.04 kB/atom , which is ten times larger than expected from conventional thermal expansion. This transition is accompanied by an abrupt softening of the transverse optic phonon. We present first-principles calculations showing a strong coupling between lattice distortions and magnetic excitations.

  8. Site preferences and lattice vibrations of Nd6Fe13- T Si (=Co, Ni)

    Institute of Scientific and Technical Information of China (English)

    黄天顺; 成海霞; 王晓旭; 张振峰; 安志伟; 张国华

    2015-01-01

    The site preferences of the rare earth intermetallics Nd6Fe13−xTxSi (T =Co, Ni) are investigated by using interatomic pair potentials which are converted from a lattice-inversion method. Calculation shows that the order of the site preference of Co is 4d, 16k, 16l1, and 16l2 and that of Ni is 16l2, 16l1, 16k, and 4d in Nd6Fe13−xTxSi. Calculated lattice and positional parameters are found to agree with those reported in the literature. Furthermore, the phonon density of states for Nd6Fe13−xTxSi is also evaluated, and a qualitative analysis featuring the coordination and the relevant potentials is carried out.

  9. Lattice Vibrations Change the Solid Solubility of an Alloy at High Temperatures

    Science.gov (United States)

    Shulumba, Nina; Hellman, Olle; Raza, Zamaan; Alling, Björn; Barrirero, Jenifer; Mücklich, Frank; Abrikosov, Igor A.; Odén, Magnus

    2016-11-01

    We develop a method to accurately and efficiently determine the vibrational free energy as a function of temperature and volume for substitutional alloys from first principles. Taking Ti1 -xAlxN alloy as a model system, we calculate the isostructural phase diagram by finding the global minimum of the free energy corresponding to the true equilibrium state of the system. We demonstrate that the vibrational contribution including anharmonicity and temperature dependence of the mixing enthalpy have a decisive impact on the calculated phase diagram of a Ti1 -xAlxN alloy, lowering the maximum temperature for the miscibility gap from 6560 to 2860 K. Our local chemical composition measurements on thermally aged Ti0.5Al0.5N alloys agree with the calculated phase diagram.

  10. Calculations of lattice vibrational mode lifetimes using Jazz: a Python wrapper for LAMMPS

    Science.gov (United States)

    Gao, Y.; Wang, H.; Daw, M. S.

    2015-06-01

    Jazz is a new python wrapper for LAMMPS [1], implemented to calculate the lifetimes of vibrational normal modes based on forces as calculated for any interatomic potential available in that package. The anharmonic character of the normal modes is analyzed via the Monte Carlo-based moments approximation as is described in Gao and Daw [2]. It is distributed as open-source software and can be downloaded from the website http://jazz.sourceforge.net/.

  11. Synthesis, Crystal Structure, Vibration Spectral, and DFT Studies of 4-Aminoantipyrine and Its Derivatives

    Directory of Open Access Journals (Sweden)

    Ping Wei

    2013-01-01

    Full Text Available Three compounds derived from 4-aminoantipyrine (AA were synthesized and their structures confirmed by melting point, elemental analysis, FT-IR, and 1H-NMR. The molecular structures of the four compounds were characterized by single-crystal X-ray diffraction and calculated by using the density functional theory (DFT method with 6-31G (d basis set. The calculated molecular geometries and the vibration frequencies of the AA derivatives in the ground state have been compared with the experimental data. The results show that the optimized geometries can reproduce well the crystal structural parameters, and the theoretical vibration frequencies show good agreement with the experimental data, although the experimental data are different from the theoretical ones due to the intermolecular forces. Besides, the molecular electrostatic potential (MEP and the frontier molecular orbital (FMO analysis of the compounds were investigated by theoretical calculations.

  12. The influence of vibrations on time reference signals generated using quartz crystals

    Science.gov (United States)

    Drumea, Andrei; Marcu, Alina; Plotog, Ioan

    2016-12-01

    32.768 kHz low frequency crystals are found in a large part of today's embedded systems that use microcontrollers especially in battery supplied applications which need low power consumption1]. Their main role is to offer a stable time reference. There are situations in which time measurement is needed when the system works in a mechanically unstable environment (cars, industrial equipment). The paper presents the studies done on the behavior of 32.768 kHz quartz crystals that are part of embedded systems which operate in a vibrating environment, in terms of period and long-time jitter of the generated time reference signal. The investigations of this effect were done using a test bench especially designed for this purpose which can measure the presented parameters determined by controlled mechanical stimulus (waveform, amplitude and frequency of the vibrations).

  13. Lattice effects in the light actinides

    Energy Technology Data Exchange (ETDEWEB)

    Lawson, A.C.; Cort, B.; Roberts, J.A.; Bennett, B.I.; Brun, T.O.; Dreele, R.B. von [Los Alamos National Lab., NM (United States); Richardson, J.W. Jr. [Argonne National Lab., IL (United States)

    1998-12-31

    The light actinides show a variety of lattice effects that do not normally appear in other regions of the periodic table. The article will cover the crystal structures of the light actinides, their atomic volumes, their thermal expansion behavior, and their elastic behavior as reflected in recent thermal vibration measurements made by neutron diffraction. A discussion of the melting points will be given in terms of the thermal vibration measurements. Pressure effects will be only briefly indicated.

  14. Laser-assisted synthesis of diamond crystals in open air through vibrational excitation of precursor molecules

    Science.gov (United States)

    Xie, Z. Q.; Zhou, Y. S.; He, X. N.; Gao, Y.; Park, J. B.; Guillemet, T.; Lu, Y. F.

    2011-03-01

    Fast growth of diamond crystals in open air was achieved by laser-assisted combustion synthesis through vibrational excitation of precursor molecules. A wavelength-tunable CO2 laser (spectrum range from 9.2 to 10.9 μm) was used for the vibrational excitation in synthesis of diamond crystals. A pre-mixed C2H4/C2H2/O2 gas mixture was used as precursors. Through resonant excitation of the CH2-wagging mode of ethylene (C2H4) molecules using the CO2 laser tuned at 10.532 Μm, high-quality diamond crystals were grown on silicon substrates with a high growth rate of ~139 μm/hr. Diamond crystals with a length up to 5 mm and a diameter of 1 mm were grown in 36 hours. Sharp Raman peaks at 1332 cm-1 with full width at half maximum (FWHM) values around 4.5 cm-1 and distinct X-ray diffraction spectra demonstrated the high quality of the diamond crystals. The effects of the resonant excitation of precursor molecules by the CO2 laser were investigated using optical emission spectroscopy.

  15. Spin-3/2 Ising model AFM/AFM two-layer lattice with crystal field

    Institute of Scientific and Technical Information of China (English)

    Erhan Albayrak; Ali Yigit

    2009-01-01

    The spin-3/2 Ising model is investigated for the case of antiferromagnetic (AFM/AFM) interactions on the two-layer Bethe lattice by using the exact recursion relations in the pairwise approach for given coordination numbers q = 3, 4 and 6 when the layers are under the influences of equal external magnetic and equal crystal fields. The ground state, (GS) phase diagrams are obtained on the different planes in detail and then the temperature-dependent phase diagrams of the system are calculated accordingly. It is observed that the system presents both second- and first-order phase transitions for all q, therefore, tricritical points. It is also found that the system exhibits double-critical end points and isolated points. The model aiso presents two Néel temperatures, T_N, and the existence of which leads to the reentrant behaviour.

  16. High Sensitivity Refractive Index Sensor Based on Dual-Core Photonic Crystal Fiber with Hexagonal Lattice

    Directory of Open Access Journals (Sweden)

    Haiyang Wang

    2016-10-01

    Full Text Available A refractive index sensor based on dual-core photonic crystal fiber (PCF with hexagonal lattice is proposed. The effects of geometrical parameters of the PCF on performances of the sensor are investigated by using the finite element method (FEM. Two fiber cores are separated by two air holes filled with the analyte whose refractive index is in the range of 1.33–1.41. Numerical simulation results show that the highest sensitivity can be up to 22,983 nm/RIU(refractive index unit when the analyte refractive index is 1.41. The lowest sensitivity can reach to 21,679 nm/RIU when the analyte refractive index is 1.33. The sensor we proposed has significant advantages in the field of biomolecule detection as it provides a wide-range of detection with high sensitivity.

  17. High Sensitivity Refractive Index Sensor Based on Dual-Core Photonic Crystal Fiber with Hexagonal Lattice.

    Science.gov (United States)

    Wang, Haiyang; Yan, Xin; Li, Shuguang; An, Guowen; Zhang, Xuenan

    2016-10-08

    A refractive index sensor based on dual-core photonic crystal fiber (PCF) with hexagonal lattice is proposed. The effects of geometrical parameters of the PCF on performances of the sensor are investigated by using the finite element method (FEM). Two fiber cores are separated by two air holes filled with the analyte whose refractive index is in the range of 1.33-1.41. Numerical simulation results show that the highest sensitivity can be up to 22,983 nm/RIU(refractive index unit) when the analyte refractive index is 1.41. The lowest sensitivity can reach to 21,679 nm/RIU when the analyte refractive index is 1.33. The sensor we proposed has significant advantages in the field of biomolecule detection as it provides a wide-range of detection with high sensitivity.

  18. Lattice location of platinum ions implanted into single crystal zirconia and their annealing behaviour

    Energy Technology Data Exchange (ETDEWEB)

    Cao, D.X. [Royal Melbourne Inst. of Tech., VIC (Australia); Sood, D.K. [Academia Sinica, Shanghai, SH (China). Shanghai Inst. of Nuclear Research; Brown, I.G. [Lawrence Berkeley Lab., CA (United States)

    1993-12-31

    Single crystal samples of (100) oriented cubic zirconia stabilised with 9.5 mol % yttria were implanted with platinum ions, using a metal vapour vacuum arc (MEVVA) high current ion implanter, to a nominal dose of 1x10{sup 17} ions/cm{sup 2}. The implanted samples were annealed isothermally in air ambient at 1200 deg C, from 1-24 hours. Rutherford Backscattering Spectrometry and Channeling (RBSC) of 2 MeV He ions are employed to determine depth distributions of ion damage, Pt ions and substitutionality of Pt ions before and after annealing. The damage behaviour, Pt migration and lattice location are discussed in terms of metastable phase formation and solid solubility considerations. 7 refs., 3 figs.

  19. Dispersion relations of externally and thermally excited dust lattice modes in 2D complex plasma crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yang Xuefeng; Cui Jian; Zhang Yuan [School of Mathematical Sciences, Dalian University of Technology, Dalian 116024 (China); Liu Yue [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

    2012-07-15

    The dispersion relations of the externally and thermally (naturally) excited dust lattice modes (both longitudinal and transverse) in two-dimensional Debye-Yukawa complex plasma crystals are investigated. The dispersion relations are calculated numerically by taking the neutral gas damping effects into account and the numerical results are in agreement with the experimental data given by Nunomura et al.[Phys. Rev. E 65, 066402 (2002)]. It is found that for the mode excited by an external disturbance with a real frequency, the dispersion properties are changed at a critical frequency near where the group velocity of the mode goes to zero. Therefore, the high frequency branch with negative dispersion cannot be reached. In contrast, for the thermally excited mode, the dispersion curve can extend all the way to the negative dispersion region, while a 'cut-off' wave number exists at the long wavelength end of the dispersion in the transverse mode.

  20. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    Science.gov (United States)

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous-crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  1. Control of fluid flow during Bridgman crystal growth using low-frequency vibrational stirring

    Science.gov (United States)

    Zawilski, Kevin Thomas

    The goal of this research program was to develop an in depth understanding of a promising new method for stirring crystal growth melts called coupled vibrational stirring (CVS). CVS is a mixing technique that can be used in sealed systems and produces rapid mixing through vortex flows. Under normal operating conditions, CVS uses low-frequency vibrations to move the growth crucible along a circular path, producing a surface wave and convection in the melt. This research focused on the application of CVS to the vertical Bridgman technique. CVS generated flows were directly studied using a physical modeling system containing water/glycerin solutions. Sodium nitrate was chosen as a model growth system because the growth process could be directly observed using a transparent furnace. Lead magnesium niobate-lead titanate (PMNT) was chosen as the third system because of its potential application for high performance solid state transducers and actuators. In this study, the critical parameters for controlling CVS flows in cylindrical Bridgman systems were established. One of the most important results obtained was the dependence of an axial velocity gradient on the vibrational frequency. By changing the frequency, the intensity of fluid flow at a given depth can be easily manipulated. The intensity of CVS flows near the crystal-melt interface was found to be important. When flow intensity near the interface increased during growth, large growth rate fluctuations and significant changes in interface shape were observed. To eliminate such fluctuations, a constant flow rate near the crystal-melt interface was maintained by decreasing the vibrational frequency. A continuous frequency ramp was found to be essential to grow crystals of good quality under strong CVS flows. CVS generated flows were also useful in controlling the shape of the growth interface. In the sodium nitrate system without stirring, high growth rates produced a very concave interface. By adjusting the flow

  2. Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4

    DEFF Research Database (Denmark)

    Zaharko, O.; Christensen, Niels Bech; Cervellino, A.

    2011-01-01

    We study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below T-N = 8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks...

  3. Influence of lattice vibrations on the field driven electronic transport in chains with correlated disorder

    Science.gov (United States)

    da Silva, L. D.; Sales, M. O.; Ranciaro Neto, A.; Lyra, M. L.; de Moura, F. A. B. F.

    2016-12-01

    We investigate electronic transport in a one-dimensional model with four different types of atoms and long-ranged correlated disorder. The latter was attained by choosing an adequate distribution of on-site energies. The wave-packet dynamics is followed by taking into account effects due to a static electric field and electron-phonon coupling. In the absence of electron-phonon coupling, the competition between correlated disorder and the static electric field promotes the occurrence of wave-packet oscillations in the regime of strong correlations. When the electron-lattice coupling is switched on, phonon scattering degrades the Bloch oscillations. For weak electron-phonon couplings, a coherent oscillatory-like dynamics of the wave-packet centroid persists for short periods of time. For strong couplings the wave-packet acquires a diffusive-like displacement and spreading. A slower sub-diffusive spreading takes place in the regime of weak correlations.

  4. A comparative simulation study on three lattice systems for the phase separation of polymer-dispersed liquid crystals

    Indian Academy of Sciences (India)

    Y J Jeon; M Jamil; Hyo-Dong Lee; J T Rhee

    2008-09-01

    This article reports a comparative study of the phase separation process in a polymer-dispersed liquid crystal, based on a Metropolis Monte Carlo simulation study of three lattice systems. We propose a model for the different processes occurring in the formation of polymer-dispersed liquid crystals (PDLCs). The mechanism of PDLC is studied as a function of quench temperature, concentration and degree of polymerization of liquid crystals and polymers. The obtained resultant phase diagrams of the three systems are approximated and compared with the Flory–Huggins theory, and show a good agreement. It has been observed in the simulation results that among all the three systems, the 40 × 40 × 40 lattice showed the most accurate, reliable and stable results.

  5. Vibrational and third-order nonlinear optical study on hydroxyethylammonium picrate (HEAP) single crystals

    Science.gov (United States)

    Sudharsana, N.; Nagalakshmi, R.; Krishnakumar, V.; Sharma, A.; Fausto, R.; Row, T. N. Guru; Pal, Rumpa

    2012-06-01

    Single crystals of hydroxyethylammonium picrate (C8 H10N4O8; HEAP) have been grown for the first time by slow evaporation solution growth technique at room temperature, using ethanol as solvent. FT-IR and Raman spectra were recorded for HEAP at room temperature. The main vibrational bands related to NH3+ and CO- (picrate) groups, involved in charge transfer, are discussed. Second-order hyperpolarizability(γ) for the single crystal was evaluated theoretically to be 3.48×10-28 e.s.u. A Z-scan study of HEAP showed that the relative third-order nonlinear refractive index is -9.2×10-5cm2/W. The measured third-order nonlinear properties confirm the suitability of the crystal for optical limiting and switching applications.

  6. Application of Reed-Vibration Mechanical Spectroscopy for Liquids in Studying Liquid Crystallization

    Science.gov (United States)

    Zhou, Heng-Wei; Wang, Li-Na; Zhang, Li-Li; Huang, Yi-Neng

    2013-08-01

    By using the reed-vibration mechanical spectroscopy for liquids (RMS-L), we measured the complex Young's modulus of dimethyl phthalate (DP) during a cooling and heating circulation starting from room temperature at about 2 KHz. The results show that there is no crystallization in the cooling supercooled liquid (CSL) of DP, but a crystallization process in the heating supercooled liquid (HSL) after the reverse glass transition. Based on the measured modulus, crystal volume fraction (v) during the HSL crystallization was calculated. Moreover, the Avrami exponent (n) was obtained according to the JJMA equation and v data. In view of n versus temperature and v, the nucleation dynamics was analyzed, and especially, there has already existed saturate nuclei in DP HSL before the crystallization. Furthermore, the authors inferred that the nuclei are induced by the random frozen stress in the glass, but there is no nucleus in CSL. The above results indicated that RMS-L might provide a new way to measure and analyze the crystallization of liquids.

  7. Growth, structural, vibrational, optical, laser and dielectric aspects of L-alanine alaninium nitrate single crystal

    Science.gov (United States)

    Caroline, M. Lydia; Prakash, M.; Geetha, D.; Vasudevan, S.

    2011-09-01

    Bulk single crystals of L-alanine alaninium nitrate [abbreviated as LAAN], an intriguing material for frequency conversion has been grown from its aqueous solution by both slow solvent evaporation and by slow cooling techniques. The optimized pH value to grow good quality LAAN single crystal was found to be 2.5. The grown crystals were subjected to single crystal X-ray diffraction studies to determine the unit cell dimensions and morphology. Vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopic technique were investigated. Also, the presence of hydrogen and carbon atoms in the grown sample was confirmed using proton and carbon NMR analyses. The dielectric constant and dielectric loss measurements of the as grown crystal at different temperatures and frequencies of the applied field are measured and reported. LAAN has good optical transmission in the entire visible region with cutoff wavelength within the UV region confirms its suitability for device fabrications. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064 nm. Its Laser Damage Threshold (LDT) was measured and also tested by using a Q-switched Nd:YAG laser and the value of LDT of LAAN is 17.76 GW/cm 2 respectively, is found to be better than certain organic and semiorganic materials.

  8. Intermolecular interaction studies in ammonium squarate: crystal structure and vibrational spectra

    Science.gov (United States)

    Georgopoulos, Stéfanos L.; Diniz, Renata; Rodrigues, Bernardo L.; Yoshida, Maria I.; de Oliveira, Luiz Fernando C.

    2005-10-01

    Ammonium squarate salt [(NH 4) 2C 4O 4] crystallizes in the monoclinic space group P2 1/c. The crystal presents the squarate ions displayed in layers parallel to a crystallographic axis and forming hydrogen bonds interactions with NH4+ cations, localized between squarate anions layers. The squarate anion presents similar CC and CO bond distances which indicate a degree of electronic delocalization in the rings. A π-stacking interaction is observed between squarate rings separated by interplanar distance and centroid ring distance of respectively 3.41 and 3.71 Å. The electron delocalization was also observed in the vibrational spectra. The infrared spectrum shows a narrow band around 1530 cm -1, assigned to a coupled stretching mode of CO and CC groups, indicating the high symmetry of the squarate ion. The Raman spectrum also shows this effect in the 1000 to 1200 cm -1 region (related to CC stretching mode), where it is expected a decrease of the number of bands if compared to squarate ion in aqueous solution, where the symmetry is actually D4 h; in the (NH 4) 2C 4O 4 Raman spectrum just one strong band is observed at 1120 cm -1. All the vibrational results indicate the symmetry is very close to the one observed for the solvated ion in aqueous solution; once again the vibrational analysis appears as an important tool in recognizing the oxocarbon ion geometry in the solid state.

  9. Single crystal XRD, vibrational and quantum chemical calculation of pharmaceutical drug paracetamol: A new synthesis form.

    Science.gov (United States)

    Anitha, R; Gunasekaran, M; Kumar, S Suresh; Athimoolam, S; Sridhar, B

    2015-01-01

    The common house hold pharmaceutical drug, paracetamol (PAR), has been synthesized from 4-chloroaniline as a first ever report. After the synthesis, good quality single crystals were obtained for slow evaporation technique under the room temperature. The crystal and molecular structures were re-determined by the single crystal X-ray diffraction. The vibrational spectral measurements were carried out using FT-IR and FT-Raman spectroscopy in the range of 4000-400 cm(-1). The single crystal X-ray studies shows that the drug crystallized in the monoclinic system polymorph (Form-I). The crystal packing is dominated by N-H⋯O and O-H⋯O classical hydrogen bonds. The ac diagonal of the unit cell features two chain C(7) and C(9) motifs running in the opposite directions. These two chain motifs are cross-linked to each other to form a ring R4(4)(22) motif and a chain C2(2)(6) motif which is running along the a-axis of the unit cell. Along with the classical hydrogen bonds, the methyl group forms a weak C-H⋯O interactions in the crystal packing. It offers the support for molecular assembly especially in the hydrophilic regions. Further, the strength of the hydrogen bonds are studied the shifting of vibrational bands. Geometrical optimizations of the drug molecule were done by the Density Functional Theory (DFT) using the B3LYP function and Hartree-Fock (HF) level with 6-311++G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra are compared with experimental results which show significant agreement. The factor group analysis of the molecule was carried out by the various molecular symmetry, site and factor group species using the standard correlation method. The Natural Bond Orbital (NBO) analysis was carried out to interpret hyperconjugative interaction and intramolecular charge transfer (ICT). The chemical softness, chemical hardness, electro-negativity, chemical potential and electrophilicity index of the molecule were found out first

  10. Effects of Thermal Lattice Vibration on the Effective Potential of Weak-Coupling Bipolaron in a Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    额尔敦朝鲁; 乌云其木格; 肖欣; 韩超; 辛伟

    2012-01-01

    Based on the Huybrechts' linear-combination operator, effects of thermal lattice vibration on the effective potential of weak-coupling bipolaron in semiconductor quantum dots are studied by using the LLP variational method and quantum statistical theory. The results show that the absolute value of the induced potential of the bipolaron increases with increasing the electron-phonon coupling strength, but decreases with increasing the temperature and the distance of electrons, respectively; the absolute value of the effective potential increases with increasing the radius of the quantum dot, electron-phonon coupling strength and the distance of electrons, respectively, but decreases with increasing the temperature; the temperature and electron-phonon interaction have the important influence on the formation and state properties of the bipolaron: the bipolarons in the bound state are closer and more stable when the electron-phonon coupling strength is larger or the temperature is lower; the confinement potential and coulomb repulsive potential between electrons are unfavorable to the formation of bipolarons in the bound state.

  11. Methane steam reforming rates over Pt, Rh and Ni(111) accounting for H tunneling and for metal lattice vibrations

    Science.gov (United States)

    German, Ernst D.; Sheintuch, Moshe

    2017-02-01

    Microkinetic models of methane steam reforming (MSR) over bare platinum and rhodium (111) surfaces are analyzed in present work using calculated rate constants. The individual rate constants are classified into three different sets: (i) rate constants of adsorption and desorption steps of CH4, H2O, CO and of H2; (ii) rate constants of dissociation and formation of A-H bonds (A = C, O, and H), and (iii) rate constants of dissociation and formation of C-O bond. The rate constants of sets (i) and (iii) are calculated using transition state theory and published thermochemical data. The rate constants of H-dissociation reactions (set (ii)) are calculated in terms of a previously-developed approach that accounts for thermal metal lattice vibrations and for H tunneling through a potential barrier of height which depends on distance of AH from a surface. Pre-exponential factors of several group (ii) steps were calculated to be usually lower than the traditional kBT/h due to tunneling effect. Surface composition and overall MSR rates over platinum and rhodium surfaces are compared with those over nickel surface showing that operating conditions strongly affect on the activity order of the catalysts.

  12. Crystal studies, vibrational spectra and non-linear optical properties of L-histidine chloride monohydrate.

    Science.gov (United States)

    Ben Ahmed, A; Feki, H; Abid, Y; Boughzala, H; Minot, C

    2010-01-01

    This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a non-linear optical material L-histidine chloride monohydrate. Due to the lack of sufficiently precise information on geometric parameters available in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of L-histidine chloride monohydrate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro-symmetric space group P2(1)2(1)2(1) of orthorhombic system. IR spectrum has been recorded in the range [400-4000 cm(-1)]. All the experimental vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our calculations. The optimized geometric bond lengths and bond angles obtained by using DFT//B3LYP/6-31G (d) method show a good agreement with the experimental data. The calculated vibrational spectra are in well agreement with the experimental one. To investigate microscopic second-order non-linear optical NLO behavior of the examined complex, the electric dipole mu, the polarizability alpha and the hyperpolarizability beta were computed using DFT//B3LYP/6-31G (d) method. The time-dependent density functional theory (TD-DFT) was employed to descript the molecular electron structure of the title compound using the B3LYP/6-31G (d) method. According to our calculations, L-histidine chloride monohydrate exhibits non-zero beta value revealing microscopic second-order NLO behavior. Copyright 2009 Elsevier B.V. All rights reserved.

  13. Crystal studies, vibrational spectra and non-linear optical properties of L-histidine chloride monohydrate

    Science.gov (United States)

    Ahmed, A. Ben; Feki, H.; Abid, Y.; Boughzala, H.; Minot, C.

    2010-01-01

    This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a non-linear optical material L-histidine chloride monohydrate. Due to the lack of sufficiently precise information on geometric parameters available in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of L-histidine chloride monohydrate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro-symmetric space group P2 12 12 1 of orthorhombic system. IR spectrum has been recorded in the range [400-4000 cm -1]. All the experimental vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our calculations. The optimized geometric bond lengths and bond angles obtained by using DFT//B3LYP/6-31G (d) method show a good agreement with the experimental data. The calculated vibrational spectra are in well agreement with the experimental one. To investigate microscopic second-order non-linear optical NLO behavior of the examined complex, the electric dipole μ, the polarizability α and the hyperpolarizability β were computed using DFT//B3LYP/6-31G (d) method. The time-dependent density functional theory (TD-DFT) was employed to descript the molecular electron structure of the title compound using the B3LYP/6-31G (d) method. According to our calculations, L-histidine chloride monohydrate exhibits non-zero β value revealing microscopic second-order NLO behavior.

  14. Bloch oscillation and Landau-Zener tunnelling in a modulated optical lattice in a photovoltaic photorefractive crystal

    Institute of Scientific and Technical Information of China (English)

    Zhang Bing-Zhi; Cui Hu; Li Xiang-Heng; She Wei-Long

    2009-01-01

    We theoretically study the beam dynamical hehaviour in a modulated optical lattice with a quadratic potential in a photovoltaic photorefractive crystal. We find that two different Bloch oscillation patterns appear for the excitation of both broad and narrow light beams. One kind of optical Landau-Zener tunnelling also appears upon the Bloch oscillation and can be controlled by adjusting the parameter of the optical lattice. Unlike the case of linear potential, the energy radiation due to Landau-Zener tunnelling can be confined in modulated lattices of this kind. For high input intensity levels, the Landau-Zener tunnelling is suppressed by the photovoltaic photorefractive nonlinearity and a symmetry breaking of beam propagation from the modulational instability appears.

  15. Lattice location of O18 in ion implanted Fe crystals by Rutherford backscattering spectrometry, channeling and nuclear reaction analysis

    Science.gov (United States)

    Vairavel, Mathayan; Sundaravel, Balakrishnan; Panigrahi, Binaykumar

    2016-09-01

    There are contradictory theoretical predictions of lattice location of oxygen interstitial atom at tetrahedral and octahedral interstices in bcc Fe. For validating these predictions, 300 keV O18 ions with fluence of 5 × 1015 ions/cm2 are implanted into bcc Fe single crystals at room temperature and annealed at 400 °C. The Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA)/channeling measurements are carried out with 850 keV protons. The lattice location of implanted O18 is analysed using the α-particles yield from O18(p,α)N15 nuclear reaction. The tilt angular scans of α-particle yield along and axial directions are performed at room temperature. Lattice location of O18 is found to be at tetrahedral interstitial site by comparing the experimental scan with simulated scans using FLUX7 software.

  16. Shear dependent nonlinear vibration in a high quality factor single crystal silicon micromechanical resonator

    Science.gov (United States)

    Zhu, H.; Shan, G. C.; Shek, C. H.; Lee, J. E.-Y.

    2012-07-01

    The frequency response of a single crystal silicon resonator under nonlinear vibration is investigated and related to the shear property of the material. The shear stress-strain relation of bulk silicon is studied using a first-principles approach. By incorporating the calculated shear property into a device-level model, our simulation closely predicts the frequency response of the device obtained by experiments and further captures the nonlinear features. These results indicate that the observed nonlinearity stems from the material's mechanical property. Given the high quality factor (Q) of the device reported here (˜2 × 106), this makes it highly susceptible to such mechanical nonlinear effects.

  17. Low-temperature embrittlement and fracture of metals with different crystal lattices – Dislocation mechanisms

    Directory of Open Access Journals (Sweden)

    V.M. Chernov

    2016-12-01

    Full Text Available The state of a low-temperature embrittlement (cold brittleness and dislocation mechanisms for formation of the temperature of a ductile-brittle transition and brittle fracture of metals (mono- and polycrystals with various crystal lattices (BCC, FCC, HCP are considered. The conditions for their formation connected with a stress-deformed state and strength (low temperature yield strength as well as the fracture breaking stress and mobility of dislocations in the top of a crack of the fractured metal are determined. These conditions can be met for BCC and some HCP metals in the initial state (without irradiation and after a low-temperature damaging (neutron irradiation. These conditions are not met for FCC and many HCP metals. In the process of the damaging (neutron irradiation such conditions are not met also and the state of low-temperature embrittlement of metals is absent (suppressed due to arising various radiation dynamic processes, which increase the mobility of dislocations and worsen the strength characteristics.

  18. Vortex lattice mobility and effective pinning potentials in the peak effect region in YBCO crystals

    Indian Academy of Sciences (India)

    G Pasquini; V Bekeris

    2006-01-01

    The peak effect (PE) in the critical current density in both low and high temperature superconductors has been the subject of a large amount of experimental and theoretical work in the last few/several years. In the case of YBCO, crucial discussions describing a dynamic or a static picture are not settled. In that region of field and temperature the mobility of the vortex lattice (VL) is found to be dependent on the dynamical history. Recently we reported evidence that the VL reorganizes and accesses to robust VL configurations (VLCs) with different effective pinning potential wells arising in response to different system histories. One of the keys to understand the nature of the PE is to investigate the VL behavior in the vicinity of the various VLCs in the region of the PE. The stability of these VLCs was investigated and it was found that they have distinct characteristic relaxation times, which may be related to elastic or plastic creep processes. In this paper we review some of these results and propose a scenario to describe the PE in YBCO crystals.

  19. Lattice Boltzmann simulation of asymmetric flow in nematic liquid crystals with finite anchoring

    Science.gov (United States)

    Zhang, Rui; Roberts, Tyler; Aranson, Igor S.; de Pablo, Juan J.

    2016-02-01

    Liquid crystals (LCs) display many of the flow characteristics of liquids but exhibit long range orientational order. In the nematic phase, the coupling of structure and flow leads to complex hydrodynamic effects that remain to be fully elucidated. Here, we consider the hydrodynamics of a nematic LC in a hybrid cell, where opposite walls have conflicting anchoring boundary conditions, and we employ a 3D lattice Boltzmann method to simulate the time-dependent flow patterns that can arise. Due to the symmetry breaking of the director field within the hybrid cell, we observe that at low to moderate shear rates, the volumetric flow rate under Couette and Poiseuille flows is different for opposite flow directions. At high shear rates, the director field may undergo a topological transition which leads to symmetric flows. By applying an oscillatory pressure gradient to the channel, a net volumetric flow rate is found to depend on the magnitude and frequency of the oscillation, as well as the anchoring strength. Taken together, our findings suggest several intriguing new applications for LCs in microfluidic devices.

  20. Anisotropic lattice expansion of three-dimensional colloidal crystals and its impact on hypersonic phonon band gaps.

    Science.gov (United States)

    Wu, Songtao; Zhu, Gaohua; Zhang, Jin S; Banerjee, Debasish; Bass, Jay D; Ling, Chen; Yano, Kazuhisa

    2014-05-21

    We report anisotropic expansion of self-assembled colloidal polystyrene-poly(dimethylsiloxane) crystals and its impact on the phonon band structure at hypersonic frequencies. The structural expansion was achieved by a multistep infiltration-polymerization process. Such a process expands the interplanar lattice distance 17% after 8 cycles whereas the in-plane distance remains unaffected. The variation of hypersonic phonon band structure induced by the anisotropic lattice expansion was recorded by Brillouin measurements. In the sample before expansion, a phononic band gap between 3.7 and 4.4 GHz is observed; after 17% structural expansion, the gap is shifted to a lower frequency between 3.5 and 4.0 GHz. This study offers a facile approach to control the macroscopic structure of colloidal crystals with great potential in designing tunable phononic devices.

  1. Analysis of optomechanical coupling in two-dimensional square lattice phoxonic crystal slab cavities

    Science.gov (United States)

    El-Jallal, Said; Oudich, Mourad; Pennec, Yan; Djafari-Rouhani, Bahram; Laude, Vincent; Beugnot, Jean-Charles; Martínez, Alejandro; Escalante, José María; Makhoute, Abdelkader

    2013-11-01

    We theoretically investigate phonon-photon interaction in cavities created in a phoxonic crystal slab constituted by a two-dimensional (2D) square array of holes in a silicon membrane. The structure without defects provides 2D band gaps for both electromagnetic and elastic waves. We consider two types of cavities, namely, an L3 cavity (a row of three holes is removed) and a cross-shape cavity, which both possess highly confined phononic and photonic localized modes suitable for enhancing their interaction. In our theoretical study, we take into account two mechanisms that contribute to optomechanical interaction, namely, the photoelastic and the interface motion effects. We show that, depending on the considered pair of photonic and phononic modes, the two mechanisms can have similar or very different magnitudes, and their contributions can be either in or out of phase. We find out that only acoustic modes with a specific symmetry are allowed to couple with photonic cavity modes. The coupling strength is quantified by two different methods. In the first method, we compute a direct estimation of coupling rates by overlap integrals, while in the second one, we analyze the temporal modulation of the resonant photonic frequency by the phonon-induced acoustic vibrational motion during one acoustic period. Interestingly, we obtain high optomechanical interaction, with the coupling rate reaching more than 2.4 MHz for some specific phonon-photon pairs.

  2. The focusing effect of electromagnetic waves in two-dimensional photonic crystals with gradually varying lattice constant

    Directory of Open Access Journals (Sweden)

    F Bakhshi Garmi

    2016-02-01

    Full Text Available In this paper we studied the focusing effect of electromagnetic wave in the two-dimensional graded photonic crystal consisting of Silicon rods in the air background with gradually varying lattice constant. The results showed that graded photonic crystal can focus wide beams on a narrow area at frequencies near the lower edge of the band gap, where equal frequency contours are not concave. For calculation of photonic band structure and equal frequency contours, we have used plane wave expansion method and revised plane wave expansion method, respectively. The calculation of the electric and magnetic fields was performed by finite difference time domain method.

  3. Deformed lattice states in a Zn{sub 0.9}V{sub 0.1}Se cubic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Maksimov, V. I., E-mail: kokailo@rambler.ru; Dubinin, S. F.; Surkova, T. P.; Parkhomenko, V. D. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)

    2016-01-15

    Neutron scattering patterns have been recorded for a bulk Zn{sub 0.9}V{sub 0.1}Se cubic crystal at room temperature; they are indicative of macroscopic deformation in the material and its significant inhomogeneity. Specific features of the previously found state, preceding the fcc ↔ hcp structural transformation of the sphalerite lattice upon strong destabilization induced by vanadium ions in the doped ZnSe matrix, are discussed taking into account the data obtained.

  4. Soliton delivery of few-cycle optical gigawatt pulses in Kagome-lattice hollow-core photonic crystal fibers

    Science.gov (United States)

    Im, Song-Jin; Husakou, Anton; Herrmann, Joachim

    2010-08-01

    We study the delivery of few-cycle soliton-like pulses at 800 nm with gigawatt power or microjoule energy through a hollow-core kagome-lattice photonic crystal fiber over 1 m with preserved temporal and spectral shape. We show that with optimized pressure of the argon filling, 5 fs input pulses are compressed up to 2.5 fs after 20 cm and restore their shape after 1 m propagation.

  5. Structural, quantum chemical, vibrational and thermal studies of a hydrogen bonded zwitterionic co-crystal (nicotinic acid: pyrogallol)

    Science.gov (United States)

    Prabha, E. Arockia Jeya Yasmi; Kumar, S. Suresh; Athimoolam, S.; Sridhar, B.

    2017-02-01

    In the present work, a new co-crystal of nicotinic acid with pyrogallol (NICPY) has been grown in the zwitterionic form and the corresponding structural, vibrational, thermal, solubility and anti-cancer characteristics have been reported. The single crystal X-ray diffraction analysis confirms that the structural molecular packing of the crystal stabilized through N-H⋯O and O-H⋯O hydrogen bond. The stabilization energy of the hydrogen bond motifs were calculated in the solid state. Vibrational spectral studies such as Fourier transform-infrared (FT-IR) and FT-Raman were adopted to understand the zwitterionic co-crystalline nature of the compound, which has been compared with theoretically calculated vibrational frequencies. The thermal stability of the grown co-crystal was analyzed by TG/DTA study. The solubility of the NICPY co-crystal was investigated in water at different temperature and compared with that of the nicotinic acid, which is the parent compound of NICPY co-crystal. The grown crystals were treated with human cervical cancer cell line (HeLa) to analyze the cytotoxicity of NICPY crystals and compared with the parent compound, which shows that NICPY has moderate activity against human cervical cancer cell line.

  6. Influence of vibrations during crystallization on mechanical properties and porosity of AlSi11 alloy

    Directory of Open Access Journals (Sweden)

    T. Ciucka

    2009-04-01

    Full Text Available Today’s industry aims at such situation, where number of defective products, so called defects shall approach to zero. Therefore,one introduces a various changes in technology of production, introduces improvements which would help in accomplishment of thisobjective. Another important factor is introduction of different type of testing, which shall help in assessment which factor has significant effect on quantity of rejects, and which one could be neglected. Existence of casting rejects is unavoidable; therefore a new ideas, technologies and innovations are necessary in the entire widely understood foundry branch, in order to minimize such adverse effect. Performance of tests aimed at unequivocal determination of an effect of vibrations during crystallization on mechanical properties and porosity of the AK11 alloy was the objective of the present work. To do this, there were produced 36 castings from AK11 alloy. All thecastings underwent machining operations. Half of the casting was destined to strength tests, the other half served to determination of an effect of vibrations on porosity of the alloy. The specimens were divided into 12 groups, depending on amplitude of vibrations and tiltangle of metal mould during pouring operation.

  7. Crystal structure, vibrational spectra and theoretical studies of L-histidinium dihydrogen phosphate-phosphoric acid

    Science.gov (United States)

    Ahmed, A. Ben; Feki, H.; Abid, Y.; Boughzala, H.; Minot, C.; Mlayah, A.

    2009-02-01

    In this work, we report a combined experimental and theoretical study on molecular structure and vibrational spectra of L-histidinium dihydrogen phosphate-phosphoric acid, with particular emphasize on the correlation between the intermolecular hydrogen bonds and the hyperpolarizability. Single crystal of L-histidinium dihydrogen phosphate-phosphoric acid has been subjected to X-ray diffraction and Raman spectroscopy. The title compound crystallises in the non-centrosymmetric space group P2 1. Raman spectra have been recorded in the frequency range [150-3350 cm -1]. To obtain a more reliable assignment of the Raman and IR spectra, we have calculated the geometry and the frequencies using HF and DFT methods. All the experimental vibrational bands have been discussed and assigned to normal mode or to combinations and overtones on the basis of our calculations. The optimized geometric bond lengths and bond angles obtained by using HF and DFT (B3LYP and BLYP) are in well agreement with the experimental data. The results of DFT-B3LYP method have shown better fit to experimental ones than HF in evaluating vibrational frequencies. To investigate microscopic second order non-linear optical behaviour of the examined complex, the electric dipole μ, the polarizability α and the hyperpolarizability β were computed using DFT//B3LYP/6-31 G(d) method. According to our calculation, the title compound exhibits non-zero β value revealing microscopic second order NLO behaviour.

  8. Theory of the normal modes of vibrations in the lanthanide type crystals

    Energy Technology Data Exchange (ETDEWEB)

    Acevedo, Roberto [Instituto de Ciencias Basicas. Facultad de Ingenieria, Universidad Diego Portales, Avenida Ejercito 441, Santiago (Chile); Soto-Bubert, Andres, E-mail: roberto.acevedo@umayor.cl

    2008-11-01

    For the lanthanide type crystals, a vast and rich, though incomplete amount of experimental data has been accumulated, from linear and non linear optics, during the last decades. The main goal of the current research work is to report a new methodology and strategy to put forward a more representative approach to account for the normal modes of vibrations for a complex N-body system. For illustrative purposes, the chloride lanthanide type crystals Cs{sub 2}NaLnCl{sub 6} have been chosen and we develop new convergence tests as well as a criterion to deal with the details of the F-matrix (potential energy matrix). A novel and useful concept of natural potential energy distributions (NPED) is introduced and examined throughout the course of this work. The diagonal and non diagonal contributions to these NPED-values, are evaluated for a series of these crystals explicitly. Our model is based upon a total of seventy two internal coordinates and ninety eight internal Hooke type force constants. An optimization mathematical procedure is applied with reference to the series of chloride lanthanide crystals and it is shown that the strategy and model adopted is sound from both a chemical and a physical viewpoints. We can argue that the current model is able to accommodate a number of interactions and to provide us with a very useful physical insight. The limitations and advantages of the current model and the most likely sources for improvements are discussed in detail.

  9. PARALLEL FINITE ELEMENT ANALYSIS OF HIGH FREQUENCY VIBRATIONS OF QUARTZ CRYSTAL RESONATORS ON LINUX CLUSTER

    Institute of Scientific and Technical Information of China (English)

    Ji Wang; Yu Wang; Wenke Hu; Wenhua Zhao; Jianke Du; Dejin Huang

    2008-01-01

    Quartz crystal resonators are typical piezoelectric acoustic wave devices for frequency control applications with mechanical vibration frequency at the radio-frequency (RF) range. Precise analyses of the vibration and deformation are generally required in the resonator design and improvement process. The considerations include the presence of electrodes, mountings, bias fields such as temperature, initial stresses, and acceleration. Naturally, the finite element method is the only effective tool for such a coupled problem with multi-physics nature. The main challenge is the extremely large size of resulted linear equations. For this reason, we have been employing the Mindlin plate equations to reduce the computational difficulty. In addition, we have to utilize the parallel computing techniques on Linux clusters, which are widely available for academic and industrial applications nowadays, to improve the computing efficiency. The general principle of our research is to use open source software components and public domain technology to reduce cost for developers and users on a Linux cluster. We start with a mesh generator specifically for quartz crystal resonators of rectangular and circular types, and the Mindlin plate equations are implemented for the finite element analysis. Computing techniques like parallel processing, sparse matrix handling, and the latest eigenvalue extraction package are integrated into the program. It is clear from our computation that the combination of these algorithms and methods on a cluster can meet the memory requirement and reduce computing time significantly.

  10. Towards true 3-dimensional BCC colloidal crystals with controlled lattice orientation

    NARCIS (Netherlands)

    Dziomkina, N.; Hempenius, Mark A.; Vancso, Gyula J.

    2009-01-01

    A fabrication method of colloidal crystals possessing the BCC crystal structure is described. BCC colloidal crystals with a thickness of up to seven colloidal layers were grown in the direction of the (100) crystal plane. Defect free colloidal crystals with a homogeneous surface coverage were

  11. Influence of peripheral vibrations and traveling magnetic fields on VGF growth of Sb-doped Ge crystals

    Science.gov (United States)

    Dropka, Natasha; Frank-Rotsch, Christiane; Rudolph, Peter

    2016-11-01

    We performed 3D numerical and experimental studies to assess the potential of peripheral low frequency mechanical vibrations for improving the homogeneity of Sb-doped 4″ Ge crystals grown by vertical gradient freeze (VGF). For this study, a novel bell-shaped graphite vibrator was developed for the generation of the axial vibrations in the direction of three-phase junction. Melt stirring by downward traveling magnetic field (TMF) was used as a benchmark. The results showed superiority of peripheral vibrations to TMF stirring concerning radial and longitudinal doping distribution and initial stirring rate. Experimentally observed standing free surface waves in Ge were caused by shielding effect of the vibrator on TMF.

  12. Calculations of the electronic levels, spin-Hamiltonian parameters and vibrational spectra for the CrCl3 layered crystals

    Science.gov (United States)

    Avram, C. N.; Gruia, A. S.; Brik, M. G.; Barb, A. M.

    2015-12-01

    Calculations of the Cr3+ energy levels, spin-Hamiltonian parameters and vibrational spectra for the layered CrCl3 crystals are reported for the first time. The crystal field parameters and the energy level scheme were calculated in the framework of the Exchange Charge Model of crystal field. The spin-Hamiltonian parameters (zero-field splitting parameter D and g-factors) for Cr3+ ion in CrCl3 crystals were obtained using two independent techniques: i) semi-empirical crystal field theory and ii) density functional theory (DFT)-based model. In the first approach, the spin-Hamiltonian parameters were calculated from the perturbation theory method and the complete diagonalization (of energy matrix) method. The infrared (IR) and Raman frequencies were calculated for both experimental and fully optimized geometry of the crystal structure, using CRYSTAL09 software. The obtained results are discussed and compared with the experimental available data.

  13. Near-field imaging of a square-lattice metallic photonic-crystal slab at the second band

    Institute of Scientific and Technical Information of China (English)

    Feng Shuai; Feng Zhi-Fang; Ren Kun; Ren Cheng; Li Zhi-Yuan; Cheng Bing-Ying; Zhang Dao-Zhong

    2006-01-01

    Imaging properties of a two-dimensional photonic crystal slab lens are investigated through the finite-difference time-domain method. In this paper, we consider the photonic crystal slab consisting of a square lattice of square metallic rods immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the photonic crystal slab, we find that a good-quality image can form at the frequencies in the second TM-polarized photonic band. Comparing the images formed at different frequencies, we can clearly see that an excellent-quality image is formed by the mechanisms of simultaneous action of the self-collimation effect and the negative-refraction effect.

  14. Elastic wave band gaps tuned by configuring radii of rods in two-dimensional phononic crystals with a hybrid square-like lattice

    Science.gov (United States)

    Liu, Rongqiang; Zhao, Haojiang; Zhang, Yingying; Guo, Honghwei; Deng, Zongquan

    2015-12-01

    The plane wave expansion (PWE) method is used to calculate the band gaps of two-dimensional (2D) phononic crystals (PCs) with a hybrid square-like (HSL) lattice. Band structures of both XY-mode and Z-mode are calculated. Numerical results show that the band gaps between any two bands could be maximized by altering the radius ratio of the inclusions at different positions. By comparing with square lattice and bathroom lattice, the HSL lattice is more efficient in creating larger gaps.

  15. Crystal structure, conformation, vibration and optical band gap analysis of bis[ rac-propranolol nitrate

    Science.gov (United States)

    Franklin, S.; Balasubramanian, T.; Nehru, K.; Kim, Youngmee

    2009-06-01

    The crystal structure of the title rac-propranolol salt, CHNO2+·NO3-, consists of two protonated propranolol residues and nitrate anions. Three virtually flat fragments, characteristics of most of the β-adrenolytics with oxy-methylene bridge are present in both the cations (A and B). The plane of the propranolol chain is twisted with respect to the plane of the aromatic ring in both the cations. Present study investigates the conformation and hydrogen bonding interactions, which play an important role in biological functions. A gauche conformation is observed for the oxo-methylene bridge of cation A, while a trans conformation prevails in cation B. These conformations are found in majority of β-blockers. Presence of twenty intermolecular hydrogen bonds mediating through the anions stabilizes the crystal packing. Vibration analysis and earlier theoretical predictions complement the structure analysed. From the UV-Vis spectral analysis for the crystal, the optical band gap is found to be Eg = 5.12 eV, where as the chloride salt has Eg = 3.81 eV. The increase in the band gap may be attributed by the increase in the number of intermolecular hydrogen bonds. Good optical transmittance in the entire visible region and the direct band gap property suggest that it is a suitable candidate for optical applications in UV region.

  16. Study on Lattice Parameter Variance and Eutectic Reaction during Crystal Growth of Nd,Cr∶GSGG by Czochralksi Method

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    During the crystal growth of Nd, Cr∶GSGG by Czochralski method, in some cases eutectic reaction occurred in the nether region of the crystal, and the boule was divided into two obvious different parts, which is upper Nd,Cr∶GSGG crystal and the nether coexisting Nd,Cr∶GSGG and GdScO3. By X-ray powder diffraction, the structure change of NdCr∶GSGG crystal of Φ 27 mm×120 mm with eutectic along its grown direction was studied. By the least square method and extrapolation function f=sinθ-sinθ1-t(t is an adjustable parameter), the lattice parameters of Nd,Cr∶GSGG and additional GdScO3 phase were computed. The results indicate that the lattice parameters of Nd,Cr∶GSGG increase along its growth direction, which changes from a=(1.25650±0.00007) nm of the top to (1.25798±0.00010) nm of the bottom. In the process of Nd,Cr∶GSGG growth, Gd3+ in Nd,Cr∶GSGG is partly replaced by Nd3+ with larger ionic radii, and the volatilization of Ga component results in its composition variance, which cause the lattice parameters increase along growth direction. In the eutectic section, there are the Nd,Cr∶GSGG and the second phase orthorhombic GdScO3. The lattice parameters of GdScO3 are a=0.5443±0.0007, b=0.5699±0.0005 and c=(0.7865±0.0009) nm, and that of Nd,Cr∶GSGG is (1.25798±0.00010) nm. In the final growth stage, excessive volatilization of Ga composition during the crystal growth causes the growth melt deflect of the Nd,Cr∶GSGG solid solution range seriously, and results in the eutectic reaction, and the outgrowth of Nd,Cr∶GSGG and GdScO3. So it is necessary to decrease the effect of gallium volatilization during the growth in order to avoid eutectic growth and obtain a high-quality Nd,Cr∶GSGG.

  17. Quantum simulating the frustrated Heisenberg model in a molecular dipolar crystal

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yan-Li, E-mail: ylzhou@nudt.edu.cn [College of Science, National University of Defense Technology, 410073 Changsha (China); Ou, Bao-Quan [College of Science, National University of Defense Technology, 410073 Changsha (China); Wu, Wei [College of Science, National University of Defense Technology, 410073 Changsha (China); State Key Laboratory of High Performance Computing, National University of Defense Technology, 410073 Changsha (China)

    2015-10-23

    We study the simulation of spin models with polar molecules in a dipolar crystal. We employ a master equation approach to describe the dynamics of the system and to research the dissipation of the model. The reduced dynamics of the polar molecules lead to frustrated Heisenberg models with tuneable long-range interactions, via spin-dependent dipole–dipole interactions forces to the lattice vibrations. The influence of the lattice vibrations is calculated and analyzed in detail. - Highlights: • We simulate spin models with polar molecules in a dipolar crystal. • We employ a master equation to describe the dynamics of the system. • The influence of the lattice vibrations is calculated.

  18. Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study

    Energy Technology Data Exchange (ETDEWEB)

    Fonari, A.; Corbin, N. S.; Coropceanu, V., E-mail: jean-luc.bredas@kaust.edu.sa, E-mail: coropceanu@gatech.edu [School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States); Vermeulen, D.; McNeil, L. E. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3255 (United States); Goetz, K. P.; Jurchescu, O. D. [Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109-7507 (United States); Bredas, J. L., E-mail: jean-luc.bredas@kaust.edu.sa, E-mail: coropceanu@gatech.edu [School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States); Solar and Photovoltaics Engineering Research Center, Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900 (Saudi Arabia)

    2015-12-14

    We establish a reliable quantum-mechanical approach to evaluate the vibrational properties of donor-acceptor molecular crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as the electron donor and PMDA as the electron acceptor, is taken as a representative system for which experimental non-resonance Raman spectra are also reported. We first investigate the impact that the amount of nonlocal Hartree-Fock exchange (HFE) included in a hybrid density functional has on the geometry, normal vibrational modes, electronic coupling, and electron-vibrational (phonon) couplings. The comparison between experimental and theoretical Raman spectra indicates that the results based on the αPBE functional with 25%-35% HFE are in better agreement with the experimental results compared to those obtained with the pure PBE functional. Then, taking αPBE with 25% HFE, we assign the vibrational modes and examine their contributions to the relaxation energy related to the nonlocal electron-vibration interactions. The results show that the largest contribution (about 90%) is due to electron interactions with low-frequency vibrational modes. The relaxation energy in anthracene-PMDA is found to be about five times smaller than the electronic coupling.

  19. Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study

    KAUST Repository

    Fonari, A.

    2015-12-10

    We establish a reliable quantum-mechanical approach to evaluate the vibrational properties of donor-acceptor molecular crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as the electron donor and PMDA as the electron acceptor, is taken as a representative system for which experimental non-resonance Raman spectra are also reported. We first investigate the impact that the amount of nonlocal Hartree-Fock exchange (HFE) included in a hybrid density functional has on the geometry, normal vibrational modes, electronic coupling, and electron-vibrational (phonon) couplings. The comparison between experimental and theoreticalRaman spectra indicates that the results based on the αPBE functional with 25%-35% HFE are in better agreement with the experimental results compared to those obtained with the pure PBE functional. Then, taking αPBE with 25% HFE, we assign the vibrational modes and examine their contributions to the relaxation energy related to the nonlocal electron-vibration interactions. The results show that the largest contribution (about 90%) is due to electron interactions with low-frequency vibrational modes. The relaxation energy in anthracene-PMDA is found to be about five times smaller than the electronic coupling.

  20. Provable forst-order transitions for liquid crystal and lattice gauge models with continuous symmetries

    CERN Document Server

    Van Enter, A C D

    2003-01-01

    We consider various sufficiently nonlinear sigma models for nematic ordering of RP^{N-1} type and of lattice gauge type with continous symmetries. We rigorously show that they exhibit a first-order transition in the temperature. The result holds in dimension 2 or more for the RP{N-1} models and in dimension 3 or more for the lattice gauge models. In the two-dimensional case our results clarify and solve a recent controversy about the possibilty of such transitions. For lattice gauge models our methods provide the first prof of a first-order transition in a model with a continous gauge symmetry.

  1. Guide modes in photonic crystal heterostructures composed of rotating non-circular air cylinders in two-dimensional lattices

    CERN Document Server

    Zhou Yun Song; Wang Fu He

    2003-01-01

    We investigate the properties of guide modes localized at the interfaces of photonic crystal (PC) heterostructures which are composed of two semi-infinite two-dimensional PCs consisting of non-circular air cylinders with different rotating angles embedded in a homogeneous host dielectric. Photonic band gap structures are calculated with the use of the plane-wave expansion method in combination with a supercell technique. We consider various configurations, for instance, rectangular (square) lattice-rectangular (square) air cylinders, and different rotating angles of the cylinders in the lattices on either side of the interface of a heterostructure. We find that the absolute gap width and the number of guide modes strongly depend on geometric and physical parameters of the heterostructures. It is anticipated that the guide modes in such heterostructures can be engineered by adjusting parameters.

  2. Calculations of the Spin-Lattice Coupling Coefficients Fij and Zij for MgO:Co2+Crystal

    Institute of Scientific and Technical Information of China (English)

    ZHENG Wen-Chen; WU Shao-Yi

    2001-01-01

    According to a uniform and simple method of calculating spin-lattice coupling coefficients and the pert1rbation formulas of gi factors and hyperfine structure constants Ai based on the cluster approach for 3d7 ions in cubic,tetragonal and trigonal octahedral crystal fields, the spin-lattice coupling coefficients Fij (F11, Fl2, F44), Zij (Z11, Z12,Z44) and also g factor and hyperfine constant A for MgO:Co2+ are calculated by using the parameters obtained from the optical spectra without adjustable parameters. The calculated results show good agreement with the observed values.The difiiculty in explaining the coeficients Fij and Zij is therefore removed.``

  3. Thermal conductivity prediction of nanoscale phononic crystal slabs using a hybrid lattice dynamics-continuum mechanics technique

    Directory of Open Access Journals (Sweden)

    Charles M. Reinke

    2011-12-01

    Full Text Available Recent work has demonstrated that nanostructuring of a semiconductor material to form a phononic crystal (PnC can significantly reduce its thermal conductivity. In this paper, we present a classical method that combines atomic-level information with the application of Bloch theory at the continuum level for the prediction of the thermal conductivity of finite-thickness PnCs with unit cells sized in the micron scale. Lattice dynamics calculations are done at the bulk material level, and the plane-wave expansion method is implemented at the macrosale PnC unit cell level. The combination of the lattice dynamics-based and continuum mechanics-based dispersion information is then used in the Callaway-Holland model to calculate the thermal transport properties of the PnC. We demonstrate that this hybrid approach provides both accurate and efficient predictions of the thermal conductivity.

  4. Thermal conductivity prediction of nanoscale phononic crystal slabs using a hybrid lattice dynamics-continuum mechanics technique

    Science.gov (United States)

    Reinke, Charles M.; Su, Mehmet F.; Davis, Bruce L.; Kim, Bongsang; Hussein, Mahmoud I.; Leseman, Zayd C.; Olsson-III, Roy H.; El-Kady, Ihab

    2011-12-01

    Recent work has demonstrated that nanostructuring of a semiconductor material to form a phononic crystal (PnC) can significantly reduce its thermal conductivity. In this paper, we present a classical method that combines atomic-level information with the application of Bloch theory at the continuum level for the prediction of the thermal conductivity of finite-thickness PnCs with unit cells sized in the micron scale. Lattice dynamics calculations are done at the bulk material level, and the plane-wave expansion method is implemented at the macrosale PnC unit cell level. The combination of the lattice dynamics-based and continuum mechanics-based dispersion information is then used in the Callaway-Holland model to calculate the thermal transport properties of the PnC. We demonstrate that this hybrid approach provides both accurate and efficient predictions of the thermal conductivity.

  5. Local vibration modes of shallow thermal donors in nitrogen-doped CZ silicon crystals

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, N. [RIAST, Osaka Prefecture University, Sakai, 599-8570 (Japan) and Nitrogen Measurement WG, JEITA, Tokyo, 101-0062 (Japan)]. E-mail: inouen@riast.osakafu-u.ac.jp; Nakatsu, M. [RIAST, Osaka Prefecture University, Sakai, 599-8570 (Japan); Ono, H. [Japan Fine Ceramics Center, Tokyo, 105-0003 (Japan); Nitrogen Measurement WG, JEITA, Tokyo, 101-0062 (Japan)

    2006-04-01

    Local vibration mode (LVM) infrared absorption from shallow thermal donors (STD) composed of nitrogen-oxygen complexes in nitrogen-doped CZ silicon crystals was examined. The samples whose STD concentration had been determined were measured. The sample dependence of the peaks at 810 and 1018cm{sup -1} was similar to that of STD but the estimated concentration was slightly higher. New LVM peaks were found at 855, 973, 982, 1002cm{sup -1} and so on. Their magnitude and sample dependence agreed well with those of STD. Annealing temperature dependence of other samples supported the results. Annealing time dependence of STD concentration at 650 deg. C was examined. STD peaks at 250, 242 and those at 240, 234 and 238cm{sup -1} behaved differently, suggesting the presence of two kinds of STD origin.

  6. Vibration energy harvester with sustainable power based on a single-crystal piezoelectric cantilever array.

    Science.gov (United States)

    Kim, Moonkeun; Lee, Sang-Kyun; Ham, Yong-Hyun; Yang, Yil Suk; Kwon, Jong-Kee; Kwon, Kwang-Ho

    2012-08-01

    We designed and fabricated a bimorph cantilever array for sustainable power with an integrated Cu proof mass to obtain additional power and current. We fabricated a cantilever system using single-crystal piezoelectric material and compared the calculations for single and arrayed cantilevers to those obtained experimentally. The vibration energy harvester had resonant frequencies of 60.4 and 63.2 Hz for short and open circuits, respectively. The damping ratio and quality factor of the cantilever device were 0.012 and 41.66, respectively. The resonant frequency at maximum average power was 60.8 Hz. The current and highest average power of the harvester array were found to be 0.728 mA and 1.61 mW, respectively. The sustainable maximum power was obtained after slightly shifting the short-circuit frequency. In order to improve the current and power using an array of cantilevers, we also performed energy conversion experiments.

  7. Measurements on microscopic barium ferrite single crystals using a vibrating reed magnetometer

    Science.gov (United States)

    Schippan, R.; Hempel, K. A.

    1982-11-01

    The magnetization processes occuring in a small individual particle (dimensions about 4 μm) of a barium ferrite single crystal are investigated using a high sensitivity vibrating reed magnetometer.1,2 With this apparatus magnetic moments smaller than 10-9 A cm2 may be detected if the particle is fixed to a hollow quartz reed which is kept under vacuum. The operating frequency is tuned to the resonance frequency of the reed. The examination exhibits a perfect rectangular primary hysteresis loop which indicates that the magnetic moment of the sample is completely reversed by a single Barkhausen jump. By repeating the reversal, a wide range of jump field strengths is revealed. Two types of minor loops are demonstrated depending on the magnitude of the jump field strength.

  8. Soliton assisted control of source to drain electron transport along natural channels - crystallographic axes - in two-dimensional triangular crystal lattices

    Science.gov (United States)

    Chetverikov, A. P.; Ebeling, W.; Velarde, M. G.

    2016-09-01

    We present computational evidence of the possibility of fast, supersonic or subsonic, nearly loss-free ballistic-like transport of electrons bound to lattice solitons (a form of electron surfing on acoustic waves) along crystallographic axes in two-dimensional anharmonic crystal lattices. First we study the structural changes a soliton creates in the lattice and the time lapse of recovery of the lattice. Then we study the behavior of one electron in the polarization field of one and two solitons with crossing pathways with suitably monitored delay. We show how an electron surfing on a lattice soliton may switch to surf on the second soliton and hence changing accordingly the direction of its path. Finally we discuss the possibility to control the way an excess electron proceeds from a source at a border of the lattice to a selected drain at another border by following appropriate straight pathways on crystallographic axes.

  9. Electron paramagnetic resonance and optical spectroscopy of Yb sup 3 sup + ions in SrF sub 2 and BaF sub 2; an analysis of distortions of the crystal lattice near Yb sup 3 sup +

    CERN Document Server

    Falin, M L; Latypov, V A; Leushin, A M

    2003-01-01

    SrF sub 2 and BaF sub 2 crystals, doped with the Yb sup 3 sup + ions, have been investigated by electron paramagnetic resonance and optical spectroscopy. As-grown crystals of SrF sub 2 and BaF sub 2 show the two paramagnetic centres for the cubic (T sub c) and trigonal (T sub 4) symmetries of the Yb sup 3 sup + ions. Empirical diagrams of the energy levels were established and the potentials of the crystal field were determined. Information was obtained on the SrF sub 2 and BaF sub 2 phonon spectra from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyse the crystal lattice distortions in the vicinity of the impurity ion and the F sup - ion compensating for the excess positive charge in T sub 4. Within the frames of a superposition model, it is shown that three F sup - ions from the nearest surrounding cube, located symmetrically with respect to the C sub 3 axis from the side of the ion-compensator, approach the impurity ion and cling to the axis of the...

  10. A strong NH…Br vibrational behaviour studied through X-ray, vibrational spectra and quantum chemical studies in an isomorphous crystal: 2-Nitroanilinium bromide.

    Science.gov (United States)

    Anitha, R; Athimoolam, S; Gunasekaran, M

    2015-03-05

    A needle shaped transparent light brown crystals of 2-nitroanilinium bromide were successfully synthesized and crystallized from an aqueous mixture by slow evaporation technique. Single crystal XRD studies confirm the crystalline phase of this isomorphous compound which contains a positively charge 2-nitroanilinium cation and a negatively charged bromide anion. The solid phase FT-IR and FT-Raman spectra of the compound have been recorded in the range of 4000-400cm(-1). The observed modes are correlated by the factor group theory analysis and different IR and Raman active species were identified. Geometrical optimisations were carried out and harmonic vibrational wave numbers were computed for the minimum energy molecular structure at RHF level invoking 6-311++G(d,p) and SDD basis sets. Optimised molecular geometry was compared with the crystallographic data. The calculated wavenumbers were compared with the experimental values. The NH vibrational bands are shifted from its normal range and the shifting is associated with the influence of the intermolecular hydrogen bonds in the crystal. A strong intensity peak in theoretical and corresponding band in experimental confirms the presence of NH…Br interaction as predicted in crystalline state.

  11. Design and optical characterization of high-Q guided-resonance modes in the slot-graphite photonic crystal lattice.

    Science.gov (United States)

    Martínez, Luis Javier; Huang, Ningfeng; Ma, Jing; Lin, Chenxi; Jaquay, Eric; Povinelli, Michelle L

    2013-12-16

    A new photonic crystal structure is generated by using a regular graphite lattice as the base and adding a slot in the center of each unit cell to enhance field confinement. The theoretical Q factor in an ideal structure is over 4 × 10(5). The structure was fabricated on a silicon-on-insulator wafer and optically characterized by transmission spectroscopy. The resonance wavelength and quality factor were measured as a function of slot height. The measured trends show good agreement with simulation.

  12. An alternative use of Kieffer's lattice dynamics model using vibrational density of states for constructing thermodynamic databases

    NARCIS (Netherlands)

    Jacobs, M.H.G.; van den Berg, A.P.; Schmid-Fetzer, R.

    2013-01-01

    We use Kieffer's model to represent the vibrational density of states (VDoS) and thermodynamic properties of pure substances in pressure-temperature space. We show that this model can be simplified to a vibrational model in which the VDoS is represented by multiple Einstein frequencies without

  13. First-principles-based calculations of vibrational normal modes in polyatomic materials with translational symmetry: application to PETN molecular crystal.

    Science.gov (United States)

    Velizhanin, Kirill A; Kilina, Svetlana; Sewell, Thomas D; Piryatinski, Andrei

    2008-10-23

    Numerical studies of vibrational energy transport and associated (non)linear infrared and Raman response in polyatomic materials require knowledge of the multidimensional vibrational potential-energy surface and the ability to perform normal-mode analysis on that potential. The presence of translational symmetry, as in crystals, leads to the observed dispersion of the unit cell normal modes and has to be accounted for in calculations of energy transfer rates and other spectroscopic quantities. Here we report on the implementation of a computational approach that combines the generalized supercell method and density functional theory electronic structure calculations to investigate the vibrational structure in translationally symmetric materials containing relatively large numbers of atoms in the unit cell (58 atoms in the present study). The method is applied to calculate the phonon and vibron dispersion relations and the vibrational density of states in pentaerythritol tetranitrate (PETN) molecular crystal which is an important energetic material. The results set the stage for future investigations of vibrational energy transport and associated nonlinear spectroscopic signatures in this class of materials.

  14. Novel phases in a square-lattice frustrated ferromagnet : 1/3 -magnetization plateau, helicoidal spin liquid, and vortex crystal

    Science.gov (United States)

    Seabra, Luis; Sindzingre, Philippe; Momoi, Tsutomu; Shannon, Nic

    2016-02-01

    A large part of the interest in magnets with frustrated antiferromagnetic interactions comes from the many new phases found in applied magnetic field. In this article, we explore some of the new phases which arise in a model with frustrated ferromagnetic interactions, the J1-J2-J3 Heisenberg model on a square lattice. Using a combination of classical Monte Carlo simulation and spin-wave theory, we uncover behavior reminiscent of some widely studied frustrated antiferromagnets, but with a number of new twists. We first demonstrate that, for a suitable choice of parameters, the phase diagram as a function of magnetic field and temperature is nearly identical to that of the Heisenberg antiferromagnet on a triangular lattice, including the celebrated 1 /3 -magnetization plateau. We then examine how this phase diagram changes when the model is tuned to a point where the classical ground state is highly degenerate. In this case, two new phases emerge: a classical, finite-temperature spin liquid, characterized by a "ring" in the spin structure factor S (q ) ; and a vortex crystal, a multiple-Q state with finite magnetization, which can be viewed as an ordered lattice of magnetic vortices. All of these new phases persist for a wide range of magnetic fields. We discuss the relationship between these results and published studies of frustrated antiferromagnets, together with some of the materials where these new phases might be observed in experiment.

  15. The cone phase of liquid crystals: Triangular lattice of double-tilt cylinders

    Indian Academy of Sciences (India)

    Yashodhan Hatwalne; N V Madhusudana

    2003-08-01

    We predict the existence of a new defect-lattice phase near the nematic–smectic-C (NC) transition. This tilt-analogue of the blue phase is a lattice of double-tilt cylinders which are disclination lines in the smectic layer normal as well as the c-field. We discuss the structure and stability of the cone phase. We suggest that many ‘nematics’ exhibiting short range layering and tilt order may in fact be in the molten cone phase, which is a line liquid.

  16. First principle investigation of crystal lattice structure, thermodynamics and mechanical properties in ZnZrAl2 intermetallic compound

    Science.gov (United States)

    Wei, Zhenyi; Tou, Shushi; Wu, Bo; Bai, Kewu

    2016-12-01

    ZnZrAl2 is a kind of heterogeneous nucleation to promote the refine of grain of ZA43 alloy. ZnZrAl2 intermetallic is also considered as a candidate for superalloys. The crystal lattice structure, alloy thermodynamics and mechanical properties of ZnZrAl2 intermetallic compound were investigated by ab initio calculations based on density functional theory (DFT). In particular, the site preference of atoms in different sublattices was predicted based on alloy thermodynamics. At ground state, the most stable structure is L12 structure with sublattice model (Zn)1a(Zr0.3333Al0.6667)3c or (Zr)1a(Zn0.3333Al0.6667)3c, and the occupying preferences of Zn, Zr and Al atoms are independent with the increasing temperature. The bulk, shear, Young's modulus and the Poisson's ratio of the L12 structure ZnZrAl2 were calculated based on the site occupying configurations. The results show that ZnZrAl2 is a brittle material in nature. Electronic structures analysis revealed that Al-Zr atoms possess a covalent bonding character, while the Zn-Zr atoms have a metallic bonding character. ZnZrAl2 has stable mechanical properties at high temperature. The grain refinement effect of ZnZrAl2 precipitates in Zn-Al alloys were discussed based on crystal lattice match theory.

  17. Probing the sheath electric field with a crystal lattice by using thermophoresis in dusty plasma

    CERN Document Server

    Land, Victor; Matthews, Lorin; Hyde, Truell

    2010-01-01

    A two-dimensional dust crystal levitated in the sheath of a modified Gaseous Electronics Conference (GEC) reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained by measuring global characteristics of the levitated crystal obtained from top-view pictures. From the force balance, the electric field in the sheath is reconstructed. From the Bohm criterion, we conclude that the dust crystal is levitated mainly above and just below the classical Bohm point.

  18. Lattice damage and waveguide properties of a proton-exchanged LiNbO3 crystal after oxygen-ion implantation

    Science.gov (United States)

    Huang, Qing; Liu, Peng; Liu, Tao; Guo, Sha-Sha; Zhang, Lian; Wang, Xue-Lin

    2012-09-01

    A z-cut LiNbO3 crystal was immersed in a molten benzoic acid for 10 min and then was implanted with 6-MeV oxygen ions at a fluence of 6 × 1014 ions/cm2. Lattice damage in this crystal was measured by a Rutherford backscattering and channeling technique and was compared with lattice damage in a proton-exchanged LiNbO3 crystal and an oxygen-ion-implanted LiNbO3 crystal. A totally amorphous layer was formed at the crystal's surface after both proton exchange and oxygen-ion implantation processes were performed, even though either process alone never led to a relative disorder of the lattice up to 0.2. It indicates that the crystal lattice in the proton-exchanged layer is unstable and can be easily damaged by ion implantation subsequently. The waveguide structure formed by proton exchange was destroyed by oxygen-ion implantation. Oxygen-ion implantation induced an increase in extraordinary refractive index and formed another waveguide structure underneath the amorphous surface layer.

  19. H/D isotopic and temperature effects in the polarized IR spectra of hydrogen-bond cyclic trimers in the crystal lattices of acetone oxime and 3,5-dimethylpyrazole.

    Science.gov (United States)

    Flakus, Henryk T; Hachuła, Barbara; Garbacz, Aleksandra

    2012-11-29

    Polarized IR spectra of hydrogen-bonded acetone oxime and 3,5-dimethylpyrazole crystals were measured at 293 and 77 K in the ν(X-H) and ν(X-D) band frequency ranges. These crystals contain molecular trimers in their lattices. The individual crystal spectral properties remain in a close relation with the electronic structure of the two different molecular systems. We show that a vibronic coupling mechanism involving the hydrogen-bond protons and the electrons on the π-electronic systems in the molecules determines the way in which the vibrational exciton coupling between the hydrogen bonds in the trimers occurs. A strong coupling in 3,5-dimethylpyrazole trimers prefers a "tail-to-head"-type Davydov coupling widespread via the π-electrons. A weak through-space exciton coupling in acetone oxime trimers involves three adjacent hydrogen bonds in each cycle. The relative contribution of each exciton coupling mechanism in the trimer spectra generation is temperature and the molecular electronic structure-dependent. This explains the observed difference in the temperature-induced evolution of the compared spectra. The mechanism of the H/D isotopic "self-organization" processes in the crystal hydrogen bonds was also analyzed. The two types of the hydrogen-bond trimers exhibit the same way, in which the H/D isotopic recognition mechanism occurs. In acetone oxime and 3,5-dimethylpyrazole trimers, identical hydrogen isotope atoms exist in these entire hydrogen-bond systems.

  20. Towards vibrational spectroscopy on surface-attached colloids performed with a quartz crystal microbalance

    Directory of Open Access Journals (Sweden)

    Diethelm Johannsmann

    2016-12-01

    Full Text Available Colloidal spheres attached to a quartz crystal microbalance (QCM produce the so-called “coupled resonances”. They are resonators of their own, characterized by a particle resonance frequency, a resonance bandwidth, and a modal mass. When the frequency of the main resonator comes close to the frequency of the coupled resonance, the bandwidth goes through a maximum. A coupled resonance can be viewed as an absorption line in acoustic shear-wave spectroscopy. The known concepts from spectroscopy apply. This includes the mode assignment problem, selection rules, and the oscillator strength. In this work, the mode assignment problem was addressed with Finite Element calculations. These reveal that a rigid sphere in contact with a QCM displays two modes of vibration, termed “slipping” and “rocking”. In the slipping mode, the sphere rotates about its center; it exerts a tangential force onto the resonator surface at the point of contact. In the rocking mode, the sphere rotates about the point of contact; it exerts a torque onto the substrate. In liquids, both axes of rotation are slightly displaced from their ideal positions. Characteristic for spectroscopy, the two modes do not couple to the mechanical excitation equally well. The degree of coupling is quantified by an oscillator strength. Because the rocking mode mostly exerts a torque (rather than a tangential force, its coupling to the resonator's tangential motion is weak; the oscillator strength consequently is small. Recent experiments on surface-adsorbed colloidal spheres can be explained by the mode of vibration being of the rocking type.

  1. Energy Transport between Hole Gas and Crystal Lattice in Diluted Magnetic Semiconductor

    OpenAIRE

    Kivioja, J. M.; Prunnila, M.; Novikov, S.; Kuivalainen, P.; Ahopelto, J.

    2006-01-01

    The temperature dependent energy transfer rate between charge carriers and lattice has been experimentally investigated in ferromagnetic semiconductors. Studied 100 nm thick low-temperature MBE grown Mn_{x}Ga_{1-x}As samples had manganese concentrations x=3.7 % and 4.0 %. Curie temperatures estimated from temperatures of peak resistivities were 60 K and 62 K, respectively.

  2. A methodology to determine the elastic moduli of crystals by matching experimental and simulated lattice strain pole figures using discrete harmonics

    Energy Technology Data Exchange (ETDEWEB)

    Wielewski, Euan J.; Boyce, Donald; Park, Jun-Sang; Miller, M P; Dawson, Paul

    2017-03-01

    Determining reliable single crystal material parameters for complex polycrystalline materials is a significant challenge for the materials community. In this work, a novel methodology for determining those parameters is outlined and successfully applied to the titanium alloy, Ti-6Al-4V. Utilizing the results from a lattice strain pole figure experiment conducted at the Cornell High Energy Synchrotron Source, an iterative approach is used to optimize the single crystal elastic moduli by comparing experimental and simulated lattice strain pole figures at discrete load steps during a uniaxial tensile test. Due to the large number of unique measurements taken during the experiments, comparisons were made by using the discrete spherical harmonic modes of both the experimental and simulated lattice strain pole figures, allowing the complete pole figures to be used to determine the single crystal elastic moduli. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  3. Lattice constant and hardness of InSb:Bi bulk crystals grown by vertical directional solidification

    Science.gov (United States)

    Maske, Dilip; Deshpande, Manisha; Choudhary, Rashmi; Gadkari, Dattatray

    2016-05-01

    Ingots of the Bi doped InSb (InSb1-xBix) bulk semiconductor crystals were grown by specially designed Vertical Directional Solidification (VDS) technique. Substrates of seven crystals grown with various composition values of x (0 ≤ x 0.05.

  4. Molecular morphology and crystallization in the quantum limit

    DEFF Research Database (Denmark)

    Bohr, Jakob

    2002-01-01

    The effects of phonons on crystallization and crystal morphology are investigated. It is shown that the commensuration of the lattice vibrations with the lattice will favor certain crystal morphologies. Vibrational effects can also be important for the molecular structure of chain molecules...... protein are estimated to differ by several electron volts. For a biomolecule, such energy is significant and may contribute to cold denaturing as seen for proteins. This is consistent with the empirical observation that cold denaturation is exothermic and hot denaturation endothermic....

  5. Single crystal, vibrational and computational studies of Theophylline (a bronchodilator drug) and its chloride salt

    Science.gov (United States)

    Mary Novena, L.; Suresh Kumar, S.; Athimoolam, S.; Saminathan, K.; Sridhar, B.

    2017-04-01

    The crystal structure of Theophylline (TH) and Theophyillinium chloride monohydrate (THC) and its complete molecular structure analysis on theoretical and experimental methods is reported here. The hydrogen bonding studies were carried out as a special note of the present work. The electron density analyses of the compounds were also analyzed in view of the intermolecular interactions. Moreover, it is an ever first quantum chemical report of this drug (TH) and its chloride salt. In TH crystal, the water molecule connects the Theophylline molecules through Osbnd H⋯N hydrogen bond forming discrete D22(7) motif and dimeric ring R22(10) motif through Nsbnd H⋯O hydrogen bond. In THC, the two classical (Nsbnd H⋯O, Nsbnd H⋯Cl) and one non-classical (Csbnd H⋯O) hydrogen bonds produce two pentameric chain C55 (16) and C55(17) motifs. These two chain motifs are interconnected by Osbnd H⋯O hydrogen bond and cross linked by Nsbnd H⋯Cl and Osbnd H⋯Cl hydrogen bonds to produce octametric ring R88(27) and R88(28) motifs. The solubility test is carried out to enhance the drug solubility and the therapeutic effectiveness of the drug. Experimentally obtained vibrational wavenumbers are compared with the spectra obtained theoretically for both the compound. The strong intensity bands and the shifting of bands due to intermolecular hydrogen bonds are also investigated. The Mulliken atomic charges, HOMO-LUMO and thermodynamic properties are calculated using Density Functional Theory (DFT) and Hartree-Fock Theory (HF) using 6-311++G(d,p) basis set.

  6. 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.

  7. The interaction of organic adsorbate vibrations with substrate lattice waves in methyl-Si(111)-(1 × 1).

    Science.gov (United States)

    Brown, Ryan D; Hund, Zachary M; Campi, Davide; O'Leary, Leslie E; Lewis, Nathan S; Bernasconi, M; Benedek, G; Sibener, S J

    2014-07-14

    A combined helium atom scattering and density functional perturbation theory study has been performed to elucidate the surface phonon dispersion relations for both the CH3-Si(111)-(1 × 1) and CD3-Si(111)-(1 × 1) surfaces. The combination of experimental and theoretical methods has allowed characterization of the interactions between the low energy vibrations of the adsorbate and the lattice waves of the underlying substrate, as well as characterization of the interactions between neighboring methyl groups, across the entire wavevector resolved vibrational energy spectrum of each system. The Rayleigh wave was found to hybridize with the surface rocking libration near the surface Brillouin zone edge at both the M̄-point and K̄-point. The calculations indicated that the range of possible energies for the potential barrier to the methyl rotation about the Si-C axis is sufficient to prevent the free rotation of the methyl groups at a room temperature interface. The density functional perturbation theory calculations revealed several other surface phonons that experienced mode-splitting arising from the mutual interaction of adjacent methyl groups. The theory identified a Lucas pair that exists just below the silicon optical bands. For both the CH3- and CD3-terminated Si(111) surfaces, the deformations of the methyl groups were examined and compared to previous experimental and theoretical work on the nature of the surface vibrations. The calculations indicated a splitting of the asymmetric deformation of the methyl group near the zone edges due to steric interactions of adjacent methyl groups. The observed shifts in vibrational energies of the -CD3 groups were consistent with the expected effect of isotopic substitution in this system.

  8. Honeycomb-Lattice Heisenberg-Kitaev Model in a Magnetic Field: Spin Canting, Metamagnetism, and Vortex Crystals

    Science.gov (United States)

    Janssen, Lukas; Andrade, Eric C.; Vojta, Matthias

    2016-12-01

    The Heisenberg-Kitaev model is a paradigmatic model to describe the magnetism in honeycomb-lattice Mott insulators with strong spin-orbit coupling, such as A2IrO3 (A =Na , Li ) and α -RuCl3 . Here, we study in detail the physics of the Heisenberg-Kitaev model in an external magnetic field. Using a combination of Monte Carlo simulations and spin-wave theory, we map out the classical phase diagram for different directions of the magnetic field. Broken SU(2) spin symmetry renders the magnetization process rather complex, with sequences of phases and metamagnetic transitions. In particular, we find various large-unit-cell and multi-Q phases including a vortex-crystal phase for a field in the [111 ] direction. We also discuss quantum corrections in the high-field phase.

  9. Engineering the near-field imaging of a rectangular-lattice photonic-crystal slab in the second band

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Imaging properties of a two-dimensional rectangular-lattice photonic crystal (PC) slab consisting of air holes immersed in a dielectric are studied in this work. The field patterns of electromagnetic waves radiated from a point source through the PC slab are calculated with the finite-difference time-domain method. Comparing the field patterns with the corresponding equifrequency-surface contours simulated by the plane-wave expansion method, we find that an excellent-quality near-field image may be formed through the PC slab by the mechanisms of the simultaneous action of the self-collimation effect and the negative-refraction effect. Near-field imaging may be obtained within two different frequency regions in two vertical directions of the PC slab.

  10. Nuclear Spin-Lattice Relaxation of Single Crystal Sr{sub 14}Cu{sub 24}O{sub 41}

    Energy Technology Data Exchange (ETDEWEB)

    Ohsugi, S., E-mail: ohsugi@cit.sangitan.ac.jp [College of Industrial Technology, Department of Electrical Engineering and Electronics (Japan); Matsumoto, S. [National Institute for Materials Science, Tsukuba Magnet Laboratory (Japan); Kitaoka, Y. [Osaka University, Department of Physical Science, Graduate School of Engineering Science (Japan); Matsuda, M. [Japan Atomic Energy Research Institute, Advanced Science Research Center (Japan); Uehara, M. [Aoyama-Gakuin University, Department of Physics (Japan); Nagata, T. [Ochanomizu University, Department of Physics (Japan); Akimitsu, J. [Aoyama-Gakuin University, Department of Physics (Japan)

    2004-12-15

    Nuclear spin-lattice relaxation rate T{sub 1}{sup -1} has been measured for the ladder sites of two single crystals Sr{sub 14}Cu{sub 24}O{sub 41} (Sr14-A,B) by {sup 63}Cu NMR/NQR. The hole localization around 100 K appears as a peak in the T variation of T{sub 1}{sup -1}(NQR). On the other hand, it is suppressed in the T{sub 1}{sup -1} (NMR) data under the magnetic field H {approx} 11 T, and a new peak appears around 20 K. T{sub 1}{sup -1}(NMR) around the peak is more enlarged for Sr14-B than for Sr14-A. Hence, holes on the ladders of Sr14-B tend to be more localized. This is considered to be an origin for the occurrence of the magnetic order in Sr14-B under H {approx} 11 T.

  11. Engineering the near-field imaging of a rectangular-lattice photonic-crystal slab in the second band

    Institute of Scientific and Technical Information of China (English)

    FENG Shuai; AO Ling; WANG YiQuan

    2009-01-01

    Imaging properties of a two-dimensional rectangular-lattice photonic crystal (PC) slab consisting of air holes immersed in a dielectric are studied in this work. The field patterns of electromagnetic waves radiated from a point source through the PC slab are calculated with the finite-difference time-domain method. Comparing the field patterns with the corresponding equifrequency-surface contours simu-lated by the plane-wave expansion method, we find that an excellent-quality near-field image may be formed through the PC slab by the mechanisms of the simultaneous action of the self-collimation effect and the negative-refraction effect. Near-field imaging may be obtained within two different frequency regions in two vertical directions of the PC slab.

  12. Mie-Grüneisen Equation of State Based on the Physical Mechanics Analysis of Three-Dimensional Lattice Thermal Vibration%基于晶体三维点阵热振动物理力学分析的Mie-Grüneisen状态方程

    Institute of Scientific and Technical Information of China (English)

    李晓杰; 闫鸿浩; 王小红; 王宇新; 孙明

    2014-01-01

    According to crystal lattice structures,a three-dimensional lattice physical mechanics model in constant volume state was built up to study the atom thermal vibration.The equation of thermal energy and external force on the thermal vibrating lattice was deduced absolutely from the principle of mechanical vibration.By introducing macroscopic physical statics into microscopic atomic thermal vibration equation,Mie-Grüneisen equation of state for solids and the formula of Grüneisen parameter were deduced directly from the physical mechanical model.Finally,based on the arrangement of atoms in simple cubic,face-centered cubic,body-centered cubic,diamond cubic and close-packed hexagonal crystal,it was proved that the Grüneisen parameters of these symmetrical crystals can be expressed in a uniform formula,irrelevant to their actual arrangement of atoms.%根据晶体结构建立了三维定容热振动的微观物理力学模型,由力学方程推导出了点阵热振动能量与外力的微观热振动的力学关系。在微观热振动关系中引入宏观统计物理量,直接从物理力学模型得到了Mie-Grüneisen固体状态方程和 Grüneisen系数的表达式。根据晶体结构中的原子排列规律,对简单立方、面心立方、体心立方、金刚石立方晶体和理想密排六方晶体的Grüneisen系数的表达式进行了证明。结果表明,这些对称性晶体结构的 Grüneisen系数与冷压具有统一的微分关系,与晶体结构无关。

  13. Polymer lattices as mechanically tunable 3-dimensional photonic crystals operating in the infrared

    Energy Technology Data Exchange (ETDEWEB)

    Chernow, V. F., E-mail: vchernow@caltech.edu [Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California 91125 (United States); Alaeian, H. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Dionne, J. A. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Greer, J. R. [Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California 91125 (United States); The Kavli Nanoscience Institute, California Institute of Technology, Pasadena, California 91125 (United States)

    2015-09-07

    Broadly tunable photonic crystals in the near- to mid-infrared region could find use in spectroscopy, non-invasive medical diagnosis, chemical and biological sensing, and military applications, but so far have not been widely realized. We report the fabrication and characterization of three-dimensional tunable photonic crystals composed of polymer nanolattices with an octahedron unit-cell geometry. These photonic crystals exhibit a strong peak in reflection in the mid-infrared that shifts substantially and reversibly with application of compressive uniaxial strain. A strain of ∼40% results in a 2.2 μm wavelength shift in the pseudo-stop band, from 7.3 μm for the as-fabricated nanolattice to 5.1 μm when strained. We found a linear relationship between the overall compressive strain in the photonic crystal and the resulting stopband shift, with a ∼50 nm blueshift in the reflection peak position per percent increase in strain. These results suggest that architected nanolattices can serve as efficient three-dimensional mechanically tunable photonic crystals, providing a foundation for new opto-mechanical components and devices across infrared and possibly visible frequencies.

  14. Lattice vibrations of the superconducting oxide spinels (Li, Mg){sub 1+x}Ti{sub 2-x}O{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Green, M.A.; Dalton, M.; Day, P. [Royal Institution of Great Britain, 21 Albemarle Street, London W1X 4BS (United Kingdom); Prassides, K. [Royal Institution of Great Britain, 21 Albemarle Street, London W1X 4BS (United Kingdom); School of Chemistry, Physics and Environmental Science, Sussex University, Falmer, Brighton BN1 9QJ (United Kingdom); Neumann, D.A. [NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)

    1997-12-08

    The lattice vibrational spectra of the spinel phases, Li{sub 1+x}Ti{sub 2-x}O{sub 4} (x=0, 0.33) and Li{sub 1-y}Mg{sub y}Ti{sub 2}O{sub 4} (y = 0.1, 0.3) (space group Fd3-barm), have been measured as a function of temperature and composition by neutron inelastic scattering. Calculations of phonon densities of states (PDOSs) using interatomic potentials were performed and compared with the experimental data. Extensive phonon softening and hardening are observed on Li and Mg substitution throughout the energy range 10-100 MeV and are discussed in terms of electron - phonon coupling and its relevance to superconductivity. The observed PDOSs show no change on cooling through the superconducting transition temperature, T{sub c}. (author)

  15. A novel tetraarylpyrene host: Conformation-dependent inclusion of guest molecules in the crystal lattice

    Indian Academy of Sciences (India)

    Palani Natarajan; Paloth Venugopalan; Jarugu Narasimha Moorthy

    2010-09-01

    Tetrakis(2,6-dimethyl-4-acetoxyphenyl)pyrene H2 containing flexible acetate functionalities at the para positions of sterically-hindered and rigid aryl rings functions as an inclusion host system. Depending on the orientations of the acetate functionalities, a variety of conformers may indeed be expected. A limited number of the crystal structures of the inclusions compounds of H2 reveal that one indeed observes 2 different conformations for the host based on the orientations of the acetate functionalities. The inclusion compound of H2 with benzene guest molecules is particularly appealing in terms of how the latter are held in trough domains of the host by weak C−H$\\cdots$O and C−H$\\cdots$ hydrogen bonds. More experimentation and analyses of crystal structures of such systems is expected to lead to better insights toward realizing multicomponent molecular crystals in a rational manner.

  16. Design of a Photonic-Crystal Channel-Drop Filter Based on the Two-Dimensional Triangular-Lattice Hole Structure

    Institute of Scientific and Technical Information of China (English)

    Kyu; Hwan; Hwang; G.; Hugh; Song; Chanmook; Lim; Soan; Kim; Kyung-Won; Chun; Mahn; Yong; Park

    2003-01-01

    A channel-drop filter has been designed based on the two-dimensional triangular-lattice hole photonic-crystal structure, which consists of two line defects and two point defects, by a two-dimensional finite-difference time-domain simulation.

  17. Analysis of the crystal lattice instability for cage–cluster systems using the superatom model

    Energy Technology Data Exchange (ETDEWEB)

    Serebrennikov, D. A., E-mail: dserebrennikov@innopark.kantiana.ru, E-mail: dimafania@mail.ru; Clementyev, E. S. [I. Kant Baltic Federal University, “Functional Nanomaterials” Scientific–Educational Center (Russian Federation); Alekseev, P. A. [“Kurchatov Institute” National Research Center (Russian Federation)

    2016-09-15

    We have investigated the lattice dynamics for a number of rare-earth hexaborides based on the superatom model within which the boron octahedron is substituted by one superatom with a mass equal to the mass of six boron atoms. Phenomenological models have been constructed for the acoustic and lowenergy optical phonon modes in RB{sub 6} (R = La, Gd, Tb, Dy) compounds. Using DyB{sub 6} as an example, we have studied the anomalous softening of longitudinal acoustic phonons in several crystallographic directions, an effect that is also typical of GdB{sub 6} and TbB{sub 6}. The softening of the acoustic branches is shown to be achieved through the introduction of negative interatomic force constants between rare-earth ions. We discuss the structural instability of hexaborides based on 4f elements, the role of valence instability in the lattice dynamics, and the influence of the number of f electrons on the degree of softening of phonon modes.

  18. Effect of size discrepancy of. gamma. - and. gamma. '-phases crystal lattice parameters on heat resisting dispersion hardening nickel alloys

    Energy Technology Data Exchange (ETDEWEB)

    Petrushin, N.V.; Ignatova, I.A.; Logunov, A.V.; Samojlov, A.I.; Razumovskij, I.M.

    Effect of Cr, Co, Nb and W alloying elements on crystal lattice parameters of ..gamma.. ahd ..gamma..' phases in Ni-Cr-Co-W-Al-Ti- Nb-Hf alloys and on their dimensional misfit at 293 and 1173 K is studied. Alloying at which alloys have the parameter of ..gamma..-solid solution lattice less than that of ..gamma..'-phase results in low heat-resistant properties and in considerable difference of coefficients of thermal expansion of the phases. Definite positive misfit of ..gamma..- and ..gamma..'-phase lattices and a low temperature gradient are the conditions of high heat resistance of complex-alloyed nickel alloys. Possible mechanisms of lattice misfit effect on strength and coalescence kinetics of the second phase in heterogeneous alloys at high temperatures are discussed.

  19. Combined measurement of surface, grain boundary and lattice diffusion coefficients on olivine bi-crystals

    Science.gov (United States)

    Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes

    2014-05-01

    Diffusion along interface and grain boundaries provides an efficient pathway and may control chemical transport in rocks as well as their mechanical strength. Besides the significant relevance of these diffusion processes for various geologic processes, experimental data are still very limited (e.g., Dohmen & Milke, 2010). Most of these data were measured using polycrystalline materials and the formalism of LeClaire (1951) to fit integrated concentration depth profiles. To correctly apply this formalism, certain boundary conditions of the diffusion problem need to be fulfilled, e.g., surface diffusion is ignored, and furthermore the lattice diffusion coefficient has to be known from other studies or is an additional fitting parameter, which produces some ambiguity in the derived grain boundary diffusion coefficients. We developed an experimental setup where we can measure the lattice and grain boundary diffusion coefficients simultaneously but independent and demonstrate the relevance of surface diffusion for typical grain boundary diffusion experiments. We performed Mg2SiO4 bicrystal diffusion experiments, where a single grain boundary is covered by a thin-film of pure Ni2SiO4 acting as diffusant source, produced by pulsed laser deposition. The investigated grain boundary is a 60° (011)/[100]. This specific grain boundary configuration was modeled using molecular dynamics for comparison with the experimental observations in the transmission electron microscope (TEM). Both, experiment and model are in good agreement regarding the misorientation, whereas there are still some disagreements regarding the strain fields along the grain boundary that are of outmost importance for the strengths of the material. The subsequent diffusion experiments were carried out in the temperature range between 800° and 1450° C. The inter diffusion profiles were measured using the TEMs energy dispersive x-ray spectrometer standardized using the Cliff-Lorimer equation and EMPA

  20. Site preferences and lattice vibrations of Nd6Fe13 - x TxSi (T = Co, Ni)

    Science.gov (United States)

    Huang, Tian-Shun; Cheng, Hai-Xia; Wang, Xiao-Xu; Zhang, Zhen-Feng; An, Zhi-Wei; Zhang, Guo-Hua

    2015-10-01

    The site preferences of the rare earth intermetallics Nd6Fe13-xTxSi (T = Co, Ni) are investigated by using interatomic pair potentials which are converted from a lattice-inversion method. Calculation shows that the order of the site preference of Co is 4d, 16k, 16l1, and 16l2 and that of Ni is 16l2, 16l1, 16k, and 4d in Nd6Fe13-xTxSi. Calculated lattice and positional parameters are found to agree with those reported in the literature. Furthermore, the phonon density of states for Nd6Fe13-xTxSi is also evaluated, and a qualitative analysis featuring the coordination and the relevant potentials is carried out. Project supported by the National Natural Science Foundation of China (Grant Nos. 11272048 and 50971024) and the National Key Basic Research Program of China (Grant No. 2011CB606401).

  1. Learning about the Unit Cell and Crystal Lattice with Computerized Simulations and Games: A Pilot Study

    Science.gov (United States)

    Luealamai, Sutha; Panijpan, Bhinyo

    2012-01-01

    The authors have developed a computer-based learning module on the unit cell of various types of crystal. The module has two components: the virtual unit cell (VUC) part and the subsequent unit cell hunter part. The VUC is a virtual reality simulation for students to actively arrive at the unit cell from exploring, from a broad view, the crystal…

  2. Learning about the Unit Cell and Crystal Lattice with Computerized Simulations and Games: A Pilot Study

    Science.gov (United States)

    Luealamai, Sutha; Panijpan, Bhinyo

    2012-01-01

    The authors have developed a computer-based learning module on the unit cell of various types of crystal. The module has two components: the virtual unit cell (VUC) part and the subsequent unit cell hunter part. The VUC is a virtual reality simulation for students to actively arrive at the unit cell from exploring, from a broad view, the crystal…

  3. Non-spherical voids and lattice reorientation patterning in a shock-loaded Al single crystal

    DEFF Research Database (Denmark)

    Hong, Chuanshi; Fæster, Søren; Hansen, Niels

    2017-01-01

    An Al single crystal shock loaded in the direction and captured at incipient spallation was examined by combining X-ray tomography, electron backscatter diffraction on a scanning electron microscope, and transmission electron microscopy (TEM). Octahedral voids with {1 1 1} faces were...

  4. Crystal lattice dependency of the free radicals found in irradiated glycine

    NARCIS (Netherlands)

    Bie, M.J.A. de; Braams, R.

    1969-01-01

    The EPR spectra, and hence the stable free radicals, are different for the - or γ-irradiated α-, β- and γ-crystal forms of polycrystalline glycone. Therefore comparisons of the trideutero-glycine EPR spectrum with the EPR spectra of non-deuterated glycine are open to question

  5. Terahertz lattice dynamics of the potassium rare-earth binary molybdates

    Science.gov (United States)

    Poperezhai, S.; Gogoi, P.; Zubenko, N.; Kutko, K.; Kutko, V. I.; Kovalev, A. S.; Kamenskyi, D.

    2017-03-01

    We report a systematic study of low-energy lattice vibrations in the layered systems KY(MoO4)2, KDy(MoO4)2, KEr(MoO4)2, and KTm(MoO4)2. A layered crystal structure and low symmetry of the local environment of the rare-earth ion cause the appearance of vibrational and electronic excitations in Terahertz frequencies. The interaction between these excitations leads to sophisticated dynamical properties, including non-linear effects in paramagnetic resonance spectra. The THz study in magnetic field allows for the clear distinction between lattice vibrations and electronic excitations. We measured the THz transmission spectra and show that the low energy lattice vibrations in binary molybdates can be well described within the quasi-one-dimensional model. The developed model describes the measured far-infrared spectra, and results of our calculations agree with previous Raman and ultrasound studies.

  6. Crystal lattice of martensite and the reserve of recoverable strain of thermally and thermomechanically treated Ti-Ni shape-memory alloys

    Science.gov (United States)

    Prokoshkin, S. D.; Korotitskiy, A. V.; Brailovski, V.; Inaekyan, K. E.; Dubinskiy, S. M.

    2011-08-01

    X-ray diffraction has been used to study shape-memory alloys of composition Ti-(49.73-51.05 at %) Ni subjected to quenching and thermomechanical treatment (TMT) by the scheme "cold deformation ( e = 0.3-1.9) + postdeformation annealing (200-500°C) to provide different defectness of the parent B2 austenite. For the quenched alloys, the concentration dependences of the lattice parameters of the B19' martensite, maximum lattice strain upon martensitic transformation, the crystallographic orientation of the lattice in single crystals, and the reserve of recoverable strain in polycrystals have been determined. The lattice parameters of martensite formed from polygonized, i.e., nanosubgranular, or from nanocrystalline austenite differ from the corresponding parameters of quenched martensite formed from recrystallized austenite, and their difference increases with increasing defectness of the parent-austenite lattice. An increase in the defectness of the austenite lattice is accompanied by a decrease in the reserve of recoverable strain. The deformation of the existing martensite or the formation of stress-assisted martensite under the anisotropic action of external stresses changes the interplanar spacing and the thermal expansion coefficient in different crystallographic directions but does not affect the averaged lattice parameters near the M s- M f interval and the reserve of recoverable strain.

  7. Ultrasonic characterization of Cu-Al-Ni single crystals lattice stability in the vicinity of the phase transition.

    Science.gov (United States)

    Landa, Michal; Novák, Václav; Sedlák, Petr; Sittner, Petr

    2004-04-01

    Measurements of elastic constants of the austenite phase when approaching the phase transformation either upon cooling or stressing is of the crucial interest for the shape memory alloy field. Acoustic properties (wave velocity and also attenuation changes) of the Cu-Al-Ni single crystal were investigated in situ during stress-induced martensitic transformation at constant (room) temperature. The parent austenite cubic lattice of the Cu-Al-Ni exhibits very high elastic anisotropy (anisotropy factor A approximately 12). The measurements were made using nine combinations of (i) applied uniaxial compression in a given crystal direction, (ii) the wave propagation and (iii) polarization vectors. The chosen configurations are sufficient for evaluation of all independent third order elastic constants (TOEC). The longitudinal modes were also measured by the immersion technique, using the transducer pair in a water tank installed on the testing machine. The device works as "a ultrasonic extensometer" measuring a transverse strain of the specimen. The dependencies of both natural and initial wave velocities on the applied stress may be evaluated. Three elastic constants of the stress-induced martensite were determined. The elastic properties were found to vary with the increasing stress above the Ms transformation temperature, which is interpreted as a precursor for the martensitic transformation. The onset of the transformation was additionally identified from the acoustic emission measurement.

  8. Development and Application of New Solid-State Models for Low-Energy Vibrations, Lattice Defects, Entropies of Mixing, and Magnetic Properties

    Science.gov (United States)

    Schliesser, Jacob M.

    Low-temperature heat capacity data contain information on the physical properties of materials, and new models continue to be developed to aid in the analysis and interpretation of heat capacity data into physically meaningful properties. This work presents the development of two such models and their application to real material systems. Equations describing low-energy vibrational modes with a gap in the density of states (DOS) have been derived and tested on several material systems with known gaps in the DOS, and the origins of such gaps in the DOS are presented. Lattice vacancies have been shown to produce a two-level system that can be modeled with a sum of low-energy Schottky anomalies that produce an overall linear dependence on temperature in the low-temperature heat capacity data. These two models for gaps in the vibrational DOS and the relationship between a linear heat capacity and lattice vacancies and many well-known models have been applied to several systems of materials to test their validity and applicability as well as provide greater information on the systems themselves. A series of bulk and nanoscale Mn-Fe and Co-Fe spinel solid solutions were analyzed using the entropies derived from heat capacity data, and excess entropies of mixing were determined. These entropies show that changes in valence, cation distribution, bonding, and the microstructure between the mixing ions is non-ideal, especially in the nanoparticles. The heat capacity data of ten Al doped TiO2 anatase nanoparticle samples have also been analyzed to show that the Al3+ dopant ions form small regions of short-range order, similar to a glass, within the TiO2 particles, while the overall structure of TiO2 remains unchanged. This has been supported by X-ray diffraction (XRD) and electron energy-loss spectroscopy and provides new insights to the synthesis and characterization of doped materials. The final investigation examines nanocrystalline CuO using heat capacities, magnetization

  9. Etching efficiency of tracks differently oriented with respect to the symmetry axis of a crystal lattice of olivine monocrystals from Marjalahti pallasite

    Energy Technology Data Exchange (ETDEWEB)

    Bagulya, A.V.; Goncharova, L.A. [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Ivliev, A.I., E-mail: cosmo@geokhi.r [Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygina str., 19, 119991 (Russian Federation); Kalinina, G.V., E-mail: ugeochem@geochem.home.chg.r [Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygina str., 19, 119991 (Russian Federation); Kashkarov, L.L. [Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygina str., 19, 119991 (Russian Federation); Konovalova, N.S.; Okat' eva, N.M. [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Polukhina, N.G., E-mail: poluhina@sci.lebedev.r [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Roussetski, A.S.; Starkov, N.I.; Tsarev, V.A. [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Vladymyrov, M.S., E-mail: neworld@itep.r [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation)

    2009-10-15

    The results of measurements of the major track parameters for tracks formed by the accelerated {sup 131}Xe (E = 1.5 GeV) nuclei in individual olivine grains from the Marjalahti pallasite are presented. For each of ten treated crystals, the structure and the main crystal lattice symmetry axis were determined by the X-ray diffraction analysis. The basic track parameters (etching rate V{sub TR} and etched length L) were shown to be independent of the angle between the monocrystal main symmetry axis for each examined crystal and the direction of the accelerated nucleus beam.

  10. Short wavelength (UV + VIS) guidance in kagomé lattice hollow core photonic crystal fibre

    Science.gov (United States)

    Février, Sébastien; Beaudou, Benoît

    2010-04-01

    Hollow-core microstructured fibres are designed for the short wavelength domains, either visible or ultra-violet ones. The experimental results confirm that kagomé-lattice antiresonant fibres are good candidate for this purpose. Thorough numerical modelling is carried out in order to determine the physical causes responsible for the loss level observed. From these computations the following conclusions are drawn: (i) the sole antiresonant core surround dictates the location of the transmission windows and (ii) the cladding bridges are sources of extra leakage from the core to the surrounding solid cladding. A straightforward model is therefore devised to determine accurately the loss level in this kind of structure by quasi-analytical calculus.

  11. Designing an ultra negative dispersion Photonic Crystal Fiber (PCFs) with square lattice geometry

    CERN Document Server

    Maji, Partha Sona

    2015-01-01

    In this article we have theoretically investigated the dispersion characteristics of dual-core PCF, based on square-lattice geometry by varying different parameters. The fiber exhibits a very large negative dispersion because of rapid slope change of the refractive indices at the coupling wavelength between the inner core and outer core. The dependence of different geometrical parameters namely hole-to-hole spacing (pitch) and different air-hole diameter (d) was investigated in detail. By proper adjustment of the available parameters, a high negative dispersion value of -47,500 ps/nm/km has been achieved around the wavelength of 1550nm. Our proposed fiber will be an excellent device for dispersion compensation in long-haul data transmission as being thousand times more than the available DCFs.

  12. Molecular motions in thermotropic liquid crystals studied by NMR spin-lattice relaxation

    Energy Technology Data Exchange (ETDEWEB)

    Zamar, R.C.; Gonzalez, C.E.; Mensio, O. [Cordoba Univ. Nacional (Argentina). Facultad de Matematica, Astronomia y Fisica

    1998-12-01

    Nuclear magnetic resonance relaxation experiments with field cycling techniques proved to be a valuable tool for studying molecular motions in liquid crystals, allowing a very broad Larmor frequency variation, sufficient to separate the cooperative motions from the liquid like molecular diffusion. In new experiments combining NMR field cycling with the Jeener-Broekaert order-transfer pulse sequence, it is possible to measure the dipolar order relaxation time (T{sub 1D}), in addition to the conventional Zeeman relaxation time (T{sub 1Z}) in a frequency range of several decades. When applying this technique to nematic thermotropic liquid crystals, T{sub 1D} showed to depend almost exclusively on the order fluctuation of the director mechanism in the whole frequency range. This unique characteristic of T{sub 1D} makes dipolar order relaxation experiments specially useful for studying the frequency and temperature dependence of the spectral properties of the collective motions. (author)

  13. Acoustic band gaps of the woodpile sonic crystal with the simple cubic lattice

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Liang-Yu; Chen, Lien-Wen, E-mail: chenlw@mail.ncku.edu.t [Department of Mechanical Engineering, National Cheng Kung University, Tainan 70101, Taiwan (China)

    2011-02-02

    This study theoretically and experimentally investigates the acoustic band gap of a three-dimensional woodpile sonic crystal. Such crystals are built by blocks or rods that are orthogonally stacked together. The adjacent layers are perpendicular to each other. The woodpile structure is embedded in air background. Their band structures and transmission spectra are calculated using the finite element method with a periodic boundary condition. The dependence of the band gap on the width of the stacked rods is discussed. The deaf bands in the band structure are observed by comparing with the calculated transmission spectra. The experimental transmission spectra for the {Gamma}-X and {Gamma}-X' directions are also presented. The calculated results are compared with the experimental results.

  14. Temperature-Induced Lattice Relaxation of Perovskite Crystal Enhances Optoelectronic Properties and Solar Cell Performance

    KAUST Repository

    Banavoth, Murali

    2016-12-14

    Hybrid organic-inorganic perovskite crystals have recently become one of the most important classes of photoactive materials in the solar cell and optoelectronic communities. Albeit improvements have focused on state-of-the-art technology including various fabrication methods, device architectures, and surface passivation, progress is yet to be made in understanding the actual operational temperature on the electronic properties and the device performances. Therefore, the substantial effect of temperature on the optoelectronic properties, charge separation, charge recombination dynamics, and photoconversion efficiency are explored. The results clearly demonstrated a significant enhancement in the carrier mobility, photocurrent, charge carrier lifetime, and solar cell performance in the 60 ± 5 °C temperature range. In this temperature range, perovskite crystal exhibits a highly symmetrical relaxed cubic structure with well-aligned domains that are perpendicular to a principal axis, thereby remarkably improving the device operation. This finding provides a new key variable component and paves the way toward using perovskite crystals in highly efficient photovoltaic cells.

  15. Vibrational properties and phonon anharmonicity in ZnS{sub 1−x}Se{sub x}: Inelastic neutron scattering, Raman scattering, X-ray diffraction measurements and lattice dynamical studies

    Energy Technology Data Exchange (ETDEWEB)

    Basak, Tista, E-mail: tistabasak1@gmail.com [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, Maharashtra (India); Rao, Mala N.; Chaplot, S.L.; Salke, Nilesh; Rao, Rekha [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, Maharashtra (India); Dhanasekaran, R. [Crystal Growth Centre, Anna University, SP Road, Chennai 600025 (India); Rajarajan, A.K. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, Maharashtra (India); Rols, S. [Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9, Grenoble (France); Mittal, R.; Jayakrishnan, V.B.; Sastry, P.U. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, Maharashtra (India)

    2014-01-15

    Inelastic neutron scattering, Raman and X-ray diffraction measurements coupled with lattice dynamical calculations (employing a semi-empirical transferable potential model) have been carried out to gain a detailed understanding of the peculiar vibrational spectrum exhibited by the mixed crystal ZnS{sub 1−x}Se{sub x}. Raman scattering measurements performed over a varying range of temperature (100–800 K) and pressure (up to 13 GPa) have confirmed that the additional mode observed in the spectra are visible over the entire range of temperature and pressure. Correlation of the individual motions of atoms (obtained from computed total and partial phonon density of states) with the inelastic neutron scattering measurements (carried out over the entire Brillouin zone) have then indicated that the existence of the additional mode in ZnS{sub 1−x}Se{sub x} is due to the vibrations of the Se atom being in resonance with that of the S atom. Further, it has been shown that the presence of this additional mode can be tuned by varying the mass of the atom at the Se site. In addition, an analysis of bond-length distribution with increasing Se concentration have elucidated that bond-length spread is not responsible for the presence of the additional mode. An analysis of the peak shifts of the Raman modes with temperature and pressure indicate that the anharmonicity of the vibrational modes increases with increasing compositional disorder. This is attributed to the fact that increasing Se concentration gives rise to a distribution of bond-lengths in ZnS{sub 1−x}Se{sub x}, which is responsible for this compositional disorder induced anharmonicity. Our computations have thus revealed that mass of the anion is responsible for the presence of additional mode while bond-length distribution gives rise to the existence of compositional disorder induced anharmonicity in ZnS{sub 1−x}Se{sub x}. Further, it is observed that the contribution of explicit anharmonicity to the total

  16. Lattice damage assessment and optical waveguide properties in LaAlO3 single crystal irradiated with swift Si ions

    Science.gov (United States)

    Liu, Y.; Crespillo, M. L.; Huang, Q.; Wang, T. J.; Liu, P.; Wang, X. L.

    2017-02-01

    As one of the representative ABO3 perovskite-structured oxides, lanthanum aluminate (LaAlO3) crystal has emerged as one of the most valuable functional-materials, and has attracted plenty of fundamental research and promising applications in recent years. Electronic, magnetic, optical and other properties of LaAlO3 strongly depend on its crystal structure, which could be strongly modified owing to the nuclear or electronic energy loss deposited in an ion irradiation environment and, therefore, significantly affecting the performance of LaAlO3-based devices. In this work, utilizing swift (tens of MeV) Si-ion irradiation, the damage behavior of LaAlO3 crystal induced by nuclear or electronic energy loss has been studied in detail utilizing complementary characterization techniques. Differing from other perovskite-structured crystals in which the electronic energy loss could lead to the formation of an amorphous region based on the thermal spike mechanism, in this case, intense electronic energy loss in LaAlO3 will not induce any obvious structural damage. The effects of ion irradiation on the mechanical properties, including hardness increase and elastic modulus decrease, have been confirmed. On the other hand, considering the potential applications of LaAlO3 in the field of integrated optoelectronics, the optical-waveguide properties of the irradiation region have been studied. The significant correspondence (symmetrical inversion) between the iWKB-reconstructed refractive-index profile and SRIM-simulated dpa profile further proves the effects (irradiation-damage production and refractive-index decrease) of nuclear energy loss during the swift-ion penetration process in LaAlO3 crystal. In the case of the rather-thick damage layer produced by swift-ion irradiation, obtaining a damage profile will be constrained owing to the analysis-depth limitation of the characterization techniques (RBS/channeling), and our analysis process (optical guided-mode measurement and

  17. Anharmonic OH vibrations in Mg(OH)2 (brucite): two-dimensional calculations and crystal-induced blueshift.

    Science.gov (United States)

    Hermansson, Kersti; Probst, Michael M; Gajewski, Grzegorz; Mitev, Pavlin D

    2009-12-28

    A two-dimensional quantum-mechanical vibrational model has been used to calculate the anharmonic OH vibrational frequencies in the layered Mg(OH)(2) (brucite) crystal. The underlying potential energy surface was generated by density functional theory (DFT) calculations. The resulting OH frequencies are upshifted (blueshifted) by about +75 cm(-1) with respect to the gas-phase OH frequency (+120 cm(-1) in experiments; the discrepancy is mainly due to inadequacies in the DFT and pseudopotential models). The Raman-IR split is about 50 cm(-1), both in the calculations and in experiments. We find that the blueshift phenomenon in brucite can qualitatively be explained by a parabolalike "OH frequency versus electric field" correlation curve pertaining to an OH(-) ion exposed to an electric field. We also find that it is primarily the neighbors within the Mg(OH)(2) layer that induce the blueshift while the interlayer interaction gives a smaller (and redshifting) contribution.

  18. Crystal structure, vibrational, spectral investigation, quantum chemical DFT calculations and thermal behavior of Diethyl [hydroxy (phenyl) methyl] phosphonate

    Science.gov (United States)

    Ouksel, Louiza; Chafaa, Salah; Bourzami, Riadh; Hamdouni, Noudjoud; Sebais, Miloud; Chafai, Nadjib

    2017-09-01

    Single Diethyl [hydroxy (phenyl) methyl] phosphonate (DHPMP) crystal with chemical formula C11H17O4P, was synthesized via the base-catalyzed Pudovik reaction and Lewis acid as catalyst. The results of SXRD analyzes indicate that this compound crystallizes into a mono-clinic system with space group P21/n symmetry and Z = 4. The crystal structure parameters are a = 9.293 Å, b = 8.103 Å, c = 17.542 Å, β = 95.329° and V = 1315.2 Å3, the structure displays one inter-molecular O-H⋯O hydrogen bonding. The UV-Visible absorption spectrum shows that the crystal exhibits a good optical transmission in the visible domain, and strong absorption in middle ultraviolet one. The vibrational frequencies of various functional groups present in DHPMP crystal have been deduced from FT-IR and FT-Raman spectra and then compared with theoretical values performed with DFT (B3LYP) method using 6-31G (p, d) basis sets. Chemical and thermodynamic parameters such as: ionization potential (I), electron affinity (A), hardness (σ), softness (η), electronegativity (χ) and electrophilicity index (ω), are also calculated using the same theoretical method. The thermal decomposition behavior of DHPMP, studied by using thermogravimetric analysis (TDG), shows a thermal stability until to 125 °C.

  19. Optical Absorption of Impurities and Defects in Semiconducting Crystals Electronic Absorption of Deep Centres and Vibrational Spectra

    CERN Document Server

    Pajot, Bernard

    2013-01-01

    This book outlines, with the help of several specific examples, the important role played by absorption spectroscopy in the investigation of deep-level centers introduced in semiconductors and insulators like diamond, silicon, germanium and gallium arsenide by high-energy irradiation, residual impurities, and defects produced during crystal growth. It also describes the crucial role played by vibrational spectroscopy to determine the atomic structure and symmetry of complexes associated with light impurities like hydrogen, carbon, nitrogen and oxygen, and as a tool for quantitative analysis of these elements in the materials.

  20. Effect of lattice disorder on the thermal conductivity of ZnBeSe, ZnMgSe and ZnBeMgSe crystals

    Energy Technology Data Exchange (ETDEWEB)

    Strzałkowski, K., E-mail: skaroll@fizyka.umk.pl

    2015-08-01

    Zn{sub 1−x−y}Be{sub x}Mg{sub y}Se mixed crystals investigated in this work were grown from the melt by the high pressure high temperature modified Bridgman method in the range of composition 0 < x,y < 0.33. Photopyroelectric (PPE) calorimetry in the back (BPPE) and front (FPPE) configuration was applied for thermal investigation of solid samples. The thermal diffusivity and effusivity of investigated crystals were derived from the experimental data. Since dynamic thermal parameters are connected with each other, thermal conductivity of the specimens was calculated from theoretical dependencies between them. The influence of the beryllium (x) and magnesium (y) content on thermal properties of these crystals have been presented and discussed. Order-disorder effects observed for these materials previously have been also taken into account. Finally, thermal diagrams, i.e. thermal conductivity versus composition were presented and discussed applying model given by Sadao Adachi. - Highlights: • Investigated II–VI crystals were obtained by a high pressure modified Bridgman method. • A complete thermal characterization of Zn{sub 1−x−y}Be{sub x}Mg{sub y}Se semiconductors was carried out. • The effect of lattice disorder on thermal properties was presented and discussed. • Obtained data were analyzed applying lattice thermal conductivity model. • Contribution to thermal resistivity arising from lattice disorder was calculated.

  1. Properties of localization in silicon-based lattice periodicity breaking photonic crystal waveguides

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Yuquan; Wang, Xiaofei; Wang, Yufang; Zhang, Guoquan; Fan, Wande; Cao, Xuewei, E-mail: xwcao@nankai.edu.cn [School of Physics, Nankai University, Tianjin, 300071 (China); Wu, Yuanbin [School of Physics, Nankai University, Tianjin, 300071 (China); Dip. di Fisica, Università di Roma “La Sapienza”, Piazzale Aldo Moro 5, I-00185 Roma (Italy); EDSFA, Université de Nice Sophia Antipolis, 06103 Nice (France)

    2013-11-15

    The light localization effects in silicon photonic crystal cavities at different disorder degrees have been studied using the finite difference time domain (FDTD) method in this paper. Numerical results showed that localization occurs and enhancement can be gained in the region of the cavity under certain conditions. The stabilities of the localization effects due to the structural perturbations have been investigated too. Detailed studies showed that when the degree of structural disorder is small(about 10%), the localization effects are stable, the maximum enhancement factor can reach 16.5 for incident wavelength of 785 nm and 23 for 850 nm in the cavity, with the degree of disorder about 8%. The equivalent diameter of the localized spot is almost constant at different disorder degrees, approximating to λ/7, which turned out to be independent on the structural perturbation.

  2. On the interplay between heavy-fermion and soft crystal field excitations in Kondo lattices

    Energy Technology Data Exchange (ETDEWEB)

    Kagan, Yu.; Kikoin, K.A.; Mishchenko, A.S. [Rossijskij Nauchnyj Tsentr ``Kurchatovskij Inst.``, Moscow (Russian Federation)

    1997-06-13

    On the grounds of the microscopic theory of heavy-fermion spin-liquids a novel description of low-energy excitation spectra in CeNiSn and related compounds is offered. The anomalous properties of orthorhombic CeNiSn and related materials are explained by the interplay between the fermi-type spinon excitations with the energy scale T{sup *}{approx}T{sub K} and the one-site crystal field excitations with the energy {Delta}{sub CF}

  3. Quantum computation in a one-dimensional crystal lattice with NMR force microscopy

    CERN Document Server

    Ladd, T D; Dana, A; Yamaguchi, F; Yamamoto, Y

    2000-01-01

    A proposal for a scalable, solid-state implementation of a quantum computer is presented. Qubits are fluorine nuclear spins in a solid crystal of fluorapatite [Ca_5 F(PO_4)_3] with resonant frequencies separated by a large field gradient. Quantum logic is accomplished using nuclear-nuclear dipolar couplings with decoupling and selective recoupling RF pulse sequences. Magnetic resonance force microscopy is used for readout. This proposal takes advantage of many of the successful aspects of solution NMR quantum computation, including ensemble measurement and long T_1, but it allows for more qubits and the potential for initialization. As many as 300 qubits can be implemented in the realistic laboratory extremes of T=10 mK and B_0=20 T with the existing sensitivity of force microscopy.

  4. Beta-alanine-oxalic acid (1:1) hemihydrate crystal: structure, 13C NMR and vibrational properties, protonation character.

    Science.gov (United States)

    Godzisz, D; Ilczyszyn, M; Ilczyszyn, M M

    2003-03-01

    The crystal structure of beta-alanine-oxalic acid (1:1) hemihydrate complex has been reinvestigated by X-ray diffraction method at 293 K. Formation of monoclinic crystal system belonging to C2/c space group and consisting of semi-oxalate chains, diprotonated beta-alanine dimers and water molecules bonded to both these units is confirmed. New results are obtained for distances in the carboxylic groups and hydrogen bonds. These structural observations are used for protonation degree monitoring on the carboxylic oxygen atoms. They are in accordance with our vibrational study. The 13C NMR spectra provide insights into the solid structure of this complex, character of its hydrogen bonds and the beta-alanine protonation.

  5. Regio-Regular Oligo and Poly(3-hexyl thiophene): Precise Structural Markers from the Vibrational Spectra of Oligomer Single Crystals.

    KAUST Repository

    Brambilla, Luigi

    2014-10-14

    © 2014 American Chemical Society. In this work, we report a comparative analysis of the infrared and Raman spectra of octa(3-hexylthiophene) (3HT)8, trideca(3-hexylthiophene) (3HT)13, and poly(3-hexylthiophene) P3HT recorded in various phases, namely, amorphous, semicrystalline, polycrystalline and single crystal. We have based our analysis on the spectra of the (3HT)8 single crystal (whose structure has been determined by selected area electron diffraction) taken as reference and on the results of DFT calculations and molecular vibrational dynamics. New and precise spectroscopic markers of the molecular structures show the existence of three phases, namely: hairy (phase 1), ordered (phase 2), and disordered/amorphous (phase 3). Conceptually, the identified markers can be used for the molecular structure analysis of other similar systems.

  6. The effects of annealing on the structural, optical, and vibrational properties of lattice-matched GaAsSbN/GaAs grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bharatan, S. [North Carolina A& T State University; Iyer, Prof Shanthi [North Carolina A& T State University; Nunna, K. [North Carolina A& T State University; Collis, W J [North Carolina A& T State University; Matney, K. [Bede Scientific Inc, Englewood, Colorado; Reppert, J. [Clemson University; Rao, A. M. [Clemson University; Kent, Paul R [ORNL

    2007-01-01

    The structural, optical, and vibrational properties of a GaAsSbN epilayer lattice matched to GaAs with a band gap of 1 eV have been investigated using a variety of characterization techniques. These layers have potential applications in GaAs based tandem solar cells that utilize the near infrared region of the solar spectrum. The epilayers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma nitrogen source. The Sb and N compositions of the nearly lattice-matched layers are 6.8% and 2.6%, respectively, as determined by high resolution x-ray diffraction and secondary ion mass spectroscopy (SIMS) analysis. The high crystalline quality of the layers is attested by the presence of well resolved Pendellosung fringes on a triple axis (004) x-ray scan and dynamical truncation rods observed on the corresponding (004) reciprocal space map. The effects of in situ annealing in As ambient and ex situ annealing in N ambient on the low temperature photoluminescence (PL) characteristics are discussed. Ex situ (in situ) annealed samples display an 8 K PL peak energy of 1 eV with a full width at half maximum of 18 meV (26 meV). Raman spectral analysis, the temperature dependence of the PL peak energy, and SIMS profiles indicate that outdiffusions of N and As are suppressed in the in situ annealed samples and improvement in Ga-N bonding is observed, leading to higher PL intensities in these samples. In addition, indirect evidence of atomic scale ordering has been observed. The stability of these structures appears to be dependent on the annealing conditions.

  7. Discrete breathers in crystals

    Science.gov (United States)

    Dmitriev, S. V.; Korznikova, E. A.; Baimova, Yu A.; Velarde, M. G.

    2016-05-01

    It is well known that periodic discrete defect-containing systems, in addition to traveling waves, support vibrational defect-localized modes. It turned out that if a periodic discrete system is nonlinear, it can support spatially localized vibrational modes as exact solutions even in the absence of defects. Since the nodes of the system are all on equal footing, it is only through the special choice of initial conditions that a group of nodes can be found on which such a mode, called a discrete breather (DB), will be excited. The DB frequency must be outside the frequency range of the small-amplitude traveling waves. Not resonating with and expending no energy on the excitation of traveling waves, a DB can theoretically conserve its vibrational energy forever provided no thermal vibrations or other perturbations are present. Crystals are nonlinear discrete systems, and the discovery in them of DBs was only a matter of time. It is well known that periodic discrete defect-containing systems support both traveling waves and vibrational defect-localized modes. It turns out that if a periodic discrete system is nonlinear, it can support spatially localized vibrational modes as exact solutions even in the absence of defects. Because the nodes of the system are all on equal footing, only a special choice of the initial conditions allows selecting a group of nodes on which such a mode, called a discrete breather (DB), can be excited. The DB frequency must be outside the frequency range of small-amplitude traveling waves. Not resonating with and expending no energy on the excitation of traveling waves, a DB can theoretically preserve its vibrational energy forever if no thermal vibrations or other perturbations are present. Crystals are nonlinear discrete systems, and the discovery of DBs in them was only a matter of time. Experimental studies of DBs encounter major technical difficulties, leaving atomistic computer simulations as the primary investigation tool. Despite

  8. Lattice damage and waveguide properties of medium- and high-energy C3+ ions-irradiated LaAlO3 crystals

    Science.gov (United States)

    Qiao, Mei; Wang, Tie-Jun; Song, Hong-Lian; Zhang, Jing; Liu, Yong; Liu, Peng; Zhang, Huai-Jin; Wang, Xue-Lin

    2017-01-01

    To investigate irradiation effects of LaAlO3 crystals, planar waveguides were fabricated via the medium- and high-energy C3+ ions irradiation. The characterizations of waveguides showed that irradiation at different conditions induced diverse variations of the number of guiding modes, refractive index profiles and lattice damage. Rutherford backscattering/channeling spectra in combination with X-ray diffraction and micro-Raman spectra was used to probe the lattice damage distributions in the near surface of irradiated areas, where the electronic energy loss is predominant. The annealing process with the restoring of the lattice damage to some extent was investigated at temperatures ranging from 533 to 773 K. Meanwhile, as a crucial element of integrated optics and optoelectronics, the light propagation properties of optical waveguide were also investigated. These enable a feasible application of LaAlO3 in integrated optical system.

  9. A novel two-dimensional MgB6 crystal: metal-layer stabilized boron kagome lattice.

    Science.gov (United States)

    Xie, Sheng-Yi; Li, Xian-Bin; Tian, Wei Quan; Chen, Nian-Ke; Wang, Yeliang; Zhang, Shengbai; Sun, Hong-Bo

    2015-01-14

    Based on first-principles calculations, we designed for the first time a boron-kagome-based two-dimensional MgB6 crystal, in which two boron kagome layers sandwich a triangular magnesium layer. The two-dimensional lattice is metallic with several bands across the Fermi level, and among them a Dirac point appears at the K point of the first Brillouin zone. This metal-stabilized boron kagome system displays electron-phonon coupling, with a superconductivity critical transition temperature of 4.7 K, and thus it is another possible superconducting Mg-B compound besides MgB2. Furthermore, the proposed 2D MgB6 can also be used for hydrogen storage after decoration with Ca. Up to five H2 molecules can be attracted by one Ca with an average binding energy of 0.225 eV. The unique properties of 2D MgB6 will spur broad interest in nanoscience and technology.

  10. Emergence of Zeolite Analogs and other Microporous Crystals in an Atomic Lattice Model of Silica and Related Materials.

    Science.gov (United States)

    Jin, Lin; Auerbach, Scott M; Monson, Peter A

    2012-03-15

    The potential of tailored nanopores to transform technologies such as drug delivery, biofuel production, and optical-electronic devices depends on fundamental knowledge of the self-assembly of ordered nanoporous solids. Atomic-level geometries of critical nuclei that lead to such solids have remained hidden in the nanoscale blind spot between local (5 nm) probes of structure. Heroic efforts at molecular simulation of nanopore formation have provided massive libraries of hypothetical structures; (1-5) however, to date no statistical simulation has generated a crystallization pathway from random initial condition to ordered nanoporous solid, until now. In this work, we show that a recently developed atomic lattice model of silica and related materials can form ordered nanoporous solids with a rich variety of structures including known chalcogenides, zeolite analogs, and layered materials. We find that whereas canonical Monte Carlo simulations of the model consistently produce the amorphous solids studied in our previous work, parallel tempering Monte Carlo gives rise to ordered nanoporous solids. The utility of parallel tempering highlights the existence of barriers between amorphous and crystalline phases of our model. Moreover, the self-assembly or nanoporous crystalline phases in the model open the door to detailed understanding of nanopore nucleation.

  11. Investigations of the EPR parameters and local lattice structure for the rhombic Cu{sup 2+} centre in TZSH crystal

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chao-Ying; Liu, Shi-Fei; Fu, Jin-Xian [Shangrao Normal University, Jiangxi (China). School of Physics and Electronic Information

    2016-07-01

    The electron paramagnetic resonance (EPR) parameters [i.e. g factors g{sub i} (i=x, y, z) and hyperfine structure constants A{sub i}] and the local lattice structure for the Cu{sup 2+} centre in Tl{sub 2}Zn(SO{sub 4}){sub 2}.6H{sub 2}O (TZSH) crystal were theoretically investigated by utilising the perturbation formulae of these parameters for a 3d{sup 9} ion under rhombically elongated octahedra. In the calculations, the admixture of d orbitals in the ground state and the ligand orbital and spin-orbit coupling interactions are taken into account based on the cluster approach. The theoretical EPR parameters show good agreement with the observed values, and the Cu{sup 2+}-H{sub 2}O bond lengths are obtained as follows: R{sub x}∼1.98 Aa, R{sub y}∼2.09 Aa, R{sub z}∼2.32 Aa. The results are discussed.

  12. Loading of praziquantel in the crystal lattice of solid lipid nanoparticles - studies by DSC and SAXS

    Energy Technology Data Exchange (ETDEWEB)

    Souza, A.L.R.; Cassimiro, D.L.; Almeida, A.E.; Ribeiro, C.A.; Gremiao, M.P.D. [UNESP, Araraquara, SP (Brazil); Sarmento, V.H.V. [Universidade Federal de Sergipe (UFS), Itabaiana, SE (Brazil); Andreani, T.; Silva, A.M.; Souto, E.B. [Universidade de Tras-os-Montes e Alto Douro, Vila Real (Portugal)

    2012-07-01

    Full text: Praziquantel (PZQ) is the drug of choice for oral treatment of schistosomiasis and other fluke infections that affect humans. Its low oral bioavailability demands the development of innovative strategies to overcome the first pass metabolism. In this work, solid lipid nanoparticles loaded with PZQ (PZQ-SLN) were prepared by a modified oil-in-water microemulsion method selecting stearic acid as lipid phase after solubility screening studies. The mean particle size (Z-Ave) and zeta potential (ZP) were 500 nm and -34.0 mV, respectively. Morphology and shape of PZQ-SLN were analysed by scanning electron microscopy revealing the presence of spherical particles with smooth surface. Differential scanning calorimetry suggested that SLN comprised a less ordered arrangement of crystals and the drug was molecularly dispersed in the lipid matrix. No supercooled melts were detected. The entrapment efficiency (EE) and loading capacity of PZQ, determined by high performance liquid chromatography, were 99.0 and 17.5, respectively. Effective incorporation of PZQ into the particles was confirmed by small angle X-ray scattering revealing the presence of a lipid lamellar structure. Stability parameters of PZQ-SLN stored at room temperature (25 deg C) and at 4 deg C were checked by analysing Z-Ave, ZP and the EE for a period of 60 days Results showed a relatively long-term physical stability after storage at 4 deg C, without drug expulsion. (author)

  13. Lattice dynamics of diamond-like crystals from a tight-binding calculation of valence bands

    Science.gov (United States)

    Roman, R.; Pascual, J.

    1988-11-01

    We report on the results of calculations of the TA(X) phonon energy in the series of C, Si, Ge, Sn homopolar crystals. The starting point is the tight-binding model for the electronic Hamiltonian where Es and Ep are taken to be the free atomic energies while the interatomic matrix elements are described by a universal d-2 Harrison's scaling law. The change of the total energy with the atomic distortion is given in terms of changes in the valence band energy and changes in the overlap energy. The numerical calculations for Si gives U1 = -21.77eV and U2 = 60.44eV, close to the values predicted by Harrison U1 = -17.76eV and U2 = 53.28eV. The calculations of the TA(X) phonon energy gives (in the case the interatomic distances are held constant): 26.09 THz (C), 6.46 THz (Si), 3.37THz (Ge) and 1.91 THz (Sn), in reasonably good agreement with the experimental results 24.1 THz (C), 4.49 THz (Si), 2.39 THz (Ge) and 1.26 THz (Sn).

  14. Influence of Vibrations During Crystallization on Mechanical Properties and Porosity of EN AC-AlSi17 Alloy

    Directory of Open Access Journals (Sweden)

    T. Ciućka

    2013-01-01

    Full Text Available Today’s industry aims at such situation, where number of defective products, so called defects shall approach to zero. Therefore, oneintroduces a various changes in technology of production, introduces improvements which would help in accomplishment of this objective.Another important factor is introduction of different type of testing, which shall help in assessment which factor has significant effect on quantity of rejects, and which one could be neglected. Existence of casting rejects is unavoidable; therefore a new ideas, technologies and innovations are necessary in the entire widely understood foundry branch, in order to minimize such adverse effect. Performance of tests aimed at unequivocal determination of an effect of vibrations during crystallization on mechanical properties and porosity of the EN ACAlSi17 alloy was the objective of the present work. To do this, there were produced 36 castings from EN AC-AlSi17 alloy. All the castings underwent machining operations. Half of the casting was destined to strength tests, the other half served to determination of an effect of vibrations on porosity of the alloy. The specimens were divided into 12 groups, depending on amplitude of vibrations and tilt angle of metal mould during pouring operation.

  15. Influence of vibrations during crystallization on mechanical properties and porosity of AlSi13Cu2 alloy

    Directory of Open Access Journals (Sweden)

    T.Ciućka

    2010-01-01

    Full Text Available Today’s industry aims at such situation, where number of defective products, so called defects shall approach to zero. Therefore, one introduces a various changes in technology of production, introduces improvements which would help in accomplishment of this objective. Another important factor is introduction of different type of testing, which shall help in assessment which factor has significant effect on quantity of rejects, and which one could be neglected. Existence of casting rejects is unavoidable; therefore a new ideas, technologies and innovations are necessary in the entire widely understood foundry branch, in order to minimize such adverse effect. Performance of tests aimed at unequivocal determination of an effect of vibrations during crystallization on mechanical properties and porosity of the AlSi13Cu2 alloy was the objective of the present work. To do this, there were produced 36 castings from AlSi13Cu2 alloy. All the castings underwent machining operations. Half of the casting was destined to strength tests, the other half served to determination of an effect of vibrations on porosity of the alloy. The specimens were divided into 12 groups, depending on amplitude of vibrations and tilt angle of metal mould during pouring operation.

  16. Synthesis, crystal structure, vibrational spectroscopy and photoluminescence of new hybrid compound containing chlorate anions of stanate (II)

    Science.gov (United States)

    Lassoued, Mohamed Saber; Abdelbaky, Mohammed S. M.; Lassoued, Abdelmajid; Meroño, Rafael Mendoza; Gadri, Abdellatif; Ammar, Salah; Ben Salah, Abdelhamid; García-Granda, Santiago

    2017-08-01

    The present work aimed at studying a new organic-inorganic bis (4-amino quinolinium) hexachloro stanate (II) dihydrate compound. It was prepared and characterized by single crystal X-ray diffraction, X-ray powder, Hirshfeld surface, Spectroscopy measurement, thermal study and photoluminescence properties. It was found to crystallize in the monoclinic system (P21/c space group) with the following lattice parameters: a = 7.2558(6) Å, b = 13.4876(5) Å, c = 17.2107(13) Å, β = 102.028 (12)°. Its crystal structure was determined and refined down to an R value of 0.06 and a wR value of 0.087. The structure consisted of two different alternating organic-inorganic layers. The crystal packing was stabilized by Nsbnd H⋯Cl and Osbnd H⋯Cl hydrogen bonds and π-π interactions. Hirshfeld surface analysis was used to investigate intermolecular interactions, as well 2D finger plots were conducted to reveal the contribution of these interactions in the crystal structure quantitatively. The X-ray powder is in agreement with the X-ray structure. Scanning electronic microscopy (SEM) was carried out. Furthermore, the room temperature Infra Red (IR) spectrum of the title compound was analyzed on the basis of data found in the literature. Solid state 13C NMR spectrum shows ten signals, confirming the solid state structure determined by X-ray diffraction. Thermal analysis shows two anomalies at 380 and 610 °C. The optical properties of the crystal were studied using optical absorption UV-visible and photoluminescence (PL) spectroscopy, which were investigated at room temperature.

  17. Influence of gravitational and vibrational convection on the heat- and mass transfer in the melt during crystal growing by Bridgman and floating zone methods

    Science.gov (United States)

    Fedorov, Oleg

    2016-07-01

    Space materials science is one of the priorities of different national and international space programs. The physical processes of heat and mass transfer in microgravity (including effect of g-jitter) is far from complete clarity, especially for important practical technology for producing crystals from the melt. The idea of the impact on crystallizing melt by low frequency vibration includes not only the possibility to suppress unwanted microaccelerations, but also to actively influence the structure of the crystallization front. This approach is one of the most effective ways to influence the quality of materials produced in flight conditions. The subject of this work is the effect of vibrations on the thermal and hydrodynamic processes during crystal growth using Bridgman and floating zone techniques, which have the greatest prospect of practical application in space. In the present approach we consider the gravitational convection, Marangoni convection, as well as the effect of vibration on the melt for some special cases. The results of simulation were compared with some experimental data obtained by the authors using a transparent model substance - succinonitrile (Bridgman method), and silicon (floating zone method). Substances used, process parameters and characteristics of the experimental units correspond the equipment developed for onboard research and serve as a basis for selecting optimum conditions vibration exposure as a factor affecting the solidification pattern. The direction of imposing vibrations coincides with the axis of the crystal, the frequency is presented by the harmonic law, and the force of gravity was varied by changing its absolute value. Mathematical model considered axisymmetric approximation of joint convective-conductive energy transfer in the system crystal - melt. Upon application of low-frequency oscillations of small amplitude along the axis of growing it was found the suppression of the secondary vortex flows near the

  18. Measurements of γ/γ' Lattice Misfit and γ' Volume Fraction for a Ru-containing Nickel-based Single Crystal Superalloy

    Institute of Scientific and Technical Information of China (English)

    X.P. Tan; J.L. Liu; X P Song; T. Jin; X.F. Sun; Z.Q. Hu

    2011-01-01

    A conventional X-ray difFractometer has been used to determine the -y/y' lattice misfit and γ' volume fraction for a Ru-containing nickel-based single crystal superalloy at room temperature. The rocking curve was used to characterize the distribution of subgrains. The diffraction peaks obtained by w-20 scan were used to determine the γ/γ' lattice misfit and γ' volume fraction. A three peaks fitting model was proposed. The peak fitting results are in good agreement with the model. The X-ray diffraction results indicate that the nickel-based single crystal superalloy was not a perfect monocrystalline material, which is comprised of many subgrains; and each subgrain also consists of large numbers of mosaic structures. In addition, two anomalous reflection phenomena were found during the experiment and discussed with respect to their occurrence and impact on the measurement. The experimental results show that the γ/γ' lattice misfit and ~/r volume fraction will be various at the different regions of its dendritic microstructure. The average γ/γ' lattice misfit and γ' volume fraction of the experimental alloy are approximately-0.2% and 70%, respectively. Furthermore, the γ' volume fraction calculated by atom microprobe (AP) data is also basically consistent with the experimental results.

  19. NMR spin-lattice relaxation study of 7Li and 93Nb nuclei in Ti- or Fe-doped LiNbO3:Mg single crystals

    Directory of Open Access Journals (Sweden)

    Tae Ho Yeom

    2016-04-01

    Full Text Available In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

  20. Excess vibrational modes of a crystal in an external non-affine field

    Indian Academy of Sciences (India)

    SASWATI GANGULY; SURAJIT SENGUPTA

    2017-07-01

    Thermal displacement fluctuations in a crystal may be classified as either “affine” or “non-affine”. While the former couples to external stress with familiar consequences, the response of a crystal when nonaffine displacements are enhanced using the thermodynamically conjugate field, is relatively less studied. We examine this using a simple model of a crystal in two dimensions for which analytical calculations are possible. Enhancing non-affine fluctuations destabilises the crystal. The population of small frequency phonon modesincreases, with the phonon density of states shifting, as a whole, towards zero frequency. Even though the crystal is free of disorder, we observe growing length and time scales. Our results, which may have implications for the glass transition and structural phase transitions in solids, are compared to molecular dynamics simulations. Possibility of experimental verification of these results is also discussed.

  1. Synthesis, crystal structure, vibrational spectroscopy, optical properties and theoretical studies of a new organic-inorganic hybrid material: [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2.

    Science.gov (United States)

    Ben Ahmed, A; Feki, H; Abid, Y

    2014-12-10

    A new organic-inorganic hybrid material, [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2, has been synthesized and characterized by X-ray diffraction, FT-IR, Raman spectroscopy and UV-Visible absorption. The studied compound crystallizes in the triclinic system, space group P1¯ with the following parameters: a=8.4749(6)(Å), b=17.1392(12)(Å), c=17.1392(12)(Å), α=117.339(0)°, β=99.487(0)°, γ=99.487(0)° and Z=2. The crystal lattice is composed of a two discrete (BiBr6)(3-) anions surrounded by six ((CH3)2NH2)(+) cations. Complex hydrogen bonding interactions between (BiBr6)(3-) and organic cations from a three-dimensional network. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra and optical properties of the investigated molecule in the ground state. The full geometry optimization of designed system is performed using DFT method at B3LYP/LanL2DZ level of theory using the Gaussian03. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The vibrational spectral data obtained from FT-IR and Raman spectra are assigned based on the results of the theoretical calculations. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental UV-Visible spectrum. The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO-LUMO boundary. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Crystal structure, Hirshfeld surface analysis, vibrational, thermal behavior and UV spectroscopy of (2,6-diaminopyridinium) dihydrogen arsenate

    Science.gov (United States)

    Bouaziz, Emna; Ben Hassen, Chawki; Chniba-Boudjada, Nassira; Daoud, Abdelaziz; Mhiri, Tahar; Boujelbene, Mohamed

    2017-10-01

    A new organic dihydrogenomonoarsenate (C5H8N3)H2AsO4 was synthesized by slow evaporation method at room temperature and characterized by X-ray single crystal diffraction. This compound crystallizes in the monoclinic system with the centro-symmetric space group P21/n. Unit cell parameters are a = 10.124 (5)Ǻ, b = 6.648 (5)Ǻ, c = 13.900 (5)Ǻ, β = 105.532° with Z = 4. The crystal structure was solved and refined to R = 0.038 with 2001 independent reflections. Hirshfeld surfaces analysis were used to visualize the fidelity of the crystal structure which has been determined by X-ray data collection on single crystals (C5H8N3)H2AsO4. Due the strong hydrogen Osbnd H⋯O bond network connecting the H2AsO4 groups, the anionic arrangement must be described as infinite (H2AsO4)nn-of dimers chains spreading, in a zig zag fashion, parallel to the b direction. The organic groups (C5H8N3)+ are anchored between adjacent polyanions through multiple hydrogen bonds Nsbnd H⋯O. The thermal decomposition of precursors studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), indicate the existence of two mass loss regions correspond to degradation of the title compound. The existence of vibrational modes correspond to the organic and inorganic groups are identified by the infrared and Raman spectroscopy in the frequency ranges 500-4000 and 25-4000 cm-1, respectively.

  3. Dynamic transition in current-driven disordered flux-line lattice in single-crystal of Bi-2212

    Energy Technology Data Exchange (ETDEWEB)

    Ammor, L.; Ruyter, A.

    2014-11-15

    We have measured the current–voltage characteristics for both as-grown and irradiated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} single crystals at T = 5 K in a magnetic field applied parallel to c axis. The results show a variety of dynamical behavior above the depinning threshold, depending on the vortex–vortex interaction (λ{sub ab}/a{sub 0}) strength and the nature of the quenched disorder (point-like or columnar defects). When the flux lattice is soft, our experimental measurements in both samples have been attributed to plastic flow, including strong metastability and history dependence of the depinning process. The vortex motion in this regime is thought of relatively weakly pinned vortices past more strongly pinned neighbors. A power-law scaling, fit between voltage and applied current can be obtained for the onset of motion in both samples, with different apparent critical exponent depending on defect nature and the strength of interactions. In the plastic regime, the usual scaling ansatz associated with dynamic critical phenomena V scales as (I − I{sub c}){sup β}, where β ∼ 2.2 ± 0.1 and 1.22 ± 0.021 for as-grown and β ≈ 1.49 ± 0.07 for irradiated samples, respectively. Finally, in both cases of defects, with increasing the strength of vortex–vortex interaction a dynamical transition is observed as confirmed by the discontinuity in the vortex–vortex interactions dependence of the critical exponent β. More, our results confirm the important role of the system dimensionnality on vortex dynamics.

  4. Crystal growth, vibrational, optical, thermal and theoretical studies of a nonlinear optical material: 2-Methyl 3,5-dinitrobenzoic acid

    Energy Technology Data Exchange (ETDEWEB)

    Sangeetha, K. [Department of Physics, Sri Sarada College for Women, Salem-16 (India); Guru Prasad, L. [Department of Science & Humanities, M. Kumarasamy College of Engineering, Karur (India); Mathammal, R. [Department of Physics, Sri Sarada College for Women, Salem-16 (India)

    2016-11-15

    Single crystals of 2-methyl 3,5-dinitro benzoic acid with reasonable size have been grown by slow evaporation solution growth method using ethanol as solvent. Quantum chemical calculation of 2-methyl 3,5-Dinitro benzoic acid was carried out by using DFT/B3LYP/6-31+G(d,p) method. The powder X-ray diffraction pattern was recorded and indexed. Both the experimental and theoretical vibrational spectrum validates the presence of functional groups. Polarizability, first order hyperpolarizability and the electric dipole moment values have been computed theoretically. The {sup 1}H and {sup 13}C NMR chemical shift of the molecule was calculated and compared with experimental results. TG/DSC analysis has been employed to understand the thermal and physio-chemical stability of the title compound. Frequency conversion property of the crystal was tested by Kurtz and Perry method. Optical absorption behavior of the grown crystal was examined by recording the optical spectrum and band gap energy was also estimated. The calculated HOMO and LUMO energy shows the charge transfer nature of the molecule.

  5. Crystal growth, vibrational, optical, thermal and theoretical studies of a nonlinear optical material: 2-Methyl 3,5-dinitrobenzoic acid

    Science.gov (United States)

    Sangeetha, K.; Guru Prasad, L.; Mathammal, R.

    2016-11-01

    Single crystals of 2-methyl 3,5-dinitro benzoic acid with reasonable size have been grown by slow evaporation solution growth method using ethanol as solvent. Quantum chemical calculation of 2-methyl 3,5-Dinitro benzoic acid was carried out by using DFT/B3LYP/6-31+G(d,p) method. The powder X-ray diffraction pattern was recorded and indexed. Both the experimental and theoretical vibrational spectrum validates the presence of functional groups. Polarizability, first order hyperpolarizability and the electric dipole moment values have been computed theoretically. The 1H and 13C NMR chemical shift of the molecule was calculated and compared with experimental results. TG/DSC analysis has been employed to understand the thermal and physio-chemical stability of the title compound. Frequency conversion property of the crystal was tested by Kurtz and Perry method. Optical absorption behavior of the grown crystal was examined by recording the optical spectrum and band gap energy was also estimated. The calculated HOMO and LUMO energy shows the charge transfer nature of the molecule.

  6. Crystal structures and magnetic properties of the honeycomb-lattice antiferromagnet M2(pymca)3(ClO4), (M = Fe, Co, Ni)

    Science.gov (United States)

    Honda, Zentaro; Kodama, Takafumi; Hagiwara, Masayuki; Kida, Takanori; Okutani, Akira; Sakai, Masamichi; Fukuda, Takeshi; Kamata, Norihiko

    2016-09-01

    We report on the syntheses, crystal structures, and magnetic properties of a series of transition metal coordination polymers M2(pymca)3(ClO4), (pymca = pyrimidine-2-carboxylic acid, M = Fe (1), Co (2), and Ni (3)). These compounds are found to crystallize in a trigonal crystal system, space group P31m, with the lattice constants a = 9.727 Å and c = 5.996 Å for 1, a = 9.608 Å and c = 5.996 Å for 2, and a = 9.477 Å and c = 5.958 Å for 3 at room temperature. In these compounds, each pymca ligand connects to two M2+ ions, forming a honeycomb network in the ab plane. The temperature dependences of magnetic susceptibilities in these compounds show broad maxima, indicating antiferromagnetic interactions within two-dimensional honeycomb layers. We also observed an antiferromagnetic phase transition at low temperatures by magnetic susceptibility and heat capacity measurements. From the crystal structures and magnetic properties, we conclude that the compounds 1, 2, and 3 are good realizations of honeycomb-lattice antiferromagnets.

  7. Crystal structure and vibrational properties of KMg 4(PO 4) 3

    Science.gov (United States)

    Tomaszewski, Paweł Edward; Mączka, Mirosław; Majchrowski, Andrzej; Waśkowska, Alicja; Hanuza, Jerzy

    2005-10-01

    Single crystals of potassium magnesium phosphate KMg 4(PO 4) 3 have been obtained from flux and characterized by means of single-crystal X-ray diffraction method and IR and Raman spectroscopy. This compound crystallizes in the Pnnm space group with a=16.361(3), b=9.562(19), c=6.171(12) Å and Z=4. The structure is built up of PO 4 tetrahedra, MgO 6 octahedra and MgO 5 polyhedra connected via P sbnd O sbnd Mg bridges to form a three-dimensional framework enclosing tunnels along b-axis occupied by K + ions. IR and Raman spectra are consistent with the crystal structure. The internal and external modes are observed in the 350-1210 cm -1 range and below 330 cm -1, respectively.

  8. Sensor for monitoring the vibration of a laser beam based on holographic polymer dispersed liquid crystal films.

    Science.gov (United States)

    Li, Ming Shian; Wu, Shing Trong; Fuh, Andy Ying-Guey

    2010-12-06

    A continuous multiple exposure diffraction grating (CMEDG) is fabricated holographically on polymer dispersed liquid crystal (PDLC) films using two-beam interference with multiple exposures. The grating is fabricated by exposing a PDLC film to 18 repeated exposure/non-exposure cycles with an angular step of ~10°/10° while it revolves a circle on a rotation stage. The structure of the sample thus formed is analyzed using a scanning electron microscope (SEM) and shows arc-ripples around the center. From the diffraction patterns of the formed grating obtained using a normally incident laser beam, some or all of the 18 recorded arc beams can be reconstructed, as determined by the probing location. Thus, it can be applied for use as a beam-vibration sensor for a laser.

  9. An analytical model for the determination of crystallite size and crystal lattice microstrain distributions in nanocrystalline materials from the variance of the X-ray diffraction peaks

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Bajo, F. [Universidad de Extremadura, Departamento de Fisica Aplicada, Badajoz (Spain); Ortiz, A.L. [Universidad de Extremadura, Departamento de Ingenieria Mecanica, Energetica y de los Materiales, Badajoz (Spain); Cumbrera, F.L. [Universidad de Extremadura, Departamento de Fisica, Badajoz (Spain)

    2009-01-15

    An analytical model for the determination of crystallite size and crystal lattice microstrain distributions in nanocrystalline (nc) materials by X-ray diffractometry (XRD) is presented. It entails generalizing the variance method to establish analytically the connection between the variance coefficients of the physically broadened XRD peaks and the characteristic parameters of explicit distributions of crystallite sizes and crystal lattice microstrains, which results in a more detailed characterization of the nc-materials. The proposed model is generic in nature and has the potential to be used under the assumption of different mathematical functions for the two distributions, which suggests that it may have an important role to play in the characterization of nc-materials. Nevertheless, the specialization to the case of nc-materials with log-normal crystallite size distribution and three typical types of lattice microstrains is used as an illustration and to formulate explicit analytical expressions of interest. Finally, the usefulness of the proposed model is demonstrated on standard XRD profiles. (orig.)

  10. Tunable all-angle negative refraction and photonic band gaps in two-dimensional plasma photonic crystals with square-like Archimedean lattices

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hai-Feng, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing Univ. Aeronaut. Astronaut.), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu, Shao-Bin, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn; Jiang, Yu-Chi [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing Univ. Aeronaut. Astronaut.), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2014-09-15

    In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.

  11. Tunable all-angle negative refraction and photonic band gaps in two-dimensional plasma photonic crystals with square-like Archimedean lattices

    Science.gov (United States)

    Zhang, Hai-Feng; Liu, Shao-Bin; Jiang, Yu-Chi

    2014-09-01

    In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.

  12. Characterization of a polychromatic neutron beam diffracted by pyrolytic graphite crystals

    CERN Document Server

    Byun, S H; Choi, H D

    2002-01-01

    The beam spectrum for polychromatic neutrons diffracted by pyrolytic graphite crystals was characterized. The theoretical beam spectrum was obtained using the diffraction model for a mosaic crystal. The lattice vibration effects were included in the calculation using the reported vibration amplitude of the crystal and the measured time-of-flight spectra in the thermal region. The calculated beam spectrum was compared with the results obtained in the absence of thermal motion. The lattice vibration effects became more important for the higher diffraction orders and a large decrease in the neutron flux induced by the vibrations was identified in the epithermal region. The validity of the beam spectrum was estimated by comparing with the effective quantities determined from prompt gamma-ray measurements and Cd-ratios measured both for 1/nu and non-1/nu nuclides.

  13. Temperature dependence of lattice disorder in Ar-irradiated (1 0 0), (1 1 0) and (1 1 1) MgO single crystals

    Science.gov (United States)

    Usov, I. O.; Valdez, J. A.; Sickafus, K. E.

    2011-02-01

    To better appreciate dynamic annealing processes in ion irradiated MgO single crystals of three low-index crystallographic orientations, lattice damage variation with irradiation temperature was investigated. Irradiations were performed with 100 keV Ar ions to a fluence of 1 × 10 15 Ar/cm 2 in a temperature interval from -150 to 1100 °C. Rutherford backscattering spectroscopy combined with ion channeling was used to analyze lattice damage. Damage recovery with increasing irradiation temperature proceeded via two characteristic stages separated by 200 °C. Strong radiation damage anisotropy was observed at temperatures below 200 °C, with (1 1 0) MgO being the most radiation damage tolerant. Above 200 °C damage recovery was isotropic and almost complete recovery was reached at 1100 °C. We attributed this orientation dependence to a variation of dynamic annealing mechanisms with irradiation temperature.

  14. Stepwise behavior of vortex-lattice melting transition in tilted magnetic fields in single crystals of Bi(2)Sr(2)CaCu(2)O(8 + delta).

    Science.gov (United States)

    Mirković, J; Savel'ev, S E; Sugahara, E; Kadowaki, K

    2001-01-29

    The vortex-lattice melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) single crystals was studied using in-plane resistivity measurements in magnetic fields tilted away from the c axis to the ab plane. In order to avoid the surface barrier effect which hinders the melting transition in the conventional transport measurements, we used the Corbino geometry of electric contacts. The complete H(c) - H(ab) phase diagram of the melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) is obtained for the first time. The c-axis melting field component H(c)(melt) exhibits the novel, stepwise dependence on the in-plane magnetic fields H(ab) which is discussed on the basis of the crossing vortex-lattice structure. The peculiar resistance behavior observed near the ab plane suggests the change of phase transition character from first to second order.

  15. THICKNESS-SHEAR VIBRATION OF CIRCULAR CRYSTAL PLATE IN CYLINDRICAL SHELL AS PRESSURE SENSOR

    Institute of Scientific and Technical Information of China (English)

    HU Yuan-tai; CUI Zhi-jian; JIANG Shu-nong; YANG Jia-shi

    2006-01-01

    Based on the theory for small fields superposed on relatively larger fields in an electroelastic body, a theoretical analysis is performed on a circular plate thicknessshear crystal resonator sealed in a circular cylindrical shell for pressure measurement.A simple expression is obtained for pressure induced frequency shifts in the resonator,which is examined for design optimization. Numerical results show that the frequency shifts depend linearly on the pressure, and that a pressure sensor with a softer outer shell or a smaller thickness ratio of the crystal plate to the outer shell has higher sensitivity.

  16. Relationships among chemical composition, lattice constants, and acoustic properties for Ca3Ta(Ga1-xAlx)3Si2O14 single crystals

    Science.gov (United States)

    Ohashi, Yuji; Kitahara, Masanori; Kudo, Tetsuo; Arakawa, Mototaka; Yokota, Yuui; Shoji, Yasuhiro; Yamaji, Akihiro; Kurosawa, Shunsuke; Kamada, Kei; Yoshikawa, Akira

    2017-06-01

    The relationship among lattice constant a, Al content, and acoustic properties were experimentally examined using a plate specimen perpendicular to Y-axis prepared from Ca3Ta(Ga0.75Al0.25)3Si2O14 [CTGAS(0.25)] single crystal grown by Czochralski method. As the acoustic properties, leaky surface acoustic wave (LSAW) velocities with different propagation directions, X- and Z-propagations, and longitudinal wave velocity propagating along Y-axis direction were measured by the line-focus-beam/plane-wave ultrasonic-material-characterization (LFB/PW-UMC) system. The measured results of LSAW velocity distributions revealed inhomogeneity in radial direction of the crystal ingot exhibiting lower velocity area at the center of the ingot. In addition, the distributions of lattice constant a and chemical composition (especially Al content) were measured along the radial direction. Abnormal changes suggesting existence of residual stresses concentrated on the central part of the crystal ingot other than the effect of chemical composition change were detected from the relationships among the measured parameters.

  17. Crystal and molecular structure of N-(4-nitrophenyl)-β-alanine—Its vibrational spectra and theoretical calculations

    Science.gov (United States)

    Marchewka, M. K.; Drozd, M.; Janczak, J.

    2011-08-01

    The N-(4-nitrophenyl)-β-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title β-alanine derivative crystallizes in the P2 1/ c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of β-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O-H⋯O hydrogen bonds with O⋯O distance of 2.656(2) Å forming a dimeric structure. The dimers of β-alanine derivative weakly interact via N-H⋯O hydrogen bonds between the H atom of β-amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double C dbnd C bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition.

  18. Crystal and molecular structure of N-(4-nitrophenyl)-β-alanine--its vibrational spectra and theoretical calculations.

    Science.gov (United States)

    Marchewka, M K; Drozd, M; Janczak, J

    2011-08-15

    The N-(4-nitrophenyl)-β-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title β-alanine derivative crystallizes in the P2(1)/c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of β-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O-H···O hydrogen bonds with O···O distance of 2.656(2) Å forming a dimeric structure. The dimers of β-alanine derivative weakly interact via N-H···O hydrogen bonds between the H atom of β-amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double CC bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition.

  19. Study on Luminescence Properties and Crystal-Lattice Environment of Eu2+ in Sr4-xMgxSi3O8Cl4∶Eu2+ Phosphor

    Institute of Scientific and Technical Information of China (English)

    夏志国; 孙家跃; 杜海燕

    2004-01-01

    According to the Van Uitert experimental equation, crystal-lattice environment of Eu2+ in the Sr4Si3O8Cl4 crystal was discussed. By adding Mg2+ to the host lattice, Sr4-xMgxSi3O8Cl4∶Eu2+ was synthesized and the emission peak shifted from blue-green (488 nm) to blue-violet (411 nm) with the increase of amount of the magnesium which replaced the strontium. By analyzing the spectra of Sr4-xMgxSi3O8Cl4∶Eu2+ the two Eu2+ emission centers were found because of the change of crystal-lattice environment in the host and the crystal structure was obtained by X-ray diffraction data.

  20. Investigation of the crystal lattice defects by means of the positrons annihilations; Badania defektow sieci krystalicznej metoda anihilacji pozytonow

    Energy Technology Data Exchange (ETDEWEB)

    Dryzek, J. [Institute of Nuclear Physics, Cracow (Poland)

    1994-12-31

    In this report the positrons annihilation methods as a tool for the crystal defects studies is presented. The short description of the positron - crystal interactions and different positron capture models are discussed. 192 refs, 67 figs, 6 tabs.

  1. Refining the spin Hamiltonian in the spin-1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2 using single crystals.

    Science.gov (United States)

    Han, Tianheng; Chu, Shaoyan; Lee, Young S

    2012-04-13

    We report thermodynamic measurements of the S=1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2, a promising candidate system with a spin-liquid ground state. Using single crystal samples, the magnetic susceptibility both perpendicular and parallel to the kagome plane has been measured. A small, temperature-dependent anisotropy has been observed, where χ(z)/χ(p)>1 at high temperatures and χ(z)/χ(p)kagome Heisenberg antiferromagnet model to the experiments on ZnCu3(OH)6Cl2.

  2. Effect of inclining strain on the crystal lattice along an extended series of lanthanide hydroxysulfates Ln(OH)SO4 (Ln = Pr-Yb, except Pm).

    Science.gov (United States)

    Zehnder, Ralph A; Wilson, Christopher S; Christy, Hunter T; Harris, Kenneth S; Chauhan, Varun; Schutz, Victor; Sullivan, Matthew; Zeller, Matthias; Fronczek, Frank R; Myers, Jacob A; Dammann, Kyle; Duck, James; Smith, Peter M; Okuma, Antony; Johnson, Kristin; Sovesky, Robert; Stroudt, Cameron; Renn, Robert A

    2011-02-07

    A series of trivalent lanthanide hydroxysulfates, Ln(OH)SO(4), (Ln = Pr through Yb, except radioactive Pm) has been synthesized via hydrothermal methods from Ln(2)(SO(4))(3)·8H(2)O by reaction with aqueous NaOH at 170 °C in Teflon lined Parr steel autoclaves, and were characterized by single crystal X-ray diffraction and FT-IR spectroscopy. Two types of arrangements were found in the solid state. The lighter (Ln = Pr-Nd, Sm-Gd) and heavier lanthanide(III) hydroxysulfates (Tb-Yb) are each isostructural. Both structure types exhibit the monoclinic space group P2(1)/n, but the unit cell content is doubled with two crystallographically distinct LnO(8) polyhedra for the heavier lanthanide compounds. The lighter complexes maintain the coordination number 9, forming a three-dimensional extended lattice. The heavier counterparts exhibit the coordination number 8, and arrange as infinite columns of two crystallographically different LnO(8) polyhedra, while extending along the "c" axis. These columns of LnO(8) polyhedra are surrounded and separated by six columns of sulfate ions, also elongating in the "c" direction. The rigid sulfate entities seem to obstruct the closing in of the lighter LnO(9) polyhedra, and show an inclining degree of torsion into the "ac" layers. The crystal lattice of the lighter 4f complexes can sufficiently withstand the tension buildup, caused by the decreasing Ln(3+) radius, up to Gd(OH)SO(4). The energy profile of this structural arrangement then seems to exceed levels at which this structure type is favorable. The lattice arrangement of the heavier Ln-analogues seems to offer a lower energy profile. This appears to be the preferred arrangement for the heavier lanthanide hydroxysulfates, whose crystal lattice exhibits more flexibility, as the coordination sphere of these analogues is less crowded. The IR absorbance frequencies of the hydroxide ligands correlate as a function of the Ln(3+) ionic radius. This corresponds well with the X-ray single

  3. Glassy Spin Dynamics in Geometrically Frustrated Buckled Colloidal Crystals

    Science.gov (United States)

    Zhou, Di; Wang, Feng; Li, Bo; Lou, Xiaojie; Han, Yilong

    2017-04-01

    Geometrical frustration arises when the lattice geometry prevents local interaction energies from minimizing simultaneously. Whether and how geometrically frustrated spins or charges in clean crystals exhibit glassy dynamics remain elusive due to the lack of measurements on microscopic dynamics. Here, we employ buckled monolayer colloidal crystals to mimic frustrated antiferromagnetic Ising spins on triangular lattices and measure single-spin dynamics using video microscopy. Both attractive and repulsive colloidal crystals buckled into zigzag stripes with glassy dynamics at low effective temperatures in experiment and simulation. The simple local spin configurations enable uncovering correlations among structure, dynamics, and soft vibrational modes. Machine learning analysis further reveals facilitated dynamics to be an important mechanism of structural relaxation. Moreover, our simulation reveals a similar structure and dynamics in lattice Coulomb liquids. Hence, spin-lattice coupling and long-range interaction can similarly lift degeneracy, induce a rugged landscape, and, thus, produce glassy dynamics.

  4. Freeform Fabrication of Magnetophotonic Crystals with Diamond Lattices of Oxide and Metallic Glasses for Terahertz Wave Control by Micro Patterning Stereolithography and Low Temperature Sintering

    Directory of Open Access Journals (Sweden)

    Maasa Nakano

    2013-04-01

    Full Text Available Micrometer order magnetophotonic crystals with periodic arranged metallic glass and oxide glass composite materials were fabricated by stereolithographic method to reflect electromagnetic waves in terahertz frequency ranges through Bragg diffraction. In the fabrication process, the photo sensitive acrylic resin paste mixed with micrometer sized metallic glass of Fe72B14.4Si9.6Nb4 and oxide glass of B2O3·Bi2O3 particles was spread on a metal substrate, and cross sectional images of ultra violet ray were exposed. Through the layer by layer stacking, micro lattice structures with a diamond type periodic arrangement were successfully formed. The composite structures could be obtained through the dewaxing and sintering process with the lower temperature under the transition point of metallic glass. Transmission spectra of the terahertz waves through the magnetophotonic crystals were measured by using a terahertz time domain spectroscopy.

  5. Interrelation of the structure, vibrational spectra and critical temperature of (123)-superconductors. [YScBaSrCuO; YBaSrCuAlO; GdBaCuO; YBaCuO

    Energy Technology Data Exchange (ETDEWEB)

    Limonov, M.F.; Markov, Yu.F.; Panfilov, A.G.; Razbirin, B.S.; Syrnikov, P.P. (A.F. Ioffe Physico-Technical Inst., St. Petersburg (Russia)); Bush, A.A. (Inst. of Informatics MIREA, Moscow (Russia))

    1992-02-01

    Raman spectrum changes resulting from different variations of the crystal lattice YBa{sub 2}Cu{sub 3}O{sub {delta}} (such as the substitutions Y {yields} rare-earth element R, Ba {yields} Sr, {delta}=6{yields}{delta}=7) have been studied. The concentration associated shift of vibrational frequencies of the oxygen atoms located in different layers of the lattice is shown to obey a general law: certain vibrations soften whereas the others harden. This vibrational behaviour is explained by the wave-like reconstruction of the crystal lattice (123). For the whole superconductor family RBa{sub 2}Cu{sub 3}O{sub 7} and for YBa{sub 2}Cu{sub 3}O{sub 7} at hydrostatic pressure the increase in Tc with increasing frequency of the highest frequency A{sub g}-vibration is established. The results show the essential role of phonons in the high-Tc superconductivity mechanism. (orig.).

  6. Adsorption, Desorption, Surface Diffusion, Lattice Defect Formation, and Kink Incorporation Processes of Particles on Growth Interfaces of Colloidal Crystals with Attractive Interactions

    Directory of Open Access Journals (Sweden)

    Yoshihisa Suzuki

    2016-07-01

    Full Text Available Good model systems are required in order to understand crystal growth processes because, in many cases, precise incorporation processes of atoms or molecules cannot be visualized easily at the atomic or molecular level. Using a transmission-type optical microscope, we have successfully observed in situ adsorption, desorption, surface diffusion, lattice defect formation, and kink incorporation of particles on growth interfaces of colloidal crystals of polystyrene particles in aqueous sodium polyacrylate solutions. Precise surface transportation and kink incorporation processes of the particles into the colloidal crystals with attractive interactions were observed in situ at the particle level. In particular, contrary to the conventional expectations, the diffusion of particles along steps around a two-dimensional island of the growth interface was not the main route for kink incorporation. This is probably due to the number of bonds between adsorbed particles and particles in a crystal; the number exceeds the limit at which a particle easily exchanges its position to the adjacent one along the step. We also found novel desorption processes of particles from steps to terraces, attributing them to the assistance of attractive forces from additionally adsorbing particles to the particles on the steps.

  7. Direct observation of lattice strain in Si1-xGex/Si crystals using planar channeling patterns

    NARCIS (Netherlands)

    Breese, MBH; deKerckhove, DG; King, PJC; Smulders, PJM

    1997-01-01

    This paper describes the direct observation of lattice strain in channeling patterns produced by 3 MeV protons transmitted through strained Si1-xGex/Si bilayers close to planar channeling directions. Blocking lines arising from each layer can be separately resolved at certain alignments, whereas onl

  8. Lateral vibration effects in atomic-scale friction

    Energy Technology Data Exchange (ETDEWEB)

    Roth, R. [Climate and Environment Physics, Physics Institute, University of Bern, Bern (Switzerland); Oeschger Centre for Climate Change Research, University of Bern, Bern (Switzerland); Fajardo, O. Y.; Mazo, J. J. [Departamento de Física de la Materia Condensada and Instituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain); Meyer, E. [Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland); Gnecco, E. [Instituto Madrileño de Estudios Avanzados en Nanociencia, IMDEA Nanociencia, 28049 Madrid (Spain)

    2014-02-24

    The influence of lateral vibrations on the stick-slip motion of a nanotip elastically pulled on a flat crystal surface is studied by atomic force microscopy measurements on a NaCl(001) surface in ultra-high vacuum. The slippage of the nanotip across the crystal lattice is anticipated at increasing driving amplitude, similarly to what is observed in presence of normal vibrations. This lowers the average friction force, as explained by the Prandtl-Tomlinson model with lateral vibrations superimposed at finite temperature. Nevertheless, the peak values of the lateral force, and the total energy losses, are expected to increase with the excitation amplitude, which may limit the practical relevance of this effect.

  9. Vibrational line shapes in the amalgamated limit: (para-D2)x(ortho-D2)1-x mixed crystals

    Science.gov (United States)

    de Kinder, J.; Bouwen, A.; Schoemaker, D.; Boukahil, A.; Huber, D. L.

    1994-05-01

    The D2 vibrons have been studied by high-resolution Raman scattering in mixed crystals of (p-D2)x(o-D2)1-x. The o-D2 and p-D2 vibrational transitions are found to overlap. Line shapes calculated by the coherent potential approximation are in good qualitative agreement with the experimental data. The linewidth of the o-D2 transition is much larger than the linewidth of the p-H2 transition in (o-H2)x(p-H2)1-x mixed crystals with comparable J=1 concentrations. Possible explanations for this difference are discussed.

  10. REFINEMENT OF THE CRYSTAL STRUCTURE OF GUANIDINIUM ALUMINUM SULFATE HEXAHYDRATE.

    Science.gov (United States)

    FERROELECTRIC CRYSTALS, * CRYSTAL STRUCTURE ), (*GUANIDINES, CRYSTAL STRUCTURE ), (*ALUMINUM COMPOUNDS, CRYSTAL STRUCTURE ), SULFATES, HYDRATES, X RAY DIFFRACTION, CHROMIUM COMPOUNDS, CRYSTAL LATTICES, CHEMICAL BONDS

  11. Size-Dependent Elastic Modulus and Vibration Frequency of Nanocrystals

    Directory of Open Access Journals (Sweden)

    Lihong Liang

    2011-01-01

    Full Text Available The elastic properties and the vibration characterization are important for the stability of materials and devices, especially for nanomaterials with potential and broad application. Nanomaterials show different properties from the corresponding bulk materials; the valid theoretical model about the size effect of the elastic modulus and the vibration frequency is significant to guide the application of nanomaterials. In this paper, a unified analytical model about the size-dependent elastic modulus and vibration frequency of nanocrystalline metals, ceramics and semiconductors is established based on the inherent lattice strain and the binding energy change of nanocrystals compared with the bulk crystals, and the intrinsic correlation between the elasticity and the vibration properties is discussed. The theoretical predictions for Cu, Ag, Si thin films, nanoparticles, and TiO2 nanoparticles agree with the experimental results, the computational simulations, and the other theoretical models.

  12. Vibrational relaxation dynamics of catalysts on TiO{sub 2} Rutile (1 1 0) single crystal surfaces and anatase nanoporous thin films

    Energy Technology Data Exchange (ETDEWEB)

    Ricks, Allen M.; Anfuso, Chantelle L.; Rodríguez-Córdoba, William; Lian, Tianquan, E-mail: tlian@emory.edu

    2013-08-30

    Highlights: • Investigated vibrational relaxation dynamics of a CO{sub 2}-reduction catalyst on TiO{sub 2} surfaces. • IR pump-vibration sum-frequency generation probe spectroscopy on Rutile (1 1 0) surface. • IR-pump/IR probe transient absorption spectroscopy on nano-crystalline thin films. • CO stretching modes show a ultrafast population equilibration followed by population decay. - Abstract: Time-resolved vibrational sum frequency generation (VSFG) spectroscopy has been used to investigate the vibrational relaxation dynamics of the rhenium bipyridyl CO{sub 2}-reduction catalyst Re(CO){sub 3}Cl(dcbpy) [dcbpy = 4,4′-dicarboxy-2,2′-bipyridine] adsorbed onto the (1 1 0) surface of a Rutile TiO{sub 2} single crystal. IR pump-VSFG probe spectra of the a′(1) CO stretching mode indicate a ultrafast population equilibration between three CO stretching modes followed by their population relaxation via intramolecular vibrational energy transfer. Similar vibational relaxation dynamics was also observed for the same complex on anatase TiO{sub 2} nanocrystalline thin films measured by IR pump-IR probe transient absorption spectroscopy. The relaxation dynamics of ReCOA on TiO{sub 2}, in DMF solution, and immobilized on Au through alkane thiol linkers were compared to examine possible effects of adsorbate-TiO{sub 2} interaction.

  13. Crystal structures and vibrational spectroscopy of neutral platinum(IV) amine iodo complexes

    Science.gov (United States)

    Thiele, G.; Danzeisen, O. F.; Rotter, H. W.; Goanta, M.

    1999-05-01

    A series of platinum(IV) amine iodo complexes of the type [PtL 2I 4] was synthesized for the first time and their infrared and Raman spectra were recorded. The crystal structures of cis-[Pt(net) 2I 4], (net=ethylamine) (space group Pnma, a=14.668(3), b=8.787(2), c=11.433(2) Å), trans-[Pt(net) 2I 4] (space group C2/c, a=11.276(2), b=8.866(2), c=12.542(3) Å, β=114.86(3)°) and [Pt(en)I 4] (en=ethylendiamine) (space group P1, a=6.780(1), b=11.613(2), c=14.703(3) Å, α=71.87(3), β=80.78(3), γ=80.08 (3)°) were determined. Formation of linear chains of molecules with short intermolecular I-I distances was observed for cis-[Pt(net) 2I 4]. The spectroscopic behavior is discussed according to these results.

  14. Synthesis, crystal structure, vibrational and dielectric properties of di-benzyl-ammonium selenite monohydrate

    Science.gov (United States)

    Jmal, Ameni; Oueslati, Abderrazek; Hamdi, Besma; Jarraya, Khaled

    2017-02-01

    The new hybrid compound [C6H5CH2NH3]2·SeO3·H2O was synthesized and found to crystallize in the triclinic space group P 1 bar . This structure can be described as an alternation between organic and inorganic chains connected by two types of N-Hrad O and O-Hrad O hydrogen bonds. The two and antiparallel cations [C6H5CH2NH3]+are arranged in a face-to-face pattern with a distance of 3.911(10)Å between them, indicating the existence of π-π interaction. The thermal properties show that the mass losses take place in three steps, which correspond to dehydration and degradation of the title compound. The IR and Raman spectra prove the existence and independence of the organic and inorganic groups as well as a water molecule. The equivalent circuit is modeled by a combination series of two parallel R-CPE circuits. Dielectric studies show that this material is ionic-protonic conductor at low temperature and becomes electronic one at high temperature.

  15. Effect of Metal Dopant on Ninhydrin—Organic Nonlinear Optical Single Crystals

    Directory of Open Access Journals (Sweden)

    R. S. Sreenivasan

    2013-01-01

    Full Text Available In the present work, metal (Cu2+-substituted ninhydrin single crystals were grown by slow evaporation method. The grown crystals have been subjected to single crystal XRD, powder X-ray diffraction, FTIR, dielectric and SHG studies. Single crystal X-ray diffraction analysis reveals that the compound crystallizes in monoclinic system with noncentrosymmetric space group P21 with lattice parameters a=11.28 Å, b=5.98 Å, c=5.71 Å, α=90∘, β=98.57, γ=90∘, and V=381 (Å3, which agrees very well with the reported value. The sharp and strong peaks in the powder X-ray diffraction pattern confirm the good crystallinity of the grown crystals. The presence of dopants marginally altered the lattice parameters without affecting the basic structure of the crystal. The UV-Vis transmittance spectrum shows that the crystal has a good optical transmittance in the entire visible region with lower cutoff wavelength 314 nm. The vibrational frequencies of various functional groups in the crystals have been derived from FT-IR analysis. Based on the shifts in the vibrations, the presence of copper in the lattice of the grown crystal is clearly established from the pure ninhydrin crystals. Both dielectric constant and dielectric loss decrease with the increase in frequency. The second harmonic generation efficiency was measured by employing powder Kurtz method.

  16. Lattice vibrations study of Ga{sub 1-x}In{sub x}As{sub y}Sb{sub 1-y} quaternary alloys with low (In, As) content grown by liquid phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Olvera-Herandez, J [Centro de Investigacion en Dispositivos Semiconductores (CIDS), BUAP, Puebla, Pue. 72570 (Mexico); Olvera-Cervantes, J [Centro de Investigacion en Dispositivos Semiconductores (CIDS), BUAP, Puebla, Pue. 72570 (Mexico); Rojas-Lopez, M [Centro de Investigacion en BiotecnologIa Aplicada (CIBA), IPN, Tlaxcala, Tlax. 72160 (Mexico); Navarro-Contreras, H [Instituto de Investigacion en Comunicacion Optica (IICO), UASLP, 78100, San Luis PotosI, S.L.P. (Mexico); Vidal, M A [Instituto de Investigacion en Comunicacion Optica (IICO), UASLP, 78100, San Luis PotosI, S.L.P. (Mexico); Anda, F de [Instituto de Investigacion en Comunicacion Optica (IICO), UASLP, 78100, San Luis PotosI, S.L.P. (Mexico)

    2006-01-01

    Raman scattering spectroscopy was used to measure and analyze the lattice vibrations in some quaternary Ga{sub 1-x}In{sub x}As{sub y}Sb{sub 1-y} alloys with low (In, As) contents (0.03 lattice matched to the GaSb substrate as obtained from the (004) reflection. The experimental diffractograms were simulated to estimate alloy composition, thickness and lattice mismatch of the layer. Raman scattering results show phonon frequencies associated to the TO and LO GaAs-like modes as well as GaSb + InAs-like mode, which are characteristic of this quaternary alloy. The As content dependence of the phonon frequency measured in this alloy for low (In, As) contents agree well with the modified Random-Element Isodisplacement (REI) model and also with other available experimental reports. This method can also be used to estimate alloy compositions for this kind of quaternary alloys.

  17. Complex vibrational analysis of an antiferroelectric liquid crystal based on solid-state oriented quantum chemical calculations and experimental molecular spectroscopy.

    Science.gov (United States)

    Drużbicki, Kacper; Mikuli, Edward; Kocot, Antoni; Ossowska-Chruściel, Mirosława Danuta; Chruściel, Janusz; Zalewski, Sławomir

    2012-08-02

    The experimental and theoretical vibrational spectroscopic study of one of a novel antiferroelectric liquid crystals (AFLC), known under the MHPSBO10 acronym, have been undertaken. The interpretation of both FT-IR and FT-Raman spectra was focused mainly on the solid-state data. To analyze the experimental results along with the molecular properties, density functional theory (DFT) computations were performed using several modern theoretical approaches. The presented calculations were performed within the isolated molecule model, probing the performance of modern exchange-correlations functionals, as well as going beyond, i.e., within hybrid (ONIOM) and periodic boundary conditions (PBC) methodologies. A detailed band assignment was supported by the normal-mode analysis with SQM ab initio force field scaling. The results are supplemented by the noncovalent interactions analysis (NCI). The relatively noticeable spectral differences observed upon Crystal to AFLC phase transition have also been reported. For the most prominent vibrational modes, the geometries of the transition dipole moments along with the main components of vibrational polarizability were analyzed in terms of the molecular frame. One of the goals of the paper was to optimize the procedure of solid-state calculations to obtain the results comparable with the all electron calculations, performed routinely for isolated molecules, and to test their performance. The presented study delivers a complex insight into the vibrational spectrum with a noticeable improvement of the theoretical results obtained for significantly attracting mesogens using modern molecular modeling approaches. The presented modeling conditions are very promising for further description of similar large molecular crystals.

  18. Electron spin echo of Cu(2+) in the triglycine sulfate crystal family (TGS, TGSe, TGFB): electron spin-lattice relaxation, Debye temperature and spin-phonon coupling.

    Science.gov (United States)

    Lijewski, S; Goslar, J; Hoffmann, S K

    2006-07-05

    The electron spin-lattice relaxation of Cu(2+) has been studied by the electron spin echo technique in the temperature range 4.2-115 K in triglycine sulfate (TGS) family crystals. Assuming that the relaxation is due to Raman relaxation processes the Debye temperature Θ(D) was determined as 190 K for TGS, 168 K for triglycine selenate (TGSe) and 179 K for triglycine fluoroberyllate (TGFB). We also calculated the Θ(D) values from the sound velocities derived from available elastic constants. The elastic Debye temperatures were found as 348 K for TGS, 288 K for TGSe and 372 K for TGFB. The results shown good agreement with specific heat data for TGS. The elastic Θ(D) are considerably larger than those determined from the Raman spin-lattice relaxation. The possible reasons for this discrepancy are discussed. We propose to use a modified expression describing two-phonon Raman relaxation with a single variable only (Θ(D)) after elimination of the sound velocity. Moreover, we show that the relaxation data can be fitted using the elastic Debye temperature value as a constant with an additional relaxation process contributing at low temperatures. This mechanism can be related to a local mode of the Cu(2+) defect in the host lattice. Electron paramagnetic resonance g-factors and hyperfine splitting were analysed in terms of the molecular orbital theory and the d-orbital energies and covalency factors of the Cu(gly)(2) complexes were found. Using the structural data and calculated orbital energies the spin-phonon coupling matrix element of the second-order Raman process was calculated as 553 cm(-1) for TGS, 742 cm(-1) for TGSe and 569 cm(-1) for TGFB.

  19. Phonon spectrum, electron spin-lattice relaxation and spin-phonon coupling of Cu2+ ions in BaF2 crystal

    Science.gov (United States)

    Hoffmann, Stanislaw K.; Lijewski, Stefan

    2015-03-01

    Electron spin-lattice relaxation rate is determined by electron spin echo method in temperature range 4-60 K. The Raman relaxation processes dominate and its theory is outlined in a form suitable for calculations of relaxation rate using real phonon spectrum. A few approximations have been considered: when phonon spectrum and Debye temperature are not available; when Debye temperature is available but phonon spectrum is not; and when spin-phonon coupling is known. All these approximations use the Debye model of phonons and give a non-satisfactory description the temperature dependence of the relaxation rate. A perfect description of experimental results is obtained when real phonon spectrum is considered. The value of the spin-phonon coupling parameter was determined as G = = 1362cm-1 . This value is discussed by a comparison with G-values published for various ions and crystals.

  20. The vibrational spectra of N-phenylpyrrole in the gas phase, in argon matrices and in single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Schweke, D. [Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Farkas Center for Light-Induced Processes, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Brauer, B. [Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Fritz Haber Research Center, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Gerber, R.B. [Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Fritz Haber Research Center, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Department of Chemistry, University of California, Irvine, CA 92697 (United States); Haas, Y. [Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Farkas Center for Light-Induced Processes, Hebrew University of Jerusalem, Jerusalem 91904 (Israel)], E-mail: yehuda@chem.ch.huji.ac.il

    2007-03-30

    The infrared spectrum of N-phenylpyrrole (PP) was measured in the gas phase and in an argon matrix, and the Raman spectrum was obtained in a single crystal. The measured matrix shifts are found to be small: many bands are not split, and the shifts from the gas phase values are less than 1%. Splitting to two sub-bands is observed for some bands, indicating the presence of two major trapping sites, in agreement with previous predictions. The spectra are analyzed with the help of harmonic calculations on the free molecule and on its adduct with one or two argon atoms, and anharmonic frequency calculations on the free molecule. Harmonic frequencies were obtained at the MP2/cc-pVDZ and DFT-B3LYP/cc-pVDZ levels. Anharmonic frequencies were obtained by the correlation-corrected vibrational self-consistent field (CC-VSCF) method with a variant of the PM3 semiempirical electronic structure method, calibrated for much improved spectroscopic accuracy. The potential surfaces used in the CC-VSCF calculation obtained by adjusting standard PM3 surfaces so that they provide harmonic frequencies that are comparable to those obtained at the DFT-B3LYP/cc-pVDZ level. Agreement between the experimental and theoretical results is in general very good, allowing the assignments of most bands. The harmonic frequency calculations of PP-Ar clusters, at the MP2/cc-pVDZ level show that the environment can greatly affect the intensities of some of the transitions, which is in accord with experiment.

  1. Synthesis and characterization of tetraethylammonium tetrachlorocobaltate crystals

    Indian Academy of Sciences (India)

    M A Kandhaswamy; V Srinivasan

    2002-02-01

    Single crystals of tetraethylammonium tetrachlorocobaltate were grown by solution method and characterized through single crystal X-ray diffraction, thermogravimetric analysis (TGA), differential scanning calorimetric studies (DSC) and infrared spectroscopic technique (IR). The crystals were bright, transparent and blue coloured. The unit cell parameters were found to be = = 9.0363 Å and = 14.9879 Å and = = = 90°, showing tetragonal lattice from the XRD data. Thermogravimetric analysis showed a loss of weight at 683 K from which the decomposition reaction was formulated. Thermal anomalies were found for this crystal at temperatures 200 K, 220 K in the cooling cycle and at temperatures 200 K, 240 K in the heating cycle, respectively which showed that this crystal was associated with first order phase transition. All the vibrational frequencies corresponding to (TEA)+ ions and CoCl$^{2-}_4$ ions were assigned from the IR spectral data of this crystal.

  2. Trans-dichlorotetrakis(1H-pyrazole-κN2)copper(II): Synthesis, crystal structure, hydrogen bonding graph-sets, vibrational and DFT studies

    Science.gov (United States)

    Direm, Amani; Tursun, Mahir; Parlak, Cemal; Benali-Cherif, Nourredine

    2015-08-01

    The copper complex [Cu(HPrz)4]Cl2 (HPrz = Pyrazole) was synthesized and its structure was characterized by FT-IR, Raman and single-crystal X-ray diffraction (XRD) techniques. The structural conformers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of the compound were examined by means of the density functional theory (DFT) method, the Becke-3-Lee-Yang-Parr (B3LYP) functional, the 6-311+G(3df,p) and lanl2dz basis sets. Reliable vibrational assignments were investigated by the potential energy distribution (PED) analysis. The compound crystallizes in the monoclinic space group C2/c with the unit cell parameters a = 13.5430 (10) Å, b = 9.1480 (10) Å, c = 14.6480 (10) Å and β = 116.7° (5). There is a good agreement between the theoretically predicted structural parameters and vibrational frequencies and those obtained experimentally. The findings of this work reveals further insight into molecular copper(II) pyrazole systems.

  3. Intermolecular Vibrations of Hydrophobic Amino Acids

    Science.gov (United States)

    Williams, Michael Roy Casselman

    Hydrophobic amino acids interact with their chemical environment through a combination of electrostatic, hydrogen bonding, dipole, induced dipole, and dispersion forces. These interactions all have their own characteristic energy scale and distance dependence. The low-frequency (0.1-5 THz, 5-150 cm-1) vibrational modes of amino acids in the solid state are a direct indicator of the interactions between the molecules, which include interactions between an amino acid functional group and its surroundings. This information is central to understanding the dynamics and morphology of proteins. The alpha-carbon is a chiral center for all of the hydrophobic amino acids, meaning that they exist in two forms, traditionally referred to as L- and D-enantiomers. This nomenclature indicates which direction the molecule rotates plane-polarized visible light (levorotory and dextrorotory). Chiral a-amino acids in proteins are exclusively the L-variety In the solid state, the crystal lattice of the pure L-enantiomer is the mirror image of the D-enantiomer crystal lattice. These solids are energetically identical. Enantiomers also have identical spectroscopic properties except when the measurement is polarization sensitive. A mixture of equal amounts D- and L-amino acid enantiomers can crystallize into a racemic (DL-) structure that is different from that of the pure enantiomers. Whether a solution of both enantiomers will crystallize into a racemic form or spontaneously resolve into a mixture of separate D- and L-crystals largely depends on the interactions between molecules available in the various possible configurations. This is an active area of research. Low-frequency vibrations with intermolecular character are very sensitive to changes in lattice geometry, and consequently the vibrational spectra of racemic crystals are usually quite distinct from the spectra of the crystals of the corresponding pure enantiomers in the far-infrared (far-IR). THz time-domain spectroscopy (THz

  4. Temperature dependent lattice instability in single crystals of ferromagnetic CdCr2Se4 diluted with In and Sb

    DEFF Research Database (Denmark)

    Waskowska, A.; Gerward, Leif; Olsen, J.S.

    2008-01-01

    to occur at the same temperature as the magnetic transition, T-c = 130 K, which also is the same T-c as for the parent crystal CdCr2Se4. The low temperature phase has been described in orthorhombic space group Fddd. For In admixture, a structural transition occurs in the paramagnetic state at about T...

  5. Localized vibrational modes in diamond

    Science.gov (United States)

    Murzaev, R. T.; Bachurin, D. V.; Korznikova, E. A.; Dmitriev, S. V.

    2017-03-01

    Discrete breather (DB) or, synonymously, intrinsic localized mode (ILM) is a spatially localized and time-periodic vibrational mode in a defect-free nonlinear lattice, e.g., in a crystal lattice. Standing DB and DB clusters (double and triple) are studied in diamond using molecular dynamics method with the AIREBO interatomic potentials. Single DB can be easily excited by applying initial shifts, A0, to a pair of nearest atoms along the valence bond in the opposite directions. Admissible excitation amplitudes are 0.09 ≤A0 /a0 ≤ 0.12, where a0 is the equilibrium interatomic distance. The core of a DB is a pair of nearest carbon atoms oscillating out-of-phase, while the neighboring atoms oscillate with one order of magnitude lower amplitudes. DB frequency is above the top of the phonon spectrum and increases with the oscillation amplitude. DB lives for more than 100 oscillation periods which approximately corresponds to 2 ps. The range of initial amplitudes and other conditions necessary for the excitation of double and triple DB clusters as well as their lifetime are investigated in detail. Two different mechanisms of energy exchange between DBs in the DB clusters are revealed, which is the main result of the present study. Our results contribute to a deeper understanding of the nonlinear lattice dynamics of diamond.

  6. Research on the vibration band gaps of isolators applied to ship hydraulic pipe supports based on the theory of phononic crystals

    Science.gov (United States)

    Wei, Zhendong; Li, Baoren; Du, Jingmin; Yang, Gang

    2016-04-01

    According to the theory of phononic crystals, a new isolator applied to ship hydraulic pipe-support with a one-dimensional periodic composite structure is designed, which is composed of metal and rubber. The vibration of the ship hydraulic pipeline can be suppressed by the band gaps (BGs) of the isolator. The band structure and frequency response function of the isolator is figured out by the transfer matrix method and the finite element method respectively. The frequency ranges and width of the BGs can be modulated to obtain the best structure of the isolator by changing the geometrical parameters. The experimental results provide an attenuation of over 20 dB in the frequency range of the BGs, and the results show good agreement with those of the numeric calculations. The research provides an effective way to control the vibration of ship hydraulic pipelines.

  7. ASE suppression in Er3+ doped dual-core triangular lattice Photonic Crystal Fibers (PCFs) for communication wavelength

    CERN Document Server

    Maji, Partha Sona

    2014-01-01

    In this article, silica based triangular lattice PCF has been investigated towards both narrowband and broadband dispersion compensation for application in the communication wavelength. A dual core structure is obtained by introducing two different air-hole diameters in the cladding of the PCF. Dependence of individual structural parameters towards high negative dispersion (both narrowband and broadband) has been investigated in details with multipole mode based solver. The numerical investigation exhibits narrowband of very large negative dispersion of -37,300 ps/nm/km around the wavelength of 1550 nm. Present investigation also reports broadband dispersion values varying from -800 ps/nm/km to -2600 ps/nm/km over a 200 nm wavelength (1400 nm to 1600 nm) range, and kappa values near 300 nm, which matches well with standard single mode fiber. Using the principle of power transfer from the inner core to the outer core after the coupling wavelength, we have investigated possible design of ASE suppressed amplifie...

  8. Anomalous Hall effect in a ferromagnetic Fe3Sn2 single crystal with a geometrically frustrated Fe bilayer kagome lattice

    Science.gov (United States)

    Wang, Qi; Sun, Shanshan; Zhang, Xiao; Pang, Fei; Lei, Hechang

    2016-08-01

    The anomalous Hall effect (AHE) is investigated for a ferromagnetic Fe3Sn2 single crystal with a geometrically frustrated kagome bilayer of Fe. The scaling behavior between anomalous Hall resistivity ρxy A and longitudinal resistivity ρx x is quadratic and further analysis implies that the AHE in the Fe3Sn2 single crystal should be dominated by the intrinsic Karplus-Luttinger mechanism rather than extrinsic skew-scattering or side-jump mechanisms. Moreover, there is a sudden jump of anomalous Hall conductivity σxy A appearing at about 100 K where the spin-reorientation transition from the c axis to the a b plane is completed. This change of σxy A might be related to the evolution of the Fermi surface induced by the spin-reorientation transition.

  9. Low-temperature change of lattice parameters in LiKB{sub 4}O{sub 7} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Adamiv, Volodymyr; Burak, Yaroslav; Teslyuk, Ihor [Institute of Physical Optics, Lviv (Ukraine)

    2009-02-15

    Structural investigations of LiKB{sub 4}O{sub 7} crystals in the 13-290 K temperature range have been carried out by means of the high-resolution powder diffraction technique applying synchrotron radiation. It is shown that the structural phase transitions are absent and all the linear thermal expansion coefficients {alpha}{sub ij} are positive in the investigated temperature range. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. The Influence of Crystal Structure on the Lattice Sites and Formation Energies of Hydrogen in Wurtzite and Zinc-Blende GaN

    Energy Technology Data Exchange (ETDEWEB)

    Wright, A.F.

    1999-02-01

    Charge-state calculations based on density-functional theory are used to study the formation energy of hydrogen in wurtzite and zinc-blende GaN as a function of Fermi level Comparison of these results reveals notable differences including a 0.56 eV lower formation energy for H2 in wurtzite, and different configurations for H2 and H- in the two crystal structures. Furthermore, H+ is found to be equally stable at bond-centered and anti-bonding sites in wurtzite, whereas it is unstable at a bond-centered site in zinc blende. These differences are due to distinct features of the two crystal structures including: the lower symmetry of wurtzite which provides a wider selection of bonding sites for H+, and the existence of extended three-fold symmetric channels oriented along the c-axis in wurtzite which provide more favorable bonding configurations for H2 and H-.N-H+ stretch-mode vibration frequencies, clustering of ?3+ in p-type material, and diffusion barriers for H" are also investigated in wurtzite GaN. A diffusion barrier of 1.6 eV is found for H- in wurtzite GaN, significantly lower than a previous estimate, and a tendency for H+ clustering in p-type material is found.

  11. Vibrational spectroscopic and thermo dynamical property studies, Fukui functions, HOMO-LUMO, NLO, NBO and crystal structure analysis of a new Schiff base bearing phenoxy-imine group

    Science.gov (United States)

    Ceylan, Ümit; Çapan, Ali; Yalçın, Şerife Pınar; Sönmez, Mehmet; Aygün, Muhittin

    2017-05-01

    This study covers the synthesis, structural characterization by experimental FT-IR, 1H NMR and 13C NMR, UV-Vis and single crystal XRD and comparison with theoretical calculations of a Schiff base compound bearing phenoxy group, C34H28N2O4 by using the DFT method 6-311G(d,p) basis set. The molecular geometry, the dipole moments, electrostatic potential, vibrational frequencies, HOMO-LUMO energy were calculated. NBO, NLO, thermodynamic properties and Fukui function were studied. In this work, theoretical values show good agreement with experimental values.

  12. Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2

    Science.gov (United States)

    May, Andrew F.; Calder, Stuart; Parker, David S.; Sales, Brian C.; McGuire, Michael A.

    2016-01-01

    Identifying and characterizing systems with coupled and competing interactions is central to the development of physical models that can accurately describe and predict emergent behavior in condensed matter systems. This work demonstrates that the metallic compound CuFe2Ge2 has competing magnetic ground states, which are shown to be strongly coupled to the lattice and easily manipulated using temperature and applied magnetic fields. Temperature-dependent magnetization M measurements reveal a ferromagnetic-like onset at 228 (1) K and a broad maximum in M near 180 K. Powder neutron diffraction confirms antiferromagnetic ordering below TN ≈ 175 K, and an incommensurate spin density wave is observed below ≈125 K. Coupled with the small refined moments (0.5–1 μB/Fe), this provides a picture of itinerant magnetism in CuFe2Ge2. The neutron diffraction data also reveal a coexistence of two magnetic phases that further highlights the near-degeneracy of various magnetic states. These results demonstrate that the ground state in CuFe2Ge2 can be easily manipulated by external forces, making it of particular interest for doping, pressure, and further theoretical studies. PMID:27739477

  13. Comparative Study Between GGA and LDA Approximation Using First- Principles Calculations of Structural, Electronic, Optical and Vibrational Properties of CaTiO3 Crystal

    Science.gov (United States)

    Medeiros, Subenia; Araujo, Maeva

    2015-03-01

    The structural, electronic, vibrational, and optical properties of perovskite CaTiO3 in the cubic, orthorhombic, and tetragonal phase are calculated in the framework of density functional theory (DFT) with different exchange-correlation potentials by CASTEP package. The calculated band structure shows an indirect band gap of 1.88 eV at the Γ-R points in the Brillouin zone to the cubic structure, a direct band gap of 2.41 eV at the Γ- Γ points to the orthorhombic structure, and an indirect band gap of 2.31 eV at theM - Γ points to the tetragonal phase. It is still known that the CaTiO3 has a static dielectric constant that extrapolates to a value greater than 300 at zero temperature, and the dielectric response is dominated by low frequency (ν ~ 90cm-1) polar optical modes in which cation motion opposes oxygen motion. Our calculated lattice parameters, elastic constants, optical properties, and vibrational frequencies are found to be in good agreement with the available theoretical and experimental values. The results for the effective mass in the electron and hole carriers are also presented in this work.

  14. Advanced applications of ion channeling for the study of imperfections in crystals

    Energy Technology Data Exchange (ETDEWEB)

    Swanson, M.L. [North Carolina Univ., Chapel Hill, NC (United States)

    1997-03-01

    A review will be given of the applications of medium energy ion channeling for the studies of imperfections in the near-surface regions of crystals. The following topics will be discussed: (1.) epitaxial layers, including elemental depositions of a few monolayers, strained-layer superlattices, and compound layers; (2.) lattice defects, including ion damage in diamond, dislocation networks in Si, and anomalous lattice vibrations in high temperature superconductors; (3.) lattice sites of solute atoms, including substitutional sites in compounds (LiNbO{sub 3} and GaP), and interstitial sites produced by association with point defects. (author)

  15. A two—dimensional photonic crystal with six large bandgaps formed by a hexagonal lattice of anisotropic cylinders

    Institute of Scientific and Technical Information of China (English)

    庄飞; 吴良; 等

    2002-01-01

    The plane-wave expansion method is used to calculate the band structure of a two-dimensional photonic crystal formed by a hexagonal structure of anisotropic cylinders.Two cylindrical inclusions in the unit cell have two different radii,R1 and R2(R1

  16. Pair distribution of ions in Coulomb lattice

    CERN Document Server

    Witt, H E D; Chugunov, A I; Baiko, D A; Yakovlev, D G

    2003-01-01

    The pair distribution function g(r) ident to g(x, y, z) and the radial pair distribution function g(r) of ions in body-centred-cubic and face-centred-cubic Coulomb crystals are calculated within the harmonic-lattice (HL) approximation in a wide temperature range, from the high-temperature classical limit (T >> h-bar w sub p , w sub p being the ion plasma frequency) to the low-temperature quantum limit (T || h-bar w sub p). In the classical limit, g(r) is also calculated by the Monte Carlo (MC) method. MC and HL results are demonstrated to be in good agreement. With decreasing T, the correlation peaks of g(r) and g(r) become narrower. At T || h-bar w sub p they become temperature independent (determined by zero-point ion vibrations).

  17. Crystal growth, structural and thermal studies of amino acids admixtured L-arginine phosphate monohydrate single crystals

    Science.gov (United States)

    Anandan, P.; Saravanan, T.; Parthipan, G.; Kumar, R. Mohan; Bhagavannarayana, G.; Ravi, G.; Jayavel, R.

    2011-05-01

    To study the improved characteristics of L-arginine phosphate monohydrate (LAP) crystals, amino acids mixed LAP crystals have been grown by slow cooling method. Amino acids like glycine, L-alanine, and L-valine have been selected for doping. Optical quality bulk crystals have been harvested after a typical growth period of about twenty days. The effect of amino acids in the crystal lattice and molecular vibrational frequencies of various functional groups in the crystals have been studied using X-ray powder diffraction and Fourier Transform infrared (FTIR) analyses respectively. Thermal behavior of the amino acids mixed LAP crystals have been studied from the TG and DTG analyses. High-resolution X-ray diffraction studies have been carried out to find the crystalline nature. Optical transmission studies have been carried out by UV-vis spectrophotometer. The cut off wavelength is below 240 nm for the grown crystals.

  18. Chemical synthesis, crystal structure, vibrational spectroscopy, non-linear optical properties and DFT calculation of bis (2,6-diaminopyridinium) sulfate monohydrate

    Science.gov (United States)

    Ben Hassen, Chaouki; Dammak, Thameur; Chniba-Boudjada, Nassira; Mhiri, Tahar; Boujelbene, Mohamed

    2017-01-01

    Single crystals of a new organic inorganic hybrid compound "bis (2,6-diaminopyridinium) sulfate monohydrate [C5H8N3]2SO4·H2O ([2,6-HDAP]2SO4·H2O)" was synthesized by slow evaporation method at room temperature and characterized by X-ray single crystal diffraction, infrared spectroscopy and DFT calculation. The new hybrid compound crystallizes in the orthorhombic system with the non-centro symmetric space group Pna21 and the following parameters a = 14.759(2) Å, b = 7.076 (2) Å and c = 28.159 (2) Å. The atomic arrangement can be described as inorganic chains following the b axis connected with the organic groups by means of Nsbnd H⋯O hydrogen bonds to form 3D network. Antiparallelly π-π stacked 2,6-HDAP cations form molecular columns in the spaces between the chains. The optimized molecular structure, vibrational spectra and the optical properties were calculated by the density functional theory (DFT) method using the B3LYP function with the LanL2DV basis set. The wavenumber calculated are in good agreement with the observed frequency values. The calculated hyperpolarizability βtot is about 4.5 times more than that of the reference crystal KDP. Hence, the large β value shows that the title compound is an attractive object for future studies of nonlinear optical properties.

  19. Towards an understanding of the molecular mechanism of solvation of drug molecules: a thermodynamic approach by crystal lattice energy, sublimation, and solubility exemplified by hydroxybenzoic acids.

    Science.gov (United States)

    Perlovich, German L; Volkova, Tatyana V; Bauer-Brandl, Annette

    2006-07-01

    Temperature dependencies of saturated vapor pressure and heat capacities for the 2-, 3-, and 4-hydroxybenzoic acids were measured and thermodynamic functions of sublimation calculated (2-hydroxybenzoic acid: DeltaG(sub) (298) = 38.5 kJ/mol; DeltaH(sub) (298) = 96.6 +/- 0.8 kJ/mol; DeltaS(sub) (298) = 191 +/- 3 J/mol . K; 3-hydroxybenzoic acid: DeltaG(sub) (298) = 50.6 kJ/mol; DeltaH(sub) (298) = 105.2 +/- 0.8 kJ/mol; DeltaS(sub) (298) = 180 +/- 2 J/mol . K; 4-hydroxybenzoic acid: DeltaG(sub) (298) = 55.0 kJ/mol; DeltaH(sub) (298) = 113.3 +/- 0.7 kJ/mol; DeltaS(sub) (298) = 193 +/- 2 J/mol . K). Analysis of crystal lattice packing energies based on geometry optimization of the molecules in the crystal using diffraction data and the program Dmol(3) was carried out. The energetic contributions of van der Waals, Coulombic, and hydrogen bond terms to the total packing energy were analyzed. The fraction of hydrogen bond energy in the packing energy increases as: 3-hydroxybenzoic (29.7%) Enthalpies of evaporation were estimated from enthalpies of sublimation and fusion. Temperature dependencies of the solubility in n-octanol and n-hexane were measured. The thermodynamic functions of solubility and solvation processes were deduced. Specific and nonspecific solvation terms were distinguished using the transfer from the "inert" n-hexane to the other solvents. The transfer of the molecules from water to n-octanol is enthalpy driven process.

  20. Lattice Bosons

    CERN Document Server

    Chakrabarti, J; Bagchi, B; Chakrabarti, Jayprokas; Basu, Asis; Bagchi, Bijon

    2000-01-01

    Fermions on the lattice have bosonic excitations generated from the underlying periodic background. These, the lattice bosons, arise near the empty band or when the bands are nearly full. They do not depend on the nature of the interactions and exist for any fermion-fermion coupling. We discuss these lattice boson solutions for the Dirac Hamiltonian.

  1. The crystal structure and vibrational spectra of two molecules emitting dual fluorescence: 4-(1H-Pyrrol-1-yl)benzonitrile (PBN) and 5-cyano-2-(1pyrrolyl)-pyridine (CPP)

    Energy Technology Data Exchange (ETDEWEB)

    Schweke, D.; Abramov, S. [Department of Physical Chemistry and the Farkas Center for Light Induced Processes, Hebrew University of Jerusalem, Jerusalem (Israel); Haas, Y. [Department of Physical Chemistry and the Farkas Center for Light Induced Processes, Hebrew University of Jerusalem, Jerusalem (Israel)], E-mail: yehuda@chem.ch.huji.ac.il

    2007-05-21

    Crystal structures and vibrational spectra are reported for the two title molecules which exhibit dual fluorescence due to the existence of a low lying charge transfer excited state. The data show that in the ground state PBN is twisted whereas CPP is planar, and the crystal structures are quite different. The experimental spectra are in very good agreement with quantum mechanical calculations, which also predict considerable differences between the vibrational spectra of CPP in the ground state and in the charge transfer excited state.

  2. Elimination of spurious lattice fermion solutions and noncompact lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Lee, T.D.

    1997-09-22

    It is well known that the Dirac equation on a discrete hyper-cubic lattice in D dimension has 2{sup D} degenerate solutions. The usual method of removing these spurious solutions encounters difficulties with chiral symmetry when the lattice spacing l {ne} 0, as exemplified by the persistent problem of the pion mass. On the other hand, we recall that in any crystal in nature, all the electrons do move in a lattice and satisfy the Dirac equation; yet there is not a single physical result that has ever been entangled with a spurious fermion solution. Therefore it should not be difficult to eliminate these unphysical elements. On a discrete lattice, particle hop from point to point, whereas in a real crystal the lattice structure in embedded in a continuum and electrons move continuously from lattice cell to lattice cell. In a discrete system, the lattice functions are defined only on individual points (or links as in the case of gauge fields). However, in a crystal the electron state vector is represented by the Bloch wave functions which are continuous functions in {rvec {gamma}}, and herein lies one of the essential differences.

  3. Analysis of crystallite size and microdeformation crystal lattice the tungsten carbide milling in mill high energy; Analise do tamanho do cristalito e microdeformacao da rede cristalina do carbeto de tugstenio moidos em moinho de alta energia

    Energy Technology Data Exchange (ETDEWEB)

    Silva, F.T. da; Nunes, M.A.M. [Universidade Federal do Rio Grande do Norte (PPGCEM/UFRN), Natal (Brazil). Programa de Pos-Graduacao em Ciencia e Engenharia de Materiais; Oliveira, R.M.V. de; Silva, G.G. da [Instituto Federal do Rio Grande do Norte (IFRN), Natal (Brazil); Souza, C.P. de; Gomes, U.U. [Universidade Federal do Rio Grande do Norte (UFRN), Natal (Brazil)

    2010-07-01

    The tungsten carbide (WC) has wide application due to its properties like high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The microstructural characteristics of the starting powders influences the final properties of the carbide. In this context, the use of nanoparticle powders is an efficient way to improve the final properties of the WC. The high energy milling stands out from other processes to obtain nanometric powders due to constant microstructural changes caused by this process. Therefore, the objective is to undertake an analysis of microstructural characteristics on the crystallite size and microdeformations of the crystal lattice using the technique of X-ray diffraction (XRD) using the Rietveld refinement. The results show an efficiency of the milling process to reduce the crystallite size, leading to a significant deformation in the crystal lattice of WC from 5h milling. (author)

  4. A novel coordination polymer of 7-azaindole-3-carboxylic acid with sodium ions: crystal and molecular structures, vibrational spectra and DFT calculations

    Science.gov (United States)

    Morzyk-Ociepa, Barbara; Szmigiel, Ksenia; Petrus, Rafał; Turowska-Tyrk, Ilona; Michalska, Danuta

    2017-09-01

    A novel two-dimensional coordination polymer, catena-poly[(μ2-7-azaindole-3-carboxylato-O:N)-di-aqua-sodium], [Na(7AI3CAH)(H2O)2]n has been synthesized and investigated by a single crystal X-ray diffraction, vibrational spectroscopy and DFT calculations. The sodium complex crystallizes in the triclinic system, space group Pī with a = 7.2226 (4), b = 7.4342 (7), c = 8.8428 (8) Å, α = 103.568 (8), β = 93.425 (6), γ = 91.233 (6)°, V = 460.42 (7) A3 and Z = 2. The asymmetric unit contains two crystallographically independent, half occupied sodium cations surrounded by one 7AI3CAH anion and two water molecules. The O-deprotonated 7-azaindole-3-carboxylate ligand (7AI3CAH) bridges the adjacent Na ions via one oxygen atom of the carboxylate group and via the pyridine nitrogen atom of the 7-azaindole group, which is quite unusual. The sodium cations are six-coordinated in a distorted octahedral geometry, where two apical positions are occupied by two water molecules. Extensive intermolecular Nsbnd H⋯O and Osbnd H⋯O hydrogen bonds stabilize the crystal structure of the complex. The infrared and Raman spectra of [Na(7AI3CAH)(H2O)2]n were recorded in the solid state. The theoretical wavenumbers, infrared intensities, Raman scattering activities and Raman intensities were calculated at the B3LYP/6-311++G(d,p) level for a theoretical model of the title compound including an inter ligand Nsbnd H⋯O(aqua) interaction. A detailed vibrational assignment has been made on the basis of the calculated potential energy distribution.

  5. Comments on: “Crystal growth and comparison of vibrational and thermal properties of semi-organic nonlinear optical materials”

    Indian Academy of Sciences (India)

    Srinivasan Bikshandarkoil R; Fernandes Royle

    2016-03-01

    In {\\it Pramana – J. Phys. } 75, 683 (2010), Gunasekaran et al reported that they have grown the nonlinear optical crystals, urea thiourea mercuric chloride (UTHC) and urea thiourea mercuric sulphate (UTHS).We argue that UTHC and UTHS are dubious crystals and are not what the authors propose.

  6. Evidence for lattice strain and non-ideal behaviour in the (La1-xEux)PO4 solid solution from X-ray diffraction and vibrational spectroscopy

    Science.gov (United States)

    Geisler, Thorsten; Popa, Karin; Konings, Rudy

    2016-06-01

    The monazite-type solid solution of LaPO_4 and EuPO_4 has been studied by X-ray diffraction, infrared (IR) and Raman spectroscopic techniques. A substantial excess molar volume has been derived from the X-ray data, and the Raman and IR spectra show band broadening typical for mixing of cations of different size on the cation sublattice. The IR spectra were interpreted by the autocorrelation method and the excess autocorrelation parameter Δ{corr}^{ex} shows clear deviation from ideal solution behaviour, similar to the observed broadening of the Raman bands. The results can be interpreted in terms of local lattice strains resulting from the ion size effects of substitution of La^{3+} by Eu^{3+}, and correlate very well with calorimetric measurements of the excess enthalpy that was previously measured.

  7. Crystal structure, Hirshfeld and vibrational study at ambient temperature of propylammonium pentachlorobismuthate [n-C3H7NH3]2BiCl5 (III)

    Science.gov (United States)

    Lambarki, F.; Ouasri, A.; Zouihri, H.; Rhandour, A.

    2017-08-01

    The crystal structure of [n-C3H7NH3]2BiCl5 compound is determined at 298 K in the orthorhombic system [Pbca; Z = 4; a = 12.6440(4) Å, b = 11.9209(3) Å, c = 21.9634(6) Å and V = 3310.50 (16) Å3]. The anionic sublattice of the crystal is made up of isolated Bi2Cl104- dimers composed of two equivalent slightly distorted BiCl63- octahedra sharing one edge. The organic part consists of two disordered propylammonium C3H7NH3+ cations which orient their amine groups to the neighboring anions. The infrared and Raman spectra were recorded at room temperature in 50-3500 and 450-4000 cm-1 frequency regions, respectively. The vibrational study confirms the presence of organic cations C3H7NH3+ and Bi2Cl104- dimers that are connected to each other by Nsbnd H⋯Cl hydrogen bonding. The significant intermolecular interactions in the crystal structure are identified and analyzed using the Hirshfeld surface and fingerprint plots computational methods.

  8. Non-Equilibrium Creation of Intrinsically Localized Vibrations in Uranium Using X-Ray and Neutron Scattering

    Energy Technology Data Exchange (ETDEWEB)

    Manley, M; Alatas, A; Trouw, F; Leu, B M; Lynn, J W; Chen, Y; Hults, W L

    2007-07-02

    In an anharmonic crystal, large-amplitude vibrational fluctuations on the scale of the lattice spacing can develop frequencies that do not resonate with the normal modes, causing energy to become trapped in intrinsically localized modes (ILMs)--also called 'discrete breathers' or 'lattice solitons'. This mechanism has been observed in analogous systems on a larger scale, but unambiguous sightings in atomic lattice vibrations, where quantum mechanics may play a role, have proved difficult. Two challenges have hampered progress: (1) the need to separate ILMs from defect modes, and (2) complications that arise at high temperatures, including feature broadening and multiphonon processes. Here we solve these problems by using x-ray and neutron scattering to induce ILM-forming amplitude fluctuations in uranium at low temperatures, thereby creating nonequilibrium ILMs. Creation of ILMs occurs at a discrete energy, indicating an unexpected quantum character to ILM formation and greatly simplifying detection.

  9. High quality factor and high sensitivity photonic crystal rectangular holes slot nanobeam cavity with parabolic modulated lattice constant for refractive index sensing

    Science.gov (United States)

    Sun, Fujun; Zhou, Jian; Huang, Lijun; Fu, Zhongyuan; Tian, Huiping

    2017-09-01

    In this paper, we present a novel optical sensor based on photonic crystal slot nanobeam cavity (PCSNC) with rectangular air holes. By introducing a continuous slot and quadratically modulated hole spacing (lattice constant a) structure, the majority of the optical field is localized in the slot region, which enhances the light-matter interaction. With applying the three dimensional finite-difference time-domain (3D-FDTD) simulations, three key geometric parameters (hole width wx, slot width ws and the number of the holes N) are optimized to achieve a high sensitivity (S) while keeping a high quality (Q) factor. The highest S over 1000 nm/RIU (refractive index unit) is achieved when the slot width equals to 200 nm. The highest Q-factor of 2.15×107 is obtained when 30 holes are placed on both sides of the host waveguide with the slot width of 80 nm. Considering the transmission efficiency and the trade-off between S and Q-factor, the slot width and the number of the tapered region are chosen as 80 nm and 20, respectively. A high S approximately 835 nm/RIU and a Q-factor about 5.50×105 with small effective mode volume of 0.03(λ/nair)3 are achieved simultaneously, resulting in an ultra-high figure-of-merit (FOM) above 2.92×105. Furthermore, the active sensing region of the optimized structure occupies only about 12 μm×0.08 μm, which makes the device attractive for realizing on-chip integrated sensor arrays.

  10. Towards an understanding of the molecular mechanism of solvation of drug molecules: a thermodynamic approach by crystal lattice energy, sublimation, and solubility exemplified by paracetamol, acetanilide, and phenacetin.

    Science.gov (United States)

    Perlovich, German L; Volkova, Tatyana V; Bauer-Brandl, Annette

    2006-10-01

    Temperature dependencies of saturated vapor pressure for the monoclinic modification of paracetamol (acetaminophen), acetanilide, and phenacetin (acetophenetidin) were measured and thermodynamic functions of sublimation calculated (paracetamol: DeltaGsub298=60.0 kJ/mol; DeltaHsub298=117.9+/-0.7 kJ/mol; DeltaSsub298=190+/-2 J/mol.K; acetanilide: DeltaGsub298=40.5 kJ/mol; DeltaHsub298=99.8+/-0.8 kJ/mol; DeltaSsub298=197+/-2 J/mol.K; phenacetin: DeltaGsub298=52.3 kJ/mol; DeltaHsub298=121.8+/-0.7 kJ/mol; DeltaSsub298=226+/-2 J/mol.K). Analysis of packing energies based on geometry optimization of molecules in the crystal lattices using diffraction data and the program Dmol3 was carried out. Parameters analyzed were: (a) energetic contribution of van der Waals forces and hydrogen bonding to the total packing energy; (b) contributions of fragments of the molecules to the packing energy. The fraction of hydrogen bond energy in the packing energy increases as: phenacetin (17.5%)Enthalpies of evaporation were estimated from enthalpies of sublimation and fusion. Activity coefficients of the drugs in n-octanol were calculated from cryoscopic data and by estimation of dilution enthalpy obtained from solubility and calorimetric experiments (for infinite dissolution). Solubility temperature dependencies in n-octanol and n-hexane were measured. The thermodynamic functions of solubility and solvation processes were deduced. Specific and nonspecific solvation terms were distinguished using the transfer from the "inert" n-hexane to the other solvents. The transfer of the molecules from water to n-octanol is enthalpy driven for paracetamol; for acetanilide and phenacetin, entropy driven.

  11. Pressure-induced phase-transition sequence in CoF2: An experimental and first-principles study on the crystal, vibrational, and electronic properties

    Science.gov (United States)

    Barreda-Argüeso, J. A.; López-Moreno, S.; Sanz-Ortiz, M. N.; Aguado, F.; Valiente, R.; González, J.; Rodríguez, F.; Romero, A. H.; Muñoz, A.; Nataf, L.; Baudelet, F.

    2013-12-01

    We report a complete structural study of CoF2 under pressure. Its crystal structure and vibrational and electronic properties have been studied both theoretically and experimentally using first-principles density functional theory (DFT) methods, x-ray diffraction, x-ray absorption at Co K-edge experiments, Raman spectroscopy, and optical absorption in the 0-80 GPa range. We have determined the structural phase-transition sequence in CoF2 and corresponding transition pressures. The results are similar to other transition-metal difluorides such as FeF2 but different to ZnF2 and MgF2, despite that the Co2+ size (ionic radius) is similar to Zn2+ and Mg2+. We found that the complete phase-transition sequence is tetragonal rutile (P42/mnm) → CaCl2 type (orthorhombic Pnnm) → distorted PdF2 (orthorhombic Pbca)+PdF2 (cubic Pa3¯) in coexistence → fluorite (cubic Fm3¯m) → cotunnite (orthorhombic Pnma). It was observed that the structural phase transition to the fluorite at 15 GPa involves a drastic change of coordination from sixfold octahedral to eightfold cubic with important modifications in the vibrational and electronic properties. We show that the stabilization of this high-pressure cubic phase is possible under nonhydrostatic conditions since ideal hydrostaticity would stabilize the distorted-fluorite structure (tetragonal I4/mmm) instead. Although the first rutile → CaCl2-type second-order phase transition is subtle by Raman spectroscopy, it was possible to define it through the broadening of the Eg Raman mode which is split in the CaCl2-type phase. First-principles DFT calculations are in fair agreement with the experimental Raman mode frequencies, thus providing an accurate description for all vibrational modes and elastic properties of CoF2 as a function of pressure.

  12. Growth, spectral, optical and thermal characterization of new metallorganic crystal--bisthiourea nickel chloride.

    Science.gov (United States)

    Ramachandraraja, C; Joseph, A Antony; Sundararajan, R S; Shankar, V Siva; Murugakoothan, P

    2009-12-01

    The novel nonlinear optical single crystal of bisthiourea nickel chloride (BTNC) was grown successfully by slow evaporation technique using water as solvent. The lattice parameters of the grown crystal have been determined by X-ray diffraction studies. Vibrational spectra were recorded to determine the symmetries of molecular vibrations. Presence of various functional groups of BTNC was identified through FTIR and Raman spectroscopic analyses. Optical absorbance spectrum recorded in the wavelength range of UV-vis-NIR revealed that this crystal has good optical transparency in the range 200-2000 nm. The second harmonic generation test of BTNC revealed the nonlinear nature of the crystal. The BTNC crystal was analyzed by differential thermal and thermo gravimetric analysis (DTA-TGA) to obtain its thermal stability.

  13. Catalyzed hydrogenation of nitrogen and ethylene on metal (Fe, Pt) single crystal surfaces and effects of coadsorption: A sum frequency generation vibrational spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Westerberg, Staffan Per Gustav [Univ. of California, Berkeley, CA (United States)

    2004-01-01

    High-pressure catalytic reactions and associated processes, such as adsorption have been studied on a molecular level on single crystal surfaces. Sum Frequency Generation (SFG) vibrational spectroscopy together with Auger Electron Spectroscopy (AES), Temperature Programmed Desorption (TPD) and Gas Chromatography (GC) were used to investigate the nature of species on catalytic surfaces and to measure the catalytic reaction rates. Special attention has been directed at studying high-pressure reactions and in particular, ammonia synthesis in order to identify reaction intermediates and the influence of adsorbates on the surface during reaction conditions. The adsorption of gases N2, H2, O2 and NH3 that play a role in ammonia synthesis have been studied on the Fe(111) crystal surface by sum frequency generation vibrational spectroscopy using an integrated Ultra-High Vacuum (UHV)/high-pressure system. SFG spectra are presented for the dissociation intermediates, NH2 (~3325 cm-1) and NH (~3235 cm-1) under high pressure of ammonia (200 Torr) on the clean Fe(111) surface. Addition of 0.5 Torr of oxygen to 200 Torr of ammonia does not significantly change the bonding of dissociation intermediates to the surface. However, it leads to a phase change of nearly 180° between the resonant and non-resonant second order non-linear susceptibility of the surface, demonstrated by the reversal of the SFG spectral features. Heating the surface in the presence of 200 Torr ammonia and 0.5 Torr oxygen reduces the oxygen coverage, which can be seen from the SFG spectra as another relative phase change of 180°. The reduction of the oxide is also supported by Auger electron spectroscopy. The result suggests that the phase change of the spectral features could serve as a sensitive indicator of the chemical environment of the adsorbates.

  14. Catalyzed hydrogenation of nitrogen and ethylene on metal (Fe, Pt) single crystal surfaces and effects of coadsorption: A sum frequency generation vibrational spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Westerberg, Staffan Per Gustav

    2004-12-15

    High-pressure catalytic reactions and associated processes, such as adsorption have been studied on a molecular level on single crystal surfaces. Sum Frequency Generation (SFG) vibrational spectroscopy together with Auger Electron Spectroscopy (AES), Temperature Programmed Desorption (TPD) and Gas Chromatography (GC) were used to investigate the nature of species on catalytic surfaces and to measure the catalytic reaction rates. Special attention has been directed at studying high-pressure reactions and in particular, ammonia synthesis in order to identify reaction intermediates and the influence of adsorbates on the surface during reaction conditions. The adsorption of gases N{sub 2}, H{sub 2}, O{sub 2} and NH{sub 3} that play a role in ammonia synthesis have been studied on the Fe(111) crystal surface by sum frequency generation vibrational spectroscopy using an integrated Ultra-High Vacuum (UHV)/high-pressure system. SFG spectra are presented for the dissociation intermediates, NH{sub 2} ({approx}3325 cm{sup -1}) and NH ({approx}3235 cm{sup -1}) under high pressure of ammonia (200 Torr) on the clean Fe(111) surface. Addition of 0.5 Torr of oxygen to 200 Torr of ammonia does not significantly change the bonding of dissociation intermediates to the surface. However, it leads to a phase change of nearly 180{sup o} between the resonant and non-resonant second order non-linear susceptibility of the surface, demonstrated by the reversal of the SFG spectral features. Heating the surface in the presence of 200 Torr ammonia and 0.5 Torr oxygen reduces the oxygen coverage, which can be seen from the SFG spectra as another relative phase change of 180{sup o}. The reduction of the oxide is also supported by Auger electron spectroscopy. The result suggests that the phase change of the spectral features could serve as a sensitive indicator of the chemical environment of the adsorbates.

  15. Frustrated quantum-spin system on a triangle coupled with e{sub g} lattice vibrations: correspondence to Longuet-Higgins et al' s Jahn-Teller model

    Energy Technology Data Exchange (ETDEWEB)

    Yamasaki, Hisatsugu [Department of Applied Physics, Osaka City University, Osaka 558-8585 (Japan); Natsume, Yuhei [Graduate School of Science and Technology, Chiba University, Chiba 263-8522 (Japan); Terai, Akira [Department of Applied Physics, Osaka City University, Osaka 558-8585 (Japan); Nakamura, Katsuhiro [Department of Applied Physics, Osaka City University, Osaka 558-8585 (Japan)

    2004-09-01

    We investigate the frustrated quantum three-spin model (S{sub 1},S{sub 2},S{sub 3}) of spin = 1/2 on a triangle, in which spins are coupled with lattice-vibrational modes through the antiferromagnetic exchange interaction depending on distances between spin sites. The present model corresponds to the dynamic Jahn-Teller system E{sub g} - e{sub g} proposed by Longuet-Higgins et al (1958 Proc. R. Soc. A 244 1). This correspondence is revealed by using the transformation to Nakamura-Bishop's bases used in Phys. Rev. Lett. 54 861 (1985). Furthermore, we elucidate the relationship between a chiral order parameter {chi}-circumflex = S{sub 1}{center_dot}(S{sub 2}xS{sub 3}) in the spin system and the electronic orbital angular momentum l-circumflex{sub z} in E{sub g} - e{sub g} vibronic model: the regular oscillatory behaviour of the expectation value <{chi}-circumflex> with increasing energy can be found as in the case of for vibronic structures. The increase of the additional anharmonicity(chaoticity) is found to yield a rapidly decaying irregular oscillation of <{chi}-circumflex>. (letter to the editor)

  16. Vibrational Signatures in the THz Spectrum of 1,3-DNB: A First-Principles and Experimental Study

    OpenAIRE

    Ahmed, Towfiq; Azad, Abul K.; Chellappa, Raja; Higginbotham-Duque, Amanda; Dattelbaum, Dana M.; Zhu, Jian-Xin; Moore, David; Matthias J. Graf

    2016-01-01

    Understanding the fundamental processes of light-matter interaction is important for detection of explosives and other energetic materials, which are active in the infrared and terahertz (THz) region. We report a comprehensive study on electronic and vibrational lattice properties of structurally similar 1,3-dinitrobenzene (1,3- DNB) crystals through first-principles electronic structure calculations and THz spectroscopy measurements on polycrystalline samples. Starting from reported x-ray cr...

  17. Three-Dimensional Reciprocal-Lattice Analysis Using Azimuth-Scan Reflection High-Energy Electron Diffraction: Determination of Complex Crystal Orientations of Al Grains on Si(111) Surface

    Science.gov (United States)

    Hattori, Ken; Oi, Hideo; Tanaka, Kota; Kumagai, Tomohiro; Daimon, Hiroshi

    2012-05-01

    We have applied a three-dimensional (3D) reciprocal-lattice analysis method using a typical reflection high-energy electron diffraction (RHEED) system - all RHEED patterns in scanning sample-surface azimuth are converted into 3D reciprocal-lattice space. This analysis method can determine complex crystal orientations of nanoclusters, islands, and grains with multiple domains, which are difficult to obtain from a small number of non-converted two-dimensional RHEED patterns. For an Al-deposited Si(111) surface followed by annealing, we successfully determined new crystal orientations of Al grains: Al(001), Al(012) and Al(011) ∥ Si(111) with Al[100] ∥ Si. The typical acquisition time of 3D RHEED patterns is 10-20 min, which is shorter than that by a standard X-ray diffraction system with φ and ω scans for 3D reciprocal-lattice mapping. This is one of the advantages of this analysis method, in addition to the convenient observation of in situ vacuum-fabricated nanocrystals on substrate surfaces with high sensitivity.

  18. Superradiance Lattice

    CERN Document Server

    Wang, Da-Wei; Zhu, Shi-Yao; Scully, Marlan O

    2014-01-01

    We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in the momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on an electromagnetically induced transparency (EIT) system. For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective electric field. The quantum behaviours of electrons in lattices, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing and dynamic localization can be observed in the SL. The SL can be extended to two, three and even higher dimensions where no analogous real space lattices exist and new physics are waiting to be explored.

  19. Crystal field analysis of Pm$^{3+}$ (4$^{f4}) and Sm$^{3+}$ (4$^{f5}) and lattice location studies of $^{147}$Nd and $^{147}$Pm in w-AlN

    CERN Document Server

    Vetter, Ulrich; Nijjar, Anmol S; Zandi, Bahram; Öhl, Gregor; Wahl, Ulrich; De Vries, Bart; Hofsäss, Hans; Dietrich, Marc

    2006-01-01

    We report a detailed crystal field analysis of Pm3+ and Sm3+ as well as lattice location studies of 147Pm and 147Nd in 2H-aluminum nitride (w-AlN). The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of 60 keV. The decay chain of interest in this work is 147Nd→147Pm→147Sm (stable). Lattice location studies applying the emission channeling technique were carried out using the β− particles and conversion electrons emitted in the radioactive decay of 147Nd→147Pm. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of 873 K as well as 1373 K. The main fraction of about 60% of both 147Pm as well as 147Nd atoms was located on substitutional Al sites in the AlN lattice; the remainder of the ions were located randomly within the AlN lattice. Following radioactive decay of 147Nd, the cathodoluminescence spectra of Pm3+ and Sm3+ were obtained between 500 nm and 1050 nm at sample temperatures between 12 K and 300 K. High-re...

  20. Thermal Vibrational Convection

    Science.gov (United States)

    Gershuni, G. Z.; Lyubimov, D. V.

    1998-08-01

    Recent increasing awareness of the ways in which vibrational effects can affect low-gravity experiments have renewed interest in the study of thermal vibrational convection across a wide range of fields. For example, in applications where vibrational effects are used to provide active control of heat and mass transfer, such as in heat exchangers, stirrers, mineral separators and crystal growth, a sound understanding of the fundamental theory is required. In Thermal Vibrational Convection, the authors present the theory of vibrational effects caused by a static gravity field, and of fluid flows which appear under vibration in fluid-filled cavities. The first part of the book discusses fluid-filled cavities where the fluid motion only appears in the presence of temperature non-uniformities, while the second considers those situations where the vibrational effects are caused by a non-uniform field. Throughout, the authors concentrate on consideration of high frequency vibrations, where averaging methods can be successfully applied in the study of the phenomena. Written by two of the pioneers in this field, Thermal Vibrational Convection will be of great interest to scientists and engineers working in the many areas that are concerned with vibration, and its effect on heat and mass transfer. These include hydrodynamics, hydro-mechanics, low gravity physics and mechanics, and geophysics. The rigorous approach adopted in presenting the theory of this fascinating and highly topical area will facilitate a greater understanding of the phenomena involved, and will lead to the development of more and better-designed experiments.

  1. THE CRYSTAL STRUCTURE OF ANTIMONY (III) SULFOBROMIDE, SBSBR,

    Science.gov (United States)

    ANTIMONY COMPOUNDS, *SULFUR COMPOUNDS, CRYSTAL STRUCTURE , CRYSTAL STRUCTURE , BROMIDES, SYMMETRY(CRYSTALLOGRAPHY), FOURIER ANALYSIS, MOLECULAR STRUCTURE, CRYSTAL LATTICES, CHEMICAL BONDS, X RAY DIFFRACTION.

  2. Beta-alanine-hydrochloride (2:1) crystal: structure, 13C NMR and vibrational properties, protonation character.

    Science.gov (United States)

    Godzisz, D; Ilczyszyn, M; Ciunik, Z

    2003-01-15

    The crystal structure of beta-alanine-hydrochloride (2:1) complex (2A-HCl) has been determined by X-ray diffraction method at 298 and 100 K as monoclinic, space group C2/c, Z=4. The crystal comprises chloride anions and protonated beta-alanine dimers: two beta-alanine zwitterions are joined by strong, symmetric (Ci) hydrogen bond with the O...O distance of 2.473 A at room temperature. Powder FT-IR and FT-Raman as well as solid state 13C NMR spectra provide insights into the solid structure of this complex, character of its hydrogen bonds and the beta-alanine protonation.

  3. Localized structures in Kagome lattices

    Energy Technology Data Exchange (ETDEWEB)

    Saxena, Avadh B [Los Alamos National Laboratory; Bishop, Alan R [Los Alamos National Laboratory; Law, K J H [UNIV OF MASSACHUSETTS; Kevrekidis, P G [UNIV OF MASSACHUSETTS

    2009-01-01

    We investigate the existence and stability of gap vortices and multi-pole gap solitons in a Kagome lattice with a defocusing nonlinearity both in a discrete case and in a continuum one with periodic external modulation. In particular, predictions are made based on expansion around a simple and analytically tractable anti-continuum (zero coupling) limit. These predictions are then confirmed for a continuum model of an optically-induced Kagome lattice in a photorefractive crystal obtained by a continuous transformation of a honeycomb lattice.

  4. Lattice sums then and now

    CERN Document Server

    Borwein, J M; McPhedran, R C

    2013-01-01

    The study of lattice sums began when early investigators wanted to go from mechanical properties of crystals to the properties of the atoms and ions from which they were built (the literature of Madelung's constant). A parallel literature was built around the optical properties of regular lattices of atoms (initiated by Lord Rayleigh, Lorentz and Lorenz). For over a century many famous scientists and mathematicians have delved into the properties of lattices, sometimes unwittingly duplicating the work of their predecessors. Here, at last, is a comprehensive overview of the substantial body of

  5. Determination of inconsistency of crystal lattice parameters of. gamma. - and. gamma. '-phases of nickel heat resisting alloys by Fourier-analysis of x-ray diffraction reflex profiles

    Energy Technology Data Exchange (ETDEWEB)

    Samojlov, A.I.; Ignatova, I.A.; Krivko, A.I.; Kozlova, V.S.; Dodonova, L.P.

    1983-01-01

    A method is outlined that enables with the use of Fourier-analysis of summary unresolved X-ray diffraction profile of the matrix ..gamma.. and intermetallic ..gamma..' phases of nickel heat resisting alloys of the Ni-Cr-Co-Al-Ti-Nb-W-Mo-V -Hf system, to calculate the location of reflexes of each phase, that is, to determine the periods of their crystal lattices in the alloy (in monolith) directly without electrolytic separation of ..gamma..'-phase. The limits of the method applicability were determined.

  6. Crystal structure and terahertz spectroscopy of α,α,α‧,α‧-tetrabromo-p-xylene modeled using solid-state density functional theory

    Science.gov (United States)

    Pellizzeri, Steven; Smith, Tiffany M.; Delaney, Sean P.; Korter, Timothy M.; Zubieta, Jon

    2014-01-01

    The previously unknown crystal structure of α,α,α‧,α‧-tetrabromo-p-xylene has been determined using single-crystal X-ray diffraction, and it was discovered that the molecular packing primarily involves electrostatic interactions between neighboring molecules. Due to the unusual nature of the packing in this system, the vibrational motions were investigated. The low energy lattice and molecular vibrations unique to molecular crystals were measured in the terahertz (THz) region (10-100 cm-1). These vibrational motions were then reproduced using solid-state density functional theory (DFT) as implemented in CRYSTAL09, and it was found that the majority of the motions in this region involve either whole molecular translation or molecular scissoring.

  7. Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals

    Science.gov (United States)

    Han, Dong-Soo; Vogel, Andreas; Jung, Hyunsung; Lee, Ki-Suk; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Fischer, Peter; Meier, Guido; Kim, Sang-Koog

    2013-07-01

    Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions have been predicted. Here, we experimentally observe wave modes of collective vortex gyration in one-dimensional (1D) periodic arrays of magnetic disks using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by both vortex polarization and chirality ordering, as revealed by the explicit analytical form of 1D infinite arrays. A thorough understanding thereof is fundamental both for lattice vibrations and vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic disk arrays with vortex-state ordering, referred to as magnetic metastructure, offer potential implementation into information processing devices.

  8. Noninvasive Vibrational Mode Spectroscopy of Ion Coulomb Crystals through Resonant Collective Coupling to an Optical Cavity Field

    DEFF Research Database (Denmark)

    Dantan, Aurélien; Marler, Joan; Albert, Magnus

    2010-01-01

    We report on a novel noninvasive method to determine the normal mode frequencies of ion Coulomb crystals in traps based on the resonance enhanced collective coupling between the electronic states of the ions and an optical cavity field at the single photon level. Excitations of the normal modes...... are observed through a Doppler broadening of the resonance. An excellent agreement with the predictions of a zero-temperature uniformly charged liquid plasma model is found. The technique opens up for investigations of the heating and damping of cold plasma modes, as well as the coupling between them....

  9. Syntheses, crystal structures, NMR spectroscopy, and vibrational spectroscopy of Sr(PO{sub 3}F).H{sub 2}O and Sr(PO{sub 3}F)

    Energy Technology Data Exchange (ETDEWEB)

    Jantz, Stephan G.; Hoeppe, Henning A. [Lehrstuhl fuer Festkoerperchemie, Institut fuer Physik, Universitaet Augsburg (Germany); Wuellen, Leo van; Fischer, Andreas [Lehrstuhl fuer Chemische Physik und Materialwissenschaften, Institut fuer Physik, Universitaet Augsburg (Germany); Libowitzky, Eugen [Institute for Mineralogy and Crystallography, Faculty of Geosciences, Geography and Astronomy, University of Vienna (Austria); Baran, Enrique J. [Centro de Quimica Inorganica (CEQUINOR/CONICET, UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata (Argentina); Weil, Matthias [Institute for Chemical Technologies and Analytics, Division Structural Chemistry, Vienna University of Technology (Austria)

    2016-03-15

    Single crystals of Sr(PO{sub 3}F).H{sub 2}O {P2_1/c, Z = 4, a = 7.4844(2) Aa, b = 7.0793(2) Aa, c = 8.4265(2) Aa, β = 108.696(1) , V = 422.91(2) Aa"3, 2391 F_o"2, 70 parameters, R_1[F"2 > 2σ(F"2)] = 0.036; wR_2(F"2 all) = 0.049, S = 1.054} were grown from an aqueous solution by a metathesis reaction. The structure comprises [SrO{sub 8}] polyhedra and PO{sub 3}F tetrahedra that form a layered arrangement parallel to (100). The topotactic dehydration of this phase proceeds between 80 and 140 C to afford Sr(PO{sub 3}F). The monazite-type crystal structure of Sr(PO{sub 3}F) was elucidated from the X-ray powder data by simulated annealing [P2{sub 1}/c, Z = 4, a = 6.71689(9) Aa, b = 7.11774(11) Aa, c = 8.66997(13) Aa, β = 128.0063(7) , V = 326.605(8) Aa{sup 3}, R{sub p} = 0.010, R{sub wp} = 0.015, R{sub F} = 0.030]. During dehydration, the structure of Sr(PO{sub 3}F) .H{sub 2}O collapses along [100] from a layered arrangement into a framework structure, accompanied by a change of the coordination number of the Sr{sup 2+} ions from eight to nine. The magic-angle spinning (MAS) NMR and vibrational spectroscopy data of both phases are discussed. (Copyright copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Hydrogenation of the alpha,beta-Unsaturated Aldehydes Acrolein, Crotonaldehyde, and Prenal over Pt Single Crystals: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

    Energy Technology Data Exchange (ETDEWEB)

    Kliewer, C.J.; Somorjai, G.A.

    2008-11-26

    Sum-frequency generation vibrational spectroscopy (SFG-VS) and kinetic measurements using gas chromatography have been used to study the surface reaction intermediates during the hydrogenation of three {alpha},{beta}-unsaturated aldehydes, acrolein, crotonaldehyde, and prenal, over Pt(111) at Torr pressures (1 Torr aldehyde, 100 Torr hydrogen) in the temperature range of 295K to 415K. SFG-VS data showed that acrolein has mixed adsorption species of {eta}{sub 2}-di-{sigma}(CC)-trans, {eta}{sub 2}-di-{sigma}(CC)-cis as well as highly coordinated {eta}{sub 3} or {eta}{sub 4} species. Crotonaldehyde adsorbed to Pt(111) as {eta}{sub 2} surface intermediates. SFG-VS during prenal hydrogenation also suggested the presence of the {eta}{sub 2} adsorption species, and became more highly coordinated as the temperature was raised to 415K, in agreement with its enhanced C=O hydrogenation. The effect of catalyst surface structure was clarified by carrying out the hydrogenation of crotonaldehyde over both Pt(111) and Pt(100) single crystals while acquiring the SFG-VS spectra in situ. Both the kinetics and SFG-VS showed little structure sensitivity. Pt(100) generated more decarbonylation 'cracking' product while Pt(111) had a higher selectivity for the formation of the desired unsaturated alcohol, crotylalcohol.

  11. Syntheses, Vibrational Spectroscopy, and Crystal Structure Determination from X-Ray Powder Diffraction Data of Alkaline Earth Dicyanamides M[N(CN)

    Energy Technology Data Exchange (ETDEWEB)

    Juergens, Barbara; Irran, Elisabeth; Schnick, Wolfgang

    2001-03-01

    The alkaline earth dicyanamides Mg[N(CN){sub 2}]{sub 2}, Ca[N(CN){sub 2}]{sub 2}, Sr[N(CN){sub 2}]{sub 2}, and Ba[N(CN){sub 2}]{sub 2} were synthesized by ion exchange using Na[N(CN){sub 2}] and the respective nitrates or bromides as starting materials. The crystal structures were determined from X-ray powder diffractometry: Mg[N(CN){sub 2}]{sub 2}, Pnnm, Z=2, a=617.14(3), b=716.97(3), and c=740.35(5) pm; Ca[N(CN){sub 2}]{sub 2} and Sr[N(CN){sub 2}]{sub 2}, C2/c, Z=4; Ca[N(CN){sub 2}]{sub 2}, a=1244.55(3), b=607.97(1), and c=789.81(1) pm, {beta}=98.864(2){degree}; Sr[N(CN){sub 2}]{sub 2}, a=1279.63(2), b=624.756(8), and c=817.56(1) pm, {beta}=99.787(1){degree}; Ba[N(CN){sub 2}]{sub 2}, Pnma, Z=4, a=1368.68(7), b=429.07(7), and c=1226.26(2) pm. The dicyanamides consist of the respective alkaline earth cations and bent planar [N(CN){sub 2}]{sup -} ions. The structural features were correlated with vibrational spectroscopic data. The thermal behavior was studied by thermoanalytical experiments.

  12. Hydrogenation of the alpha,beta-unsaturated aldehydes acrolein, crotonaldehyde, and prenal over Pt single crystals: a kinetic and sum-frequency generation vibrational spectroscopy study.

    Science.gov (United States)

    Kliewer, Christopher J; Bieri, Marco; Somorjai, Gabor A

    2009-07-29

    Sum-frequency generation vibrational spectroscopy (SFG-VS) and kinetic measurements using gas chromatography have been used to study the surface reaction intermediates during the hydrogenation of three alpha,beta-unsaturated aldehydes, acrolein, crotonaldehyde, and prenal, over Pt(111) at Torr pressures (1 Torr of aldehyde, 100 Torr of hydrogen) in the temperature range of 295-415 K. SFG-VS data showed that acrolein has mixed adsorption species of eta(2)-di-sigma(CC)-trans, eta(2)-di-sigma(CC)-cis as well as highly coordinated eta(3) or eta(4) species. Crotonaldehyde adsorbed to Pt(111) as eta(2) surface intermediates. SFG-VS during prenal hydrogenation also suggested the presence of the eta(2) adsorption species and became more highly coordinated as the temperature was raised to 415 K, in agreement with its enhanced C=O hydrogenation. The effect of catalyst surface structure was clarified by carrying out the hydrogenation of crotonaldehyde over both Pt(111) and Pt(100) single crystals while acquiring the SFG-VS spectra in situ. Both the kinetics and SFG-VS showed little structure sensitivity. Pt(100) generated more decarbonylation "cracking" product while Pt(111) had a higher selectivity for the formation of the desired unsaturated alcohol, crotyl alcohol.

  13. Temperature dependence of atomic vibrations in mono-layer graphene

    NARCIS (Netherlands)

    Allen, C.S.; Liberti, E.; Kim, J.S.; Xu, Q.; Fan, Y.; He, K.; Robertson, A.W.; Zandbergen, H.W.; Warner, J.H.; Kirkland, A.I.

    2015-01-01

    We have measured the mean square amplitude of both in- and out-of-plane lattice vibrations for mono-layer graphene at temperatures ranging from ∼100 K to 1300 K. The amplitude of lattice vibrations was calculated from data extracted from selected area electron diffraction patterns recorded across a

  14. Hopping Time Scales and the Phonon-Liquid Electron-Crystal Picture in Thermoelectric Copper Selenide

    Science.gov (United States)

    Voneshen, D. J.; Walker, H. C.; Refson, K.; Goff, J. P.

    2017-04-01

    The suppression of transverse phonons by liquidlike diffusion in superionic conductors has been proposed as a means to dramatically reduce thermal conductivity in thermoelectric materials [H. Lui et al. Nat. Mater. 11, 422 (2012), 10.1038/nmat3273]. We have measured the ion transport and lattice dynamics in the original phonon-liquid electron-crystal Cu2Se using neutron spectroscopy. We show that hopping time scales are too slow to significantly affect lattice vibrations and that the transverse phonons persist at all temperatures. Substantial changes to the phonon spectrum occur well below the transition to the superionic phase, and the ultralow thermal conductivity is instead attributed to anharmonicity.

  15. Study the two dimensional triangular lattice photonic crystal band gap and coupling characters%二维三角形光子晶体带隙与耦合特性研究

    Institute of Scientific and Technical Information of China (English)

    李未; 陈小玲

    2011-01-01

    利用二维三角晶格介质柱光子晶体TE偏振的禁带与介质柱半径的变化关系,分析了二维光子晶体的带隙分布及斜边耦合特性.结果表明,光子禁带的大小受到构成光子晶体的介电材料的空间排列分布以及介质柱半径大小的影响;束缚在光子晶体中的光波可以在波导和谐振腔中进行传输,达到选择输出光波的目的.%The paper study the relation between two dimensional triangular lattice photonic crystal band gap for TE polarizationand dielectric cylinder radius, and study distribution of two dimensional photonic crystal defect state. Results show, the photonic crystal band gaps were distributed by dielectric material space distribution and medium size of the radius; Tied in the photon crystals of light waves can transmission in waveguides and resonator cavity to select the output of light waves.

  16. Lattice theory

    CERN Document Server

    Donnellan, Thomas; Maxwell, E A; Plumpton, C

    1968-01-01

    Lattice Theory presents an elementary account of a significant branch of contemporary mathematics concerning lattice theory. This book discusses the unusual features, which include the presentation and exploitation of partitions of a finite set. Organized into six chapters, this book begins with an overview of the concept of several topics, including sets in general, the relations and operations, the relation of equivalence, and the relation of congruence. This text then defines the relation of partial order and then partially ordered sets, including chains. Other chapters examine the properti

  17. THE CRYSTAL STRUCTURE OF 2-(4’-AMINO-5’AMINO PYRIMIDY) -2-PENTENE-4-ONE.

    Science.gov (United States)

    NITROGEN HETEROCYCLIC COMPOUNDS, CRYSTAL STRUCTURE ), (*AMINES, CRYSTAL STRUCTURE ), (*KETONES, CRYSTAL STRUCTURE ), CRYSTAL LATTICES, FOURIER ANALYSIS, LEAST SQUARES METHOD, MOLECULAR STRUCTURE, PYRIMIDINES, CHEMICAL BONDS

  18. Solitons in nonlinear lattices

    CERN Document Server

    Kartashov, Yaroslav V; Torner, Lluis

    2010-01-01

    This article offers a comprehensive survey of results obtained for solitons and complex nonlinear wave patterns supported by purely nonlinear lattices (NLs), which represent a spatially periodic modulation of the local strength and sign of the nonlinearity, and their combinations with linear lattices. A majority of the results obtained, thus far, in this field and reviewed in this article are theoretical. Nevertheless, relevant experimental settings are surveyed too, with emphasis on perspectives for implementation of the theoretical predictions in the experiment. Physical systems discussed in the review belong to the realms of nonlinear optics (including artificial optical media, such as photonic crystals, and plasmonics) and Bose-Einstein condensation (BEC). The solitons are considered in one, two, and three dimensions (1D, 2D, and 3D). Basic properties of the solitons presented in the review are their existence, stability, and mobility. Although the field is still far from completion, general conclusions c...

  19. Local determination of the amount of integration of an atom into a crystal surface

    Science.gov (United States)

    Volgmann, K.; Gawronski, H.; Zaum, Ch; Rusina, G. G.; Borisova, S. D.; Chulkov, E. V.; Morgenstern, K.

    2014-10-01

    Collective vibrational modes of crystal lattices, called phonons, determine fundamental material properties, such as their thermal and electrical conductivities. Bulk phonon spectra are influenced by point defects. More recently, the importance of phonons on nanostructures has come into the focus of attention. Here we show a spatially resolved phonon spectra of point defects that reveal distinctly different signatures for a cavity alone and an impurity atom fully integrated into the surface as opposed to one placed into a cavity. The spectra are indicative for delocalized phonons and localized vibrations, respectively, as confirmed by theory.

  20. Inter-hydrogen bond coupling in crystals with molecular chains in their lattices investigated by polarized IR spectroscopy: 4-Bromo-3,5-dimethylpyrazole and 3,4-dimethoxyphenylacetic acid.

    Science.gov (United States)

    Hachuła, Barbara; Flakus, Henryk T; Polasz, Anna

    2014-05-21

    We report the results of the experimental and theoretical studies of the polarized IR crystalline spectra of 4-bromo-3,5-dimethylpyrazole (4Br35DMPz) and 3,4-dimethoxyphenylacetic acid (34DMPAA) as well as the spectra of their deuterium-bonded analogues. The results of model calculations of the temperature impact exerted on to the band shapes measured in the X-H- and X-D bond stretching vibration regions, performed on the basis of the "strong-coupling" model, are also shown. These studies confirm a direct relationship between the spectral properties in IR and the electronic structure of the associating molecules in the crystals. Two different competing exciton coupling mechanisms involving hydrogen bonds, the "tail-to-head" (TH) in 4Br35DMPz and the "side-to-side" coupling in 34DMPAA, were recognized. The molecular electronic structure determines the relative contribution of each individual vibrational exciton coupling mechanism in the spectra generation. It also strongly influences the temperature-induced evolution of the Davydov-splitting effects in the crystalline spectra. Dynamical co-operative interactions responsible for a non-random distribution of protons and deuterons in the crystal hydrogen bonds can also be identified in the investigated systems.

  1. The crystal structure, vibrational spectra, thermal behaviour and second harmonic generation of aminoguanidinium(1+) hydrogen L-tartrate monohydrate

    Science.gov (United States)

    Macháčková, Zorka; Němec, Ivan; Teubner, Karel; Němec, Petr; Vaněk, Přemysl; Mička, Zdeněk

    2007-04-01

    Aminoguanidinium(1+) hydrogen L-tartrate monohydrate was prepared by crystallisation from aqueous solution and X-ray structural analysis was carried out. The substance crystallises in the orthorhombic system in space group P2 12 12 1, a = 7.1380(2) Å, b = 9.9700(4) Å, c = 14.0790(6) Å, V = 1001.94(7) Å 3, Z = 4, R = 0.0271 for 2272 observed reflections. The crystal structure consists of a 3D framework formed by hydrogen tartrate anions and water molecules with incorporated aminoguanidinium(1+) cations connected by a system of hydrogen bonds. The FTIR and FT Raman spectra of natural and N,O-deuterated compounds were measured and discussed at laboratory temperature. DSC measurements were carried out in the temperature range from 95 to 380 K. A weak anomaly was observed at a temperature of 268 K. Quantitative measurements of second harmonic generation of powdered aminoguanidinium(1+) hydrogen tartrate monohydrate at 800 nm were performed relative to KDP and a relative efficiency of 14% was observed.

  2. The influence of the long-range order on the vibrational spectra of structures based on sodalite cage.

    Science.gov (United States)

    Mikuła, A; Król, M; Koleżyński, A

    2015-06-05

    Zeolites are a group of tecto-aluminosilicates with numerous practical applications, e.g. gas separators, molecular sieves and sorbents. The unique properties result from porous structure of channels and cages which are built from smaller units - the so-called Secondary Building Units (SBU), and sometimes also larger groups (Breck, 1974; Ciciszwili et al., 1974; Mozgawa, 2008; Čejka and van Bekkum, 2005). The aim of this study was the examination of the influence of long-range order on vibrational spectra of sodalite and zeolite A. Ab initio calculations (geometry optimizations and vibrational spectra calculations) of sodalite cage and selected SBU were carried out by means of Gaussian09 (Frisch et al., 2009) (in the case of isolated clusters) and Crystal09 (Dovesi et al., 2005, 2009) (for periodic structures). The obtained results were compared with the experimental spectra of sodalite and zeolite A crystal structures, synthesized under hydrothermal conditions. These results allowed analyzing of the long-range ordering influence on the vibrational spectra, as well as the identification of the characteristic vibrations in β cage based frameworks. It has been found, that based on small structural fragment (SBU) models a characteristic vibrations can be identify. However, full spectra analysis and especially the interpretation of far-infrared region of the spectra require using periodic models under the influence of translational crystal lattice.

  3. Hamiltonian monodromy as lattice defect

    OpenAIRE

    Zhilinskii, B.

    2003-01-01

    The analogy between monodromy in dynamical (Hamiltonian) systems and defects in crystal lattices is used in order to formulate some general conjectures about possible types of qualitative features of quantum systems which can be interpreted as a manifestation of classical monodromy in quantum finite particle (molecular) problems.

  4. Material Properties of Various Cast Aluminum Alloys Made Using a Heated Mold Continuous Casting Technique with and without Ultrasonic Vibration

    Directory of Open Access Journals (Sweden)

    Mitsuhiro Okayasu

    2015-08-01

    Full Text Available This work was carried out to develop high-quality cast aluminum alloys using a new casting technology. For this purpose, commercial Al alloys were created by heated mold continuous casting (HMC with ultrasonic vibration (UV. With the HMC process, the grain size and the crystal orientation of the Al alloys were controlled, i.e., fine grains with a uniformly organized lattice formation. In addition, an attempt was made to modify the microstructural formation by cavitation. These microstructural characteristics made excellent mechanical properties. Using UV in the continuous casting process, more fine and spherical grains were slightly disordered, which was detected using electron backscattered diffraction. The mechanical properties of the UV HMC Al alloys were slightly higher than those for the related cast Al alloys without UV. Moreover, the severe vibration caused higher mechanical properties. The lattice and dislocation characteristics of the cast samples made with and without UV processes were analyzed systematically using electron backscattered diffraction.

  5. Femtosecond Spectroscopy of Electron-Lattice Coupling in LuMnO3

    Science.gov (United States)

    Lou, Shitao

    2005-03-01

    Hexagonal manganite LuMnO3 is a ferroelectric (Tc 900 K) and strongly frustrated antiferromagnetic (TN 90 K) crystal. Strong coupling between lattice, electronic, and magnetic degrees of freedom make it a promissing electronic material. We have used femtosecond pump-probe spectroscopy to observe the interaction of electron excitation and lattice vibration in real time. Optical excitation at a sharp absorption peak at 800 nm corresponding to a Mn d(x^2-y^2),(xy)->d(3z^2-r^2)transition served as the primary excitation step. Reflectivity changes as a function of delay time reveal electronic relaxation and coherent oscillations of several optical phonon modes. Electron and phonon excitation and relaxation dynamics were studied using different polarization geometries and symmetry analysis. The interaction mechanisms of photons, electrons, and coherent phonons are discussed.

  6. Infrared spectroscopic study on lattice dynamics in CaFeO3

    Science.gov (United States)

    Zhang, C. X.; Xia, H. L.; Liu, H.; Dai, Y. M.; Xu, B.; Yang, R.; Qiu, Z. Y.; Sui, Q. T.; Long, Y. W.; Meng, S.; Qiu, X. G.

    2017-02-01

    The change of the lattice dynamics upon the charge disproportionation (CD) transition has been investigated for the CaFeO3 crystal by measuring its infrared optical spectra. Across the CD transition, CaFeO3 undergoes a metal-insulator transition, and it is found that below TC D≈ 290 K the low-frequency optical conductivity gradually decreases to a rather low value and is dominated by a series of infrared-active phonons. Intriguingly, accompanied by the CD transition, two prominent phonon modes at ˜243 and ˜559 cm-1associated with the vibrations of Fe-O bonds show obvious redshift and asymmetric line shapes characterized by a Fano profile, suggesting a strong electron-phonon coupling. This coupling behavior reveals an intimate relationship between charge and lattice in the CD transition of CaFeO3.

  7. Position-space rescaling and hierarchical lattice models of disordered one-dimensional systems (Invited)

    Science.gov (United States)

    Tremblay, A.-M. S.; Breton, P.

    1984-03-01

    The application of exact and approximate position-space renormalization group techniques to the calculation of densities of states for problems with Gaussian generating functions (such as free tight-binding electrons, harmonic vibrations, spin waves, or random walks on Euclidian or 'fractal' lattices) is briefly reviewed. It is also shown that for one-dimensional Gaussian theories with disorder, the approximate recursion relations proposed by Goncalves da Silva and Koiller (GK) are exact for problems formulated on Berker-Ostlund lattices. A generalization of the GK scheme which allows one to calculate the optical zone-center density of states is formulated and then applied to the study of oneand two-mode behavior in mixed diatomic crystals.

  8. Vibrational states on Pd surfaces

    Science.gov (United States)

    Sklyadneva, I. Yu.; Rusina, G. G.; Chulkov, E. V.

    1997-04-01

    We present the calculation of vibrational modes and lattice relaxation for the Pd(100), (110) and (111) surfaces. The surface phonon frequencies and polarizations are obtained using embedded-atom potentials. Comparison of the calculated frequency values with available experimental data gives agreement within 0.2 THz.

  9. On the lattice rotations accompanying slip

    DEFF Research Database (Denmark)

    Wronski, M.; Wierzbanowski, K.; Leffers, Torben

    2013-01-01

    of the crystal lattices, and this texture may have a strong effect on the properties of the materials. The texture is introduced by lattice rotations in the individual grains during processing. The present critical assessment deals with the lattice rotations during rolling of face centred cubic (fcc) metals...... and alloys. Sixteen years ago, a modification of the traditional procedure for the calculation of these lattice rotations was suggested, a modification that would permit a realistic modelling of the development of the brass type texture, one of the two types of texture developed during rolling of fcc...

  10. Transmission Electron Microscope Measures Lattice Parameters

    Science.gov (United States)

    Pike, William T.

    1996-01-01

    Convergent-beam microdiffraction (CBM) in thermionic-emission transmission electron microscope (TEM) is technique for measuring lattice parameters of nanometer-sized specimens of crystalline materials. Lattice parameters determined by use of CBM accurate to within few parts in thousand. Technique developed especially for use in quantifying lattice parameters, and thus strains, in epitaxial mismatched-crystal-lattice multilayer structures in multiple-quantum-well and other advanced semiconductor electronic devices. Ability to determine strains in indivdual layers contributes to understanding of novel electronic behaviors of devices.

  11. Three-color vibrational CARS thermometry of fuel-rich ethylene/air flames using a potassium gadolinium tungstate Raman-active crystal as a source of narrowband probe radiation.

    Science.gov (United States)

    Meißner, Christian; Tröger, Johannes W; Kozlov, Dimitrii N; Beyrau, Frank; Seeger, Thomas

    2017-04-10

    Three-color broadband vibrational coherent anti-Stokes Raman scattering (CARS) temperature measurements were carried out in laminar fuel-rich sooting ethylene/air flames. Stimulated Raman scattering (SRS) of a picosecond pump laser pulse in a Raman-active potassium gadolinium tungstate [KGd(WO4)2] crystal was employed as a source of narrowband probe radiation. In the three-color CARS experiment, this wavelength-shifted radiation enables N2-based vibrational CARS temperature measurements in sooting flames free of the signal interference with the absorption/emission bands of the flame intermediate radicals C2. Spatial temperature profiles for different fuel-rich atmospheric pressure ethylene/air flames are presented in comparison with the results of two-color broadband vibrational and dual-broadband pure rotational CARS temperature measurements. The comparison shows the suitability of the three-color CARS measurement technique employing the KGd(WO4)2 crystal for accurate, C2 interference-free, temperature measurements in sooting flames.

  12. Calculation of Conduction Spectra in Quantum Dot Composed of Penrose Lattice

    Energy Technology Data Exchange (ETDEWEB)

    Tomita, Ryutaro; Fujimoto, Shigeo; Natsume, Yuhei [Graduate School of Science and Technology, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)

    2007-04-15

    Conductance through finite two-dimensional Penrose lattices (PLs) are calculated as a function of gate voltage. To investigate effects of lattice defects and lattice vibrations, three types of PLs are taken into account; (A) PL without lattice defects, (B) PL with lattice defects, and (C) PL with lattice vibrations, which is applied the electric field across the conductor. When energy levels of PL coincides with the chemical potential of the electrodes with increasing gate voltage, electron transfer through PL takes place. However, electron transfer is forbidden at certain states; These states have confined states, which have multiple-degeneracy in their electronic states. In addition, the states are localized due to interference of their wave-functions though the wave-function of each state is extended. We would like to point out that rigidity of confined states with respect to lattice defects and lattice vibrations.

  13. Crystal Electrostatic Energy

    CERN Document Server

    Ivanchin, Alexander

    2010-01-01

    It has been shown that to calculate the parameters of the electrostatic field of the ion crystal lattice it sufficient to take into account ions located at a distance of 1-2 lattice spacings. More distant ions make insignificant contribution. As a result, the electrostatic energy of the ion lattice in the alkaline halide crystal produced by both positive and negative ions is in good agreement with experiment when the melting temperature and the shear modulus are calculated. For fcc and bcc metals the ion lattice electrostatic energy is not sufficient to obtain the observed values of these parameters. It is possible to resolve the contradiction if one assumes that the electron density is strongly localized and has a crystal structure described by the lattice delta - function. As a result, positive charges alternate with negative ones as in the alkaline halide crystal. Such delta-like localization of the electron density is known as a model of nearly free electrons.

  14. High Precision Calculations of the Lennard-Jones Lattice Constants for Five Lattices

    Science.gov (United States)

    Stein, Matthew

    2017-01-01

    The total potential energy of a crystal as described by the Lennard-Jones (L-J) potential depends in part upon the calculation of lattice constants. Knowing these constants to high precision is useful for prediction of the lattice type and simulation of crystals such as rare-gas solids or germanium detectors, but reaching higher precision is computationally costly and challenging. Presented here is the extension of the precision of the lattice constants, Lp, up to 32 decimal digits, and in some cases corrections from previous publication. The Lp terms are given for 4 cubic, face-centered cubic, body-centered cubic, hexagonal-close-pack, and diamond lattices. This precision was obtained through the use of careful parallelization technique, exploitation of the symmetries of each lattice, and the ``onionization'' of the simulated crystal. The results of this computation, along with the tools and algorithm strategies to make this computation possible, are explained in detail graphically.

  15. Liquid Between Macromolecules in Protein Crystals: Static Versus Dynamics

    Science.gov (United States)

    Chernov, A. A.

    2005-01-01

    Protein crystals are so fragile that they often can not be handled by tweezers. Indeed, measurements of the Young modulus, E, of lysozyme crystals resulted in E approx. equals 0.1 - 1 GPa, the lower figures, 0.1 - 0.5 GPa, being obtained from triple point bending of as-grown and not cross-linked crystals sitting in solution. The bending strength was found to be approx.10(exp -2) E. On the other hand, ultrasound speed and Mandelstam-Raman-Brilloin light scattering experiments led to much higher figures, E approx. equals 2.7 GPa. The lower figures for E were found from static or low frequency crystal deformations measurements, while the higher moduli are based on high frequency lattice vibrations, 10(exp 7) - 10(exp 10) 1/s. The physical reason for the about an order of magnitude discrepancy is in different behavior of water filling space between protein molecules. At slow lattice deformation, the not-bound intermolecular water has enough time to flow from the compressed to expanded regions of the deformed crystal. At high deformation frequencies in the ultra- and hypersound waves, the water is confined in the intermolecular space and, on that scale, behaves like a solid, thus contributing to the elastic crystal moduli. In this case, the reciprocal crystal modulus is expected to be an average of the water protein and water compressibilities (reciprocal compressibilities): the bulk modulus for lysozyme is 26 GPa, for water it is 7 GPa. Anisotropy of the crystal moduli comes from intermolecular contacts within the lattice while the high frequency hardness comes from the bulk of protein molecules and water bulk moduli. These conclusions are based on the analysis of liquid flow in porous medium to be presented.

  16. Unusual Magnetic State with Dual Magnetic Excitations in the Single Crystal of S = 1/2 Kagome Lattice Antiferromagnet CaCu3(OH)6Cl2 • 0.6H2O

    Science.gov (United States)

    Yoshida, Hiroyuki; Noguchi, Naoya; Matsushita, Yoshitaka; Ishii, Yuto; Ihara, Yoshihiko; Oda, Migaku; Okabe, Hirotaka; Yamashita, Satoshi; Nakazawa, Yasuhiro; Takata, Atsushi; Kida, Takanori; Narumi, Yasuo; Hagiwara, Masayuki

    2017-03-01

    We have succeeded in preparing single crystals of CaCu3(OH)6Cl2 • 0.6H2O, a candidate for the S = 1/2 Kagome lattice antiferromagnet. Magnetic properties of the compound are dominated by the nearest neighbor antiferromagnetic interaction J1, and the next nearest neighbor ferromagnetic J2 and an antiferromagnetic Jd across a hexagon, which is different from related compounds Kapellasite and Haydeeite with ferromagnetic J1. Magnetic susceptibility exhibits a sudden increase below 13 K and a cusp anomaly at T* = 7.2 K in the ab-plane, whereas only a moderate enhancement is observed below T* along the c-axis. A tiny peak detected in heat capacity at T* indicates the occurrence of a magnetic phase transition. The low temperature magnetic heat capacity was reproduced by assuming a two-dimensional spin-wave component and a temperature-linear term. The spin-wave contribution suggests a magnon excitation in a short-range ordered region, whereas the relatively large T-linear term 5.9 mJ/(Cu-mol·K2) at H = 0 T of this insulating compound suggests the existence of an unusual quasi-particle excitation below T*. They apparently reveal the unconventionality of the ground state of this S = 1/2 Kagome lattice antiferromagnet.

  17. Lattice QCD on fine lattices

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, Stefan [DESY (Germany). Neumann Inst. for Computing

    2016-11-01

    These configurations are currently in use in many on-going projects carried out by researchers throughout Europe. In particular this data will serve as an essential input into the computation of the coupling constant of QCD, where some of the simulations are still on-going. But also projects computing the masses of hadrons and investigating their structure are underway as well as activities in the physics of heavy quarks. As this initial project of gauge field generation has been successful, it is worthwhile to extend the currently available ensembles with further points in parameter space. These will allow to further study and control systematic effects like the ones introduced by the finite volume, the non-physical quark masses and the finite lattice spacing. In particular certain compromises have still been made in the region where pion masses and lattice spacing are both small. This is because physical pion masses require larger lattices to keep the effects of the finite volume under control. At light pion masses, a precise control of the continuum extrapolation is therefore difficult, but certainly a main goal of future simulations. To reach this goal, algorithmic developments as well as faster hardware will be needed.

  18. Novel zinc(II) and copper(II) complexes of a Mannich base derived from lawsone: Synthesis, single crystal X-ray analysis, ab initio density functional theory calculations and vibrational analysis.

    Science.gov (United States)

    Neves, Amanda P; Vargas, Maria D; Téllez Soto, Claudio A; Ramos, Joanna M; Visentin, Lorenzo do C; Pinheiro, Carlos B; Mangrich, Antônio S; de Rezende, Edivaltrys I P

    2012-08-01

    Zinc(II) and copper(II) complexes of a tridentate Mannich base L1 derived from 2-hydroxy-1,4-naphthoquinone, pyridinecarboxyaldehyde and 2-aminomethylpyridine, [ZnL1Cl(2)]·H(2)O 1 and [CuL1Cl(2)]·2H(2)O 2, have been synthesized and fully characterized. The structure of complex 1 has been elucidated by a single crystal X-ray diffraction study: the zinc atom is pentacoordinate and the coordination geometry is a distorted square base pyramid, with a geometric structural parameter τ equal to 0.149. Vibrational spectroscopy and ab initio DFT calculations of both compounds have confirmed that the two complexes exhibit similar structures. Full assignment of the vibrational spectra was also supported by careful analysis of the distorted geometries generated by the normal modes. Copyright © 2012 Elsevier B.V. All rights reserved.

  19. Humidity control as a strategy for lattice optimization applied to crystals of HLA-A*1101 complexed with variant peptides from dengue virus.

    Science.gov (United States)

    Chotiyarnwong, Pojchong; Stewart-Jones, Guillaume B; Tarry, Michael J; Dejnirattisai, Wanwisa; Siebold, Christian; Koch, Michael; Stuart, David I; Harlos, Karl; Malasit, Prida; Screaton, Gavin; Mongkolsapaya, Juthathip; Jones, E Yvonne

    2007-05-01

    T-cell recognition of the antigenic peptides presented by MHC class I molecules normally triggers protective immune responses, but can result in immune enhancement of disease. Cross-reactive T-cell responses may underlie immunopathology in dengue haemorrhagic fever. To analyze these effects at the molecular level, the functional MHC class I molecule HLA-A*1101 was crystallized bound to six naturally occurring peptide variants from the dengue virus NS3 protein. The crystals contained high levels of solvent and required optimization of the cryoprotectant and dehydration protocols for each complex to yield well ordered diffraction, a process that was facilitated by the use of a free-mounting system.

  20. Shaking the entropy out of a lattice

    DEFF Research Database (Denmark)

    C. Tichy, Malte; Mølmer, Klaus; F. Sherson, Jacob

    2012-01-01

    We present a simple and efficient scheme to reduce atom-number fluctuations in optical lattices. The interaction-energy difference for atoms in different vibrational states is used to remove excess atomic occupation. The remaining vacant sites are then filled with atoms by merging adjacent wells,...

  1. Lattice Boltzmann simulations of 3D crystal growth: Numerical schemes for a phase-field model with anti-trapping current

    CERN Document Server

    Cartalade, Alain; Plapp, Mathis

    2016-01-01

    A lattice-Boltzmann (LB) scheme, based on the Bhatnagar-Gross-Krook (BGK) collision rules is developed for a phase-field model of alloy solidification in order to simulate the growth of dendrites. The solidification of a binary alloy is considered, taking into account diffusive transport of heat and solute, as well as the anisotropy of the solid-liquid interfacial free energy. The anisotropic terms in the phase-field evolution equation, the phenomenological anti-trapping current (introduced in the solute evolution equation to avoid spurious solute trapping), and the variation of the solute diffusion coefficient between phases, make it necessary to modify the equilibrium distribution functions of the LB scheme with respect to the one used in the standard method for the solution of advection-diffusion equations. The effects of grid anisotropy are removed by using the lattices D3Q15 and D3Q19 instead of D3Q7. The method is validated by direct comparison of the simulation results with a numerical code that uses t...

  2. Thin-walled reinforcement lattice structure for hollow CMC buckets

    Energy Technology Data Exchange (ETDEWEB)

    de Diego, Peter

    2017-06-27

    A hollow ceramic matrix composite (CMC) turbine bucket with an internal reinforcement lattice structure has improved vibration properties and stiffness. The lattice structure is formed of thin-walled plies made of CMC. The wall structures are arranged and located according to high stress areas within the hollow bucket. After the melt infiltration process, the mandrels melt away, leaving the wall structure to become the internal lattice reinforcement structure of the bucket.

  3. Study on transmission properties of 2-D super-lattice photonic crystals%2维超晶格结构光子晶体传输特性研究

    Institute of Scientific and Technical Information of China (English)

    闫明宝; 傅振堂; 王伟宇

    2012-01-01

    The finite difference time domain method was used to calculate the transmission characteristics of 2-D super-lattice photonic crystal formed by cylinders and elliptic rods or cylinders and composite medium rods. It is shown that the width of the band gap becomes lager and the central frequency becomes higher with increase of the sectional area of elliptical rods for the cylinder-elliptical rods super-lattice. As to the case of composite medium rods super-lattice, the thicker the nested elliptical rod, the narrower the band gap is and the lower the central frequency is when the long axis is along the direction of incident wave. However, the wider band gap appeared in the range of high frequency band and in the low frequency band the band gap vanished when the long axis direction is perpendicular to the incident wave. The study provides the theory of the manufacture of photonic crystals.%为了研究超晶格结构对光子晶体禁带的影响,应用时域有限差分法对圆/椭圆、圆/复合柱超晶格结构光子晶体的传输特性进行了计算,得到了相应的透射谱.结果表明,对圆/椭圆超晶格,禁带宽度随椭圆柱截面积的增大而变宽,中心频率变大;对于圆/复合柱超晶格结构,椭圆柱内接于圆孔时,禁带宽度随截面积的增大而变窄,中心频率变小;当长轴垂直入射波方向时,高频段出现较宽禁带,低频禁带完全消失;而椭圆孔中内嵌圆柱时,禁带宽度变化与前者相反.该研究为光子晶体器件的制作提供了理论依据.

  4. Lattice thermal expansion and anisotropic displacements in -sulfur from diffraction experiments and first-principles theory.

    Science.gov (United States)

    George, Janine; Deringer, Volker L; Wang, Ai; Müller, Paul; Englert, Ulli; Dronskowski, Richard

    2016-12-21

    Thermal properties of solid-state materials are a fundamental topic of study with important practical implications. For example, anisotropic displacement parameters (ADPs) are routinely used in physics, chemistry, and crystallography to quantify the thermal motion of atoms in crystals. ADPs are commonly derived from diffraction experiments, but recent developments have also enabled their first-principles prediction using periodic density-functional theory (DFT). Here, we combine experiments and dispersion-corrected DFT to quantify lattice thermal expansion and ADPs in crystalline α-sulfur (S8), a prototypical elemental solid that is controlled by the interplay of covalent and van der Waals interactions. We begin by reporting on single-crystal and powder X-ray diffraction measurements that provide new and improved reference data from 10 K up to room temperature. We then use several popular dispersion-corrected DFT methods to predict vibrational and thermal properties of α-sulfur, including the anisotropic lattice thermal expansion. Hereafter, ADPs are derived in the commonly used harmonic approximation (in the computed zero-Kelvin structure) and also in the quasi-harmonic approximation (QHA) which takes the predicted lattice thermal expansion into account. At the PPBE+D3(BJ) level, the QHA leads to excellent agreement with experiments. Finally, more general implications of this study for theory and experiment are discussed.

  5. Protein Crystallization

    Science.gov (United States)

    Chernov, Alexander A.

    2005-01-01

    Nucleation, growth and perfection of protein crystals will be overviewed along with crystal mechanical properties. The knowledge is based on experiments using optical and force crystals behave similar to inorganic crystals, though with a difference in orders of magnitude in growing parameters. For example, the low incorporation rate of large biomolecules requires up to 100 times larger supersaturation to grow protein, rather than inorganic crystals. Nucleation is often poorly reproducible, partly because of turbulence accompanying the mixing of precipitant with protein solution. Light scattering reveals fluctuations of molecular cluster size, its growth, surface energies and increased clustering as protein ages. Growth most often occurs layer-by-layer resulting in faceted crystals. New molecular layer on crystal face is terminated by a step where molecular incorporation occurs. Quantitative data on the incorporation rate will be discussed. Rounded crystals with molecularly disordered interfaces will be explained. Defects in crystals compromise the x-ray diffraction resolution crucially needed to find the 3D atomic structure of biomolecules. The defects are immobile so that birth defects stay forever. All lattice defects known for inorganics are revealed in protein crystals. Contribution of molecular conformations to lattice disorder is important, but not studied. This contribution may be enhanced by stress field from other defects. Homologous impurities (e.g., dimers, acetylated molecules) are trapped more willingly by a growing crystal than foreign protein impurities. The trapped impurities induce internal stress eliminated in crystals exceeding a critical size (part of mni for ferritin, lysozyme). Lesser impurities are trapped from stagnant, as compared to the flowing, solution. Freezing may induce much more defects unless quickly amorphysizing intracrystalline water.

  6. Strong spin-lattice coupling in CrSiTe3

    Directory of Open Access Journals (Sweden)

    L. D. Casto

    2015-04-01

    Full Text Available CrSiTe3 has attracted recent interest as a candidate single-layer ferromagnetic semiconductor, but relatively little is known about the bulk properties of this material. Here, we report single-crystal X-ray diffraction, magnetic properties, thermal conductivity, vibrational, and optical spectroscopies and compare our findings with complementary electronic structure and lattice dynamics principles calculations. The high temperature paramagnetic phase is characterized by strong spin-lattice interactions that give rise to glassy behavior, negative thermal expansion, and an optical response that reveals that CrSiTe3 is an indirect gap semiconductor with indirect and direct band gaps at 0.4 and 1.2 eV, respectively. Measurements of the phonons across the 33 K ferromagnetic transition provide additional evidence for strong coupling between the magnetic and lattice degrees of freedom. The Si-Te stretching and Te displacement modes are sensitive to the magnetic ordering transition, a finding that we discuss in terms of the superexchange mechanism. Spin-lattice coupling constants are also extracted.

  7. Deformable two-dimensional photonic crystal slab for cavity optomechanics

    CERN Document Server

    Antoni, T; Briant, T; Cohadon, P -F; Heidmann, A; Braive, R; Beveratos, A; Abram, I; Gatiet, L Le; Sagnes, I; Robert-Philip, I

    2011-01-01

    We have designed photonic crystal suspended membranes with optimized optical and mechanical properties for cavity optomechanics. Such resonators sustain vibration modes in the megahertz range with quality factors of a few thousand. Thanks to a two-dimensional square lattice of holes, their reflectivity at normal incidence at 1064 nm reaches values as high as 95%. These two features, combined with the very low mass of the membrane, open the way to the use of such periodic structures as deformable end-mirrors in Fabry-Perot cavities for the investigation of cavity optomechanical effects

  8. Anharmonic vibrational effects of thermoelectric Cu-Sb-Se ternary semiconductors: Density-functional theory studies

    Science.gov (United States)

    Zhang, Yongsheng; Skoug, Eric; Cain, Jeffrey; Morelli, Donald; Ozolins, Vidvuds; Wolverton, Christopher

    2012-02-01

    Strong anharmonicity can lead to intrinsically minimal thermal conductivity even in defect-free single crystals. In an effort to understand this behavior, we have investigated two Cu-Sb-Se ternary semiconductors, Cu3SbSe4 and Cu3SbSe3, by both experimental measurements and density functional theory (DFT) calculations. The experimental lattice thermal conductivity measurements show that while Cu3SbSe4 exhibits classical behavior, the lattice thermal conductivity in Cu3SbSe3 is anomalously low and nearly temperature independent. The vibrational properties of these two semiconductors are calculated by DFT phonon calculations within the quasi-harmonic approximation. The average of the Gr"uneisen parameters of the acoustic mode in Cu3SbSe3 is larger than that of Cu3SbSe4, which theoretically confirms that Cu3SbSe3 has a stronger lattice anharmonicity than Cu3SbSe4. Using our DFT-determined longitudinal and transverse Gr"uneisen parameters, Debye temperatures, and phonon velocities, we calculate the lattice the lattice thermal conductivity using the Debye-Callaway model (without the use of any adjustable parameters). The calculated thermal conductivity is in good agreement with the experimental measurements.

  9. Lattice damage and compositional changes in Xe ion irradiated InxGa1-xN (x = 0.32-1.0) single crystals

    Science.gov (United States)

    Zhang, Limin; Jiang, Weilin; Dissanayake, Amila; Peng, Jinxin; Ai, Wensi; Zhang, Jiandong; Zhu, Zihua; Wang, Tieshan; Shutthanandan, Vaithiyalingam

    2016-06-01

    Lattice disorder and compositional changes in InxGa1-xN (x = 0.32, 0.47, 0.7, 0.8, and 1.0) films on GaN/Al2O3 substrates, induced by room-temperature irradiation of 5 MeV Xe ions, have been investigated using both Rutherford backscattering spectrometry under ion-channeling conditions and time-of-flight secondary ion mass spectrometry. The results show that for a fluence of 3 × 1013 cm-2, the relative level of lattice disorder in InxGa1-xN increases monotonically from 59% to 90% with increasing indium concentration x from 0.32 to 0.7; a further increase in x up to 1.0 leads to little increase in the disorder level. In contrast to Ga-rich InxGa1-xN (x = 0.32 and 0.47), significant volume swelling of up to ˜25% accompanied with oxidation in In-rich InxGa1-xN (x = 0.7, 0.8, and 1.0) is observed. In addition, irradiation-induced atomic mixing occurs at the interface of In-rich InxGa1-xN and GaN. The results from this study indicate an extreme susceptibility of the high In-content InxGa1-xN to heavy-ion irradiation, and suggest that cautions must be exercised in applying ion-implantation techniques to these materials at room temperature. Further studies of the irradiation behavior at elevated temperatures are warranted.

  10. In situ X-ray diffraction strain-controlled study of Ti–Nb–Zr and Ti–Nb–Ta shape memory alloys: crystal lattice and transformation features

    Energy Technology Data Exchange (ETDEWEB)

    Dubinskiy, S. [École de technologie supérieure, 1100, Notre-Dame Street West, Montreal, Quebec H3C 1K3 (Canada); National University of Science and Technology “MISIS”, 4, Leninskiy prosp., Moscow 119049 (Russian Federation); Prokoshkin, S. [National University of Science and Technology “MISIS”, 4, Leninskiy prosp., Moscow 119049 (Russian Federation); Brailovski, V., E-mail: vladimir.brailovski@etsmtl.ca [École de technologie supérieure, 1100, Notre-Dame Street West, Montreal, Quebec H3C 1K3 (Canada); Inaekyan, K. [École de technologie supérieure, 1100, Notre-Dame Street West, Montreal, Quebec H3C 1K3 (Canada); Korotitskiy, A. [National University of Science and Technology “MISIS”, 4, Leninskiy prosp., Moscow 119049 (Russian Federation)

    2014-02-15

    Phase and structure transformations in biomedical Ti–21.8Nb–6.0Zr (TNZ) and Ti–19.7Nb–5.8Ta (TNT) shape memory alloys (at.%) under and without load in the − 150 to 100 °S temperature range are studied in situ using an original tensile module for a low-temperature chamber of an X-ray diffractometer. Alpha″- and beta-phase lattice parameters, the crystallographic resource of recovery strain, phase and structure transformation sequences, and microstress appearance and disappearance are examined, compared and discussed. For both alloys, the crystallographic resource of recovery strain decreases with temperature increase to become 4.5% for TNZ and 2.5% for TNT alloy (at RT). Loading at low temperatures leads to additional α″-phase formation and reorientation. Heating under load, as compared to strain-free heating, affects the reverse transformation sequence of both alloys in different ways. For TNZ alloy, strain-free heating results in simultaneous ω→β and α″→β transformations, whereas during heating under stress, they are sequential: β + ω→α″ precedes α″→β. For TNT alloy, strain-free heating results in reverse α″→β transformation, whereas during heating under stress, α″→β transformation is preceded by α″-phase reorientation. - Highlights: • Comparative in situ XRD analysis of Ti–Nb–Zr(Ta) shape memory alloys is realized. • Lattice parameters of β- and α″-phases are calculated in the − 150 to + 100 °C range. • The higher the temperature, the lower the α″→β transformation strain. • Loading at low temperatures results in α″-phase formation and reorientation. • Transformation sequences upon heating with and without loading are different.

  11. Lattice damage and compositional changes in Xe ion irradiated InxGa1-xN (x = 0.32-1.0) single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Limin; Jiang, Weilin; Dissanayake, Amila C.; Peng, Jinxin; Ai, Wensi; Zhang, Jiandong; Zhu, Zihua; Wang, Tieshan; Shutthanandan, V.

    2016-06-27

    Lattice disorder and compositional changes in InxGa1-xN (x=0.32, 0.47, 0.7, 0.8 and 1.0) films on GaN/Al2O3 substrates, induced by room-temperature irradiation of 5 MeV Xe ions, have been investigated using both Rutherford backscattering spectrometry under ion-channeling conditions and time-of-flight secondary ion mass spectrometry. The results show that for a fluence of 3E13 cm-2, the relative level of lattice disorder in InxGa1-xN increases monotonically from 59% to 90% with increasing indium concentration x from 0.32 to 0.7; a further increase in x up to 1.0 leads to little increase in the disorder level. In contrast to Ga-rich InxGa1-xN (x=0.32 and 0.47), significant volume swelling of up to ~25% accompanied with oxidation in In-rich InxGa1-xN (x=0.7, 0.8 and 1.0) is observed. In addition, irradiation-induced atomic mixing occurs at the interface of In-rich InxGa1-xN and GaN. The results from this study indicate an extreme susceptibility of the high In-content InxGa1-xN to heavy-ion irradiation, and suggest that cautions must be exercised in applying ion-implantation techniques to these materials at room temperature. Further studies of the irradiation behavior at elevated temperatures are warranted.

  12. Dual Lattice of ℤ-module Lattice

    Directory of Open Access Journals (Sweden)

    Futa Yuichi

    2017-07-01

    Full Text Available In this article, we formalize in Mizar [5] the definition of dual lattice and their properties. We formally prove that a set of all dual vectors in a rational lattice has the construction of a lattice. We show that a dual basis can be calculated by elements of an inverse of the Gram Matrix. We also formalize a summation of inner products and their properties. Lattice of ℤ-module is necessary for lattice problems, LLL(Lenstra, Lenstra and Lovász base reduction algorithm and cryptographic systems with lattice [20], [10] and [19].

  13. Humidity control as a strategy for lattice optimization applied to crystals of HLA-A*1101 complexed with variant peptides from dengue virus

    Energy Technology Data Exchange (ETDEWEB)

    Chotiyarnwong, Pojchong [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Stewart-Jones, Guillaume B.; Tarry, Michael J. [Division of Structural Biology and Oxford Protein Production Facility (OPPF), The Henry Wellcome Building for Genomic Medicine, Roosevelt Drive, Headington, Oxford OX3 7BN (United Kingdom); Dejnirattisai, Wanwisa [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Siebold, Christian; Koch, Michael; Stuart, David I.; Harlos, Karl [Division of Structural Biology and Oxford Protein Production Facility (OPPF), The Henry Wellcome Building for Genomic Medicine, Roosevelt Drive, Headington, Oxford OX3 7BN (United Kingdom); Malasit, Prida [Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Medical Biotechnology Unit, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Bangkok (Thailand); Screaton, Gavin [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Mongkolsapaya, Juthathip, E-mail: j.mongkolsapaya@imperial.ac.uk [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Jones, E. Yvonne, E-mail: j.mongkolsapaya@imperial.ac.uk [Division of Structural Biology and Oxford Protein Production Facility (OPPF), The Henry Wellcome Building for Genomic Medicine, Roosevelt Drive, Headington, Oxford OX3 7BN (United Kingdom); Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom)

    2007-05-01

    Crystals of an MHC class I molecule bound to naturally occurring peptide variants from the dengue virus NS3 protein contained high levels of solvent and required optimization of cryoprotectant and dehydration protocols for each complex to yield well ordered diffraction, a process facilitated by the use of a free-mounting system. T-cell recognition of the antigenic peptides presented by MHC class I molecules normally triggers protective immune responses, but can result in immune enhancement of disease. Cross-reactive T-cell responses may underlie immunopathology in dengue haemorrhagic fever. To analyze these effects at the molecular level, the functional MHC class I molecule HLA-A*1101 was crystallized bound to six naturally occurring peptide variants from the dengue virus NS3 protein. The crystals contained high levels of solvent and required optimization of the cryoprotectant and dehydration protocols for each complex to yield well ordered diffraction, a process that was facilitated by the use of a free-mounting system.

  14. Lattice strain induced magnetism in substituted nanocrystalline cobalt ferrite

    Science.gov (United States)

    Kumar, Rajnish; Kar, Manoranjan

    2016-10-01

    Strontium (Sr) substituted cobalt ferrite i.e. Co1-xSrxFe2O4 (x=0.00, 0.01, 0.015, 0.02, 0.05, 0.1) have been synthesized by the citric acid modified sol-gel method. Crystal structure and phase purity have been studied by the X-ray powder diffraction technique. The Rietveld refinement of XRD pattern using the space group Fd 3 bar m shows monotonically increasing of lattice parameter with the increase in Sr concentration. Magnetic hysteresis loops measurement has been carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of ±1.5 T. Magnetocrystalline anisotropy constant were calculated by employing the Law of Approach (LA) to the saturation. It is observed that magnetocrystalline anisotropy has anomaly for x=0.01 (Co0.99Sr0.01Fe2O4) sample. Strain mediated modification of magnetic properties in Sr substituted cobalt ferrite has been observed. The saturation magnetization for doping concentration i.e. x=0.01 abruptly increase while for x>0.01 decreases with the increase in Sr concentration. A correlation between lattice strain and magnetic behavior in non-magnetic Sr- substituted nano-crystalline cobalt ferrite has been reported.

  15. Band warping, band non-parabolicity, and Dirac points in electronic and lattice structures

    Science.gov (United States)

    Resca, Lorenzo; Mecholsky, Nicholas A.; Pegg, Ian L.

    2017-10-01

    We illustrate at a fundamental level the physical and mathematical origins of band warping and band non-parabolicity in electronic and vibrational structures. We point out a robust presence of pairs of topologically induced Dirac points in a primitive-rectangular lattice using a p-type tight-binding approximation. We analyze two-dimensional primitive-rectangular and square Bravais lattices with implications that are expected to generalize to more complex structures. Band warping is shown to arise at the onset of a singular transition to a crystal lattice with a larger symmetry group, which allows the possibility of irreducible representations of higher dimensions, hence band degeneracy, at special symmetry points in reciprocal space. Band warping is incompatible with a multi-dimensional Taylor series expansion, whereas band non-parabolicities are associated with multi-dimensional Taylor series expansions to all orders. Still band non-parabolicities may merge into band warping at the onset of a larger symmetry group. Remarkably, while still maintaining a clear connection with that merging, band non-parabolicities may produce pairs of conical intersections at relatively low-symmetry points. Apparently, such conical intersections are robustly maintained by global topology requirements, rather than any local symmetry protection. For two p-type tight-binding bands, we find such pairs of conical intersections drifting along the edges of restricted Brillouin zones of primitive-rectangular Bravais lattices as lattice constants vary relatively to each other, until these conical intersections merge into degenerate warped bands at high-symmetry points at the onset of a square lattice. The conical intersections that we found appear to have similar topological characteristics as Dirac points extensively studied in graphene and other topological insulators, even though our conical intersections have none of the symmetry complexity and protection afforded by the latter more

  16. Breathers in strongly anharmonic lattices.

    Science.gov (United States)

    Rosenau, Philip; Pikovsky, Arkady

    2014-02-01

    We present and study a family of finite amplitude breathers on a genuinely anharmonic Klein-Gordon lattice embedded in a nonlinear site potential. The direct numerical simulations are supported by a quasilinear Schrodinger equation (QLS) derived by averaging out the fast oscillations assuming small, albeit finite, amplitude vibrations. The genuinely anharmonic interlattice forces induce breathers which are strongly localized with tails evanescing at a doubly exponential rate and are either close to a continuum, with discrete effects being suppressed, or close to an anticontinuum state, with discrete effects being enhanced. Whereas the D-QLS breathers appear to be always stable, in general there is a stability threshold which improves with spareness of the lattice.

  17. Optical Lattices with Micromechanical Mirrors

    CERN Document Server

    Hammerer, K; Genes, C; Zoller, P; Treutlein, P; Camerer, S; Hunger, D; Haensch, T W

    2010-01-01

    We investigate a setup where a cloud of atoms is trapped in an optical lattice potential of a standing wave laser field which is created by retro-reflection on a micro-membrane. The membrane vibrations itself realize a quantum mechanical degree of freedom. We show that the center of mass mode of atoms can be coupled to the vibrational mode of the membrane in free space, and predict a significant sympathetic cooling effect of the membrane when atoms are laser cooled. The controllability of the dissipation rate of the atomic motion gives a considerable advantage over typical optomechanical systems enclosed in optical cavities, in that it allows a segregation between the cooling and coherent dynamics regimes. The membrane can thereby be kept in a cryogenic environment, and the atoms at a distance in a vacuum chamber.

  18. Crystal structure, vibrational spectra, optical and DFT studies of bis (3-azaniumylpropyl) azanium pentachloroantimonate (III) chloride monohydrate (C6H20N3)SbCl5·Cl·H2O

    Science.gov (United States)

    Ahmed, Houssem Eddine; Kamoun, Slaheddine

    2017-09-01

    The crystal structure of (C6H20N3)SbCl5·Cl·H2O is built up of [NH3(CH2)3NH2(CH2)3NH3]3 + cations, [SbCl5]2 - anions, free Cl- anions and neutral water molecules connected together by Nsbnd H ⋯ Cl, Nsbnd H ⋯ O and Osbnd H ⋯ Cl hydrogen bonds. The optical band gap determined by diffuse reflection spectroscopy (DRS) is 3.78 eV for a direct allowed transition. Optimized molecular geometry, atomic Mulliken charges, harmonic vibrational frequencies, HOMO-LUMO and related molecular properties of the (C6H20N3)SbCl5·Cl·H2O compound were calculated by Density functional theory (DFT) using B3LYP method with GenECP sets. The calculated structural parameters (bond lengths and angles) are in good agreement with the experimental XRD data. The vibrational unscaled wavenumbers were calculated and scaled by a proper scaling factor of 0.984. Acceptable consistency was observed between calculated and experimental results. The assignments of wavenumbers were made on the basis of potential energy distribution (PED) using Vibrational Energy Distribution Analysis (VEDA) software. The HOMO-LUMO study was extended to calculate various molecular parameters like ionization potential, electron affinity, global hardness, electro-chemical potential, electronegativity and global electrophilicity of the given molecule.

  19. Infrared Spectroscopic Study of Vibrational Modes in Methylammonium Lead Halide Perovskites.

    Science.gov (United States)

    Glaser, Tobias; Müller, Christian; Sendner, Michael; Krekeler, Christian; Semonin, Octavi E; Hull, Trevor D; Yaffe, Omer; Owen, Jonathan S; Kowalsky, Wolfgang; Pucci, Annemarie; Lovrinčić, Robert

    2015-08-06

    The organic cation and its interplay with the inorganic lattice underlie the exceptional optoelectronic properties of organo-metallic halide perovskites. Herein we report high-quality infrared spectroscopic measurements of methylammonium lead halide perovskite (CH3NH3Pb(I/Br/Cl)3) films and single crystals at room temperature, from which the dielectric function in the investigated spectral range is derived. Comparison with electronic structure calculations in vacuum of the free methylammonium cation allows for a detailed peak assignment. We analyze the shifts of the vibrational peak positions between the different halides and infer the extent of interaction between organic moiety and the surrounding inorganic cage. The positions of the NH3(+) stretching vibrations point to significant hydrogen bonding between the methylammonium and the halides for all three perovskites.

  20. An analytical description of transient thermal processes in harmonic crystals

    Science.gov (United States)

    Kuzkin, V. A.; Krivtsov, A. M.

    2017-05-01

    We consider two transient thermal processes in uniformly heated harmonic crystals: (i) equalibration of kinetic and potential energies and (ii) redistribution of the kinetic energy among the spatial directions. Equations describing these two processes in two-dimensional and three-dimensional crystals are derived. Analytical solutions of these equations for the square and triangular lattices are obtained. It is shown that the characteristic time of the transient processes is of the order of ten periods of atomic vibrations. The difference between the kinetic and potential energies oscillates in time. For the triangular lattice, amplitude of the oscillations decays inversely proportional to time, while for the square lattice it decays inversely proportional to the square root of time. In general, there is no equipartition of the kinetic energy among spatial directions, i.e. the kinetic temperature demonstrates tensor properties. In addition, the covariance of velocities of different particles is nonzero even at the steady state. The analytical results are supported by numerical simulations. It is also shown that the obtained solutions accurately describe the transient thermal processes in weakly nonlinear crystals at short times.

  1. Cyanide bridged hetero-metallic polymeric complexes: Syntheses, vibrational spectra, thermal analyses and crystal structures of complexes [M(1,2-dmi)2Ni(μ-CN)4]n (M = Zn(II) and Cd(II))

    Science.gov (United States)

    Kürkçüoğlu, Güneş Süheyla; Sayın, Elvan; Şahin, Onur

    2015-12-01

    Two cyanide bridged hetero-metallic complexes of general formula, [M(1,2-dmi)2Ni(μ-CN)4]n (1,2-dmi = 1,2-dimethylimidazole and M = Zn(II) or Cd(II)) have been synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal analyses and elemental analyses. The crystallographic analyses reveal that the complexes, [Zn(1,2-dmi)2Ni(μ-CN)4] (1) and [Cd(1,2-dmi)2Ni(μ-CN)4] (2), have polymeric 2D networks. In the complexes, four cyanide groups of [Ni(CN)4]2- coordinated to the adjacent M(II) ions and distorted octahedral geometries of complexes are completed by two nitrogen atoms of trans 1,2-dmi ligands. The structures of 1 and 2 are similar and linked via intermolecular hydrogen bonding, C-H⋯Ni interactions to give rise to 3D networks. Vibration assignments are given for all the observed bands and the spectral features also supported to the crystal structures of heteronuclear complexes. The FT-IR and Raman spectra of the complexes are very much consistent with the structural data presented.

  2. Crystal and molecular structures, temperature dependence of the IR and Raman spectra and vibrational dynamics of aquo 4,6-dimethyl-5H-[1,2,3]triazolo[4,5-c]pyridine in a new zwitterionic form

    Science.gov (United States)

    Dymińska, Lucyna; Janczak, Jan; Sheweshen, Khalil Salem M.; Lorenc, Jadwiga; Hanuza, Jerzy

    2017-09-01

    The crystal and molecular structures of aquo 4,6-dimethyl-5H-[1,2,3]triazolo[4,5-c]pyridine in a zwitterionic form have been determined by X-ray diffraction and DFT quantum chemical calculations. The compound adopts a triclinic crystal structure, space group P-1 = Ci1 (No. 2) with Z = 2 and the unit cell parameters: a = 6.7452 Å, b = 9.5292 Å, c = 9.5554 Å and α = 69.279°, β = 73.951°, γ = 74.242°. The temperature dependence of its IR and Raman spectra have been measured and discussed in terms of proton transfer dynamics. The molecular structure and simulated vibrational spectra of the studied compound have been determined using the DFT B3LYP/6-311G(2d,2p) approach. Vibrational characteristics of a triazolo-pyridinium system in the studied compound has been proposed. A role of water molecules in stabilization of the compound space structure has been considered.

  3. Hamiltonian tomography of photonic lattices

    Science.gov (United States)

    Ma, Ruichao; Owens, Clai; LaChapelle, Aman; Schuster, David I.; Simon, Jonathan

    2017-06-01

    In this paper we introduce an approach to Hamiltonian tomography of noninteracting tight-binding photonic lattices. To begin with, we prove that the matrix element of the low-energy effective Hamiltonian between sites α and β may be obtained directly from Sα β(ω ) , the (suitably normalized) two-port measurement between sites α and β at frequency ω . This general result enables complete characterization of both on-site energies and tunneling matrix elements in arbitrary lattice networks by spectroscopy, and suggests that coupling between lattice sites is a topological property of the two-port spectrum. We further provide extensions of this technique for measurement of band projectors in finite, disordered systems with good band flatness ratios, and apply the tool to direct real-space measurement of the Chern number. Our approach demonstrates the extraordinary potential of microwave quantum circuits for exploration of exotic synthetic materials, providing a clear path to characterization and control of single-particle properties of Jaynes-Cummings-Hubbard lattices. More broadly, we provide a robust, unified method of spectroscopic characterization of linear networks from photonic crystals to microwave lattices and everything in between.

  4. Suppressing molecular vibrations in organic semiconductors by inducing strain.

    Science.gov (United States)

    Kubo, Takayoshi; Häusermann, Roger; Tsurumi, Junto; Soeda, Junshi; Okada, Yugo; Yamashita, Yu; Akamatsu, Norihisa; Shishido, Atsushi; Mitsui, Chikahiko; Okamoto, Toshihiro; Yanagisawa, Susumu; Matsui, Hiroyuki; Takeya, Jun

    2016-01-01

    Organic molecular semiconductors are solution processable, enabling the growth of large-area single-crystal semiconductors. Improving the performance of organic semiconductor devices by increasing the charge mobility is an ongoing quest, which calls for novel molecular and material design, and improved processing conditions. Here we show a method to increase the charge mobility in organic single-crystal field-effect transistors, by taking advantage of the inherent softness of organic semiconductors. We compress the crystal lattice uniaxially by bending the flexible devices, leading to an improved charge transport. The mobility increases from 9.7 to 16.5 cm(2) V(-1) s(-1) by 70% under 3% strain. In-depth analysis indicates that compressing the crystal structure directly restricts the vibration of the molecules, thus suppresses dynamic disorder, a unique mechanism in organic semiconductors. Since strain can be easily induced during the fabrication process, we expect our method to be exploited to build high-performance organic devices.

  5. The crystal structure and thermal expansion of the perovskite-type Nd0.75Sm0.25GaO3: powder diffraction and lattice dynamical studies

    Science.gov (United States)

    Senyshyn, A.; Oganov, A. R.; Vasylechko, L.; Ehrenberg, H.; Bismayer, U.; Berkowski, M.; Matkovskii, A.

    2004-01-01

    The structure of Nd0.75Sm0.25GaO3 was studied by high-resolution powder diffraction methods using conventional x-ray and synchrotron radiation in the temperature range 85-1173 K. The GdFeO3 structure type was confirmed for Nd0.75Sm0.25GaO3 in the temperature region investigated and no structural transitions were observed. The cell parameters show a monotonic and anisotropic increase with temperature. The interatomic potential was fitted using the GULP code. Using this potential, a self-consistent approximation following the Debye model was constructed from the elastic constants of the crystals. The total phonon DOS, its projections onto atomic species, heat capacity Cv, Grüneisen parameter ggr and thermal expansion coefficient agr were considered in the framework of quasiharmonic lattice dynamics and the Debye model. The shape of the phonon DOS calculated from lattice dynamics differs significantly from the respected Debye DOS. The rare earth, gallium and oxygen atoms dominate in different frequency regions of the phonon spectrum. The heat capacity is well reproduced by the Debye model below 100 K, where acoustic phonons play an important role and above 800 K when the classical limit is reached. Predicted values of Grüneisen parameter and thermal expansion coefficients in the frame of the Debye model are {\\sim } 35% too low. Therefore, the thermal properties of Nd0.75Sm0.25GaO3 cannot be explained by acoustic phonons only and hence, Nd0.75Sm0.25GaO3 cannot be described perfectly as a Debye-like solid with respect to its thermodynamic properties.

  6. The crystal structure and thermal expansion of the perovskite-type Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3}: powder diffraction and lattice dynamical studies

    Energy Technology Data Exchange (ETDEWEB)

    Senyshyn, A [Lviv Polytechnic National University, Bandera Street 12, 79013 Lviv (Ukraine); Oganov, A R [Laboratory of Crystallography, Department of Materials, ETH Zurich, CH-8092 Zurich (Switzerland); Vasylechko, L [Lviv Polytechnic National University, Bandera Street 12, 79013 Lviv (Ukraine); Ehrenberg, H [Darmstadt University of Technology, Institute for Materials Science, Petersenstrasse 23, D-64287 Darmstadt (Germany); Bismayer, U [Mineralogisch-Petrographisches Institut, Universitat Hamburg, Grindelallee 48, D-20146 Hamburg (Germany); Berkowski, M [Institute of Physics Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Matkovskii, A [Lviv Polytechnic National University, Bandera Street 12, 79013 Lviv (Ukraine)

    2004-01-28

    The structure of Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} was studied by high-resolution powder diffraction methods using conventional x-ray and synchrotron radiation in the temperature range 85 - 1173 K. The GdFeO{sub 3} structure type was confirmed for Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} in the temperature region investigated and no structural transitions were observed. The cell parameters show a monotonic and anisotropic increase with temperature. The interatomic potential was fitted using the GULP code. Using this potential, a self-consistent approximation following the Debye model was constructed from the elastic constants of the crystals. The total phonon DOS, its projections onto atomic species, heat capacity C{sub v}, Grueneisen parameter {gamma} and thermal expansion coefficient {alpha} were considered in the framework of quasiharmonic lattice dynamics and the Debye model. The shape of the phonon DOS calculated from lattice dynamics differs significantly from the respected Debye DOS. The rare earth, gallium and oxygen atoms dominate in different frequency regions of the phonon spectrum. The heat capacity is well reproduced by the Debye model below 100 K, where acoustic phonons play an important role and above 800 K when the classical limit is reached. Predicted values of Grueneisen parameter and thermal expansion coefficients in the frame of the Debye model are {approx} 35% too low. Therefore, the thermal properties of Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} cannot be explained by acoustic phonons only and hence, Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} cannot be described perfectly as a Debye-like solid with respect to its thermodynamic properties.

  7. Role of the crystal lattice constants and band structures in the optoelectronic spectra of CdGa{sub 2}S{sub 4} by DFT approaches

    Energy Technology Data Exchange (ETDEWEB)

    Rahnamaye Aliabad, H.A. [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Vaezi, Hamide [Department of Physics, Khayyam Institute of Higher Education, Mashhad (Iran, Islamic Republic of); Basirat, Shiva [Department of Physics, Payame Noor University of Mashhad, Mashhad (Iran, Islamic Republic of); Ahmad, Iftikhar [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Abbottabad University of Science and Technology, Havelian (Pakistan)

    2017-07-17

    The electronical and optical properties of CdGa{sub 2}S{sub 4} under high pressures were studied using the full potential linearized augmented plane wave (FP-LAPW) method within the GGA and mBJ exchange correlation potentials from 0.0 to 16.92 GPa. The obtained results show that the lattice constants, bandgap values, and optoelectronic properties are sensitive to applied external pressures. The mBJ results indicate that the bandgap increases and the static dielectric constants decrease with increasing the pressure. The two none zero dielectric tensor components show considerable anisotropy between the perpendicular and parallel components. The maximum absorption for x direction in all pressures takes place in vacuum UV region. Also, the plasma frequency shifts to the higher energies with increasing the pressure for application in optical devices. The calculated results by mBJ are in close agreement with the experimental values. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. 各向异性金刚石结构的光子晶体%Anisotropic Photonic Crystals with Diamond Lattice

    Institute of Scientific and Technical Information of China (English)

    詹仪; 郑义; 李效增; 李秀霞

    2009-01-01

    基于平面波展开法,理论分析了填充率、介质各向异性的程度对单轴金刚石结构三维光子晶体禁带的影响.结果表明,当填充率和介质各向异性取合适的值,单轴各向异性金刚石结构光子晶体存在着完全带隙.介质各向异性的引入使该晶体的带隙变窄甚至完全关闭.在各个布里渊区域里,带隙率和带隙宽度随介质各向异性程度的变化而变化.各向异性的引入为调整光子禁带提供了一种方法.%With the plane-wave expansion method, the photonic-band-gap structure for a diamond lattice consisting of a uniaxial anisotropic-dielectric sphere in air was studied through tuning three inequivalent 1/3 Brillouin zone. The results show that choosing the suitable range of filling fraction and anisotropy, a full band gap opens in the whole Brillouin zone for this anisotropic PBG structure. The gap to midgap ratio and bandgap width is tunable as a result of the changing extraordinary axis orientation of the uniaxial sphere. Anisotropy in sphere dielectric function is found to narrow or even close band gaps. The band gap width and close rate are affected by the extraordinary axis directions and anisotropy. The results in turn suggest a potential approach to obtain some degree of tunability of the photonic band structures.

  9. 旋转方形散射体对三角晶格磁振子晶体带结构的优化∗%Spin-wave band gaps created by rotating square ro ds in triangular lattice magnonic crystals

    Institute of Scientific and Technical Information of China (English)

    胡晓颖; 郭晓霞; 胡文弢; 呼和满都拉; 郑晓霞; 荆丽丽

    2015-01-01

    =0.6 we calculated the first normalized gap width ∆Ω/Ωg. when f =0.6 andθ=0◦, the first gap width∆Ω=0.812(µ0ω/g) and the normalized gap width∆Ω/Ωg=0.9187. The results show that from the first normalized gap widths the largest one can be found when f = 0.6 and θ = 5◦, the first gap width∆Ω = 0.937 ( µ0ω/g) and the normalized gap width ∆Ω/Ωg = 0.9591. The results show that the numerical, rotating square rods can make the low frequency band gap widen in the triangular lattice of two-dimensional magnonic crystal.

  10. On the influence of soft crystal field excitations on the spectrum of spin excitations in CeNiSn-type Kondo lattices

    Energy Technology Data Exchange (ETDEWEB)

    Kagan, Yu.; Kikoin, K.A.; Mishchenko, A.S. [RRC Kurchatov Inst., Moscow (Russian Federation). Super Conductivity and Solid State

    1997-02-01

    On the grounds of the microscopic theory of heavy-fermion spin liquids a novel description of low-energy excitation spectra in CeNiSn and related compounds is offered. The anomalous properties of orthorhombic CeNiSn and related materials are explained by the interplay between the fermi-type spinon excitations with the energy scale T{sup *} {approx} T{sub K} and the one-site crystal field excitations with the energy {Delta}{sub CF} < T{sup *}. The theory gives both quantitative and qualitative description of inelastic neutron scattering spectra and low-temperature thermodynamics. It resolves also the apparent contradiction between metallic conductivity and gap-wise behavior of thermodynamic properties and spin response at low temperatures. (orig.). 8 refs.

  11. The growth and optical properties of Bi12SiO20 single crystals

    Directory of Open Access Journals (Sweden)

    STEVAN DJURIC

    2002-04-01

    Full Text Available Single crystals of Bi12SiO20 were grown from the melt by the Czochralski technique. The critical crystal diameter dc = 10 mm and the critical rate of rotation wc = 20 rpm were calculated by equations from the hydrodynamics of a melt. The rate of crystal growth was experimentally obtained to be 5 mm/h. The crystal growth was in the [ 111] direction. The lattice parameter a = 1.0096 nm was determined by X-ray powder diffraction. The reflectance spectra were recorded in the wave numbers range 20–5000 cm-1 at different temperatures. For all the recorded spectra the values of the vibrational TO and LO modes were found using the Kramers-Kronig analysis (KKA. Twentyfive TO and LO modes were found at 70 K, and eighteen at 295 K. The obtained results are discussed and compared with published data.

  12. Free µ-Lattices

    DEFF Research Database (Denmark)

    Santocanale, Luigi

    2002-01-01

    A μ-lattice is a lattice with the property that every unary polynomial has both a least and a greatest fix-point. In this paper we define the quasivariety of μ-lattices and, for a given partially ordered set P, we construct a μ-lattice JP whose elements are equivalence classes of games in a preor...

  13. X-ray diffraction, vibrational and photoluminescence studies of the self-organized quantum well crystal H{sub 3}N(CH{sub 2}){sub 6}NH{sub 3}PbBr{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Dammak, T. [Laboratoire de Physique Appliquee (LPA), Faculte des Sciences de Sfax, 3018, BP 802 (Tunisia)], E-mail: thameurlpa@yahoo.fr; Fourati, N. [Laboratoire de Physique Appliquee (LPA), Faculte des Sciences de Sfax, 3018, BP 802 (Tunisia); Boughzala, H. [Laboratoire de Cristallochimie et des Materiaux, Faculte des Sciences de Tunis (Tunisia); Mlayah, A. [Centre d' Elaboration des Materiaux et d' Etudes Structurales (CEMES), CNRS-Universite Paul Sabatier, 29 rue Jeanne Marvig, 31055 Toulouse, Cedex 4 (France); Abid, Y. [Laboratoire de Physique Appliquee (LPA), Faculte des Sciences de Sfax, 3018, BP 802 (Tunisia)

    2007-12-15

    We have prepared new semiconductor H{sub 3}N(CH{sub 2}){sub 6}NH{sub 3}PbBr{sub 4} crystals which are self-assembled organic-inorganic hybrid materials. The grown crystals have been studied by X-ray diffraction, infrared absorption and Raman spectroscopy scattering. We found that the title compound, abbreviated 2C{sub 6}PbBr{sub 4}, crystallizes in a two-dimensional (2D) structure with a P2{sub 1}/a space group. In the inorganic semiconductor sub-lattice, the corner sharing PbBr{sub 6} octahedra form infinite 2D chains. The organic C{sub 6}H{sub 18}N{sub 2}{sup +} ions form the insulator barriers between the inorganic semiconductor layers. Such a packing leads to a self-assembled multiple quantum well structure. Raman and infrared spectra of the title compound were recorded in the 50-500 and 400-4000 cm{sup -1} frequency regions, respectively. The assignment of the observed Raman lines was performed by comparison with the homologous compounds. Transmission measurements on thin films of 2C{sub 6}PbBr{sub 4}, obtained by the spin coating method, revealed a strong absorption peak at 380 nm. Luminescence measurements showed an emission line at 402 nm associated with radiative recombinations of excitons confined within the PbBr{sub 6} layers. The electron-hole binding energy is estimated at 180 meV.

  14. Jacobi photonic lattices and their SUSY partners.

    Science.gov (United States)

    Zúñiga-Segundo, A; Rodríguez-Lara, B M; Fernández C, David J; Moya-Cessa, H M

    2014-01-13

    We present a classical analog of quantum optical deformed oscillators in arrays of waveguides. The normal modes of these one-dimensional photonic crystals are given in terms of Jacobi polynomials. We show that it is possible to attack the problem via factorization by exploiting the corresponding quantum optical model. This allows us to provide an unbroken supersymmetric partner of the proposed Jacobi lattices. Thanks to the underlying SU(1, 1) group symmetry of the lattices, we present the analytic propagators and impulse functions for these one-dimensional photonic crystals.

  15. Ultra-low transmission loss (7.7 dB/km at 750 nm) inhibited-coupling guiding hollow-core photonic crystal fibers with a single ring of tubular lattice cladding

    CERN Document Server

    Debord, B; Chafer, M; Baz, A; Maurel, M; Blondy, J M; Hugonnot, E; Scol, F; Vincetti, L; Gerome, F; Benabid, F

    2016-01-01

    The advent of photonic bandgap (PBG) guiding hollow- core photonic crystal fiber (HC-PCF) sparked the hope of guiding light with attenuation below the fundamental silica Rayleigh scattering limit (SRSL) of conventional step-index fibers. Unfortunately, the combination of the strong core-cladding optical-overlap, the surface roughness at the silica cladding struts and the presence of interface-modes limited the lowest reported transmission-loss to 1.2 dB/km at 1550 nm. This hope is recently revived by the introduction of hypocycloid core- contour (i.e. negative curvature) in inhibited-coupling (IC) guiding HC-PCF, and the reduction of their confinement loss to a level that makes them serious contenders for light transmission below the SRSL in UV- VIS-NIR spectral range. Here, we report on several IC guiding HC-PCFs with a hypocycloid core-contour and a cladding structure made of a single ring from a tubular lattice. The fibers guide in the UV-VIS and NIR, and among which we list one with a record transmission ...

  16. Waves & vibrations

    OpenAIRE

    Nicolas, Maxime

    2016-01-01

    Engineering school; This course is designed for students of Polytech Marseille, engineering school. It covers first the physics of vibration of the harmonic oscillator with damping and forcing, coupled oscillators. After a presentation of the wave equation, the vibration of strings, beams and membranes are studied.

  17. Lattice dynamical studies of HTSC materials

    Energy Technology Data Exchange (ETDEWEB)

    Pintschovius, L.; Pyka, N.; Reichardt, W. (Kernforschungszentrum Karlsruhe, INFP (Germany)); Rumiantsev, A.Yu.; Mitrofanov, N.L.; Ivanov, A.S. (I.V. Kurchatov-Inst. of Atomic Energy, Moscow (USSR)); Collin, G.; Bourges, P. (Lab. Leon Brillouin, CEA-CNRS, CEN Saclay, 91 - Gif-sur-Yvette (France))

    1991-12-01

    A survey is presented on recent progress in the understanding of the lattice dynamics in Nd{sub 2}CuO{sub 4}, (La,Sr){sub 2}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 6/7}. Classical anharmonicity and twinning were found to be major complications for the interpretation of the data. The lattice vibrations of the cuprates can now largely be described within the framework of shell models for strongly ionic compounds. Phonon anomalies inferred from a comparison of doped and undoped compounds resemble those found in classical superconductors. (orig.).

  18. Lattice thermal expansion and anisotropic displacements in 𝜶-sulfur from diffraction experiments and first-principles theory

    Science.gov (United States)

    George, Janine; Deringer, Volker L.; Wang, Ai; Müller, Paul; Englert, Ulli; Dronskowski, Richard

    2016-12-01

    Thermal properties of solid-state materials are a fundamental topic of study with important practical implications. For example, anisotropic displacement parameters (ADPs) are routinely used in physics, chemistry, and crystallography to quantify the thermal motion of atoms in crystals. ADPs are commonly derived from diffraction experiments, but recent developments have also enabled their first-principles prediction using periodic density-functional theory (DFT). Here, we combine experiments and dispersion-corrected DFT to quantify lattice thermal expansion and ADPs in crystalline α-sulfur (S8), a prototypical elemental solid that is controlled by the interplay of covalent and van der Waals interactions. We begin by reporting on single-crystal and powder X-ray diffraction measurements that provide new and improved reference data from 10 K up to room temperature. We then use several popular dispersion-corrected DFT methods to predict vibrational and thermal properties of α-sulfur, including the anisotropic lattice thermal expansion. Hereafter, ADPs are derived in the commonly used harmonic approximation (in the computed zero-Kelvin structure) and also in the quasi-harmonic approximation (QHA) which takes the predicted lattice thermal expansion into account. At the PPBE+D3(BJ) level, the QHA leads to excellent agreement with experiments. Finally, more general implications of this study for theory and experiment are discussed.

  19. Anisotropic dissipation in lattice metamaterials

    Directory of Open Access Journals (Sweden)

    Dimitri Krattiger

    2016-12-01

    Full Text Available Plane wave propagation in an elastic lattice material follows regular patterns as dictated by the nature of the lattice symmetry and the mechanical configuration of the unit cell. A unique feature pertains to the loss of elastodynamic isotropy at frequencies where the wavelength is on the order of the lattice spacing or shorter. Anisotropy may also be realized at lower frequencies with the inclusion of local resonators, especially when designed to exhibit directionally non-uniform connectivity and/or cross-sectional geometry. In this paper, we consider free and driven waves within a plate-like lattice−with and without local resonators−and examine the effects of damping on the isofrequency dispersion curves. We also examine, for free waves, the effects of damping on the frequency-dependent anisotropy of dissipation. Furthermore, we investigate the possibility of engineering the dissipation anisotropy by tuning the directional properties of the prescribed damping. The results demonstrate that uniformly applied damping tends to reduce the intensity of anisotropy in the isofrequency dispersion curves. On the other hand, lattice crystals and metamaterials are shown to provide an excellent platform for direction-dependent dissipation engineering which may be realized by simple changes in the spatial distribution of the damping elements.

  20. Ultra-cold atoms in far-detuned optical lattices

    CERN Document Server

    Jones, P H

    2001-01-01

    This thesis describes the design and construction of a laser cooling experiment for the study of optical lattices, and reports on the results of experiments aimed at 'quantum state preparation' by means of resolved-sideband Raman cooling in a far-detuned optical lattice. Preliminary experiments were performed on cold atoms in a magneto-optical trap, in an optical molasses and in an optical lattice to determine their properties and optimise the conditions for the loading of a far-detuned optical lattice. Temperature measurement techniques such as ballistic expansion and recoil-induced resonances were used. The vibrational levels and coherences of the optical lattice were investigated with conventional probe absorption spectroscopy and a novel method based on coherent transients, which revealed evidence that the anharmonicity of the potential wells is the dominant factor in determining the widths of Raman transitions between levels. A two-dimensional far-detuned (non-dissipative) lattice was loaded from a spati...

  1. Channeling efficiency dependence on bending radius and thermal vibration amplitude of the model for the channeling of high-energy particles in straight and bent crystals implemented in Geant4

    Energy Technology Data Exchange (ETDEWEB)

    Bagli, Enrico [INFN Sezione di Ferrara, Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1, 44100 Ferrara (Italy); Asai, Makoto; Dotti, Andrea [SLAC National Accelerator Laboratory, 2575 Sand Hill Rd, Menlo Park, CA 94025 (United States); Guidi, Vincenzo [INFN Sezione di Ferrara, Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1, 44100 Ferrara (Italy); Verderi, Marc [Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)

    2015-07-15

    Monte Carlo simulations of the interaction of particles with matter are usually done with downloadable toolkits such as Geant4. A model suitable for the implementation into Geant4 for the interaction of high-energy particles in straight and bent crystals was developed and implemented. The model relies on the continuum potential approximation. The variation of the Geant4 model for the description of the orientational effect as a function of the physical parameters for the calculation of the interplanar potential is presented. The simulations are capable of reproducing the variation of the efficiency of channeling as a function of the thermal vibration amplitude and the bending radius of a bent Si strip. The study can be useful for the simulation of the channeling effect in experiments at GeV/c energies.

  2. Pyrrole Hydrogenation over Rh(111) and Pt(111) Single-Crystal Surfaces and Hydrogenation Promotion Mediated by 1-Methylpyrrole: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

    Energy Technology Data Exchange (ETDEWEB)

    Kliewer, Christopher J.; Bieri, Marco; Somorjai, Gabor A.

    2008-03-04

    Sum-frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to study the adsorption and hydrogenation of pyrrole over both Pt(111) and Rh(111) single-crystal surfaces at Torr pressures (3 Torr pyrrole, 30 Torr H{sub 2}) to form pyrrolidine and the minor product butylamine. Over Pt(111) at 298 K it was found that pyrrole adsorbs in an upright geometry cleaving the N-H bond to bind through the nitrogen evidenced by SFG data. Over Rh(111) at 298 K pyrrole adsorbs in a tilted geometry relative to the surface through the p-aromatic system. A pyrroline surface reaction intermediate, which was not detected in the gas phase, was seen by SFG during the hydrogenation over both surfaces. Significant enhancement of the reaction rate was achieved over both metal surfaces by adsorbing 1-methylpyrrole before reaction. SFG vibrational spectroscopic results indicate that reaction promotion is achieved by weakening the bonding between the N-containing products and the metal surface because of lateral interactions on the surface between 1-methylpyrrole and the reaction species, reducing the desorption energy of the products. It was found that the ring-opening product butylamine was a reaction poison over both surfaces, but this effect can be minimized by treating the catalyst surfaces with 1-methylpyrrole before reaction. The reaction rate was not enhanced with elevated temperatures, and SFG suggests desorption of pyrrole at elevated temperatures.

  3. Observation of resonant lattice modes by inelastic neutron scattering

    DEFF Research Database (Denmark)

    Bjerrum Møller, Hans; Mackintosh, A.R.

    1965-01-01

    Observation by inelastic neutron scattering of resonant lattice modes due to small concentration of W atoms in Cr host crystal; frequencies and lifetimes of phonons with frequencies near that of resonant mode are considerably affected by presence of defects....

  4. Lattice dynamics of strontium tungstate

    Indian Academy of Sciences (India)

    Prabhatasree Goel; R Mittal; S L Chaplot; A K Tyagi

    2008-11-01

    We report here measurements of the phonon density of states and the lattice dynamics calculations of strontium tungstate (SrWO4). At ambient conditions this compound crystallizes to a body-centred tetragonal unit cell (space group I41/a) called scheelite structure. We have developed transferable interatomic potentials to study the lattice dynamics of this class of compounds. The model parameters have been fitted with respect to the experimentally available Raman and infra-red frequencies and the equilibrium unit cell parameters. Inelastic neutron scattering measurements have been carried out in the triple-axis spectrometer at Dhruva reactor. The measured phonon density of states is in good agreement with the theoretical calculations, thus validating the inter-atomic potential developed.

  5. Lattice dynamics of α-cristobalite and the Boson peak in silica glass

    Science.gov (United States)

    Wehinger, Björn; Bosak, Alexeï; Refson, Keith; Mirone, Alessandro; Chumakov, Aleksandr; Krisch, Michael

    2015-08-01

    The lattice dynamics of the silica polymorph α -cristobalite has been investigated by a combination of diffuse and inelastic x-ray scattering and ab initio lattice dynamics calculations. Phonon dispersion relations and vibrational density of states are reported and the phonon eigenvectors analyzed by a detailed comparison of scattering intensities. The experimentally validated calculation is used to identify the vibration contributing most to the first peak in the density of vibrational states. The comparison of its displacement pattern to the silica polymorphs α -quartz and coesite and to vitreous silica reveals a distinct similarity and allows for decisive conclusions on the vibrations causing the so-called Boson peak in silica glass.

  6. Band transport model for discotic liquid crystals

    Science.gov (United States)

    Lever, L. J.; Kelsall, R. W.; Bushby, R. J.

    2005-07-01

    A theoretical model is presented for charge transport in discotic liquid crystals in which a charge is delocalized over more than one lattice site. As such, charge transport is via a banded conduction process in a narrow bandwidth system and takes place over coherent lengths of a few molecules. The coherent lengths are disrupted by the geometrical disorder of the system and are treated as being terminated by quantum tunnel barriers. The transmission probabilities at these barriers have been calculated as a function of the charge carrier energy. Phononic interactions are also considered and the charge carrier scattering rates are calculated for intermolecular and intramolecular vibrations. The results of the calculations have been used to develop a Monte Carlo simulation of the charge transport model. Simulated data are presented and used to discuss the nature of the tunnel barriers required to reproduce experimental data. We find that the model successfully reproduces experimental time of flight data including temperature dependence.

  7. High-frequency thermal processes in harmonic crystals

    CERN Document Server

    Kuzkin, Vitaly A

    2016-01-01

    We consider two high-frequency thermal processes in uniformly heated harmonic crystals relaxing towards equilibrium: (i) equilibration of kinetic and potential energies and (ii) redistribution of energy among spatial directions. Equation describing these processes with deterministic initial conditions is derived. Solution of the equation shows that characteristic time of these processes is of the order of ten periods of atomic vibrations. After that time the system practically reaches the stationary state. It is shown analytically that in harmonic crystals temperature tensor is not isotropic even in the stationary state. As an example, harmonic triangular lattice is considered. Simple formula relating the stationary value of the temperature tensor and initial conditions is derived. The function describing equilibration of kinetic and potential energies is obtained. It is shown that the difference between the energies (Lagrangian) oscillates around zero. Amplitude of these oscillations decays inversely proport...

  8. Supramolecular architectures in luminescent Zn(II) and Cd(II) complexes containing imidazole derivatives: Crystal structures, vibrational and thermal properties, Hirshfeld surface analysis and electrostatic potentials

    Science.gov (United States)

    Di Santo, Alejandro; Echeverría, Gustavo A.; Piro, Oscar E.; Pérez, Hiram; Ben Altabef, Aida; Gil, Diego M.

    2017-04-01

    Three novel zinc and cadmium complexes with 1-methylimidazole and 2-methylimidazole as ligands, mono-nuclear dichloro-bis(1-methylimidazole) zinc(II) and dibromo-bis(2-methylimidazole)cadmium(II) monohydrate complexes, and poly-nuclear bis(1-methylimidazole)-di-(μ2-bromo)cadmium(II) complex, namely, compounds 1-3, respectively, have been synthesized. The complexes were characterized by IR and Raman spectroscopies, thermal analysis and fluorescence. All the compounds exhibit interesting luminescent properties in solid state originated from intra-ligand (π→π*) transitions. Crystal structures of 1-3 were determined by single-crystal X-ray diffraction. Compound 1 crystallizes in P21/n space group, the Zn(II) ion lies at a crystal general position in a tetrahedral environment, and the mono-nuclear units are weakly bonded to one another by Csbnd H⋯Cl hydrogen bonds. Compound 2 crystallizes in Pnma space group, and mirror-related tetrahedral units around Cd(II) ion are H-bonded through a water molecule. Compound 3 crystallizes in P21/c space group, and the Cd(II) ion presents a centrosymmetric octahedral coordination. Neighboring and equatorial edge-sharing octahedra conform a polymeric arrangement that extends along the crystal a-axis. Weak hydrogen bonds are the major driving forces in the crystal packing of the three complexes. Hirshfeld surface analysis reveals a detailed scrutiny of intermolecular interactions experienced by each complex. The surfaces mapped over dnorm property highlight the X···H (X = Cl, Br) as the main intermolecular contacts for the three complexes, being also relevant the presence of O⋯H contacts for complex 2. The surfaces mapped over Shape index and curvedness properties for the two Cd complexes allow identify π … π stacking interactions which are absent in the Zn complex. 2D fingerprint plots have been used to quantify the relative contribution of the intermolecular contacts to crystal stability of compounds, showing

  9. Good Vibrations

    OpenAIRE

    Panesar, Lucy

    2007-01-01

    Good Vibrations was a market research exercise conducted by Felicity (my alter-ego) and assistants to help develop marketing and packaging for an electro-therapeutic device (vibrator) used to treat hysteria and other female stress related disorders. It was a live art work commissioned by The Live Art Development Agency for East End Collaborations on 6th May 2007 and the South London Gallery for Bonkersfest on 2nd June 2007.

  10. Vibration sensors

    Science.gov (United States)

    Gupta, Amita; Singh, Ranvir; Ahmad, Amir; Kumar, Mahesh

    2003-10-01

    Today, vibration sensors with low and medium sensitivities are in great demand. Their applications include robotics, navigation, machine vibration monitoring, isolation of precision equipment & activation of safety systems e.g. airbags in automobiles. Vibration sensors have been developed at SSPL, using silicon micromachining to sense vibrations in a system in the 30 - 200 Hz frequency band. The sensing element in the silicon vibration sensor is a seismic mass suspended by thin silicon hinges mounted on a metallized glass plate forming a parallel plate capacitor. The movement of the seismic mass along the vertical axis is monitored to sense vibrations. This is obtained by measuring the change in capacitance. The movable plate of the parallel plate capacitor is formed by a block connected to a surrounding frame by four cantilever beams located on sides or corners of the seismic mass. This element is fabricated by silicon micromachining. Several sensors in the chip sizes 1.6 cm x 1.6 cm, 1 cm x 1 cm and 0.7 cm x 0.7 cm have been fabricated. Work done on these sensors, techniques used in processing and silicon to glass bonding are presented in the paper. Performance evaluation of these sensors is also discussed.

  11. Interaction of electronic excitations of Tm3+ ions with acoustic vibrations in KTm(MoO4)2

    Science.gov (United States)

    Kamenskyi, D.; Poperezhai, S.; Gogoi, P.; Engelkamp, H.; Maan, J. C.; Wosnitza, J.; Kut'ko, V.

    2014-01-01

    Electron paramagnetic resonance spectra of KTm(MoO4)2 were measured as a function of magnetic field between 3 and 11.5 cm-1 at T =2 K. We found that in addition to the absorption line caused by the electronic excitation of Tm3+ ions, the spectra contain sidebands. Far-infrared transmission measured with polarized light from 10 to 75 cm-1 revealed vibration modes at 16.7 and 25.7 cm-1 for polarizations Eω∥a and Eω∥c, respectively. We show that sidebands in the spectra of paramagnetic resonance result from a parametric resonance between the electronic excitations of the Tm3+ ions and the acoustic vibrations of the crystal lattice.

  12. Geometry and dynamics in Hamiltonian lattices

    NARCIS (Netherlands)

    Rink, B.W.

    2003-01-01

    E. Fermi, J. Pasta and S. Ulam introduced the Fermi-Pasta-Ulam lattice in the 1950s as a classical mechanical model for a mono-atomic crystal or a one-dimensional continuum. The model consisted of a discrete number of equal point masses that interact with their nearest neighbours only. On the basis

  13. Introduction to Louis Michel's lattice geometry through group action

    CERN Document Server

    Zhilinskii, Boris

    2015-01-01

    Group action analysis developed and applied mainly by Louis Michel to the study of N-dimensional periodic lattices is the central subject of the book. Different basic mathematical tools currently used for the description of lattice geometry are introduced and illustrated through applications to crystal structures in two- and three-dimensional space, to abstract multi-dimensional lattices and to lattices associated with integrable dynamical systems. Starting from general Delone sets the authors turn to different symmetry and topological classifications including explicit construction of orbifolds for two- and three-dimensional point and space groups. Voronoï and Delone cells together with positive quadratic forms and lattice description by root systems are introduced to demonstrate alternative approaches to lattice geometry study. Zonotopes and zonohedral families of 2-, 3-, 4-, 5-dimensional lattices are explicitly visualized using graph theory approach. Along with crystallographic applications, qualitative ...

  14. Discrete breathers in hexagonal dusty plasma lattices.

    Science.gov (United States)

    Koukouloyannis, V; Kourakis, I

    2009-08-01

    The occurrence of single-site or multisite localized vibrational modes, also called discrete breathers, in two-dimensional hexagonal dusty plasma lattices is investigated. The system is described by a Klein-Gordon hexagonal lattice characterized by a negative coupling parameter epsilon in account of its inverse dispersive behavior. A theoretical analysis is performed in order to establish the possibility of existence of single as well as three-site discrete breathers in such systems. The study is complemented by a numerical investigation based on experimentally provided potential forms. This investigation shows that a dusty plasma lattice can support single-site discrete breathers, while three-site in phase breathers could exist if specific conditions, about the intergrain interaction strength, would hold. On the other hand, out of phase and vortex three-site breathers cannot be supported since they are highly unstable.

  15. Optical vortex array in spatially varying lattice

    CERN Document Server

    Kapoor, Amit; Senthilkumaran, P; Joseph, Joby

    2015-01-01

    We present an experimental method based on a modified multiple beam interference approach to generate an optical vortex array arranged in a spatially varying lattice. This method involves two steps which are: numerical synthesis of a consistent phase mask by using two-dimensional integrated phase gradient calculations and experimental implementation of produced phase mask by utilizing a phase only spatial light modulator in an optical 4f Fourier filtering setup. This method enables an independent variation of the orientation and period of the vortex lattice. As working examples, we provide the experimental demonstration of various spatially variant optical vortex lattices. We further confirm the existence of optical vortices by formation of fork fringes. Such lattices may find applications in size dependent trapping, sorting, manipulation and photonic crystals.

  16. Fractional Bloch oscillations in photonic lattices

    CERN Document Server

    Corrielli, Giacomo; Della Valle, Giuseppe; Longhi, Stefano; Osellame, Roberto; 10.1038/ncomms2578

    2013-01-01

    Bloch oscillations, the oscillatory motion of a quantum particle in a periodic potential, are one of the most fascinating effects of coherent quantum transport. Originally studied in the context of electrons in crystals, Bloch oscillations manifest the wave nature of matter and are found in a wide variety of different physical systems. Here we report on the first experimental observation of fractional Bloch oscillations, using a photonic lattice as a model system of a two-particle extended Bose-Hubbard Hamiltonian. In our photonic simulator, the dynamics of two correlated particles hopping on a one-dimensional lattice is mapped into the motion of a single particle in a two-dimensional lattice with engineered defects and mimicked by light transport in a square waveguide lattice with a bent axis.

  17. Fractional Bloch oscillations in photonic lattices.

    Science.gov (United States)

    Corrielli, Giacomo; Crespi, Andrea; Della Valle, Giuseppe; Longhi, Stefano; Osellame, Roberto

    2013-01-01

    Bloch oscillations, the oscillatory motion of a quantum particle in a periodic potential, are one of the most fascinating effects of coherent quantum transport. Originally studied in the context of electrons in crystals, Bloch oscillations manifest the wave nature of matter and are found in a wide variety of different physical systems. Here we report on the first experimental observation of fractional Bloch oscillations, using a photonic lattice as a model system of a two-particle extended Bose-Hubbard Hamiltonian. In our photonic simulator, the dynamics of two correlated particles hopping on a one-dimensional lattice is mapped into the motion of a single particle in a two-dimensional lattice with engineered defects and mimicked by light transport in a square waveguide lattice with a bent axis.

  18. Ultralocality on the lattice

    CERN Document Server

    Campos, R G; Campos, Rafael G.; Tututi, Eduardo S.

    2002-01-01

    It is shown that the nonlocal Dirac operator yielded by a lattice model that preserves chiral symmetry and uniqueness of fields, approaches to an ultralocal and invariant under translations operator when the size of the lattice tends to zero.

  19. New integrable lattice hierarchies

    Energy Technology Data Exchange (ETDEWEB)

    Pickering, Andrew [Area de Matematica Aplicada, ESCET, Universidad Rey Juan Carlos, c/ Tulipan s/n, 28933 Mostoles, Madrid (Spain); Zhu Zuonong [Departamento de Matematicas, Universidad de Salamanca, Plaza de la Merced 1, 37008 Salamanca (Spain) and Department of Mathematics, Shanghai Jiao Tong University, Shanghai 200030 (China)]. E-mail: znzhu2@yahoo.com.cn

    2006-01-23

    In this Letter we give a new integrable four-field lattice hierarchy, associated to a new discrete spectral problem. We obtain our hierarchy as the compatibility condition of this spectral problem and an associated equation, constructed herein, for the time-evolution of eigenfunctions. We consider reductions of our hierarchy, which also of course admit discrete zero curvature representations, in detail. We find that our hierarchy includes many well-known integrable hierarchies as special cases, including the Toda lattice hierarchy, the modified Toda lattice hierarchy, the relativistic Toda lattice hierarchy, and the Volterra lattice hierarchy. We also obtain here a new integrable two-field lattice hierarchy, to which we give the name of Suris lattice hierarchy, since the first equation of this hierarchy has previously been given by Suris. The Hamiltonian structure of the Suris lattice hierarchy is obtained by means of a trace identity formula.

  20. Atomistic modelling study of lanthanide incorporation in the crystal lattice of an apatite; Etude par modelisation atomistique de l'incorporation de lanthanides dans le reseau cristallin d'une apatite phosphocalcique

    Energy Technology Data Exchange (ETDEWEB)

    Louis-Achille, V

    1999-07-01

    Studies of natural and synthetic apatites allow to propose such crystals as matrix for nuclear waste storage. The neodymium substituted britholite, Ca{sub 9}Nd(PO{sub 4}){sub 5}(SiO{sub 4})F{sub 2}. is a model for the trivalent actinide storage Neodymium can be substituted in two types of sites. The aim of this thesis is to compare the chemical nature of this two sites in fluoro-apatite Ca{sub 9}(PO{sub 4}){sub 6}F{sub 2} and then in britholite, using ab initio atomistic modeling. Two approaches are used: one considers the infinite crystals and the second considers clusters. The calculations of the electronic structure for both were performed using Kohn and Sham density functional theory in the local approximation. For solids, pseudopotentials were used, and wave functions are expanded in plane waves. For clusters, a frozen core approximation was used, and the wave functions are expanded in a linear combination of Slater type atomic orbitals. The pseudopotential is semi-relativistic for neodymium, and the Hamiltonian is scalar relativistic for the clusters. The validation of the solid approach is performed using two test cases: YPO{sub 4} and ScPO{sub 4}. Two numerical tools were developed to compute electronic deformation density map, and calculate partial density of stases. A full optimisation of the lattice parameters with a relaxation of the atomic coordinates leads to correct structural and thermodynamic properties for the fluoro-apatite, compared to experience. The electronic deformation density maps do not show any significant differences. between the two calcium sites. but Mulliken analysis on the solid and on the clusters point out the more ionic behavior of the calcium in site 2. A neodymium substituted britholite is then studied. Neodymium location only induces local modifications in; the crystalline structure and few changes in the formation enthalpy. The electronic study points out an increase of the covalent character the bonding involving neodymium