Pseudogap in the Eliashberg approach based on electron-phonon and electron-electron-phonon interaction

Energy Technology Data Exchange (ETDEWEB)

Szczesniak, R. [Institute of Physics, Czestochowa University of Technology (Poland); Institute of Physics, Jan Dlugosz University in Czestochowa (Poland); Durajski, A.P.; Duda, A.M. [Institute of Physics, Czestochowa University of Technology (Poland)

2017-04-15

The properties of the superconducting and the anomalous normal state were described by using the Eliashberg method. The pairing mechanism was reproduced with the help of the Hamiltonian, which models the electron-phonon and the electron-electron-phonon interaction (EEPh). The set of the Eliashberg equations, which determines the order parameter function (φ), the wave function renormalization factor (Z), and the energy shift function (χ), was derived. It was proven that for the sufficiently large values of the EEPh potential, the doping dependence of the order parameter (φ/Z) has the analogous course to that observed experimentally in cuprates. The energy gap in the electron density of states is induced by Z and χ - the contribution from φ is negligible. The electron density of states possesses the characteristic asymmetric form and the pseudogap is observed above the critical temperature. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Electron-phonon coupling from finite differences

Science.gov (United States)

Monserrat, Bartomeu

2018-02-01

The interaction between electrons and phonons underlies multiple phenomena in physics, chemistry, and materials science. Examples include superconductivity, electronic transport, and the temperature dependence of optical spectra. A first-principles description of electron-phonon coupling enables the study of the above phenomena with accuracy and material specificity, which can be used to understand experiments and to predict novel effects and functionality. In this topical review, we describe the first-principles calculation of electron-phonon coupling from finite differences. The finite differences approach provides several advantages compared to alternative methods, in particular (i) any underlying electronic structure method can be used, and (ii) terms beyond the lowest order in the electron-phonon interaction can be readily incorporated. But these advantages are associated with a large computational cost that has until recently prevented the widespread adoption of this method. We describe some recent advances, including nondiagonal supercells and thermal lines, that resolve these difficulties, and make the calculation of electron-phonon coupling from finite differences a powerful tool. We review multiple applications of the calculation of electron-phonon coupling from finite differences, including the temperature dependence of optical spectra, superconductivity, charge transport, and the role of defects in semiconductors. These examples illustrate the advantages of finite differences, with cases where semilocal density functional theory is not appropriate for the calculation of electron-phonon coupling and many-body methods such as the GW approximation are required, as well as examples in which higher-order terms in the electron-phonon interaction are essential for an accurate description of the relevant phenomena. We expect that the finite difference approach will play a central role in future studies of the electron-phonon interaction.

Tunable Topological Phononic Crystals

KAUST Repository

Chen, Zeguo

2016-05-27

Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.

Tunable Topological Phononic Crystals

KAUST Repository

Chen, Zeguo; Wu, Ying

2016-01-01

Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.

Two-phonon bound states in imperfect crystals

International Nuclear Information System (INIS)

Behera, S.N.; Samsur, Sk.

1980-01-01

The question of the occurrence of two-phonon bound states in imperfect crystals is investigated. It is shown that the anharmonicity mediated two-phonon bound state which is present in perfect crystals gets modified due to the presence of impurities. Moreover, the possibility of the occurrence of a purely impurity mediated two-phonon bound state is demonstrated. The bound state frequencies are calculated using the simple Einstein oscillator model for the host phonons. The two-phonon density of states for the imperfect crystal thus obtained has peaks at the combination and difference frequencies of two host phonons besides the peaks at the bound state frequencies. For a perfect crystal the theory predicts a single peak at the two-phonon bound state frequency in conformity with experimental observations and other theoretical calculations. Experimental data on the two-phonon infrared absorption and Raman scattering from mixed crystals of Gasub(1-c)Alsub(c)P and Gesub(1-c)Sisub(c) are analysed to provide evidence in support of impurity-mediated two-phonon bound states. The relevance of the zero frequency (difference spectrum) peak to the central peak, observed in structural phase transitions, is conjectured. (author)

Enhanced Electron-Phonon Coupling at Metal Surfaces

Energy Technology Data Exchange (ETDEWEB)

Plummer, Ward E.

2010-08-04

The Born-Oppenheimer approximation (BOA) decouples electronic from nuclear motion, providing a focal point for most quantum mechanics textbooks. However, a multitude of important chemical, physical and biological phenomena are driven by violations of this approximation. Vibronic interactions are a necessary ingredient in any process that makes or breaks a covalent bond, for example, conventional catalysis or enzymatically delivered biological reactions. Metastable phenomena associated with defects and dopants in semiconductors, oxides, and glasses entail violation of the BOA. Charge exchange in inorganic polymers, organic slats and biological systems involves charge- induced distortions of the local structure. A classic example is conventional superconductivity, which is driven by the electron-lattice interaction. High-resolution angle-resolved photoemission experiments are yielding new insight into the microscopic origin of electron-phonon coupling (EPC) in anisotropic two-dimensional systems. Our recent surface phonon measurement on the surface of a high-Tc material clearly indicates an important momentum dependent EPC in these materials. In the last few years we have shifted our research focus from solely looking at electron phonon coupling to examining the structure/functionality relationship at the surface of complex transition metal compounds. The investigation on electron phonon coupling has allowed us to move to systems where there is coupling between the lattice, the electrons and the spin.

Understanding the electron-phonon interaction in polar crystals: Perspective presented by the vibronic theory

Science.gov (United States)

Pishtshev, A.; Kristoffel, N.

2017-05-01

We outline our novel results relating to the physics of the electron-TO-phonon (el-TO-ph) interaction in a polar crystal. We explained why the el-TO-ph interaction becomes effectively strong in a ferroelectric, and showed how the electron density redistribution establishes favorable conditions for soft-behavior of the long-wavelength branch of the active TO vibration. In the context of the vibronic theory it has been demonstrated that at the macroscopic level the interaction of electrons with the polar zone-centre TO phonons can be associated with the internal long-range dipole forces. Also we elucidated a methodological issue of how local field effects are incorporated within the vibronic theory. These result provided not only substantial support for the vibronic mechanism of ferroelectricity but also presented direct evidence of equivalence between vibronic and the other lattice dynamics models. The corresponding comparison allowed us to introduce the original parametrization for constants of the vibronic interaction in terms of key material constants. The applicability of the suggested formula has been tested for a wide class of polar materials.

A highly attenuating and frequency tailorable annular hole phononic crystal for surface acoustic waves.

Science.gov (United States)

Ash, B J; Worsfold, S R; Vukusic, P; Nash, G R

2017-08-02

Surface acoustic wave (SAW) devices are widely used for signal processing, sensing and increasingly for lab-on-a-chip applications. Phononic crystals can control the propagation of SAW, analogous to photonic crystals, enabling components such as waveguides and cavities. Here we present an approach for the realisation of robust, tailorable SAW phononic crystals, based on annular holes patterned in a SAW substrate. Using simulations and experiments, we show that this geometry supports local resonances which create highly attenuating phononic bandgaps at frequencies with negligible coupling of SAWs into other modes, even for relatively shallow features. The enormous bandgap attenuation is up to an order-of-magnitude larger than that achieved with a pillar phononic crystal of the same size, enabling effective phononic crystals to be made up of smaller numbers of elements. This work transforms the ability to exploit phononic crystals for developing novel SAW device concepts, mirroring contemporary progress in photonic crystals.The control and manipulation of propagating sound waves on a surface has applications in on-chip signal processing and sensing. Here, Ash et al. deviate from standard designs and fabricate frequency tailorable phononic crystals with an order-of-magnitude increase in attenuation.

Electronic Contributions to the Phonon Damping in Metals

Energy Technology Data Exchange (ETDEWEB)

Johnson, Rune

1968-07-15

An imaginary part of the dielectric matrix is derived based on a first order perturbation expansion of the valence electron states in a local potential model of the crystal. The results are used to estimate the electronic contributions to the phonon damping in aluminum and lead. The corrections which have been obtained are of the same order of magnitude at small phonon momenta as the damping earlier calculated for the free electrons. However, the discrepancies between the theoretical and experimental results still remain. The major contribution to damping seems to originate in anharmonic effects, even at 80 deg K.

Acousto-optical phonon excitation in cubic piezoelectric slabs and crystal growth orientation effects

DEFF Research Database (Denmark)

Willatzen, Morten; Duggen, Lars

2017-01-01

In this paper we investigate theoretically the influence of piezoelectric coupling on phonon dispersion relations. Specifically we solve dispersion relations for a fully coupled zinc-blende freestanding quantum well for different orientations of the crystal unit cell. It is shown that the phonon...... mode density in GaAs can change by a factor of approximately 2–3 at qx a = 1 for different crystal-growth directions relative to the slab thickness direction. In particular, it is found that optical and acoustic phonon modes are always piezoelectrically coupled, independent of the crystal...... that the piezoelectric effect leads to a drastically enhanced coupling of acoustic and optical phonon modes and increase in the local phonon density of states near the plasma frequency where the permittivity approaches zero....

Semi-Dirac points in phononic crystals

KAUST Repository

Zhang, Xiujuan

2014-01-01

A semi-Dirac cone refers to a peculiar type of dispersion relation that is linear along the symmetry line but quadratic in the perpendicular direction. It was originally discovered in electron systems, in which the associated quasi-particles are massless along one direction, like those in graphene, but effective-mass-like along the other. It was reported that a semi-Dirac point is associated with the topological phase transition between a semi-metallic phase and a band insulator. Very recently, the classical analogy of a semi-Dirac cone has been reported in an electromagnetic system. Here, we demonstrate that, by accidental degeneracy, two-dimensional phononic crystals consisting of square arrays of elliptical cylinders embedded in water are also able to produce the particular dispersion relation of a semi-Dirac cone in the center of the Brillouin zone. A perturbation method is used to evaluate the linear slope and to affirm that the dispersion relation is a semi-Dirac type. If the scatterers are made of rubber, in which the acoustic wave velocity is lower than that in water, the semi-Dirac dispersion can be characterized by an effective medium theory. The effective medium parameters link the semi-Dirac point to a topological transition in the iso-frequency surface of the phononic crystal, in which an open hyperbola is changed into a closed ellipse. This topological transition results in drastic change in wave manipulation. On the other hand, the theory also reveals that the phononic crystal is a double-zero-index material along the x-direction and photonic-band-edge material along the perpendicular direction (y-direction). If the scatterers are made of steel, in which the acoustic wave velocity is higher than that in water, the effective medium description fails, even though the semi-Dirac dispersion relation looks similar to that in the previous case. Therefore different wave transport behavior is expected. The semi-Dirac points in phononic crystals described in

Remarkable reduction of thermal conductivity in phosphorene phononic crystal

International Nuclear Information System (INIS)

Xu, Wen; Zhang, Gang

2016-01-01

Phosphorene has received much attention due to its interesting physical and chemical properties, and its potential applications such as thermoelectricity. In thermoelectric applications, low thermal conductivity is essential for achieving a high figure of merit. In this work, we propose to reduce the thermal conductivity of phosphorene by adopting the phononic crystal structure, phosphorene nanomesh. With equilibrium molecular dynamics simulations, we find that the thermal conductivity is remarkably reduced in the phononic crystal. Our analysis shows that the reduction is due to the depressed phonon group velocities induced by Brillouin zone folding, and the reduced phonon lifetimes in the phononic crystal. Interestingly, it is found that the anisotropy ratio of thermal conductivity could be tuned by the ‘non-square’ pores in the phononic crystal, as the phonon group velocities in the direction with larger projection of pores is more severely suppressed, leading to greater reduction of thermal conductivity in this direction. Our work provides deep insight into thermal transport in phononic crystals and proposes a new strategy to reduce the thermal conductivity of monolayer phosphorene. (paper)

Phonon scattering in metallic glasses

International Nuclear Information System (INIS)

Black, J.L.

1979-01-01

The purpose of this article is to review some recent theoretical and experimental developments in the study of metallic glasses at temperatures near or below 1K. In this temperature regime, it appears that practically all glasses, whether metallic or insulating, behave in a similar fashion. The fact that such similarities occur, despite substantial structural differences between metallic and insulating glasses, constitutes a major theoretical challenge. This challenge, however, is not directly addressed in what follows. Instead, the evidence for universal behavior and the theory which is necessary to understand this evidence are emphasized. It turns out that most of this evidence involves a comparison of phonon scattering in metallic glasses with its counterpart in insulating glasses

Interplay between electron-phonon and electron-electron interactions

International Nuclear Information System (INIS)

Roesch, O.; Gunnarsson, O.; Han, J.E.; Crespi, V.H.

2005-01-01

We discuss the interplay between electron-electron and electron-phonon interactions for alkali-doped fullerides and high temperature superconductors. Due to the similarity of the electron and phonon energy scales, retardation effects are small for fullerides. This raises questions about the origin of superconductivity, since retardation effects are believed to be crucial for reducing effects of the Coulomb repulsion in conventional superconductors. We demonstrate that by treating the electron-electron and electron-phonon interactions on an equal footing, superconductivity can be understood in terms of a local pairing. The Jahn-Teller character of the important phonons in fullerides plays a crucial role for this result. To describe effects of phonons in cuprates, we derive a t-J model with phonons from the three-band model. Using exact diagonalization for small clusters, we find that the anomalous softening of the half-breathing phonon as well as its doping dependence can be explained. By comparing the solution of the t-J model with the Hartree-Fock approximation for the three-band model, we address results obtained in the local-density approximation for cuprates. We find that genuine many-body results, due to the interplay between the electron-electron and electron-phonon interactions, play an important role for the the results in the t-J model. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Electron-optical phonon coupling in superconductors

International Nuclear Information System (INIS)

Rietschel, H.

1975-01-01

The role of the optical phonons in superconductivity is investigated in the case of compounds with different atomic masses Msub(k). It is shown that the electron mass enhancement factor lambda is independent of Msub(k) if the force constant matrix is mass independent. However, when using lambda to calculate Tsub(c), it must be decomposed into its acoustical and optical contributions, which depend separately on Msub(k). Interference scattering from a light and a heavy mass is studied and its contributions to lambda within the free electron approximation. Numerical results are presented for a rocksalt structure crystal with nearest and next nearest neighbour coupling. These results indicate that the optical phonon contributions to lambda may substantially increase Tsub(c). (orig.) [de

Normal processes of phonon-phonon scattering and thermal conductivity of germanium crystals with isotopic disorder

CERN Document Server

Kuleev, I G

2001-01-01

The effect of normal processes of the phonon-phonon scattering on the thermal conductivity of the germanium crystals with various isotopic disorder degrees is considered. The phonon pulse redistribution in the normal scattering processes both inside each oscillatory branch (the Simons mechanism) and between various phonon oscillatory branches (the Herring mechanism) is accounted for. The contributions of the longitudinal and cross-sectional phonons drift motion into the thermal conductivity are analyzed. It is shown that the pulse redistribution in the Herring relaxation mechanism leads to essential suppression of the longitudinal phonons drift motion in the isotopically pure germanium crystals. The calculations results of thermal conductivity for the Herring relaxation mechanism agree well with experimental data on the germanium crystals with various isotopic disorder degrees

Electron-phonon interaction on an Al(001) surface

International Nuclear Information System (INIS)

Sklyadneva, I Yu; Chulkov, E V; Echenique, P M

2008-01-01

We report an ab initio study of the electron-phonon (e-ph) interaction and its contribution to the lifetime broadening of excited hole (electron) surface states on Al(001). The calculations based on density-functional theory were carried out using a linear response approach in the plane-wave pseudopotential representation. The obtained results show that both the electron-phonon coupling and the linewidth experience a weak variation with the energy and momentum position of a hole (electron) surface state in the energy band. An analysis of different contributions to the e-ph coupling reveals that bulk phonon modes turn out to be more involved in the scattering processes of excited electrons and holes than surface phonon modes. It is also shown that the role of the e-ph coupling in the broadening of the Rayleigh surface phonon mode is insignificant compared to anharmonic effects

Electronic bandstructure of an incommensurate crystal

International Nuclear Information System (INIS)

Rasing, T.

1984-06-01

The consequences of an incommensurate lattice modulation on the electronic energy levels have been studied by optical transmission experiments on Rb 2 ZnBr 4 . The results are analyzed with a simple tight-binding model in which the superspace symmetry of the crystal is taken into account. The lattice translational symmetry of crystalline matter leads to the well known concepts of the Brillouin zones, Bloch electrons, phonons and the like. In a crystal where the lattice is periodically distorted with a period that is incommensurate with the underlying lattice, this translational symmetry is broken. Nonetheless, incommensurate crystals are perfectly ordered and can be described by higher dimensional so-called superspace groups. In this paper we will show how this superspace approach provides a natural framework to understand their electronic bandstructure as well. 5 references, 3 figures

Controlling elastic waves with small phononic crystals containing rigid inclusions

KAUST Repository

Peng, Pai

2014-05-01

We show that a two-dimensional elastic phononic crystal comprising rigid cylinders in a solid matrix possesses a large complete band gap below a cut-off frequency. A mechanical model reveals that the band gap is induced by negative effective mass density, which is affirmed by an effective medium theory based on field averaging. We demonstrate, by two examples, that such elastic phononic crystals can be utilized to design small devices to control low-frequency elastic waves. One example is a waveguide made of a two-layer anisotropic elastic phononic crystal, which can guide and bend elastic waves with wavelengths much larger than the size of the waveguide. The other example is the enhanced elastic transmission of a single-layer elastic phononic crystal loaded with solid inclusions. The effective mass density and reciprocal of the modulus of the single-layer elastic phononic crystal are simultaneously near zero. © CopyrightEPLA, 2014.

Electron-phonon heat exchange in quasi-two-dimensional nanolayers

Science.gov (United States)

Anghel, Dragos-Victor; Cojocaru, Sergiu

2017-12-01

We study the heat power P transferred between electrons and phonons in thin metallic films deposited on free-standing dielectric membranes. The temperature range is typically below 1 K, such that the wavelengths of the excited phonon modes in the system is large enough so that the picture of a quasi-two-dimensional phonon gas is applicable. Moreover, due to the quantization of the components of the electron wavevectors perpendicular to the metal film's surface, the electrons spectrum forms also quasi two-dimensional sub-bands, as in a quantum well (QW). We describe in detail the contribution to the electron-phonon energy exchange of different electron scattering channels, as well as of different types of phonon modes. We find that heat flux oscillates strongly with thickness of the film d while having a much smoother variation with temperature (Te for the electrons temperature and Tph for the phonons temperature), so that one obtains a ridge-like landscape in the two coordinates, (d, Te) or (d, Tph), with crests and valleys aligned roughly parallel to the temperature axis. For the valley regions we find P ∝ Te3.5 - Tph3.5. From valley to crest, P increases by more than one order of magnitude and on the crests P cannot be represented by a simple power law. The strong dependence of P on d is indicative of the formation of the QW state and can be useful in controlling the heat transfer between electrons and crystal lattice in nano-electronic devices. Nevertheless, due to the small value of the Fermi wavelength in metals, the surface imperfections of the metallic films can reduce the magnitude of the oscillations of P vs. d, so this effect might be easier to observe experimentally in doped semiconductors.

Electronic Conductivity of Vanadium-Tellurite Glass-Ceramics

DEFF Research Database (Denmark)

Kjeldsen, Jonas; Yue, Yuanzheng; Bragatto, Caio B.

2013-01-01

In this paper, we investigate the electronic conductivity of 2TeO2-V2O5 glass-ceramics with crystallinity ranging from 0 to 100 wt.%, i.e., from entirely amorphous to completely crystalline. The glass is prepared by the melt quenching technique, and the crystal is prepared by subsequent heat...... spectroscopy. We find similar activation energies for both glass and crystal, implying that they have similar conduction mechanisms, i.e., thermally activated hopping. The electronic conductivity of 2TeO2-V2O5 glass is about one order of magnitude higher than that of the corresponding crystal......, and a percolation phenomenon occurs at a glass fraction of 61 wt.%, increasing from a lower conductivity in the crystal to a higher conductivity in the glass. We explain the behavior of electronic conduction in the 2TeO2-V2O5 glass-ceramics by considering constriction effects between particles as well...

Nonlinear electron-phonon heat exchange

International Nuclear Information System (INIS)

Woods, L.M.; Mahan, G.D.

1998-01-01

A calculation of the energy exchange between phonons and electrons is done for a metal at very low temperatures. We consider the energy exchange due to two-phonon processes. Second-order processes are expected to be important at temperatures less than 1 K. We include two different second-order processes: (i) the Compton-like scattering of phonons, and (ii) the electron-dual-phonon scattering from the second-order electron-phonon interaction. It is found that the Compton-like process contains a singular energy denominator. The singularity is removed by introducing quasiparticle damping. For pure metals we find that the energy exchange depends upon the lifetime of the electrons and it is proportional to the temperature of the lattice as T L 8 . The same calculation is performed for the electron-dual-phonon scattering and it is found that the temperature dependence is T L 9 . The results can be applied to quantum dot refrigerators. copyright 1998 The American Physical Society

Ionizing particle detection based on phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Aly, Arafa H., E-mail: arafa16@yahoo.com, E-mail: arafa.hussien@science.bsu.edu.eg; Mehaney, Ahmed; Eissa, Mostafa F. [Physics Department, Faculty of Science, Beni-Suef University, Beni-Suef (Egypt)

2015-08-14

Most conventional radiation detectors are based on electronic or photon collections. In this work, we introduce a new and novel type of ionizing particle detector based on phonon collection. Helium ion radiation treats tumors with better precision. There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. Helium-4 is formed in fusion reactor technology and in enormous quantities during Big Bang nucleo-synthesis. In this study, we introduce a technique for helium-4 ion detection (sensing) based on the innovative properties of the new composite materials known as phononic crystals (PnCs). PnCs can provide an easy and cheap technique for ion detection compared with conventional methods. PnC structures commonly consist of a periodic array of two or more materials with different elastic properties. The two materials are polymethyl-methacrylate and polyethylene polymers. The calculations showed that the energies lost to target phonons are maximized at 1 keV helium-4 ion energy. There is a correlation between the total phonon energies and the transmittance of PnC structures. The maximum transmission for phonons due to the passage of helium-4 ions was found in the case of making polyethylene as a first layer in the PnC structure. Therefore, the concept of ion detection based on PnC structure is achievable.

Thermal transport in phononic crystals: The role of zone folding effect

Science.gov (United States)

Dechaumphai, Edward; Chen, Renkun

2012-04-01

Recent experiments [Yu et al., Nature Nanotech 5, 718 (2010); Tang et al., Nano Lett. 10, 4279 (2010); Hopkins etal., Nano Lett. 11, 107(2011)] on silicon based nanoscale phononic crystals demonstrated substantially reduced thermal conductivity compared to bulk Si, which cannot be explained by incoherent phonon boundary scattering within the Boltzmann Transport Equation (BTE). In this paper, partial coherent treatment of phonons, where phonons are regarded as either wave or particles depending on their frequencies, was considered. Phonons with mean free path smaller than the characteristic size of phononic crystals are treated as particles and the transport in this regime is modeled by BTE with phonon boundary scattering taken into account. On the other hand, phonons with mean free path longer than the characteristic size are treated as waves. In this regime, phonon dispersion relations are computed using the Finite Difference Time Domain (FDTD) method and are found to be modified due to the zone folding effect. The new phonon spectra are then used to compute phonon group velocity and density of states for thermal conductivity modeling. Our partial coherent model agrees well with the recent experimental results on in-plane thermal conductivity of phononic crystals. Our study highlights the importance of zone folding effect on thermal transport in phononic crystals.

Thermal conductivity of Glycerol's liquid, glass, and crystal states, glass-liquid-glass transition, and crystallization at high pressures.

Science.gov (United States)

Andersson, Ove; Johari, G P

2016-02-14

To investigate the effects of local density fluctuations on phonon propagation in a hydrogen bonded structure, we studied the thermal conductivity κ of the crystal, liquid, and glassy states of pure glycerol as a function of the temperature, T, and the pressure, p. We find that the following: (i) κcrystal is 3.6-times the κliquid value at 140 K at 0.1 MPa and 2.2-times at 290 K, and it varies with T according to 138 × T(-0.95); (ii) the ratio κliquid (p)/κliquid (0.1 MPa) is 1.45 GPa(-1) at 280 K, which, unexpectedly, is about the same as κcrystal (p)/κcrystal (0.1 MPa) of 1.42 GPa(-1) at 298 K; (iii) κglass is relatively insensitive to T but sensitive to the applied p (1.38 GPa(-1) at 150 K); (iv) κglass-T plots show an enhanced, pressure-dependent peak-like feature, which is due to the glass to liquid transition on heating; (v) continuous heating cold-crystallizes ultraviscous glycerol under pressure, at a higher T when p is high; and (vi) glycerol formed by cooling at a high p and then measured at a low p has a significantly higher κ than the glass formed by cooling at a low p. On heating at a fixed low p, its κ decreases before its glass-liquid transition range at that p is reached. We attribute this effect to thermally assisted loss of the configurational and vibrational instabilities of a glass formed at high p and recovered at low p, which is different from the usual glass-aging effect. While the heat capacity, entropy, and volume of glycerol crystal are less than those for its glass and liquid, κcrystal of glycerol, like its elastic modulus and refractive index, is higher. We discuss these findings in terms of the role of fluctuations in local density and structure, and the relations between κ and the thermodynamic quantities.

Band structures of two dimensional solid/air hierarchical phononic crystals

International Nuclear Information System (INIS)

Xu, Y.L.; Tian, X.G.; Chen, C.Q.

2012-01-01

The hierarchical phononic crystals to be considered show a two-order “hierarchical” feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.

Band structures of two dimensional solid/air hierarchical phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Xu, Y.L.; Tian, X.G. [State Key Laboratory for Mechanical Structure Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Chen, C.Q., E-mail: chencq@tsinghua.edu.cn [Department of Engineering Mechanics, AML and CNMM, Tsinghua University, Beijing 100084 (China)

2012-06-15

The hierarchical phononic crystals to be considered show a two-order 'hierarchical' feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.

The Electron-Phonon Interaction in Strongly Correlated Systems

International Nuclear Information System (INIS)

Castellani, C.; Grilli, M.

1995-01-01

We analyze the effect of strong electron-electron repulsion on the electron-phonon interaction from a Fermi-liquid point of view and show that the electron-electron interaction is responsible for vertex corrections, which generically lead to a strong suppression of the electron-phonon coupling in the v F q/ω >>1 region, while such effect is not present when v F q/ω F is the Fermi velocity and q and ω are the transferred momentum and frequency respectively. In particular the e-ph scattering is suppressed in transport properties which are dominated by low-energy-high-momentum processes. On the other hand, analyzing the stability criterion for the compressibility, which involves the effective interactions in the dynamical limit, we show that a sizable electron-phonon interaction can push the system towards a phase-separation instability. Finally a detailed analysis of these ideas is carried out using a slave-boson approach for the infinite-U three-band Hubbard model in the presence of a coupling between the local hole density and a dispersionless optical phonon. (author)

Band structures in fractal grading porous phononic crystals

Science.gov (United States)

Wang, Kai; Liu, Ying; Liang, Tianshu; Wang, Bin

2018-05-01

In this paper, a new grading porous structure is introduced based on a Sierpinski triangle routine, and wave propagation in this fractal grading porous phononic crystal is investigated. The influences of fractal hierarchy and porosity on the band structures in fractal graidng porous phononic crystals are clarified. Vibration modes of unit cell at absolute band gap edges are given to manifest formation mechanism of absolute band gaps. The results show that absolute band gaps are easy to form in fractal structures comparatively to the normal ones with the same porosity. Structures with higher fractal hierarchies benefit multiple wider absolute band gaps. This work provides useful guidance in design of fractal porous phononic crystals.

Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals

International Nuclear Information System (INIS)

Xu, Zhenlong; Wu, Fugen; Guo, Zhongning

2012-01-01

The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies. -- Highlights: ► We report a new class of quasi-periodic hetero-structures, arc-shaped phononic crystals (APCs). ► The results show the first PBGs start with zero Hz with low modes. ► Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials.

Integrated phononic crystal resonators based on adiabatically-terminated phononic crystal waveguides

Directory of Open Access Journals (Sweden)

Razi Dehghannasiri

2016-12-01

Full Text Available In this letter, we demonstrate a new design for integrated phononic crystal (PnC resonators based on confining acoustic waves in a heterogeneous waveguide-based PnC structure. In this architecture, a PnC waveguide that supports a single mode at the desired resonance frequencies is terminated by two waveguide sections with no propagating mode at those frequencies (i.e., have mode gap. The proposed PnC resonators are designed through combining the spatial-domain and the spatial-frequency domain (i.e., the k-domain analysis to achieve a smooth mode envelope. This design approach can benefit both membrane-based and surface-acoustic-wave-based architectures by confining the mode spreading in k-domain that leads to improved electromechanical excitation/detection coupling and reduced loss through propagating bulk modes.

Mapping momentum-dependent electron-phonon coupling and nonequilibrium phonon dynamics with ultrafast electron diffuse scattering

Science.gov (United States)

Stern, Mark J.; René de Cotret, Laurent P.; Otto, Martin R.; Chatelain, Robert P.; Boisvert, Jean-Philippe; Sutton, Mark; Siwick, Bradley J.

2018-04-01

Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone has remained elusive. Here we demonstrate that ultrafast electron diffuse scattering (UEDS) directly provides such information. By exploiting symmetry-based selection rules and time resolution, scattering from different phonon branches can be distinguished even without energy resolution. Using graphite as a model system, we show that UEDS patterns map the relative EPC and PPC strength through their profound sensitivity to photoinduced changes in phonon populations. We measure strong EPC to the K -point TO phonon of A1' symmetry (K -A1' ) and along the entire TO branch between Γ -K , not only to the Γ -E2 g phonon. We also determine that the subsequent phonon relaxation of these strongly coupled optical phonons involve three stages: decay via several identifiable channels to TA and LA phonons (1 -2 ps), intraband thermalization of the non-equilibrium TA/LA phonon populations (30 -40 ps) and interband relaxation of the TA/LA modes (115 ps). Combining UEDS with ultrafast angle-resolved photoelectron spectroscopy will yield a complete picture of the dynamics within and between electron and phonon subsystems, helping to unravel complex phases in which the intertwined nature of these systems has a strong influence on emergent properties.

Rigorous bounds on the free energy of electron-phonon models

NARCIS (Netherlands)

Raedt, Hans De; Michielsen, Kristel

1997-01-01

We present a collection of rigorous upper and lower bounds to the free energy of electron-phonon models with linear electron-phonon interaction. These bounds are used to compare different variational approaches. It is shown rigorously that the ground states corresponding to the sharpest bounds do

Electron-phonon and spin-phonon coupling in NaV2O5 : Charge fluctuations effects

NARCIS (Netherlands)

Sherman, E.Ya.; Fischer, M.; Lemmens, P; Loosdrecht, P.H.M. van; Güntherodt, G.

1999-01-01

We show that the asymmetric crystal environment of the V site in the ladder compound NaV2O5 leads to a strong coupling of vanadium 3d electrons to phonons. This coupling causes fluctuations of the charge on the V ions, and favors a transition to a charge-ordered state at low temperatures. In the low

Electronic structures and abnormal phonon behaviors of cobalt-modified Na0.5Bi0.5TiO3-6%BaTiO3 single crystals

Science.gov (United States)

Huang, T.; Zhang, P.; Xu, L. P.; Chen, C.; Zhang, J. Z.; Hu, Z. G.; Luo, H. S.; Chu, J. H.

2016-10-01

Optical properties, electronic structures, and structural variations of x wt% cobalt (Co) doped Na0.5Bi0.5TiO3-6%BaTiO3 (x=0%, 0.5%, 0.8%) single crystals have been studied by temperature-dependent optical ellipsometry and Raman spectra from 250 to 650 K. Based on the temperature evolution of electronic transitions (Ecp1 and Ecp2) and the phonon modes involving Ti-O vibrations, two critical temperature points exhibit an increasing trend with Co dopants, which are related to structural variations for ferroelectric to anti-ferroelectric, and anti-ferroelectric to paraelectric transition, respectively. Additionally, distinguishing abnormal phonon behaviors can be observed from Raman spectra for the crystal of x=0.5% and 0.8%, which show reverse frequency shift of the modes involving Ti-O vibration. It can be ascribed to different relative concentration of Co2+ and Co3+ in the crystals, which has been confirmed by X-ray Photoelectron Spectroscopy data.

Electronic structures and abnormal phonon behaviors of cobalt-modified Na0.5Bi0.5TiO3-6%BaTiO3 single crystals

Directory of Open Access Journals (Sweden)

T. Huang

2016-10-01

Full Text Available Optical properties, electronic structures, and structural variations of x wt% cobalt (Co doped Na0.5Bi0.5TiO3-6%BaTiO3 (x=0%, 0.5%, 0.8% single crystals have been studied by temperature-dependent optical ellipsometry and Raman spectra from 250 to 650 K. Based on the temperature evolution of electronic transitions (Ecp1 and Ecp2 and the phonon modes involving Ti-O vibrations, two critical temperature points exhibit an increasing trend with Co dopants, which are related to structural variations for ferroelectric to anti-ferroelectric, and anti-ferroelectric to paraelectric transition, respectively. Additionally, distinguishing abnormal phonon behaviors can be observed from Raman spectra for the crystal of x=0.5% and 0.8%, which show reverse frequency shift of the modes involving Ti-O vibration. It can be ascribed to different relative concentration of Co2+ and Co3+ in the crystals, which has been confirmed by X-ray Photoelectron Spectroscopy data.

The kinetics of low-temperature electron-phonon relaxation in a metallic film following instantaneous heating of the electrons

International Nuclear Information System (INIS)

Bezuglyi, A.I.; Shklovskii, V.A.

1997-01-01

The theoretical analysis of experiments on pulsed laser irradiation of metallic films sputtered on insulating supports is usually based on semiphenomenological dynamical equations for the electron and phonon temperatures, an approach that ignores the nonuniformity and the nonthermal nature of the phonon distribution function. In this paper we discuss a microscopic model that describes the dynamics of the electron-phonon system in terms of kinetic equations for the electron and phonon distribution functions. Such a model provides a microscopic picture of the nonlinear energy relaxation of the electron-phonon system of a rapidly heated film. We find that in a relatively thick film the energy relaxation of electrons consists of three stages: the emission of nonequilibrium phonons by 'hot' electrons, the thermalization of electrons and phonons due to phonon reabsorption, and finally the cooling of the thermalized electron-phonon system as a result of phonon exchange between film and substrate. In thin films, where there is no reabsorption of nonequilibrium phonons, the energy relaxation consists of only one stage, the first. The relaxation dynamics of an experimentally observable quantity, the phonon contribution to the electrical conductivity of the cooling film, is directly related to the dynamics of the electron temperature, which makes it possible to use the data of experiments on the relaxation of voltage across films to establish the electron-phonon and phonon-electron collision times and the average time of phonon escape from film to substrate

Bloch wave deafness and modal conversion at a phononic crystal boundary

Directory of Open Access Journals (Sweden)

Vincent Laude

2011-12-01

Full Text Available We investigate modal conversion at the boundary between a homogeneous incident medium and a phononic crystal, with consideration of the impact of symmetry on the excitation of Bloch waves. We give a quantitative criterion for the appearance of deaf Bloch waves, which are antisymmetric with respect to a symmetry axis of the phononic crystal, in the frame of generalized Fresnel formulas for reflection and transmission at the phononic crystal boundary. This criterion is used to index Bloch waves in the complex band structure of the phononic crystal, for directions of incidence along a symmetry axis. We argue that within deaf frequency ranges transmission is multi-exponential, as it is within frequency band gaps.

Confinement effects on electron and phonon degrees of freedom in nanofilm superconductors: A Green function approach

Science.gov (United States)

Saniz, R.; Partoens, B.; Peeters, F. M.

2013-02-01

The Green function approach to the Bardeen-Cooper-Schrieffer theory of superconductivity is used to study nanofilms. We go beyond previous models and include effects of confinement on the strength of the electron-phonon coupling as well as on the electronic spectrum and on the phonon modes. Within our approach, we find that in ultrathin films, confinement effects on the electronic screening become very important. Indeed, contrary to what has been advanced in recent years, the sudden increases of the density of states when new bands start to be occupied as the film thickness increases, tend to suppress the critical temperature rather than to enhance it. On the other hand, the increase of the number of phonon modes with increasing number of monolayers in the film leads to an increase in the critical temperature. As a consequence, the superconducting critical parameters in such nanofilms are determined by these two competing effects. Furthermore, in sufficiently thin films, the condensate consists of well-defined subcondensates associated with the occupied bands, each with a distinct coherence length. The subcondensates can interfere constructively or destructively giving rise to an interference pattern in the Cooper pair probability density.

Infrared-active optical phonons in LiFePO4 single crystals

Science.gov (United States)

Stanislavchuk, T. N.; Middlemiss, D. S.; Syzdek, J. S.; Janssen, Y.; Basistyy, R.; Sirenko, A. A.; Khalifah, P. G.; Grey, C. P.; Kostecki, R.

2017-07-01

Infrared-active optical phonons were studied in olivine LiFePO4 oriented single crystals by means of both rotating analyzer and rotating compensator spectroscopic ellipsometry in the spectral range between 50 and 1400 cm-1. The eigenfrequencies, oscillator strengths, and broadenings of the phonon modes were determined from fits of the anisotropic harmonic oscillator model to the data. Optical phonons in a heterosite FePO4 crystal were measured from the delithiated ab-surface of the LiFePO4 crystal and compared with the phonon modes of the latter. Good agreement was found between experimental data and the results of solid-state hybrid density functional theory calculations for the phonon modes in both LiFePO4 and FePO4.

Crystallization In Multicomponent Glasses

International Nuclear Information System (INIS)

Kruger, A.A.; Hrma, P.R.

2009-01-01

In glass processing situations involving glass crystallization, various crystalline forms nucleate, grow, and dissolve, typically in a nonuniform temperature field of molten glass subjected to convection. Nuclear waste glasses are remarkable examples of multicomponent vitrified mixtures involving partial crystallization. In the glass melter, crystals form and dissolve during batch-to-glass conversion, melter processing, and product cooling. Crystals often agglomerate and sink, and they may settle at the melter bottom. Within the body of cooling glass, multiple phases crystallize in a non-uniform time-dependent temperature field. Self-organizing periodic distribution (the Liesegnang effect) is common. Various crystallization phenomena that occur in glass making are reviewed.

CRYSTALLIZATION IN MULTICOMPONENT GLASSES

Energy Technology Data Exchange (ETDEWEB)

KRUGER AA; HRMA PR

2009-10-08

In glass processing situations involving glass crystallization, various crystalline forms nucleate, grow, and dissolve, typically in a nonuniform temperature field of molten glass subjected to convection. Nuclear waste glasses are remarkable examples of multicomponent vitrified mixtures involving partial crystallization. In the glass melter, crystals form and dissolve during batch-to-glass conversion, melter processing, and product cooling. Crystals often agglomerate and sink, and they may settle at the melter bottom. Within the body of cooling glass, multiple phases crystallize in a non-uniform time-dependent temperature field. Self-organizing periodic distribution (the Liesegnang effect) is common. Various crystallization phenomena that occur in glass making are reviewed.

Electron-phonon interactions and the phonon anomaly in β-phase NiTi

International Nuclear Information System (INIS)

Zhao, G.L.; Harmon, B.N.

1993-01-01

The electronic structure of β-phase NiTi has been calculated using a first-principles linear-combination-of-atomic-orbitals method. The resulting band structure was fitted with a nonorthogonal tight-binding Hamiltonian from which electron-phonon matrix elements were evaluated. The soft phonon near Q 0 =(2/3, 2) / (3 ,0)π/a, which is responsible for the premartensitic phase transition in β-phase NiTi, is found to arise from the strong electron-phonon coupling of nested electronic states on the Fermi surface. Thermal vibrations and changes in electronic occupation cause a smearing of the nested features, which in turn cause a hardening of the phonon anomaly

Broadband sound blocking in phononic crystals with rotationally symmetric inclusions.

Science.gov (United States)

Lee, Joong Seok; Yoo, Sungmin; Ahn, Young Kwan; Kim, Yoon Young

2015-09-01

This paper investigates the feasibility of broadband sound blocking with rotationally symmetric extensible inclusions introduced in phononic crystals. By varying the size of four equally shaped inclusions gradually, the phononic crystal experiences remarkable changes in its band-stop properties, such as shifting/widening of multiple Bragg bandgaps and evolution to resonance gaps. Necessary extensions of the inclusions to block sound effectively can be determined for given incident frequencies by evaluating power transmission characteristics. By arraying finite dissimilar unit cells, the resulting phononic crystal exhibits broadband sound blocking from combinational effects of multiple Bragg scattering and local resonances even with small-numbered cells.

Theory of electron-phonon-dislon interacting system—toward a quantized theory of dislocations

Science.gov (United States)

Li, Mingda; Tsurimaki, Yoichiro; Meng, Qingping; Andrejevic, Nina; Zhu, Yimei; Mahan, Gerald D.; Chen, Gang

2018-02-01

We provide a comprehensive theoretical framework to study how crystal dislocations influence the functional properties of materials, based on the idea of a quantized dislocation, namely a ‘dislon’. In contrast to previous work on dislons which focused on exotic phenomenology, here we focus on their theoretical structure and computational power. We first provide a pedagogical introduction that explains the necessity and benefits of taking the dislon approach and why the dislon Hamiltonian takes its current form. Then, we study the electron-dislocation and phonon-dislocation scattering problems using the dislon formalism. Both the effective electron and phonon theories are derived, from which the role of dislocations on electronic and phononic transport properties is computed. Compared with traditional dislocation scattering studies, which are intrinsically single-particle, low-order perturbation and classical quenched defect in nature, the dislon theory not only allows easy incorporation of quantum many-body effects such as electron correlation, electron-phonon interaction, and higher-order scattering events, but also allows proper consideration of the dislocation’s long-range strain field and dynamic aspects on equal footing for arbitrary types of straight-line dislocations. This means that instead of developing individual models for specific dislocation scattering problems, the dislon theory allows for the calculation of electronic structure and electrical transport, thermal transport, optical and superconducting properties, etc, under one unified theory. Furthermore, the dislon theory has another advantage over empirical models in that it requires no fitting parameters. The dislon theory could serve as a major computational tool to understand the role of dislocations on multiple materials’ functional properties at an unprecedented level of clarity, and may have wide applications in dislocated energy materials.

Crystallization in Y-Si-Al-O-N glasses

Energy Technology Data Exchange (ETDEWEB)

Leng-Ward, G; Lewis, M H

1985-05-01

The development of crystallization in oxynitride glasses has been characterized using transmission electron microscopy and scanning electron microscopy, X-ray (energy-dispersive) microanalysis, and powder X-ray diffraction techniques. A series of glasses was prepared while maintaining the ratio of yttrium-to-silicon-to-aluminium, but replacing oxygen with nitrogen up to the nitrogen solubility limit. On annealing at 1250 C, the oxide glass fully crystallized into yttrium disilicate (Y2Si2O7). Al2O3 and mullite (Al6Si2O13) while, with increasing nitrogen content, the disilicate phase was progressively replaced by yttrium aluminium garnet (Y3Al5O12) and nitrogen was mainly incorporated into Si2N2O. Annealing of the nitrogen glasses at 1100 C produced partial crystallization involving an intermediate phase related to nitrogen-wollastonite. Phase separation in an as-quenched SiO2-rich Y-Si-Al-O composition glass is illustrated. 9 references.

Phononic crystals with one-dimensional defect as sensor materials

Science.gov (United States)

Aly, Arafa H.; Mehaney, Ahmed

2017-09-01

Recently, sensor technology has attracted great attention in many fields due to its importance in many engineering applications. In the present work, we introduce a study using the innovative properties of phononic crystals in enhancing a new type of sensors based on the intensity of transmitted frequencies inside the phononic band gaps. Based on the transfer matrix method and Bloch theory, the expressions of the reflection coefficient and dispersion relation are presented. Firstly, the influences of filling fraction ratio and the angle of incidence on the band gap width are discussed. Secondly, the localization of waves inside band gaps is discussed by enhancing the properties of the defected phononic crystal. Compared to the periodic structure, localization modes involved within the band structure of phononic crystals with one and two defect layers are presented and compared. Trapped localized modes can be detected easily and provide more information about defected structures. Such method could increase the knowledge of manufacturing defects by measuring the intensity of propagated waves in the resonant cavities and waveguides. Moreover, several factors enhance the role of the defect layer on the transmission properties of defected phononic crystals are presented. The acoustic band gap can be used to detect or sense the type of liquids filling the defect layer. The liquids make specific resonant modes through the phononic band gaps that related to the properties of each liquid. The frequency where the maximum resonant modes occur is correlated to material properties and allows to determine several parameters such as the type of an unknown material.

Effective electron-electron and electron-phonon interactions in the Hubbard-Holstein model

International Nuclear Information System (INIS)

Aprea, G.; Di Castro, C.; Grilli, M. . E-mail marco.grilli@roma1.infn.it; Lorenzana, J.

2006-01-01

We investigate the interplay between the electron-electron and the electron-phonon interaction in the Hubbard-Holstein model. We implement the flow-equation method to investigate within this model the effect of correlation on the electron-phonon effective coupling and, conversely, the effect of phonons in the effective electron-electron interaction. Using this technique we obtain analytical momentum-dependent expressions for the effective couplings and we study their behavior for different physical regimes. In agreement with other works on this subject, we find that the electron-electron attraction mediated by phonons in the presence of Hubbard repulsion is peaked at low transferred momenta. The role of the characteristic energies involved is also analyzed

Electron mobility limited by optical phonons in wurtzite InGaN/GaN core-shell nanowires

Science.gov (United States)

Liu, W. H.; Qu, Y.; Ban, S. L.

2017-09-01

Based on the force-balance and energy-balance equations, the optical phonon-limited electron mobility in InxGa1-xN/GaN core-shell nanowires (CSNWs) is discussed. It is found that the electrons tend to distribute in the core of the CSNWs due to the strong quantum confinement. Thus, the scattering from first kind of the quasi-confined optical (CO) phonons is more important than that from the interface (IF) and propagating (PR) optical phonons. Ternary mixed crystal and size effects on the electron mobility are also investigated. The results show that the PR phonons exist while the IF phonons disappear when the indium composition x < 0.047, and vice versa. Accordingly, the total electron mobility μ first increases and then decreases with indium composition x, and reaches a peak value of approximately 3700 cm2/(V.s) when x = 0.047. The results also show that the mobility μ increases as increasing the core radius of CSNWs due to the weakened interaction between the electrons and CO phonons. The total electron mobility limited by the optical phonons exhibits an obvious enhancement as decreasing temperature or increasing line electron density. Our theoretical results are expected to be helpful to develop electronic devices based on CSNWs.

Electron-phonon coupling in quasi free-standing graphene

DEFF Research Database (Denmark)

Christian Johannsen, Jens; Ulstrup, Søren; Bianchi, Marco

2013-01-01

Quasi free-standing monolayer graphene can be produced by intercalating species like oxygen or hydrogen between epitaxial graphene and the substrate crystal. If the graphene is indeed decoupled from the substrate, one would expect the observation of a similar electronic dispersion and many......-body effects, irrespective of the substrate and the material used to achieve the decoupling. Here we investigate the electron-phonon coupling in two different types of quasi free-standing monolayer graphene: decoupled from SiC via hydrogen intercalation and decoupled from Ir via oxygen intercalation. Both...

Theory of Raman scattering in coupled electron-phonon systems

Science.gov (United States)

Itai, K.

1992-01-01

The Raman spectrum is calculated for a coupled conduction-electron-phonon system in the zero-momentum-transfer limit. The Raman scattering is due to electron-hole excitations and phonons as well. The phonons of those branches that contribute to the electron self-energy and the correction of the electron-phonon vertex are assumed to have flat energy dispersion (the Einstein phonons). The effect of electron-impurity scattering is also incorporated. Both the electron-phonon interaction and the electron-impurity interaction cause the fluctuation of the electron distribution between different parts of the Fermi surface, which results in overdamped zero-sound modes of various symmetries. The scattering cross section is obtained by solving the Bethe-Salpeter equation. The spectrum shows a lower threshold at the smallest Einstein phonon energy when only the electron-phonon interaction is taken into consideration. When impurities are also taken into consideration, the threshold disappears.

The Effects of Different Electron-Phonon Couplings on the Spectral and Transport Properties of Small Molecule Single-Crystal Organic Semiconductors

Directory of Open Access Journals (Sweden)

Carmine Antonio Perroni

2014-03-01

Full Text Available Spectral and transport properties of small molecule single-crystal organic semiconductors have been theoretically analyzed focusing on oligoacenes, in particular on the series from naphthalene to rubrene and pentacene, aiming to show that the inclusion of different electron-phonon couplings is of paramount importance to interpret accurately the properties of prototype organic semiconductors. While in the case of rubrene, the coupling between charge carriers and low frequency inter-molecular modes is sufficient for a satisfactory description of spectral and transport properties, the inclusion of electron coupling to both low-frequency inter-molecular and high-frequency intra-molecular vibrational modes is needed to account for the temperature dependence of transport properties in smaller oligoacenes. For rubrene, a very accurate analysis in the relevant experimental configuration has allowed for the clarification of the origin of the temperature-dependent mobility observed in these organic semiconductors. With increasing temperature, the chemical potential moves into the tail of the density of states corresponding to localized states, but this is not enough to drive the system into an insulating state. The mobility along different crystallographic directions has been calculated, including vertex corrections that give rise to a transport lifetime one order of magnitude smaller than the spectral lifetime of the states involved in the transport mechanism. The mobility always exhibits a power-law behavior as a function of temperature, in agreement with experiments in rubrene. In systems gated with polarizable dielectrics, the electron coupling to interface vibrational modes of the gate has to be included in addition to the intrinsic electron-phonon interaction. While the intrinsic bulk electron-phonon interaction affects the behavior of mobility in the coherent regime below room temperature, the coupling with interface modes is dominant for the

Systematic Studies on Anharmonicity of Rattling Phonons in Type I Clathrates by Low Temperature Heat Capacity Measurements

Science.gov (United States)

Tanigaki, Katsumi; Wu, Jiazhen; Tanabe, Yoichi; Heguri, Satoshi; Shiimotani, Hidekazu; Tohoku University Collaboration

2014-03-01

Clathrates are featured by cage-like polyhedral hosts mainly composed of the IVth group elements of Si, Ge, or Sn and alkali metal or alkaline-earth metal elements can be accommodated inside as a guest atom. One of the most intriguing issues in clathrates is their outstanding high thermoelectric performances thanks to the low thermal conductivity. Being irrespective of good electric conductivity σ, the guest atom motions provide a low-energy lying less-dispersive phonons and can greatly suppress thermal conductivity κ. This makes clathrates close to the concept of ``phonon glass electron crystal: PGEC'' and useful in thermoelectric materials from the viewpoint of the figure of merit. In the present study, we show that the local phonon anharmonicity indicated by the tunneling-term of the endohedral atoms (αT) and the itinerant-electron term (γeT), both of which show T-linear dependences in specific heat Cp, can successfully be separated by employing single crystals with various carrier concentrations in a wide range of temperture experimennts. The factors affecting on the phonon anharmonicity as well as the strength of electron-phonon interactions will be discussed based on our recent experiments. The research was financially supported by Ministry of Education, Science, Sports and Culture, Grant in Aid for Science, and Technology of Japan.

Hybrid functional calculation of electronic and phonon structure of BaSnO3

International Nuclear Information System (INIS)

Kim, Bog G.; Jo, J.Y.; Cheong, S.W.

2013-01-01

Barium stannate, BaSnO 3 (BSO), with a cubic perovskite structure, has been highlighted as a promising host material for the next generation transparent oxide electrodes. This study examined theoretically the electronic structure and phonon structure of BSO using hybrid density functional theory based on the HSE06 functional. The electronic structure results of BSO were corrected by extending the phonon calculations based on the hybrid density functional. The fundamental thermal properties were also predicted based on a hybrid functional calculation. Overall, a detailed understanding of the electronic structure, phonon modes and phonon dispersion of BSO will provide a theoretical starting-point for engineering applications of this material. - Graphical Abstract: (a) Crystal structure of BaSnO 3 . The center ball is Ba and small (red) ball on edge is oxygen and SnO 6 octahedrons are plotted as polyhedron. (b) Electronic band structure along the high symmetry point in the Brillouin zone using the HSE06 hybrid functional. (c) The phonon dispersion curve calculated using the HSE06 hybrid functional (d) Zone center lowest energy F 1u phonon mode. Highlights: ► We report the full hybrid functional calculation of not only the electronic structure but also the phonon structure for BaSnO 3 . ► The band gap calculation of HSE06 revealed an indirect gap with 2.48 eV. ► The effective mass at the conduction band minimum and valence band maximum was calculated. ► In addition, the phonon structure of BSO was calculated using the HSE06 functional. ► Finally, the heat capacity was calculated and compared with the recent experimental result.

Effect of the electronic structure of the etched CdTe single crystals on the exciton radiation processes

International Nuclear Information System (INIS)

Tkachuk, P.M.; Tkachuk, V.Yi.; Mel'nichuk, S.V.; Kurik, M.V.

2005-01-01

Under optical excitation the structure of the radiation beyond fundamental absorption of the orientated CdTe single crystals caused by LO-phonon scattering processes of the electron-hole states is observed. Crystals have been doped with impurity of Cl as a result of the surface preparing by etching in Br-methanol. Electronic structure of the single crystals surface layer is identified on the basis of two-phonon radiation absorption investigation. Taking into account the modes selection rules the one and two phonon scattering mechanisms for two crystals surface orientations are determined

SAW-Based Phononic Crystal Microfluidic Sensor-Microscale Realization of Velocimetry Approaches for Integrated Analytical Platform Applications.

Science.gov (United States)

Oseev, Aleksandr; Lucklum, Ralf; Zubtsov, Mikhail; Schmidt, Marc-Peter; Mukhin, Nikolay V; Hirsch, Soeren

2017-09-23

The current work demonstrates a novel surface acoustic wave (SAW) based phononic crystal sensor approach that allows the integration of a velocimetry-based sensor concept into single chip integrated solutions, such as Lab-on-a-Chip devices. The introduced sensor platform merges advantages of ultrasonic velocimetry analytic systems and a microacoustic sensor approach. It is based on the analysis of structural resonances in a periodic composite arrangement of microfluidic channels confined within a liquid analyte. Completed theoretical and experimental investigations show the ability to utilize periodic structure localized modes for the detection of volumetric properties of liquids and prove the efficacy of the proposed sensor concept.

Electron-phonon superconductivity in YIn3

Science.gov (United States)

Billington, D.; Llewellyn-Jones, T. M.; Maroso, G.; Dugdale, S. B.

2013-08-01

First-principles calculations of the electron-phonon coupling were performed on the cubic intermetallic compound YIn3. The electron-phonon coupling constant was found to be λep = 0.42. Using the Allen-Dynes formula with a Coulomb pseudopotential of μ* = 0.10, a Tc of approximately 0.77 K is obtained which is reasonably consistent with the experimentally observed temperature (between 0.8 and 1.1 K). The results indicate that conventional electron-phonon coupling is capable of producing the superconductivity in this compound.

Research on bandgaps in two-dimensional phononic crystal with two resonators.

Science.gov (United States)

Gao, Nansha; Wu, Jiu Hui; Yu, Lie

2015-02-01

In this paper, the bandgap properties of a two-dimensional phononic crystal with the two resonators is studied and embedded in a homogenous matrix. The resonators are not connected with the matrix but linked with connectors directly. The dispersion relationship, transmission spectra, and displacement fields of the eigenmodes of this phononic crystal are studied with finite-element method. In contrast to the phononic crystals with one resonators and hollow structure, the proposed structures with two resonators can open bandgaps at lower frequencies. This is a very interesting and useful phenomenon. Results show that, the opening of the bandgaps is because of the local resonance and the scattering interaction between two resonators and matrix. An equivalent spring-pendulum model can be developed in order to evaluate the frequencies of the bandgap edge. The study in this paper is beneficial to the design of opening and tuning bandgaps in phononic crystals and isolators in low-frequency range. Copyright © 2014 Elsevier B.V. All rights reserved.

One-dimensional hypersonic phononic crystals.

Science.gov (United States)

Gomopoulos, N; Maschke, D; Koh, C Y; Thomas, E L; Tremel, W; Butt, H-J; Fytas, G

2010-03-10

We report experimental observation of a normal incidence phononic band gap in one-dimensional periodic (SiO(2)/poly(methyl methacrylate)) multilayer film at gigahertz frequencies using Brillouin spectroscopy. The band gap to midgap ratio of 0.30 occurs for elastic wave propagation along the periodicity direction, whereas for inplane propagation the system displays an effective medium behavior. The phononic properties are well captured by numerical simulations. The porosity in the silica layers presents a structural scaffold for the introduction of secondary active media for potential coupling between phonons and other excitations, such as photons and electrons.

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.

Multiple topological phases in phononic crystals

KAUST Repository

Chen, Zeguo; Wu, Ying

2017-01-01

We report a new topological phononic crystal in a ring-waveguide acoustic system. In the previous reports on topological phononic crystals, there are two types of topological phases: quantum Hall phase and quantum spin Hall phase. A key point in achieving quantum Hall insulator is to break the time-reversal (TR) symmetry, and for quantum spin Hall insulator, the construction of pseudo-spin is necessary. We build such pseudo-spin states under particular crystalline symmetry (C-6v) and then break the degeneracy of the pseudo-spin states by introducing airflow to the ring. We study the topology evolution by changing both the geometric parameters of the unit cell and the strength of the applied airflow. We find that the system exhibits three phases: quantum spin Hall phase, conventional insulator phase and a new quantum anomalous Hall phase.

Multiple topological phases in phononic crystals

KAUST Repository

Chen, Zeguo

2017-11-20

We report a new topological phononic crystal in a ring-waveguide acoustic system. In the previous reports on topological phononic crystals, there are two types of topological phases: quantum Hall phase and quantum spin Hall phase. A key point in achieving quantum Hall insulator is to break the time-reversal (TR) symmetry, and for quantum spin Hall insulator, the construction of pseudo-spin is necessary. We build such pseudo-spin states under particular crystalline symmetry (C-6v) and then break the degeneracy of the pseudo-spin states by introducing airflow to the ring. We study the topology evolution by changing both the geometric parameters of the unit cell and the strength of the applied airflow. We find that the system exhibits three phases: quantum spin Hall phase, conventional insulator phase and a new quantum anomalous Hall phase.

Electron-phonon interaction and scattering in Si and Ge: Implications for phonon engineering

International Nuclear Information System (INIS)

Tandon, Nandan; Albrecht, J. D.; Ram-Mohan, L. R.

2015-01-01

We report ab-initio results for electron-phonon (e-ph) coupling and display the existence of a large variation in the coupling parameter as a function of electron and phonon dispersion. This variation is observed for all phonon modes in Si and Ge, and we show this for representative cases where the initial electron states are at the band gap edges. Using these e-ph matrix elements, which include all possible phonon modes and electron bands within a relevant energy range, we evaluate the imaginary part of the electron self-energy in order to obtain the associated scattering rates. The temperature dependence is seen through calculations of the scattering rates at 0 K and 300 K. The results provide a basis for understanding the impacts of phonon scattering vs. orientation and geometry in the design of devices, and in analysis of transport phenomena. This provides an additional tool for engineering the transfer of energy from carriers to the lattice

Origin of electronic properties of PbGa2Se4 crystal: Experimental and theoretical investigations

International Nuclear Information System (INIS)

Babuka, T.; Kityk, I.V.; Parasyuk, O.V.; Myronchuk, G.; Khyzhun, O.Y.; Fedorchuk, A.O.; Makowska-Janusik, M.

2015-01-01

Graphical abstract: In the presented work the structural and electronic properties of the PbGa 2 Se 4 single crystal were investigated experimentally as well as theoretically. The XPS spectra, Urbach’s rule and steepness parameters of PbGa 2 Se 4 single crystal have been investigated for the first time. The quantum chemical calculations were also never performed before for the studied structure. The theoretically obtained data help to explain the properties of material. - Highlights: • Urbach’s rule and steepness parameters for PbGa 2 Se 4 crystals explored for the first time. • Non-reactivity of the PbGa 2 Se 4 surface was established by XPS. • DFT approach shows its efficiency to describe electronic properties of PbGa 2 Se 4 . • Electronic parameters are affected by existence of electron–phonon interaction. - Abstract: The PbGa 2 Se 4 crystal is a promising material for optoelectronic applications. It is caused by coexistence of the large polarized Pb cations and a huge contribution of anharmonic phonon subsystem caused by chalcogenide anions. In the present work the electronic and optical properties of the mentioned material were studied theoretically as well as experimentally by optical and X-ray photoelectron spectroscopy methods. The DFT approach has been used for the quantum chemical electronic properties calculations. Urbach rule and steepness parameters of the PbGa 2 Se 4 crystal have been evaluated for the first time. These parameters and Urbach energies increase with increasing temperature of the samples that is typical for the semiconducting materials. The XPS measurements of the investigated crystal reveal that all the spectral features are originated from core-level states of the constituent elements. Simultaneously these results also confirm non-reactivity of the PbGa 2 Se 4 surface. However, the titled single crystal possesses a number of intrinsic structural defects and vacancies thereby affecting its electronic properties. The

Topology optimization of two-dimensional asymmetrical phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Dong, Hao-Wen [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Su, Xiao-Xing [School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044 (China); Wang, Yue-Sheng, E-mail: yswang@bjtu.edu.cn [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Zhang, Chuanzeng [Department of Civil Engineering, University of Siegen, D-57068 Siegen (Germany)

2014-01-17

The multiple elitist genetic algorithm with the adaptive fuzzy fitness granulation (AFFG) is used to design the phononic crystals with large relative bandgap width (BGW) for combined out-of-plane and in-plane wave modes. Without assumption on the symmetry of the unit-cell, we obtain an asymmetrical phononic crystal with the relative BGW which is quite larger than that of the optimized symmetrical structure. With the help of AFFG, the number of the fitness function evaluations is reduced by over 50% and the procedure converges 5 times faster than the conventional evolutionary algorithm to reach the same final fitness values.

The directional propagation characteristics of elastic wave in two-dimensional thin plate phononic crystals

International Nuclear Information System (INIS)

Wen Jihong; Yu, Dianlong; Wang Gang; Zhao Honggang; Liu Yaozong; Wen Xisen

2007-01-01

The directional propagation characteristics of elastic wave during pass bands in two-dimensional thin plate phononic crystals are analyzed by using the lumped-mass method to yield the phase constant surface. The directions and regions of wave propagation in phononic crystals for certain frequencies during pass bands are predicted with the iso-frequency contour lines of the phase constant surface, which are then validated with the harmonic responses of a finite two-dimensional thin plate phononic crystals with 16x16 unit cells. These results are useful for controlling the wave propagation in the pass bands of phononic crystals

Suppression of Raman electron spin relaxation of radicals in crystals. Comparison of Cu2+ and free radical relaxation in triglycine sulfate and Tutton salt single crystals.

Science.gov (United States)

Hoffmann, S K; Goslar, J; Lijewski, S

2011-08-31

Electron spin-lattice relaxation was measured by the electron spin echo method in a broad temperature range above 4.2 K for Cu(2+) ions and free radicals produced by ionizing radiation in triglycine sulfate (TGS) and Tutton salt (NH4)(2)Zn(SO4)2 ⋅ 6H2O crystals. Localization of the paramagnetic centres in the crystal unit cells was determined from continuous wave electron paramagnetic resonance spectra. Various spin relaxation processes and mechanisms are outlined. Cu(2+) ions relax fast via two-phonon Raman processes in both crystals involving the whole phonon spectrum of the host lattice. This relaxation is slightly slower for TGS where Cu(2+) ions are in the interstitial position. The ordinary Raman processes do not contribute to the radical relaxation which relaxes via the local phonon mode. The local mode lies within the acoustic phonon band for radicals in TGS but within the optical phonon range in (NH4)(2)Zn(SO4)2 ⋅ 6H2O. In the latter the cross-relaxation was considered. A lack of phonons around the radical molecules suggested a local crystal amorphisation produced by x- or γ-rays.

Wigner-like crystallization of Anderson-localized electron systems with low electron densities

CERN Document Server

Slutskin, A A; Pepper, M

2002-01-01

We consider an electron system under conditions of strong Anderson localization, taking into account interelectron long-range Coulomb repulsion. We establish that at sufficiently low electron densities and sufficiently low temperatures the Coulomb electron interaction brings about ordering of the Anderson-localized electrons into a structure that is close to an ideal (Wigner) crystal lattice, provided the dimension of the system is > 1. This Anderson-Wigner glass (AWG) is a new macroscopic electron state that, on the one hand, is beyond the conventional Fermi glass concept, and on the other hand, qualitatively differs from the known 'plain' Wigner glass (inherent in self-localized electron systems) in that the random slight electron displacements from the ideal crystal sites essentially depend on the electron density. With increasing electron density the AWG is found to turn into the plain Wigner glass or Fermi glass, depending on the width of the random spread of the electron levels. It is shown that the res...

Theory of the Influence of Phonon-Phonon and Electron-Phonon Interactions on the Scattering of Neutrons by Crystals; Theorie de l'influence des interactions phonon-phonon et electron-phonon sur la diffusion des neutrons par des cristaux; Teoriya vliyaniya vzaimodejstvij fonon-fonon iehlvktron-fonon na rasseyanie nejtronov kristalla-; Teoria de la influencia de las interacciones fonon-fonon y electron-fonon en la dispersion de neutrones por cristales

Energy Technology Data Exchange (ETDEWEB)

Kokkedee, J J.J. [Institute for Theoretical Physics of the University of Utrecht (Netherlands)

1963-01-15

As predicted by harmonic theory the coherent inelastic spectrums of neutrons, scattered by a single, non-conducting crystal, for a particular angle of scattering consists of a number of delta-function peaks superposed on a continuous background. The peaks correspond to one-phonon processes in which one phonon is absorbed or emitted by the neutron; the background arises from multi-phonon processes. When anharmonic forces (phonon-phonon interactions) are present, the delta-function peaks are broadened into finite peaks, while their central frequencies are shifted with respect to the harmonic values. In the case of a metal there is in addition to phonon-phonon interactions an interaction between phonons and conduction electrons, which also gives a contribution to the displacement and broadening oftheone-phononpeaks. Continuing earlier work of Van Hove (sho considered the relatively simple case of a non-conductin crystal in its ground state (T = 0{sup o}K) ), we have studied the shifts and widths of the scattering peaks as a 'result of the above-mentioned interactions by means of many particle perturbation theory, making extensive use of diagram techniques. Prerequisite to the entire discussion is the assumption that, independent of the strength of the interactions, the width of each peak is small compared to the value of the frequency at its centre; only then the peaks can be considered as being well defined with respect to the background to higher order in the interactions. This condition is expected to be fulfilled for temperatures which are not too high and values of the phonon wave vector which are not too large. Our procedure yields closed formulae for the partial scattering function describing the peaks, which can be evaluated to arbitrarily high accuracy. In particular an expansion for calculating the line shift and line width in powers of u/d and in terms of simple connected diagrams is obtained (u is an average atomic or ionic displacement, d is the smallest

Electrons and Phonons in Semiconductor Multilayers

Science.gov (United States)

Ridley, B. K.

1996-11-01

This book provides a detailed description of the quantum confinement of electrons and phonons in semiconductor wells, superlattices and quantum wires, and shows how this affects their mutual interactions. It discusses the transition from microscopic to continuum models, emphasizing the use of quasi-continuum theory to describe the confinement of optical phonons and electrons. The hybridization of optical phonons and their interactions with electrons are treated, as are other electron scattering mechanisms. The book concludes with an account of the electron distribution function in three-, two- and one-dimensional systems, in the presence of electrical or optical excitation. This text will be of great use to graduate students and researchers investigating low-dimensional semiconductor structures, as well as to those developing new devices based on these systems.

Isothermal crystallization kinetics in simulated high-level nuclear waste glass

International Nuclear Information System (INIS)

Vienna, J.D.; Hrma, P.; Smith, D.E.

1997-01-01

Crystallization kinetics of a simulated high-level waste (HLW) glass were measured and modelled. Kinetics of acmite growth in the standard HW39-4 glass were measured using the isothermal method. A time-temperature-transformation (TTT) diagram was generated from these data. Classical glass-crystal transformation kinetic models were empirically applied to the crystallization data. These models adequately describe the kinetics of crystallization in complex HLW glasses (i.e., RSquared = 0.908). An approach to measurement, fitting, and use of TTT diagrams for prediction of crystallinity in a HLW glass canister is proposed

Electron-phonon coupling in one dimension

International Nuclear Information System (INIS)

Apostol, M.; Baldea, I.

1981-08-01

The Ward identity is derived for the electron-phonon coupling in one dimension and the spectrum of elementary excitations is calculated by assuming that the Fermi distribution is not strongly distorted by interaction. The electron-phonon vertex is renormalized in the case of the forward scattering and Migdal's theorem is discussed. A model is proposed for the giant Kohn anomaly. The dip in the phonon spectrum is obtained and found to be in agreement with the experimental data for KCP. (author)

Optical phonon scattering on electronic mobility in Al2O3/AlGaN/AlN/GaN heterostructures

Science.gov (United States)

Zhou, X. J.; Qu, Y.; Ban, S. L.; Wang, Z. P.

2017-12-01

Considering the built-in electric fields and the two-mode property of transverse optical phonons in AlGaN material, the electronic eigen-energies and wave functions are obtained by solving Schrödinger equation with the finite difference method. The dispersion relations and potentials of the optical phonons are given by the transfer matrix method. The mobility of the two dimensional electron gas influenced by the optical phonons in Al2O3/AlGaN/AlN/GaN heterostructures is investigated based on the theory of Lei-Ting force balance equation. It is found that the scattering from the half-space phonons is the main factor affecting the electronic mobility, and the influence of the other phonons can be ignored. The results show that the mobility decreases with increasing the thicknesses of Al2O3 and AlN layers, but there is no definite relationship between the mobility and the thickness of AlGaN barrier. The mobility is obviously reduced by increasing Al component in AlGaN crystal to show that the effect of ternary mixed crystals is important. It is also found that the mobility increases first and then decreases as the increment of the fixed charges, but decreases always with increasing temperature. The heterostructures constructed here can be good candidates as metal-oxide-semiconductor high-electron-mobility-transistors since they have higher electronic mobility due to the influence from interface phonons weakened by the AlN interlayer.

Crystallization of copper metaphosphate glass

Science.gov (United States)

Bae, Byeong-Soo; Weinberg, Michael C.

1993-01-01

The effect of the valence state of copper in copper metaphosphate glass on the crystallization behavior and glass transition temperature has been investigated. The crystallization of copper metaphosphate is initiated from the surface and its main crystalline phase is copper metaphosphate (Cu(PO)3),independent of the (Cu sup 2+)/(Cu(total)). However, the crystal morphology, the relative crystallization rates, and their temperature dependences are affected by the (Cu sup 2+)/(Cu (total)) ratio in the glass. On the other hand, the totally oxidized glass crystallizes from all over the surface. The relative crystallization rate of the reduced glass to the totally oxidized glass is large at low temperature, but small at high temperature. The glass transition temperature of the glass increases as the (Cu sup 2+)/(Cu(total)) ratio is raised. It is also found that the atmosphere used during heat treatment does not influence the crystallization of the reduced glass, except for the formation of a very thin CuO surface layer when heated in air.

From glass to crystal - Nucleation, growth and de-mixing, from research to applications

International Nuclear Information System (INIS)

Neuville, Daniel R.; Cormier, Laurent; Caurant, Daniel; Montagne, Lionel; Charpentier, Thibault; Chevalier, Jerome; Comte, Monique; Dargaud, Olivier; Ligny, Dominique de; Deniard, Philippe; Dussardier, Bernard; Dussauze, Marc; Fargin, Evelyne; Gremillard, Laurent; Gredin, Patrick; Jousseaume, Cecile; Lafait, Jacques; Lancry, Mathieu; Lefebvre, Leila; Levelut, Claire; Magallanes-Pedromo, Marlin; Massiot, Dominique; Mear, Francois O.; Meille, Sylvain; Meng, Nicolas; Mortier, Michel; Papin, Sophie; Papon, Gautier; Pastouret, Main; Petit, Yannick; Poumellec, Bertrand; Pradel, Annie; Reillon, Vincent; Rodriguez, Vincent; Rogez, Jacques; Roussel, Pascal; Royon, Arnaud; Schuller, Sophie; Tricot, Gregory; Vigouroux, Helene

2013-01-01

This book first presents the conventional nucleation theory: vitrification, homogeneous and heterogeneous nucleation, induction time, crystal growth, Oswald law. The second part addresses the evolutions beyond this theory: cluster dynamics, validity of the Stokes-Einstein relationship, non conventional germ system, Gibbs generalized approach, two-stage model. The third part addresses the thermodynamic stability and the global kinetics of transformation: thermodynamic stability and instability of a vitreous system, phenomenological approach to transformation kinetics. The fourth part addresses the de-mixing process on glasses: thermodynamic description of phase separation, de-mixing kinetics, influence of glass structure on de-mixing trend, de-mixing characterisation. The next parts describe the crystal-chemical approach to the main crystalline phases noticed in glass-ceramics (silicate phases and phosphates), the elaboration and control of glass-ceramic microstructure (controllable parameters, elaboration processes, characterization methods, microstructure types, design of glass-ceramics with desired properties by control of crystallisation mechanisms), X ray diffraction in the case of glass-ceramics, calorimetry and differential thermal analysis for the study of glass ceramics, the application of electronic microscopy to the study of nucleation and crystallisation in glasses, small-angle scattering of X rays and neutrons, the use of nuclear magnetic resonance to understand the disorder and crystallisation in vitreous materials, the use of Raman spectrometry to study mechanisms of nucleation and crystal growth, large instruments aimed at an in situ approaches to crystallisation, commercial applications of glass-ceramics, applications of biomaterials in glass and glass-ceramics, the coloration of metal nanoparticles, transparent glass-ceramics, the formation and applications of nanoparticles in silica-based optic fibres, the both-way relationship between non linear

Renormalization effects and phonon density of states in high temperature superconductors

Directory of Open Access Journals (Sweden)

Vinod Ashokan

2013-02-01

Full Text Available Using the versatile double time thermodynamic Green's function approach based on many body theory the renormalized frequencies, phonon energy line widths, shifts and phonon density of states (PDOS are investigated via a newly formulated Hamiltonian (does not include BCS type Hamiltonian that includes the effects of electron-phonon, anharmonicities and that of isotopic impurities. The automatic appearance of pairons, temperature, impurity and electron-phonon coupling of renormalized frequencies, widths, shifts and PDOS emerges as a characteristic feature of present theory. The numerical investigations on PDOS for the YBa2Cu3O7 − δ crystal predicts several new feature of high temperature superconductors (HTS and agreements with experimental observations.

Controlling elastic waves with small phononic crystals containing rigid inclusions

KAUST Repository

Peng, Pai; Qiu, Chunyin; Liu, Zhengyou; Wu, Ying

2014-01-01

waveguide made of a two-layer anisotropic elastic phononic crystal, which can guide and bend elastic waves with wavelengths much larger than the size of the waveguide. The other example is the enhanced elastic transmission of a single-layer elastic phononic

The lattice dynamical studies of rare earth compounds: electron-phonon interactions

International Nuclear Information System (INIS)

Jha, Prafulla K.; Sanyal, Sankar P.; Singh, R.K.

2002-01-01

During the last two decades chalcogenides and pnictides of rare earth (RE) atoms have drawn considerable attention of the solid state physicists because of their peculiar electronic, magnetic, optical and phonon properties. Some of these compounds e.g. sulphides and selenides of cerium (Ce), samarium (Sm), yttrium (Y), ytterbium (Yb), europium (Eu) and thulium (Tm) and their alloys show nonintegral valence (between 2 and 3), arising due to f-d electron hybridization at ambient temperature and pressure. The rare earth mixed valence compounds (MVC) reviewed in this article crystallize in simple cubic structure. Most of these compounds show the existence of strong electron-phonon coupling at half way to the zone boundary. This fact manifests itself through softening of the longitudinal acoustic mode, negative value of elastic constant C 12 etc. The purpose of this contribution is to review some of the recent activities in the fields of lattice dynamics and allied properties of rare earth compounds. The present article is primarily devoted to review the effect of electron-phonon interactions on the dynamical properties of rare earth compounds by using the lattice dynamical model theories based on charged density deformations and long-range many body forces. While the long range charge transfer effect arises due to f-d hybridization of nearly degenerate 4f-5d bands of rare earth ions, the density deformation comes into the picture of breathing motion of electron shells. These effects of charge transfer and charge density deformation when considered in the lattice dynamical models namely the three body force rigid ion model (TRM) and breathing shell model (BSM) are quite successful in explaining the phonon anomalies in these compounds and undoubtedly unraveled many important physical process governing the phonon anomalies in rare earth compounds

Wigner-like crystallization of Anderson-localized electron systems with low electron densities

International Nuclear Information System (INIS)

Slutskin, A.A.; Kovtun, H.A.; Pepper, M.

2002-01-01

We consider an electron system under conditions of strong Anderson localization, taking into account interelectron long-range Coulomb repulsion. We establish that at sufficiently low electron densities and sufficiently low temperatures the Coulomb electron interaction brings about ordering of the Anderson-localized electrons into a structure that is close to an ideal (Wigner) crystal lattice, provided the dimension of the system is > 1. This Anderson-Wigner glass (AWG) is a new macroscopic electron state that, on the one hand, is beyond the conventional Fermi glass concept, and on the other hand, qualitatively differs from the known 'plain' Wigner glass (inherent in self-localized electron systems) in that the random slight electron displacements from the ideal crystal sites essentially depend on the electron density. With increasing electron density the AWG is found to turn into the plain Wigner glass or Fermi glass, depending on the width of the random spread of the electron levels. It is shown that the residual disorder of the AWG is characterized by a multi-valley ground-state degeneracy akin to that in a spin glass. Some general features of the AWG are discussed, and a new conduction mechanism of a creep type is predicted

Thermal conductivity of electron-doped CaMnO3 perovskites: Local lattice distortions and optical phonon thermal excitation

International Nuclear Information System (INIS)

Wang Yang; Sui Yu; Wang Xianjie; Su Wenhui; Liu Xiaoyang; Fan, Hong Jin

2010-01-01

The thermal transport properties of a series of electron-doped CaMnO 3 perovskites have been investigated. Throughout the temperature range 5-300 K, phonon thermal conductivity is dominant, and both electron and spin wave contributions are negligible. The short phonon mean free paths in this system result in the relatively low thermal conductivities. The strong phonon scatterings stem from the A-site mismatch and bond-length fluctuations induced by local distortions of MnO 6 octahedra. The thermal conductivity in the magnetically ordered state is enhanced as a result of the decrease in spin-phonon scattering. The results also indicate that above the magnetic ordering temperature, observable thermal excitation of optical phonons occurs. The contribution of optical phonons to thermal conductivity becomes non-negligible and is proposed to play an important role in the glass-like thermal transport behavior (i.e. positive temperature dependence of the thermal conductivity) in the paramagnetic state. These features can be understood in terms of an expression of thermal conductivity that includes both acoustic and optical phonon terms.

Properties of magnetized Coulomb crystals of ions with polarizable electron background

Science.gov (United States)

Kozhberov, A. A.

2018-06-01

We have studied phonon and thermodynamic properties of a body-centered cubic (bcc) Coulomb crystal of ions with weakly polarized electron background in a uniform magnetic field B. At B = 0, the difference between phonon moments calculated using the Thomas-Fermi (TF) and random phase approximations is always less than 1% and for description of phonon properties of a crystal, TF formalism was used. This formalism was successfully applied to investigate thermodynamic properties of magnetized Coulomb crystals. It was shown that the influence of the polarization of the electron background is significant only at κ TF a > 0.1 and T ≪ T p ( 1 + h2 ) - 1 / 2 , where κTF is the Thomas-Fermi wavenumber, a is the ion sphere radius, T p ≡ ℏ ω p is the ion plasma temperature, h ≡ ω B / ω p , ωB is the ion cyclotron frequency, and ωp is the ion plasma frequency.

Study of phonon-induced energy transfer processes in crystals using heat pulses

International Nuclear Information System (INIS)

Burns, A.R.

1978-03-01

The artificial generation of acoustic lattice vibrations by a heat pulse technique is developed in order to probe phonon interactions in molecular crystals. Specifically, the phonon-assisted delocalization of ''trapped'' excited triplet state energy in the aromatic crystal 1,2,4,5-tetrachlorobenzene (TCB) is studied in a quantitative manner by monitoring the time-resolved decrease in trap phosphorescence intensity due to the propagation of a well-defined heat pulse. The excitation distribution in a single trap system, such as the X-trap in neat h 2 -TCB, is discussed in terms of the energy partition function relating the temperature dependence of the trap phosphorescence intensity to the trap depth, exciton bandwidth, and the number of exciton band states. In a multiple trap system, such as the hd and h 2 isotopic traps in d 2 -TCB, the excitation distribution is distinctly non-Boltzmann; yet it may be discussed in terms of a preferential energy transfer between the two trap states via the exciton band. For both trap systems, a previously developed kinetic model is presented which relates the efficiency of trap-band energy exchange to the density of band states and the trap-phonon coupling matrix elements. A bolometric technique for determining the thermal response time of the heater/crystal system is presented. The phonon mean free path in the crystal is size-limited, and the heater/crystal boundary conductance is reasonably close to previously reported values. The theory of heat pulse phonon spectroscopy is presented and discussed in terms of black-body phonon radiation

Crystal growth in zinc borosilicate glasses

Science.gov (United States)

Kullberg, Ana T. G.; Lopes, Andreia A. S.; Veiga, João P. B.; Monteiro, Regina C. C.

2017-01-01

Glass samples with a molar composition (64+x)ZnO-(16-x)B2O3-20SiO2, where x=0 or 1, were successfully synthesized using a melt-quenching technique. Based on differential thermal analysis data, the produced glass samples were submitted to controlled heat-treatments at selected temperatures (610, 615 and 620 °C) during various times ranging from 8 to 30 h. The crystallization of willemite (Zn2SiO4) within the glass matrix was confirmed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Under specific heat-treatment conditions, transparent nanocomposite glass-ceramics were obtained, as confirmed by UV-vis spectroscopy. The influence of temperature, holding time and glass composition on crystal growth was investigated. The mean crystallite size was determined by image analysis on SEM micrographs. The results indicated an increase on the crystallite size and density with time and temperature. The change of crystallite size with time for the heat-treatments at 615 and 620 °C depended on the glass composition. Under fixed heat-treatment conditions, the crystallite density was comparatively higher for the glass composition with higher ZnO content.

Tri-component phononic crystals for underwater anechoic coatings

International Nuclear Information System (INIS)

Zhao, Honggang; Liu, Yaozong; Wen, Jihong; Yu, Dianlong; Wen, Xisen

2007-01-01

Localized resonance in phononic crystal, composed of three-dimensional arrays of composite units, has been discovered recently. The composite unit is a high-density sphere coated by soft silicon rubber. In this Letter, the absorptive properties induced by the localized resonance are systemically investigated. The mode conversions during the Mie scattering of a single coated lead sphere in unbounded epoxy are analyzed by referring the elements of the scattering matrix. Then the anechoic properties of a slab containing a plane of such composite scatterers are investigated with the multiple-scattering method by accounting the effects of the multiple scattering and the viscous dissipation. The results show that the longitudinal to transverse mode conversion nearby the locally resonant region is an effective way to enhance the anechoic performance of the finite slab of phononic crystal. Then, the influences of the viscoelasticity of the silicon rubber and the coating thickness on the acoustic properties of the finite slab are investigated for anechoic optimization. Finally, we synthetically consider the destructive scattering in the finite slab of phononic crystal and the backing, and design an anechoic slab composed of bi-layer coated spheres. The results show that the most of the incident energy is absorbed at the desired frequency band

Crystallization of high-strength nano-scale leucite glass-ceramics.

Science.gov (United States)

Theocharopoulos, A; Chen, X; Wilson, R M; Hill, R; Cattell, M J

2013-11-01

Fine-grained, high strength, translucent leucite dental glass-ceramics are synthesized via controlled crystallization of finely milled glass powders. The objectives of this study were to utilize high speed planetary milling of an aluminosilicate glass for controlled surface crystallization of nano-scale leucite glass-ceramics and to test the biaxial flexural strength. An aluminosilicate glass was synthesized, attritor or planetary milled and heat-treated. Glasses and glass-ceramics were characterized using particle size analysis, X-ray diffraction and scanning electron microscopy. Experimental (fine and nanoscale) and commercial (Ceramco-3, IPS Empress Esthetic) leucite glass-ceramics were tested using the biaxial flexural strength (BFS) test. Gaussian and Weibull statistics were applied. Experimental planetary milled glass-ceramics showed an increased leucite crystal number and nano-scale median crystal sizes (0.048-0.055 μm(2)) as a result of glass particle size reduction and heat treatments. Experimental materials had significantly (p0.05) strength difference. All other groups' mean BFS and characteristic strengths were found to be significantly different (pglass-ceramics with high flexural strength. These materials may help to reduce problems associated with brittle fracture of all-ceramic restorations and give reduced enamel wear. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Study on the crystallization of the metal glass with the ferromagnetic resonance and transmission electron microscopy techniques

International Nuclear Information System (INIS)

Biasi, R.S. de; Rodrigues, R.W.D.; Pascual, R.; Pessoa, C.S.

1983-01-01

The crystallization of the metal glass METGLAS 2826A has been studied with the ferromagnetic resonance and electron transmission microscopy techniques. The first-derivative linewidth of the absorption curve was measured for several times of isothermal treatments at 375 0 C. After an initial decrease, attributed to stress relaxation, the linewidth increases linearly with the transformed fraction of the first crystallization phase. Comparison with the electron microscopy results shows that the ferromagnetic resonance technique is particularly useful for short and medium aging times. (Author) [pt

Electron-phonon interactions in correlated systems

International Nuclear Information System (INIS)

Wysokinski, K.I.

1996-01-01

There exist attempts to describe the superconducting mechanism operating in HTS as based on antiferromagnetic fluctuations. It is not our intention to dwell on the superconducting mechanism, even though this is very a important issue. The main aim is to discuss the problem of interplay between electron-phonon and electron-electron interactions in correlated systems. We believe such analysis can be of importance for various materials and not only HTS'S. We shall however mainly refer to experiments on this last class of superconductors. Severe complications are to be expected by studying the problem. As is well known electron correlations are very important in narrow band systems, where the relevant electronic scale E F is quite small. In those circumstances, the phonon energy scale ω D is of comparable magnitude, with the ratio ω D /E F of order 1 signalling a possible break down of the Migdal - Eliashberg description of the electron-phonon interaction in metals. Here we shall assume the validity of the Migdal-Eliashberg approximation and concentrate on the mutual influence of electron and phonon subsystems. In the next section we shall discuss experimental motivation for and theoretical work related to the present problem. Section 3 contains a brief discussion of our theory. It is a self-consistent theory a la Migdal with strong correlations treated with an auxiliary boson technique. We conclude with results and their discussion. (orig.)

Effects of the electron-phonon coupling activation in collision cascades

Energy Technology Data Exchange (ETDEWEB)

Zarkadoula, Eva, E-mail: zarkadoulae@ornl.gov [Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Samolyuk, German [Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Weber, William J. [Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Department of Materials Science & Engineering, University of Tennessee, Knoxville, TN 37996 (United States)

2017-07-15

Using the two-temperature (2T-MD) model in molecular dynamics simulations, we investigate the condition of switching the electronic stopping term off when the electron-phonon coupling is activated in the damage production due to 50 keV Ni ion cascades in Ni and equiatomic NiFe. Additionally, we investigate the effect of the electron-phonon coupling activation time in the damage production. We find that the switching condition has negligible effect in the produced damage, while the choice of the activation time of the electron-phonon coupling can affect the amount of surviving damage. - Highlights: •The electron-phonon interactions in irradiation affect the energy dissipation. •The resulting damage depends on the electron-phonon interaction activation time. •The electronic stopping acts on the ions before the electron-phonon interactions.

Phonon spectra in SiO2 glasses

International Nuclear Information System (INIS)

Perez R, J.F.; Jimenez S, S.; Gonzalez H, J.; Vorobiev, Y.V.; Hernandez L, M.A.; Parga T, J.R.

1999-01-01

Phonon spectra in SiO 2 sol-gel made glasses annealed under different conditions are investigated using infrared absorption and Raman scattering. These data are compared with those obtained in commercial optical-quality quartz. All the materials exhibit the same phonon bands, the exact position and the intensity depend on the measuring technique and on the sample preparation method. The phonon spectra in this material are interpreted on the basis of a simple quasi-linear description of elastic waves in an O-Si-O chain. It is shown that the main features observed in the range 400-1400 cm -1 can be predicted using a quasi-linear chain model in which the band at 1070 cm -1 is assigned to the longitudinal optical waves in the O-Si-O chain with the smallest possible wavelength at the Brillouin zone boundary, the band located around 450 cm -1 is assigned to the transversal optical waves and the band at 800 cm -1 to the longitudinal acoustical waves with the same wavelength. The degree of structural disorder can be also deduced within the framework of the proposed model. (Author)

Glass transition and crystallization kinetics of a barium borosilicate glass by a non-isothermal method

International Nuclear Information System (INIS)

Lopes, Andreia A. S.; Soares, Roque S.; Lima, Maria M. A.; Monteiro, Regina C. C.

2014-01-01

The glass transition and crystallization kinetics of a glass with a molar composition 60BaO-30B 2 O 3 -10SiO 2 were investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves exhibited an endothermic peak associated with the glass transition and two partially overlapped exothermic peaks associated with the crystallization of the glass. The dependence of the glass transition temperature (T g ) and of the maximum crystallization temperature (T p ) on the heating rate was used to determine the activation energy associated with the glass transition (E g ), the activation energy for crystallization (E c ), and the Avrami exponent (n). X-ray diffraction (XRD) revealed that barium borate (β-BaB 2 O 4 ) was the first crystalline phase to be formed followed by the formation of barium silicate (Ba 5 Si 8 O 21 ). The variations of activation energy for crystallization and of Avrami exponent with the fraction of crystallization (χ) were also examined. When the crystallization fraction (χ) increased from 0.1 to 0.9, the value of local activation energy (E c (χ)) decreased from 554 to 458 kJ/mol for the first exothermic peak and from 1104 to 831 kJ/mol for the second exothermic peak. The value determined for the Avrami exponent was near 2 indicating a similar one-dimensional crystallization mechanism for both crystalline phases. This was confirmed by the morphological studies performed by scanning electron microscopy (SEM) on glass samples heat-treated at the first and at the second crystallization temperatures

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.

Stability and electronic structure of Zr-based ternary metallic glasses and relevant compounds

International Nuclear Information System (INIS)

Hasegawa, M.; Soda, K.; Sato, H.; Suzuki, T.; Taketomi, T.; Takeuchi, T.; Kato, H.; Mizutani, U.

2007-01-01

The electronic structure of the Zr-based metallic glasses has been investigated by theoretical and experimental approaches. One approach is band calculations of the Zr 2 Ni (Zr 66.7 Ni 33.3 ) compound to investigate the electronic structure of the Zr 66.7 Ni 33.3 metallic glass (ΔT x = 0 K) of which the local atomic structure is similar to that of the Zr 2 Ni compound. The other is photoemission spectroscopy of the Zr 50 Cu 35 Al 15 bulk metallic glass (BMG) (ΔT x = 69 K). Here ΔT x = T x - T g where T x and T g are crystallization and glass transition temperature, respectively. Both results and previous ones on the Zr 55 Cu 30 Ni 5 Al 10 BMG indicate that there is a pseudogap at the Fermi level in the electronic structure of these Zr-based metallic glasses, independent of the value of the ΔT x . This implies that the pseudogap at the Fermi level is one of the factors that stabilize the glass phase of Zr-based metallic glasses

Isotopic effects on phonon anharmonicity in layered van der Waals crystals: Isotopically pure hexagonal boron nitride

Science.gov (United States)

Cuscó, Ramon; Artús, Luis; Edgar, James H.; Liu, Song; Cassabois, Guillaume; Gil, Bernard

2018-04-01

Hexagonal boron nitride (h -BN) is a layered crystal that is attracting a great deal of attention as a promising material for nanophotonic applications. The strong optical anisotropy of this crystal is key to exploit polaritonic modes for manipulating light-matter interactions in 2D materials. h -BN has also great potential for solid-state neutron detection and neutron imaging devices, given the exceptionally high thermal neutron capture cross section of the boron-10 isotope. A good knowledge of phonons in layered crystals is essential for harnessing long-lived phonon-polariton modes for nanophotonic applications and may prove valuable for developing solid-state 10BN neutron detectors with improved device architectures and higher detection efficiencies. Although phonons in graphene and isoelectronic materials with a similar hexagonal layer structure have been studied, the effect of isotopic substitution on the phonons of such lamellar compounds has not been addressed yet. Here we present a Raman scattering study of the in-plane high-energy Raman active mode on isotopically enriched single-crystal h -BN. Phonon frequency and lifetime are measured in the 80-600-K temperature range for 10B-enriched, 11B-enriched, and natural composition high quality crystals. Their temperature dependence is explained in the light of perturbation theory calculations of the phonon self-energy. The effects of crystal anisotropy, isotopic disorder, and anharmonic phonon-decay channels are investigated in detail. The isotopic-induced changes in the phonon density of states are shown to enhance three-phonon anharmonic decay channels in 10B-enriched crystals, opening the possibility of isotope tuning of the anharmonic phonon decay processes.

Low-frequency spatial wave manipulation via phononic crystals with relaxed cell symmetry

International Nuclear Information System (INIS)

Celli, Paolo; Gonella, Stefano

2014-01-01

Phononic crystals enjoy unique wave manipulation capabilities enabled by their periodic topologies. On one hand, they feature frequency-dependent directivity, which allows directional propagation of selected modes even at low frequencies. However, the stellar nature of the propagation patterns and the inability to induce single-beam focusing represent significant limitations of this functionality. On the other hand, one can realize waveguides by defecting the periodic structure of a crystal operating in bandgap mode along some desired path. Waveguides of this type are only activated in the relatively high and narrow frequency bands corresponding to total bandgaps, which limits their potential technological applications. In this work, we introduce a class of phononic crystals with relaxed cell symmetry and we exploit symmetry relaxation of a population of auxiliary microstructural elements to achieve spatial manipulation of elastic waves at very low frequencies, in the range of existence of the acoustic modes. By this approach, we achieve focusing without modifying the default static properties of the medium and by invoking mechanisms that are well suited to envision adaptive configurations for semi-active wave control

Lumped model for rotational modes in phononic crystals

KAUST Repository

Peng, Pai

2012-10-16

We present a lumped model for the rotational modes induced by the rotational motion of individual scatterers in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model provides a physical interpretation of the origin of the rotational modes, reveals the important role played by the rotational motion in determining the band structure, and reproduces the dispersion relations in a certain range. The model increases the possibilities of manipulating wave propagation in phononic crystals. In particular, expressions derived from the model for eigenfrequencies at high symmetry points unambiguously predict the presence of a new type of Dirac-like cone at the Brillouin center, which is found to be the result of accidental degeneracy of the rotational and dipolar modes.

Lumped model for rotational modes in phononic crystals

KAUST Repository

Peng, Pai; Mei, Jun; Wu, Ying

2012-01-01

We present a lumped model for the rotational modes induced by the rotational motion of individual scatterers in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model provides a physical interpretation of the origin of the rotational modes, reveals the important role played by the rotational motion in determining the band structure, and reproduces the dispersion relations in a certain range. The model increases the possibilities of manipulating wave propagation in phononic crystals. In particular, expressions derived from the model for eigenfrequencies at high symmetry points unambiguously predict the presence of a new type of Dirac-like cone at the Brillouin center, which is found to be the result of accidental degeneracy of the rotational and dipolar modes.

Quasiparticle properties of a coupled quantum-wire electron-phonon system

DEFF Research Database (Denmark)

Hwang, E. H.; Hu, Ben Yu-Kuang; Sarma, S. Das

1996-01-01

We study leading-order many-body effects of longitudinal-optical phonons on electronic properties of one-dimensional quantum-wire systems. We calculate the quasiparticle properties of a weakly polar one-dimensional electron gas in the presence of both electron-phonon and electron-electron interac......We study leading-order many-body effects of longitudinal-optical phonons on electronic properties of one-dimensional quantum-wire systems. We calculate the quasiparticle properties of a weakly polar one-dimensional electron gas in the presence of both electron-phonon and electron......-electron interactions, The leading-order dynamical screening approximation (GW approximation) is used to obtain the electron self-energy, the quasiparticle spectral function, and the quasiparticle damping rate in our calculation by treating electrons and phonons on an equal footing. Our theory includes effects (within...... theoretical results for quasiparticle properties....

Electron-phonon interaction in Chevrel-phase compounds

International Nuclear Information System (INIS)

Rainer, D.; Pobell, F.

1981-03-01

Experiments on the electron-phonon interaction in Chevrel-phase compounds (CPC) and a theoretical discussion of their results are presented. The authors particularly discuss measurements of the isotope effect of the transition temperature in Mo 6 Se 8 and SnMo 6 S 8 and tunneling spectroscopy experiments on Cu 1 . 8 Mo 6 S 8 and PbMo 6 S 8 . These investigations have been performed to get information about the strength of the electron-phonon interaction in CPC, and about the question whether there are phonon modes which couple particularly strongly to the electrons in these compounds. (orig./GSCH)

Crystal-Tolerant Glass Approach For Mitigation Of Crystal Accumulation In Continuous Melters Processing Radioactive Waste

International Nuclear Information System (INIS)

Kruger, Albert A.; Rodriguez, Carmen P.; Lang, Jesse B.; Huckleberry, Adam R.; Matyas, Josef; Owen, Antoinette T.

2012-01-01

High-level radioactive waste melters are projected to operate in an inefficient manner as they are subjected to artificial constraints, such as minimum liquidus temperature (T L ) or maximum equilibrium fraction of crystallinity at a given temperature. These constraints substantially limit waste loading, but were imposed to prevent clogging of the melter with spinel crystals [(Fe, Ni, Mn, Zn)(Fe, Cr) 2 O 4 ]. In the melter, the glass discharge riser is the most likely location for crystal accumulation during idling because of low glass temperatures, stagnant melts, and small diameter. To address this problem, a series of lab-scale crucible tests were performed with specially formulated glasses to simulate accumulation of spinel in the riser. Thicknesses of accumulated layers were incorporated into empirical model of spinel settling. In addition, T L of glasses was measured and impact of particle agglomeration on accumulation rate was evaluated. Empirical model predicted well the accumulation of single crystals and/or smallscale agglomerates, but, excessive agglomeration observed in high-Ni-Fe glass resulted in an under-prediction of accumulated layers, which gradually worsen over time as an increased number of agglomerates formed. Accumulation rate of ∼14.9 +- 1 nm/s determined for this glass will result in ∼26 mm thick layer in 20 days of melter idling

Coherent heat transport in 2D phononic crystals with acoustic impedance mismatch

International Nuclear Information System (INIS)

Arantes, A; Anjos, V

2016-01-01

In this work we have calculated the cumulative thermal conductivities of micro-phononic crystals formed by different combinations of inclusions and matrices at a sub-Kelvin temperature regime. The low-frequency phonon spectra (up to tens of GHz) were obtained by solving the generalized wave equation for inhomogeneous media with the plane wave expansion method. The thermal conductivity was calculated from Boltzmann transport theory highlighting the role of the low-frequency thermal phonons and neglecting phonon–phonon scattering. A purely coherent thermal transport regime was assumed throughout the structures. Our findings show that the cumulative thermal conductivity drops dramatically when compared with their bulk counterpart. Depending on the structural composition this reduction may be attributed to the phonon group velocity due to a flattening of the phonon dispersion relation, the extinction of phonon modes in the density of states or due to the presence of complete band gaps. According to the contrast between the inclusions and the matrices, three types of two dimensional phononic crystals were considered: carbon/epoxy, carbon/polyethylene and tungsten/silicon, which correspond respectively to a moderate, strong and very strong mismatch in the mechanical properties of these materials. (paper)

Effects of electron-phonon interaction on thermal and electrical transport through molecular nano-conductors

Energy Technology Data Exchange (ETDEWEB)

Lü, Jing-Tao, E-mail: jtlu@hust.edu.cn [School of Physics, Huazhong University of Science and Technology, 430074 Wuhan (China); Zhou, Hangbo [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, 117551 Singapore (Singapore); NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 117456 Singapore (Singapore); Jiang, Jin-Wu [Shanghai Institute of Applied Mathematics and Mechanics, Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai University, 200072 Shanghai (China); Wang, Jian-Sheng [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, 117551 Singapore (Singapore)

2015-05-15

The topic of this review is the effects of electron-phonon interaction (EPI) on the transport properties of molecular nano-conductors. A nano-conductor connects to two electron leads and two phonon leads, possibly at different temperatures or chemical potentials. The EPI appears only in the nano-conductor. We focus on its effects on charge and energy transport. We introduce three approaches. For weak EPI, we use the nonequilibrium Green’s function method to treat it perturbatively. We derive the expressions for the charge and heat currents. For weak system-lead couplings, we use the quantum master equation approach. In both cases, we use a simple single level model to study the effects of EPI on the system’s thermoelectric transport properties. It is also interesting to look at the effect of currents on the dynamics of the phonon system. For this, we derive a semi-classical generalized Langevin equation to describe the nano-conductor’s atomic dynamics, taking the nonequilibrium electron system, as well as the rest of the atomic degrees of freedom as effective baths. We show simple applications of this approach to the problem of energy transfer between electrons and phonons.

Effects of electron-phonon interaction on thermal and electrical transport through molecular nano-conductors

International Nuclear Information System (INIS)

Lü, Jing-Tao; Zhou, Hangbo; Jiang, Jin-Wu; Wang, Jian-Sheng

2015-01-01

The topic of this review is the effects of electron-phonon interaction (EPI) on the transport properties of molecular nano-conductors. A nano-conductor connects to two electron leads and two phonon leads, possibly at different temperatures or chemical potentials. The EPI appears only in the nano-conductor. We focus on its effects on charge and energy transport. We introduce three approaches. For weak EPI, we use the nonequilibrium Green’s function method to treat it perturbatively. We derive the expressions for the charge and heat currents. For weak system-lead couplings, we use the quantum master equation approach. In both cases, we use a simple single level model to study the effects of EPI on the system’s thermoelectric transport properties. It is also interesting to look at the effect of currents on the dynamics of the phonon system. For this, we derive a semi-classical generalized Langevin equation to describe the nano-conductor’s atomic dynamics, taking the nonequilibrium electron system, as well as the rest of the atomic degrees of freedom as effective baths. We show simple applications of this approach to the problem of energy transfer between electrons and phonons

Electronic states in crystals of finite size quantum confinement of bloch waves

CERN Document Server

Ren, Shang Yuan

2017-01-01

This book presents an analytical theory of the electronic states in ideal low dimensional systems and finite crystals based on a differential equation theory approach. It provides precise and fundamental understandings on the electronic states in ideal low-dimensional systems and finite crystals, and offers new insights into some of the basic problems in low-dimensional systems, such as the surface states and quantum confinement effects, etc., some of which are quite different from what is traditionally believed in the solid state physics community. Many previous predictions have been confirmed in subsequent investigations by other authors on various relevant problems. In this new edition, the theory is further extended to one-dimensional photonic crystals and phononic crystals, and a general theoretical formalism for investigating the existence and properties of surface states/modes in semi-infinite one-dimensional crystals is developed. In addition, there are various revisions and improvements, including us...

Unusual Crystallization Behavior Close to the Glass Transition

Science.gov (United States)

Desgranges, Caroline; Delhommelle, Jerome

2018-03-01

Using molecular simulations, we shed light on the mechanism underlying crystal nucleation in metal alloys and unravel the interplay between crystal nucleation and glass transition, as the conditions of crystallization lie close to this transition. While decreasing the temperature of crystallization usually results in a lower free energy barrier, we find an unexpected reversal of behavior for glass-forming alloys as the temperature of crystallization approaches the glass transition. For this purpose, we simulate the crystallization process in two glass-forming Copper alloys, Ag6 Cu4 , which has a positive heat of mixing, and CuZr, characterized by a large negative heat of mixing. Our results allow us to identify this unusual behavior as directly correlated with a nonmonotonic temperature dependence for the formation energy of connected icosahedral structures, which are incompatible with crystalline order and impede the development of the crystal nucleus, leading to an unexpectedly larger free energy barrier at low temperature. This, in turn, promotes the formation of a predominantly closed-packed critical nucleus, with fewer defects, thereby suggesting a new way to control the structure of the crystal nucleus, which is of key importance in catalysis.

Exciton Scattering approach for conjugated macromolecules: from electronic spectra to electron-phonon coupling

Science.gov (United States)

Tretiak, Sergei

2014-03-01

The exciton scattering (ES) technique is a multiscale approach developed for efficient calculations of excited-state electronic structure and optical spectra in low-dimensional conjugated macromolecules. Within the ES method, the electronic excitations in the molecular structure are attributed to standing waves representing quantum quasi-particles (excitons), which reside on the graph. The exciton propagation on the linear segments is characterized by the exciton dispersion, whereas the exciton scattering on the branching centers is determined by the energy-dependent scattering matrices. Using these ES energetic parameters, the excitation energies are then found by solving a set of generalized ``particle in a box'' problems on the graph that represents the molecule. All parameters can be extracted from quantum-chemical computations of small molecular fragments and tabulated in the ES library for further applications. Subsequently, spectroscopic modeling for any macrostructure within considered molecular family could be performed with negligible numerical effort. The exciton scattering properties of molecular vertices can be further described by tight-binding or equivalently lattice models. The on-site energies and hopping constants are obtained from the exciton dispersion and scattering matrices. Such tight-binding model approach is particularly useful to describe the exciton-phonon coupling, energetic disorder and incoherent energy transfer in large branched conjugated molecules. Overall the ES applications accurately reproduce the optical spectra compared to the reference quantum chemistry results, and make possible to predict spectra of complex macromolecules, where conventional electronic structure calculations are unfeasible.

Tunable topological phases in photonic and phononic crystals

KAUST Repository

Chen, Zeguo

2018-02-18

Topological photonics/phononics, inspired by the discovery of topological insulators, is a prosperous field of research, in which remarkable one-way propagation edge states are robust against impurities or defect without backscattering. This dissertation discusses the implementation of multiple topological phases in specific designed photonic and phononic crystals. First, it reports a tunable quantum Hall phase in acoustic ring-waveguide system. A new three-band model focused on the topological transitions at the Γ point is studied, which gives the functionality that nontrivial topology can be tuned by changing the strengths of the couplings and/or the broken time-reversal symmetry. The resulted tunable topological edge states are also numerically verified. Second, based on our previous studied acoustic ring-waveguide system, we introduce anisotropy by tuning the couplings along different directions. We find that the bandgap topology is related to the frequency and directions. We report our proposal on a frequency filter designed from such an anisotropic topological phononic crystal. Third, motivated by the recent progress on quantum spin Hall phases, we propose a design of time-reversal symmetry broken quantum spin Hall insulators in photonics, in which a new quantum anomalous Hall phase emerges. It supports a chiral edge state with certain spin orientations, which is robust against the magnetic impurities. We also report the realization of the quantum anomalous Hall phase in phononics.

Effects of thermo-order-mechanical coupling on band structures in liquid crystal nematic elastomer porous phononic crystals.

Science.gov (United States)

Yang, Shuai; Liu, Ying

2018-08-01

Liquid crystal nematic elastomers are one kind of smart anisotropic and viscoelastic solids simultaneously combing the properties of rubber and liquid crystals, which is thermal sensitivity. In this paper, the wave dispersion in a liquid crystal nematic elastomer porous phononic crystal subjected to an external thermal stimulus is theoretically investigated. Firstly, an energy function is proposed to determine thermo-induced deformation in NE periodic structures. Based on this function, thermo-induced band variation in liquid crystal nematic elastomer porous phononic crystals is investigated in detail. The results show that when liquid crystal elastomer changes from nematic state to isotropic state due to the variation of the temperature, the absolute band gaps at different bands are opened or closed. There exists a threshold temperature above which the absolute band gaps are opened or closed. Larger porosity benefits the opening of the absolute band gaps. The deviation of director from the structural symmetry axis is advantageous for the absolute band gap opening in nematic state whist constrains the absolute band gap opening in isotropic state. The combination effect of temperature and director orientation provides an added degree of freedom in the intelligent tuning of the absolute band gaps in phononic crystals. Copyright © 2018 Elsevier B.V. All rights reserved.

Ab initio determination of effective electron-phonon coupling factor in copper

Science.gov (United States)

Ji, Pengfei; Zhang, Yuwen

2016-04-01

The electron temperature Te dependent electron density of states g (ε), Fermi-Dirac distribution f (ε), and electron-phonon spectral function α2 F (Ω) are computed as prerequisites before achieving effective electron-phonon coupling factor Ge-ph. The obtained Ge-ph is implemented into a molecular dynamics (MD) and two-temperature model (TTM) coupled simulation of femtosecond laser heating. By monitoring temperature evolutions of electron and lattice subsystems, the result utilizing Ge-ph from ab initio calculation shows a faster decrease of Te and increase of Tl than those using Ge-ph from phenomenological treatment. The approach of calculating Ge-ph and its implementation into MD-TTM simulation is applicable to other metals.

Anharmonic vibrational properties in periodic systems: energy, electron-phonon coupling, and stress

OpenAIRE

Monserrat, Bartomeu; Drummond, N. D.; Needs, R. J.

2013-01-01

A unified approach is used to study vibrational properties of periodic systems with first-principles methods and including anharmonic effects. Our approach provides a theoretical basis for the determination of phonon-dependent quantities at finite temperatures. The low-energy portion of the Born-Oppenheimer energy surface is mapped and used to calculate the total vibrational energy including anharmonic effects, electron-phonon coupling, and the vibrational contribution to the stress tensor. W...

Unraveling the acoustic electron-phonon interaction in graphene

DEFF Research Database (Denmark)

Kaasbjerg, Kristen; Thygesen, Kristian S.; Jacobsen, Karsten W.

2012-01-01

Using a first-principles approach we calculate the electron-phonon couplings in graphene for the transverse and longitudinal acoustic phonons. Analytic forms of the coupling matrix elements valid in the long-wavelength limit are found to give an almost quantitative description of the first...... that the intrinsic effective acoustic deformation potential of graphene is Ξeff=6.8 eV and that the temperature dependence of the mobility μ~T-α in the Bloch-Gru¨neisen regime increases beyond an α=4 dependence even in the absence of screening when the true coupling matrix elements are considered. The α>4...

Primary crystallization in Al-rich metallic glasses at unusually low temperatures

International Nuclear Information System (INIS)

Bokeloh, J.; Boucharat, N.; Roesner, H.; Wilde, G.

2010-01-01

The initial stage of the primary crystallization reaction and the glass transition of the marginal metallic glass Al 89 Y 6 Fe 5 were investigated by conventional differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), microcalorimetry, X-ray diffraction (XRD) and transmission electron microscopy. A sharp onset of the primary crystallization was found by microcalorimetry and XRD studies at temperatures which were 120 deg. C below the primary crystallization peak observed in conventional DSC. A systematic MDSC study of annealed samples revealed a wide spectrum of glass transition onsets, which show a strong dependence on the annealing conditions. In addition, the glass transition onsets can be linked to the initial stage of the primary crystallization. The spectrum of glass transition onsets observed is discussed with respect to the occurrence of phase separation preceding the nucleation and growth of dendritic aluminium nanocrystals.

Band structures and localization properties of aperiodic layered phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Yan Zhizhong, E-mail: zzyan@bit.edu.cn [Department of Applied Mathematics, Beijing Institute of Technology, Beijing 100081 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57078 Siegen (Germany)

2012-03-15

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

Phononic Crystal Waveguide Transducers for Nonlinear Elastic Wave Sensing.

Science.gov (United States)

Ciampa, Francesco; Mankar, Akash; Marini, Andrea

2017-11-07

Second harmonic generation is one of the most sensitive and reliable nonlinear elastic signatures for micro-damage assessment. However, its detection requires powerful amplification systems generating fictitious harmonics that are difficult to discern from pure nonlinear elastic effects. Current state-of-the-art nonlinear ultrasonic methods still involve impractical solutions such as cumbersome signal calibration processes and substantial modifications of the test component in order to create material-based tunable harmonic filters. Here we propose and demonstrate a valid and sensible alternative strategy involving the development of an ultrasonic phononic crystal waveguide transducer that exhibits both single and multiple frequency stop-bands filtering out fictitious second harmonic frequencies. Remarkably, such a sensing device can be easily fabricated and integrated on the surface of the test structure without altering its mechanical and geometrical properties. The design of the phononic crystal structure is supported by a perturbative theoretical model predicting the frequency band-gaps of periodic plates with sinusoidal corrugation. We find our theoretical findings in excellent agreement with experimental testing revealing that the proposed phononic crystal waveguide transducer successfully attenuates second harmonics caused by the ultrasonic equipment, thus demonstrating its wide range of potential applications for acousto/ultrasonic material damage inspection.

Matrix-product-state method with local basis optimization for nonequilibrium electron-phonon systems

Science.gov (United States)

Heidrich-Meisner, Fabian; Brockt, Christoph; Dorfner, Florian; Vidmar, Lev; Jeckelmann, Eric

We present a method for simulating the time evolution of quasi-one-dimensional correlated systems with strongly fluctuating bosonic degrees of freedom (e.g., phonons) using matrix product states. For this purpose we combine the time-evolving block decimation (TEBD) algorithm with a local basis optimization (LBO) approach. We discuss the performance of our approach in comparison to TEBD with a bare boson basis, exact diagonalization, and diagonalization in a limited functional space. TEBD with LBO can reduce the computational cost by orders of magnitude when boson fluctuations are large and thus it allows one to investigate problems that are out of reach of other approaches. First, we test our method on the non-equilibrium dynamics of a Holstein polaron and show that it allows us to study the regime of strong electron-phonon coupling. Second, the method is applied to the scattering of an electronic wave packet off a region with electron-phonon coupling. Our study reveals a rich physics including transient self-trapping and dissipation. Supported by Deutsche Forschungsgemeinschaft (DFG) via FOR 1807.

Phonon interference control of atomic-scale metamirrors, meta-absorbers, and heat transfer through crystal interfaces

Science.gov (United States)

Kosevich, Yu. A.; Potyomina, L. G.; Darinskii, A. N.; Strelnikov, I. A.

2018-03-01

The paper theoretically studies the possibility of using the effects of phonon interference between paths through different interatomic bonds for the control of phonon heat transfer through internal crystal interfaces and for the design of phonon metamirrors and meta-absorbers. These metamirrors and meta-absorbers are considered to be defect nanolayers of atomic-scale thicknesses embedded in a crystal. Several analytically solvable three-dimensional lattice-dynamics models of the phonon metamirrors and meta-absorbers at the internal crystal planes are described. It is shown that due to destructive interference in the two or more phonon paths, the internal crystal planes, fully or partially filled with weakly bound or heavy-isotope defect atoms, can completely reflect or completely absorb phonons at the transmission antiresonances, whose wavelengths are larger than the effective thickness of the metamirror or meta-absorber. Due to cooperative superradiant effect, the spectral widths of the two-path interference antiresonances for the plane waves are given by the square of partial filling fraction in the defect crystal plane. Our analysis reveals that the presence of two or more phonon paths plays the dominant role in the emergence of the transmission antiresonances in phonon scattering at the defect crystal planes and in reduction of the thermal interface conductance in comparison with the Fano-resonance concept. We study analytically phonon transmission through internal crystal plane in a model cubic lattice of Si-like atoms, partially filled with Ge-like defect atoms. Such a plane can serve as interference phonon metamirror with the transmission antiresonances in the vicinities of eigenmode frequencies of Ge-like defect atoms in the terahertz frequency range. We predict the extraordinary phonon transmission induced by the two-path constructive interference of the lattice waves in resonance with the vibrations of rare host atoms, periodically distributed in the

Anomalous Doppler effects in bulk phononic crystal

International Nuclear Information System (INIS)

Cai Feiyan; He Zhaojian; Zhang Anqi; Ding Yiqun; Liu Zhengyou

2010-01-01

Doppler effects in simple cubic phononic crystal are studied theoretically and numerically. In addition to observing Doppler shifts from a moving source's frequencies inside the gap, we find that Doppler shifts can be multi-order, anisotropic, and the dominant order of shift depends on the band index that the source's frequency is in.

Toward single electron resolution phonon mediated ionization detectors

Energy Technology Data Exchange (ETDEWEB)

Mirabolfathi, Nader, E-mail: mirabolfathi@physics.tamu.edu [Department of Physics and Astronomy, Texas A& M University (United States); Harris, H. Rusty; Mahapatra, Rupak; Sundqvist, Kyle; Jastram, Andrew [Department of Physics and Astronomy, Texas A& M University (United States); Serfass, Bruno; Faiez, Dana; Sadoulet, Bernard [Department of Physics, University of California at Berkeley (United States)

2017-05-21

Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ∼14 eV{sub ee}. CDMSlite is currently the most sensitive experiment to WIMPs of mass ∼5 GeV/c{sup 2} but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a×2 Luke phonon gain, world best RMS resolution of sigma ∼7 eV{sub ee} for 0.25 kg (d=75 mm, h=1 cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25 mm) will reach a resolution of ∼2.8 eV{sub ee}. In order to achieve better resolution of ∼ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.

Polymorphic crystallization of metal-metalloid-glasses above the glass transition temperature

International Nuclear Information System (INIS)

Koster, U.; Schunemann, U.; Stephenson, G.B.; Brauer, S.; Sutton, M.

1992-01-01

Crystallization of metal-metalloid glasses is known to proceed by nucleation and growth processes. Using crystallization statistics in partially crystallized glasses, at temperatures below the glass transition temperature, time-dependent heterogeneous nucleation has been found to occur at a number of quenched-in nucleation sites. Close to the glass transition temperature crystallization proceeds so rapidly that partially crystallized microstructures could not be obtained. Initial results form fully crystallized glasses exhibit evidence for a transient homogeneous nucleation process at higher temperatures. These conclusions are derived post mortem. At there may be some change of the microstructure after crystallization is finished or during he subsequent quenching, it is desirable to directly obtain information during the early stages of crystallization. Recently reported work by Sutton et al. showed that structural changes can be observed in situ during crystallization by time-resolved x-ray diffraction on time scales as short as milliseconds. The aim o the paper is to present the authors study of the crystallization behavior at temperatures near the glass transition by in-situ x-ray diffraction studies and by microstructural analysis after rapid heating experiments. The results are compared to those derived from a computer model of the crystallization process

Glass transition, crystallization kinetics and pressure effect on crystallization of ZrNbCuNiBe bulk metallic glass

DEFF Research Database (Denmark)

Xing, P.F.; Zhuang, Yanxin; Wang, W.H.

2002-01-01

The glass transition behavior and crystallization kinetics of Zr48Nb8Cu14Ni12Be18 bulk metallic glass have been investigated by differential scanning calorimetry and x-ray powder diffraction (XRD). The activation energies of both glass transition and crystallization events have been obtained using...... the Kissinger method. Results indicate that this glass crystallizes by a three-stage reaction: (1) phase separation and primary crystallization of glass, (2) formation of intermetallic compounds, and (3) decomposition of intermetallic compounds and crystallization of residual amorphous phase. The pressure...

Generation, detection and spectroscopic studies of high-frequency nonequilibrium phonons in crystals

International Nuclear Information System (INIS)

Dennis, W.M.; Yen, W.M.

2007-01-01

In this article we will review studies conducted in the past two decades on the dynamic properties of high-frequency (THz) phonons generated monochromatically with high power far infrared (FIR) laser pulses using defect-induced phonon absorption and detected using a vibronic sideband spectrometer fashioned after that devised by Kaplyanskii, the honoree of this special issue. The temporal and spectral evolution of the phonon signature provides information on the mechanisms that dominate the relaxation of high-frequency phonons in real crystals

Electron-plasmon and electron-phonon satellites in the angle-resolved photoelectron spectra of n -doped anatase TiO2

Science.gov (United States)

Caruso, Fabio; Verdi, Carla; Poncé, Samuel; Giustino, Feliciano

2018-04-01

We develop a first-principles approach based on many-body perturbation theory to investigate the effects of the interaction between electrons and carrier plasmons on the electronic properties of highly doped semiconductors and oxides. Through the evaluation of the electron self-energy, we account simultaneously for electron-plasmon and electron-phonon coupling in theoretical calculations of angle-resolved photoemission spectra, electron linewidths, and relaxation times. We apply this methodology to electron-doped anatase TiO2 as an illustrative example. The simulated spectra indicate that electron-plasmon coupling in TiO2 underpins the formation of satellites at energies comparable to those of polaronic spectral features. At variance with phonons, however, the energy of plasmons and their spectral fingerprints depends strongly on the carrier concentration, revealing a complex interplay between plasmon and phonon satellites. The electron-plasmon interaction accounts for approximately 40% of the total electron-boson interaction strength, and it is key to improve the agreement with measured quasiparticle spectra.

Electron hopping and optic phonons in Eu3S4

International Nuclear Information System (INIS)

Guentherodt, G.

1981-01-01

Raman scattering on single crystals of Eu 3 S 4 does not show the allowed q=o phonon modes in the cubic phase and exhibits no new modes in the distorted low temperature phase (T 2- ions. This mode does not show any anomaly near the charge order -disorder phase transition Tsub(t)=186 K. Temperature tunable spin fluctuations associated with the temperature activated Eu 2+ → Eu 3+ electron hopping are detected in the scattering intensity, superimposed on the usual thermal spin disorder. (author)

Quantum Kinetic Theory and Applications Electrons, Photons, Phonons

CERN Document Server

Vasko, Fedir T

2006-01-01

This lecture-style monograph is addressed to several categories of readers. First, it will be useful for graduate students studying theory. Second, the topics covered should be interesting for postgraduate students of various specializations. Third, the researchers who want to understand the background of modern theoretical issues in more detail can find a number of useful results here. The phenomena covered involve kinetics of electron, phonon, and photon systems in solids. The dynamical properties and interactions of electrons, phonons, and photons are briefly described in Chapter 1. Further, in Chapters 2-8, the authors present the main theoretical methods: linear response theory, various kinetic equations for the quasiparticles under consideration, and diagram technique. The presentation of the key approaches is always accompanied by solutions of concrete problems to illustrate ways to apply the theory. The remaining chapters are devoted to various manifestations of quantum transport in solids. The choice...

Neutron-Phonon Interaction Studies in Copper, Zinc and Magnesium Single Crystals

International Nuclear Information System (INIS)

Maliszewski, E.; Sosnowski, J.; Blinowski, K.; Kozubowski, J.; Padlo, L.; Sledziewska, D.

1963-01-01

The phonon dispersion relations in copper single crystals has been studied by means of a triple-axis crystal neutron spectrometer. In the [100] direction the transversal branch, not reported in the papers of Cabie and Jacrot, has been found. This branch fits well to the recent data of sound velocity; however, it differs partly from the X-ray results of Jacobsen. For the longitudinal branch in the [100] direction the dispersion curve obtained by Cribier and Jacrot is lying well above the Jacobsen's curve, and the experimental points reported in the present paper support the results of Cribier and Jacrot. The phonon dispersion relations in zinc and magnesium single crystals has been studied using the cold neutron method and by means of a triple-axis crystal neutron spectrometer as well. The scattering surfaces in the [1010] plane were traced, the AT and AL branches found and the phonon dispersion relations in the [001] and [010] directions obtained. The results have been compared with those obtained by Johnson with X-rays. In the [001] direction the present results fit well lo Johnson's foe the AL branch. In the [010] direction for the AT branch a large discrepancy has been found between Johnson's and the present results. Some explanation of this discrepancy is given. Similar measurements in the same directions in magnesium single crystals are under way and will be reported. (author) [fr

Electron-phonon coupling at metal surfaces

International Nuclear Information System (INIS)

Hellsing, B.; Eiguren, A.; Chulkov, E.V.

2002-01-01

Chemical reactions at metal surfaces are influenced by inherent dissipative processes which involve energy transfer between the conduction electrons and the nuclear motion. We shall discuss how it is possible to model this electron-phonon coupling in order to estimate its importance. A relevant quantity for this investigation is the lifetime of surface-localized electron states. A surface state, quantum well state or surface image state is located in a surface-projected bandgap and becomes relatively sharp in energy. This makes a comparison between calculations and experimental data most attractive, with a possibility of resolving the origin of the lifetime broadening of electron states. To achieve more than an order of magnitude estimate we point out the importance of taking into account the phonon spectrum, electron surface state wavefunctions and screening of the electron-ion potential. (author)

Electron-phonon coupling in the rare-earth metals

DEFF Research Database (Denmark)

Skriver, Hans Lomholt; Mertig, I.

1990-01-01

-phonon parameters were calculated within the Gaspari-Gyorffy formulation. For the heavier rare earths Gd–Tm spin polarization was included both in the band-structure calculations and in the treatment of the electron-phonon coupling to take into account the spin splitting of the conduction electrons induced by the 4...

Electron-Mediated Phonon-Phonon Coupling Drives the Vibrational Relaxation of CO on Cu(100)

Science.gov (United States)

Novko, D.; Alducin, M.; Juaristi, J. I.

2018-04-01

We bring forth a consistent theory for the electron-mediated vibrational intermode coupling that clarifies the microscopic mechanism behind the vibrational relaxation of adsorbates on metal surfaces. Our analysis points out the inability of state-of-the-art nonadiabatic theories to quantitatively reproduce the experimental linewidth of the CO internal stretch mode on Cu(100) and it emphasizes the crucial role of the electron-mediated phonon-phonon coupling in this regard. The results demonstrate a strong electron-mediated coupling between the internal stretch and low-energy CO modes, but also a significant role of surface motion. Our nonadiabatic theory is also able to explain the temperature dependence of the internal stretch phonon linewidth, thus far considered a sign of the direct anharmonic coupling.

A comprehensive phononics of phonon assisted energy transfer in the Yb3+ aided upconversion luminescence of Tm3+ and Ho3+ in solids

International Nuclear Information System (INIS)

Debnath, Radhaballabh; Bose, Saptasree

2015-01-01

The theory of phonon assisted energy transfer is being widely used to explain the Yb 3+ ion aided normal and upconversion emission of various rare earth ions in different Yb 3+ co-doped solids. The reported phonon dynamics in many of these studies are either incomplete or erroneous. Here we report Yb 3+ aided upconversion luminescence properties of Tm 3+ and Ho 3+ in (Yb 3+ /Tm 3+ ) and (Yb 3+ /Ho 3+ ) co-doped two BaO–tellurite glasses and explain their phononics in the light of Dexter's theory by proposing a comprehensive scheme. The approach is valid for other systems of different phonon structures. - Highlights: • Yb 3+ aided upconversion luminescence properties of Tm 3+ and Ho 3+ in (Yb 3+ /Tm 3+ ) and (Yb 3+ /Ho 3+ ) co-doped two BaO–tellurite glasses, are reported. • Phonon assisted energy transfer in these systems are explained in the light of Dexter's theory by proposing a comprehensive scheme of phononics. • The approach is valid for other systems of different phonon structures

Lattice instability and soft phonons in single-crystal La/sub 2-//sub x/Sr/sub x/CuO4

International Nuclear Information System (INIS)

Boeni, P.; Axe, J.D.; Shirane, G.

1988-01-01

The dispersion of the low-lying phonon branches of several doped and undoped single crystals of La/sub 2-//sub x/Sr/sub x/CuO 4 have been investigated by using inelastic-neutron-scattering techniques. The zone-center modes are in good agreement with Raman measurements. The reported peaks in the phonon density of states show up at energies that correspond to extrema in the dispersion curves of the transverse and longitudinal acoustic branches near the zone boundary. The tetragonal-to-orthorhombic phase transition is caused by a softening of transverse-optic-phonon mode at the X point. The rotational nature of the soft mode leads to moderate weak electron-phonon coupling and the mode is unlikely to enhance significantly conventional phonon mediated superconductivity. We did not observe any evidence for the predicted breathing-mode instability near the zone boundary

Avoided crossing of rattler modes in thermoelectric materials

DEFF Research Database (Denmark)

Christensen, Mogens; Abrahamsen, Asger Bech; Christensen, Niels Bech

2008-01-01

thermoelectric materials, and the challenge is to limit the conduction of heat by phonons, without simultaneously reducing the charge transport. This is named the 'phonon glass-electron crystal' concept and may be realized in host-guest systems. The guest entities are believed to have independent oscillations......, so-called rattler modes, which scatter the acoustic phonons and reduce the thermal conductivity. We have investigated the phonon dispersion relation in the phonon glass-electron crystal material Ba8Ga16Ge30 using neutron triple-axis spectroscopy. The results disclose unambiguously the theoretically...

Phonon limited electronic transport in Pb

Science.gov (United States)

Rittweger, F.; Hinsche, N. F.; Mertig, I.

2017-09-01

We present a fully ab initio based scheme to compute electronic transport properties, i.e. the electrical conductivity σ and thermopower S, in the presence of electron-phonon interaction. We explicitly investigate the \

Electron mobility variance in the presence of an electric field: Electron-phonon field-induced tunnel scattering

International Nuclear Information System (INIS)

Melkonyan, S.V.

2012-01-01

The problem of electron mobility variance is discussed. It is established that in equilibrium semiconductors the mobility variance is infinite. It is revealed that the cause of the mobility variance infinity is the threshold of phonon emission. The electron-phonon interaction theory in the presence of an electric field is developed. A new mechanism of electron scattering, called electron-phonon field-induced tunnel (FIT) scattering, is observed. The effect of the electron-phonon FIT scattering is explained in terms of penetration of the electron wave function into the semiconductor band gap in the presence of an electric field. New and more general expressions for the electron-non-polar optical phonon scattering probability and relaxation time are obtained. The results show that FIT transitions have principle meaning for the mobility fluctuation theory: mobility variance becomes finite.

Long-wavelength optical phonon behavior in uniaxial strained graphene: Role of electron-phonon interaction

OpenAIRE

Assili, Mohamed; Haddad, Sonia

2014-01-01

We derive the frequency shifts and the broadening of $\\Gamma$ point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic...

Electron-phonon relaxation and excited electron distribution in gallium nitride

Energy Technology Data Exchange (ETDEWEB)

Zhukov, V. P. [Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, Pervomayskaya st. 91, Yekaterinburg (Russian Federation); Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tyuterev, V. G., E-mail: valtyut00@mail.ru [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State Pedagogical University, Kievskaya st. 60, Tomsk (Russian Federation); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain); Echenique, P. M. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain)

2016-08-28

We develop a theory of energy relaxation in semiconductors and insulators highly excited by the long-acting external irradiation. We derive the equation for the non-equilibrium distribution function of excited electrons. The solution for this function breaks up into the sum of two contributions. The low-energy contribution is concentrated in a narrow range near the bottom of the conduction band. It has the typical form of a Fermi distribution with an effective temperature and chemical potential. The effective temperature and chemical potential in this low-energy term are determined by the intensity of carriers' generation, the speed of electron-phonon relaxation, rates of inter-band recombination, and electron capture on the defects. In addition, there is a substantial high-energy correction. This high-energy “tail” largely covers the conduction band. The shape of the high-energy “tail” strongly depends on the rate of electron-phonon relaxation but does not depend on the rates of recombination and trapping. We apply the theory to the calculation of a non-equilibrium distribution of electrons in an irradiated GaN. Probabilities of optical excitations from the valence to conduction band and electron-phonon coupling probabilities in GaN were calculated by the density functional perturbation theory. Our calculation of both parts of distribution function in gallium nitride shows that when the speed of the electron-phonon scattering is comparable with the rate of recombination and trapping then the contribution of the non-Fermi “tail” is comparable with that of the low-energy Fermi-like component. So the high-energy contribution can essentially affect the charge transport in the irradiated and highly doped semiconductors.

Phonon spectra, electronic, and thermodynamic properties of WS2 nanotubes.

Science.gov (United States)

Evarestov, Robert A; Bandura, Andrei V; Porsev, Vitaly V; Kovalenko, Alexey V

2017-11-15

Hybrid density functional theory calculations are performed for the first time on the phonon dispersion and thermodynamic properties of WS 2 -based single-wall nanotubes. Symmetry analysis is presented for phonon modes in nanotubes using the standard (crystallographic) factorization for line groups. Symmetry and the number of infra-red and Raman active modes in achiral WS 2 nanotubes are given for armchair and zigzag chiralities. It is demonstrated that a number of infrared and Raman active modes is independent on the nanotube diameter. The zone-folding approach is applied to find out an impact of curvature on electron and phonon band structure of nanotubes rolled up from the monolayer. Phonon frequencies obtained both for layers and nanotubes are used to compute the thermal contributions to their thermodynamic functions. The temperature dependences of energy, entropy, and heat capacity of nanotubes are estimated with respect to those of the monolayer. The role of phonons in the stability estimation of nanotubes is discussed based on Helmholtz free energy calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Effect of the Substrate on Phonon Properties of Graphene Estimated by Raman Spectroscopy

Science.gov (United States)

Tivanov, M. S.; Kolesov, E. A.; Korolik, O. V.; Saad, A. M.; Komissarov, I. V.

2018-01-01

Low-temperature Raman studies of supported graphene are presented. A linear temperature dependence of 2D peak linewidths was observed with the coefficients of 0.036 and 0.033 cm^{-1}/K for graphene on copper and glass substrates, respectively, while G peak linewidths remained unchanged throughout the whole temperature range. The different values observed for graphene on glass and copper substrates were explained in terms of the substrate effect on phonon-phonon and electron-phonon interaction properties of the material. The results of the present study can be used to consider substrate effects on phonon transport in graphene for nanoelectronic device engineering.

Signature of electron-phonon interaction in high temperature superconductors

Directory of Open Access Journals (Sweden)

Vinod Ashokan

2011-09-01

Full Text Available The theory of thermal conductivity of high temperature superconductors (HTS based on electron and phonon line width (life times formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high Tc superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La1.8Sr0.2CuO4 in the temperature range 0 − 200K. The theory is equally and successfully applicable to all other high Tc superconductors.

Surface acoustic waves in two dimensional phononic crystal with anisotropic inclusions

Directory of Open Access Journals (Sweden)

Ketata H.

2012-06-01

Full Text Available An analysis is given to the band structure of the two dimensional solid phononic crystal considered as a semi infinite medium. The lattice includes an array of elastic anisotropic materials with different shapes embedded in a uniform matrix. For illustration two kinds of phononic materials are assumed. A particular attention is devoted to the computational procedure which is mainly based on the plane wave expansion (PWE method. It has been adapted to Matlab environment. Numerical calculations of the dispersion curves have been achieved by introducing particular functions which transform motion equations into an Eigen value problem. Significant improvements are obtained by increasing reasonably the number of Fourier components even when a large elastic mismatch is assumed. Such approach can be generalized to different types of symmetry and permit new physical properties as piezoelectricity to be added. The actual semi infinite phononic structure with a free surface has been shown to support surface acoustic waves (SAW. The obtained dispersion curves reveal band gaps in the SAW branches. It has been found that the influence, of the filling factor and anisotropy on their band gaps, is different from that of bulk waves.

Electron-phonon coupling and superconductivity in the (4/3)-monolayer of Pb on Si(111): Role of spin-orbit interaction

Science.gov (United States)

Sklyadneva, I. Yu.; Heid, R.; Bohnen, K.-P.; Echenique, P. M.; Chulkov, E. V.

2018-05-01

The effect of spin-orbit coupling on the electron-phonon interaction in a (4/3)-monolayer of Pb on Si(111) is investigated within the density-functional theory and linear-response approach in the mixed-basis pseudopotential representation. We show that the spin-orbit interaction produces a large weakening of the electron-phonon coupling strength, which appears to be strongly overestimated in the scalar relativistic calculations. The effect of spin-orbit interaction is largely determined by the induced modification of Pb electronic bands and a stiffening of the low-energy part of phonon spectrum, which favor a weakening of the electron-phonon coupling strength. The state-dependent strength of the electron-phonon interaction in occupied Pb electronic bands varies depending on binding energy rather than electronic momentum. It is markedly larger than the value averaged over electron momentum because substrate electronic bands make a small contribution to the phonon-mediated scattering and agrees well with the experimental data.

Omnidirectional refractive devices for flexural waves based on graded phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Torrent, Daniel, E-mail: daniel.torrent@iemn.univ-lille1.fr; Pennec, Yan; Djafari-Rouhani, Bahram [Institut d' Electronique, de Microléctronique et de Nanotechnologie, UMR CNRS 8520, Université de Lille 1, 59655 Villeneuve d' Ascq (France)

2014-12-14

Different omnidirectional refractive devices for flexural waves in thin plates are proposed and numerically analyzed. Their realization is explained by means phononic crystal plates, where a previously developed homogenization theory is employed for the design of graded index refractive devices. These devices consist of a circular cluster of inclusions with a properly designed gradient in their radius. With this approach, the Luneburg and Maxwell lenses and a family of beam splitters for flexural waves are proposed and analyzed. Results show that these devices work properly in a broadband frequency region, being therefore an efficient approach for the design of refractive devices specially interesting for nano-scale applications.

Phonon properties of americium phosphide

Energy Technology Data Exchange (ETDEWEB)

Arya, B. S., E-mail: bsarya13@yahoo.com [Department of Physics, Govt. Narmada P G College, Hoshangabad -461001 (India); Aynyas, Mahendra [Department of Physics, C. S. A. Govt. P. G. College Sehore-46601 (India); Sanyal, S. P. [Department of Physics, Barkatullah University, Bhopal-462026 (India)

2016-05-23

Phonon properties of AmP have been studied by using breathing shell models (BSM) which includes breathing motion of electrons of the Am atoms due to f-d hybridization. The phonon dispersion curves, specific heat calculated from present model. The calculated phonon dispersion curves of AmP are presented follow the same trend as observed in uranium phosphide. We discuss the significance of this approach in predicting the phonon dispersion curves of these compounds and examine the role of electron-phonon interaction.

First-principles method for electron-phonon coupling and electron mobility

DEFF Research Database (Denmark)

Gunst, Tue; Markussen, Troels; Stokbro, Kurt

2016-01-01

We present density functional theory calculations of the phonon-limited mobility in n-type monolayer graphene, silicene, and MoS2. The material properties, including the electron-phonon interaction, are calculated from first principles. We provide a detailed description of the normalized full......-band relaxation time approximation for the linearized Boltzmann transport equation (BTE) that includes inelastic scattering processes. The bulk electron-phonon coupling is evaluated by a supercell method. The method employed is fully numerical and does therefore not require a semianalytic treatment of part...... of the problem and, importantly, it keeps the anisotropy information stored in the coupling as well as the band structure. In addition, we perform calculations of the low-field mobility and its dependence on carrier density and temperature to obtain a better understanding of transport in graphene, silicene...

Calculation of dynamic and electronic properties of perfect and defect crystals by semiempirical quantum mechanical methods

International Nuclear Information System (INIS)

Zunger, A.

1975-07-01

Semiempirical all-valence-electron LCAO methods, that were previously used to study the electronic structure of molecules are applied to three problems in solid state physics: the electronic band structure of covalent crystals, point defect problems in solids and lattice dynamical study of molecular crystals. Calculation methods for the electronic band structure of regular solids are introduced and problems regarding the computation of the density matrix in solids are discussed. Three models for treating the electronic eigenvalue problem in the solid, within the proposed calculation schemes, are discussed and the proposed models and calculation schemes are applied to the calculation of the electronic structure of several solids belonging to different crystal types. The calculation models also describe electronic properties of deep defects in covalent insulating crystals. The possible usefulness of the semieipirical LCAO methods in determining the first order intermolecular interaction potential in solids and an improved model for treating the lattice dynamics and related thermodynamical properties of molecular solids are presented. The improved lattice dynamical is used to compute phonon dispersion curves, phonon density of states, stable unit cell structure, lattice heat capacity and thermal crystal parameters, in α and γ-N 2 crystals, using the N 2 -N 2 intermolecular interaction potential that has been computed from the semiempirical LCAO methods. (B.G.)

Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot

Science.gov (United States)

Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Song, Ruifang

2015-01-01

In this paper, a novel two-dimensional phononic crystal composed of periodic Jerusalem cross slot in air matrix with a square lattice is presented. The dispersion relations and the transmission coefficient spectra are calculated by using the finite element method based on the Bloch theorem. The formation mechanisms of the band gaps are analyzed based on the acoustic mode analysis. Numerical results show that the proposed phononic crystal structure can yield large band gaps in the low-frequency range. The formation mechanism of opening the acoustic band gaps is mainly attributed to the resonance modes of the cavities inside the Jerusalem cross slot structure. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the band gaps can be modulated in an extremely large frequency range by the geometry parameters such as the slot length and width. These properties of acoustic waves in the proposed phononic crystals can potentially be applied to optimize band gaps and generate low-frequency filters and waveguides.

Analysis of Longitudinal Waves in Rod-Type Piezoelectric Phononic Crystals

Directory of Open Access Journals (Sweden)

Longfei Li

2016-04-01

Full Text Available Phononic crystals can be used to control elastic waves due to their frequency bands. This paper analyzes the passive and active control as well as the dispersion properties of longitudinal waves in rod-type piezoelectric phononic crystals over large frequency ranges. Based on the Love rod theory for modeling the longitudinal wave motions in the constituent rods and the method of reverberation-ray matrix (MRRM for deriving the member transfer matrices of the constituent rods, a modified transfer matrix method (MTMM is proposed for the analysis of dispersion curves by combining with the Floquet–Bloch principle and for the calculation of transmission spectra. Numerical examples are provided to validate the proposed MTMM for analyzing the band structures in both low and high frequency ranges. The passive control of longitudinal-wave band structures is studied by discussing the influences of the electrode’s thickness, the Poisson’s effect and the elastic rod inserts in the unit cell. The influences of electrical boundaries (including electric-open, applied electric capacity, electric-short and applied feedback control conditions on the band structures are investigated to illustrate the active control scheme. From the calculated comprehensive frequency spectra over a large frequency range, the dispersion properties of the characteristic longitudinal waves in rod-type piezoelectric phononic crystals are summarized.

Optical-phonon-induced frictional drag in coupled two-dimensional electron gases

DEFF Research Database (Denmark)

Hu, Ben Yu-Kuang

1998-01-01

The role of optical phonons in frictional drag between two adjacent but electrically isolated two-dimensional electron gases is investigated. Since the optical phonons in III-V materials have a considerably larger coupling to electrons than acoustic phonons (which are the dominant drag mechanism ...

Research on the Band Gap Characteristics of Two-Dimensional Phononic Crystals Microcavity with Local Resonant Structure

Directory of Open Access Journals (Sweden)

Mao Liu

2015-01-01

Full Text Available A new two-dimensional locally resonant phononic crystal with microcavity structure is proposed. The acoustic wave band gap characteristics of this new structure are studied using finite element method. At the same time, the corresponding displacement eigenmodes of the band edges of the lowest band gap and the transmission spectrum are calculated. The results proved that phononic crystals with microcavity structure exhibited complete band gaps in low-frequency range. The eigenfrequency of the lower edge of the first gap is lower than no microcavity structure. However, for no microcavity structure type of quadrilateral phononic crystal plate, the second band gap disappeared and the frequency range of the first band gap is relatively narrow. The main reason for appearing low-frequency band gaps is that the proposed phononic crystal introduced the local resonant microcavity structure. This study provides a good support for engineering application such as low-frequency vibration attenuation and noise control.

Flexural phonon limited phonon drag thermopower in bilayer graphene

Science.gov (United States)

Ansari, Mohd Meenhaz; Ashraf, SSZ

2018-05-01

We investigate the phonon drag thermopower from flexural phonons as a function of electron temperature and carrier concentration in the Bloch-Gruneisen regime in non-strained bilayer graphene using Boltzmann transport equation approach. The flexural phonons are expected to be the major source of intrinsic scattering mechanism in unstrained bilayer graphene due to their large density. The flexural phonon modes dispersion relation is quadratic so these low energy flexural phonons abound at room temperature and as a result deform the bilayer graphene sheet in the out of plane direction and affects the transport properties. We also produce analytical result for phonon-drag thermopower from flexural phonons and find that phonon-drag thermopower depicts T2 dependence on temperature and n-1 on carrier concentration.

Resonance laser-plasma excitation of coherent terahertz phonons in the bulk of fluorine-bearing crystals under high-intensity femtosecond laser irradiation

Energy Technology Data Exchange (ETDEWEB)

Potemkin, F V; Mareev, E I [International Laser Center, M. V. Lomonosov Moscow State University, Moscow (Russian Federation); Khodakovskii, N G [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Mikheev, P M

2013-08-31

The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation. (interaction of laser radiation with matter)

Effect of Holstein phonons on the electronic properties of graphene

International Nuclear Information System (INIS)

Stauber, T; Peres, N M R

2008-01-01

We obtain the self-energy of the electronic propagator due to the presence of Holstein polarons within the first Born approximation. This leads to a renormalization of the Fermi velocity of 1%. We further compute the optical conductivity of the system at the Dirac point and at finite doping within the Kubo formula. We argue that the effects due to Holstein phonons are negligible and that the Boltzmann approach, which does not include inter-band transitions and can thus not treat optical phonons due to their high energy of ℎω 0 ∼ 0.1-0.2 eV, remains valid

Spectral element method for band-structure calculations of 3D phononic crystals

International Nuclear Information System (INIS)

Shi, Linlin; Liu, Na; Zhou, Jianyang; Zhou, Yuanguo; Wang, Jiamin; Liu, Qing Huo

2016-01-01

The spectral element method (SEM) is a special kind of high-order finite element method (FEM) which combines the flexibility of a finite element method with the accuracy of a spectral method. In contrast to the traditional FEM, the SEM exhibits advantages in the high-order accuracy as the error decreases exponentially with the increase of interpolation degree by employing the Gauss–Lobatto–Legendre (GLL) polynomials as basis functions. In this study, the spectral element method is developed for the first time for the determination of band structures of 3D isotropic/anisotropic phononic crystals (PCs). Based on the Bloch theorem, we present a novel, intuitive discretization formulation for Navier equation in the SEM scheme for periodic media. By virtue of using the orthogonal Legendre polynomials, the generalized eigenvalue problem is converted to a regular one in our SEM implementation to improve the efficiency. Besides, according to the specific geometry structure, 8-node and 27-node hexahedral elements as well as an analytic mesh have been used to accurately capture curved PC models in our SEM scheme. To verify its accuracy and efficiency, this study analyses the phononic-crystal plates with square and triangular lattice arrangements, and the 3D cubic phononic crystals consisting of simple cubic (SC), bulk central cubic (BCC) and faced central cubic (FCC) lattices with isotropic or anisotropic scatters. All the numerical results considered demonstrate that SEM is superior to the conventional FEM and can be an efficient alternative method for accurate determination of band structures of 3D phononic crystals. (paper)

Lattice dynamics and electron/phonon interactions in epitaxial transition-metal nitrides

Science.gov (United States)

Mei, Antonio Rodolph Bighetti

Transition metal (TM) nitrides, due to their unique combination of remarkable physical properties and simple NaCl structure, are presently utilized in a broad range of applications and as model systems in the investigation of complex phenomena. Group-IVB nitrides TiN, ZrN, and HfN have transport properties which include superconductivity and high electrical conductivity; consequentially, they have become technologically important as electrodes and contacts in the semiconducting and superconducting industries. The Group-VB nitride VN, which exhibits enhanced ductility, is a fundamental component in superhard and tough nanostructured hard coatings. In this thesis, I investigate the lattice dynamics responsible for controlling superconductivity and electrical conductivities in Group-IVB nitrides and elasticity and structural stability of the NaCl-structure Group-VB nitride VN. Our group has already synthesized high-quality epitaxial TiN, HfN, and CeN layers on MgO(001) substrates. By irradiating the growth surface with high ion fluxes at energies below the bulk lattice-atom displacement threshold, dense epitaxial single crystal TM nitride films with extremely smooth surfaces have been grown using ultra-high vacuum magnetically-unbalanced magnetron sputter deposition. Using this approach, I completed the Group-IVB nitride series by growing epitaxial ZrN/MgO(001) films and then grew Group-VB nitride VN films epitaxially on MgO(001), MgO(011), and MgO(111). The combination of high-resolution x-ray diffraction (XRD) reciprocal lattice maps (RLMs), high-resolution cross-sectional transmission electron microscopy (HR-XTEM), and selected-area electron diffraction (SAED) show that single-crystal stoichiometric ZrN films grown at 450 °C are epitaxially oriented cube-on-cube with respect to their MgO(001) substrates, (001) ZrN||(001)MgO and [100]ZrN||[100]MgO. The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm. X-ray reflectivity results reveal that

Electron and Phonon Transport in Molecular Junctions

DEFF Research Database (Denmark)

Li, Qian

Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions....... The system we are interested in here are π-stacked molecules connected with two semi-infinite leads. π-stacked aromatic rings, connected via π-π electronic coupling, provides a rather soft mechanical bridge while maintaining high electronic conductivity. We investigate electron transport...... transmission at the Fermi energy. We propose and analyze a way of using π   stacking to design molecular junctions to control heat transport. We develop a simple model system to identify optimal parameter regimes and then use density functional theory (DFT) to extract model parameters for a number of specific...

Phonon limited electronic transport in Pb

DEFF Research Database (Denmark)

Rittweger, Florian; Hinsche, Nicki Frank; Mertig, Ingrid

2017-01-01

We present a fully ab initio based scheme to compute electronic transport properties, i.e. the electrical conductivity σ and thermopower S, in the presence of electron-phonon interaction. We explicitly investigate the k-dependent structure of the Éliashberg spectral function, the coupling strength...

Phonon-assisted hopping of an electron on a Wannier-Stark ladder in a strong electric field

International Nuclear Information System (INIS)

Emin, D.; Hart, C.F.

1987-01-01

With the application of a spatially constant electric field, the degeneracy of electronic energy levels of geometrically equivalent sites of a crystal is generally lifted. As a result, the electric field causes the electronic eigenstates of a one-dimensional periodic chain to become localized. In particular, they are Wannier-Stark states. With sufficiently large electric-field strengths these states become sufficiently well localized that it becomes appropriate to consider electronic transport to occur via a succession of phonon-assisted hops between the localized Wannier-Stark states. In this paper, we present calculations of the drift velocity arising from acoustic- and optical-phonon-assisted hopping motion between Wannier-Stark states. When the intersite electronic transfer energy is sufficiently small so that the Wannier-Stark states are essentially each confined to a single atomic site, the transport reduces to that of a small polaron. In this regime, while the drift velocity initially rises with increasing electric field strength, the drift velocity ultimately falls with increasing electric-field strength at extremely large electric fields. More generally, for common values of the electronic bandwidth and electric field strength, the Wannier-Stark states span many sites. At sufficiently large electric fields, the energy separation between Wannier-Stark states exceeds the energy uncertainty associated with the carrier's interaction with phonons. Then, it is appropriate to treat the electronic transport in terms of phonon-assisted hopping between Wannier-Stark states. The resulting high-field drift velocity falls with increasing field strength in a series of steps. Thus, we find a structured negative differential mobility at large electric fields

Electron-phonon interaction and its manifestation in high-temperature superconductors

International Nuclear Information System (INIS)

Maksimov, E.G.

1995-01-01

Different types of band structure approaches for a description of electrons in systems with strong correlations are discussed. It is shown that all methods considered give different electron energy dispersions and Fermi surfaces. The good agreement between measured Fermi surfaces and those calculated by LDA shows that the spatial dispersion of the correlation interaction is not so important in HTSC systems. The same conclusion can be obtained from the optical and photoemission spectra. It is shown that the most important contribution beyond a band structure approach is given by an energy dependence of the electron self-energy. The most likely interaction responsible for this energy dependence is the electron-phonon one. Evidences about this fact are given

Designing Phononic Crystals with Wide and Robust Band Gaps

Science.gov (United States)

Jia, Zian; Chen, Yanyu; Yang, Haoxiang; Wang, Lifeng

2018-04-01

Phononic crystals (PnCs) engineered to manipulate and control the propagation of mechanical waves have enabled the design of a range of novel devices, such as waveguides, frequency modulators, and acoustic cloaks, for which wide and robust phononic band gaps are highly preferable. While numerous PnCs have been designed in recent decades, to the best of our knowledge, PnCs that possess simultaneous wide and robust band gaps (to randomness and deformations) have not yet been reported. Here, we demonstrate that by combining the band-gap formation mechanisms of Bragg scattering and local resonances (the latter one is dominating), PnCs with wide and robust phononic band gaps can be established. The robustness of the phononic band gaps are then discussed from two aspects: robustness to geometric randomness (manufacture defects) and robustness to deformations (mechanical stimuli). Analytical formulations further predict the optimal design parameters, and an uncertainty analysis quantifies the randomness effect of each designing parameter. Moreover, we show that the deformation robustness originates from a local resonance-dominant mechanism together with the suppression of structural instability. Importantly, the proposed PnCs require only a small number of layers of elements (three unit cells) to obtain broad, robust, and strong attenuation bands, which offer great potential in designing flexible and deformable phononic devices.

Designing Phononic Crystals with Wide and Robust Band Gaps

Energy Technology Data Exchange (ETDEWEB)

Chen, Yanyu [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jia, Zian [State University of New York at Stony Brook; Yang, Haoxiang [State University of New York at Stony Brook; Wang, Lifeng [State University of New York at Stony Brook

2018-04-16

Phononic crystals (PnCs) engineered to manipulate and control the propagation of mechanical waves have enabled the design of a range of novel devices, such as waveguides, frequency modulators, and acoustic cloaks, for which wide and robust phononic band gaps are highly preferable. While numerous PnCs have been designed in recent decades, to the best of our knowledge, PnCs that possess simultaneous wide and robust band gaps (to randomness and deformations) have not yet been reported. Here, we demonstrate that by combining the band-gap formation mechanisms of Bragg scattering and local resonances (the latter one is dominating), PnCs with wide and robust phononic band gaps can be established. The robustness of the phononic band gaps are then discussed from two aspects: robustness to geometric randomness (manufacture defects) and robustness to deformations (mechanical stimuli). Analytical formulations further predict the optimal design parameters, and an uncertainty analysis quantifies the randomness effect of each designing parameter. Moreover, we show that the deformation robustness originates from a local resonance-dominant mechanism together with the suppression of structural instability. Importantly, the proposed PnCs require only a small number of layers of elements (three unit cells) to obtain broad, robust, and strong attenuation bands, which offer great potential in designing flexible and deformable phononic devices.

Band structures in Sierpinski triangle fractal porous phononic crystals

International Nuclear Information System (INIS)

Wang, Kai; Liu, Ying; Liang, Tianshu

2016-01-01

In this paper, the band structures in Sierpinski triangle fractal porous phononic crystals (FPPCs) are studied with the aim to clarify the effect of fractal hierarchy on the band structures. Firstly, one kind of FPPCs based on Sierpinski triangle routine is proposed. Then the influence of the porosity on the elastic wave dispersion in Sierpinski triangle FPPCs is investigated. The sensitivity of the band structures to the fractal hierarchy is discussed in detail. The results show that the increase of the hierarchy increases the sensitivity of ABG (Absolute band gap) central frequency to the porosity. But further increase of the fractal hierarchy weakens this sensitivity. On the same hierarchy, wider ABGs could be opened in Sierpinski equilateral triangle FPPC; whilst, a lower ABG could be opened at lower porosity in Sierpinski right-angled isosceles FPPCs. These results will provide a meaningful guidance in tuning band structures in porous phononic crystals by fractal design.

Band structures in Sierpinski triangle fractal porous phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Wang, Kai; Liu, Ying, E-mail: yliu5@bjtu.edu.cn; Liang, Tianshu

2016-10-01

In this paper, the band structures in Sierpinski triangle fractal porous phononic crystals (FPPCs) are studied with the aim to clarify the effect of fractal hierarchy on the band structures. Firstly, one kind of FPPCs based on Sierpinski triangle routine is proposed. Then the influence of the porosity on the elastic wave dispersion in Sierpinski triangle FPPCs is investigated. The sensitivity of the band structures to the fractal hierarchy is discussed in detail. The results show that the increase of the hierarchy increases the sensitivity of ABG (Absolute band gap) central frequency to the porosity. But further increase of the fractal hierarchy weakens this sensitivity. On the same hierarchy, wider ABGs could be opened in Sierpinski equilateral triangle FPPC; whilst, a lower ABG could be opened at lower porosity in Sierpinski right-angled isosceles FPPCs. These results will provide a meaningful guidance in tuning band structures in porous phononic crystals by fractal design.

Coupled electron-phonon transport from molecular dynamics with quantum baths

DEFF Research Database (Denmark)

Lu, Jing Tao; Wang, J. S.

2009-01-01

Based on generalized quantum Langevin equations for the tight-binding wavefunction amplitudes and lattice displacements, electron and phonon quantum transport are obtained exactly using molecular dynamics (MD) in the ballistic regime. The electron-phonon interactions can be handled with a quasi...

Analysis of Bending Waves in Phononic Crystal Beams with Defects

Directory of Open Access Journals (Sweden)

Yongqiang Guo

2018-01-01

Full Text Available Existing investigations on imperfect phononic crystal beams mainly concern periodic multi-span beams carrying either one or two channel waves with random or deterministic disorder in span-length. This paper studies the two channel bending waves in phononic crystal beams consisting of many phases of materials with defects introduced as one structural segment having different cross-sectional dimensions or material parameters. The method of reverberation-ray matrix (MRRM based on the Timoshenko beam theory, which can conduct high-frequency analysis, is extended for the theoretical analysis of dispersion and transmission of bending waves. The supercell technique and the Floquet–Bloch theorem are adopted for modeling the dispersion characteristics, and the whole finite structural model is used to calculate the transmission spectra. Experimental measurements and numerical calculations are provided to validate the displacement transmission obtained by the proposed MRRM, with the effect of damping on transmission spectra being concerned. The high-frequency calculation applicability of the proposed MRRM is also confirmed by comparing the present results with the corresponding ones either using the transfer matrix method (TMM or MRRM based on Euler—Bernoulli beam theory. The influences of defect size, defect form, and unit-cell number on the transmission spectra and the band structures are discussed. The drawn conclusions may be useful for designing or evaluating the defected phononic crystal beams in bending wave control. In addition, our conclusions are especially potential for identifying the defect location through bending wave signals.

Thermal conductance of a surface phonon-polariton crystal made up of polar nanorods

Energy Technology Data Exchange (ETDEWEB)

Ordonez-Miranda, Jose; Joulain, Karl; Ezzahri, Younes [Univ. de Poitiers, Futuroscope Chasseneuil (France). Inst. Pprime, CNRS

2017-05-01

We demonstrate that the energy transport of surface phonon-polaritons can be large enough to be observable in a crystal made up of a three-dimensional assembly of nanorods of silicon carbide. The ultralow phonon thermal conductivity of this nanostructure along with its high surface area-to-volume ratio allows the predominance of the polariton energy over that generated by phonons. The dispersion relation, propagation length, and thermal conductance of polaritons are numerically determined as functions of the radius and temperature of the nanorods. It is shown that the thermal conductance of a crystal with nanorods at 500 K and diameter (length) of 200 nm (20 μm) is 0.55 nW.K{sup -1}, which is comparable to the quantum of thermal conductance of polar nanowires.

Experimental and theoretical investigation of the elastic moduli of silicate glasses and crystals

Science.gov (United States)

Philipps, Katharina; Stoffel, Ralf Peter; Dronskowski, Richard; Conradt, Reinhard

2017-02-01

A combined quantum-mechanical and thermodynamic approach to the mechanical properties of multicomponent silicate glasses is presented. Quantum chemical calculations based on density-functional theory (DFT) on various silicate systems were performed to explore the crystalline polymorphs existing for a given chemical composition. These calculations reproduced the properties of known polymorphs even in systems with extensive polymorphism, like MgSiO3. Properties resting on the atomic and electronic structure, i.e., molar volumes (densities) and bulk moduli were predicted correctly. The theoretical data (molar equilibrium volumes, bulk moduli) were then used to complement the available experimental data. In a phenomenological evaluation, experimental data of bulk moduli, a macroscopic property resting on phononic structure, were found to linearly scale with the ratios of atomic space demand to actual molar volume in a universal way. Silicates ranging from high-pressure polymorphs to glasses were represented by a single master line. This suggests that above the Debye limit (in practice: above room temperature), the elastic waves probe the short range order coordination polyhedra and their next-neighbor linkage only, while the presence or absence of an extended translational symmetry is irrelevant. As a result, glasses can be treated - with respect to the properties investigated - as commensurable members of polymorphic series. Binary glasses fit the very same line as their one-component end-members, again both in the crystalline and glassy state. Finally, it is shown that the macroscopic properties of multicomponent glasses also are linear superpositions of the properties of their constitutional phases (as determined from phase diagrams or by thermochemical calculations) taken in their respective glassy states. This is verified experimentally for heat capacities and Young’s moduli of industrial glass compositions. It can be concluded, that the combined quantum

Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

Energy Technology Data Exchange (ETDEWEB)

Zhou, X.J.

2010-04-30

thought possible only a decade ago. This revolution of the ARPES technique and its scientific impact result from dramatic advances in four essential components: instrumental resolution and efficiency, sample manipulation, high quality samples and well-matched scientific issues. The purpose of this treatise is to go through the prominent results obtained from ARPES on cuprate superconductors. Because there have been a number of recent reviews on the electronic structures of high-T{sub c} materials, we will mainly present the latest results not covered previously, with a special attention given on the electron-phonon interaction in cuprate superconductors. What has emerged is rich information about the anomalous electron-phonon interaction well beyond the traditional views of the subject. It exhibits strong doping, momentum and phonon symmetry dependence, and shows complex interplay with the strong electron-electron interaction in these materials. ARPES experiments have been instrumental in identifying the electronic structure, observing and detailing the electron-phonon mode coupling behavior, and mapping the doping evolution of the high-T{sub c} cuprates. The spectra evolve from the strongly coupled, polaronic spectra seen in underdoped cuprates to the Migdal-Eliashberg like spectra seen in the optimally and overdoped cuprates. In addition to the marked doping dependence, the cuprates exhibit pronounced anisotropy with direction in the Brillouin zone: sharp quasiparticles along the nodal direction that broaden significantly in the anti-nodal region of the underdoped cuprates, an anisotropic electron-phonon coupling vertex for particular modes identified in the optimal and overdoped compounds, and preferential scattering across the two parallel pieces of Fermi surface in the antinodal region for all doping levels. This also contributes to the pseudogap effect. To the extent that the Migdal-Eliashberg picture applies, the spectra of the cuprates bear resemblance to that

Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

International Nuclear Information System (INIS)

Zhou, X.J.

2010-01-01

only a decade ago. This revolution of the ARPES technique and its scientific impact result from dramatic advances in four essential components: instrumental resolution and efficiency, sample manipulation, high quality samples and well-matched scientific issues. The purpose of this treatise is to go through the prominent results obtained from ARPES on cuprate superconductors. Because there have been a number of recent reviews on the electronic structures of high-T c materials, we will mainly present the latest results not covered previously, with a special attention given on the electron-phonon interaction in cuprate superconductors. What has emerged is rich information about the anomalous electron-phonon interaction well beyond the traditional views of the subject. It exhibits strong doping, momentum and phonon symmetry dependence, and shows complex interplay with the strong electron-electron interaction in these materials. ARPES experiments have been instrumental in identifying the electronic structure, observing and detailing the electron-phonon mode coupling behavior, and mapping the doping evolution of the high-T c cuprates. The spectra evolve from the strongly coupled, polaronic spectra seen in underdoped cuprates to the Migdal-Eliashberg like spectra seen in the optimally and overdoped cuprates. In addition to the marked doping dependence, the cuprates exhibit pronounced anisotropy with direction in the Brillouin zone: sharp quasiparticles along the nodal direction that broaden significantly in the anti-nodal region of the underdoped cuprates, an anisotropic electron-phonon coupling vertex for particular modes identified in the optimal and overdoped compounds, and preferential scattering across the two parallel pieces of Fermi surface in the antinodal region for all doping levels. This also contributes to the pseudogap effect. To the extent that the Migdal-Eliashberg picture applies, the spectra of the cuprates bear resemblance to that seen in established

Experimental study on the sound absorption characteristics of continuously graded phononic crystals

Directory of Open Access Journals (Sweden)

X. H. Zhang

2016-10-01

Full Text Available Novel three-dimensional (3D continuously graded phononic crystals (CGPCs have been designed, and fabricated by 3D printing. Each of the CGPCs is an entity instead of a combination of several other samples, and the porosity distribution of the CGPC along the incident direction is nearly linear. The sound absorption characteristics of CGPCs were experimentally investigated and compared with those of uniform phononic crystals (UPCs and discretely stepped phononic crystals (DSPCs. Experimental results show that CGPCs demonstrate excellent sound absorption performance because of their continuously graded structures. CGPCs have higher sound absorption coefficients in the large frequency range and more sound absorption coefficient peaks in a specific frequency range than UPCs and DSPCs. In particular, the sound absorption coefficients of the CGPC with a porosity of 0.6 and thickness of 30 mm are higher than 0.56 when the frequency is 1350–6300 Hz and are all higher than 0.2 in the studied frequency range (1000–6300 Hz. CGPCs are expected to have potential application in noise control, especially in the broad frequency and low-frequency ranges.

Factors controlling crystallization of miserite glass-ceramic.

Science.gov (United States)

Muhammed, Fenik K; Moorehead, Robert; van Noort, Richard; Pollington, Sarah

2015-12-01

The purpose of this study was to investigate a range of variables affecting the synthesis of a miserite glass-ceramic (GC). Miserite glass was synthesized by the melt quench technique. The crystallization kinetics of the glass were determined using Differential Thermal Analysis (DTA). The glasses were ground with dry ball-milling and then sieved to different particle sizes prior to sintering. These particle sizes were submitted to heat treatment regimes in a high temperature furnace to form the GC. The crystal phases of the GC were analyzed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to examine the microstructure of the cerammed glass. XRD analysis confirmed that the predominant crystalline phase of the GC was miserite along with a minor crystalline phase of cristobalite only when the particle size is <20 μm and the heat treatment at 1000°C was carried out for 4h and slowly cooled at the furnace rate. For larger particle sizes and faster cooling rates, a pseudowollastonite crystalline phase was produced. Short sintering times produced either a pseudowollastonite or xonotolite crystalline phase. The current study has shown that particle size and heat treatment schedules are major factors in controlling the synthesis of miserite GC. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

A comprehensive phononics of phonon assisted energy transfer in the Yb{sup 3+} aided upconversion luminescence of Tm{sup 3+} and Ho{sup 3+} in solids

Energy Technology Data Exchange (ETDEWEB)

Debnath, Radhaballabh, E-mail: drdebnathr@gmail.com; Bose, Saptasree

2015-05-15

The theory of phonon assisted energy transfer is being widely used to explain the Yb{sup 3+} ion aided normal and upconversion emission of various rare earth ions in different Yb{sup 3+} co-doped solids. The reported phonon dynamics in many of these studies are either incomplete or erroneous. Here we report Yb{sup 3+} aided upconversion luminescence properties of Tm{sup 3+} and Ho{sup 3+} in (Yb{sup 3+}/Tm{sup 3+}) and (Yb{sup 3+}/Ho{sup 3+}) co-doped two BaO–tellurite glasses and explain their phononics in the light of Dexter's theory by proposing a comprehensive scheme. The approach is valid for other systems of different phonon structures. - Highlights: • Yb{sup 3+} aided upconversion luminescence properties of Tm{sup 3+} and Ho{sup 3+} in (Yb{sup 3+}/Tm{sup 3+}) and (Yb{sup 3+}/Ho{sup 3+}) co-doped two BaO–tellurite glasses, are reported. • Phonon assisted energy transfer in these systems are explained in the light of Dexter's theory by proposing a comprehensive scheme of phononics. • The approach is valid for other systems of different phonon structures.

Phonon interactions with methyl radicals in single crystals

Directory of Open Access Journals (Sweden)

James W. Wells

2017-04-01

Full Text Available The high temperature ESR spectra’s anomalous appearance at very low temperatures for the methyl radical created in single crystals is explained by magnetic dipole interactions with neighboring protons. These protons acting via phonon vibrations induce resonant oscillations with the methyl group to establish a very temperature sensitive ‘‘relaxation’’ mode that allows the higher energy ‘‘E’’ state electrons with spin 12 to ‘‘decay’’ into ‘‘A’’ spin 12 states. Because of the amplitude amplification with temperature, the ‘‘E’’ state population is depleted and the ‘‘A’’ state population augmented to produce the high temperature ESR spectrum. This phenomenon is found to be valid for all but the very highest barriers to methyl group tunneling. In support, a time dependent spin population study shows this temperature evolution in the state populations under this perturbation.

Metal/dielectric thermal interfacial transport considering cross-interface electron-phonon coupling: Theory, two-temperature molecular dynamics, and thermal circuit

Science.gov (United States)

Lu, Zexi; Wang, Yan; Ruan, Xiulin

2016-02-01

The standard two-temperature equations for electron-phonon coupled thermal transport across metal/nonmetal interfaces are modified to include the possible coupling between metal electrons with substrate phonons. The previous two-temperature molecular dynamics (TT-MD) approach is then extended to solve these equations numerically at the atomic scale, and the method is demonstrated using Cu/Si interface as an example. A key parameter in TT-MD is the nonlocal coupling distance of metal electrons and nonmetal phonons, and here we use two different approximations. The first is based on Overhauser's "joint-modes" concept, while we use an interfacial reconstruction region as the length scale of joint region rather than the phonon mean-free path as in Overhauser's original model. In this region, the metal electrons can couple to the joint phonon modes. The second approximation is the "phonon wavelength" concept where electrons couple to phonons nonlocally within the range of one phonon wavelength. Compared with the original TT-MD, including the cross-interface electron-phonon coupling can slightly reduce the total thermal boundary resistance. Whether the electron-phonon coupling within the metal block is nonlocal or not does not make an obvious difference in the heat transfer process. Based on the temperature profiles from TT-MD, we construct a new mixed series-parallel thermal circuit. We show that such a thermal circuit is essential for understanding metal/nonmetal interfacial transport, while calculating a single resistance without solving temperature profiles as done in most previous studies is generally incomplete. As a comparison, the simple series circuit that neglects the cross-interface electron-phonon coupling could overestimate the interfacial resistance, while the simple parallel circuit in the original Overhauser's model underestimates the total interfacial resistance.

Phonon anomalies and electron-phonon coupling of metal surfaces and thin films; Phononenanomalien und Elektron-Phonon-Kopplung an Metalloberflaechen und duennen Schichten

Energy Technology Data Exchange (ETDEWEB)

Flach, B.

2000-01-01

This thesis has two topics: One is the investigation of an adsorbate induced phonon anomaly on W(110) and Mo{sub 1-x}Re{sub x}(110) (x = 5, 15, 25%) with inelastic helium atom scattering (HAS). The other one is the study of the growth, morphology and dynamics of ultra-thin lithium films deposited on W(110). In 1992 a giant phonon anomaly was found by J. Luedecke on the hydrogen saturated W(110) and Mo(110) surfaces. The anomaly consists of a deep and sharp indentation in the phonon dispersion curves in which the phonon energy nearly drops to zero ({omega}{sub 1}). In addition, a small and broad dip in the surface Rayleigh mode is observed ({omega}{sub 2}). The anomaly appears in the anti {gamma}-H- as well as in the anti {gamma}-S-direction of the surface Brillouin zone (SBZ). Since its first discovery, numerous other experimental and theoretical studies have followed. In the present work the effects is reinvestigated and experimental parameters, such as the crystal temperature and the incident energy, were changed in order to study their influence on the anomalous phonon behavior. In the case of H/Mo(110) the substrate was changed as well by alloying with small amounts of rhenium. In the present experiments a strong crystal temperature dependence of the {omega}{sub 2}-branch was found which leads to lower energies at the 'dip' for smaller temperatures, while the {omega}{sub 1}-anomaly remains unchanged. Such behavior agrees well with the picture that the {omega}{sub 2}-branch is due to a Kohn anomaly. (orig.)

Crystal growth and optical properties of CdS-doped lead silicate glass

International Nuclear Information System (INIS)

Liu Hao; Liu Qiming; Zhao Xiujian

2007-01-01

The crystal growth and optical properties of CdS microcrystallite-doped lead silicate glass is investigated in this paper. The existence of CdS nanocrystals was confirmed via X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results reveal that a two-stage heat-treat procedure can produce a better size distribution of CdS nanocrystals than a one-stage heat-treat procedure in glasses. The second harmonic generation (SHG) from the base glass and CdS microcrystallite doped glasses was observed, and the effects of the heat treatments and the thermal poling temperature on the crystallization of CdS and second-order harmonic (SH) intensity were discussed, respectively. It is indicated that samples doped with CdS microcrystallite showed larger SH intensity than that of the base glass. Use of a higher thermal poling temperature than the glass transformation temperature does not result in a good SH intensity in glasses

Crystallization behaviors and seal application of basalt based glass-ceramics

Science.gov (United States)

Ateş, A.; Önen, U.; Ercenk, E.; Yılmaz, Ş.

2017-02-01

Basalt based glass-ceramics were prepared by conventional melt-quenching technique and subsequently converted to glass-ceramics by a controlled nucleation and crystallization process. Glass materials were obtained by melt at 1500°C and quenched in cold water. The powder materials were made by milling and spin coating. The powders were applied on the 430 stainless steel interconnector material, and heat treatment was carried out. The interface characteristics between the glass-ceramic layer and interconnector were investigated by using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The results showed that the basalt base glass-ceramic sealant material exhibited promising properties to use for SOFC.

Crystallization and chemical durability of glasses in the system Bi2O3-SiO2

International Nuclear Information System (INIS)

Fredericci, C.

2011-01-01

The crystallization of the Bi 2 O 3 -SiO 2 -TiO 2 -Al 2 O 3 -Na 2 O-K 2 O and Bi 2 O 3 -SiO 2 -ZnO-Al 2 O 3 -B 2 O 3 -Na 2 O glasses was studied using glass samples prepared by traditional melt-quench method. Differential thermal analysis (DTA) curves suggested that surface crystallization played a major role in the crystallization of the glass samples. X-ray diffraction (XRD) analysis revealed the crystallization of bismuth silicate for both glasses and bismuth silicate and zinc silicate for the glass containing ZnO. Through scanning electron microscopy (MEV) and energy dispersive spectroscopy (EDS), it was possible to observe that the crystals of zinc silicate (Zn 2 SiO 4 ) were readily attacked by hot 0,1 N sulfuric acid, whereas bismuth silicate crystals were more resistant to acidic attack etching. (author)

Interaction of non-equilibrium phonons with electron-hole plasmas in germanium

International Nuclear Information System (INIS)

Kirch, S.J.

1985-01-01

This thesis presents results of experiments on the interaction of phonons and photo-excited electron-hole plasmas in Ge at low temperature. The first two studies involved the low-temperature fluid phase known as the electron-hole liquid (EHL). The third study involved a wider range of temperatures and includes the higher temperature electron-hole plasma (EHP). In the first experiment, superconducting tunnel junctions are used to produce quasi-monochromatic phonons, which propagate through the EHL. The magnitude of the absorption of these non-equilibrium phonons gives a direct measure of the coupling constant, the deformation potential. In the second experiment, the nonequilibrium phonons are generated by laser excitation of a metal film. An unusual sample geometry allows examination of the EHL-phonon interaction near the EHL excitation surface. This coupling is examined for both cw and pulsed EHL excitation. In the third experiment, the phonons are byproducts of the photo-excited carrier thermalization. The spatial, spectral and temporal dependence of the recombination luminescence is examined. A phonon wind force is observed to dominate the transport properties of the EHL and the EHP. These carriers are never observed to move faster than the phonon velocity even during the laser pulse

Phonon superradiance and phonon laser effect in nanomagnets.

Science.gov (United States)

Chudnovsky, E M; Garanin, D A

2004-12-17

We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.

Interaction Between Electrons, Magnons and Phonons in Nickel. RCN Report

International Nuclear Information System (INIS)

Frikkee, E.

1971-02-01

By means of inelastic neutron scattering, a localized electron excitation was observed in Ni and (4% Fe). The excitation interacts with magnons and phonons, and is assumed to correspond with transitions between the nearly-degenerate electronstates Δ 6 ↑ and Δ 7 ↑ near X, which are situated just below the Fermi level.Selection rules for electron-phonon and electronmagnon scattering are determined by means of group theory. It is found that in particular the transverse (Δ 5 ) phonons in the [100] direction are perturbed. The observed neutron-electron scattering turns out to be an indirect process, which is only possible due to the interaction between the (Δ 6 , Δ 7 ) electrons and the lattice. The basic mechanism for the observed effects is the electron spin-orbit coupling, which establishes the interaction between the electron spin system and the lattice. (author)

Controlling competing electronic orders via non-equilibrium acoustic phonons

Science.gov (United States)

Schuett, Michael; Orth, Peter; Levchenko, Alex; Fernandes, Rafael

The interplay between multiple electronic orders is a hallmark of strongly correlated systems displaying unconventional superconductivity. While doping, pressure, and magnetic field are the standard knobs employed to assess these different phases, ultrafast pump-and-probe techniques opened a new window to probe these systems. Recent examples include the ultrafast excitation of coherent optical phonons coupling to electronic states in cuprates and iron pnictides. In this work, we demonstrate theoretically that non-equilibrium acoustic phonons provide a promising framework to manipulate competing electronic phases and favor unconventional superconductivity over other states. In particular, we show that electrons coupled to out-of-equilibrium anisotropic acoustic phonons enter a steady state in which the effective electronic temperature varies around the Fermi surface. Such a momentum-dependent temperature can then be used to selectively heat electronic states that contribute primarily to density-wave instabilities, reducing their competition with superconductivity. We illustrate this phenomenon by computing the microscopic steady-state phase diagram of the iron pnictides, showing that superconductivity is enhanced with respect to the competing antiferromagnetic phase.

Electron and phonon spectra in La2-xSrxCuI4+δ

International Nuclear Information System (INIS)

Nomerovannaya, L.V.; Makhnev, A.A.; Malyuk, A.N.; Bolotin, G.A.; Shtrapenin, G.L.; Ignatenkov, A.N.

1995-01-01

Ellipsometric measurements of optical constants and measurements of reflection spectra of La 2-x Sr x CuI 4+δ monocrystals were carried out. Variation of peculiarities of electron and phonon spectra at strontium doping was followed. Formulae to calculate ε dielectric permittivity tensor component on the ground of ellipsometric measurements for tetragonal and orthorhombic crystals are given. Effect of superstoichiometric oxygen content on anisotropy of La 2 CuO 4+δ optical properties was studied. 18 refs., 5 figs., 1 tab

Rigid muffin-tin approximation for the electron-phonon interaction in transition metals

International Nuclear Information System (INIS)

Butler, W.H.

1980-01-01

Progress in calculating the electron-phonon parameters of transition metals has been based on either the rigid muffin-tin approximation (RMTA) or the fitted modified tight-binding approximation (FMTBA). The RMTA has been shown to be remarkably accurate for average electron-phonon properties, but there are indications that RMTA matrix elements may be too small at low momentum transfer. An attempt is made to demonstrate these assertions concerning the accuracy of RMTA and the numerous electron-phonon calculations are placed in a broader perspective by a demonstration of how they can be used to explain the trends in the strength of the electron-phonon coupling among the transition metals and the A-15 compounds

Rigid muffin-tin approximation for the electron-phonon interaction in transition metals

Energy Technology Data Exchange (ETDEWEB)

Butler, W.H.

1980-01-01

Progress in calculating the electron-phonon parameters of transition metals has been based on either the rigid muffin-tin approximation (RMTA) or the fitted modified tight-binding approximation (FMTBA). The RMTA has been shown to be remarkably accurate for average electron-phonon properties, but there are indications that RMTA matrix elements may be too small at low momentum transfer. An attempt is made to demonstrate these assertions concerning the accuracy of RMTA and the numerous electron-phonon calculations are placed in a broader perspective by a demonstration of how they can be used to explain the trends in the strength of the electron-phonon coupling among the transition metals and the A-15 compounds. (GHT)

Phonon-impurity relaxation and acoustic wave absorption in yttrium-aluminium garnet crystals with impurities

International Nuclear Information System (INIS)

Ivanov, S.N.; Kotelyanskij, I.M.; Medved', V.V.

1983-01-01

The experimental results of investigations of the influence of substitution impurities in the yttrium-aluminium garnet lattice on absorption of high-frequency acoustic waves are presented. It is shown that the phonon-impurity relaxation processses affect at most the wave absorption and have resonance character when the acoustic wave interacts with the thermal phonon group in the vicinity of the perturbed part of the phonon spectrum caused by the impurity. The differences of time values between inelastic and elastic thermal phonons relaxations determined from the data on longitudinal and shear waves in pure and impurity garnet crystals are discussed

Influences of chemical aging on the surface morphology and crystallization behavior of basaltic glass fibers

DEFF Research Database (Denmark)

Lund, Majbritt Deichgræber; Yue, Yuanzheng

2008-01-01

The impact of aging in high humidity and water on the surface morphology and crystallization behavior of basaltic glass fibers has been studied using scanning electron microscopy, transmission electron microscopy, calorimetry and X-ray diffraction. The results show that interaction between...... the fibers and the surrounding media (high humidity or water at 70 C) leads to chemical changes strongly affecting the surface morphology. The crystallization peak temperature of the basaltic glass fibers are increased without changing the onset temperature, this may be caused by a chemical depletion...

Crystallization in lead tungsten fluorophosphate glasses

International Nuclear Information System (INIS)

Nardi, R.P.R.D.; Braz, C.E.; Cassanjes, F.C.; Poirier, G.

2014-01-01

The glass forming ability was investigated in the ternary system NaPO 3 -WO 3 -PbF 2 with a constant NaPO 3 /WO 3 ratio of 3/2 and increasing amounts of PbF 2 . It has been found that glass samples can be obtained from PbF 2 contents from 0 mole% to 60 mole%. The most lead fluoride concentrated samples (50% and 60%) were chosen for a crystallization study in order to investigate the possibility of obtaining glass-ceramics containing crystalline lead fluoride. DSC measurements allowed to determine the characteristic temperatures such as Tg, Tx, Tp and Tf. These glass samples were heat-treated near the crystallization peaks observed by thermal analysis. X-ray diffraction results of these heat-treated glasses pointed out that the dominant phase which precipitates from the glass sample containing 50% of PbF 2 is the lead fluorophosphates phase Pb 5 F(PO 4 ) 3 whereas the sample containing 60% of PbF 2 exhibits a preferential crystallization of cubic lead fluoride β-PbF 2 . (author)

Design of materials configurations for enhanced phononic and electronic properties

Science.gov (United States)

Daraio, Chiara

The discovery of novel nonlinear dynamic and electronic phenomena is presented for the specific cases of granular materials and carbon nanotubes. This research was conducted for designing and constructing optimized macro-, micro- and nano-scale structural configurations of materials, and for studying their phononic and electronic behavior. Variation of composite arrangements of granular elements with different elastic properties in a linear chain-of-sphere, Y-junction or 3-D configurations led to a variety of novel phononic phenomena and interesting physical properties, which can be potentially useful for security, communications, mechanical and biomedical engineering applications. Mechanical and electronic properties of carbon nanotubes with different atomic arrangements and microstructures were also investigated. Electronic properties of Y-junction configured carbon nanotubes exhibit an exciting transistor switch behavior which is not seen in linear configuration nanotubes. Strongly nonlinear materials were designed and fabricated using novel and innovative concepts. Due to their unique strongly nonlinear and anisotropic nature, novel wave phenomena have been discovered. Specifically, violations of Snell's law were detected and a new mechanism of wave interaction with interfaces between NTPCs (Nonlinear Tunable Phononic Crystals) was established. Polymer-based systems were tested for the first time, and the tunability of the solitary waves speed was demonstrated. New materials with transformed signal propagation speed in the manageable range of 10-100 m/s and signal amplitude typical for audible speech have been developed. The enhancing of the mitigation of solitary and shock waves in 1-D chains were demonstrated and a new protective medium was designed for practical applications. 1-D, 2-D and 3-D strongly nonlinear system have been investigated providing a broad impact on the whole area of strongly nonlinear wave dynamics and creating experimental basis for new

CRYSTALLIZATION KINETICS OF GLASS-CERAMICS BY DIFFERENTIAL THERMAL ANALYSIS

Directory of Open Access Journals (Sweden)

A. NOZAD

2011-06-01

Full Text Available The crystallization behavior of fluorphlogopite, a glass-ceramic in the MgO–SiO2–Al2O3–K2O–B2O3–F system, was studied by substitution of Li2O for K2O in the glass composition. DTA, XRD and SEM were used for the study of crystallization behavior, formed phases and microstructure of the resulting glass-ceramics. Crystallization kinetics of the glass was investigated under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The crystallization results were analyzed, and both the activation energy of crystallization process as well as the crystallization mechanism were characterized. Calculated kinetic parameters indicated that the appropriate crystallization mechanism was bulk crystallization for base glass and the sample with addition of Li2O. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses was in the range of 234-246 KJ/mol and in the samples with addition of Li2O was changed to the range of 317-322 KJ/mol.

Transient thermal and nonthermal electron and phonon relaxation after short-pulsed laser heating of metals

International Nuclear Information System (INIS)

Giri, Ashutosh; Hopkins, Patrick E.

2015-01-01

Several dynamic thermal and nonthermal scattering processes affect ultrafast heat transfer in metals after short-pulsed laser heating. Even with decades of measurements of electron-phonon relaxation, the role of thermal vs. nonthermal electron and phonon scattering on overall electron energy transfer to the phonons remains unclear. In this work, we derive an analytical expression for the electron-phonon coupling factor in a metal that includes contributions from equilibrium and nonequilibrium distributions of electrons. While the contribution from the nonthermal electrons to electron-phonon coupling is non-negligible, the increase in the electron relaxation rates with increasing laser fluence measured by thermoreflectance techniques cannot be accounted for by only considering electron-phonon relaxations. We conclude that electron-electron scattering along with electron-phonon scattering have to be considered simultaneously to correctly predict the transient nature of electron relaxation during and after short-pulsed heating of metals at elevated electron temperatures. Furthermore, for high electron temperature perturbations achieved at high absorbed laser fluences, we show good agreement between our model, which accounts for d-band excitations, and previous experimental data. Our model can be extended to other free electron metals with the knowledge of the density of states of electrons in the metals and considering electronic excitations from non-Fermi surface states

Interface-guided mode of Lamb waves in a two-dimensional phononic crystal plate

International Nuclear Information System (INIS)

Huang Ping-Ping; Yao Yuan-Wei; Zhang Xin; Li Jing; Hu Ai-Zhen; Wu Fu-Gen

2015-01-01

We investigate the interface-guided mode of Lamb waves in a phononic crystal heterostructures plate, which is composed of two different semi-infinite phononic crystal (PC) plates. The interface-guided modes of the Lamb wave can be obtained by the lateral lattice slipping or by the interface longitudinal gliding. Significantly, it is observed that the condition to generate the interface-guided modes of the Lamb wave is more demanding than that of the studied fluid–fluid system. The interface-guided modes are strongly affected not only by the relative movement of the two semi-infinite PCs but also by the thickness of the PC plate. (paper)

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.

Electronic, phonon and superconducting properties of LaPtBi half-Heusler compound

Science.gov (United States)

Shrivastava, Deepika; Sanyal, Sankar P.

2018-05-01

In the framework of density functional theory based on plane wave pseudopotential method and linear response technique, we have studied the electronic, phonon and superconducting properties of LaPtBi half-Heusler compound. The electronic band structure and density of states show that it is gapless semiconductor which is consistent with previous results. The positive phonon frequencies confirm the stability of this compound in cubic MgAgAs phase. Superconductivity is studied in terms of Eliashberg spectral function (α2F(ω)), electron-phonon coupling constants (λ). The value of electron-phonon coupling parameter is found to be 0.41 and the superconducting transition temperature is calculated to be 0.76 K, in excellent agreement with the experimentally reported values.

Glass precursor approach to high-temperature superconductors

Science.gov (United States)

Bansal, Narottam P.

1992-01-01

The available studies on the synthesis of high T sub c superconductors (HTS) via the glass precursor approach were reviewed. Melts of the Bi-Sr-Ca-Cu-O system as well as those doped with oxides of some other elements (Pb, Al, V, Te, Nb, etc.) could be quenched into glasses which, on further heat treatments under appropriate conditions, crystallized into the superconducting phase(s). The nature of the HTS phase(s) formed depends on the annealing temperature, time, atmosphere, and the cooling rate and also on the glass composition. Long term annealing was needed to obtain a large fraction of the 110 K phase. The high T sub c phase did not crystallize out directly from the glass matrix, but was preceded by the precipitation of other phases. The 110 K HTS was produced at high temperatures by reaction between the phases formed at lower temperatures resulting in multiphase material. The presence of a glass former such as B2O3 was necessary for the Y-Ba-Cu-O melt to form a glass on fast cooling. A discontinuous YBa2Cu3O(7-delta) HTS phase crystallized out on heat treatment of this glass. Attempts to prepare Tl-Ba-Ca-Cu-O system in the glassy state were not successful.

Confinement of acoustical modes due to the electron-phonon interaction within 2D-electron gas

International Nuclear Information System (INIS)

Kochelap, V.A.; Gulseren, O.

1992-09-01

We study the confinement of acoustical modes within 2DEG due only to the electron-phonon interaction. The confined modes split out from the bulk phonons even at uniform lattice parameters, when the 2DEG is created by means of modulation doping. The effect is more pronounced when the wave vector q of the modes increases and is maximum at q = 2 k F (k F is the Fermi wave vector). In the case of several electron sheets the additional features of the confinement effect appear. In the limit of the strong electron-phonon coupling and high surface concentration of the electrons the considered system can suffer Peierls-type phase transition. In this case periodical deformation of the lattice and charge density wave are confined within the electron sheet. (author). 18 refs, 2 figs

Electron spin relaxation governed by Raman processes both for Cu2+ ions and carbonate radicals in KHCO3 crystals: EPR and electron spin echo studies

Science.gov (United States)

Hoffmann, Stanislaw K.; Goslar, Janina; Lijewski, Stefan

2012-08-01

EPR studies of Cu2+ and two free radicals formed by γ-radiation were performed for KHCO3 single crystal at room temperature. From the rotational EPR results we concluded that Cu2+ is chelated by two carbonate molecules in a square planar configuration with spin-Hamiltonian parameters g|| = 2.2349 and A|| = 18.2 mT. Free radicals were identified as neutral HOCOrad with unpaired electron localized on the carbon atom and a radical anion CO3·- with unpaired electron localized on two oxygen atoms. The hyperfine splitting of the EPR lines by an interaction with a single hydrogen atom of HOCOrad was observed with isotropic coupling constants ao = 0.31 mT. Two differently oriented radical sites were identified in the crystal unit cell. Electron spin-lattice relaxation measured by electron spin echo methods shows that both Cu2+ and free radicals relax via two-phonon Raman processes with almost the same relaxation rate. The temperature dependence of the relaxation rate 1/T1 is well described with the effective Debye temperature ΘD = 175 K obtained from a fit to the Debye-type phonon spectrum. We calculated a more realistic Debye temperature value from available elastic constant values of the crystal as ΘD = 246 K. This ΘD-value and the Debye phonon spectrum approximation give a much worse fit to the experimental results. Possible contributions from a local mode or an optical mode are considered and it is suggested that the real phonon spectrum should be used for the relaxation data interpretation. It is unusual that free radicals in KHCO3 relax similarly to the well localized Cu2+ ions, which suggests a small destruction of the host crystal lattice by the ionizing irradiation allowing well coupling between radical and lattice dynamics.

Interpretation of resistivity of Nd1.85Ce0.15CuO4-y using the electron-phonon spectral function determined from tunneling data

International Nuclear Information System (INIS)

Tralshawala, N.; Zasadzinski, J.F.; Coffey, L.; Huang, Q.

1991-01-01

Tunneling measurements of α 2 F(ω) of Nd 1.85 Ce 0.15 CuO 4-y are shown to be in good agreement with recent published results of the phonon density of states F(ω) from neutron scattering. The locations of peaks and valleys in both functions are similar, but the spectral weights differ, suggesting that α 2 has a strong energy dependence. We have used α 2 F(ω) to estimate the phonon contribution, ρ phonon (T), to published data of the temperature-dependent resistivity, ρ(T), for thin films and single crystals of Nd 1.85 Ce 0.15 CuO 4-y . When the phonon contribution is subtracted from the experimental data, a clear T 2 contribution remains over most of the temperature range. The T 2 contribution is interpreted to be due to three-dimensional electron-electron scattering, ρ e-e . There is also a correlation between the magnitude of ρ e-e , and the value of the plasma frequency, ω p [obtained from the determination of ρ phonon (T)], with a scaling which approximates ω p -10/3 . Such a scaling is expected from the carrier-concentration dependence of electron-electron scattering

Bulk glass ceramics containing Yb{sup 3+}/Er{sup 3+}: β-NaGdF{sub 4} nanocrystals: Phase-separation-controlled crystallization, optical spectroscopy and upconverted temperature sensing behavior

Energy Technology Data Exchange (ETDEWEB)

Chen, Daqin, E-mail: dqchen@fjirsm.ac.cn [College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018 (China); Wan, Zhongyi; Zhou, Yan [College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018 (China); Huang, Ping, E-mail: phuang@fjirsm.ac.cn [Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China); Zhong, Jiasong; Ding, Mingye [College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018 (China); Xiang, Weidong; Liang, Xiaojuan [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (China); Ji, Zhenguo, E-mail: jizg@hdu.edu.cn [College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018 (China)

2015-07-25

Highlights: • Hexagonal NaGdF{sub 4} nanocrystals embedded bulk glass ceramics were fabricated. • The incorporation of Ln{sup 3+} dopants into the β-NaGdF{sub 4} lattice was demonstrated. • Upconversion luminescence was highly intensified after glass crystallization. • Such glass ceramics had possible application in the optical temperature sensors. - Abstract: Lanthanide doped hexagonal β-NaGdF{sub 4} nanocrystals embedded transparent bulk glass ceramics were successfully fabricated via a phase-separation-controlled crystallization route. Elemental mapping in the scanning transmission electron microscope and optical spectroscopy analysis demonstrated the partition of the active centers into the β-NaGdF{sub 4} crystalline lattice. As a result, upconversion luminescence of the glass ceramic co-doped with Yb{sup 3+} and Er{sup 3+} is about 60 times as high as that of the precursor glass, attributing to the modification of Yb{sup 3+}/Er{sup 3+} surrounding from phase-separated amorphous nanoparticle to β-NaGdF{sub 4} crystalline lattice with low phonon energy and high crystallinity after crystallization. Furthermore, the temperature-dependent green upconversion emissions assigned to {sup 2}H{sub 11/2} → {sup 4}I{sub 15/2} (520 nm) and {sup 4}S{sub 3/2} → {sup 4}I{sub 15/2} (540 nm) transitions were investigated, and the corresponding fluorescence intensity ratio of these two thermally coupled emitting-states greatly enhanced with increase of temperature. Using such fabricated glass ceramic as an optical thermometric medium, the maximum sensitivity reached as high as 0.0037 K{sup −1} at 580 K. It is expected that the investigated Er{sup 3+}/Yb{sup 3+} codoped glass ceramic might be a very promising candidate for accurate optical temperature sensors.

Electron and phonon drag in thermoelectric transport through coherent molecular conductors

DEFF Research Database (Denmark)

Lü, Jing-Tao; Wang, Jian-Sheng; Hedegård, Per

2016-01-01

We study thermoelectric transport through a coherent molecular conductor connected to two electron and two phonon baths using the nonequilibrium Green's function method. We focus on the mutual drag between electron and phonon transport as a result of ‘momentum’ transfer, which happens only when...

Investigation of crystallization in glasses containing fission products

International Nuclear Information System (INIS)

Malow, G.

1979-01-01

Five potential solidification products for high-level waste (four borosilicate glasses and one celsian glass ceramic) have been investigated in terms of crystallization. In all glasses and in the glass ceramic, crystallization, and recrystallization, respectively, were observed by heating above 773 0 K, however, at very different periods of time (0.1d greater than or equal to 100d). The noble metals precipitated into various phases. Crystal growth proceeded at the phase boundary glass-noble metal. In all products rare earth phases crystallized. Silicate phases rarely formed. The leach resistance (by the grain titration and Soxhlet tests) decreased after heat treatment in all cases. The changes were found to be within one order of magnitude for all products. 2 figures, 4 tables

Early stage crystallization kinetics in metallic glass-forming alloys

International Nuclear Information System (INIS)

Louzguine-Luzgin, Dmitri V.

2014-01-01

Highlights: • Heterogeneous nucleation may precede the homogeneous one in an alloy. • High kinetic constants and the nucleation rate at the initial stage. • Metallic glasses have heterogeneous nucleation sites which saturate later. -- Abstract: The crystallization kinetics and structural changes of a few metallic glassy alloys were monitored using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. Microstructural observations were used to estimate the nucleation and growth rates. A clear comparison of the differences in the crystallization kinetics in the metallic glassy samples is observed at the early and later crystallization stages

Multiphonon contribution to the polaron formation in cuprates with strong electron correlations and strong electron-phonon interaction

Science.gov (United States)

Ovchinnikov, Sergey G.; Makarov, Ilya A.; Kozlov, Peter A.

2017-03-01

In this work dependences of the electron band structure and spectral function in the HTSC cuprates on magnitude of electron-phonon interaction (EPI) and temperature are investigated. We use three-band p-d model with diagonal and offdiagonal EPI with breathing and buckling phonon mode in the frameworks of polaronic version of the generalized tight binding (GTB) method. The polaronic quasiparticle excitation in the system with EPI within this approach is formed by a hybridization of the local multiphonon Franck-Condon excitations with lower and upper Hubbard bands. Increasing EPI leads to transfer of spectral weight to high-energy multiphonon excitations and broadening of the spectral function. Temperature effects are taken into account by occupation numbers of local excited polaronic states and variations in the magnitude of spin-spin correlation functions. Increasing the temperature results in band structure reconstruction, spectral weight redistribution, broadening of the spectral function peak at the top of the valence band and the decreasing of the peak intensity. The effect of EPI with two phonon modes on the polaron spectral function is discussed.

Glass-like phonon scattering from a spontaneous nanostructure in AgSbTe2.

Science.gov (United States)

Ma, J; Delaire, O; May, A F; Carlton, C E; McGuire, M A; VanBebber, L H; Abernathy, D L; Ehlers, G; Hong, Tao; Huq, A; Tian, Wei; Keppens, V M; Shao-Horn, Y; Sales, B C

2013-06-01

Materials with very low thermal conductivity are of great interest for both thermoelectric and optical phase-change applications. Synthetic nanostructuring is most promising for suppressing thermal conductivity through phonon scattering, but challenges remain in producing bulk samples. In crystalline AgSbTe2 we show that a spontaneously forming nanostructure leads to a suppression of thermal conductivity to a glass-like level. Our mapping of the phonon mean free paths provides a novel bottom-up microscopic account of thermal conductivity and also reveals intrinsic anisotropies associated with the nanostructure. Ground-state degeneracy in AgSbTe2 leads to the natural formation of nanoscale domains with different orderings on the cation sublattice, and correlated atomic displacements, which efficiently scatter phonons. This mechanism is general and suggests a new avenue for the nanoscale engineering of materials to achieve low thermal conductivities for efficient thermoelectric converters and phase-change memory devices.

Introduction to the crystallization phenomenon in nuclear glass

International Nuclear Information System (INIS)

Jacquet Francillon, N.

1997-01-01

Crystallization is a subject for concern because of its potentially detrimental effects on the technological feasibility of high-temperature melting, and on the chemical durability of the material at intermediate and low temperatures during interim storage or after disposal. The tendency of glass to crystallize depends to a large extent on the composition of the frit and/or of the waste to be solidified. It depends too of the thermal history of the glass generally, the knowledge is mainly upon determination of the time-temperature-transition (TTT) curves, crystal identification and quantification techniques, and their effects on the durability of the glass matrix. French experience is presented. Only a few authors addressed the long-term development of crystalline phases, notably at temperatures below the vitreous transition temperature Tg. Some recommendations for glass crystallization studies are made but glass crystallization after disposal is acceptable provided some conditions are met. (author)

Crystallization in lead tungsten fluorophosphate glasses

Energy Technology Data Exchange (ETDEWEB)

Nardi, R.P.R.D.; Braz, C.E.; Cassanjes, F.C.; Poirier, G., E-mail: gael.poirier@unifal-mg.edu.br [Universidade Federal de Alfenas (UNIFAL), Pocos de Caldas, MG (Brazil). Instituto de Ciencia e Tecnologia

2014-07-01

The glass forming ability was investigated in the ternary system NaPO{sub 3}-WO{sub 3}-PbF{sub 2} with a constant NaPO{sub 3}/WO{sub 3} ratio of 3/2 and increasing amounts of PbF{sub 2}. It has been found that glass samples can be obtained from PbF{sub 2} contents from 0 mole% to 60 mole%. The most lead fluoride concentrated samples (50% and 60%) were chosen for a crystallization study in order to investigate the possibility of obtaining glass-ceramics containing crystalline lead fluoride. DSC measurements allowed to determine the characteristic temperatures such as Tg, Tx, Tp and Tf. These glass samples were heat-treated near the crystallization peaks observed by thermal analysis. X-ray diffraction results of these heat-treated glasses pointed out that the dominant phase which precipitates from the glass sample containing 50% of PbF{sub 2} is the lead fluorophosphates phase Pb{sub 5}F(PO{sub 4}){sub 3} whereas the sample containing 60% of PbF{sub 2} exhibits a preferential crystallization of cubic lead fluoride β-PbF{sub 2}. (author)

The strong thermoelectric effect in nanocarbon generated by the ballistic phonon drag of electrons

International Nuclear Information System (INIS)

Eidelman, E D; Vul', A Ya

2007-01-01

The thermoelectric power and thermoelectric figure of merit for carbon nanostructure consisting of graphite-like (sp 2 ) and diamond-like (sp 3 ) regions have been investigated. The probability of electron collisions with quasi-ballistic phonons in sp 2 regions has been analysed for the first time. We have shown that the probability is not small. We have analysed the influence of various factors on the process of the electron-ballistic phonon drag (the phonon drag effect). The thermoelectric power and thermoelectric figure of merit under conditions of ballistic transport were found to be substantially higher than those in the cases of drag by thermalized phonons and of electron diffusion. The thermoelectric figure of merit (ZT) in the case of a ballistic phonon contribution to the phonon drag of electrons should be 50 times that for chaotic phonons and 500 times that in the case of the diffusion process. In that case ZT should be a record (ZT≥2-3)

Wave propagation in one-dimensional solid-fluid quasi-periodic and aperiodic phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Chen Ali, E-mail: alchen@bjtu.edu.cn [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Wang Yuesheng [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57068 Siegen (Germany)

2012-02-01

The propagation of the elastic waves in one-dimensional (1D) solid-fluid quasi-periodic phononic crystals is studied by employing the concept of the localization factor, which is calculated by the transfer matrix method. The solid-fluid interaction effect at the interfaces between the solid and the fluid components is considered. For comparison, the periodic systems and aperiodic Thue-Morse sequence are also analyzed in this paper. The splitting phenomenon of the pass bands and bandgaps are discussed for these 1D solid-fluid systems. At last the influences of the material impedance ratios on the band structures of the 1D solid-fluid quasi-periodic phononic crystals arranged as Fibonacci sequence are discussed.

Ab initio study of the electron-phonon coupling at the Cr(001) surface

Science.gov (United States)

Peters, L.; Rudenko, A. N.; Katsnelson, M. I.

2018-04-01

It is experimentally well established that the Cr(001) surface exhibits a sharp resonance around the Fermi level. However, there is no consensus about its physical origin. It is proposed to be either due to a single particle dz2 surface state renormalized by electron-phonon coupling or the orbital Kondo effect involving the degenerate dx z/ dy z states. In this paper we examine the electron-phonon coupling of the Cr(001) surface by means of ab-initio calculations in the form of density functional perturbation theory. More precisely, the electron-phonon mass-enhancement factor of the surface layer is investigated for the 3d states. For the majority and minority spin dz2 surface states we find values of 0.19 and 0.16. We show that these calculated electron-phonon mass-enhancement factors are not in agreement with the experimental data even if we use realistic values for the temperature range and surface Debye frequency for the fit of the experimental data. More precisely, then experimentally an electron-phonon mass-enhancement factor of 0.70 ±0.10 is obtained, which is not in agreement with our calculated values of 0.19 and 0.16. Our findings suggest that the experimentally observed resonance at the Cr(001) surface is not due to electron-phonon effects but due to electron-electron correlation effects.

Features of electron-phonon interactions in nanotubes with chiral symmetry in magnetic field

CERN Document Server

Kibis, O V

2001-01-01

Interaction of the electrons with acoustic phonons in the nanotube with chiral symmetry by availability of the magnetic field, parallel to the nanotube axis, is considered. It is shown that the electron energy spectrum is asymmetric relative to the electron wave vector inversion and for that reason the electron-phonon interaction appears to be different for similar phonons with mutually contrary directions of the wave vector. This phenomenon leads to origination of the electromotive force by the spatially uniform electron gas heating and to appearance of the quadrupole component in the nanotube volt-ampere characteristics

The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

Energy Technology Data Exchange (ETDEWEB)

Mardaani, Mohammad, E-mail: mohammad-m@sci.sku.ac.ir; Rabani, Hassan, E-mail: rabani-h@sci.sku.ac.ir [Department of Physics, Faculty of Science, Shahrekord University, P. O. Box 115, Shahrekord (Iran, Islamic Republic of); Nanotechnology Research Center, Shahrekord University, 8818634141 Shahrekord (Iran, Islamic Republic of); Esmaili, Esmat; Shariati, Ashrafalsadat [Department of Physics, Faculty of Science, Shahrekord University, P. O. Box 115, Shahrekord (Iran, Islamic Republic of)

2015-08-07

A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance.

The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

International Nuclear Information System (INIS)

Mardaani, Mohammad; Rabani, Hassan; Esmaili, Esmat; Shariati, Ashrafalsadat

2015-01-01

A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance

Defect-mediated phonon dynamics in TaS2 and WSe2

Directory of Open Access Journals (Sweden)

Daniel R. Cremons

2017-07-01

Full Text Available We report correlative crystallographic and morphological studies of defect-dependent phonon dynamics in single flakes of 1T-TaS2 and 2H-WSe2 using selected-area diffraction and bright-field imaging in an ultrafast electron microscope. In both materials, we observe in-plane speed-of-sound acoustic-phonon wave trains, the dynamics of which (i.e., emergence, propagation, and interference are strongly dependent upon discrete interfacial features (e.g., vacuum/crystal and crystal/crystal interfaces. In TaS2, we observe cross-propagating in-plane acoustic-phonon wave trains of differing frequencies that undergo coherent interference approximately 200 ps after initial emergence from distinct interfacial regions. With ultrafast bright-field imaging, the properties of the interfering wave trains are observed to correspond to the beat frequency of the individual oscillations, while intensity oscillations of Bragg spots generated from selected areas within the region of interest match well with the real-space dynamics. In WSe2, distinct acoustic-phonon dynamics are observed emanating and propagating away from structurally dissimilar morphological discontinuities (vacuum/crystal interface and crystal terrace, and results of ultrafast selected-area diffraction reveal thickness-dependent phonon frequencies. The overall observed dynamics are well-described using finite element analysis and time-dependent linear-elastic continuum mechanics.

Quantum theory of scattering of channeled electrons and positrons in a crystal

International Nuclear Information System (INIS)

Bazylev, V.A.; Goloviznin, V.V.

1982-01-01

The quantum theory of elastic scattering of electrons and positrons on plane or axial channeling in a thin crystal is developed. The role of coherent (without phonon excitation) and incoherent scattering by atoms of the plane (chain) is investigated. It is shown that incoherent scattering which leads to dechanneling cannot be reduced to scattering by an isolated atom. Allowance for ordered arrangement of the atoms in the plane (chain) of the crystal leads to suppression of the motion levels. It is also shown that on movement of a particle along the plane in directions strongly differing from those of the principal axes, the scattering is incoherent and is determined by thermal vibrations of the nuclei. As the direction of the particle momentum approaches those of the principal axes, the role of coherent scattering without recoil by the crystal lattice nuclei increases and may become dicisive. The probability of large- angle scattering increases relatively in this case. Under certain conditions coherent scattering may become resonant [ru

Phonon-assisted damping of plasmons in three- and two-dimensional metals

Science.gov (United States)

Caruso, Fabio; Novko, Dino; Draxl, Claudia

2018-05-01

We investigate the effects of crystal lattice vibrations on the dispersion of plasmons. The loss function of the homogeneous electron gas (HEG) in two and three dimensions is evaluated numerically in the presence of electronic coupling to an optical phonon mode. Our calculations are based on many-body perturbation theory for the dielectric function as formulated by the Hedin-Baym equations in the Fan-Migdal approximation. The coupling to phonons broadens the spectral signatures of plasmons in the electron-energy loss spectrum (EELS) and it induces the decay of plasmons on timescales shorter than 1 ps. Our results further reveal the formation of a kink in the plasmon dispersion of the two-dimensional HEG, which marks the onset of plasmon-phonon scattering. Overall, these features constitute a fingerprint of plasmon-phonon coupling in EELS of simple metals. It is shown that these effects may be accounted for by resorting to a simplified treatment of the electron-phonon interaction which is amenable to first-principles calculations.

EFFECT OF INTERFACIAL ADHESION ON CRYSTALLIZATION AND MECHANICAL PROPERTIES OF POLY (ETHYLENE TEREPHTHALATE)/GLASS BEAD COMPOSITES

Institute of Scientific and Technical Information of China (English)

OU Yuchun; YU Zhongzhen; ZHU Jin; LI Ge; ZHU Shanguang

1996-01-01

The interfacial adhesion between poly (ethylene terephthalate) (PET) and glass bead was investigated by scanning electron microscope and parallel-plate rheometer. Effect of interfacial adhesion on the crystallization and mechanical properties of PET/glass bead composites was also studied by differential scanning calorimeter and mechanical testers.The results obtained indicate that the glass bead has a heterogeneous nucleation effect on the PET crystallization. Although better interfacial adhesion is advantageous to the increase of the tensile strength of the composite, yet it is unfavorable to the crystallization of PET. It should be pointed out that the crystallization rate of filled PET is always higher than that of pure PET, regardless of the state of interfacial adhesion.

Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus.

Science.gov (United States)

Ling, Xi; Huang, Shengxi; Hasdeo, Eddwi H; Liang, Liangbo; Parkin, William M; Tatsumi, Yuki; Nugraha, Ahmad R T; Puretzky, Alexander A; Das, Paul Masih; Sumpter, Bobby G; Geohegan, David B; Kong, Jing; Saito, Riichiro; Drndic, Marija; Meunier, Vincent; Dresselhaus, Mildred S

2016-04-13

Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to date, as shown by a number of inconsistencies in the recent literature. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight, both experimentally and theoretically, a nontrivial dependence between anisotropy and flake thickness and photon and phonon energies. We show that once understood, the anisotropic optical absorption appears to be a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness, as commonly used previously.

Zero-phonon lines and electron–phonon interaction characteristics of near-surface layer radiation color centers in lithium fluoride

Energy Technology Data Exchange (ETDEWEB)

Voitovich, A.P., E-mail: voitovich@ifanbel.bas-net.by [Institute of Physics, National Academy of Sciences of Belarus, 68 Nezavisimosti Avenue, 220072 Minsk (Belarus); Kalinov, V.S. [Institute of Physics, National Academy of Sciences of Belarus, 68 Nezavisimosti Avenue, 220072 Minsk (Belarus); Mudryi, A.V. [Scientific-Practical Materials Research Center, National Academy of Sciences of Belarus, 19 Brovka Street, 220072 Minsk (Belarus); Pavlovskii, V.N.; Runets, L.P.; Svitsiankou, I.E. [Institute of Physics, National Academy of Sciences of Belarus, 68 Nezavisimosti Avenue, 220072 Minsk (Belarus)

2016-04-15

Zero-phonon lines have been registered in photoluminescence spectra of near-surface layer radiation color centers in lithium fluoride nanocrystals. They have been assigned to transitions of the definite types centers. The frequencies of phonons participating in the transitions of the different type centers located both in the near-surface layer and in the crystal bulk have been measured and compared. The Huang-Rhys parameters for the transitions of these centers have been determined. It has been found that the Huang-Rhys parameters for the studied transitions in the near-surface layer centers of the certain composition are less than for those in the crystal bulk centers of the same composition. This feature is connected with the difference of the electron density distribution in defects. Temperature dependences of the zero-phonon lines widths and shifts have been measured. It has been determined that both widths and shifts grow faster with the increase of a temperature for the defects transitions with the lesser Huang-Rhys parameters. Phonons lifetimes are estimated from the experimental data.

Zero-phonon lines and electron–phonon interaction characteristics of near-surface layer radiation color centers in lithium fluoride

International Nuclear Information System (INIS)

Voitovich, A.P.; Kalinov, V.S.; Mudryi, A.V.; Pavlovskii, V.N.; Runets, L.P.; Svitsiankou, I.E.

2016-01-01

Zero-phonon lines have been registered in photoluminescence spectra of near-surface layer radiation color centers in lithium fluoride nanocrystals. They have been assigned to transitions of the definite types centers. The frequencies of phonons participating in the transitions of the different type centers located both in the near-surface layer and in the crystal bulk have been measured and compared. The Huang-Rhys parameters for the transitions of these centers have been determined. It has been found that the Huang-Rhys parameters for the studied transitions in the near-surface layer centers of the certain composition are less than for those in the crystal bulk centers of the same composition. This feature is connected with the difference of the electron density distribution in defects. Temperature dependences of the zero-phonon lines widths and shifts have been measured. It has been determined that both widths and shifts grow faster with the increase of a temperature for the defects transitions with the lesser Huang-Rhys parameters. Phonons lifetimes are estimated from the experimental data.

Long-wavelength optical phonon behavior in uniaxial strained graphene: Role of electron-phonon interaction

Science.gov (United States)

Assili, M.; Haddad, S.

2014-09-01

We derive the frequency shifts and the broadening of Γ-point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic spectrum, induced by the strain, results in a polarization dependence of the LO and TO modes. This dependence is in agreement with the experimental results showing a periodic modulation of the Raman intensity of the split G peak. Moreover, the anomalous behavior of the frequency shift reported in undeformed graphene is found to be robust under strain.

Electron - polar acoustical phonon interactions in nitride based diluted magnetic semiconductor quantum well via hot electron magnetotransport

International Nuclear Information System (INIS)

Pandya, Ankur; Shinde, Satyam; Jha, Prafulla K.

2015-01-01

In this paper the hot electron transport properties like carrier energy and momentum scattering rates and electron energy loss rates are calculated via interactions of electrons with polar acoustical phonons for Mn doped BN quantum well in BN nanosheets via piezoelectric scattering and deformation potential mechanisms at low temperatures with high electric field. Electron energy loss rate increases with the electric field. It is observed that at low temperatures and for low electric field the phonon absorption is taking place whereas, for sufficient large electric field, phonon emission takes place. Under the piezoelectric (polar acoustical phonon) scattering mechanism, the carrier scattering rate decreases with the reduction of electric field at low temperatures wherein, the scattering rate variation with electric field is limited by a specific temperature beyond which there is no any impact of electric field on such scattering

Electron-longitudinal-acoustic-phonon scattering in double-quantum-dot based quantum gates

International Nuclear Information System (INIS)

Zhao Peiji; Woolard, Dwight L.

2008-01-01

We propose a nanostructure design which can significantly suppress longitudinal-acoustic-phonon-electron scattering in double-quantum-dot based quantum gates for quantum computing. The calculated relaxation rates vs. bias voltage exhibit a double-peak feature with a minimum approaching 10 5 s -1 . In this matter, the energy conservation law prohibits scattering contributions from phonons with large momenta; furthermore, increasing the barrier height between the double quantum dots reduces coupling strength between the dots. Hence, the joint action of the energy conservation law and the decoupling greatly reduces the scattering rates. The degrading effects of temperatures can be reduced simply by increasing the height of the barrier between the dots

Crystallization in high-level waste glass: A review of glass theory and noteworthy literature

Energy Technology Data Exchange (ETDEWEB)

Christian, J. H. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

2015-08-01

There is a fundamental need to continue research aimed at understanding nepheline and spinel crystal formation in high-level waste (HLW) glass. Specifically, the formation of nepheline solids (K/NaAlSiO₄) during slow cooling of HLW glass can reduce the chemical durability of the glass, which can cause a decrease in the overall durability of the glass waste form. The accumulation of spinel solids ((Fe, Ni, Mn, Zn)(Fe,Cr)₂O₄), while not detrimental to glass durability, can cause an array of processing problems inside of HLW glass melters. In this review, the fundamental differences between glass and solid-crystals are explained using kinetic, thermodynamic, and viscosity arguments, and several highlights of glass-crystallization research, as it pertains to high-level waste vitrification, are described. In terms of mitigating spinel in the melter and both spinel and nepheline formation in the canister, the complexity of HLW glass and the intricate interplay between thermal, chemical, and kinetic factors further complicates this understanding. However, new experiments seeking to elucidate the contributing factors of crystal nucleation and growth in waste glass, and the compilation of data from older experiments, may go a long way towards helping to achieve higher waste loadings while developing more efficient processing strategies.

Phononic Crystal Made of Multilayered Ridges on a Substrate for Rayleigh Waves Manipulation

Directory of Open Access Journals (Sweden)

Mourad Oudich

2017-12-01

Full Text Available We present a phononic crystal to achieve efficient manipulation of surface acoustic waves (SAW. The structure is made of finite phononic micro-ridges arranged periodically in a substrate surface. Each ridge is constructed by staking silicon and tungsten layers so that it behaves as one-dimensional phononic crystal which exhibits band gaps for elastic waves. The band gap allows the existence of resonance modes where the elastic energy is either confined within units in the free end of the ridge or the ones in contact with the substrate. We show that SAW interaction with localized modes in the free surface of the ridge gives rise to sharp attenuation in the SAW transmission, while the modes confined within the ridge/substrate interface cause broad band attenuations of SAW. Furthermore, we demonstrate that the coupling between the two kinds of modes within the band gap gives high SAW transmission amplitude in the form of Fano-like peaks with high quality factor. The structure could provide an interesting solution for accurate SAW control for sensing applications, for instance.

Crystallization and structural approaches of rare earths aluminosilicate glasses (Ln = La, Y, Sc)

International Nuclear Information System (INIS)

Sadiki, N.; Coutures, J.P.; Hennet, L.; Florian, P.; Vaills, Y.; Massiot, D.

2010-01-01

The crystallization behaviour of aluminosilicate glasses of lanthanum, yttrium and scandium has been studied by DTA, XRD, SEM-EDX and EPMA analysis. Young modulus E and hardness H have been measured by using nano-indentation and elastic modulus C 11 and C 44 by Brillouin scattering. The Young modulus measured by nano-indentation agree to those determined by Brillouin scattering and those calculated using Makishima-Mackenzie and Rocherulle model's. The results of DTA analysis indicate that (a) the glass transition temperatures T g are higher for yttrium and scandium containing glasses than their lanthanum counterparts, the melting observed in the yttrium glasses and recently in the scandium glasses correspond to the ternary eutectic Ln 2 O 3 -Al 2 O 3 -SiO 2 (Ln = Y, Sc) (b) the thermal stability is strongly related to the ionic radii of the rare earth. The last results obtained on scandium containing glasses confirm this hypothesis. The XRD results show that the nature of the observed crystallized phases is consistent with the phase diagrams. We also have investigated by NMR-MAS of 27 Al (high field- 17.6 T) these glasses. The results indicate that Al(V) species are correlated to the ionic radii of the rare earth. X-rays and neutron scattering experiments have been respectively performed on the high energy diffraction beam lines ID11 and ID15 at ESRF. The interatomic distances and first-shell coordination numbers were determined. The results are consistent with those performed by NMR-MAS. (authors)

Development of phonon and photon detectors for rare events searches using scintillating crystals

Energy Technology Data Exchange (ETDEWEB)

Ahrens, Felix; Enss, Christian; Fleischmann, Andreas; Gastaldo, Loredana; Hassel, Clemens; Hendricks, Sebastian; Kempf, Sebastian [Kirchhoff-Institut fuer Physik, Universit at Heidelberg (Germany); Kim, Yong-Hamb [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Loidl, Martin; Navick, Xavier-Francois; Rodrigues, Matias [Commissariat a l' energie atomique, Saclay (France)

2016-07-01

The use of scintillating crystals in cryogenic experiments searching for neutrinoless double beta decay and for direct interaction of dark matter particles allows for an efficient background reduction due to particle discrimination. We develop phonon and photon detectors based on metallic magnetic calorimeters (MMCs) to perform simultaneous measurements of heat and light generated by the interaction of a particle in a scintillating crystal. As designed we expect for the phonon sensor an energy resolution of ΔE{sub FWHM}<100 eV and a signal rise time τ<200 μs whereas for the photon detector we expect ΔE{sub FWHM}<5 eV and τ<50 μs. We discuss the design and the fabrication of these detectors and present recent results.

Crystallization and spectroscopic properties investigations of Er3+ doped transparent glass ceramics containing CaF2

International Nuclear Information System (INIS)

Hu Zhongjian; Wang Yuansheng; Ma En; Bao Feng; Yu Yunlong; Chen Daqin

2006-01-01

Transparent oxyfluoride glass ceramics with composition of 45SiO 2 -25Al 2 O 3 -5CaCO 3 -10NaF-15CaF 2 -0.5ErF 3 (in mol%) were developed through controlled crystallization of melt-quenched glass. Non-isothermal crystallization kinetics investigation showed that the average apparent activation energy E a and Avrami exponent n are about 283 kJ/mol and 2.22, respectively, indicating the crystallization a three dimensional crystal growth process controlled by the diffusion with a decreasing nucleation rate. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) observation revealed the precipitation of CaF 2 crystallites sized about 15 nm among the glass matrix after heat-treatment at 650 deg. C for 2 h. For as-made glass, no upconversion signals were detected when excited with a 30 mW diode laser at 980 nm, while strong upconversion emissions at 545, 660 and 800 nm were obtained for transparent glass ceramic under similar excitation condition

Crystallization kinetics of BaO-Al2O3-SiO2 glasses

Science.gov (United States)

Bansal, Narottam P.; Hyatt, Mark J.

1989-01-01

Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

Beam paths of flexural Lamb waves at high frequency in the first band within phononic crystal-based acoustic lenses

Directory of Open Access Journals (Sweden)

J. Zhao

2014-12-01

Full Text Available This work deals with an analytical and numerical study of the focusing of the lowest order anti-symmetric Lamb wave in gradient index phononic crystals. Computing the ray trajectories of the elastic beam allowed us to analyze the lateral dimensions and shape of the focus, either in the inner or behind the phononic crystal-based acoustic lenses, for frequencies within a broad range in the first band. We analyzed and discussed the focusing behaviors inside the acoustic lenses where the focalization at sub-wavelength scale was achieved. The focalization behind the gradient index phononic crystal is shown to be efficient as well: we report on FMHM = 0.63λ at 11MHz.

Glass transition behavior and crystallization kinetics of Cu0.3(SSe20)0.7 chalcogenide glass

International Nuclear Information System (INIS)

Soliman, A.A.

2005-01-01

The glass transition behavior and crystallization kinetics of Cu 0.3 (SSe 20 ) 0.7 chalcogenide glass were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD). Two crystalline phases (SSe 20 and Cu 2 Se) were identified after annealing the glass at 773 K for 24 h. The activation energy of the glass transition (E g ), the activation energy of crystallization (E c ), the Avrami exponent (n) and the dimensionality of growth (m) were determined. Results indicate that this glass crystallizes by a two-stage bulk crystallization process upon heating. The first transformation, in which SSe 20 precipitates from the amorphous matrix with a three-dimensional crystal growth. The second transformation, in which the residual amorphous phase transforms into Cu 2 Se compound with a two-dimensional crystal growth

Structural and thermoelectric properties of the type-I Sn clathrates Cs8Sn46−n(n=0,2) from Density Functional Theory (DFT)

KAUST Repository

Egbele, Peter O.; Shoko, Elvis; Joubert, Daniel P.

2018-01-01

Sn clathrates are promising phonon glass, electron crystal materials (PGEC), in which the phonon free paths are short and the electron free paths are long. We analysed the relaxed structure of Sn clathrates using four different Density Funtional

Strong electron-phonon interaction in the high-Tc superconductors: Evidence from the infrared

International Nuclear Information System (INIS)

Timusk, T.; Porter, C.D.; Tanner, D.B.

1991-01-01

We show that low-frequency structure in the infrared reflectance of the high-temperature superconductor YBa 2 Cu 3 O 7 results from the electron-phonon interaction. Characteristic antiresonant line shapes are seen in the phonon region of the spectrum and the frequency-dependent scattering rate of the mid-infrared electronic continuum has peaks at 150 cm -1 (19 meV) and at 360 cm -1 (45 meV) in good agreement with phonon density-of-states peaks in neutron time-of-flight spectra that develop in superconducting samples. The interaction between the phonons and the charge carriers can be understood in terms of a charged-phonon model

Influence of TiO2 content on the crystallization and microstructure of machinable glass-ceramics

Directory of Open Access Journals (Sweden)

Debasis Pradip Mukherjee

2016-03-01

Full Text Available Glasses based on the SiO2–Al2O3–MgO–K2O–B2O3–MgF2 system added with TiO2 were synthesized and characterized by differential scanning calorimetry (DSC, X-ray powder diffraction (XRD, Fourier transform infrared spectroscopy (FTIR and scanning electron microscopy (SEM techniques. The results showed that by increasing the TiO2 content, glass transition temperature (Tg, both the crystallization peak temperature (TpI and TpII and activation energy (E increased. The interconnected large blocky card-like crystals were identified as fluorophlogopite as a major crystalline phase for all three glass-ceramic specimens by (XRD and subsequently confirmed by SEM. The Vickers hardness (Hv value for glass-ceramic specimens decreases with progressively increasing TiO2 content (1–10 wt% and Titania containing MGT-3 glass-ceramic specimen with interconnected large blocky card-like fluorophlogopite mica crystals possess lower Hv (4.26 GPa as well as good machinability (m = 0.12 useable for machinable applications. The study shows that Titania promoted initial crystallization of glass and can be used as an effective nucleting agent.

Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

Science.gov (United States)

Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

2004-01-01

The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

Optical properties of Eu{sup 3+}-doped antimony-oxide-based low phonon disordered matrices

Energy Technology Data Exchange (ETDEWEB)

Som, Tirtha; Karmakar, Basudeb, E-mail: basudebk@cgcri.res.i [Glass Technology Laboratory, Glass Division, Central Glass and Ceramic Research Institute (Council of Scientific and Industrial Research), 196 Raja S C Mullick Road, Kolkata 700032 (India)

2010-01-27

A new series of monolithic Eu{sub 2}O{sub 3}-doped high antimony oxide (40-80 mol%) content disordered matrices (glasses) of low phonon energy (about 600 cm{sup -1}) in the K{sub 2}O-B{sub 2}O{sub 3}-Sb{sub 2}O{sub 3} (KBS) system was prepared by the melt-quench technique. Infrared reflection spectroscopy was used to establish the low phonon energy of the glasses. Amorphicity and devitrification of the glasses were confirmed by x-ray diffraction analysis. UV-vis absorption spectra of Eu{sup 3+} have been measured and the band positions have been justified with quantitative calculation of the nephelauxetic parameter and covalent bonding characteristics of the host. These Eu{sub 2}O{sub 3}-doped glasses upon excitation at 393 nm radiation exhibit six emission bands in the range 500-750 nm due to their low phonon energy. Of these, the magnetic dipole {sup 5}D{sub 0} -> {sup 7}F{sub 1} transition shows small Stark splitting while the electric dipole {sup 5}D{sub 0}->{sup 7}F{sub 2} transition undergoes remarkable Stark splitting into two components. They have been explained by the crystal field effect. The Judd-Ofelt parameters, {Omega}{sub t{sub =2,4,6}}, were also evaluated and the change of {Omega}{sub t} with the glass composition was correlated with the asymmetric effect at Eu{sup 3+} ion sites and the fundamental properties like covalent character and optical basicity. We are the first to report the spectroscopic properties of the Eu{sup 3+} ion in KBS low phonon antimony glasses.

Propagation of Elastic Waves in a One-Dimensional High Aspect Ratio Nanoridge Phononic Crystal

Directory of Open Access Journals (Sweden)

Abdellatif Gueddida

2018-05-01

Full Text Available We investigate the propagation of elastic waves in a one-dimensional (1D phononic crystal constituted by high aspect ratio epoxy nanoridges that have been deposited at the surface of a glass substrate. With the help of the finite element method (FEM, we calculate the dispersion curves of the modes localized at the surface for propagation both parallel and perpendicular to the nanoridges. When the direction of the wave is parallel to the nanoridges, we find that the vibrational states coincide with the Lamb modes of an infinite plate that correspond to one nanoridge. When the direction of wave propagation is perpendicular to the 1D nanoridges, the localized modes inside the nanoridges give rise to flat branches in the band structure that interact with the surface Rayleigh mode, and possibly open narrow band gaps. Filling the nanoridge structure with a viscous liquid produces new modes that propagate along the 1D finite height multilayer array.

Quantum Phonon Optics: Squeezing Quantum Noise in the Atomic Displacements.

Science.gov (United States)

Hu, X.; Nori, F.

1996-03-01

We have investigated(X. Hu and F. Nori, Physical Review B, in press; preprints.) coherent and squeezed quantum states of phonons. Squeezed states are interesting because they allow the possibility of modulating the quantum fluctuations of atomic displacements below the zero-point quantum noise level of phonon vacuum states. We have studiedfootnotemark[1] the possibility of squeezing quantum noise in the atomic displacement using a polariton-based approach and also a method based on the three-phonon anharmonic interaction. Our focus here is on the first approach. We have diagonalized the polariton Hamiltonian and calculated the corresponding expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators (the later is the phonon analog of the electric field operator for photons). Our results shows that squeezing of quantum fluctuations in the atomic displacements can be achieved with appropriate initial states of both photon and phonon fields. The degree of squeezing is directly related to the crystal susceptibility, which is indicative of the interaction strength between the incident light and the crystal.

SmB6 electron-phonon coupling constant from time- and angle-resolved photoelectron spectroscopy

Science.gov (United States)

Sterzi, A.; Crepaldi, A.; Cilento, F.; Manzoni, G.; Frantzeskakis, E.; Zacchigna, M.; van Heumen, E.; Huang, Y. K.; Golden, M. S.; Parmigiani, F.

2016-08-01

SmB6 is a mixed valence Kondo system resulting from the hybridization between localized f electrons and delocalized d electrons. We have investigated its out-of-equilibrium electron dynamics by means of time- and angle-resolved photoelectron spectroscopy. The transient electronic population above the Fermi level can be described by a time-dependent Fermi-Dirac distribution. By solving a two-temperature model that well reproduces the relaxation dynamics of the effective electronic temperature, we estimate the electron-phonon coupling constant λ to range from 0.13 ±0.03 to 0.04 ±0.01 . These extremes are obtained assuming a coupling of the electrons with either a phonon mode at 10 or 19 meV. A realistic value of the average phonon energy will give an actual value of λ within this range. Our results provide an experimental report on the material electron-phonon coupling, contributing to both the electronic transport and the macroscopic thermodynamic properties of SmB6.

Elastic scattering by hot electrons and apparent lifetime of longitudinal optical phonons in gallium nitride

Energy Technology Data Exchange (ETDEWEB)

Khurgin, Jacob B., E-mail: jakek@jhu.edu [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Bajaj, Sanyam; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

2015-12-28

Longitudinal optical (LO) phonons in GaN generated in the channel of high electron mobility transistors (HEMT) are shown to undergo nearly elastic scattering via collisions with hot electrons. The net result of these collisions is the diffusion of LO phonons in the Brillouin zone causing reduction of phonon and electron temperatures. This previously unexplored diffusion mechanism explicates how an increase in electron density causes reduction of the apparent lifetime of LO phonons, obtained from the time resolved Raman studies and microwave noise measurements, while the actual decay rate of the LO phonons remains unaffected by the carrier density. Therefore, the saturation velocity in GaN HEMT steadily declines with increased carrier density, in a qualitative agreement with experimental results.

The effect of UV exposure and heat treatment on crystallization behavior of photosensitive glasses

Science.gov (United States)

Kıbrıslı, Orhan; Ersundu, Ali Erçin

2018-05-01

In this study, photosensitive glasses in the Na2O-ZnO-Al2O3-SiO2 system with photosensitizing agents (cerium, silver, tin, antimony) and halogenides (NaF and KBr) were synthesized through a conventional melt-quenching technique. The crystallization mechanism was investigated for solely heat-treated and UV-exposed + heat-treated samples using differential thermal analysis (DTA), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) techniques to understand the effect of UV exposure on crystallization behavior of photosensitive glasses. Accordingly, non-isothermal DTA measurements were performed at different heating rates to determine crystallization peak, T p, and onset, T c, temperatures. For solely heat-treated samples, the kinetic parameters such as the Avrami constant, n, and morphology index, m, were calculated as 1 from the Ozawa method indicating surface crystallization and the value of crystallization activation energy was calculated as 944 kJ/mol using modified Kissinger method. On the contrary, bulk crystallization was found to be predominant for UV exposed + heat-treated samples revealing that UV exposure is the primary cause of bulk crystallization in photosensitive glasses.

Crystallization and properties of a spodumene-willemite glass ceramic

International Nuclear Information System (INIS)

Hu, A.M.; Li, M.; Dali, D.L. Mao; Liang, K.M.

2005-01-01

Spodumene-willemite glass ceramics were produced by replacement of Al 2 O 3 in lithium aluminium silicate by ZnO. With replacement of Al 2 O 3 by ZnO, the batch melting temperature, glass transition temperature (T g ) and crystallization temperature (T p ) all decreased. The main crystalline phases precipitated were eucriptite, β-spodumene and willemite (Zn 2 SiO 4 ). All compositions of glass ceramics showed bulk crystallization. As ZnO content increased, the grain sizes and thermal expansion coefficients increased, while the flexural strength and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated with crystallization and morphology of glass ceramics

Light scattering by surface phonons in crystals

International Nuclear Information System (INIS)

Albuquerque, D.L.

1980-01-01

Theory of inelastic light scattering by surface acoustic phonons homogeneous crystals is presented. The Green functions are determined by the use of a classical linear response method and used to evaluate the Brillouin cross section. The acoustic modes are found from solutions to the acoustical-wave equation and boundary conditions appropriated. Two light-scattering mechanisms, amely the surface corrugation and bulk elasto-optic effect are analyzed by deriving optical fields which satisfy both the acousto-optically driven wave equation and the electromagnetic boundary conditions. No restrictions are imposed concerning the angle of incidence of the light. Some representative computed Brillouin ineshapes are also presented and their features discussed. (author) [pt

Design and Fabrication Challenges for Millimeter-Scale Three-Dimensional Phononic Crystals

Directory of Open Access Journals (Sweden)

Frieder Lucklum

2017-11-01

Full Text Available While phononic crystals can be theoretically modeled with a variety of analytical and numerical methods, the practical realization and comprehensive characterization of complex designs is often challenging. This is especially important for the nearly limitless possibilities of periodic, three-dimensional structures. In this contribution, we take a look at these design and fabrication challenges of different 3D phononic elements based on recent research using additive manufacturing. Different fabrication technologies introduce specific limitations in terms of, e.g., material choices, minimum feature size, aspect ratios, or support requirements that have to be taken into account during design and theoretical modeling. We discuss advantages and disadvantages of additive technologies suitable for millimeter and sub-millimeter feature sizes. Furthermore, we present comprehensive experimental characterization of finite, simple cubic lattices in terms of wave polarization and propagation direction to demonstrate the substantial differences between complete phononic band gap and application oriented directional band gaps of selected propagation modes.

Electronic structure and electron-phonon coupling in layered copper oxide superconductors

International Nuclear Information System (INIS)

Pickett, W.E.; Cohen, R.E.; Krakauer, H.

1991-01-01

Experimental data on the layered Cu-O superconductors seem more and more to reflect normal Fermi-liquid behavior and substantial correspondence with band structure predictions. Recent self-consistent, microscopic band theoretic calculations of the electronic structure, lattice instabilities, phonon frequencies, and electron-phonon coupling characteristics and strength for La 2 CuO 4 and YBa 2 Cu 3 O 7 are reviewed. A dominant feature of the coupling is a novel Madelung-like contribution which would be screened out in high density of states superconductors but survives in cuprates because of weak screening. Local density functional theory correctly predicts the instability of (La, Ba) 2 CuO 4 to both the low-temperature orthorhombic phase (below room temperature) and the lower-temperature tetragonal phase (below 50 K). (orig.)

Anomalous vibrational properties in the continuum limit of glasses

Science.gov (United States)

Shimada, Masanari; Mizuno, Hideyuki; Ikeda, Atsushi

2018-02-01

The low-temperature thermal properties of glasses are anomalous with respect to those of crystals. These thermal anomalies indicate that the low-frequency vibrational properties of glasses differ from those of crystals. Recent studies revealed that, in the simplest model of glasses, i.e., the harmonic potential system, phonon modes coexist with soft localized modes in the low-frequency (continuum) limit. However, the nature of low-frequency vibrational modes of more realistic models is still controversial. In the present work, we study the Lennard-Jones (LJ) system using large-scale molecular-dynamics (MD) simulation and establish that the vibrational property of the LJ glass converges to coexistence of the phonon modes and the soft localized modes in the continuum limit as in the case of the harmonic potential system. Importantly, we find that the low-frequency vibrations are rather sensitive to the numerical scheme of potential truncation, which is usually implemented in the MD simulation, and this is the reason why contradictory arguments have been reported by previous works. We also discuss the physical origin of this sensitiveness by means of a linear stability analysis.

Crystallization in high-level waste glass: A review of glass theory and noteworthy literature

Energy Technology Data Exchange (ETDEWEB)

Christian, J. H. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

2015-08-18

There is a fundamental need to continue research aimed at understanding nepheline and spinel crystal formation in high-level waste (HLW) glass. Specifically, the formation of nepheline solids (K/NaAlSiO₄) during slow cooling of HLW glass can reduce the chemical durability of the glass, which can cause a decrease in the overall durability of the glass waste form. The accumulation of spinel solids ((Fe, Ni, Mn, Zn)(Fe, Cr)₂O₄), while not detrimental to glass durability, can cause an array of processing problems inside HLW glass melters. In this review, the fundamental differences between glass and solid-crystals are explained using kinetic, thermodynamic, and viscosity arguments, and several highlights of glass-crystallization research, as it pertains to high-level waste vitrification, are described. In terms of mitigating spinel in the melter and both spinel and nepheline formation in the canister, the complexity of HLW glass and the intricate interplay between thermal, chemical, and kinetic factors further complicates this understanding. However, new experiments seeking to elucidate the contributing factors of crystal nucleation and growth in waste glass, and the compilation of data from older experiments, may go a long way towards helping to achieve higher waste loadings while developing more efficient processing strategies. Higher waste loadings and more efficient processing strategies will reduce the overall HLW Hanford Tank Waste Treatment and Immobilization Plant (WTP) vitrification facilities mission life.

The electronic conduction of glass and glass ceramics containing various transition metal oxides

International Nuclear Information System (INIS)

Yoshida, T.; Matsuno, Y.

1980-01-01

Nb 2 O 5 -V 2 O 5 -P 2 O 5 glasses containing only Group Va oxides have been investigated to elucidate their electronic conduction and structure, as compared with other glasses obtained by the addition of various transition metal oxides to vanadium phosphate. The P 2 O 5 introduction for Nb 2 O 5 in this glass with the same amount of V 2 O 5 increased the conductivity about two times. Glass ceramics having high conductivity increased by two orders of magnitude and the activation energy for conduction decreased from about 0.5 to 0.2 eV. The crystals were confirmed to be (V,Nb) 2 O 5 and Nb phosphate, one of which was highly conductive and developed a pillar-like shape with a length of more than 20 μm. (orig.)

Advances in spectral conversion for photovoltaics: up-converting Er3+ doped YF3 nano-crystals in transparent glass ceramic

Science.gov (United States)

Marques-Hueso, Jose; Chen, Daqin; MacDougall, Sean K. W.; Wang, Yuansheng; Richards, Bryce S.

2011-09-01

Up- and down-conversion (UC, DC) constitute two singular routes to achieve improved energy harvesting of sunlight by changing its shape of the solar spectrum. To obtain a significant conversion rate two main challenges have to be overcome: i) the excited lanthanide ions have to emit efficiently, a target which has been better accomplished for DC materials; ii) the absorption in the lanthanide-based UC and DC layers has to be high to ensure a sizeable fraction of photons can be harvested. In this paper, we review such materials and their use as spectral converters for photovoltaics (PV), paying special attention to the UC and DC processes in lanthanide glasses in fluoride matrices. We discuss the challenges that need to be overcome in order to implement these materials in real PV devices. Finally, we will present the synthesis of erbium (Er3+) doped YF3 nano-crystals embedded in transparent glass ceramic (TGC) by melt quenching. This material presents a low phonon energy environment for the Er3+ ions due to the fluoride crystals, while the silica glass provides chemical and mechanical stability to the compound.

Effects of crystal refining on wear behaviors and mechanical properties of lithium disilicate glass-ceramics.

Science.gov (United States)

Zhang, Zhenzhen; Guo, Jiawen; Sun, Yali; Tian, Beimin; Zheng, Xiaojuan; Zhou, Ming; He, Lin; Zhang, Shaofeng

2018-05-01

The purpose of this study is to improve wear resistance and mechanical properties of lithium disilicate glass-ceramics by refining their crystal sizes. After lithium disilicate glass-ceramics (LD) were melted to form precursory glass blocks, bar (N = 40, n = 10) and plate (N = 32, n = 8) specimens were prepared. According to the differential scanning calorimetry (DSC) of precursory glass, specimens G1-G4 were designed to form lithium disilicate glass-ceramics with different crystal sizes using a two-step thermal treatment. In the meantime, heat-pressed lithium disilicate glass-ceramics (GC-P) and original ingots (GC-O) were used as control groups. Glass-ceramics were characterized using X-ray diffraction (XRD) and were tested using flexural strength test, nanoindentation test and toughness measurements. The plate specimens were dynamically loaded in a chewing simulator with 350 N up to 2.4 × 10 6 loading cycles. The wear analysis of glass-ceramics was performed using a 3D profilometer after every 300,000 wear cycles. Wear morphologies and microstructures were analyzed by scanning electron microscopy (SEM). One-way analysis of variance (ANOVA) was used to analyze the data. Multiple pairwise comparisons of means were performed by Tukey's post-hoc test. Materials with different crystal sizes (p properties. Specifically, G3 with medium-sized crystals presented the highest flexural strength, hardness, elastic modulus and fracture toughness. G1 and G2 with small-sized crystals showed lower flexural strength, whereas G4, GC-P, and GC-O with large-sized crystals exhibited lower hardness and elastic modulus. The wear behaviors of all six groups showed running-in wear stage and steady wear stage. G3 showed the best wear resistance while GC-P and GC-O exhibited the highest wear volume loss. After crystal refining, lithium disilicate glass-ceramic with medium-sized crystals showed the highest wear resistance and mechanical properties. Copyright © 2018

Dynamical electron-phonon coupling, G W self-consistency, and vertex effect on the electronic band gap of ice and liquid water

Science.gov (United States)

Ziaei, Vafa; Bredow, Thomas

2017-06-01

We study the impact of dynamical electron-phonon (el-ph) effects on the electronic band gap of ice and liquid water by accounting for frequency-dependent Fan contributions in the el-ph mediated self-energy within the many-body perturbation theory (MBPT). We find that the dynamical el-ph coupling effects greatly reduce the static el-ph band-gap correction of the hydrogen-rich molecular ice crystal from-2.46 to -0.23 eV in great contrast to the result of Monserrat et al. [Phys. Rev. B 92, 140302 (2015), 10.1103/PhysRevB.92.140302]. This is of particular importance as otherwise the static el-ph gap correction would considerably reduce the electronic band gap, leading to considerable underestimation of the intense peaks of optical absorption spectra of ice which would be in great disagreement to experimental references. By contrast, the static el-ph gap correction of liquid water is very moderate (-0.32 eV), and inclusion of dynamical effects slightly reduces the gap correction to -0.19 eV. Further, we determine the diverse sensitivity of ice and liquid water to the G W self-consistency and show that the energy-only self-consistent approach (GnWn ) exhibits large implicit vertex character in comparison to the quasiparticle self-consistent approach, for which an explicit calculation of vertex corrections is necessary for good agreement with experiment.

Research on soundproof properties of cylindrical shells of generalized phononic crystals

Science.gov (United States)

Liu, Ru; Shu, Haisheng; Wang, Xingguo

2017-04-01

Based on the previous studies, the concept of generalized phononic crystals (GPCs) is further introduced into the cylindrical shell structures in this paper. And a type of cylindrical shells of generalized phononic crystals (CS-GPCs) is constructed, the structural field and acoustic-structural coupled field of the composite cylindrical shells are examined respectively. For the structural field, the transfer matrix method of mechanical state vector is adopted to build the transfer matrix of radial waves propagating from inside to outside. For the acoustic-structural coupled field, the expressions of the acoustic transmission/reflection coefficients and the sound insulation of acoustic waves with the excitation of center line sound source are set up. And the acoustic transmission coefficient and the frequency response of sound insulation in this mode were numerical calculated. Furthermore, the theoretical analysis results are verified by using the method of combining the numerical calculation and finite element simulation. Finally, the effects of inner and outer fluid parameters on the transmission/reflection coefficients of CS-GPCs are analyzed in detail.

Effect of Holstein phonons on the electronic properties of graphene

OpenAIRE

Stauber, T.; Peres, N. M. R.

2007-01-01

We obtain the self-energy of the electronic propagator due to the presence of Holstein polarons within the first Born approximation. This leads to a renormalization of the Fermi velocity of one percent. We further compute the optical conductivity of the system at the Dirac point and at finite doping within the Kubo-formula. We argue that the effects due to Holstein phonons are negligible and that the Boltzmann approach which does not include inter-band transition and can thus not treat optica...

Synthesis and properties of ZnTe and Eu3+ ion co-doped glass nanocomposites

International Nuclear Information System (INIS)

Rahaman Molla, Atiar; Tarafder, Anal; Dey, Chirantan; Karmakar, Basudeb

2014-01-01

In this study, ZnTe (II-VI) semiconductor and Eu +3 -ion co-doped borosilicate glass has been prepared in the SiO 2 -K 2 O-CaO-BaO-B 2 O 3 glass system followed by controlled heat-treatment to produce glass nanocomposites. Glass transition temperature and crystallization peak temperature have been evaluated using DSC analysis. Dilatometric studies were carried out to evaluate thermal expansion co-efficient, glass transition temperature, and dilatometric softening temperature and found to be 10.7 × 10 −6 /K, 580° C and 628° C, respectively. TEM micrographs demonstrate formation of nano sized crystallites of less than 50 nm. The ZnTe crystal formation also established through selected area electron diffraction (SAED) analysis and high resolution images obtained through TEM studies. With increasing heat treatment time, optical transmission cut-off wavelength (λ cut-off ) shifted towards higher wavelength. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5 D 0 → 7 F 2 transition. An intense 394 nm excitation band corresponding to the 7 F 0 → 5 L 6 transition was observed. Emission spectra were then recorded by exciting the glass samples at 394 nm. When the glass is heat-treated for 30 min at 610° C, a 6-fold increase in the intensity of the red emission at 612 nm has been observed, which is attributed to the segregation of Eu 3+ ions into the low phonon energy ZnTe crystallites and as the size of the nanocrystals is smaller than the size of the exciton, quantum confinement effect is visible. Further increase in heat-treatment duration led to decrease in luminescence intensity due to the growth of larger size crystals. 5 D 1 → 7 F 0 transition is visible only in the samples heat-treated for 30 min and 1 h, which is a characteristic of presence of Eu 3+ ions in the low phonon energy ZnTe crystal sites. The micro hardness of the precursor glass and glass nanocomposites was evaluated; base glass shows

Interband optical absorption in the Wannier-Stark ladder under the electron-LO-phonon resonance condition

International Nuclear Information System (INIS)

Govorov, A.O.

1993-08-01

Interband optical absorption in the Wannier-Stark ladder in the presence of the electron-LO-phonon resonance is investigated theoretically. The electron-LO-phonon resonance occurs when the energy spacing between adjacent Stark-ladder levels coincides with the LO-phonon energy. We propose a model describing the polaron effect in a superlattice. Calculations show that the absorption line shape is strongly modified due to the polaron effect under the electron-LO-phonon resonance condition. We consider optical phenomena in a normal magnetic field that leads to enhancement of polaron effects. (author). 17 refs, 5 figs

Crystallization in Pd40Ni40P20 glass

DEFF Research Database (Denmark)

Jiang, Jianzhong; Saksl, K.; Nishiyama, N.

2002-01-01

Phase segregation and the effect of pressure on crystallization of bulk and ribbon Pd40Ni40P20 glasses have been studied by means of differential scanning calorimetry (DSC) and x-ray diffraction. The DSC measurements show only one glass transition event in the samples annealed at different...... temperatures in the supercooled liquid region. Phase analyses reveal at least five crystalline phases crystallized from the glass: monoclinic; body-centered tetragonal; orthorhombic; Ni2Pd2P and fcc-(Ni,Pd) solid solution phases. In the pressure range from 0 to 4.2 GPa, the crystallization temperature...... increases with pressure having a slope of 11 K/GPa. The eutectic crystallization reaction mode and crystalline phases formed are unchanged in the pressure range used. The enhancement of the crystallization temperature with increasing pressure in the glass can be explained by the suppression of atomic...

On the Boltzmann Equation of Thermal Transport for Interacting Phonons and Electrons

Directory of Open Access Journals (Sweden)

Amelia Carolina Sparavigna

2016-05-01

Full Text Available The thermal transport in a solid can be determined by means of the Boltzmann equations regarding its distributions of phonons and electrons, when the solid is subjected to a thermal gradient. After solving the coupled equations, the related thermal conductivities can be obtained. Here we show how to determine the coupled equations for phonons and electrons.

Non-isothermal crystallization kinetics of As{sub 30}Te{sub 60}Ga{sub 10} glass

Energy Technology Data Exchange (ETDEWEB)

Mohamed, Mansour; Abd-Elnaiem, Alaa M.; Abdel-Rahim, M.A.; Hafiz, M.M. [Assiut University, Physics Department, Faculty of Science, Assiut (Egypt); Hassan, R.M. [Assiut University, Physics Department, Faculty of Science, Assiut (Egypt); Aden University, Physics Department, Faculty of Education-Zingiber, Aden (Yemen)

2017-08-15

The crystallization study under non-isothermal conditions of As{sub 30}Te{sub 60}Ga{sub 10} glass was investigated. The studied composition was synthesized by melt-quenching technique and characterized by different techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The XRD analysis revealed that the as-prepared and annealed bulk glass of As{sub 30}Te{sub 60}Ga{sub 10} exhibit the amorphous, and polycrystalline nature, respectively. The DSC results showed that the heating rate affects the characteristic temperatures, for instance, the glass transition, onset, and peak crystallization temperatures. Furthermore, some thermal analysis methods such as the Kissinger and Matusita et al., approximations were employed to determine the crystallization parameters: for example Avrami exponent and the activation energies for glass transition and crystallization process. In addition, we have compared the experimental DSC data with the calculated ones based on the Johnson-Mehl-Avrami (JMA) and Sestak-Berggren SB(M,N) models. The results indicated that the SB(M,N) model is more suitable for describing the non-isothermal crystallization kinetics of the investigated composition. (orig.)

Two-dimensional phononic crystals with time-varying properties: a multiple scattering analysis

International Nuclear Information System (INIS)

Wright, D W; Cobbold, R S C

2010-01-01

Multiple scattering theory is a versatile two- and three-dimensional method for characterizing the acoustic wave transmission through many scatterers. It provides analytical solutions to wave propagation in scattering structures, and its computational complexity grows logarithmically with the number of scatterers. In this paper we show how the 2D method can be adapted to include the effects of time-varying material parameters. Specifically, a new T-matrix is defined to include the effects of frequency modulation that occurs in time-varying phononic crystals. Solutions were verified against finite difference time domain (FDTD) simulations and showed excellent agreement. This new method enables fast characterization of time-varying phononic crystals without the need to resort to lengthy FDTD simulations. Also, the method of combining T-matrices to form the T-supermatrix remains unchanged provided that the new matrix definitions are used. The method is quite compatible with existing implementations of multiple scattering theory and could be readily extended to three-dimensional multiple scattering theory

Fluorescence of Er3+ doped La2S3.3Ga2S3 glasses

International Nuclear Information System (INIS)

Reisfeld, R.; Bornstein, A.

1978-01-01

In this paper the authors report the preparation and fluorescence of Er 3+ in chalcogenide glasses. In the oxide glasses it has been shown that the multiphonon transition rates of the RE are independent of the coupling between a given oxide glass and rare earth ion, but dependent exponentially on the number of phonons of highest energy bridging the emitting and next-lower level. It is of interest to establish whether changing the glass matrix will affect the amount of electron phonon coupling. In addition, because of their low phonon energy and high refractive index, the RE doped chalcogenide glasses will form a new type of fluorescent material. This may be of interest in new RE lasers. (Auth.)

Crystallization In High Level Waste (HLW) Glass Melters: Operational Experience From The Savannah River Site

Energy Technology Data Exchange (ETDEWEB)

Fox, K. M. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

2014-02-27

processing strategy for the Hanford Tank Waste Treatment and Immobilization Plant (WTP). The basis of this alternative approach is an empirical model predicting the crystal accumulation in the WTP glass discharge riser and melter bottom as a function of glass composition, time, and temperature. When coupled with an associated operating limit (e.g., the maximum tolerable thickness of an accumulated layer of crystals), this model could then be integrated into the process control algorithms to formulate crystal tolerant high level waste (HLW) glasses targeting higher waste loadings while still meeting process related limits and melter lifetime expectancies. This report provides a review of the scaled melter testing that was completed in support of the Defense Waste Processing Facility (DWPF) melter. Testing with scaled melters provided the data to define the DWPF operating limits to avoid bulk (volume) crystallization in the un-agitated DWPF melter and provided the data to distinguish between spinels generated by K-3 refractory corrosion versus spinels that precipitated from the HLW glass melt pool. This report includes a review of the crystallization observed with the scaled melters and the full scale DWPF melters (DWPF Melter 1 and DWPF Melter 2). Examples of actual DWPF melter attainment with Melter 2 are given. The intent is to provide an overview of lessons learned, including some example data, that can be used to advance the development and implementation of an empirical model and operating limit for crystal accumulation for WTP. Operation of the first and second (current) DWPF melters has demonstrated that the strategy of using a liquidus temperature predictive model combined with a 100 °C offset from the normal melter operating temperature of 1150 °C (i.e., the predicted liquidus temperature (TL) of the glass must be 1050 °C or less) has been successful in preventing any detrimental accumulation of spinel in the DWPF melt pool, and spinel has not been

Crystallization of Yttrium and Samarium Aluminosilicate Glasses

OpenAIRE

Lago, Diana Carolina; Prado, Miguel Oscar

2016-01-01

Aluminosilicate glasses containing samarium and yttrium (SmAS and YAS glasses) exhibit high glass transition temperatures, corrosion resistance, and glass stability on heating which make them useful for technological applications. Yttrium aluminosilicate glass microspheres are currently being used for internal selective radiotherapy of liver cancer. During the preparation process, crystallization needs to be totally or partially avoided depending on the final application. Thus knowing the cry...

Interaction of phonons with intraband electronic excitations and crystal field transitions in Raman spectra of (Nd,Eu,Gd)Ba.sub.2./sub.Cu.sub.3./sub.O.sub.y./sub. crystals

Czech Academy of Sciences Publication Activity Database

Rameš, Michal; Železný, Vladimír; Gregora, Ivan; Wolf, T.; Jirsa, Miloš

2015-01-01

Roč. 197, Jul (2015), 10-17 ISSN 0921-5107 R&D Projects: GA MŠk(CZ) ME10069 Institutional support: RVO:68378271 Keywords : cuprate superconductors * phonons * crystal field * vortex pinning Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.331, year: 2015

Bulk glass formation and crystallization in zirconium based bulk metallic glass forming alloys

International Nuclear Information System (INIS)

Savalia, R.T.; Neogy, S.; Dey, G.K.; Banerjee, S.

2002-01-01

The microstructures of Zr based metallic glasses produced in bulk form have been described in the as-cast condition and after crystallization. Various microscopic techniques have been used to characterize the microstructures. The microstructure in the as-cast condition was found to contain isolated crystals and crystalline aggregates embedded in the amorphous matrix. Quenched-in nuclei of crystalline phases were found to be present in fully amorphous regions. These glasses after crystallization gave rise to nanocrystalline solids. (author)

Birefringent phononic structures

Directory of Open Access Journals (Sweden)

I. E. Psarobas

2014-12-01

Full Text Available Within the framework of elastic anisotropy, caused in a phononic crystal due to low crystallographic symmetry, we adopt a model structure, already introduced in the case of photonic metamaterials, and by analogy, we study the effect of birefringence and acoustical activity in a phononic crystal. In particular, we investigate its low-frequency behavior and comment on the factors which determine chirality by reference to this model.

Light scattering by surface phonons in crystals

International Nuclear Information System (INIS)

Albuquerque, E.L. de

1981-01-01

A theory of inelastic light scattering by surface acoustic phonons in homogeneous crystals is presented. The Green functions are determined by the use of a classical linear response method and used to evaluate the Brillouin cross section. The acoustic modes are found from solutions to the acoustical-wave equation and boundary conditions appropriated. Two light-scattering mechanisms, namely the surface corrugation and bulk elasto-optic effect are analyzed by deriving optical fields which satisfy both the acousto-optically driven wave equation and the electromagnetic boundary conditions. No restrictions are imposed concerning the angle of incidence of the light. Some representative computed Brillouin lineshapes are also presented and their features discussed. (Author) [pt

Small Fermi energy, strong electron-phonon effects and anharmonicity in MgB2

International Nuclear Information System (INIS)

Cappelluti, E.; Pietronero, L.

2007-01-01

The investigation of the electron-phonon properties in MgB 2 has attracted a huge interest after the discovery of superconductivity with T c 39 K in this compound. Although superconductivity is often described in terms of the conventional Eliashberg theory, properly generalized in the multiband/multigap scenario, important features distinguish MgB 2 from other conventional strong-coupling superconductors. Most important it is the fact that a large part of the total electron-phonon strength seems to be concentrated here in only one phonon mode, the boron-boron E 2g stretching mode. Another interesting property is the small Fermi energy of the σ bands, which are strongly coupled with the E 2g mode. In this contribution, we discuss how the coexistence of both these features give rise to an unconventional phenomenology of the electron-phonon properties

Effect of Ga substitution on the crystallization behaviour and glass forming ability of Zr-Al-Cu-Ni alloys

International Nuclear Information System (INIS)

Singh, Devinder; Yadav, T.P.; Mandal, R.K.; Tiwari, R.S.; Srivastava, O.N.

2010-01-01

The crystallization behaviour of melt spun Zr 69.5 Al 7.5-x Ga x Cu 12 Ni 11 (x = 0-7.5; in at.%) metallic glasses has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The DSC traces showed changes in crystallization behaviour with substitution of Ga. Formation of single nano-quasicrystalline phase by controlled crystallization of glasses has been found only for 0 ≤ x ≤ 1.5. Further increase of Ga content gives rise to formation of the quasicrystals together with Zr 2 Cu type crystalline phase. In addition to this, the substitution of Ga influences the size and shape of nano-quasicrystals. The glass forming abilities (GFAs) of these metallic glasses were assessed by the recognition of glass forming ability indicators, i.e. reduced glass transition temperature (T rg ) and supercooled liquid region (ΔT x ). The glass transition temperature (T g ) has been observed for all the melt spun ribbons.

Intregrating metallic wiring with three-dimensional polystyrene colloidal crystals using electron-beam lithography and three-dimensional laser lithography

International Nuclear Information System (INIS)

Tian, Yaolan; Isotalo, Tero J; Konttinen, Mikko P; Li, Jiawei; Heiskanen, Samuli; Geng, Zhuoran; Maasilta, Ilari J

2017-01-01

We demonstrate a method to fabricate narrow, down to a few micron wide metallic leads on top of a three-dimensional (3D) colloidal crystal self-assembled from polystyrene (PS) nanospheres of diameter 260 nm, using electron-beam lithography. This fabrication is not straightforward due to the fact that PS nanospheres cannot usually survive the harsh chemical treatments required in the development and lift-off steps of electron-beam lithography. We solve this problem by increasing the chemical resistance of the PS nanospheres using an additional electron-beam irradiation step, which allows the spheres to retain their shape and their self-assembled structure, even after baking to a temperature of 160 °C, the exposure to the resist developer and the exposure to acetone, all of which are required for the electron-beam lithography step. Moreover, we show that by depositing an aluminum oxide capping layer on top of the colloidal crystal after the e-beam irradiation, the surface is smooth enough so that continuous metal wiring can be deposited by the electron-beam lithography. Finally, we also demonstrate a way to self-assemble PS colloidal crystals into a microscale container, which was fabricated using direct-write 3D laser-lithography. Metallic wiring was also successfully integrated with the combination of a container structure and a PS colloidal crystal. Our goal is to make a device for studies of thermal transport in 3D phononic crystals, but other phononic or photonic crystal applications could also be envisioned. (paper)

The structural, electronic and phonon behavior of CsPbI_3: A first principles study

International Nuclear Information System (INIS)

Bano, Amreen; Khare, Preeti; Parey, Vanshree; Shukla, Aarti; Gaur, N. K.

2016-01-01

Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI_3 is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.

Phonon-induced renormalization of the electron spectrum of biased bilayer graphene

Science.gov (United States)

Kryuchkov, S. V.; Kukhar, E. I.

2018-05-01

The effect of the electron-phonon interaction on the electron subsystem of the bilayer graphene has been investigated in the case when there is a potential bias between the graphene layers. The electron-phonon interaction has been shown to lead to increasing of the curvature of the lower dispersion branch of the conduction band of the bigraphene in the vicinity of the Dirac point. The latter corresponds to the decreasing of the absolute value of the electron effective mass. The corresponding correction to the effective mass has been calculated. Dependence of this correction on the bias has been investigated. Influence of such effect on the bigraphene conductivity is discussed.

Measurements of the ballistic-phonon component resulting from nuclear and electron recoils in crystalline silicon

International Nuclear Information System (INIS)

Lee, A.T.; Cabrera, B.; Dougherty, B.L.; Penn, M.J.; Pronko, J.G.; Tamura, S.

1996-01-01

We present measurements of the ballistic-phonon component resulting from nuclear and electron recoils in silicon at ∼380 mK. The detectors used for these experiments consist of a 300-μm-thick monocrystal of silicon instrumented with superconducting titanium transition-edge sensors. These sensors detect the initial wavefront of athermal phonons and give a pulse height that is sensitive to changes in surface-energy density resulting from the focusing of ballistic phonons. Nuclear recoils were generated by neutron bombardment of the detector. A Van de Graaff proton accelerator and a thick 7 Li target were used. Pulse-height spectra were compared for neutron, x-ray, and γ-ray events. A previous analysis of this data set found evidence for an increase in the ballistic-phonon component for nuclear recoils compared to electron recoils at a 95% confidence level. An improved understanding of the detector response has led to a change in the result. In the present analysis, the data are consistent with no increase at the 68% confidence level. This change stems from an increase in the uncertainty of the result rather than a significant change in the central value. The increase in ballistic phonon energy for nuclear recoils compared to electron recoils as a fraction of the total phonon energy (for equal total phonon energy events) was found to be 0.024 +0.041 -0.055 (68% confidence level). This result sets a limit of 11.6% (95% confidence level) on the ballistic phonon enhancement for nuclear recoils predicted by open-quote open-quote hot spot close-quote close-quote and electron-hole droplet models, which is the most stringent to date. To measure the ballistic-phonon component resulting from electron recoils, the pulse height as a function of event depth was compared to that of phonon simulations. (Abstract Truncated)

Solid phase crystallized polycrystalline thin-films on glass from evaporated silicon for photovoltaic applications

International Nuclear Information System (INIS)

Song Dengyuan; Inns, Daniel; Straub, Axel; Terry, Mason L.; Campbell, Patrick; Aberle, Armin G.

2006-01-01

Polycrystalline silicon (poly-Si) thin-films are made on planar and textured glass substrates by solid phase crystallization (SPC) of in situ doped amorphous silicon (a-Si) deposited by electron-beam evaporation. These materials are referred to by us as EVA materials (SPC of evaporated a-Si). The properties of EVA poly-Si films are characterised by Raman microscopy, transmission electron microscopy, and X-ray diffraction. A narrow and symmetrical Raman peak at a wave number of about 520 cm -1 is observed for all samples, showing that the films are fully crystallized. X-ray diffraction (XRD) reveals that the films are preferentially (111)-oriented. Furthermore, the full width at half maximum of the dominant (111) XRD peaks indicates that the structural quality of the films is affected by the a-Si deposition temperature and the surface morphology of the glass substrates. A-Si deposition at 200 instead of 400 deg. C leads to an enhanced poly-Si grain size. On textured glass, the addition of a SiN barrier layer between the glass and the Si improves the poly-Si material quality. No such effect occurs on planar glass. Mesa-type solar cells are made from these EVA films on planar and textured glass. A strong correlation between the cells' current-voltage characteristics and their crystalline material quality is observed

Crystallization of Na2O-SiO2 gel and glass

Science.gov (United States)

Neilson, G. F.; Weinberg, M. C.

1984-01-01

The crystallization behavior of a 19 wt pct soda silica gel and gel-derived glass was compared to that of the ordinary glass of the same composition. Both bulk and ground glass samples were utilized. X-ray diffraction measurements were made to identify the crystalline phases and gauge the extent of crystallization. It was found that the gel crystallized in a distinctive manner, while the gel glass behavior was not qualitatively different from that of the ordinary glass.

One and two-phonon processes of the spin-flip relaxation in quantum dots: Spin-phonon coupling mechanism

Science.gov (United States)

Wang, Zi-Wu; Li, Shu-Shen

2012-07-01

We investigate the spin-flip relaxation in quantum dots using a non-radiation transition approach based on the descriptions for the electron-phonon deformation potential and Fröhlich interaction in the Pavlov-Firsov spin-phonon Hamiltonian. We give the comparisons of the electron relaxations with and without spin-flip assisted by one and two-phonon processes. Calculations are performed for the dependence of the relaxation time on the external magnetic field, the temperature and the energy separation between the Zeeman sublevels of the ground and first-excited state. We find that the electron relaxation time of the spin-flip process is more longer by three orders of magnitudes than that of no spin-flip process.

Composition and crystallization kinetics of R2O-Al2O3-SiO2 glass-ceramics

International Nuclear Information System (INIS)

Xiong, Dehua; Cheng, Jinshu; Li, Hong

2010-01-01

The crystallization behavior and microstructure of R 2 O-Al 2 O 3 -SiO 2 (R means K, Na and Li) glass were investigated by means of differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallization kinetic parameters including the crystallization apparent activation energy (E a ), the Avrami parameter (n), glass transition temperature (T g ) and the activity energy of glass transition (E t ) were also measured with different methods. The results have shown that: the DSC traces of composition A parent glass have two different precipitation crystallization peaks corresponding to E a1 (A) = 151.4 kJ/mol (Li 2 SiO 3 ) and E a2 (A) = 623.1 kJ/mol (Li 2 Si 2 O 5 ), the average value of n = 1.70 (Li 2 Si 2 O 5 ) for the surface crystallization and E t (A) = 202.8 kJ/mol. And E a (B) = 50.7 kJ/mol (Li 2 SiO 3 ), the average value of n = 3.89 (Li 2 SiO 3 ) for the bulk crystallization and E t (B) = 220.4 kJ/mol for the composition B parent glass. Because of the content of R 2 O is bigger than composition A, composition B parent glass has a lower E a , T g and a larger n, E t .

Phonon dynamics of graphene on metals

Science.gov (United States)

Taleb, Amjad Al; Farías, Daniel

2016-03-01

The study of surface phonon dispersion curves is motivated by the quest for a detailed understanding of the forces between the atoms at the surface and in the bulk. In the case of graphene, additional motivation comes from the fact that thermal conductivity is dominated by contributions from acoustic phonons, while optical phonon properties are essential to understand Raman spectra. In this article, we review recent progress made in the experimental determination of phonon dispersion curves of graphene grown on several single-crystal metal surfaces. The two main experimental techniques usually employed are high-resolution electron energy loss spectroscopy (HREELS) and inelastic helium atom scattering (HAS). The different dispersion branches provide a detailed insight into the graphene-substrate interaction. Softening of optical modes and signatures of the substrate‧s Rayleigh wave are observed for strong graphene-substrate interactions, while acoustic phonon modes resemble those of free-standing graphene for weakly interacting systems. The latter allows determining the bending rigidity and the graphene-substrate coupling strength. A comparison between theory and experiment is discussed for several illustrative examples. Perspectives for future experiments are discussed.

Enhancement of nucleation during hanging drop protein crystallization using HF treatment of cover glasses

Energy Technology Data Exchange (ETDEWEB)

Guo, Yun-Zhu; Yin, Da-Chuan; Lu, Qin-Qin; Wang, Xi-Kai; Liu, Jun [Key Laboratory for Space Bioscience and Biotechnology, Faculty of Life Sciences, Northwestern Polytechnical University, Xi' an 710072, Shaanxi (China)

2010-02-15

We examined a simple approach, i.e., etching cover glasses using hydrofluoric acid (HF), to determine whether cover glass treatment enhances nucleation in hanging drop protein crystallization. Hen egg white lysozyme and proteinase K were used as the model proteins. We found that the treatment increased the success rate of crystallization. The results indicated that the simple treatment, which is easy to adopt without changing much in the hanging drop method, can be utilized as an alternative method to enhance protein crystallization screens (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Sound and heat revolutions in phononics

Science.gov (United States)

Maldovan, Martin

2013-11-01

The phonon is the physical particle representing mechanical vibration and is responsible for the transmission of everyday sound and heat. Understanding and controlling the phononic properties of materials provides opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity and develop earthquake protection. Here I review recent progress and the development of new ideas and devices that make use of phononic properties to control both sound and heat. Advances in sonic and thermal diodes, optomechanical crystals, acoustic and thermal cloaking, hypersonic phononic crystals, thermoelectrics, and thermocrystals herald the next technological revolution in phononics.

Crystallization, Microstructure, and Viscosity Evolutions in Lithium Aluminosilicate Glass-Ceramics

Directory of Open Access Journals (Sweden)

Qiang Fu

2016-11-01

Full Text Available Lithium aluminosilicate glass-ceramics have found widespread commercial success in areas such as consumer products, telescope mirrors, fireplace windows, etc. However, there is still much to learn regarding the fundamental mechanisms of crystallization, especially related to the evolution of viscosity as a function of the crystallization (ceramming process. In this study, the impact of phase assemblage and microstructure on the viscosity was investigated using high temperature X-ray diffraction (HTXRD, beam bending viscometry (BBV, and transmission electron microscopy (TEM. Results from this study provide a first direct observation of viscosity evolution as a function of ceramming time and temperature. Sharp viscosity increases due to phase separation, nucleation and phase transformation are noticed through BBV measurement. A near-net shape ceramming can be achieved in TiO2-containing compositions by keeping the glass at a high viscosity (> 109 Pa.s throughout the whole thermal treatment.

Dephasing of LO-phonon-plasmon hybrid modes in n-type GaAs

Science.gov (United States)

Vallée, F.; Ganikhanov, F.; Bogani, F.

1997-11-01

The relaxation dynamics of coherent phononlike LO-phonon-plasmon hybrid modes is investigated in n-doped GaAs using an infrared time-resolved coherent anti-Stokes Raman scattering technique. Measurements performed for different crystal temperatures in the range 10-300 K as a function of the electron density injected by doping show a large reduction of the hybrid mode dephasing time compared to the bare LO-phonon one for densities larger than 1016 cm-3. The results are interpreted in terms of coherent decay of the LO-phonon-plasmon mixed mode in the weak-coupling regime and yield information on the plasmon and electron relaxation. The estimated average electron momentum relaxation times are smaller than those deduced from Hall mobility measurements, as expected from our theoretical model.

Electronic and optical properties of ZrB12 and YB6. Discussion on electron-phonon coupling

International Nuclear Information System (INIS)

Teyssier, J.; Kuzmenko, A.; Marel, D. van der; Lortz, R.; Junod, A.; Filippov, V.; Shitsevalova, N.

2006-01-01

We report the optical properties of high-quality single crystals of low temperature superconductors zirconiumdodecaboride ZrB 12 (T c =5.95 K) and yttrium hexaboride YB 6 (T c =7.15 K) in the range 6 meV-4.6 eV at room temperature. The experimental optical conductivity was extracted from the analysis of the reflectivity in the infrared range and ellipsometry measurement of the dielectric function in the visible range. The electronic band structure of these compounds was calculated by the self-consistent full-potential LMTO method and used to compute the interband part of the optical conductivity and the plasma frequency Ω p . A good agreement was observed between the interband part of the experimental optical conductivities and the band structure calculations. Different methods combining optical spectroscopy, resistivity, specific heat measurements and results of band structure calculations are used to determine the electron-phonon coupling constant. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Effective electron mass and phonon modes in n-type hexagonal InN

Science.gov (United States)

Kasic, A.; Schubert, M.; Saito, Y.; Nanishi, Y.; Wagner, G.

2002-03-01

Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and electronic properties of high-quality hexagonal InN. The 0.22-μm-thick highly n-conductive InN film was grown on c-plane sapphire by radio-frequency molecular-beam epitaxy. Combining our results from the ellipsometry data analysis with Hall-effect measurements, the isotropically averaged effective electron mass in InN is determined as 0.14m0. The resonantly excited zone center E1 (TO) phonon mode is observed at 477 cm-1 in the ellipsometry spectra. Despite the high electron concentration in the film, a strong Raman mode occurs in the spectral range of the unscreened A1(LO) phonon. Because an extended carrier-depleted region at the sample surface can be excluded from the ellipsometry-model analysis, we assign this mode to the lower branch of the large-wave-vector LO-phonon-plasmon coupled modes arising from nonconserving wave-vector scattering processes. The spectral position of this mode at 590 cm-1 constitutes a lower limit for the unscreened A1(LO) phonon frequency.

Thermodynamic and relative approach to compute glass-forming

Indian Academy of Sciences (India)

This study deals with the evaluation of glass-forming ability (GFA) of oxides and is a critical reading of Sun and Rawson thermodynamic approach to quantify this aptitude. Both approaches are adequate but ambiguous regarding the behaviour of some oxides (tendency to amorphization or crystallization). Indeed, ZrO2 and ...

Crystallization Kinetics of Barium and Strontium Aluminosilicate Glasses of Feldspar Composition

Science.gov (United States)

Hyatt, Mark J.; Bansal, Narottam P.

1994-01-01

Crystallization kinetics of BaO.Al2O3.2SiO2 (BAS) and SrO.Al2O3.2SiO2 (SAS) glasses in bulk and powder forms have been studied by non-isothermal differential scanning calorimetry (DSC). The crystal growth activation energies were evaluated to be 473 and 451 kJ/mol for bulk samples and 560 and 534 kJ/mol for powder specimens in BAS and SAS glasses, respectively. Development of crystalline phases on thermal treatments of glasses at various temperatures has been followed by powder x-ray diffraction. Powder samples crystallized at lower temperatures than the bulk and the crystallization temperature was lower for SAS glass than BAS. Crystallization in both glasses appeared to be surface nucleated. The high temperature phase hexacelsian, MAl2Si2O8 (M = Ba or Sr), crystallized first by nucleating preferentially on the glass surface. Also, monoclinic celsian does not nucleate directly in the glass, but is formed at higher temperatures from the transformation of the metastable hexagonal phase. In SAS the transformation to monoclinic celsian occurred rapidly after 1 h at 1100 C. In contrast, in BAS this transformation is sluggish and difficult and did not go to completion even after 10 h heat treatment at 1400 C. The crystal growth morphologies in the glasses have been observed by optical microscopy. Some of the physical properties of the two glasses are also reported.

Extreme low thermal conductivity in nanoscale 3D Si phononic crystal with spherical pores.

Science.gov (United States)

Yang, Lina; Yang, Nuo; Li, Baowen

2014-01-01

In this work, we propose a nanoscale three-dimensional (3D) Si phononic crystal (PnC) with spherical pores, which can reduce the thermal conductivity of bulk Si by a factor up to 10,000 times at room temperature. Thermal conductivity of Si PnCs depends on the porosity, for example, the thermal conductivity of Si PnCs with porosity 50% is 300 times smaller than that of bulk Si. The phonon participation ratio spectra demonstrate that more phonons are localized as the porosity increases. The thermal conductivity is insensitive to the temperature changes from room temperature to 1100 K. The extreme-low thermal conductivity could lead to a larger value of ZT than unity as the periodic structure affects very little the electric conductivity.

Parylene-C microfibrous thin films as phononic crystals

Science.gov (United States)

Chindam, Chandraprakash; Lakhtakia, Akhlesh; Awadelkarim, Osama O.

2017-07-01

Phononic bandgaps of Parylene-C microfibrous thin films ( μ\\text{FTF} s) were computationally determined by treating them as phononic crystals comprising identical microfibers arranged either on a square or a hexagonal lattice. The microfibers could be columnar, chevronic, or helical in shape, and the host medium could be either water or air. All bandgaps were observed to lie in the 0.01-162.9-MHz regime, for microfibers of realistically chosen dimensions. The upper limit of the frequency of bandgaps was the highest for the columnar μ\\text{FTF} and the lowest for the chiral μ\\text{FTF} . More bandgaps exist when the host medium is water than air. Complete bandgaps were observed for the columnar μ\\text{FTF} with microfibers arranged on a hexagonal lattice in air, the chevronic μ\\text{FTF} with microfibers arranged on a square lattice in water, and the chiral μ\\text{FTF} with microfibers arranged on a hexagonal lattice in either air or water. The softness of the Parylene-C μ\\text{FTF} s makes them mechanically tunable, and their bandgaps can be exploited in multiband ultrasonic filters.

Damping of acoustic flexural phonons in silicene: influence on high-field electronic transport

Science.gov (United States)

Rengel, Raúl; Iglesias, José M.; Mokhtar Hamham, El; Martín, María J.

2018-06-01

Silicene is a two-dimensional buckled material with broken horizontal mirror symmetry and Dirac-like dispersion. Under such conditions, flexural acoustic (ZA) phonons play a dominant role. Consequently, it is necessary to consider some suppression mechanism for electron–phonon interactions with long wavelengths in order to reach mobilities useful for electronic applications. In this work, we analyze, by means of an ensemble Monte Carlo simulator, the influence of several possibilities for the description of the effect of ZA phonon damping on electronic transport in silicene. The results show that a hard cutoff situation (total suppression for phonons with a wavelength longer than a critical one), as it has been proposed in the literature, does not yield a realistic picture regarding the electronic distribution function, and it artificially induces a negative differential resistance at moderate and high fields. Sub-parabolic dispersions, on the other hand, may provide a more realistic description in terms of the behavior of the electron distribution in the momentum space, but need extremely short cutoff wavelengths to reach functional mobility and drift velocity values.

Experimental study on slow flexural waves around the defect modes in a phononic crystal beam using fiber Bragg gratings

Energy Technology Data Exchange (ETDEWEB)

Chuang, Kuo-Chih, E-mail: chuangkc@zju.edu.cn; Zhang, Zhi-Qiang; Wang, Hua-Xin

2016-12-09

Highlights: • Slow waves around the defect modes in a phononic crystal beam are validated. • A fiber Bragg grating displacement sensing system can measure the defect mode. • The defect mode is analyzed by a transfer matrix method with a supercell technique. - Abstract: This work experimentally studies influences of the point defect modes on the group velocity of flexural waves in a phononic crystal Timoshenko beam. Using the transfer matrix method with a supercell technique, the band structures and the group velocities around the defect modes are theoretically obtained. Particularly, to demonstrate the existence of the localized defect modes inside the band gaps, a high-sensitivity fiber Bragg grating sensing system is set up and the displacement transmittance is measured. Slow propagation of flexural waves via defect coupling in the phononic crystal beam is then experimentally demonstrated with Hanning windowed tone burst excitations.

Tunable waveguide and cavity in a phononic crystal plate by controlling whispering-gallery modes in hollow pillars

DEFF Research Database (Denmark)

Jin, Yabin; Fernez, Nicolas; Pennec, Yan

2016-01-01

We investigate the properties of a phononic crystal plate with hollow pillars and introduce the existence of whispering-gallery modes (WGMs). We show that by tuning the inner radius of the hollow pillar, these modes can merge inside both Bragg and low frequency band gaps, deserving phononic crystal...... and acoustic metamaterial applications. These modes can be used as narrow pass bands for which the quality factor can be greatly enhanced by the introduction of an additional cylinder between the hollow cylinder and the plate. We discuss some functionalities of these confined WGM in both Bragg and low...

The phase transformation and crystallization kinetics of (1 - x)Li2O-xNa2O-Al2O3-4SiO2 glasses

International Nuclear Information System (INIS)

Wang, Moo-Chin; Li, Wang-Long; Cheng, Chih-Wei; Chang, Kuo-Ming; Chen, Yong-Feng; Hsi, Chi-Shiung

2010-01-01

The phase transformation and crystallization kinetics of (1 - x)Li 2 O-xNa 2 O-Al 2 O 3 -4SiO 2 glasses have been studied by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) analysis. The crystallization temperature at the exothermic peak increases from 1171 to 1212 K when the Na 2 O content increases from 0 to 0.6 mol. The crystalline phase is composed of spodumene crystallization when the Na 2 O content increases from 0 to 0.6 mol. The activation energy of spodumene crystallization decreases from 444.0 ± 22.2 to 284.0 ± 10.8 kJ mol -1 when the Na 2 O content increases from 0 to 0.4 mol. Moreover, the activation energy increases from 284.0 ± 10.8 to 446.0 ± 23.2 kJ mol -1 when the Na 2 O content increases from 0.4 to 0.6 mol. The crystallization parameters m and n approach 2, indicating that the surface nucleation and two-dimensional growth are dominant in (1 - x)Li 2 O-xNa 2 O-Al 2 O 3 -4SiO 2 glasses.

Experimental Study of Electron and Phonon Dynamics in Nanoscale Materials by Ultrafast Laser Time-Domain Spectroscopy

Science.gov (United States)

Shen, Xiaohan

With the rapid advances in the development of nanotechnology, nowadays, the sizes of elementary unit, i.e. transistor, of micro- and nanoelectronic devices are well deep into nanoscale. For the pursuit of cheaper and faster nanoscale electronic devices, the size of transistors keeps scaling down. As the miniaturization of the nanoelectronic devices, the electrical resistivity increases dramatically, resulting rapid growth in the heat generation. The heat generation and limited thermal dissipation in nanoscale materials have become a critical problem in the development of the next generation nanoelectronic devices. Copper (Cu) is widely used conducting material in nanoelectronic devices, and the electron-phonon scattering is the dominant contributor to the resistivity in Cu nanowires at room temperature. Meanwhile, phonons are the main carriers of heat in insulators, intrinsic and lightly doped semiconductors. The thermal transport is an ensemble of phonon transport, which strongly depends on the phonon frequency. In addition, the phonon transport in nanoscale materials can behave fundamentally different than in bulk materials, because of the spatial confinement. However, the size effect on electron-phonon scattering and frequency dependent phonon transport in nanoscale materials remain largely unexplored, due to the lack of suitable experimental techniques. This thesis is mainly focusing on the study of carrier dynamics and acoustic phonon transport in nanoscale materials. The weak photothermal interaction in Cu makes thermoreflectance measurement difficult, we rather measured the reflectivity change of Cu induced by absorption variation. We have developed a method to separately measure the processes of electron-electron scattering and electron-phonon scattering in epitaxial Cu films by monitoring the transient reflectivity signal using the resonant probe with particular wavelengths. The enhancement on electron-phonon scattering in epitaxial Cu films with thickness

Phonon shake-up satellites in x-ray absorption: an operator approach

International Nuclear Information System (INIS)

Bryant, G.W.

1980-01-01

The phonon shake-up that occurs when the linear and quadratic phonon potentials both change during x-ray absorption is considered. Full account of all quadratic terms and the competition between linear and quadratic shake-up effects is made. Many previous studies of quadratic phonon shake-up have used a wavefunction approach. The phonon matrix elements have been determined by explicit evaluation of the overlap integrals. However, an equations of motion approach is used to transform the time evolution operator to a form that allows an exact evaluation of the phonon matrix elements needed to describe the spectra. This theory is used to determine the strengths of the phonon shake-up satellites in x-ray absorption spectra at zero temperature. An exact expression is obtained for the strength of each satellite. During quadratic shake-up, two phonon transitions and phonon frequency shifts occur. Both effects significantly change the strength of a a satellite from that predicted for linear shake-up alone. Inclusion of the two phonon transitions enhances the high-energy satellites. Inclusion of the frequency shifts can either broaden the spectra or increase the strength of the zero phonon lines depending on the sign of the frequency shift. (author)

Structure and spectroscopy of rare earth – Doped lead phosphate glasses

International Nuclear Information System (INIS)

Pisarski, Wojciech A.; Żur, Lidia; Goryczka, Tomasz; Sołtys, Marta; Pisarska, Joanna

2014-01-01

Highlights: • Lead phosphate glasses doped with rare earth ions were prepared. • The local structure was examined using X-ray diffraction and spectroscopic methods. • Different structural phosphate groups are present in lead phosphate glasses. • The electron–phonon coupling strength and phonon energy of the glass host was determined. • Several observed emission bands are due to 4f–4f electronic transitions of rare earth ions. -- Abstract: Lead–gallium phosphate glasses doped with rare the earth ions (Eu 3+ , Dy 3+ , Tb 3+ , Er 3+ ) were synthesized. The structure of obtained glasses was examined by means of use: X-ray diffraction (XRD), nuclear magnetic resonance ( 207 Pb and 31 P NMR), fourier transform infrared (FT-IR) and Raman spectroscopy. In contrast to fully amorphous Ln-doped samples (Ln = Eu, Dy, Tb), in Er-doped sample the GaPO 4 crystalline phase was identified. It was found from the NMR, FT-IR and Raman spectroscopic techniques that, different structural phosphate groups were present in lead phosphate glasses. Based on absorption measurements, the UV–VIS cut-off wavelength for lead phosphate glass was determined and its value is close to 305 nm. Excitation and emission spectra of rare earths were also detected. From excitation spectra of Eu 3+ the electron–phonon coupling strength and phonon energy of the glass host were determined. Due to 4f 6 –4f 6 (Eu 3+ ), 4f 8 –4f 8 (Tb 3+ ), 4f 9 –4f 9 (Dy 3+ ) and 4f 11 –4f 11 (Er 3+ ) electronic transitions of trivalent rare earth ions several luminescence bands were stated

Breaking Through the Glass Ceiling: Recent Experimental Approaches to Probe the Properties of Supercooled Liquids near the Glass Transition.

Science.gov (United States)

Smith, R Scott; Kay, Bruce D

2012-03-15

Experimental measurements of the properties of supercooled liquids at temperatures near their glass transition temperatures, Tg, are requisite for understanding the behavior of glasses and amorphous solids. Unfortunately, many supercooled molecular liquids rapidly crystallize at temperatures far above their Tg, making such measurements difficult to nearly impossible. In this Perspective, we discuss some recent alternative approaches to obtain experimental data in the temperature regime near Tg. These new approaches may yield the additional experimental data necessary to test current theoretical models of the dynamical slowdown that occurs in supercooled liquids approaching the glass transition.

Band structures in a two-dimensional phononic crystal with rotational multiple scatterers

Science.gov (United States)

Song, Ailing; Wang, Xiaopeng; Chen, Tianning; Wan, Lele

2017-03-01

In this paper, the acoustic wave propagation in a two-dimensional phononic crystal composed of rotational multiple scatterers is investigated. The dispersion relationships, the transmission spectra and the acoustic modes are calculated by using finite element method. In contrast to the system composed of square tubes, there exist a low-frequency resonant bandgap and two wide Bragg bandgaps in the proposed structure, and the transmission spectra coincide with band structures. Specially, the first bandgap is based on locally resonant mechanism, and the simulation results agree well with the results of electrical circuit analogy. Additionally, increasing the rotation angle can remarkably influence the band structures due to the transfer of sound pressure between the internal and external cavities in low-order modes, and the redistribution of sound pressure in high-order modes. Wider bandgaps are obtained in arrays composed of finite unit cells with different rotation angles. The analysis results provide a good reference for tuning and obtaining wide bandgaps, and hence exploring the potential applications of the proposed phononic crystal in low-frequency noise insulation.

Band structures of phononic crystal composed of lattices with different periodic constants

International Nuclear Information System (INIS)

Hu, Jia-Guang; Xu, Wen

2014-01-01

With a square lattice mercury and water system being as the model, the band structures of nesting and compound phononic crystals with two different lattice constants were investigated using the method of the supercell plane wave expansion. It was observed that large band gaps can be achieved in low frequency regions by adjusting one of the lattice constants. Meanwhile, effects similar to interstitial impurity defects can be achieved with the increase of lattice constant of the phononic crystal. The corresponding defect modes can be stimulated in band gaps. The larger the lattice constant, the stronger the localization effect of defect modes on the wave. In addition, the change of the filling fraction of impurity exerts great influence on the frequency and localization of defect modes. Furthermore, the change of the position of impurity has notable influence on the frequency of defect modes and their localization. However, the geometry structure and orientation of impurity have little effect on the frequency of defect modes and their localization in the band gap.

Band structures in the nematic elastomers phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Yang, Shuai [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China); School of Civil Engineering and Architecture, Anyang Normal University, Anyang 455000 (China); Liu, Ying, E-mail: yliu5@bjtu.edu.cn [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China); Liang, Tianshu [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China)

2017-02-01

As one kind of new intelligent materials, nematic elastomers (NEs) represent an exciting physical system that combines the local orientational symmetry breaking and the entropic rubber elasticity, producing a number of unique physical phenomena. In this paper, the potential application of NEs in the band tuning is explored. The band structures in two kinds of NE phononic crystals (PCs) are investigated. Through changing NE intrinsic parameters, the influence of the porosity, director rotation and relaxation on the band structures in NE PCs are analyzed. This work is a meaningful try for application of NEs in acoustic field and proposes a new intelligent strategy in band turning.

Band structures in the nematic elastomers phononic crystals

International Nuclear Information System (INIS)

Yang, Shuai; Liu, Ying; Liang, Tianshu

2017-01-01

As one kind of new intelligent materials, nematic elastomers (NEs) represent an exciting physical system that combines the local orientational symmetry breaking and the entropic rubber elasticity, producing a number of unique physical phenomena. In this paper, the potential application of NEs in the band tuning is explored. The band structures in two kinds of NE phononic crystals (PCs) are investigated. Through changing NE intrinsic parameters, the influence of the porosity, director rotation and relaxation on the band structures in NE PCs are analyzed. This work is a meaningful try for application of NEs in acoustic field and proposes a new intelligent strategy in band turning.

Vertex function for the coupling of an electron with intramolecular phonons: Exact results in the antiadiabatic limit

International Nuclear Information System (INIS)

Takada, Y.; Higuchi, T.

1995-01-01

The Green's-function techniques, especially the one developed in the preceding paper [Takada, Phys. Rev. B 52, 12 708 (1995)], are employed to calculate the electron-phonon vertex part as well as the electronic self-energy exactly on both real- and imaginary-frequency axes in the electron-phonon Holstein model with the on-site Coulomb repulsion in the limit in which the intramolecular phonon energy ω 0 is much larger than the electronic bandwidth. The rigorous vertex part is found to diverge at the frequencies at which an electron is locked by such local phonons with an infinitely strong effective coupling. Characteristic frequencies of this divergence, which are not equal to multiples of ω 0 , are calculated as a function of the electron-phonon bare coupling constant. Our results for the self-energy are checked successfully with the exact ones obtained by the Lang-Firsov canonical transformation

The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy

International Nuclear Information System (INIS)

Lynch, D.W.

2004-01-01

With recent advances in energy and angle resolution, the effects of electron-phonon interactions are manifest in many valence-band photoelectron spectra (PES) for states near the Fermi level in metals

Double Dirac cones in phononic crystals

KAUST Repository

Li, Yan

2014-07-07

A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.

Double Dirac cones in phononic crystals

KAUST Repository

Li, Yan; Wu, Ying; Mei, Jun

2014-01-01

A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.

Correlation between phonon anomaly along [211] and the Fermi surface nesting features with associated electron-phonon interactions in Ni2FeGa: A first principles study

International Nuclear Information System (INIS)

Chabungbam, Satyananda; Sahariah, Munima B.

2015-01-01

First principles calculation reaffirms the presence of phonon anomaly along [211] direction in Ni 2 FeGa shape memory alloy supporting the experimental findings of J. Q. Li et al. Fermi surface scans have been performed in both austenite and martensite phase to see the possible Fermi nesting features in this alloy. The magnitude of observed Fermi surface nesting vectors in (211) plane exactly match the phonon anomaly wavevectors along [211] direction. Electron-phonon calculation in the austenite phase shows that there is significant electron-phonon coupling in this alloy which might arise out of the lattice coupling between lower acoustic modes and higher optical modes combined with the observed strong Fermi nesting features in the system. - Highlights: • Transverse acoustic (TA 2 ) modes show anomaly along [211] direction in Ni 2 FeGa. • The phonon anomaly wavevector has been correlated with the Fermi nesting vectors. • Electron-phonon coupling calculation shows significant coupling in this system. • Max. el-ph coupling occurs in transition frequencies from acoustic to optical modes

Ab initio theory of charge-carrier conduction in ultrapure organic crystals

NARCIS (Netherlands)

Hannewald, K.; Bobbert, P.A.

2004-01-01

We present an ab initio description of charge-carrier mobilities in organic molecular crystals of high purity. Our approach is based on Holstein's original concept of small-polaron bands but generalized with respect to the inclusion of nonlocal electron-phonon coupling. By means of an explicit

Phonon dispersion and Kohn anomalies in the alloy Cu8.84Al0.16

International Nuclear Information System (INIS)

Chou, H.; Shapiro, S.M.; Moss, S.C.; Mostoller, M.

1990-01-01

The authors have made detailed measurements of phonon frequencies along all high-symmetry directions on a large single crystal of Cu 0.84 Al 0.16 at room temperature. Phonon frequencies were ascertained to better than ±0.03 meV. Inter-atomic force constants and vibrational density of states were calculated by performing a Born-von Karman analysis on the complete set of phonon dispersion curves. In contrast to the case of pure Cu, no evident Kohn anomaly (neither in the phonon dispersion itself nor in the derivatives) was observed near the expected wave vector q = 2k F . The absence of Kohn anomalies in the present system could be due either to a smeared out Fermi surface or to the possibility that the electron-electron interaction which screens the inter-ionic potential is not the dominant interaction in the system: i.e., the existence of Kohn anomalies in these alloys may depend mainly on the details of the electron-phonon interaction

A Numerical Study on Phonon Spectral Contributions to Thermal Conduction in Silicon-on-Insulator Transistor Using Electron-Phonon Interaction Model

Energy Technology Data Exchange (ETDEWEB)

Kang, Hyung-sun; Koh, Young Ha; Jin, Jae Sik [Chosun College of Science and Technology, Gwangju (Korea, Republic of)

2017-06-15

The aim of this study is to understand the phonon transfer characteristics of a silicon thin film transistor. For this purpose, the Joule heating mechanism was considered through the electron-phonon interaction model whose validation has been done. The phonon transport characteristics were investigated in terms of phonon mean free path for the variations in the device power and silicon layer thickness from 41 nm to 177 nm. The results may be used for developing the thermal design strategy for achieving reliability and efficiency of the silicon-on-insulator (SOI) transistor, further, they will increase the understanding of heat conduction in SOI systems, which are very important in the semiconductor industry and the nano-fabrication technology.

Optical Basicity and Nepheline Crystallization in High Alumina Glasses

Energy Technology Data Exchange (ETDEWEB)

Rodriguez, Carmen P.; McCloy, John S.; Schweiger, M. J.; Crum, Jarrod V.; Winschell, Abigail E.

2011-02-25

The purpose of this study was to find compositions that increase waste loading of high-alumina wastes beyond what is currently acceptable while avoiding crystallization of nepheline (NaAlSiO4) on slow cooling. Nepheline crystallization has been shown to have a large impact on the chemical durability of high-level waste glasses. It was hypothesized that there would be some composition regions where high-alumina would not result in nepheline crystal production, compositions not currently allowed by the nepheline discriminator. Optical basicity (OB) and the nepheline discriminator (ND) are two ways of describing a given complex glass composition. This report presents the theoretical and experimental basis for these models. They are being studied together in a quadrant system as metrics to explore nepheline crystallization and chemical durability as a function of waste glass composition. These metrics were calculated for glasses with existing data and also for theoretical glasses to explore nepheline formation in Quadrant IV (passes OB metric but fails ND metric), where glasses are presumed to have good chemical durability. Several of these compositions were chosen, and glasses were made to fill poorly represented regions in Quadrant IV. To evaluate nepheline formation and chemical durability of these glasses, quantitative X-ray diffraction (XRD) analysis and the Product Consistency Test were conducted. A large amount of quantitative XRD data is collected here, both from new glasses and from glasses of previous studies that had not previously performed quantitative XRD on the phase assemblage. Appendix A critically discusses a large dataset to be considered for future quantitative studies on nepheline formation in glass. Appendix B provides a theoretical justification for choice of the oxide coefficients used to compute the OB criterion for nepheline formation.

Double stage crystallization of bulk Ge20Te80 glass

International Nuclear Information System (INIS)

Parthasarathy, G.; Bandyopadhyay, A.K.; Gopal, E.S.R.; Subbanna, G.N.

1984-01-01

The growing interest of the semiconducting glasses is partly because of their interesting electrical and optical properties. These properties are usually connected with their crystallization. In many glasses, the glass-supercooled liquid transition precedes crystallization. The glass transition temperature (Tsub(g)) is found to exhibit multistage processes for a few systems. In this communication, we report the observation of a double Tsub(g) effect in bulk Ge 20 Te 80 glass and also explain the structural changes taking place in the two stages. (author)

Effect of reducing conditions of synthesis on the character of the crystallization of phosphate glasses

Energy Technology Data Exchange (ETDEWEB)

Alekseeva, I.P.; Karapetyan, G.O.; Milyukov, E.M.; Rusan, V.V.

1986-03-01

The authors investigate the effect of synthesis conditions on the properties of phosphate glasses with a high concentration of rare-earth elements (REE) which are promising materials for quantum electronics. Particular attention was paid to the character of the crystallization of the glasses. A model glass of the composition La/sub 2/O/sub 3/ X 3P/sub 2/O/sub 5/ was studied which is transparent in the visible and near-IR regions of the spectrum and produced commercially.

A thermally tunable inverse opal photonic crystal for monitoring glass transition.

Science.gov (United States)

Sun, Liguo; Xie, Zhuoying; Xu, Hua; Xu, Ming; Han, Guozhi; Wang, Cheng; Bai, Xuduo; Gu, ZhongZe

2012-03-01

An optical method was developed to monitor the glass transition of the polymer by taking advantage of reflection spectrum change of the thermally tunable inverse opal photonic crystal. The thermally tunable photonic bands of the polymer inverse opal photonic crystal were traceable to the segmental motion of macromolecules, and the segmental motion was temperature dependent. By observing the reflection spectrum change of the polystyrene inverse opal photonic crystal during thermal treatment, the glass transition temperature of polystyrene was gotten. Both changes of the position and intensity of the reflection peak were observed during the glass transition process of the polystyrene inverse opal photonic crystal. The optical change of inverse opal photonic crystal was so large that the glass transition temperature could even be estimated by naked eyes. The glass transition temperature derived from this method was consistent with the values measured by differential scanning calorimeter.

Langevin Dynamics with Spatial Correlations as a Model for Electron-Phonon Coupling

Science.gov (United States)

Tamm, A.; Caro, M.; Caro, A.; Samolyuk, G.; Klintenberg, M.; Correa, A. A.

2018-05-01

Stochastic Langevin dynamics has been traditionally used as a tool to describe nonequilibrium processes. When utilized in systems with collective modes, traditional Langevin dynamics relaxes all modes indiscriminately, regardless of their wavelength. We propose a generalization of Langevin dynamics that can capture a differential coupling between collective modes and the bath, by introducing spatial correlations in the random forces. This allows modeling the electronic subsystem in a metal as a generalized Langevin bath endowed with a concept of locality, greatly improving the capabilities of the two-temperature model. The specific form proposed here for the spatial correlations produces a physical wave-vector and polarization dependency of the relaxation produced by the electron-phonon coupling in a solid. We show that the resulting model can be used for describing the path to equilibration of ions and electrons and also as a thermostat to sample the equilibrium canonical ensemble. By extension, the family of models presented here can be applied in general to any dense system, solids, alloys, and dense plasmas. As an example, we apply the model to study the nonequilibrium dynamics of an electron-ion two-temperature Ni crystal.

Infrequent blue and green emission transitions from Eu3+ in heavy metal tellurite glasses with low phonon energy

International Nuclear Information System (INIS)

Lin, H.; Tanabe, S.; Lin, L.; Yang, D.L.; Liu, K.; Wong, W.H.; Yu, J.Y.; Pun, E.Y.B.

2006-01-01

Eu 3+ doped alkali-barium-bismuth-tellurite (Eu 3+ :LKBBT) glasses were prepared by conventional melt quenching. Twelve emission bands including infrequent blue and green bands are observed and they almost cover whole visible spectral region under violet light radiation. The blue and green emissions of Eu 3+ rarely appeared in oxide glasses before, but they have been clearly recorded in Eu 3+ :LKBBT glasses even in the case of high concentration doping of Eu 3+ . The analysis based on spontaneous-radiative rate, energy gap and Raman scattering reveals that the obtaining of the abundant multichannel emissions of Eu 3+ is due to the higher refractive index and the lower phonon energy in LKBBT glass system

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

Science.gov (United States)

Lee, Nien-En; Zhou, Jin-Jian; Agapito, Luis A.; Bernardi, Marco

2018-03-01

Predicting charge transport in organic molecular crystals is notoriously challenging. Carrier mobility calculations in organic semiconductors are dominated by quantum chemistry methods based on charge hopping, which are laborious and only moderately accurate. We compute from first principles the electron-phonon scattering and the phonon-limited hole mobility of naphthalene crystal in the framework of ab initio band theory. Our calculations combine GW electronic bandstructures, ab initio electron-phonon scattering, and the Boltzmann transport equation. The calculated hole mobility is in very good agreement with experiment between 100 -300 K , and we can predict its temperature dependence with high accuracy. We show that scattering between intermolecular phonons and holes regulates the mobility, though intramolecular phonons possess the strongest coupling with holes. We revisit the common belief that only rigid molecular motions affect carrier dynamics in organic molecular crystals. Our paper provides a quantitative and rigorous framework to compute charge transport in organic crystals and is a first step toward reconciling band theory and carrier hopping computational methods.

Study of crystal-field excitations and Raman active phonons in o-DyMnO3

International Nuclear Information System (INIS)

Jandl, S.; Mansouri, S.; Mukhin, A.A.; Yu Ivanov, V.; Balbashov, A.; Gospodino, M.M.; Nekvasil, V.; Orlita, M.

2011-01-01

In DyMnO 3 orthorhombic single crystals, the weak Raman active phonon softening below T=100 K is correlated with the study of infrared active Dy 3+ CF excitations as a function of temperature and under applied magnetic field. We detect five H 13/2 CF transitions that we predict with appropriate CF Hamiltonian and we confirm that the magnetic easy axis lies in the ab plane. While the CF energy level shifts below T=100 K reflect different displacements of the oxygen ions that contribute to the phonon softening, lifting of the ground state Kramers doublet degeneracy (∼30 cm -1 ) is observed below T N =39 K due to the anisotropic Mn 3+ -Dy 3+ interaction, which could be responsible for the stability of the bc-cycloid ferroelectric phase. - Research highlights: → Origin of Raman active phonon softening in the multiferroic o-DyMnO 3 . → A crystal-field study under magnetic field of Dy 3+ in o-DyMnO 3 . → Location of the magnetic easy axis in o-DyMnO 3 . → Lifting of Kramers doublet degeneracy in o-DyMnO 3 .

Phonon squeezed states: quantum noise reduction in solids

Science.gov (United States)

Hu, Xuedong; Nori, Franco

1999-03-01

This article discusses quantum fluctuation properties of a crystal lattice, and in particular, phonon squeezed states. Squeezed states of phonons allow a reduction in the quantum fluctuations of the atomic displacements to below the zero-point quantum noise level of coherent phonon states. Here we discuss our studies of both continuous-wave and impulsive second-order Raman scattering mechanisms. The later approach was used to experimentally suppress (by one part in a million) fluctuations in phonons. We calculate the expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators, as well as the effects of the phonon squeezed states on macroscopically measurable quantities, such as changes in the dielectric constant. These results are compared with recent experiments. Further information, including preprints and animations, are available in http://www-personal.engin.umich.edu/∼nori/squeezed.html.

Heat Exchange Between Electrons and Phonons in Nanosystems at Sub-Kelvin Temperatures

Directory of Open Access Journals (Sweden)

Anghel Dragoş-Victor

2018-01-01

Full Text Available Ultra-sensitive nanoscopic detectors for electromagnetic radiation consist of thin metallic films deposited on dielectric membranes. The metallic films, of thickness d of the order of 10 nm, form the thermal sensing element (TSE, which absorbs the incident radiation and measures its power flux or the energies of individual photons. To achieve the sensitivity required for astronomical observations, the TSE works at temperatures of the order of 0.1 K. The dielectric membranes are used as support and for thermal insulation of the TSE and are of thickness L − d of the order of 100 nm (L being the total thickness of the system. In such conditions, the phonon gas in the detector assumes a quasi-two-dimensional distribution, whereas quantization of the electrons wavenumbers in the direction perpendicular to the film surfaces leads to the formation of quasi two-dimensional electronic sub-bands. The heat exchange between electrons and phonons has an important contribution to the performance of the device and is dominated by the interaction between the electrons and the antisymmetric acoustic phonons.

Relativistic electron Wigner crystal formation in a cavity for electron acceleration

CERN Document Server

Thomas, Johannes; Pukhov, Alexander

2014-01-01

It is known that a gas of electrons in a uniform neutralizing background can crystallize and form a lattice if the electron density is less than a critical value. This crystallization may have two- or three-dimensional structure. Since the wake field potential in the highly-nonlinear-broken-wave regime (bubble regime) has the form of a cavity where the background electrons are evacuated from and only the positively charged ions remain, it is suited for crystallization of trapped and accelerated electron bunch. However, in this case, the crystal is moving relativistically and shows new three-dimensional structures that we call relativistic Wigner crystals. We analyze these structures using a relativistic Hamiltonian approach. We also check for stability and phase transitions of the relativistic Wigner crystals.

Glass Transition, Crystallization of Glass-Forming Melts, and Entropy

Directory of Open Access Journals (Sweden)

Jürn W. P. Schmelzer

2018-02-01

Full Text Available A critical analysis of possible (including some newly proposed definitions of the vitreous state and the glass transition is performed and an overview of kinetic criteria of vitrification is presented. On the basis of these results, recent controversial discussions on the possible values of the residual entropy of glasses are reviewed. Our conclusion is that the treatment of vitrification as a process of continuously breaking ergodicity with entropy loss and a residual entropy tending to zero in the limit of zero absolute temperature is in disagreement with the absolute majority of experimental and theoretical investigations of this process and the nature of the vitreous state. This conclusion is illustrated by model computations. In addition to the main conclusion derived from these computations, they are employed as a test for several suggestions concerning the behavior of thermodynamic coefficients in the glass transition range. Further, a brief review is given on possible ways of resolving the Kauzmann paradox and its implications with respect to the validity of the third law of thermodynamics. It is shown that neither in its primary formulations nor in its consequences does the Kauzmann paradox result in contradictions with any basic laws of nature. Such contradictions are excluded by either crystallization (not associated with a pseudospinodal as suggested by Kauzmann or a conventional (and not an ideal glass transition. Some further so far widely unexplored directions of research on the interplay between crystallization and glass transition are anticipated, in which entropy may play—beyond the topics widely discussed and reviewed here—a major role.

Multi-channel unidirectional transmission of phononic crystal heterojunctions

Science.gov (United States)

Xu, Zhenlong; Tong, Jie; Wu, Fugen

2018-02-01

Two square steel columns are arranged in air to form two-dimensional square lattice phononic crystals (PNCs). Two PNCs can be combined into a non-orthogonal 45∘ heterojunction when the difference in the directional band gaps of the two PNC types is utilized. The finite element method is used to calculate the acoustic band structure, the heterogeneous junction transmission characteristics, acoustic field distribution, and many others. Results show that a non-orthogonal PNC heterojunction can produce a multi-channel unidirectional transmission of acoustic waves. With the square scatterer rotated, the heterojunction can select a frequency band for unidirectional transmission performance. This capability is particularly useful for constructing acoustic diodes with wide-bands and high-efficiency unidirectional transmission characteristics.

Rare earth ion controlled crystallization of mica glass-ceramics

International Nuclear Information System (INIS)

Garai, Mrinmoy; Karmakar, Basudeb

2016-01-01

In understanding the effects of rare earth ions to control the crystallization and microstructure of alkaline boroaluminosilicate system, the CeO_2, Nd_2O_3, Sm_2O_3 and Gd_2O_3 doped K_2O−MgO−B_2O_3−Al_2O_3−SiO_2−F glasses were synthesized by melt-quenching at 1550 °C. Higher density (2.82–3.06 g cm"−"3) and thermal stability (glass phase) is experiential on addition of rare earth content, which also affects in increasing the glass transition temperature (T_g) and crystallization temperature (T_c). Decrease of thermal expansion in glasses with rare earth ion content is maintained by the stabilization of glass matrix owing to their large cationic field strength. A significant change in the non-isothermal DSC thermogram observed at 750–1050 °C is attributed to fluorophlogopite crystallization. Opaque glass-ceramics were prepared from such glasses by single step heat-treatment at 1050 °C; and the predominant crystalline phases are identified as fluorophlogopite mica, KMg_3(AlSi_3O_1_0)F_2 by XRD and EDX analysis. The compact glass-ceramic microstructure by the agglomeration of fluorophlogopite mica crystallites (crystal size ∼ 100–500 nm, FESEM) is achieved in attendance of rare earth ion; and such microstructure controlled the variation of density, thermal expansion and microhardness value. Higher thermal expansion (11.11–14.08 × 10"−"6/K at 50–800 °C and 50–900 °C) of such glass-ceramics approve that these rare earth containing glasses can be useful for high temperature vacuum sealing application with metal or solid electrolyte. The increase of Vickers microhardness (5.27–5.61 GPa) in attendance of rare earth ions is attributed to the compact crystallinity of fluorophlogopite mica glass-ceramic microstructure. - Highlights: • Synthesis of rare earth oxide doped alkaline boroaluminosilicate glasses. • Development of opaque fluorophlogopite mica glass-ceramics by single-step heat treatment. • Nanocrystalline glass

Effects of crystal size on the mechanical properties of a lithium disilicate glass-ceramic

Energy Technology Data Exchange (ETDEWEB)

Li, D. [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, 28 West Xianning Road, Xi’an 710049 (China); Guo, J.W.; Wang, X.S; Zhang, S.F. [State Key Laboratory of Military Stomatology, Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, 145 West Changle Road, Xi’an 710032 (China); He, L., E-mail: helin@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, 28 West Xianning Road, Xi’an 710049 (China)

2016-07-04

Crystal size of lithium disilicate (LD) phase in a LD glass-ceramic was changed by thermally controlled crystallization of a precursory LD glass at different temperatures. Effects of the crystal size on the mechanical properties of the glass-ceramic were investigated. It was found that the flexural strength presented a hump-like variation trend with increasing the crystal size, the hardness monotonously decreased at the same time. It was further confirmed that micro residual compressive stresses existed inside the LD crystals due to the thermal expansion mismatch between the glass matrix and the crystalline phase. The levels of the residual stresses increased with increasing the crystal size. The crystal size performed dual effects on the flexural strength of the glass-ceramic: an “interlocking effect” caused by larger-sized LD crystals and a “micro residual stress effect” related to the balancing tensile stresses in the glass matrix. Higher residual tensile stresses in the glass matrix induced by larger-sized LD crystals would counteract the “interlocking effect” of the crystals, causing the strength degradation. The hardness of the glass-ceramic was mainly controlled by the “micro residual stress effect”.

Investigation of the dispersion of phonon modes in CdI2 single crystals by a method of inelastic scattering of thermal neutrons

International Nuclear Information System (INIS)

Piroga, S.A.

2001-01-01

Experimental observation using a method of inelastic scattering of thermal neutrons the longitudinal phonons in the G-Z, G-X and G-L directions in CdI 2 singe crystal has been obtained. The phonon subsystem observed in the case of CdI 2 single crystals is two dimensional. This is because of the fact that interlayer interactions are weak in compare to intra layer interactions

Doping-controlled Coherent Electron-Phonon Coupling in Vanadium Dioxide

Energy Technology Data Exchange (ETDEWEB)

Appavoo, Kannatassen [Vanderbilt Univ., Nashville, TN (United States) Interdisciplinary Materials Science; Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials; Wang, Bin [Vanderbilt Univ., Nashville, TN (United States) Dept. of Physics and Astronomy; Nag, Joyeeta [Vanderbilt Univ., Nashville, TN (United States) Dept. of Physics and Astronomy; Sfeir, Matthew Y. [Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials; Pantelides, Sokrates T. [Vanderbilt Univ., Nashville, TN (United States) Dept. of Physics and Astronomy; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Vanderbilt Univ., Nashville, TN (United States). Dept. of Electrical Engineering and Computer Science; Haglund, Richard F. [Vanderbilt Univ., Nashville, TN (United States) Interdisciplinary Materials Science and Dept. of Physics and Astronomy

2015-05-10

Broadband femtosecond transient spectroscopy and density functional calculations reveal that substitutional tungsten doping of a VO₂ film changes the coherent phonon response compared to the undoped film due to altered electronic and structural dynamics.

Nano-crystal growth in cordierite glass ceramics studied with X-ray scattering

Energy Technology Data Exchange (ETDEWEB)

Bras, Wim; Clark, Simon M.; Greaves, G. N.; Kunz, Martin; van Beek, W.; Radmilovic, V.

2009-01-16

The development of monodisperse crystalline particles in cordierite glass doped with Cr3+ after a two-step heat treatment is elucidated by a combination of time-resolved small and wide angle x-ray scattering (SAXS/WAXS) experiments with electron microscopy. The effects of bulk and surface crystallization can clearly be distinguished, and the crystallization kinetics of the bulk phase is characterized. The internal pressure due to structural differences between the crystalline and amorphous phase is measured but the physical cause of this pressure can not unambiguously be attributed. The combined measurements comprise a nearly full characterization of the crystallization processes and the resulting sample morphology.

Glass-Forming Ability and Early Crystallization Kinetics of Novel Cu-Zr-Al-Co Bulk Metallic Glasses

Directory of Open Access Journals (Sweden)

Xiaoliang Han

2016-09-01

Full Text Available In recent years, CuZr-based bulk metallic glass (BMG composites ductilized by a shape memory B2 CuZr phase have attracted great attention owing to their outstanding mechanical properties. However, the B2 CuZr phase for most CuZr-based glass-forming compositions is only stable at very high temperatures, leading to the uncontrollable formation of B2 crystals during quenching. In this work, by introducing Co (i.e., 4, 5, and 6 at. % and 10 at. % Al into CuZr-based alloys, the relatively good glass-forming ability (GFA of CuZr-based alloys still can be achieved. Meanwhile, the B2 phase can be successfully stabilized to lower temperatures than the final temperatures of crystallization upon heating CuZr-based BMGs. Unlike previous reported CuZr-based BMGs, the primary crystallization products upon heating are mainly B2 CuZr crystals but not CuZr2 and Cu10Zr7 crystals. Furthermore, the primary precipitates during solidification are still dominated by B2 crystals, whose percolation threshold is detected to lie between 10 ± 2 vol. % and 31 ± 2 vol. %. The crystallization kinetics underlying the precipitation of B2 crystals was also investigated. Our results show that the present glass-forming composites are promising candidates for the fabrication of ductile CuZr-based BMG composites.

Negative refraction imaging of solid acoustic waves by two-dimensional three-component phononic crystal

International Nuclear Information System (INIS)

Li Jing; Liu Zhengyou; Qiu Chunyin

2008-01-01

By using of the multiple scattering methods, we study the negative refraction imaging effect of solid acoustic waves by two-dimensional three-component phononic crystals composed of coated solid inclusions placed in solid matrix. We show that localized resonance mechanism brings on a group of flat single-mode bands in low-frequency region, which provides two equivalent frequency surfaces (EFS) close to circular. The two constant frequency surfaces correspond to two Bloch modes, a right-handed and a left-handed, whose leading mode are respectively transverse (T) and longitudinal (L) modes. The negative refraction behaviors of the two kinds of modes have been demonstrated by simulation of a Gaussian beam through a finite system. High-quality far-field imaging by a planar lens for transverse or longitudinal waves has been realized separately. This three-component phononic crystal may thus serve as a mode selector in negative refraction imaging of solid acoustic waves

Design of glass-ceramic complex microstructure with using onset point of crystallization in differential thermal analysis

International Nuclear Information System (INIS)

Hwang, Seongjin; Kim, Jinho; Shin, Hyo-Soon; Kim, Jong-Hee; Kim, Hyungsun

2008-01-01

Two types of frits with different compositions were used to develop a high strength substrate in electronic packaging using a low temperature co-fired ceramic process. In order to reveal the crystallization stage during heating to approximately 900 deg. C, a glass-ceramic consisting of the two types of frits, which had been crystallized to diopside and anorthite after firing, was tested at different mixing ratios of the frits. The exothermal peaks deconvoluted by a Gauss function in the differential thermal analysis curves were used to determine the onset point of crystallization of diopside or anorthite. The onset points of crystallization were affected by the mixing ratio of the frits, and the microstructure of the glass-ceramic depended on the onset point of crystallization. It was found that when multicrystalline phases appear in the microstructure, the resulting complex microstructure could be predicted from the onset point of crystallization obtained by differential thermal analysis

Sintering and crystallization behavior of CaMgSi2O6-NaFeSi2O6 based glass-ceramics

International Nuclear Information System (INIS)

Goel, Ashutosh; Kansal, Ishu; Ferrari, Anna Maria; Pascual, Maria J.; Barbieri, Luisa; Bondioli, Federica; Lancellotti, Isabella; Ribeiro, Manuel J.; Ferreira, Jose M. F.

2009-01-01

We report on the synthesis, sintering, and crystallization behaviors of a glass with a composition corresponding to 90 mol % CaMgSi 2 O 6 -10 mol % NaFeSi 2 O 6 . The investigated glass composition crystallized superficially immediately after casting of the melt and needs a high cooling rate (rapid quenching) in order to produce an amorphous glass. Differential thermal analysis and hot-stage microscopy were employed to investigate the glass forming ability, sintering behavior, relative nucleation rate, and crystallization behavior of the glass composition. The crystalline phase assemblage in the glass-ceramics was studied under nonisothermal heating conditions in the temperature range of 850-950 deg. C in both air and N 2 atmosphere. X-ray diffraction studies adjoined with the Rietveld-reference intensity ratio method were employed to quantify the amount of crystalline phases, while electron microscopy was used to shed some light on the microstructure of the resultant glass-ceramics. Well sintered glass-ceramics with diopside as the primary crystalline phase were obtained where the amount of diopside varied with the heating conditions.

Crystallization Kinetics and Characterization of Nanostructure Mica Glass-Ceramics with Optical Transparency

Directory of Open Access Journals (Sweden)

P. Alizadeh

2014-01-01

Full Text Available Transparent glasses in a system of Li2O-MgO-SiO2-Al2O3-Fchemical constituents were prepared by melt quenching method. In the fabrication of nanocrystal glass-ceramics, controlled nucleation and subsequent crystal growth were necessary to avoid loss of transparency. It was therefore important to understand thermal properties and crystallization kinetics of the glass ceramics. The crystallization behavior of the prepared glass was investigated by DTA, XRD and SEM. By crystallization heat-treatment, various crystalline phases, microstructure and transmittance were obtained. The sellaite was first precipitated as the nuclei before the crystallization of mica and then mica nanocrystals were precipitated with average size of

Bulk glass formation and crystallization in Zr54.5Cu20Al10Ni8Ti7.5 alloy

International Nuclear Information System (INIS)

Neogy, S.; Tewari, R.; Srivastava, D.; Dey, G.K.; Kumar, V.; Ranganathan, S.

2006-01-01

The present work was aimed at fabrication, characterization and crystallization of Zr 54.5 Cu 20 Al 10 Ni 8 Ti 7.5 bulk metallic glass. The glass forming alloy was made by arc melting and then subjected to copper mold casting into 3 mm diameter bulk glass rods. The as-cast microstructure was characterized by optical microscopy and transmission electron microscopy (TEM)

Phonon excess heating in electronic relaxation theory in quantum dots

Czech Academy of Sciences Publication Activity Database

Král, Karel; Lin, Ch. Y.

2008-01-01

Roč. 22, č. 20 (2008), s. 3439-3460 ISSN 0217-9792 R&D Projects: GA MŠk ME 866 Institutional research plan: CEZ:AV0Z10100520 Keywords : quantum dots * electron -phonon interaction * electron ic transport Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.558, year: 2008

Effect of copper valence on the glass structure and crystallization behavior of Bi-Pb-Cu-O glasses

International Nuclear Information System (INIS)

Hu, Yi; Lin, U.-L.; Liu, N.-H.

1997-01-01

Bi 0.43 Pb 0.35 Cu 0.22 O y glasses with different Cu + contents were prepared by melting at different temperatures. The glass structure consists of [BiO 3 [ and [BiO 6 [ units and the ratio of [BiO 3 [/[BiO 6 [ increases with increasing Cu + content. The glass transition temperature, the first crystallization temperature peak, and the thermal stability of the glasses decreases with increasing Cu + content. The value of the activation energy, E a , varies as a function of the Cu + content. The crystallization mechanism in the glasses is closely related to the glass structure, which is mainly affected by the Cu + content. (orig.)

Temperature Dependence of the Spin-Hall Conductivity of a Two-Dimensional Impure Rashba Electron Gas in the Presence of Electron-Phonon and Electron-Electron Interactions

Science.gov (United States)

Yavari, H.; Mokhtari, M.; Bayervand, A.

2015-03-01

Based on Kubo's linear response formalism, temperature dependence of the spin-Hall conductivity of a two-dimensional impure (magnetic and nonmagnetic impurities) Rashba electron gas in the presence of electron-electron and electron-phonon interactions is analyzed theoretically. We will show that the temperature dependence of the spin-Hall conductivity is determined by the relaxation rates due to these interactions. At low temperature, the elastic lifetimes ( and are determined by magnetic and nonmagnetic impurity concentrations which are independent of the temperature, while the inelastic lifetimes ( and related to the electron-electron and electron-phonon interactions, decrease when the temperature increases. We will also show that since the spin-Hall conductivity is sensitive to temperature, we can distinguish the intrinsic and extrinsic contributions.

Electronic structure of metallic glasses

International Nuclear Information System (INIS)

Oelhafen, P.; Lapka, R.; Gubler, U.; Krieg, J.; DasGupta, A.; Guentherodt, H.J.; Mizoguchi, T.; Hague, C.; Kuebler, J.; Nagel, S.R.

1981-01-01

This paper is organized in six sections and deals with (1) the glassy transition metal alloys, their d-band structure, the d-band shifts on alloying and their relation to the alloy heat of formation (ΔH) and the glass forming ability, (2) the glass to crystal phase transition viewed by valence band spectroscopy, (3) band structure calculations, (4) metallic glasses prepared by laser glazing, (5) glassy normal metal alloys, and (6) glassy hydrides

Glass formation and crystallization of Zr53Cu21Al10Ni8Ti8 alloy

International Nuclear Information System (INIS)

Neogy, S.; Tewari, R.; Srivastava, D.; Dey, G.K.; Banerjee, S.; Vaibhaw, K.; Ranganathan, S.

2010-01-01

In the present study, transmission electron microscopy techniques, like micro-diffraction, high resolution and fluctuation microscopy, have been employed to carry out detailed investigation of as-solidified and crystallized microstructures of the Zr 53 Cu 21 Al 10 Ni 8 Ti 8 alloy synthesized using melt spinning, suction casting and copper mould casting techniques. Samples produced by copper mould casting technique showed partially crystalline microstructure whereas the other techniques resulted in complete amorphous microstructures. High-resolution microscopy established that the dendrites of the big cube phase in partially crystalline glass grew by atomistic ledges. The other crystalline bct Zr 2 Ni phase, present in partially crystalline glass and also in all the crystallized microstructures, showed various types of internal faults depending upon the crystallite size. Fluctuation microscopy established that oxygen plays a major role in determining the degree of medium range order in glassy phases. In addition, variation in oxygen content changed the crystallization behaviour of glasses from a single to multiple events

Rare earth ion controlled crystallization of mica glass-ceramics

Energy Technology Data Exchange (ETDEWEB)

Garai, Mrinmoy; Karmakar, Basudeb, E-mail: basudebk@cgcri.res.in

2016-09-05

In understanding the effects of rare earth ions to control the crystallization and microstructure of alkaline boroaluminosilicate system, the CeO{sub 2}, Nd{sub 2}O{sub 3}, Sm{sub 2}O{sub 3} and Gd{sub 2}O{sub 3} doped K{sub 2}O−MgO−B{sub 2}O{sub 3}−Al{sub 2}O{sub 3}−SiO{sub 2}−F glasses were synthesized by melt-quenching at 1550 °C. Higher density (2.82–3.06 g cm{sup −3}) and thermal stability (glass phase) is experiential on addition of rare earth content, which also affects in increasing the glass transition temperature (T{sub g}) and crystallization temperature (T{sub c}). Decrease of thermal expansion in glasses with rare earth ion content is maintained by the stabilization of glass matrix owing to their large cationic field strength. A significant change in the non-isothermal DSC thermogram observed at 750–1050 °C is attributed to fluorophlogopite crystallization. Opaque glass-ceramics were prepared from such glasses by single step heat-treatment at 1050 °C; and the predominant crystalline phases are identified as fluorophlogopite mica, KMg{sub 3}(AlSi{sub 3}O{sub 10})F{sub 2} by XRD and EDX analysis. The compact glass-ceramic microstructure by the agglomeration of fluorophlogopite mica crystallites (crystal size ∼ 100–500 nm, FESEM) is achieved in attendance of rare earth ion; and such microstructure controlled the variation of density, thermal expansion and microhardness value. Higher thermal expansion (11.11–14.08 × 10{sup −6}/K at 50–800 °C and 50–900 °C) of such glass-ceramics approve that these rare earth containing glasses can be useful for high temperature vacuum sealing application with metal or solid electrolyte. The increase of Vickers microhardness (5.27–5.61 GPa) in attendance of rare earth ions is attributed to the compact crystallinity of fluorophlogopite mica glass-ceramic microstructure. - Highlights: • Synthesis of rare earth oxide doped alkaline boroaluminosilicate glasses. • Development of opaque

Evaluation the microwave heating of spinel crystals in high-level waste glass

Energy Technology Data Exchange (ETDEWEB)

Christian, J. H. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River Ecology Lab. (SREL); Washington, A. L. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River Ecology Lab. (SREL)

2015-08-18

In this report, the microwave heating of a crystal-free and a partially (24 wt%) trevorite-crystallized waste glass simulant were evaluated. The results show that a 500 mg piece of partially crystallized waste glass can be heated from room-temperature to above 1600 °C (as measured by infrared radiometry) within 2 minutes using a single mode, highly focused, 2.45 GHz microwave, operating at 300 W. X-ray diffraction measurements show that the partially crystallized glass experiences an 87 % reduction in trevorite following irradiation and thermal quenching. When a crystal-free analogue of the same waste glass simulant composition is exposed to the same microwave radiation it could not be heated above 450 °C regardless of the heating time.

An electron microscopy appraisal of tensile fracture in metallic glasses

International Nuclear Information System (INIS)

Matthews, D.T.A.; Ocelik, V.; Bronsveld, P.M.; De Hosson, J.Th.M.

2008-01-01

Three glass-forming alloy compositions were chosen for ribbon production and subsequent electron microscopy studies. In situ tensile testing with transmission electron microscopy (TEM), followed by ex situ TEM and ex situ scanning electron microscopy (SEM), allowed the deformation processes in tensile fracture of metallic glasses to be analysed. In situ shear band propagation was found to be jump-like, with the jump sites correlating with the formation of secondary shear bands. The effect of structural relaxation by in situ heating is also discussed. Nanocrystallization near the fracture surface was observed; however, no crystallization was also reported in the same sample and the reasons for this are discussed. Both the TEM and the SEM observations confirmed the presence of a liquid-like layer on or near the fracture surface of the ribbons. The formation of a liquid-like layer was characterized by the vein geometries and vein densities on the fracture surfaces and its dependence on shear displacement, δ, is discussed. A simple model is adapted to relate the temperature rise during shear banding to the glass transition and melting temperatures and this is used to explain the variety of fracture surfaces which are developed for macroscopically identical tensile testing of metallic glasses together with features which exhibit local melting

Crystallization behavior of (1 - x)Li2O.xNa2O.Al2O3.4SiO2 glasses

International Nuclear Information System (INIS)

Wang, Moo-Chin; Cheng, Chih-Wei; Chang, Kuo-Ming; Hsi, Chi-Shiung

2010-01-01

The crystallization behavior of the (1 - x)Li 2 O.xNa 2 O.Al 2 O 3 .4SiO 2 glasses has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED) and energy dispersive spectroscopy (EDS). The crystalline phase was composed of β-spodumene. The isothermal crystallization kinetics of β-spodumene from the (1 - x)Li 2 O.xNa 2 O.Al 2 O 3 .4SiO 2 glasses has also been studied by a quantitative X-ray diffraction method. The activation energy of β-spodumene formation decreases from 359.2 to 317.8 kJ/mol when the Na 2 O content increases from 0 to 0.4 mol and it increases from 317.8 to 376.9 kJ/mol when the Na 2 O content increases from 0.4 to 0.6 mol. The surface nucleation and plate-like growth were dominant in the crystallization of the (1 - x)Li 2 O.xNa 2 O.Al 2 O 3 .4SiO 2 glasses.

Large calculated electron-phonon interactions in La2-xMxCuO4

International Nuclear Information System (INIS)

Krakauer, H.; Pickett, W.E.; Cohen, R.E.

1993-01-01

Results of self-consistent linearized-augmented-plane-wave calculations within the local-density-functional approximation (LDA) are presented of the electron-phonon-induced linewidths and interaction strength of selected phonons in La 2-xMx CuO 4 at x=0.15. Through the use of a supercell geometry, rigid-ion-type approximations are avoided and the full electron-phonon matrix elements are determined from finite differences of the LDA potentials corresponding to frozen-in phonon at Γ X, and Z. At the X point, all fully symmetric A g modes (i.e., having the symmetry of the oxygen planar-breathing mode) as well as three modes having B 3g symmetry are examined. Small linewidths were found for the three B 3g modes, and moderate linewidths for the A g modes, the largest corresponding to ratios γ q,ν /ω q,ν =0.02 for the oxygen breathing and axial modes

Ultrafast electron-optical phonon scattering and quasiparticle lifetime in CVD-grown graphene.

Science.gov (United States)

Shang, Jingzhi; Yu, Ting; Lin, Jianyi; Gurzadyan, Gagik G

2011-04-26

Ultrafast quasiparticle dynamics in graphene grown by chemical vapor deposition (CVD) has been studied by UV pump/white-light probe spectroscopy. Transient differential transmission spectra of monolayer graphene are observed in the visible probe range (400-650 nm). Kinetics of the quasiparticle (i.e., low-energy single-particle excitation with renormalized energy due to electron-electron Coulomb, electron-optical phonon (e-op), and optical phonon-acoustic phonon (op-ap) interactions) was monitored with 50 fs resolution. Extending the probe range to near-infrared, we find the evolution of quasiparticle relaxation channels from monoexponential e-op scattering to double exponential decay due to e-op and op-ap scattering. Moreover, quasiparticle lifetimes of mono- and randomly stacked graphene films are obtained for the probe photon energies continuously from 1.9 to 2.3 eV. Dependence of quasiparticle decay rate on the probe energy is linear for 10-layer stacked graphene films. This is due to the dominant e-op intervalley scattering and the linear density of states in the probed electronic band. A dimensionless coupling constant W is derived, which characterizes the scattering strength of quasiparticles by lattice points in graphene.

Phonon anomalies in optical spectra of LiNbO3 single crystals

Directory of Open Access Journals (Sweden)

ANDREJA VALCIC

2004-06-01

Full Text Available LiNbO3 single crystals were grown by the Czochralski technique in an air atmosphere. The critical crystal diameter Dc = 1.5 cm and the critical rate of rotation wc = 35 rpm were calculated by equations from the hydrodynamics of the melt. The domain inversion was carried out at 1430 K using a 3.75 V/cm electric field for 10 min. The obtained crystals were cut, polished and etched to determine the presence of dislocations and single domain structures. The optical properties were studied by infrared and Raman spectroscopy as a function of temperature. With decreasing temperature, an atypical behaviour of the phonon modes could be seen in the ferroelectrics LiNbO3. The obtained results are discussed and compared with published data.

Dynamical Cooper pairing in non-equilibrium electron-phonon systems

Energy Technology Data Exchange (ETDEWEB)

Knap, Michael [Technical University of Munich (Germany); Harvard University (United States); Babadi, Mehrtash; Refael, Gil [Caltech (United States); Martin, Ivar [Argonne National Laboratory (United States); Demler, Eugene [Harvard University (United States)

2016-07-01

Ultrafast laser pulses have been used to manipulate complex quantum materials and to induce dynamical phase transitions. One of the most striking examples is the transient enhancement of superconductivity in several classes of materials upon irradiating them with high intensity pulses of terahertz light. Motivated by these experiments we analyze the Cooper pairing instabilities in non-equilibrium electron-phonon systems. We demonstrate that the light induced non-equilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We analyze the competition between these effects and show that in a broad range of parameters the dynamic enhancement of Cooper pair formation dominates over the increase in the scattering rate. This opens the possibility of transient light induced superconductivity at temperatures that are considerably higher than the equilibrium transition temperatures. Our results pave new pathways for engineering high-temperature light-induced superconducting states.

Electron-Electron and Electron-Phonon interactions effects on the tunnel electronic spectrum of PbS quantum dots

Science.gov (United States)

Wang, Hongyue; Lhuillier, Emmanuel; Yu, Qian; Mottaghizadeh, Alireza; Ulysse, Christian; Zimmers, Alexandre; Dubertret, Benoit; Aubin, Herve

2015-03-01

We present a tunnel spectroscopy study of the electronic spectrum of single PbS Quantum Dots (QDs) trapped between nanometer-spaced electrodes, measured at low temperature T=5 K. The carrier filling of the QD can be controlled either by the drain voltage in the shell filling regime or by a gate voltage. In the empty QD, the tunnel spectrum presents the expected signature of the 8x degenerated excited levels. In the drain controlled shell filling regime, the levels degeneracies are lifted by the global electrostatic Coulomb energy of the QD; in the gate controlled shell filling regime, the levels degeneracies are lifted by the intra-Coulomb interactions. In the charged quantum dot, electron-phonons interactions lead to the apparition of Franck-Condon side bands on the single excited levels and possibly Franck Condon blockade at low energy. The sharpening of excited levels at higher gate voltage suggests that the magnitude of electron-phonon interactions is decreased upon increasing the electron filling in the quantum dot. This work was supported by the French ANR Grants 10-BLAN-0409-01, 09-BLAN-0388-01, by the Region Ile-de-France in the framework of DIM Nano-K and by China Scholarship Council.

Crystallization kinetics of magnetic glass-ceramics prepared by the processing of waste materials

International Nuclear Information System (INIS)

Francis, A.A.

2006-01-01

The objective of the present investigation was to study the feasibility of conversion of an intimate mixture of blast furnace slag and blast furnace flue dust generated by a single industrial company into magnetic glass-ceramic product. Blast furnace slag (BFS) and blast furnace flue dust (BFD) are generated at a rate of 300,000 and 30,000 tons/year, respectively, from iron and steel factory. The crystallization mechanisms of a composition containing BFS and BFD in a 50/50 proportion were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallization temperature was found to vary from 900 to 1100 deg. C and two phases appeared in the crystallized samples: pyroxene Ca(Mg, Fe, Al)(Si, Al) 2 O 6 and magnetite/maghemite. Heating rate and particle sizes effects on crystal growth of powdered samples were studied by DTA. The apparent activation energy of crystal growth using the particle size 180-315 μm was determined to be 355 and 329 kJ/mol for the first and second peak, respectively. The presence of sharp and broad crystallization peaks indicate simultaneous surface and internal crystallization mechanism. Good wear resistance and chemical durability particularly in alkaline environment, combine with good hardness and magnetic properties make this glass-ceramic material potentially useful for various industrial applications

Crystallization dynamics in glass-forming systems

Energy Technology Data Exchange (ETDEWEB)

Cullinan, Timothy Edward [Iowa State Univ., Ames, IA (United States)

2016-02-19

Crystallization under far-from-equilibrium conditions is investigated for two different scenarios: crystallization of the metallic glass alloy Cu₅₀Zr₅₀ and solidification of a transparent organic compound, o-terphenyl. For Cu₅₀Zr₅₀, crystallization kinetics are quanti ed through a new procedure that directly fits thermal analysis data to the commonly utilized JMAK model. The phase evolution during crystallization is quantified through in-situ measurements (HEXRD, DSC) and ex-situ microstructural analysis (TEM, HRTEM). The influence of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined. For o-terphenyl, the relationship between crystal growth velocity and interface undercooling is systematically studied via directional solidification.

Dynamical instability, strong anharmonicity and electron-phonon coupling in KOs2O6: First-principles calculations

Science.gov (United States)

Wang, Wei; Sun, Jiafa; Li, Bin; He, Junqi

2017-09-01

First-principles pseudopotential calculations on phonon and electronic properties of β -pyrochlore superconductor KOs2O6 are performed. The imaginary soft-phonon modes with a special double-well potential for the lowest Eu(1) mode and the second lowest T1u(1) mode are reported, which indicates the dynamical instability in KOs2O6. However, the double wells are too small to induce a structural phase transformation in KOs2O6. The strong anharmonicity especially for K T2g(1) phonon mode is got, which is approved to be from the strong electron-phonon coupling that supports the superconductivity in KOs2O6.

Hot LO-phonon limited electron transport in ZnO/MgZnO channels

Science.gov (United States)

Šermukšnis, E.; Liberis, J.; Matulionis, A.; Avrutin, V.; Toporkov, M.; Özgür, Ü.; Morkoç, H.

2018-05-01

High-field electron transport in two-dimensional channels at ZnO/MgZnO heterointerfaces has been investigated experimentally. Pulsed current-voltage (I-V) and microwave noise measurements used voltage pulse widths down to 30 ns and electric fields up to 100 kV/cm. The samples investigated featured electron densities in the range of 4.2-6.5 × 1012 cm-2, and room temperature mobilities of 142-185 cm2/V s. The pulsed nature of the applied field ensured negligible, if any, change in the electron density, thereby allowing velocity extraction from current with confidence. The highest extracted electron drift velocity of ˜0.5 × 107 cm/s is somewhat smaller than that estimated for bulk ZnO; this difference is explained in the framework of longitudinal optical phonon accumulation (hot-phonon effect). The microwave noise data allowed us to rule out the effect of excess acoustic phonon temperature caused by Joule heating. Real-space transfer of hot electrons into the wider bandgap MgZnO layer was observed to be a limiting factor in samples with a high Mg content (48%), due to phase segregation and the associated local lowering of the potential barrier.

Observation of chiral phonons

KAUST Repository

Zhu, Hanyu; Yi, Jun; Li, Ming-yang; Xiao, Jun; Zhang, Lifa; Yang, Chih-Wen; Kaindl, Robert A.; Li, Lain-Jong; Wang, Yuan; Zhang, Xiang

2018-01-01

Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing.

Observation of chiral phonons

KAUST Repository

Zhu, Hanyu

2018-02-01

Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing.

Electron-Phonon Coupling and Resonant Relaxation from 1D and 1P States in PbS Quantum Dots.

Science.gov (United States)

Kennehan, Eric R; Doucette, Grayson S; Marshall, Ashley R; Grieco, Christopher; Munson, Kyle T; Beard, Matthew C; Asbury, John B

2018-05-31

Observations of the hot-phonon bottleneck, which is predicted to slow the rate of hot carrier cooling in quantum confined nanocrystals, have been limited to date for reasons that are not fully understood. We used time-resolved infrared spectroscopy to directly measure higher energy intraband transitions in PbS colloidal quantum dots. Direct measurements of these intraband transitions permitted detailed analysis of the electronic overlap of the quantum confined states that may influence their relaxation processes. In smaller PbS nanocrystals, where the hot-phonon bottleneck is expected to be most pronounced, we found that relaxation of parity selection rules combined with stronger electron-phonon coupling led to greater spectral overlap of transitions among the quantum confined states. This created pathways for fast energy transfer and relaxation that may bypass the predicted hot-phonon bottleneck. In contrast, larger, but still quantum confined nanocrystals did not exhibit such relaxation of the parity selection rules and possessed narrower intraband states. These observations were consistent with slower relaxation dynamics that have been measured in larger quantum confined systems. These findings indicated that, at small radii, electron-phonon interactions overcome the advantageous increase in energetic separation of the electronic states for PbS quantum dots. Selection of appropriately sized quantum dots, which minimize spectral broadening due to electron-phonon interactions while maximizing electronic state separation, is necessary to observe the hot-phonon bottleneck. Such optimization may provide a framework for achieving efficient hot carrier collection and multiple exciton generation.

Detecting the phonon spin in magnon-phonon conversion experiments

Science.gov (United States)

Holanda, J.; Maior, D. S.; Azevedo, A.; Rezende, S. M.

2018-05-01

Recent advances in the emerging field of magnon spintronics have stimulated renewed interest in phenomena involving the interaction between spin waves, the collective excitations of spins in magnetic materials that quantize as magnons, and the elastic waves that arise from excitations in the crystal lattice, which quantize as phonons. In magnetic insulators, owing to the magnetostrictive properties of materials, spin waves can become strongly coupled to elastic waves, forming magnetoelastic waves—a hybridized magnon-phonon excitation. While several aspects of this interaction have been subject to recent scrutiny, it remains unclear whether or not phonons can carry spin. Here we report experiments on a film of the ferrimagnetic insulator yttrium iron garnet under a non-uniform magnetic field demonstrating the conversion of coherent magnons generated by a microwave field into phonons that have spin. While it is well established that photons in circularly polarized light carry a spin, the spin of phonons has had little attention in the literature. By means of wavevector-resolved Brillouin light-scattering measurements, we show that the magnon-phonon conversion occurs with constant energy and varying linear momentum, and that the light scattered by the phonons is circularly polarized, thus demonstrating that the phonons have spin.

Controlling competing orders via nonequilibrium acoustic phonons: Emergence of anisotropic effective electronic temperature

Science.gov (United States)

Schütt, Michael; Orth, Peter P.; Levchenko, Alex; Fernandes, Rafael M.

2018-01-01

Ultrafast perturbations offer a unique tool to manipulate correlated systems due to their ability to promote transient behaviors with no equilibrium counterpart. A widely employed strategy is the excitation of coherent optical phonons, as they can cause significant changes in the electronic structure and interactions on short time scales. One of the issues, however, is the inevitable heating that accompanies these resonant excitations. Here, we explore a promising alternative route: the nonequilibrium excitation of acoustic phonons, which, due to their low excitation energies, generally lead to less heating. We demonstrate that driving acoustic phonons leads to the remarkable phenomenon of a momentum-dependent effective temperature, by which electronic states at different regions of the Fermi surface are subject to distinct local temperatures. Such an anisotropic effective electronic temperature can have a profound effect on the delicate balance between competing ordered states in unconventional superconductors, opening a so far unexplored avenue to control correlated phases.

Crystallization kinetics and optical properties of titanium-lithium tetraborate glass containing europium oxide

Energy Technology Data Exchange (ETDEWEB)

Mohamed, E.A. [Al Azhar University, Department of Physics, Faculty of Science (Girl' s Branch), Cairo (Egypt); Ratep, A. [Ain Shams University, Physics Department, Faculty of Girls, Cairo (Egypt); Abdel-Khalek, E.K.; Kashif, I. [Al-Azhar University, Department of Physics, Faculty of Science, Cairo (Egypt)

2017-07-15

The crystallization kinetics and optical properties of [60 Li{sub 2}B{sub 4}O{sub 7}-30 TiO{sub 2}-10 Eu{sub 2}O{sub 3}] (mol%) glass sample have been investigated. The present glass sample exhibits three crystallization exothermic peaks (T{sub p1}, T{sub p2,} and T{sub p3}) corresponding to the formation of LiBO{sub 2}, Li{sub 2}B{sub 4}O{sub 7,} and EuTiO{sub 3} phases, respectively. The presence of phase separation in the glass sample has been confirmed by scanning electron microscopic (SEM). The mean values of Avrami exponent (n = 3.1 and 4) around T{sub p1} and T{sub p2}, indicate that the bulk crystallization with a constant number of nuclei and with an increasing number of nuclei, respectively. The values of the local activation energy as a function of the fraction of crystallization (0.1 ≤ χ ≤ 0.9) decrease for the crystallization of LiBO{sub 2} and EuTiO{sub 3} and increase for the crystallization of Li{sub 2}B{sub 4}O{sub 7}. The values of n(χ) for T{sub p3} and T{sub p2} in the range (0.1 ≤ χ ≤ 0.9) and (0.1 ≤ χ ≤ 0.4), respectively, are larger than 4 indicate that the presence of anomalous in Avrami exponent. The trend of Judd-Ofelt intensity parameters (Ω{sub 2} > Ω{sub 4} > Ω{sub 6}) and the bonding parameter (δ) indicate that the lower symmetry and the highest covalent nature of the bonding around Eu{sup 3+} ions. (orig.)

Lanthanide-activated Na5Gd9F32 nanocrystals precipitated from a borosilicate glass: Phase-separation-controlled crystallization and optical property

International Nuclear Information System (INIS)

Chen, Daqin; Wan, Zhongyi; Zhou, Yang; Chen, Yan; Yu, Hua; Lu, Hongwei; Ji, Zhenguo; Huang, Ping

2015-01-01

Highlights: • Na 5 Gd 9 F 32 nanocrystals embedded glass ceramics were fabricated for the first time. • Such glass ceramics were achieved by phase-separation-controlled crystallization. • Elemental mapping evidenced the segregation of activators into the Na 5 Gd 9 F 32 lattice. • Luminescent color could be tuned by controlling glass crystallization temperature. - Abstract: Lanthanide-activated cubic Na 5 Gd 9 F 32 nanocrystals were precipitated from a borosilicate glass with a specifically designed composition. The precursor glass is already phase-separated after melt-quenching, which is beneficial to the realization of the controllable glass crystallization for affording desirable size, morphology and activator partition. Elemental mapping in the scanning transmission electron microscopy evidenced that the segregation of lanthanide ions into the Na 5 Gd 9 F 32 lattice was in situ formed without the requirement of long-range ionic diffusion. Impressively, such fabricated glass ceramic co-doped with Yb 3+ /Er 3+ ions exhibited intense upconversion luminescence, which was about 500 times higher than that of the precursor glass, and its luminescent color could be easily tuned from red to green by controlling glass crystallization temperature. It is anticipated that such phase-separation synthesis strategy with precise control over nanostructure of glass ceramics offer a great opportunity to design other highly transparent nanocomposites with a wide range of tunable optical properties

Comparison of electron and phonon transport in disordered semiconductor carbon nanotubes

DEFF Research Database (Denmark)

Sevincli, Haldun; Lehmann, T.; Ryndyk, D. A.

2013-01-01

as a function of length of the disordered device shows that both electrons and phonons with different energies display different transport regimes, i.e. quasi-ballistic, diffusive and localization regimes coexist. In the light of the results we discuss heating of the semiconductor device in electronic...

First-principles prediction of phononic thermal conductivity of silicene: A comparison with graphene

International Nuclear Information System (INIS)

Gu, Xiaokun; Yang, Ronggui

2015-01-01

There has been great interest in two-dimensional materials, beyond graphene, for both fundamental sciences and technological applications. Silicene, a silicon counterpart of graphene, has been shown to possess some better electronic properties than graphene. However, its thermal transport properties have not been fully studied. In this paper, we apply the first-principles-based phonon Boltzmann transport equation to investigate the thermal conductivity of silicene as well as the phonon scattering mechanisms. Although both graphene and silicene are two-dimensional crystals with similar crystal structure, we find that phonon transport in silicene is quite different from that in graphene. The thermal conductivity of silicene shows a logarithmic increase with respect to the sample size due to the small scattering rates of acoustic in-plane phonon modes, while that of graphene is finite. Detailed analysis of phonon scattering channels shows that the linear dispersion of the acoustic out-of-plane (ZA) phonon modes, which is induced by the buckled structure, makes the long-wavelength longitudinal acoustic phonon modes in silicene not as efficiently scattered as that in graphene. Compared with graphene, where most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the ZA phonon modes in silicene only have ∼10% contribution to the total thermal conductivity, which can also be attributed to the buckled structure. This systematic comparison of phonon transport and thermal conductivity of silicene and graphene using the first-principle-based calculations shed some light on other two-dimensional materials, such as two-dimensional transition metal dichalcogenides

Surface phonons

CERN Document Server

Wette, Frederik

1991-01-01

In recent years substantial progress has been made in the detection of surface phonons owing to considerable improvements in inelastic rare gas scattering tech­ niques and electron energy loss spectroscopy. With these methods it has become possible to measure surface vibrations in a wide energy range for all wave vectors in the two-dimensional Brillouin zone and thus to deduce the complete surface phonon dispersion curves. Inelastic atomic beam scattering and electron energy loss spectroscopy have started to play a role in the study of surface phonons similar to the one played by inelastic neutron scattering in the investigation of bulk phonons in the last thirty years. Detailed comparison between experimen­ tal results and theoretical studies of inelastic surface scattering and of surface phonons has now become feasible. It is therefore possible to test and to improve the details of interaction models which have been worked out theoretically in the last few decades. At this point we felt that a concise, co...

Morphologies of CaMoO sub 4 crystals in simulated nuclear waste disposal glass

Energy Technology Data Exchange (ETDEWEB)

Li, D.; Sengers, E.G.F.; Janssen, F.J.J.G. (KEMA, Arnhem (Netherlands). Chemical Technology and Material Research Dept.); Waal, H. de (TPO-TNO Glass Technology, Eindhoven (Netherlands))

1992-07-01

Fission products can diffuse through nuclear waste disposal glass due to the action of the temperature gradient caused by radioactive decay and the small thermal conductivity of the glass. Diffusion may eventually lead to crystallization. Because the densities of the products of glass crystallization may differ from that of the parent glass, crystallization causes stresses to develop, which can lead to fracture and exposure of increased surface area to environmental attack. Several kinds of crystals including, CaMoO{sub 4}, in the simulated nuclear waste disposal glass K{sub 3}, which consists of Na{sub 2}O, B{sub 2}O{sub 3}, SiO{sub 2} and other oxides, were identified previously after heat treatment. Recently it was found that CaMoO{sub 4} crystals have two kinds of morphologies in glass K{sub 3} heat-treated at temperatures between 870 and 1120 K. One kind of morphology, which is rather special, has not previously been reported. In this letter the morphologies of CaMoO{sub 4} crystals in this simulated nuclear waste disposal glass are discussed. (author).

Direct observation of a non-isothermal crystallization process in precursor Li10GeP2S12 glass electrolyte

Science.gov (United States)

Tsukasaki, Hirofumi; Mori, Shigeo; Shiotani, Shinya; Yamamura, Hideyuki; Iba, Hideki

2017-11-01

Crystallization of a precursor Li10GeP2S12 (LGPS) glass electrolyte by heat treatment significantly improves its ionic conductivity. The LGPS crystalline phase obtained by heat treatment above 450 °C shows an ionic conductivity on the order of 10-2 S/cm. To clarify the correlation between the crystallization behavior of precursor LGPS glasses and ionic conductivity, we developed an observation technique to visualize precipitated nanocrystallites and a new method to evaluate the crystallization degree via transmission electron microscopy (TEM). In-situ TEM observation revealed that LGPS nanocrystallites precipitated above 450 °C and their size remained fundamentally intact during heating. That is, the crystallization behavior could be characterized by only the formation of LGPS nanocrystallites in an amorphous matrix. In addition, the crystallization degree was quantitatively evaluated from electron diffraction patterns. The crystallization degree remarkably increased at around 450 °C and reached more than 60% above 450 °C. Based on these results, a high ionic conductivity of approximately 1.0 × 10-2 S/cm was confirmed to be directly associated with the appearance of the LGPS crystalline phase.

Crystallization kinetics of a soda lime silica glass with TiO2 addition

International Nuclear Information System (INIS)

De la Parra A, S. M.; Alvarez M, A.; Torres G, L. C.; Sanchez, E. M.

2009-01-01

Studies conducted into Na 2 O-CaO-3SiO 2 glass composition suggest that its phase transformation occurs from the surface towards the interior of the sample. In a study carried out in 1982, it was reported that no addition of nucleating agents modified the mechanism. Taking advantage of the disposition materials synthesized by nanotechnology, in this study TiO 2 in nanometer size was used with the idea that, because of its qualities, it could modify the crystallization mechanism. The glasses obtained as well as the thermally treated samples, were evaluated by the X-ray diffraction (XRD) powder method, differential thermal analysis (DTA), and by optical microscopy and high resolution transmission electron microscopy (HRTEM). Within the range of TiO 2 concentration studied (0 - 10 wt %), 10 wt % of TiO 2 considerably reduced the Na 2 O-2CaO-3SiO 2 phase crystallization process. The crystallization mechanism was not modified and TiO 2 did not form compounds with the matrix components. (Author)

Imaging off-plane shear waves with a two-dimensional phononic crystal lens

International Nuclear Information System (INIS)

Chiang Chenyu; Luan Pigang

2010-01-01

A two-dimensional flat phononic crystal (PC) lens for focusing off-plane shear waves is proposed. The lens consists of a triangular lattice hole-array, embedded in a solid matrix. The self-collimation effect is employed to guide the shear waves propagating through the lens along specific directions. The Dirichlet-to-Neumann maps (DtN) method is employed to calculate the band structure of the PC, which can avoid the problems of bad convergence and fake bands automatically in the void-solid PC structure. When the lens is illuminated by the off-plane shear waves emanating from a point source, a subwavelength image appears in the far-field zone. The imaging characteristics are investigated by calculating the displacement fields explicitly using the multiple scattering method, and the results are in good agreement with the ray-trace predictions. Our results may provide insights for designing new phononic devices.

Au{sup 3+} ion implantation on FTO coated glasses: Effect on structural, electrical, optical and phonon properties

Energy Technology Data Exchange (ETDEWEB)

Sahu, Bindu; Dey, Ranajit; Bajpai, P.K., E-mail: bajpai.pk1@gmail.com

2017-06-01

Highlights: • Effects of 11.00 MeV Au{sup 3+} ions implanted in FTO coated (thickness ≈300 nm) silicate glasses at varying fluence. • Metal clustering near the surface and subsurface region below glass-FTO interface changes electrical and optical properties significantly. • Ion implantation does not affect the crystalline structure of the coated films; however, the tetragonal distortion increases with increasing ion fluence. • Significant surface reconstruction takes place with ion beam fluence; The average roughness also decreases with increasing fluence. • The sheet resistivity increases with increasing fluence. • Raman analysis also corroborates the re-crystallization process inducing due to ion implantation. • Optical properties of the implanted surfaces changes significantly. - Abstract: Effects of 11.00 MeV Au{sup 3+} ions implanted in FTO coated (thickness ≈300 nm) silicate glasses on structural, electrical optical and phonon behavior have been explored. It has been observed that metal clustering near the surface and sub-surface region below glass-FTO interface changes electrical and optical properties significantly. Ion implantation does not affect the crystalline structure of the coated films; however, the unit cell volume decreases with increase in fluence and the tetragonal distortion (c/a ratio) also decreases systematically in the implanted samples. The sheet resistivity of the films increases from 11 × 10{sup −5} ohm-cm (in pristine) to 7.5 × 10{sup −4} ohm-cm for highest ion beam fluence ≈10{sup 15} ions/cm{sup 2}. The optical absorption decreases with increasing fluence whereas, the optical transmittance as well as reflectance increases with increasing fluence. The Raman spectra are observed at ∼530 cm{sup −1} and ∼1103 cm{sup −1} in pristine sample. The broad band at 530 cm{sup −1} shifts towards higher wave number in the irradiated samples. This may be correlated with increased disorder and strain relaxation in

Thermal expansion accompanying the glass-liquid transition and crystallization

Directory of Open Access Journals (Sweden)

M. Q. Jiang

2015-12-01

Full Text Available We report the linear thermal expansion behaviors of a Zr-based (Vitreloy 1 bulk metallic glass in its as-cast, annealed and crystallized states. Accompanying the glass-liquid transition, the as-cast Vitreloy 1 shows a continuous decrease in the thermal expansivity, whereas the annealed glass shows a sudden increase. The crystallized Vitreloy 1 exhibits an almost unchanged thermal expansivity prior to its melting. Furthermore, it is demonstrated that the nucleation of crystalline phases can induce a significant thermal shrinkage of the supercooled liquid, but with the growth of these nuclei, the thermal expansion again dominates. These results are explained in the framework of the potential energy landscape, advocating that the configurational and vibrational contributions to the thermal expansion of the glass depend on both, structure and temperature.

The Lamb wave bandgap variation of a locally resonant phononic crystal subjected to thermal deformation

Science.gov (United States)

Zhu, Yun; Li, Zhen; Li, Yue-ming

2018-05-01

A study on dynamical characteristics of a ternary locally resonant phononic crystal (PC) plate (i.e., hard scatterer with soft coating periodically disperse in stiff host matrix) is carried out in this paper. The effect of thermal deformation on the structure stiffness, which plays an important role in the PC's dynamical characteristics, is considered. Results show that both the start and the stop frequency of bandgap shift to higher range with the thermal deformation. In particular, the characteristics of band structure change suddenly at critical buckling temperature. The effect of thermal deformation could be utilized for tuning of phononic band structures, which can promote their design and further applications.

Characterizing the residual glass in a MgO/Al2O3/SiO2/ZrO2/Y2O3 glass-ceramic

Science.gov (United States)

Seidel, Sabrina; Patzig, Christian; Wisniewski, Wolfgang; Gawronski, Antje; Hu, Yongfeng; Höche, Thomas; Rüssel, Christian

2016-01-01

The non-isochemical crystallization of glasses leads to glass-ceramics in which the chemical composition of the amorphous matrix differs from that of the parent glass. It is challenging to solely analyse the properties of these residual glassy phases because they frequently contain finely dispersed crystals. In this study, the composition of the residual glass matrix after the crystallization of a glass with the mol% composition 50.6 SiO2 · 20.7 MgO · 20.7 Al2O3 · 5.6 ZrO2 · 2.4 Y2O3 is analysed by scanning transmission electron microscopy (STEM) including energy dispersive X-ray analysis (EDXS). A batch of the residual glass with the determined composition is subsequently melted and selected properties are analysed. Furthermore, the crystallization behaviour of this residual glass is studied by X-ray diffraction, scanning electron microscopy including electron backscatter diffraction and STEM-EDXS analyses. The residual glass shows sole surface crystallization of indialite and multiple yttrium silicates while bulk nucleation does not occur. This is in contrast to the crystallization behaviour of the parent glass, in which a predominant bulk nucleation of spinel and ZrO2 is observed. The crystallization of the residual glass probably leads to different crystalline phases when it is in contact to air, rather than when it is enclosed within the microstructure of the parent glass-ceramics. PMID:27734918

Influence of a photoexcited electron-hole plasma on the Raman scattering spectra of YBa2Cu3Ox single crystals

International Nuclear Information System (INIS)

Goncharov, A.F.; Denisov, V.N.; Mavrin, B.N.; Podobedov, V.B.

1988-01-01

The Raman spectra of tetragonal YBa 2 Cu 3 O x crystals in the region of ∼500 cm -1 were determined using different power densities I 0 of the exciting radiation of wavelengths 4,880, 5,145, 5,321, and 6,471 angstrom at temperatures 80-300 K. An increase in I 0 revealed changes in the spectra due to interference of the electron continuum with a 470 cm -1 phonon and also due to activation of 560-590 cm -1 dipole vibrations because of interaction of photocarriers with the crystal lattice. An analysis of the spectra yielded the electron-phonon interaction constant. The changes in the spectra were of resonant nature, but they were absent in the case of the excitation wavelengths 5,321 and 6,471 angstrom. A triple multichannel Raman spectrometer, developed by the authors, made it possible to record simultaneously a spectral interval of 500 cm -1 in the range ≥ 25 cm -1 on excitation with cw laser radiation

Structural and thermoelectric properties of the type-I Sn clathrates Cs8Sn46−n(n=0,2) from Density Functional Theory (DFT)

KAUST Repository

Egbele, Peter O.

2018-02-08

Sn clathrates are promising phonon glass, electron crystal materials (PGEC), in which the phonon free paths are short and the electron free paths are long. We analysed the relaxed structure of Sn clathrates using four different Density Funtional Exchange-Correlation functionals. The phonon structures were investigated as a first step in order to determine the phonon contribution to the thermal conductivity. We determined the Seebeck coefficient and electrical conductivity of the clathrate compound and the thermoelectric figure of merit. A glimpse into the dynamics of the system for the evaluation of the thermoelectric and electronic properties is presented.