Showing papers on "Debye model published in 2005"
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01 Jan 2005
TL;DR: In this article, the authors present an overview of the properties of optical dispersion in terms of properties such as: 1.1 Ionicity. 2.2 Specific Heat. 3.4 Microhardness. 4.5 Sound Velocity.
Abstract: Series Preface. Preface. Acknowledgements. 1 Structural Properties. 1.1 Ionicity. 1.2 Elemental Isotopic Abundance and Molecular Weight. 1.3 Crystal Structure and Space Group. 1.4 Lattice Constant and Its Related Parameters. 1.5 Structural Phase Transition. 1.6 Cleavage Plane. 2 Thermal Properties. 2.1 Melting Point and Its Related Parameters. 2.2 Specific Heat. 2.3 Debye Temperature. 2.4 Thermal Expansion Coefficient. 2.5 Thermal Conductivity and Diffusivity. 3 Elastic Properties. 3.1 Elastic Constant. 3.2 Third-Order Elastic Constant. 3.3 Young's Modulus, Poisson's Ratio and Similar. 3.4 Microhardness. 3.5 Sound Velocity. 4 Lattice Dynamic Properties. 4.1 Phonon Dispersion Relation. 4.2 Phonon Frequency. 4.3 Mode Gruneisen Parameter. 4.4 Phonon Deformation Potential. 5 Collective Effects and Some Response Characteristics. 5.1 Piezoelectric and Electromechanical Constants. 5.2 Frohlich Coupling Constant. 6 Energy-Band Structure: Energy-Band Gaps. 6.1 Basic Properties. 6.2 E0-Gap Region. 6.3 Higher-Lying Direct Gap. 6.4 Lowest Indirect Gap. 6.5 Conduction-Valley Energy Separation. 6.6 Direct-Indirect-Gap Transition Pressure. 7 Energy-Band Structure: Effective Masses. 7.1 Electron Effective Mass: G Valley. 7.2 Electron Effective Mass: Satellite Valley. 7.3 Hole Effective Mass. 8 Deformation Potentials. 8.1 Intravalley Deformation Potential: G Point. 8.2 Intravalley Deformation Potential: High-Symmetry Points. 8.3 Intervalley Deformation Potential. 9 Electron Affinity and Schottky Barrier Height. 9.1 Electron Affinity. 9.2 Schottky Barrier Height. 10 Optical Properties. 10.1 Summary of Optical Dispersion Relations. 10.2 The Reststrahlen Region. 10.3 At or Near The Fundamental Absorption Edge. 10.4 The Interband Transition Region. 10.5 Free-Carrier Absorption and Related Phenomena. 11 Elastooptic, Electrooptic and Nonlinear Optical Properties 11.1 Elastooptic Effect. 11.2 Linear Electrooptic Constant. 11.3 Quadratic Electrooptic Constant. 11.4 Franz-Keldysh Effect. 11.5 Nonlinear Optical Constant. 12 Carrier Transport Properties. 12.1 Low-Field Mobility: Electrons. 12.2 Low-Field Mobility: Holes. 12.3 High-Field Transport: Electrons. 12.4 High-Field Transport: Holes. 12.5 Minority-Carrier Transport: Electrons in p-Type Materials. 12.6 Minority-Carrier Transport: Holes in n-Type Materials. 12.7 Impact Ionization Coefficient. Index.
258 citations
TL;DR: In this article, the authors presented DMM calculations of the thermal conductance of Al-Si, Al-Ge, Cu-Si and Cu-Ge interfaces by taking into account the full phonon dispersion relationship over the entire Brillouin zone obtained using the Born-von Karman model (BKM).
Abstract: The acoustic mismatch model (AMM) and the diffuse mismatch model (DMM) have been traditionally used to calculate the thermal boundary conductance of interfaces. In these calculations, the phonon dispersion relationship is usually approximated by a linear relationship (Debye approximation). This is accurate for wave vectors close to the zone center, but deviates significantly for wave vectors near the zone edges. Here, we present DMM calculations of the thermal conductance of Al–Si, Al–Ge, Cu–Si, and Cu–Ge interfaces by taking into account the full phonon dispersion relationship over the entire Brillouin zone obtained using the Born-von Karman model (BKM). The thermal boundary conductance thus calculated deviates significantly from DMM predictions obtained using the Debye model in all cases.
212 citations
TL;DR: In this paper, the fullpotential linearized augmented plane wave (FP-LAPW) method within the density functional theory is used to investigate the structural and electronic properties of ZrSiO"4 in its low pressure phase (zircon).
132 citations
TL;DR: In this paper, the thermal conductivity of silicon nanostructures is studied to gain insight into heat conduction in silicon and related semiconductors, and it is shown that phonon-boundary scattering results in a significant reduction in thermal conductivities of crystalline silicon films of thickness below 100 nm at room temperature.
Abstract: Phonon heat conduction is one of the critical research areas for nanoelectronics. The thermal conductivity of silicon nanostructures is studied to gain insight into heat conduction in silicon and related semiconductors. We experimentally show that phonon-boundary scattering results in a significant reduction in the thermal conductivity of crystalline silicon films of thickness below 100 nm at room temperature, which is consistent with the previously reported data for silicon nanowires. Analysis of the data suggests that phonon modes that dominate heat conduction in silicon are fully excited at temperatures substantially below the Debye temperature.
125 citations
TL;DR: The effects of floppy modes in the thermodynamical properties of a system are studied and a modified Debye model is used to take into account this effect, and an approximate expression for the number of energy basins as a function of the rigidity is provided.
Abstract: The effects of floppy modes in the thermodynamical properties of a system are studied From thermodynamical arguments, we deduce that floppy modes are not at zero frequency and thus a modified Debye model is used to take into account this effect The model predicts a deviation from the Debye law at low temperatures Then, the connection between the topography of the energy landscape, the topology of the phase space, and the rigidity of a glass is explored As a result, we relate the number of constraints and floppy modes to the statistics of the landscape We apply these ideas to a simple model for which we provide an approximate expression for the number of energy basins as a function of the rigidity This helps to understand certain features of the glass transition, like the jump in the specific heat or the reversible window observed in chalcogenide glasses
123 citations
TL;DR: In this article, density functional theory calculations have been performed to obtain lattice parameters, elastic constants, and electronic properties of ideal pyrochlores with the composition ${A}{2}B}_{2}{B},2}{\mathrm{O}}_{7}$.
Abstract: Density functional theory calculations have been performed to obtain lattice parameters, elastic constants, and electronic properties of ideal pyrochlores with the composition ${A}_{2}{B}_{2}{\mathrm{O}}_{7}$ (where $A=\mathrm{La}$,Y and $B=\mathrm{Ti}$,Sn,Hf,Zr). Some thermal properties are also inferred from the elastic properties. A decrease of the sound velocity (and thus, of the Debye temperature) with the atomic mass of the $B$ ion is observed. Static and dynamical atomic charges are obtained to quantify the degree of covalency or ionicity. A large anomalous contribution to the dynamical charge is observed for Hf, Zr, and specially for Ti. It is attributed to the hybridization between occupied $2p$ states of oxygen and unoccupied $d$ states of the $B$ cation. An analysis based on Mulliken population and deformation charge integrated in the Voronoi polyhedra indicates that the ionicity of these pyrochlores increases in the order Sn-Ti-Hf-Zr. The charge deformation contour plots support this assignment.
112 citations
TL;DR: In this paper, the 2s 21 s e ionization resonance state of the hydrogen negative ion embedded in Debye plasmas is determined by calculating the density of resonance states using the stabilization method.
Abstract: The 2s 21 S e autoionization resonance state of the hydrogen negative ion embedded in Debye plasmas is determined by calculating the density of resonance states using the stabilization method. The electron affinity of the hydrogen atom is also estimated for various Debye lengths.A screened Coulomb potential obtained from the Debye model is used to represent the interaction between the charged particles. A correlated wave function consisting of a generalized exponential expansion has been used to represent the correlation effect between the three charged particles. The screening effect is taken care of forallpairsofthechargedparticles.Thecalculatedresonanceenergiesandwidths for various Debye parameters ranging from infinity to a small value along with the electron affinity are reported.
84 citations
TL;DR: In this article, the transition phase of GaN from zincblende (ZB) structure to rocksalt structure (RS) is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures are obtained through the quasi-harmonic Debye model.
80 citations
TL;DR: In this paper, a Brillouin pulse is defined and is shown to possess near optimal (if not optimal) penetration into a given Debye-type dielectric for remote sensing.
Abstract: When an ultrawide-band electromagnetic pulse penetrates into a causally dispersive dielectric, the interrelated effects of phase dispersion and frequency dependent attenuation alter the pulse in a fundamental way that results in the appearance of so-called precursor fields. For a Debye-type dielectric, the dynamical field evolution is dominated by the Brillouin precursor as the propagation depth typically exceeds a single penetration depth at the carrier frequency of the input pulse. This is because the peak amplitude in the Brillouin precursor decays only as the square root of the inverse of the propagation distance. This nonexponential decay of the Brillouin precursor makes it ideally suited for remote sensing. Of equal importance is the frequency structure of the Brillouin precursor. Although the instantaneous oscillation frequency is zero at the peak amplitude point of the Brillouin precursor, the actual oscillation frequency of this field structure is quite different, exhibiting a complicated dependence on both the material dispersion and the input pulse characteristics. Finally, a Brillouin pulse is defined and is shown to possess near optimal (if not optimal) penetration into a given Debye-type dielectric.
79 citations
TL;DR: In this article, the velocity of longitudinal and transverse ultrasonic waves in different compositions of the glass system 0.65TeO2-(0.35−−x)V2O5-xGd2O3 have been measured at room temperature using the ultrasonic pulse-echo technique at 4MHz.
77 citations
TL;DR: The surface structure of Bi(111) was investigated by low-energy electron diffraction (LEED) intensity analysis for temperatures between 140 and $313\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and by first-principles calculations.
Abstract: The surface structure of Bi(111) was investigated by low-energy electron diffraction (LEED) intensity analysis for temperatures between 140 and $313\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and by first-principles calculations. The diffraction pattern reveals a $(1\ifmmode\times\else\texttimes\fi{}1)$ surface structure and LEED intensity versus energy simulations confirm that the crystal is terminated with a Bi bilayer. Excellent agreement is obtained between the calculated and measured diffraction intensities in the whole temperature range. The first interlayer spacing shows no significant relaxation at any temperature while the second interlayer spacing expands slightly. The Debye temperatures deduced from the optimized atomic vibrational amplitudes for the two topmost layers are found to be significantly lower than in the bulk. The experimental results for the relaxations agree well with those of our first-principles calculation.
TL;DR: In this paper, a detailed and systematic lattice dynamical calculation of the newly discovered intermetallic superconductor was performed by using a lattice dynamic model theory based on pairwise interactions under the framework of the rigid ion model.
Abstract: This paper reports a detailed and systematic lattice dynamical calculation of the newly discovered intermetallic superconductor $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$ by using a lattice dynamical model theory based on pairwise interactions under the framework of the rigid ion model. The results bring out the anomalous vibrational mode instability in the phonon dispersion curves and phonon density of states of $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$. The calculated phonon dispersion curves and phonon density of states are in good agreement with the measured and density functional theoretical (DFT) data. The study also illustrates the contradicting results on the magnitude of phonon frequencies due to Mg atoms and the region of the unstable modes in the Brillouin zone of the previously computed two DFT results. The present study on DOS has enabled an atomic level understanding of the phonon density of states. The phonon density of states has been used to compute the specific heat at constant volume. The Debye temperature and temperature-dependent vibrational amplitudes of the different species are also reported. The present calculation suggests that the superconductivity in $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$ is governed by the BCS mechanism.
TL;DR: In this paper, a first investigation on the resonances in two electron systems in various model plasma environments is made, and the 2s 2 1 S e ionization resonance state in the helium atom is determined by calculating the density of resonance states using the stabilization method.
TL;DR: In this article, the existence of local vibration modes of Ba atoms in cages composed of Ga and Sn atoms is demonstrated by analysis of experimental data of structural refinement and specific heat, which give an Einstein temperature of 50 K and a Debye temperature of 200 K.
Abstract: The analysis of temperature dependence of mH suggests a crossover of a dominant scattering mechanism from ionized impurity to acoustic phonon scattering with increasing temperature. The existence of local vibration modes of Ba atoms in cages composed of Ga and Sn atoms is evidenced by analysis of experimental data of structural refinement and specific heat, which give an Einstein temperature of 50 K and a Debye temperature of 200 K. This local vibration of Ba atoms should be responsible for the low thermal conductivity s1.1 W / m K at 150 Kd. The potential of type-VIII clathrate compounds for thermoelectric application is discussed.
TL;DR: The dependence of the heat capacity on the isotopic mass has also been investigated recently for monatomic crystals such as diamond, silicon, and germanium as mentioned in this paper, as well as for more complex semiconductors.
Abstract: Until recently, the heat capacity of GaN had only been measured for polycrystalline powder samples. Semiempirical as well as first-principles calculations have appeared within the past few years. We present in this article measurements of the heat capacity of hexagonal single crystals of GaN in the $20--1400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ temperature range. We find that our data deviate significantly from the literature values for polycrystalline materials. The dependence of the heat capacity on the isotopic mass has also been investigated recently for monatomic crystals such as diamond, silicon, and germanium. Multiatomic crystals are expected to exhibit a different dependence of these heat capacities on the masses of each of the isotopes present. These effects have not been investigated in the past to our knowledge. We also present first-principles calculations of the dependence of the heat capacities of GaN, as a canonical binary material, on each of the Ga and N masses. We show that they are indeed different, as expected from the fact that the Ga mass affects mainly the acoustic, that of N the optic phonons. It is hoped that these calculations will encourage experimental measurements of the dependence of the heat capacity on isotopic masses in binary and more complex semiconductors.
TL;DR: In this article, the so-called precursor phenomena were found in the physical properties of 6-at.% Fe alloys, such as a negative temperature coefficient of electrical resistivity, low Debye temperature and a broad peak in specific heat curve.
TL;DR: In this article, the equations of state (EOS) and other thermodynamic properties of the rocksalt (RS) structure MgO are investigated by ab initio plane-wave pseudopotential density functional theory method.
Abstract: The equations of state (EOS) and other thermodynamic properties of the rocksalt (RS) structure MgO are investigated by ab initio plane-wave pseudopotential density functional theory method. The obtained results are consistent with the experimental data and those calculated by others. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V-0 on pressure P, cell volume V on temperature T, and Debye temperature Theta and specific heat C-V on pressure P are successfully obtained. The variation of the thermal expansion alpha with temperature and pressure is investigated, which shows the temperature has hardly any effect on the thermal expansion alpha at higher pressure. (c) 2005 Elsevier B.V. All rights reserved.
TL;DR: In this paper, the electron screening in the 7Li (p, α ) α reaction has been studied at E p = 30 to 100 keV for different environments: Li2WO4 insulator, Li metal, and PdLi alloys.
TL;DR: In this article, the authors have made an investigation on the resonances for positronium negative ion in various model plasma environments using the stabilization method and derived the ground-state energy eigenvalues for various Debye lengths.
Abstract: We have made an investigation on the resonances for positronium negative ion ${\mathrm{Ps}}^{\ensuremath{-}}$ in various model plasma environments. The $2{s}^{2}\phantom{\rule{0.2em}{0ex}}^{1}S^{e}$ autoionization resonance state in ${\mathrm{Ps}}^{\ensuremath{-}}$ ion is determined by calculating the density of resonance states using the stabilization method. We have also performed accurate variational calculations to obtain ground-state energy eigenvalues of ${\mathrm{Ps}}^{\ensuremath{-}}$ for various Debye lengths. A screened Coulomb potential obtained from the Debye model is used to represent the interaction between the charged particles. A correlated wave function has been used to represent the correlation effect between the three charge particles. The calculated resonance energies and widths for various Debye parameters ranging from infinity to a small value along with the ground-state energies are reported.
TL;DR: In this paper, the heat capacity and dilatation of YB12 and LuB12 tricrystal compounds were studied in the range 2.5?70?K and 4.3?300?K respectively.
Abstract: The heat capacity (Cp) and dilatation (?) of YB12 and LuB12 are studied. Cp of the zone-melted YB12 tricrystal is measured in the range 2.5?70?K, of the zone-melted LuB12 single crystal in the range 0.6?70?K, and of the LuB12 powder sample in the range 4.3?300?K; ? of the zone-melted YB12 tricrystal and LuB12 single crystals is measured in the range 5?200?K. At low temperatures a negative thermal expansion (NTE) is revealed for both compounds: for YB12 at 50?70?K, for LuB12 at 10?20?K and 60?130?K. Their high-temperature NTE is a consequence of nearly non-interacting freely oscillating metal ions (Einstein oscillators) in cavities of a simple cubic rigid Debye lattice formed by B12 cage units. The Einstein temperatures are ~254 and ~164?K, and the Debye temperatures are ~1040?K and ~1190?K for YB12 and LuB12 respectively. The LuB12 low-temperature NTE is connected with an induced low-energy defect mode. The YB12 superconducting transition has not been detected up to 2.5?K.
TL;DR: In this article, an extended x-ray absorption fine structure (EXAFS) analysis of the thermoelectric clathrates Eu{sub 8}Ga{sub 16}Ge{sub 30} and Sr{sub 6} Ga{sub 14.5] Ge{sub 15.5} was presented, showing that the lattice is quite stiff with a high correlated Debye temperature.
Abstract: We present a detailed extended x-ray absorption fine structure (EXAFS) analysis of the thermoelectric clathrates Eu{sub 8}Ga{sub 16}Ge{sub 30} and Sr{sub 8}Ga{sub 16}Ge{sub 30}, both of which have an unusually low thermal conductivity attributed to a 'rattler' motion of the filler atoms Eu and Sr. The EXAFS results show that the Ga/Ge lattice is quite stiff with a high correlated Debye temperature {approx}400 K. Eu is on-center in the site 1 cage but off-center (0.445{+-}0.020 A) in the large cage called the Eu2 site. The results for Sr are similar, but {approx}75% are off-center 0.40{+-}0.05 A and {approx}25% are on-center in the Sr2 site. Both results are in reasonable agreement with diffraction results. The temperature dependence of the nearest neighbor pair distribution widths yield low Einstein temperatures (80{+-}10 and 100{+-}10 K for Eu1 and Sr1, respectively, and 95{+-}10 and 125{+-}10 K for the shortest Eu2-Ga/Ge and Sr2-Ga/Ge pairs). In contrast, the more distant Eu2/Sr2-Ga/Ge pair distributions within the Eu2/Sr2 cage are strongly disordered even at low T, indicating considerable local disorder. This indicates that the off-center Eu or Sr atom is bonded to the side of the site 2 cage. This has two important implications for the thermal conductivity: itmore » increases the coupling between the 'rattler' vibrations and the lattice phonons and it introduces a symmetry-breaking large mass defect.« less
TL;DR: In this paper, simple models for the heat capacity and thermal conductivity of a solid are introduced, with emphasis on the density of vibrational states, and the importance of these Einstein oscillators for impeding thermal transport is discussed.
Abstract: The Einstein model of a solid usually lacks a clear illustration in introductory solid-state physics courses because most solids are much better described by the Debye model. Filled antimony skutterudites, materials that have recently attracted much attention because of their potential for thermoelectric applications, provide a canonical illustration of the Einstein model. The filling atoms are loosely bound in the atomic cage formed by their neighbors, and hence their description as independent harmonic oscillators is adequate. Simple models for the heat capacity and thermal conductivity of a solid are introduced, with emphasis on the density of vibrational states. These models are used in conjunction with experimental results obtained from heat capacity and inelastic neutron scattering measurements to demonstrate the applicability of the concept of the Einstein oscillator to the filling guests in antimony skutterudites. The importance of these Einstein oscillators for impeding thermal transport is discussed and some simple problems involving the heat capacity, thermal conductivity, and inelastic neutron scattering are proposed.
TL;DR: In this article, the electron screening in the d(d, p)t reaction has been studied for the deuterated metal Pt at a sample temperature T = 20 °C-340 °C and for Co at T =20 °C −200 °C, where the data agree with the plasma model applied to the quasi-free metallic electrons.
Abstract: The electron screening in the d(d, p)t reaction has been studied for the deuterated metal Pt at a sample temperature T = 20 °C–340 °C and for Co at T = 20 °C and 200 °C. The enhanced electron screening decreases with increasing temperature, where the data agree with the plasma model of Debye applied to the quasi-free metallic electrons. The data represent the first observation of a temperature dependence of a nuclear cross section. We also measured the screening effect for the deuterated metal Ti (an element of group 4 of the periodic table) at T = −10 °C–200 °C: above 50 °C, the hydrogen solubility dropped to values far below 1 and a large screening effect became observable. Similarly, all metals of groups 3 and 4 and the lanthanides showed a solubility of a few per cent at T = 200 °C (compared to T = 20 °C) and a large screening also became observable. Within the Debye model, the deduced number of valence electrons per metallic atom agrees with the corresponding number from the Hall coefficient, for all metals investigated.
TL;DR: In this paper, the authors considered the zero Debye length asymptotic of solutions of isentropic quantum hydrodynamic equations for semiconductors at nano-size and showed that the current density consists of the divergence free vector field involved in the incompressible Euler equation and highly oscillating gradient vector field caused by the highly electric fields for small Debye lengths.
Abstract: In the present paper we consider the zero Debye length asymptotic of solutions of isentropic quantum hydrodynamic equations for semiconductors at nano-size and show that the current density consists of the divergence free vector field involved in the incompressible Euler equation and highly oscillating gradient vector field caused by the highly electric fields for small Debye length. This means that the quantum effects possibly may not dominate the charge transport within the channel of semiconductor devices (for instance MOSFET) of nano-size for isentropic quantum fluids.
TL;DR: In this paper, a wide range glass system based on the TeO2-WO3-ZnF2 was prepared and a number of physical properties, namely, the glass transition temperature, optical energy gap, Urbach energy, optical basicity, ultrasonic velocity (longitudinal and shear), elastic moduli, Poisson's ratio and Debye temperature were investigated by using several techniques such as: differential thermal analysis, dilatometric, UV-NIR-IR spectra and pulse-echo.
Abstract: A wide range glass system based on the TeO2–WO3–ZnF2 was prepared. A number of physical properties, namely, the glass transition temperature, optical energy gap, Urbach energy, optical basicity, ultrasonic velocity (longitudinal and shear), elastic moduli, Poisson's ratio and Debye temperature were investigated by using several techniques such as: differential thermal analysis, dilatometric, UV–NIR–IR spectra and pulse-echo. These glasses have a high transmission in the visible, the near infrared and infrared regions, very low OH-vibration absorption bands and high thermal stability beyond 169 °C. The results indicated that most properties are observed to be dependent on the ZnF2 content. These physical properties are reported with a view to drawing fluorotellurite optical fibres.
TL;DR: In this paper, a correlated wave function consisting of a generalized exponential expansion has been used to represent the correlation effect of the Debye model on the 2s2p {sup 1,3}P{sup o} resonance states of helium embedded in dense plasma environments.
Abstract: We have made an investigation on the 2s2p {sup 1,3}P{sup o} resonance states of helium embedded in dense plasma environments. A screened Coulomb potential obtained from the Debye model is used to represent the interaction between the charge particles. A correlated wave function consisting of a generalized exponential expansion has been used to represent the correlation effect. Resonance energies and widths for the doubly excited He embedded in plasmas with various Debye lengths are determined using the stabilization method by calculating the density of resonance states. The resonance energies and widths for various Debye parameters ranging from infinity to a small value for the lowest {sup 1,3}P{sup o} resonance states are reported.
TL;DR: In this paper, the two-photon photoemission spectrum was found to consist mainly of nonresonant direct transitions from the lower to the upper $sp$-band across the $L$-projected band gap.
Abstract: Theoretical and experimental studies on the two-photon photoemission excited by femtosecond laser pulses from the $sp$-band of Ag(111) in normal direction are reported. At low temperatures, the two-photon photoemission spectrum is found to consist mainly of nonresonant direct transitions from the lower to the upper $sp$-band across the $L$-projected band gap involving the upper $sp$-band as virtual intermediate states. This direct photoemission signal is calculated from the Ag band structure using optical Bloch equations and dipole moments derived from the nearly free electron approximation. For finite temperatures, a minor additional temperature-dependent, continuous contribution to the two-photon photoemission spectrum is experimentally determined. This background due to the secondary electrons is theoretically modeled combining the Debye model and Fermi Liquid Theory to account for electron relaxation effects during the two-photon photoemission process.
TL;DR: In this article, the longitudinal and shear sound velocities were measured by an ultrasonic pulse-echo method at room temperature in order to evaluate the elastic moduli and Debye temperature for Ag1−xPb18SbTe20.
TL;DR: In this paper, the phonon dispersion curves of a fcc δ-phase Pu-Ga alloy along the main symmetry directions of the cubic lattice were measured using a microbeam on large grain sample concept to carry out inelastic x-ray scattering experiments.
Abstract: We have used a microbeam on large grain sample concept to carry out inelastic x-ray scattering experiments to measure the phonon dispersion curves of a fcc $\ensuremath{\delta}$-phase Pu-Ga alloy along the main symmetry directions of the cubic lattice. This approach obviates experimental difficulties with conventional inelastic neutron scattering due to the high absorption cross section of the common $^{239}\mathrm{Pu}$ isotope and the nonavailability of large (millimeter size) single crystal materials for Pu and its alloys. A classical Born-von K\'arm\'an force constant model was used to model the experimental results, and up to fourth nearest neighbor interactions had to be included to obtain sufficient agreement. Several unusual features including, a large elastic anisotropy, a small shear elastic modulus $({C}_{11}\ensuremath{-}{C}_{12})∕2$, a positive kink in the ${T}_{1}[0\ensuremath{\xi}\ensuremath{\xi}]$ branch, and a pronounced bending (toward lower energy) of the $T[\ensuremath{\xi}\ensuremath{\xi}\ensuremath{\xi}]$ branch near the $L$ point in the Brillouin zone are found. These features are discussed in light of the various phase transformations of $\ensuremath{\delta}$ plutonium. The phonon dispersion data also provide a critical test and benchmark for theoretical treatments of highly correlated $5f$ electron systems.
TL;DR: In this paper, sound velocity measurements at 10 MHz were used to investigate the elastic properties of four series of glasses with different concentrations of tetrahedral boron and PbO.
Abstract: Elastic properties of $Li_{2}O-PbO-B_{2}O_{3}$ glasses have been investigated using sound velocity measurements at 10 MHz. Four series of glasses have been investigated with different concentrations of $Li_{2}O$, PbO and $B_{2}O_{3}$. The variations of molar volume have been examined for the influences of $Li_{2}O$ and PbO. The elastic moduli reveal trends in their compositional dependence. The bulk and shear modulus increases monotonically with increase in the concentration of tetrahedral boron which increases network dimensionality. The variation of bulk moduli has also been correlated to the variation in energy densities. The Poisson's ratio found to be insensitive to the concentration of tetrahedral boron in the structure. The experimental Debye temperatures are in good agreement with the expected theoretical values. Experimental observations have been examined in view, the presence of borate network and the possibility of non-negligible participation of lead in network formation.