Showing papers on "Debye model published in 1993"
TL;DR: In this article, the heat capacity of MgSiO3 perovskite has been measured in the temperature range 140-295 K by differential scanning calorimetry.
Abstract: Heat capacity of MgSiO3 perovskite has been measured in the temperature range 140–295 K by differential scanning calorimetry. The Kieffer model approach has been used to calculate the heat capacity beyond the measured temperature range. The estimated entropy of MgSiO3 perovskite is 57.2±1.0 J/mol.K at 298 K which is higher than that of ilmenite, in accord with the negative pressure-temperature slope for the ilmenite-perovskite transition. From the heat capacity thermodynamic Debye temperature of MgSiO3 perovskite is evaluated to be 980±15 K at 298 K and 1030±20 K at temperatures above about 700 K. Thermodynamic Gruneisen parameter of MgSiO3 perovskite at 30 GPa and above 1000 K is also estimated as 1.45±0.15. An adiabatic temperature profile in the pyrolitic lower mantle is calculated with the average gradient of 0.32±0.04 K/km. The temperature at the top of the D″ layer is estimated to be 2500±100 K.
104 citations
TL;DR: It is shown that, after a resummation of leading high-temperature contributions, a complete and gauge-independent result for the non-Abelian Debye screening mass at next-to-leading order can be extracted from the static gluon propagator.
Abstract: It is shown that, after a resummation of leading high-temperature contributions, a complete and gauge-independent result for the non-Abelian Debye screening mass at next-to-leading order can be extracted from the static gluon propagator. In contrast with previous, incomplete results, the correction to the Debye mass is found to be logarithmically sensitive to the nonperturbative magnetic mass and positive, in accordance with recent high-statistics results from lattice calculations.
99 citations
TL;DR: Evidence is presented that the lattice vibrations of compacted C60/C70 fullerite microcrystals consist predominantly of localized modes, and the Einstein model of the specific heat and thermal conductivity of solids is in much better agreement with the measurements than the Debye model, which is based on collective excitations.
Abstract: The first model for lattice vibrations of solids was proposed in 1907 by Einstein who applied the quantum concept to the mechanical motion of individual atoms in a crystal lattice which he assumed to be vibrating with random phases.1 He subsequently found that this model was inadequate, its major shortcoming being that it led to a thermal conductivity which disagreed with the observation on crystals both in magnitude and temperature dependence.2 This disagreement was removed by Debye3 and by Born and von Karman4 who demonstrated that in crystalline solids the atoms vibrate collectively as elastic waves.
93 citations
TL;DR: It is found that, although the configurational free energy is the largest component of the total alloy free energy, nonconfigurational effects contribute significantly to thermodynamic properties, and hence appreciably affect the calculated Cd-Mg phase diagram.
Abstract: A theoretical study of thermodynamic properties and of the phase diagram for crystalline hcp-based Cd-Mg alloys is presented. Many first-principles studies of phase diagrams for metallic alloys have considered only configurational contributions to the free energy, which arise from the effects of substitutional disorder on the entropy and enthalpy. In this paper, the additional effects of the vibrational free energy, the electronic entropy, and the energy associated with structural relaxations on the thermodynamic properties and calculated phase equilibria for Cd-Mg alloys are studied. Ground-state properties and the densities of states of stable and metastable Cd-Mg compounds with hcp-based structures have been calculated with the linear muffin-tin orbital (LMTO) method. The results of these LMTO calculations are combined with the cluster variation method to calculate the configurational free energy and electronic entropy of ordered and disordered alloys from first principles. The vibrational free energy is treated using the Debye model; the configurational dependence of the Debye temperature is obtained semiempirically from experimentally measured entropies of formation in combination with the results of the LMTO calculations. The energy associated with structural relaxations is estimated from experimentally measured lattice parameters and elastic constants. We find that, although the configurational free energy is the largest component of the total alloy free energy, nonconfigurational effects contribute significantly to thermodynamic properties, and hence appreciably affect the calculated Cd-Mg phase diagram.
83 citations
TL;DR: In this paper, the effect of impurities and defects on the transport properties of transition-metal disilicides is evaluated by examining the electrical transport of polycrystalline thin-film silicides.
82 citations
TL;DR: X-ray-absorption fine-structure data were measured and analyzed to demonstrate the domination of single-scattering and focusing paths in XAFS and the determination of vibrational information through at least 10 A around the center atom.
Abstract: X-ray-absorption fine-structure (XAFS) data of RbBr, RbCl, and KBr at 30 K and 125 K were measured and analyzed. An ionized-atom multiple-scattering calculation and a correlated Debye model were used for fitting the theory used in the computer code FEFF to data. The modifications of FEFF necessary to obtain good fits to the data are discussed. The results demonstrate the domination of single-scattering and focusing paths in XAFS and the determination of vibrational information through at least 10 A around the center atom. Numerical calculations were performed to analyze the cause of the difference found between the forward-scattering amplitudes of Rb[sup +] and Br[sup [minus]] focusing atoms. The second and third cumulants were determined of the first and second neighbors and were used to calculate the temperature dependence of the thermal-expansion coefficient including quantum effects at low temperature. Agreement with macroscopic thermal-expansion measurements was found.
56 citations
TL;DR: By measuring the longitudinal and transverse ultrasonic sound velocities along different crystalline directions, the elastic constants C 11, C 33, C 44 and C 12 of CdSe have been determined in the temperature range 0-300 K.
44 citations
TL;DR: In this paper, high-resolution 4f core-level spectra of the Ta(110) surface region have been obtained at 80 and 300 K with 70 and 100 eV synchrotron radiation.
Abstract: High-resolution 4f core-level spectra of the Ta(110) surface region have been obtained at 80 and 300 K with 70- and 100-eV synchrotron radiation. The data show that the subsurface core-level binding-energy shift (compared to deeper-lying atoms) for a close-packed bcc(110) surface can be substantial: 65\ifmmode\pm\else\textpm\fi{}15 meV for the first underlayer atoms of Ta(110). The surface core-level shift is 360\ifmmode\pm\else\textpm\fi{}12 meV at 80 K and decreases by 13\ifmmode\pm\else\textpm\fi{}2 meV at 300 K. Final-state screening in both the bulk and surface layers is well described by a constant singularity index of 0.133\ifmmode\pm\else\textpm\fi{}0.012. An enhanced phonon broadening at the surface corresponds to a reduced perpendicular Debye temperature for the surface atoms of 128\ifmmode\pm\else\textpm\fi{}18 K compared to the bulk Debye temperature of 225 K.
41 citations
TL;DR: In this article, low-temperature specific heat and differential-scanning-calorimetry (DSC) measurements have been performed on polycrystalline C70.
Abstract: Low-temperature specific heat and differential-scanning-calorimetry (DSC) measurements have been performed on polycrystalline C70. At high temperature, the DSC measurements reveal two phase transitions at 280 and 337 K, respectively. At low-temperatures, the measurements reveal an excess of specific heat with respect to that of graphite, with a classical behavior and a Debye temperature of 145 K. At 50 K a second-order transition is observed.
38 citations
TL;DR: In this article, the widths, positions and shapes of sharp luminescence lines of the Nd3+ ion in GSGG:Cr3+, Nd 3+ were measured carefully from 78 to 600 K. The Debye temperature of GSGG is estimated to be 500 K through the fitting of the theoretical formulas to the experimental data.
36 citations
TL;DR: In this article, the temperature variations of the center shifts and of the quadrupole splittings have been interpreted using the Debye model for the lattice vibrations and the crystal-field model respectively.
Abstract: 57Fe Mossbauer measurements were performed on two natural orthopyroxenes in the temperature range between 17 and 490 K. The temperature variations of the center shifts and of the quadrupole splittings have been interpreted using the Debye model for the lattice vibrations and the crystal-field model respectively. Two approaches have been applied to evaluate the crystal field. The first one, which is commonly used by Mossbauer spectroscopists, emanates from the approximative and simplified symmetry of the ferrous sites, whereas the second one takes into account the real C1 symmetry of the ferrous sites, thus leading to a pointcharge calculation. For comparison, analogous calculations have been carried out on literature data for an iron-rich orthopyroxene (specimen XYZ).
TL;DR: In this article, a paramagnetic compound with the susceptibility equal to 2.7×10−6 emu/g at 5 K was used to measure the specific heat of YNi4B.
Abstract: YNi4B is a paramagnetic compound with the susceptibility equal to 2.7×10−6 emu/g at 5 K. From the low‐temperature specific heat, values of 458 K for the Debye temperature and 14.1 mJ/K2 mol for the coefficient of the electronic specific heat are obtained. GdNi4B is ferromagnetic below Tc=35.0 K where the λ‐type anomaly is observed in the specific heat. Magnetic and specific‐heat measurements provide strong evidence that the 3d band in YNi4B and GdNi4B is completely filled.
TL;DR: In this paper, low temperature specific heat measurements of VSi2, NbSi2 and TaSi2 are presented, showing that the interatomic forces are similar in the three disilicides.
Abstract: We present low temperature specific heat measurements of VSi2, NbSi2 and TaSi2. The three disilicides crystallize in the same hexagonal structure (C40, space group P6222). The measured values of the electronic Density of States at the Fermi Energy,D(EF), are in good agreement with theoretical band structure calculations. The obtained Debye temperatures vary asM
−1/2 (M is the molar mass of the compound), showing that the interatomic forces are similar in the three disilicides. NbSi2 and TaSi2 are found to be superconductors at 0.130K and 0.353K respectively. The variation of the transition temperatures is discussed.
TL;DR: In this paper, three intermetallic compounds in the NiZr system were irradiated with 1 MeV electrons in a high-voltage electron microscope over the temperature range 10-200 K. All three compounds were amorphized by the electron irradiation with varying degrees of amorphization tendency and different critical temperatures.
TL;DR: In this article, the authors present a new analysis of phonon conductivity which shows that at high temperature (T> theta D, the Debye temperature), the longitudinal phonons are the dominant heat carriers in germanium.
Abstract: Using the relaxation time approach, the authors present a new analysis of phonon conductivity which shows that at high temperature (T> theta D, the Debye temperature), the longitudinal phonons are the dominant heat carriers in germanium. The present result, which is a consequence of the effect of phonon dispersion on the Callaway integral for lattice thermal conductivity, is contrary to the general belief that transverse phonons carry heat at T> theta D. A qualitative justification has also been given for the three-phonon scattering parameters obtained.
TL;DR: Experimental determinations of the dependences Δρ(T)/ρ in this temperature range are in good agreement with the correction to the impurity resistivity of a normal metal due to the quantum interference between the electron-phonon and electron-impurity interactions.
Abstract: The temperature dependence of the resistivity p of thin gold films (thickness d=100-400 A) has been measured at T=30 mK-300 K. In a wide temperature range below θ D /15 (θ D is the Debye temperature) Δρ(T)/p is proportional to T 2 and does not depend on the mean free path of electrons. Experimental determinations of the dependences Δρ(T)/ρ in this temperature range are in good agreement with the correction to the impurity resistivity of a normal metal due to the quantum interference between the electron-phonon and electron-impurity interactions
TL;DR: It is argued that [kappa]=3/7 is dictated by the inelastic scattering rate and the percolation length, instead of the localization length, for the width of the transition region between quantum Hall effect plateaus.
Abstract: The electron-phonon scattering rate is calculated in a strong magnetic field for a two-dimensional electron gas moving in a smooth random potential within the framework of semiclassical approximation. This inelastic scattering rate is strongly influenced by the strong magnetic field and is found to be linear in temperature for a wide range of temperatures, corresponding to an effective reduction of the Debye temperature. Applying this result to the temperature scaling exponent [kappa] for the width of the transition region between quantum Hall effect plateaus, we argue that [kappa]=3/7 is dictated by the inelastic scattering rate and the percolation length, instead of the localization length.
TL;DR: The Debye shielding is derived in a simple way without assuming Boltzmann's equilibrium as discussed by the authors, and conditions under which it applies and some of its consequences are discussed at the elementary level.
Abstract: The Debye shielding is derived in a simple way without assuming Boltzmann’s equilibrium. The conditions under which it applies and some of its consequences are discussed at the elementary level.
TL;DR: In this paper, the authors studied high-resolution angle-resolved photoelectron energy distribution curves from Cu(100) and Cu(111) in the temperature interval 38 ⩽ T ⊽ 70,0 K for several well defined peaks, originating from bulk direct transitions as well as from surface states, determined separately the temperature dependence of emission amplitude, peak area and peak width, respectively.
TL;DR: The ``ferromagnetic'' transition of erbium around 19 K exhibits a tremendously large and sharp heat-capacity maximum of 169 J/mol K, and the electronic specific constant (density of state at the Fermi level) exhibits a 15% increase at H\ensuremath{\sim}2 T due to a spin reorientation of the basal plane moments.
Abstract: Zero-field (1.5--80 K) and high-magnetic-field (1.5--20 K) low-temperature heat-capacity measurements have been carried out on 99.97 at. % (99.996 wt %) pure polycrystalline erbium. The electronic specific-heat coefficient (in zero field) was found to be 8.7\ifmmode\pm\else\textpm\fi{}0.1 mJ/mol ${\mathrm{K}}^{2}$ and the Debye temperature to be 176.9\ifmmode\pm\else\textpm\fi{}0.4 K. The ``ferromagnetic'' transition of erbium around 19 K exhibits a tremendously large and sharp heat-capacity maximum of 169 J/mol K. Five other heat-capacity anomalies at 25.1, 27.5, 42, 48.9, and 51.4 K were observed. The 51.4-K peak is associated with antiferromagnetic ordering in the basal plane, and the other four anomalies are associated with spin-slip transitions between two different commensurate antiferromagnetic structures. An external magnetic field shifts the ferromagnetic heat-capacity peak toward higher temperatures with a remarkable suppression and broadening of the maximum, and reduces the total heat capacity below the magnetic ordering maximum for temperatures down to about 5 K. At lower temperatures, the high-magnetic field (Hg5 T) increases the sample heat capacity due to an increase in both the $^{167}\mathrm{Er}$ hyperfine coupling and electronic contributions. The effective magnetic field at the nucleus increases from 7.2 MOe at H=0 to 10.3 MOe at H=9.85 T. The electronic specific constant (density of state at the Fermi level) exhibits a 15% increase at H\ensuremath{\sim}2 T due to a spin reorientation of the basal plane moments. This change is also evident in the magnetic contribution to the heat capacity.
TL;DR: In this article, a simple and tractable modification to Debye's model is proposed which is free from the above-mentioned fault and the resulting Cole-Cole diagram is shown to deviate from an exact circle.
Abstract: Although Debye's relaxation model has been extensively used in analyzing experimental data of dielectric dispersion and absorption, the model has a fault to violate the sum rule for dielectric function. A simple and tractable modification to Debye's model is proposed which is free from the above-mentioned fault. The resulting Cole-Cole diagram is shown to deviate from an exact circle.
TL;DR: In this article, a simple model for the reproduction of the experimental heat capacities of urea, based on the Debye and Einstein functions, is described, and the debye characteristic temperature determined in this way was compared with those calculated from properties other than the heat capacity.
Abstract: The heat capacity of urea was measured with an adiabatic calorimeter in the temperature range 15–310 K. The data were extrapolated to 0 K by a model function to derive some standard thermodynamic functions including the enthalpy increments Δ 0 T H, the entropy increments Δ 0 T S, and the Giauque function (=Δ 0 TS −Δ 0 T H/T). A simple model for the reproduction of the experimental heat capacities of urea, based on the Debye and Einstein functions, is described. The Debye characteristic temperature determined in this way was compared with those calculated from properties other than the heat capacity. Any positive evidence of a suggested phase transition in urea around 190 K was not observed in the present heat capacity measurements. Possible existence of a phase with a Gibbs energy lower than that realized in the present investigation is discussed briefly.
TL;DR: The heating of a compact dispersive target by a pulsed, plane microwave is modeled and studied herein, and a new theory from which a considerable amount of information can be deduced.
Abstract: The heating of a compact dispersive target by a pulsed, plane microwave is modeled and studied herein. The dispersive character of the medium is described by a Debye model, and the conductive nature is modeled by an ionic conductivity. The electrical and thermal parameters are allowed to depend upon temperature, which gives rise to a highly nonlinear initial boundary value problem. The governing equations are averaged in the limit as $\omega T_H \to \infty $, where $T_H $ is a characteristic time at which heat diffuses in the target and w is the microwave carrier frequency. A two-step algorithm is proposed for the numerical solution of these equations. When convection is weak, the algorithm converges very slowly. However, this problem is overcome by averaging the equations in the limit $T_H /T_B \to 0$, where $T_B $ is a characteristic time describing energy loss by convection. This averaging yields a new theory from which a considerable amount of information can be deduced. Specifically, the temperature ...
TL;DR: It is shown that the total experimental entropy cannot be accounted for solely by a sum of a vibrational part and a Sommerfeld-type electronic term from a nonmagnetic electronic structure.
Abstract: We have analyzed the entropy of paramagnetic bcc Cr from the N\'eel temperature ${\mathit{T}}_{\mathit{N}}$=311 K to the melting temperature ${\mathit{T}}_{\mathit{f}}$=2136 K. It is shown that the total experimental entropy cannot be accounted for solely by a sum of a vibrational part and a Sommerfeld-type electronic term from a nonmagnetic electronic structure. The total entropy is obtained through an elaborate assessment of available experimental data on various thermodynamic properties. The vibrational part is based on phonon data obtained in neutron scattering experiments by Trampenau et al., and accounts also for anharmonic effects. The Sommerfeld-type electronic part is obtained from electron band-structure calculations. Our analysis suggests a magnetic contribution that is related to spin fluctuations and that increases with temperature. We compare Cr with the other group-VI transition metals, Mo and W, using results from our previous works. Cr, Mo, and W show striking similarities, e.g., in their anharmonic phonon softening, when considered as a function of the reduced temperature T/${\mathit{T}}_{\mathit{f}}$, where ${\mathit{T}}_{\mathit{f}}$ is the melting temperature. Since phonons dominate the heat capacity, their ${\mathit{C}}_{\mathit{p}}$ vs T/${\mathit{T}}_{\mathit{f}}$ plots are very similar.
TL;DR: In this paper, the variations in ultrasonic velocity and attenuation with temperature have been explained by a model assuming an asymmetric double-well potential having distributions of both the barrier height and the asymmetry parameter.
Abstract: The ultrasonic velocity and attenuation in four different samples of the (V2O5)x−(GeO2)1−x glass system (x = 0.5321,0.5816,0.6635 and 0.7132) have been measured at temperatures between 77 and 300 K using the ultrasonic pulse echo technique at 8 MHz. The elastic moduli and Debye temperatures have been calculated from the velocity data for each composition. The variations in ultrasonic velocity and attenuation with temperature have been explained by a model assuming an asymmetric double-well potential having distributions of both the barrier height and the asymmetry parameter.
TL;DR: The results show that the addition of hydrogen to this rare-earth metal has a qualitatively different effect than the additionof hydrogen to transition metals such as palladium, vanadium, niobium, and tantalum.
Abstract: The complete set of elastic constants for Sc and ${\mathrm{ScD}}_{0.18}$ has been measured at room temperature. The results show that the addition of hydrogen to this rare-earth metal has a qualitatively different effect than the addition of hydrogen to transition metals such as palladium, vanadium, niobium, and tantalum. In the case of Sc all five elastic constants increase with the addition of hydrogen. The bulk modulus for ${\mathrm{ScD}}_{0.18}$ is 9.5% higher than that for Sc. The Debye temperature computed from the room-temperature elastic constants is 355 K for Sc and 371 K for ${\mathrm{ScD}}_{0.18}$.
TL;DR: Abrupt change of quadrupole shifts near 122 K suggests that the spin-rotation transition proceeds abruptly, in contrast with the gradual transition reported for Fe 7 Se 8 with a triclinic superstructure.
Abstract: (Fe 1+x Ni x ) x Se 8 (x=0.02,0.05,0.08) has been studied with Mossbauer spectroscopy and x-ray diffraction. The crystal structure is found to be a triclinic superstructure of the NiAs structure while Fe 7 Se 8 has a hexagonal structure. Abrupt change of quadrupole shifts near 122 K suggests that the spin-rotation transition proceeds abruptly, in contrast with the gradual transition reported for Fe 7 Se 8 with a triclinic superstructure. The iron ions at all four sites are found to be in a highly covalent ferrous state. Both Neel and Debye temperatures are found to decrease with increasing nickel concentration
TL;DR: In this paper, the DC conductivity of BF4-doped polypyrrole films has been measured in the temperature range 77-305 K and could be well represented by Mott's variable-range hopping mechanism.
Abstract: The DC conductivity of BF4--doped polypyrrole films has been measured in the temperature range 77-305 K and could be well represented by Mott's variable-range hopping mechanism. The conductivity data were used to extract the coupling constant gamma , the effective polaron mass mp, the effective dielectric constant epsilon p the Debye temperature Theta D, the polaron radius rp, the hopping distance R, the density of states at the Fermi level N(EF) and the hopping energy W, whose magnitudes confirm the formation of small polarons in polypyrrole.
01 Jan 1993
TL;DR: Based on the many-atom interaction model and valence bond theory of metals, a new potential function for the interaction among atoms in solid is proposed in this paper, which can be simplified to have the form analogous to the Lennard-Jones potential.
Abstract: Based on the many-atom interaction model and valence bond theory of metals, a new potential function for the interaction among atoms in solid is proposed in the present work. Because the reduced bond length is taken as variable, the new potential function can be simplified to have the form analogous to the Lennard-Jones potential. Accoroding to Debye model, a series of equations for calculating various elasticities and constants K and Q in Gruneisen equation have been derived from the new potential function. The application of the new potential function to Ni, Cu and five alkli metals shows that these equations are correct.
TL;DR: In this paper, the authors investigated the origins of the enhanced specific heat of nanocrystalline platinum and suggested that the influence of light-element impurities exceeds by far the anharmonic contributions from grain boundaries.
Abstract: Nanocrystalline platinum has been investigated by differential scanning calorimetry and simultaneous thermal analysis as well as thermogravimetric analysis and mass spectroscopy in order to study the origins of enhanced specific heat of this material. The possible reasons for the enhanced specific heat are discussed in terms of anharmonic contributions caused by a reduced atomie density in grain boundaries and the presence of light-element impurities. From the experimental results it is suggested that the influence of the light-element impurities exceeds by far the anharmonic contributions from grain boundaries. Furthermore, a auasiharmonic Debye model of the grain boundary indicates that the mean grain-boundary volume expansion is less than 20%.