Showing papers on "Debye model published in 2011"
TL;DR: In this article, the compositional dependence of structural parameters and X-ray Debye temperature for CuAl x Fe 2− x O 4 ( x ǫ = 0.0, 0.4 and 0.6) spinel ferrite system has been studied by means of Xray powder diffraction (XRD) patterns analysis at 300 K.
174 citations
TL;DR: It is found that most thermodynamic properties of nanoparticles vary linearly with 1/D as a first approximation, which may be regarded as a scaling law for most of the size dependent thermodynamics properties for different materials.
Abstract: The previous model on surface free energy has been extended to calculate size dependent thermodynamic properties (i.e., melting temperature, melting enthalpy, melting entropy, evaporation temperature, Curie temperature, Debye temperature and specific heat capacity) of nanoparticles. According to the quantitative calculation of size effects on the calculated thermodynamic properties, it is found that most thermodynamic properties of nanoparticles vary linearly with 1/D as a first approximation. In other words, the size dependent thermodynamic properties Pn have the form of Pn = Pb(1 − K/D), in which Pb is the corresponding bulk value and K is the material constant. This may be regarded as a scaling law for most of the size dependent thermodynamic properties for different materials. The present predictions are consistent literature values.
125 citations
TL;DR: In conclusion, suitable core-shell material combinations for future thermoelectric materials of large electric conductivities in combination with an increased thermopower by energy filtering are proposed.
Abstract: We present the full thermoelectric characterization of nanostructured bulk PbTe and PbTe–PbSe samples fabricated from colloidal core–shell nanoparticles followed by spark plasma sintering. An unusually large thermopower is found in both materials, and the possibility of energy filtering as opposed to grain boundary scattering as an explanation is discussed. A decreased Debye temperature and an increased molar specific heat are in accordance with recent predictions for nanostructured materials. On the basis of these results we propose suitable core–shell material combinations for future thermoelectric materials of large electric conductivities in combination with an increased thermopower by energy filtering.
116 citations
TL;DR: In this article, the thermal conductivities of bulk Si and Bi2Te3 were evaluated using a Landauer approach and related to the conventional approach based on the Boltzmann transport equation.
Abstract: Using a full dispersion description of phonons, the thermal conductivities of bulk Si and Bi2Te3 are evaluated using a Landauer approach and related to the conventional approach based on the Boltzmann transport equation. A procedure to extract a well-defined average phonon mean-free-path from the measured thermal conductivity and given phonon-dispersion is presented. The extracted mean-free-path has strong physical significance and differs greatly from simple estimates. The use of simplified dispersion models for phonons is discussed, and it is shown that two different Debye temperatures must be used to treat the specific heat and thermal conductivity (analogous to the two different effective masses needed to describe the electron density and conductivity). A simple technique to extract these two Debye temperatures is presented and the limitations of the method are discussed.
113 citations
TL;DR: In this article, the lattice constant of Bi2Se3 and Sb2Te3 was determined by x-ray powder diffraction measurement in a wide temperature range, and the linear thermal expansion coefficients (α) of the crystals were extracted, and considerable anisotropy between α|| and α⊥ was observed.
Abstract: Lattice constant of Bi2Se3 and Sb2Te3 crystals is determined by x-ray powder diffraction measurement in a wide temperature range. Linear thermal expansion coefficients (α) of the crystals are extracted, and considerable anisotropy between α|| and α⊥ is observed. The low temperature values of α can be fit well by the Debye model, while an anomalous behavior at above 150 K is evidenced and explained. Gruneisen parameters of the materials are also estimated at room temperature.
109 citations
TL;DR: The quantum-classical comparison of the average trapping time with the removal of the bottleneck site, BChl 4, demonstrates the robustness of the efficient energy transfer by the mechanism of multi-site quantum coherence.
Abstract: Following the calculation of optimal energy transfer in thermal environment in our first paper (Wu et al., New J. Phys., 2010, 12, 105012), full quantum dynamics and leading-order `classical' hopping kinetics are compared in the seven-site Fenna-Matthews-Olson (FMO) protein complex. The difference between these two dynamic descriptions is due to higher-order quantum corrections. Two thermal bath models, classical white noise (the Haken-Strobl-Reineker model) and quantum Debye model, are considered. In the seven-site FMO model, we observe that higher-order corrections lead to negligible changes in the trapping time or in energy transfer efficiency around the optimal and physiological conditions (2% in the HSR model and 0.1% in the quantum Debye model for the initial site at BChl 1). However, using the concept of integrated flux, we can identify significant differences in branching probabilities of the energy transfer network between hopping kinetics and quantum dynamics (26% in the HSR model and 32% in the quantum Debye model for the initial site at BChl 1). This observation indicates that the quantum coherence can significantly change the distribution of energy transfer pathways in the flux network with the efficiency nearly the same. The quantum-classical comparison of the average trapping time with the removal of the bottleneck site, BChl 4, demonstrates the robustness of the efficient energy transfer by the mechanism of multi-site quantum coherence. To reconcile with the latest eight-site FMO model, the quantum-classical comparison with the flux network analysis is summarized in the appendix. The eight-site FMO model yields similar trapping time and network structure as the seven-site FMO model but leads to a more disperse distribution of energy transfer pathways.
98 citations
TL;DR: In this article, the lattice constant of Bi$_2$Se$_3$ and Sb$_ 2$Te$_ 3$ crystals was determined by X-ray powder diffraction measurement in a wide temperature range.
Abstract: Lattice constant of Bi$_2$Se$_3$ and Sb$_2$Te$_3$ crystals is determined by X-ray powder diffraction measurement in a wide temperature range. Linear thermal expansion coefficients ($\alpha$) of the crystals are extracted, and considerable anisotropy between $\alpha_\parallel$ and $\alpha_\perp$ is observed. The low temperature values of $\alpha$ can be fit well by the Debye model, while an anomalous behavior at above 150 K is evidenced and explained. Gruneisen parameters of the materials are also estimated at room temperature.
91 citations
TL;DR: In this article, the authors investigated the thermal relaxation of a spatially sinusoidal temperature perturbation in a dielectric crystal at a temperature comparable to or higher than the Debye temperature.
Abstract: The relaxation of a spatially sinusoidal temperature perturbation in a dielectric crystal at a temperature comparable to or higher than the Debye temperature is investigated theoretically. We assume that most phonons contributing to the specific heat have a mean free path (MFP) much shorter than the thermal transport distance and can be described by the thermal diffusion model. Low-frequency phonons that may have MFP comparable to or longer than the grating period are described by the Boltzmann transport equation. These low-frequency phonons are assumed to interact with the thermal reservoir of high-frequency phonons but not with each other. Within the single mode relaxation time approximation, an analytical expression for the thermal grating relaxation rate is obtained. We show that the contribution of ``ballistic'' phonons with long MFP to the effective thermal conductivity governing the grating decay is suppressed compared to their contribution to thermal transport at long distances. The reduction in the effective thermal conductivity in Si at room temperature is found to be significant at grating periods as large as 10 \ensuremath{\mu}m.
90 citations
TL;DR: In this paper, the authors used a single parabolic band model to predict that the extremely high carrier concentration of Mo3Sb7 can be reduced to a nearly optimized level (∼2 × 1021 cm−3) for thermoelectric figure of merit (zT) by Te-substitution with x = 1.8.
Abstract: Heavily doped compounds Mo3Sb7−xTex (x = 0, 1.0, 1.4, 1.8) were synthesized by solid state reaction and sintered by spark plasma sintering. Both X-ray diffraction and electron probe microanalysis indicated the maximum solubility of Te was around x = 1.8. The trends in the electrical transport properties can generally be understood using a single parabolic band model, which predicts that the extremely high carrier concentration of Mo3Sb7 (∼1022 cm−3) can be reduced to a nearly optimized level (∼2 × 1021 cm−3) for thermoelectric figure of merit (zT) by Te-substitution with x = 1.8. The increased lattice thermal conductivity by Te-doping was found to be due to the decreased Umklapp and electron–phonon scattering, according to a Debye model fitting. The thermoelectric figure of merit (zT) monotonously increased with increasing temperature and reached its highest value of about 0.51 at 850 K for the sample with x = 1.8, making these materials competitive with the state-of-the-art thermoelectric SiGe alloys. Evidence of significant electron–phonon scattering is found in the thermal conductivity.
80 citations
TL;DR: In this article, the elasticity, dynamic properties, and superconductivity of α, ω, and β Zr upon compression were investigated by using first-principles methods.
Abstract: The elasticity, dynamic properties, and superconductivity of α, ω, and β Zr upon compression are investigated by using first-principles methods. Our calculated elastic constants, elastic moduli, and Debye temperatures of α and ω phases are in excellent agreement with experiments. Electron-phonon coupling constant λ and electronic density of states at the Fermi level N (EF) are found to increase with pressure for these two hexagonal structures. For cubic β phase, the critical pressure for mechanical stability is predicted to be 3.13 GPa and at P = 4 GPa the low elastic modulus (E =31.97 GPa) can be obtained. Besides, the critical pressure for dynamic stability of β phase is achieved by phonon dispersion calculations to be ∼26 GPa. Over this pressure, λ and N (EF) of β phase decrease upon further compression. Our calculations show that the large value of superconducting transition temperature Tc at 30 GPa for β Zr is mainly due to the TA1 soft mode. Under further compression, the soft vibrational mode will ...
76 citations
TL;DR: In this article, the surface of an epitaxial graphene monolayer grown on Ru(0001) was used as a quite efficient external mirror for He-atom microscopy, with a specular reflectivity of $20%$ of the incident beam.
Abstract: It is shown that the surface of an epitaxial graphene monolayer grown on Ru(0001) could be used as a quite efficient external mirror for He-atom microscopy, with a specular reflectivity of $20%$ of the incident beam. Furthermore, the system is stable up to 1150 K, and the He reflectivity remains almost unchanged after exposure to air. Additionally, the high reflectivity for ${\mathrm{H}}_{2}$ molecules (11%) opens up the development of a ${\mathrm{H}}_{2}$ microprobe suitable for lithography. The Debye temperature for this epitaxial graphene monolayer has been determined from a study of the temperature dependence of the He specular intensity as a function of incident parameters. A value of 1045 K has been obtained, which is much higher than the 590 K reported for graphite under similar conditions, and close to the value of 1287 K calculated for isolated graphene.
TL;DR: A detailed theoretical study of structural, electronic, elastic, thermodynamic and optical properties of rutile type MgF2 has been carried out by means of first-principles Density Functional Theory (DFT) calculations using plane wave pseudo-potentials within the local density approximation and generalized-gradient approximation for the exchange and correlation functionals as mentioned in this paper.
TL;DR: In this article, a comprehensive theoretical investigation of paraelectric (cubic) and ferroelectric (tetragonal) BaTiO${}_{3}$ is presented, where the atomic and electronic structure, piezoelectric tensor, Debye temperature, zone center phonon frequencies, and optical absorption are calculated for both phases from first principles.
Abstract: We present a comprehensive theoretical investigation of paraelectric (cubic) and ferroelectric (tetragonal) BaTiO${}_{3}$. The atomic and electronic structure, piezoelectric tensor, Debye temperature, zone center phonon frequencies, and optical absorption are calculated for both phases from first principles. The structural and vibrational properties predicted from density functional theory are in good agreement with experiment and earlier theoretical work. The electronic structure and optical response are found to be very sensitive to quasiparticle and electron-hole attraction effects, which are accounted for by using the GW approach and by solving the Bethe-Salpeter equation, respectively. Electronic self-energy effects are found to open the band gap substantially, to 3.7 and 3.9 eV for the cubic and tetragonal phases, respectively. In contrast to earlier calculations, good agreement with the measured optical data is achieved. The ab initiothermodynamics predicts that the ferroelectric ordering will disappear at 419 K. It is shown that the phase transition is driven by the vibrational entropy of a variety of modes.
TL;DR: A theoretical study of structural, electronic and thermal properties of CdS, CdSe and CdTe compounds is presented in this paper using the full potential linearized augmented plane wave (FP-LAPW) method within density functional theory.
TL;DR: In this article, the authors carried out in situ X-ray diffraction experiments using a Kawai-type multi-anvil apparatus and a diamond anvil cell up to 71.5 GPa and 1973 K. The carbide was found to be stable under these experimental conditions.
Abstract: To investigate the physical property of Fe7C3, we carried out in situ X-ray diffraction experiments using a Kawai-type multi-anvil apparatus and a diamond anvil cell up to 71.5 GPa and 1973 K. The carbide was found to be stable under these experimental conditions. However, we found anomalous behavior in its isothermal compression and thermal expansivity. These anomalies could be due to the magnetic phase transition in Fe7C3 from a ferromagnetic ( fm ) to a paramagnetic ( pm ) phase. The Curie temperature of 523 K at 1 bar (Tsuzuki et al. 1984) decreases with pressure, and the pressure-induced magnetic transition is estimated to occur at ~18 GPa and 300 K. The pressure-volume-temperature ( P - V - T ) data set for the pm -Fe7C3 was fitted by the Mie-Gruneisen-Debye (MGD) equation of state (EOS) and the following parameters were obtained: unit-cell volume V = 184.2 ± 0.3 A3, bulk modulus K = 253 ± 7 GPa, the pressure derivative of bulk modulus K ′ = 3.6 ± 0.2, Gruneisen parameter γ = 2.57 ± 0.05, Debye temperature 𝛉 = 920 ± 140 K, and q = 2.2 ± 0.5, respectively, at zero pressure. The calculated density for Fe7C3 provides a good explanation for the density of the Earth’s inner core obtained from seismological observations.
TL;DR: In this paper, the electronic structural and dynamical properties of NiAl have been studied using density functional theory and Debye model and the obtained pressure/temperature dependence on the V / V 0 and lattice parameter, agrees with the available experimental and other theoretical data.
TL;DR: The physical properties of the σ-phase in Fe-Cr and Fe-V alloy systems have been investigated both with experimental and theoretical methods as mentioned in this paper, and the following questions relevant to the issue have been addressed: identification of σ and determination of its structural properties.
Abstract: This review addresses the physical properties of the σ-phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental—mostly with the Mossbauer spectroscopy—and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of σ and determination of its structural properties, kinetics of α-to-σ and σ-to-α phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.
TL;DR: In this paper, the structural, electronic, elastic and some thermodynamic properties of the cubic C15 structure ZrV2 compound under pressure are investigated by first-principles calculations.
Abstract: The structural, electronic, elastic and some thermodynamic properties of the cubic C15 structure ZrV2 compound under pressure are investigated by first-principles calculations. Our results for the equilibrium unit cell volume, bulk modulus and band structure are consistent with the calculated and experimental results. Cubic ZrV2 is mechanically stable according to the elastic stability criteria and shows ductile with the G/B and Cauchy pressure analysis. Moreover the pressure and temperature dependence of the bulk modulus, specific heat, Debye temperature and thermal expansion coefficient are discussed, among them our calculated Debye temperature is in good agreement with experiments.
TL;DR: The calculated phonon dispersions show that all TiO(2) polymorphs are dynamically stable at ambient pressure, indicating the high-pressure phases might be quenched to ambient conditions as ultrahard materials.
Abstract: The structural, phonon, and thermodynamic properties of six TiO2 polymorphs, i.e., rutile, anatase, columbite, baddeleyite, orthorhombic I, and cotunnite, have been systematically investigated by density functional theory. The predicted volumes, bulk modulus, and Debye temperature are in good agreement with experiments. The phonon dispersions of the TiO2 polymorphs were studied by the supercell approach, whereas the long-range dipole–dipole interactions were calculated by linear response theory to reproduce the LO–TO splitting, making accurate prediction of phonon frequencies for the polar material TiO2. The calculated phonon dispersions show that all TiO2 polymorphs are dynamically stable at ambient pressure, indicating the high-pressure phases might be quenched to ambient conditions as ultrahard materials. Furthermore, the finite temperature thermodynamic properties of TiO2 polymorphs were predicted accurately from the obtained phonon density of states, which is critical in the future study of the press...
TL;DR: In this paper, the structural, elastic, electronic, optical and thermal properties of the semiconductor perovskite CsPbCl 3 were investigated using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA) and local density approximation (LDA).
Abstract: The structural, elastic, electronic, optical and thermal properties of the semiconductor perovskite CsPbCl 3 were investigated using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA) and local density approximation (LDA). The computed lattice constant agrees reasonably with experimental and theoretical ones. The CsPbCl 3 crystal behaves as ductile material. The valence bands are separated from the conduction bands by a direct band gap R – R . We distinguished hybridization between Pb-p states and Cl-p states in the valence bonding region. Under compression at P =30 GPa, this material will have a metallic character. The thermal effect on the lattice constant, bulk modulus, Debye temperature and heat capacity C V was predicted using the quasi-harmonic Debye model. To the author's knowledge, most of the studied properties are reported for the first time.
TL;DR: In this article, structural, mechanical, electronic, and thermodynamic properties of fluorite and tetragonal phases of ZrH2 are systematically studied by employing the density functional theory within generalized gradient approximation.
TL;DR: In this article, the compositional dependence of the crystal structure and lattice thermal conductivity in the Cu3SbSe4-SbS4 system has been studied.
Abstract: The compositional dependence of the crystal structure and lattice thermal conductivity in the Cu3SbSe4-Cu3SbS4 system has been studied. The lattice parameters of the Cu3SbSe4-xSx compounds decrease linearly with x, and the tetragonal structure (space group 14−2m no. 121) of the end compounds is maintained at all compositions. The lattice thermal conductivity is much lower than that predicted by a simple rule of mixtures, which is typical for a solid solution. The Debye model produces a very reasonable fit to the experimental lattice thermal conductivity data when phonon scattering due to atomic mass and size differences between Se and S is taken into account. Compounds in this series are likely to improve upon the thermoelectric performance of Cu3SbSe4, which has shown ZT = 0.72 when optimized.
TL;DR: In this article, the structural, electronic, mechanical properties and hardness of orthorhombic B 28 and tetragonal B 48 boron phases have been studied by first-principles of pseudopotential calculations.
TL;DR: In this paper, the elastic constants and their pressure dependence are calculated following the total energy variation with strain technique for high pressure structural phase transition and the elastic properties of ScS and ScSe using the FP-APW ǫ+ǫ LO with the generalized-gradient approximation (GGA ) exchange-correlation functional.
TL;DR: The thermal conductivity of optically transparent, yttria-stabilized tetragonal zirconia having a range of grain sizes from 100 to 180 nm has been measured from just below its approximate Debye temperature up to 1000 °C.
Abstract: The thermal conductivity of optically transparent, yttria-stabilized tetragonal zirconia having a range of grain sizes from 100 to 180 nm has been measured from just below its approximate Debye temperature up to 1000 °C. It is found that the grain size dependence is most marked at room temperature, decreasing with increasing temperature until being indistinguishable at the highest temperatures. The Kapitza thermal resistance of the grain boundaries is found to be almost independent of temperature, with a value of Rk=4.5±0.5×10−9 m2K/W and an estimated grain boundary phonon transparency of ∼0.9.
TL;DR: In this article, the Debye model and the Stokes-Einstein-Debye relation in conjunction with the Maxwell-Garnett equation were used for free-solution identification through molecular finger-printing.
Abstract: Aqueous solutions of a variety of proteins at different concentrations are examined through microwave spectroscopy and compared to sodium chloride and polystyrene nanospheres. The complex permittivity is analysed in terms of the Debye model and the Stokes-Einstein-Debye relation in conjunction with the Maxwell-Garnett equation. According to Einstein’s classical theory of viscosity with Brenner’s adaptation [H. Brenner, Chem. Eng. Sci. 27, 1069 (1972)] for arbitrary solute shapes, the ratio of the alterations of static permittivity and relaxation time of low concentration solutions is found to be independent of concentration and determined by the molecular shape. Our results represent a route towards free-solution identification through molecular finger-printing.
TL;DR: In this article, the physical properties of the sigma-phase in Fe-Cr and Fe-V alloy systems are discussed both with experimental and theoretical methods, and the following questions relevant to the issue have been addressed: identification of sigma and determination of its structural properties.
Abstract: A review is presented on physical properties of the sigma-phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental -- mostly with the Mossbauer spectroscopy -- and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of sigma and determination of its structural properties, kinetics of alpha-to-sigma and sigma-to-alpha phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.
TL;DR: In this article, structural stability, elastic properties, Debye temperature and electronic structure of the main binary cubic phases Mg 17 Al 12 and Mg 2 Pb with A12 and C12 structures in the new type Pb-Mg-Al alloy, respectively.
TL;DR: In this paper, the structural, elastic, and electronic properties of rutile-type SnO2 were investigated by plane-wave pseudopotential density functional theory method, and the lattice constants, bulk modulus and its pressure derivative were all calculated.
TL;DR: In this paper, the magnetic nature of Bi3Ni system is investigated and the structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879{\AA} b = 4.0998{AA} and c = 4.099{AA}.
Abstract: We report the experimental and theoretical study on magnetic nature of Bi3Ni system. The structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879{\AA} b = 4.0998{\AA} and c = 4.099{\AA}. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5N purity stoichiometric ingredients of Ni and Bi. The superconducting transition temperature is found to be 4.1 K as confirmed from magnetization and specific heat measurements. The lower critical field (Hc1) and irreversibility field (Hirr) are around 150 and 3000Oe respectively at 2K. Upper critical field (Hc2) as determined from in field (up to 4 Tesla) ac susceptibility is found to be around 2 Tesla at 2K. The normal state specific heat is fitted using Sommerfeld-Debye equation C(T) = {\gamma}T + {\beta}T3+{\delta}T5 and the parameters obtained are {\gamma}= 11.08mJ/mol-K2, {\beta}= 3.73mJ/mol-K4 and {\delta}= 0.0140mJ/mol-K6. The calculated electronic density of states (DOS) at Fermi level N(EF) and Debye temperature {\Theta}D are 4.697 states/eV per formula unit and 127.7K respectively. We also estimated the value of electron phonon coupling constant ({\lambda}) to be 1.23, which when substituted in MacMillan equation gives Tc = 4.5K. Density functional (DFT) based calculations for experimentally determined lattice parameters show that Ni in this compound is non-magnetic and ferromagnetic interactions seem to play no role. The Stoner condition I*N(EF) = 0.136 per Ni atom also indicates that system cannot have any ferromagnetism. The fixed spin moment (FSM) calculations by fixing total magnetic moment on the unit cell also suggested that this system does not exhibit any signatures of ferromagnetism.