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Showing papers on "Debye model published in 2014"


Journal ArticleDOI
TL;DR: In this article, a quasiharmonic Debye approximation has been implemented within the aflow and materials project frameworks for high-throughput computational materials science (Automatic Gibbs Library, agl), in order to calculate thermal properties such as the Debye temperature and the thermal conductivity of materials.
Abstract: The quasiharmonic Debye approximation has been implemented within the aflow and Materials Project frameworks for high-throughput computational materials science (Automatic Gibbs Library, agl), in order to calculate thermal properties such as the Debye temperature and the thermal conductivity of materials. We demonstrate that the agl method, which is significantly cheaper computationally compared to the fully ab initio approach, can reliably predict the ordinal ranking of the thermal conductivity for several different classes of semiconductor materials. In particular, a high Pearson (i.e., linear) correlation is obtained between the experimental and agl computed values of the lattice thermal conductivity for a set of 75 compounds including materials with cubic, hexagonal, rhombohedral, and tetragonal symmetry.

237 citations


Journal ArticleDOI
TL;DR: In this paper, a two-layer heterogeneous model consisting of semiconducting grains separated by insulating grain boundaries was able to account for the observed temperature and frequency dependent electrical properties in CFGO ceramics.

217 citations


Journal ArticleDOI
TL;DR: In this article, structural, mechanical and electronic properties of Laves phases Al2Zr and Al2Hf with C14-type structure were investigated by performing the first-principle calculations.

190 citations


Posted Content
TL;DR: The results indicate that, at room temperature, the electrical resistivity increases by around 4 folds from that of bulk silver, and proposes that the silver nanowire and bulk silver share the similar phonon-electron scattering mechanism for thermal transport.
Abstract: Silver nanowires have great application potential in fields like flexible electronic devices, solar cells and transparent electrodes. It is critical and fundamental to study the thermal and electrical transport properties in a single silver nanowire. In this work, the thermal and electrical transport in an individual silver nanowire is characterized down to 35 K with the steady state electro-thermal technique. The results indicate that, at room temperature, the electrical resistivity increases by around 4 folds compared from that of its bulk counterpart. After fitting the temperature dependent electrical resistivity curves with the Bloch-Gr\"uneisen formula, the Debye temperature (151 K) of the silver nanowire is found 36% lower than that (235 K) of bulk silver, confirming strong phonon softening. The thermal conductivity is reduced by 55% compared with that of its bulk counterpart at room temperature and this reduction becomes larger as the temperature goes down. To explain the opposite trends of thermal conductivity (\k{appa}) ~ temperature (T) of silver nanowire and bulk silver, a unified thermal resistivity is used to elucidate the electron scattering mechanism. A large residual unified thermal resistivity for the silver nanowire is observed while that of the bulk silver is almost zero. The same trend of variation against T indicates that the silver nanowire and bulk silver share the same phonon-electron scattering mechanism. Additionally, due to phonon-assisted electron energy transfer across the grain boundaries, the Lorenz number of the silver nanowire is found much larger than that of bulk silver and decreases with decreasing temperature.

144 citations


Journal ArticleDOI
TL;DR: It is shown that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal.
Abstract: We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higher-density crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal.

130 citations


Journal ArticleDOI
TL;DR: In this article, the authors used the modified Debye model to analyze the dielectric properties of CoFe2-xMnxO4, referred to CFMO.
Abstract: Manganese (Mn) substituted cobalt ferrites (CoFe2-xMnxO4, referred to CFMO) have been synthesized by the solid state reaction method and their dielectric properties and ac conductivity have been evaluated as a function of applied frequency and temperature. X-ray diffraction measurements indicate that CFMO crystallize in the inverse cubic spinel phase with a lattice constant ∼8.38 A. Frequency dependent dielectric measurements at room temperature obey the modified Debye model with relaxation time of 10−4 s and spreading factor of 0.35(±0.05). The frequency (20 Hz–1 MHz) and temperature (T = 300–900 K) dependent dielectric constant analyses indicate that CFMO exhibit two dielectric relaxations at lower frequencies (1–10 kHz), while completely single dielectric relaxation for higher frequencies (100 kHz–1 MHz). The dielectric constant of CFMO is T-independent up to ∼400 K, at which point increasing trend prevails. The dielectric constant increase with T > 400 K is explained through impedance spectroscopy assuming a two-layer model, where low-resistive grains separated from each other by high-resistive grain boundaries. Following this model, the two electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also satisfactorily accounts for the two dielectric relaxations. The capacitance of the bulk of the grain determined from impedance analyses is ∼10 pF, which remains constant with T, while the grain-boundary capacitance increases up to ∼3.5 nF with increasing T. The tan δ (loss tangent)-T also reveals the typical behavior of relaxation losses in CFMO.

120 citations


Journal ArticleDOI
TL;DR: In this article, the elastocaloric effect at various temperatures in a [001]-oriented Ni45.7Mn36.6In13.3Co5.1 metamagnetic shape memory polycrystal has been investigated.
Abstract: By direct measurements, the elastocaloric effect at various temperatures in a [001]-oriented Ni45.7Mn36.6In13.3Co5.1 metamagnetic shape memory polycrystal has been investigated. A reversible temperature change of ±3.5 K, due to the relatively low stress (100 MPa) induced martensitic transformation, was observed at room temperature. A theoretical analysis based on the Debye description has revealed that the adiabatic temperature change arising from the lattice vibration plays a dominant role in the large elastocaloric effect for Ni-Mn-In-Co alloys.

117 citations


Journal ArticleDOI
TL;DR: In this paper, the structural, elastic, electronic properties and elastic anisotropy of a fully tetrahedrally bonded boron nitride (BN) allotrope with an orthorhombic structure (Pbca-BN, space group: Pbca) was investigated by first-principles calculations.

104 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used Debye approximation to model the low temperature lattice thermal conductivity and found that the large strain field fluctuation introduced by the disordered Fe ions generates extra strong phonon scatterings for lowered lattice temperature.
Abstract: Polycrystalline samples with the composition of Cu _(1−x)Fe_(1+x)S_2 (x = 0, 0.01, 0.03, 0.05, 0.1) were synthesized by a melting-annealing-sintering process. X-ray powder diffraction reveals all the samples are phase pure. The backscattered electron image and X-ray map indicate that all elements are distributed homogeneously in the matrix. The measurements of Hall coefficient, electrical conductivity, and Seebeck coefficient show that Fe is an effective n-type dopant in CuFeS_2. The electron carrier concentration of Cu_(1−x)Fe_(1+x)S_2 is tuned within a wide range leading to optimized power factors. The lattice phonons are also strongly scattered by the substitution of Fe for Cu, leading to reduced thermal conductivity. We use Debye approximation to model the low temperature lattice thermal conductivity. It is found that the large strain field fluctuation introduced by the disordered Fe ions generates extra strong phonon scatterings for lowered lattice thermal conductivity.

96 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported results from ab initio calculations with density functional theory on three cubic structures, zincblende (zb), rocksalt (rs) and cesium chloride (cc), of the ten 3D transition metal nitrides.
Abstract: We report systematic results from ab initio calculations with density functional theory on three cubic structures, zincblende (zb), rocksalt (rs) and cesium chloride (cc), of the ten 3d transition metal nitrides. We computed lattice constants, elastic constants, their derived moduli and ratios that characterize mechanical properties. Experimental measurements exist in the literature of lattice constants for rs-ScN, rs-TiN and rs-VN and of elastic constants for rs-TiN and rs-VN, all of which are in good agreement with our computational results. Similarly, computed Vickers hardness (HV) values for rs-TiN and rs-VN are consistent with earlier experimental results. Several trends were observed in our rich data set of 30 compounds. All nitrides, except for zb-CrN, rs-MnN, rs-FeN, cc-ScN, cc-CrN, cc-NiN and cc-ZnN, were found to be mechanically stable. A clear correlation in the atomic density with the bulk modulus (B) was observed with maximum values of B around FeN, MnN and CrN. The shear modulus, Young’s modulus, HV and indicators of brittleness showed similar trends and all showed maxima for cc-VN. The calculated value of HV for cc-VN was about 30 GPa, while the next highest values were for rs-ScN and rs-TiN, about 24 GPa. A relation (HV/ 2 D ) between HV and Debye temperature ( D) was investigated and verified for each structure type. A tendency for anti-correlation of the elastic constant C44, which strongly influences stability and hardness, with the number of electronic states around the Fermi energy was observed. (Some figures may appear in colour only in the online journal)

92 citations


Journal ArticleDOI
TL;DR: The intrinsic lattice thermal conductivity of phosphorene is calculated by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations and the representative mean free path (MFP), a critical size for phonon transport, is obtained.
Abstract: Phosphorene, the single layer counterpart of black phosphorus, is a novel two-dimensional semiconductor with high carrier mobility and a large fundamental direct band gap, which has attracted tremendous interest recently. Its potential applications in nano-electronics and thermoelectrics call for a fundamental study of the phonon transport. Here, we calculate the intrinsic lattice thermal conductivity of phosphorene by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations. The thermal conductivity of phosphorene at $300\,\mathrm{K}$ is $30.15\,\mathrm{Wm^{-1}K^{-1}}$ (zigzag) and $13.65\,\mathrm{Wm^{-1}K^{-1}}$ (armchair), showing an obvious anisotropy along different directions. The calculated thermal conductivity fits perfectly to the inverse relation with temperature when the temperature is higher than Debye temperature ($\Theta_D = 278.66\,\mathrm{K}$). In comparison to graphene, the minor contribution around $5\%$ of the ZA mode is responsible for the low thermal conductivity of phosphorene. In addition, the representative mean free path (MFP), a critical size for phonon transport, is also obtained.

Journal ArticleDOI
TL;DR: The results demonstrate that MLs with highly dissimilar Debye temperatures represent a rational approach to achieve ultralow thermal conductivity in inorganic materials and can also serve as a platform for investigating interfacial thermal transport.
Abstract: Thermal transport in multilayers (MLs) has attracted significant interest and shows promising applications. Unlike their single-component counterparts, MLs exhibit a thermal conductivity that can be effectively engineered by both the number density of the layers and the interfacial thermal resistance between layers, with the latter being highly tunable via the contrast of acoustic properties of each layer. In this work, we experimentally demonstrated an ultralow thermal conductivity of 0.33 ± 0.04 W m −1 K −1 at room temperature in MLs made of Au and Si with a high interfacial density of ∼0.2 interface nm −1 . The measured thermal conductivity is significantly lower than the amorphous limit of either Si or Au and is also much lower than previously measured MLs with a similar interfacial density. With a Debye temperature ratio of ∼3.9 for Au and Si, the Au/Si MLs represent the highest mismatched system in inorganic MLs measured to date. In addition, we explore the prior theoretical prediction that full phonon dispersion could better model the interfacial thermal resistance involving materials with low Debye temperatures. Our results demonstrate that MLs with highly dissimilar Debye temperatures represent a rational approach to achieve ultralow thermal conductivity in inorganic materials and can also serve as a platform for investigating interfacial thermal transport.

Journal ArticleDOI
TL;DR: A reverse nanoemulsion technique was used for the elaboration of ultra-small nanoparticles with sizes down to 2 nm to correlate the modification of the stiffness of the nanoparticles thanks to the determination of their Debye temperature.
Abstract: A reverse nanoemulsion technique was used for the elaboration of [Fe(pz){Ni(CN)4}] nanoparticles. Low-temperature micellar exchange made it possible to elaborate ultra-small nanoparticles with sizes down to 2 nm. When decreasing the size of the particles from 110 to 12 nm the spin transition shifts to lower temperatures, becomes gradual, and the hysteresis shrinks. On the other hand, a re-opening of the hysteresis was observed for smaller (2 nm) particles. A detailed 57Fe Mossbauer spectroscopy analysis was used to correlate this unusual phenomenon to the modification of the stiffness of the nanoparticles thanks to the determination of their Debye temperature.

Journal ArticleDOI
TL;DR: In this article, the structural, elastic, thermodynamic and electronic properties of L12-ordered intermetallic compounds Ni3X under pressure range from 0 to 50 GPa with a step of 10 GPa have been investigated using first-principles method based on density functional theory.

Journal ArticleDOI
TL;DR: In this article, the phonon dispersion and phonon lifetime of single layer graphene were extracted from a molecular dynamics simulation and the mode dependent thermal conductivity was calculated from phonon kinetic theory, showing that the relative contribution of different mode phonons is not sensitive to the grain size of graphene.
Abstract: Molecular dynamics simulation is performed to extract the phonon dispersion and phonon lifetime of single layer graphene. The mode dependent thermal conductivity is calculated from the phonon kinetic theory. The predicted thermal conductivity at room temperature exhibits important quantum effects due to the high Debye temperature of graphene. But the quantum effects are reduced significantly when the simulated temperature is as high as 1000 K. Our calculations show that out-of-plane modes contribute about 41.1% to the total thermal conductivity at room temperature. The relative contribution of out-of-plane modes has a little decrease with the increase of temperature. Contact with substrate can reduce both the total thermal conductivity of graphene and the relative contribution of out-of-plane modes, in agreement with previous experiments and theories. Increasing the coupling strength between graphene and substrate can further reduce the relative contribution of out-of-plane modes. The present investigations also show that the relative contribution of different mode phonons is not sensitive to the grain size of graphene. The obtained phonon relaxation time provides useful insight for understanding the phonon mean free path and the size effects in graphene.

Journal ArticleDOI
TL;DR: In this article, the authors performed ab initio calculations on 29 nitride phases of transition metals from the 3d, 4d and 5d rows, in NbO structure, calculated cohesive energy, lattice constant and elastic constants C11, C12 and C44, and derived mechanical moduli, related ratios and hardness.

Journal ArticleDOI
TL;DR: The structural, mechanical, electronic, and optical properties of orthorhombic Bi2S3 and Bi2Se3 compounds have been investigated by means of first principles calculations and the calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings.
Abstract: The structural, mechanical, electronic, and optical propertiesoforthorhombicBi2S3andBi2Se3compoundshave been investigated by means of first principles calculations. The calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings. The elastic constants are obtained, then the secondary results such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factor, and Debye temperature of polycrys- talline aggregates are derived, and the relevant mechanical properties are also discussed.Furthermore, the bandstructures and optical properties such as real and imaginary parts of dielectric functions, energy-loss function, the effective num- ber of valance electrons, and the effective optical dielectric constant have been computed. We also calculated some non- linearities for Bi2S3 and Bi2Se3 (tensors of elasto-optical co- efficients) under pressure.

Journal ArticleDOI
TL;DR: In this article, a set of Mg2.08Si0.4−xSn0.6Sbx (0 ≤ x ≤ 0.072) compounds were investigated, and a peak ZT of 1.50 was obtained at 716 K in Mg 2.08 Si0.364sn0.036.
Abstract: Mg2(Si,Sn) compounds are promising candidate low-cost, lightweight, nontoxic thermoelectric materials made from abundant elements and are suited for power generation applications in the intermediate temperature range of 600 K to 800 K. Knowledge on the transport and mechanical properties of Mg2(Si,Sn) compounds is essential to the design of Mg2(Si,Sn)-based thermoelectric devices. In this work, such materials were synthesized using the molten-salt sealing method and were powder processed, followed by pulsed electric sintering densification. A set of Mg2.08Si0.4−xSn0.6Sbx (0 ≤ x ≤ 0.072) compounds were investigated, and a peak ZT of 1.50 was obtained at 716 K in Mg2.08Si0.364Sn0.6Sb0.036. The high ZT is attributed to a high electrical conductivity in these samples, possibly caused by a magnesium deficiency in the final product. The mechanical response of the material to stresses is a function of the elastic moduli. The temperature-dependent Young’s modulus, shear modulus, bulk modulus, Poisson’s ratio, acoustic wave speeds, and acoustic Debye temperature of the undoped Mg2(Si,Sn) compounds were measured using resonant ultrasound spectroscopy from 295 K to 603 K. In addition, the hardness and fracture toughness were measured at room temperature.

Journal ArticleDOI
TL;DR: In this paper, the structural, elastic, and thermodynamic properties of the four main intermetallic phases, namely, MgZn 2, Al 2 CuMg, Al 2 Zr, and Al 3 Zr were investigated.

Journal ArticleDOI
TL;DR: In this paper, the phase stability of Boron-V compounds in zinc-blend, rock-salt and wurtzite crystallographic phases was investigated by using density functional theory, based on the full-potential linearized augmented plane wave method.

Journal ArticleDOI
TL;DR: In this article, a convolution-based three-dimensional finite-difference time-domain (3D-FDTD) formulation is implemented for modeling the electromagnetic wave propagation in the dispersive head tissues whose frequency dependent properties are represented by the derived fourth-order Debye model.
Abstract: A fourth order Debye model is derived using genetic algorithms to represent the dispersive properties of the 17 tissues that form the human head. The derived model gives accurate estimation of the electrical properties of those tissues across the frequency band from 0.1 GHz to 3 GHz that can be used in microwave systems for head imaging. A convolution-based three-dimensional finite-difference time-domain (3D-FDTD) formulation is implemented for modeling the electromagnetic wave propagation in the dispersive head tissues whose frequency dependent properties are represented by the derived fourth-order Debye model. The presented results show that the proposed 3D-FDTD and fourth-order Debye model can accurately show the electromagnetic interaction between a wide band radiation and head tissues with low computational overhead and more accurate results compared with using multi-pole Cole-Cole model.

Journal ArticleDOI
TL;DR: In this paper, a systematic ab initio study of the elastic and thermodynamic properties of γ -ZrH, δ - ZrH 1.5, γ-ZrD, and δ − ZrD 2.5 was performed using the frozen core projector augmented wave (PAW) approach and a generalised gradient approximated (GGA) exchange correlation functional.

Journal ArticleDOI
TL;DR: In this paper, theoretical Vickers hardness, thermodynamic and optical properties of four zirconium metal-based MAX phases Zr2AC (A = Al, Si, P and S) for the first time in addition to revisiting the structural, elastic and electronic properties.
Abstract: We have investigated theoretical Vickers hardness, thermodynamic and optical properties of four zirconium metal-based MAX phases Zr2AC (A = Al, Si, P and S) for the first time in addition to revisiting the structural, elastic and electronic properties. First-principles calculations are employed based on density functional theory (DFT) by means of the plane-wave pseudopotential method. The theoretical Vickers hardness has been estimated via the calculation of Mulliken bond populations and electronic density of states. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats and volume thermal expansion coefficient of all the compounds are derived from the quasi-harmonic Debye model. Further, the optical properties, e.g., dielectric functions, indices of refraction, absorption, energy loss function, reflectivity and optical conductivity of the nanolaminates have been calculated. The results are compared with available experiments and their various implications are discussed in detail. We have also shed light on the effect of different properties of Zr2AC as the A-group atom moves from Al to S across the periodic table.

Journal ArticleDOI
TL;DR: In this article, the influence of bismuth addition on structural, elastic and spectral properties of [(99.5−x) {4ZnO−3B2O3}−0.5Nd2O-3−x BiO3 where x=0, 5, 10, 20, 30, 40, 50 and 60] glasses was investigated.

Journal Article
TL;DR: In this paper, the authors performed ab initio calculations on 29 nitride phases of transition metals from the 3d, 4d and 5d rows, in NbO structure, calculated cohesive energy, lattice constant and elastic constants C11, C12 and C44, and derived mechanical moduli, related ratios and hardness.
Abstract: We have performed ab initio calculations on 29 nitride phases of transition metals from the 3d, 4d and 5d rows, in NbO structure. We calculated cohesive energy, lattice constant and elastic constants C11, C12 and C44, and derived mechanical moduli, related ratios and hardness. For five out of the ten 3d transition metal nitrides, namely, CrN, MnN, FeN, CoN and NiN, cohesive energy in this new structure is similar to that of the same composition in the rocksalt structure. The lattice constant and bulk modulus were found to be anti-correlated. We observed the correlation between the shear modulus (G), Pugh’s ratio (k) and derived Vickers hardness (HV). For identical metal element significant variations in the mechanical properties of nitrides are found between rocksalt and NbO structures. However for a fixed structure, 3d, 4d and 5d metal nitrides behave similarly. We computed Debye temperature and demonstrated its correlation with HV as proposed by Madelung, Einstein and Deus. The nitrides, CrN, MoN and WN in NbO structure show values of HV larger than 20 GPa. We showed systematically that C44, G, k and HV are anti-correlated with the number of electronic states around EF, leading to a semi-quantitative link of nitride electronic structure to mechanical instability and hardness. The local density of states demonstrating systematic evolution of the electronic structure with the number of d electrons in the metal atoms was studied. Bader charge transfer from metal to nitrogen atom was analyzed throughout the 29 nitrides showing comparison with rocksalt structure and experimental electronegativity data.

Journal ArticleDOI
10 Jul 2014-PLOS ONE
TL;DR: The study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues.
Abstract: The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 100) The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 098) and less so for normal breast (p = 082) Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues

Journal ArticleDOI
TL;DR: In this article, the structural, elastic and mechanical properties of the intermetallic compound MgRh with a CsCl-type structure were determined from a linear fit of the calculated stress-strain function according to Hooke's law.

Journal ArticleDOI
TL;DR: In this paper, the elastic, thermophysical and thermochemical properties of the rock salt-type transition metal carbides and nitrides are investigated and compared with corresponding experimental data and a good agreement is seen.

Journal ArticleDOI
TL;DR: In this paper, the electrical resistivity in the abplane of the Y1−yPryВа2Сu3О7−δ single crystals with high degree of perfection in the interval of Тc − 300 K was investigated, and the concentration dependence of the critical temperature testifies the d-pairing of the BCS model.

Journal ArticleDOI
TL;DR: In this article, the structural, thermodynamic, electronic and vibrational properties of C1b-NiTiSn half-Heusler compounds have been analyzed and the enthalpies of point defects have been calculated using large supercells.