Showing papers on "Debye model published in 2016"
TL;DR: It is revealed, using experimental detection of the interaction between two planar charged surfaces across a wide range of electrolytes, that beyond the dilute (Debye-Hückel) regime the screening length increases with increasing concentration.
Abstract: According to classical electrolyte theories interactions in dilute (low ion density) electrolytes decay exponentially with distance, with the Debye screening length the characteristic length scale. This decay length decreases monotonically with increasing ion concentration due to effective screening of charges over short distances. Thus, within the Debye model no long-range forces are expected in concentrated electrolytes. Here we reveal, using experimental detection of the interaction between two planar charged surfaces across a wide range of electrolytes, that beyond the dilute (Debye–Huckel) regime the screening length increases with increasing concentration. The screening lengths for all electrolytes studied—including aqueous NaCl solutions, ionic liquids diluted with propylene carbonate, and pure ionic liquids—collapse onto a single curve when scaled by the dielectric constant. This nonmonotonic variation of the screening length with concentration, and its generality across ionic liquids and aqueous ...
407 citations
TL;DR: In this paper, it was shown that the lattice thermal conductivity of stanene is higher than other 2D group-IV materials due to a large acoustic-optical gap and the bunching of the acoustic-phonon branches.
Abstract: It has been argued that stanene has lowest lattice thermal conductivity among two-dimensional (2D) group-IV materials because of its largest atomic mass, weakest interatomic bonding, and enhanced ZA phonon scattering due to the breaking of an out-of-plane symmetry selection rule. However, we show that, although the lattice thermal conductivity $\ensuremath{\kappa}$ for graphene, silicene, and germanene decreases monotonically with decreasing Debye temperature, unexpected higher $\ensuremath{\kappa}$ is observed in stanene. By enforcing all the invariance conditions in 2D materials and including Ge $3d$ and Sn $4d$ electrons as valence electrons for germanene and stanene, respectively, the lattice dynamics in these materials are accurately described. A large acoustic-optical gap and the bunching of the acoustic-phonon branches significantly reduce phonon scattering in stanene, leading to higher thermal conductivity than germanene. The vibrational origin of the acoustic-optical gap can be attributed to the buckled structure. Interestingly, a buckled system has two competing influences on phonon transport: the breaking of the symmetry selection rule leads to reduced thermal conductivity, and the enlarging of the acoustic-optical gap results in enhanced thermal conductivity. The size dependence of thermal conductivity is investigated as well. In nanoribbons, the $\ensuremath{\kappa}$ of silicene, germanene, and stanene is much less sensitive to size effect due to their short intrinsic phonon mean-free paths. This work sheds light on the nature of phonon transport in buckled 2D materials.
167 citations
TL;DR: In this paper, first-principle calculations based on density functional theory have been used to calculate the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp) Mg by combining transition state theory and an 8-frequency model.
156 citations
TL;DR: It is reported that K2Bi8Se13 exhibits multiple conduction bands that lie close in energy and can be activated through doping, leading to a highly enhanced Seebeck coefficient and a high power factor with elevated temperature.
Abstract: We report that K2Bi8Se13 exhibits multiple conduction bands that lie close in energy and can be activated through doping, leading to a highly enhanced Seebeck coefficient and a high power factor with elevated temperature. Meanwhile, the large unit cell, complex low symmetry crystal structure, and nondirectional bonding lead to the very low lattice thermal conductivity of K2Bi8Se13, ranging between 0.42 and 0.20 W m–1 K–1 in the temperature interval 300–873 K. Experimentally, we further support the low thermal conductivity of K2Bi8Se13 using phonon velocity measurements; the results show a low average phonon velocity (1605 ms–1), small Young’s modulus (37.1 GPa), large Gruneisen parameter (1.71), and low Debye temperature (154 K). A detailed investigation of the microstructure and defects was carried out using electron diffraction and transmission microscopy which reveal the presence of a K2.5Bi8.5Se14 minor phase intergrown along the side of the K2Bi8Se13 phase. The combination of enhanced power factor an...
116 citations
TL;DR: The distinct low-temperature dynamics observed in these two perovskites suggest qualitative differences in the interaction between the molecular cation and the surrounding inorganic framework, with potential implications for defect screening and device performance at ambient temperatures.
Abstract: Hybrid main group halide perovskites hold great technological promise in optoelectronic applications and present rich and complex evolution of structure and dynamics. Here we present low-temperature dielectric measurements and calorimetry of APbI3 [A = CH3NH3+, HC(NH2)2+] that suggest glassy behavior on cooling. In both compounds, the dielectric loss displays frequency-dependent peaks below 100 K characteristic of a glassy slowing of relaxation dynamics, with HC(NH2)2PbI3 exhibiting greater glass fragility. Consistent with quenched disorder, the low-temperature heat capacity of both perovskites deviates substantially from the ∼T3 acoustic phonon contribution predicted by the Debye model. We suggest that static disorder of the A-site molecular cation, potentially coupled to local distortions of the Pb–I sublattice, is responsible for these phenomena. The distinct low-temperature dynamics observed in these two perovskites suggest qualitative differences in the interaction between the molecular cation and th...
98 citations
SIDI1
TL;DR: In this article, the structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory.
Abstract: The structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory. Local density approximation (LDA) for exchange-correlation potential and local spin density approximation (LSDA) are employed. The structural parameters as lattice parameters a0, bulk modulus B, its pressure derivate B’ and cut-off energy (Ec) within LDA and LSDA are presented. The elastic constants were derived from the stress–strain relation at 0 K. The thermodynamic properties for LuX using the quasi-harmonic Debye model are studied. The temperature and pressure variation of volume, bulk modulus, thermal expansion coefficient, heat capacities, Debye temperature and Gibbs free energy at different pressures (0–50 GPa) and temperatures (0–1600 K) are predicted. The calculated results are in accordance with other data.
96 citations
TL;DR: Thermal transport in silicon nanowires has captured the attention of scientists for understanding phonon transport at the nanoscale, and the thermoelectric figure-of-merit (ZT) reported in rough nanowire has inspired engineers to develop cost-effective waste heat recovery systems.
Abstract: Thermal transport in silicon nanowires has captured the attention of scientists for understanding phonon transport at the nanoscale, and the thermoelectric figure-of-merit (ZT) reported in rough nanowires has inspired engineers to develop cost-effective waste heat recovery systems Thermoelectric generators composed of silicon target high-temperature applications due to improved efficiency beyond 550 K However, there have been no studies of thermal transport in silicon nanowires beyond room temperature High-temperature measurements also enable studies of unanswered questions regarding the impact of surface boundaries and varying mode contributions as the highest vibrational modes are activated (Debye temperature of silicon is 645 K) Here, we develop a technique to investigate thermal transport in nanowires up to 700 K Our thermal conductivity measurements on smooth silicon nanowires show the classical diameter dependence from 40 to 120 nm In conjunction with Boltzmann transport equation, we also prob
81 citations
TL;DR: In this article, the structural, mechanical and bonding properties of newly synthesized ternary carbide Mo2Ga2C were investigated based on density functional theory and plane-wave pseudopotential total energy method.
69 citations
TL;DR: The evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature is reported by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K.
Abstract: Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram–Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.
65 citations
TL;DR: The phonon transport properties of recently fabricated single layer antimony, antimonene are reported on, indicating its potential thermoelectric applications and finding at low frequency that the longitudinal acoustic (LA) branch dominates the thermal conductivity.
Abstract: Searching for low thermal conductivity materials is crucial for thermoelectric devices. Here we report on the phonon transport properties of recently fabricated single layer antimony, antimonene [Ares, et al., Adv. Mater., 2016, 28, 6332]. Ab initio calculations in combination with the Boltzmann transport equation (BTE) for phonons show that antimonene has a low lattice thermal conductivity (15.1 W m−1 K−1 at 300 K), indicating its potential thermoelectric applications. The low lattice thermal conductivity is due to its small group velocity, low Debye temperature and large buckling height. We also investigate in detail the mode contributions to total thermal conductivity and find at low frequency that the longitudinal acoustic (LA) branch dominates the thermal conductivity. Moreover, we show that the lattice thermal conductivity of antimonene can further be reduced by minimizing the sample size. Our findings open the field for thermoelectric applications based on antimonene.
65 citations
TL;DR: In this paper, structural stability and mechanical and thermodynamic properties of the orthorhombic and trigonal MgSiN2 polymorphs were investigated through density functional theory and quasi-harmonic Debye model (QHDM).
Abstract: Structural stability and mechanical and thermodynamic properties of the orthorhombic and trigonal MgSiN2 polymorphs (or-MgSiN2 and tr-MgSiN2) were investigated through density functional theory and quasi-harmonic Debye model (QHDM). Our calculations show that or-MgSiN2 is energetically the stable polymorph at low pressure, in agreement with previous experimental and theoretical study. Under pressure, a crystallographic transition from the orthorhombic structure to the trigonal one occurs around 25, 17.45 and 19.05 GPa as obtained from the generalized gradient approximation of Perdew-Wang (GGA-PW91), the generalized gradient approximation parameterized recently by Perdew et al (GGA-PBEsol) and the local density approximation developed by Ceperley and Alder and parameterized by Perdew and Zunger (LDA-CAPZ), respectively. Single-crystalline and polycrystalline elastic constants and related properties, namely Vickers hardness, acoustic Gruneisen parameter, minimum thermal conductivity, isotropic sound velocit...
TL;DR: In this paper, the lattice parameters, cell volume, elastic constants, bulk modulus, shear modulus and Young's modulus are calculated at zero pressure, and their values are in excellent agreement with the available data, for TiN, Ti2N and Ti3N2 by using the elastic stability criteria, it is shown that the three structures are all stable.
TL;DR: In this article, the first-principles Debye-callaway approach has been used to predict the performance of low lattice thermal conductivity thermoelectric compounds, in which the Debye temperature Θ, the phonon velocity v and the Gruneisen parameter γ can be directly determined from the calculations of the vibrational properties of compounds within the quasiharmonic approximation.
TL;DR: In this article, the authors applied density functional theory (DFT) based first-principles methods to investigate the mechanical and bonding properties of the newly synthesized T2 phase superconductor Ta5GeB2 for the first time.
Abstract: In the present paper, density functional theory (DFT) based first-principles methods are applied to investigate the mechanical and bonding properties of the newly synthesized T2 phase superconductor Ta5GeB2 for the first time. The calculated lattice constants are in reasonable agreement with the experiment. The elastic constants (Cij), bulk modulus (B), shear modulus (G), Young's modulus (Y), Poisson's ratio (v), Pugh ratio (G/B), and elastic anisotropy factor A of Ta5GeB2 are calculated and used to explore the mechanical behavior of the compound. To give an explanation of the bonding nature of this new ternary tetragonal system, the band structure, density of states, and Mulliken atomic population are investigated. The estimated Debye temperature and Vickers hardness are also used to justify both the mechanical and bonding properties of Ta5GeB2.
TL;DR: In this article, a quaternary tellurite glasses within the composition 75TeO2-10Nb2O5-10ZnO-5PbO (TNZP) doped with the following Er3+ concentrations: 2500, 3750, 5000, 6250, 7500 and 8750 pm have been prepared by using conventional melt quenching method.
TL;DR: In this article, the structural, electronic and magnetic properties of CoMnCrZ (Z = Al, Si, Ge, As) quaternary Heusler compounds were investigated using full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation (GGA).
Abstract: First-principles approach is used to study the structural, electronic and magnetic
properties of CoMnCrZ (Z = Al,
Si, Ge and As) quaternary Heusler compounds, using full-potential linearized augmented
plane wave (FP-LAPW) scheme within the generalized gradient approximation (GGA). The
computed equilibrium lattice parameters agree well with the available theoretical data.
The obtained negative formation energy shows that CoMnCrZ (Z = Al, Si, Ge, As) compounds have strong
structural stability. The elastic constants C
ij
are calculated
using the total energy variation with strain technique. The polycrystalline elastic moduli
(namely: the shear modulus, Young’s modulus, Poisson’s ratio, sound velocities, Debye
temperature and melting temperature were derived from the obtained single-crystal elastic
constants. The ductility mechanism for the studied compounds is discussed via the elastic
constants C
ij
. Our calculations
with the GGA approximation predict that CoMnCrGe, CoMnCrAl, CoMnCrSi and CoMnCrAs are
half-metallic ferrimagnets (HMFs) with a half-metallic gap E
HM
of 0.03 eV, 0.19 eV,
0.34 eV and 0.50 eV for, respectively. We also find that the half-metallicity is
maintained on a wide range of lattice constants.
TL;DR: In this paper, the elastic properties of layered thermoelectrics BiOCuSe and LaOcuSe were determined using first-principles density functional theory calculations.
Abstract: We determine the elastic properties of the layered thermoelectrics BiOCuSe and LaOCuSe using first-principles density functional theory calculations. To predict their stability, we calculate six distinct elastic constants, where all of them are positive, and suggest mechanically stable tetragonal crystals. As elastic properties relate to the nature and the strength of the chemical bond, the latter is analyzed by means of real-space descriptors, such as the electron localization function (ELF) and Bader charge. From elastic constants, a set of related properties, namely, bulk modulus, shear modulus, Young's modulus, sound velocity, Debye temperature, Gruneisen parameter, and thermal conductivity, are evaluated. Both materials are found to be ductile in nature and not brittle. We find BiOCuSe to have a smaller sound velocity and, hence, within the accuracy of the used Slack's model, a smaller thermal conductivity than LaOCuSe. Our calculations also reveal that the elastic properties and the related lattice thermal transport of both materials exhibit a much larger anisotropy than their electronic band properties that are known to be moderately anisotropic because of a moderate effective-electron-mass anisotropy. Finally, we determine the lattice dynamical properties, such as phonon dispersion, atomic displacement, and mode Gruneisen parameters, in order to correlate the elastic response, chemical bonding, and lattice dynamics.
TL;DR: In this paper, the relativistic coupled-cluster (RCC) method has been employed to describe the electron-electron interaction potential in the above atomic systems, and the results obtained from the Debye and IS models are also carried out considering similar plasma conditions.
Abstract: We analyze atomic structures of plasma-embedded aluminum (Al) atom and its ions in the weak- and strong-coupling regimes. The plasma screening effects in these atomic systems are accounted for using the Debye and ion-sphere (IS) potentials for the weakly and strongly coupled plasmas, respectively. Within the Debye model, special attention is given to investigate the spherical and nonspherical plasma screening effects considering in the electron-electron interaction potential. The relativistic coupled-cluster (RCC) method has been employed to describe the relativistic and electronic correlation effects in the above atomic systems. The variations in the ionization potentials (IPs) and excitation energies (EEs) of the plasma-embedded Al ions are presented. It is found that the atomic systems exhibit more stability when the exact screening effects are taken into account. It is also shown that in the presence of a strongly coupled plasma environment, the highly ionized Al ions show blueshifts and redshifts in the spectral lines of the transitions between the states with the same and different principal quantum numbers, respectively. Comparison among the results obtained from the Debye and IS models are also carried out considering similar plasma conditions.
TL;DR: In this paper, the temperature dependence of the thermal conductivity of 27 different single crystal oxides is reported from ≈20 K to 350 K. The authors provided a database for the selection of appropriate substrates for thin-film growth according to their desired thermal properties, for applications in which heat management is important.
Abstract: The temperature dependence of the thermal conductivity of 27 different single crystal oxides is reported from ≈20 K to 350 K These crystals have been selected among the most common substrates for growing epitaxial thin-film oxides, spanning over a range of lattice parameters from ≈37 A to ≈125 A Different contributions to the phonon relaxation time are discussed on the basis of the Debye model This work provides a database for the selection of appropriate substrates for thin-film growth according to their desired thermal properties, for applications in which heat management is important
TL;DR: In this article, a systematic density functional theory study is performed to investigate the mechanical stability, elastic moduli, Debye temperature, thermal conductivity and electronic structures of Gd 2- y Th y Zr 2 O 7 and Gd2 Zr2-y Th y O 7 compositions.
TL;DR: In this article, the electronic structure, mechanical and thermal properties of La2B2O7(B Zr, Sn, Hf and Ge) pyrochlore were investigated.
TL;DR: In this article, the structural, electronic, elastic, thermal and optical properties of VRuSb, NbRuSb and TaSb semi-Heusler compounds were investigated using density functional theory.
Abstract: Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke–Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants (Cij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.
Journal Article•
TL;DR: In this article, the authors applied density functional theory (DFT) based first-principles methods to investigate the mechanical and bonding properties of the newly synthesized T 2 phase superconductor Ta 5 GeB 2 for the first time.
Abstract: In the present paper, density functional theory (DFT) based first-principles methods are applied to investigate the mechanical and bonding properties of the newly synthesized T 2 phase superconductor Ta 5 GeB 2 for the first time. The calculated lattice constants are in reasonable agreement with the experiment. The elastic constants ( C ij ), bulk modulus ( B ), shear modulus ( G ), Young's modulus ( Y ), Poisson's ratio ( v ), Pugh ratio ( G / B ), and elastic anisotropy factor A of Ta 5 GeB 2 are calculated and used to explore the mechanical behavior of the compound. To give an explanation of the bonding nature of this new ternary tetragonal system, the band structure, density of states, and Mulliken atomic population are investigated. The estimated Debye temperature and Vickers hardness are also used to justify both the mechanical and bonding properties of Ta 5 GeB 2 .
TL;DR: The thermodynamic stability and mechanical properties of Mo 2 B and W 2 B 5 binary compounds are investigated by first principles calculations and compared with other theoretical and experimental results in this paper, where the formation enthalpy, phonon spectrum, electronic structure and mechanical modulus at different pressure are obtained and variety of chemical bonding behavior has close relationship with the change of elastic properties.
TL;DR: In this paper, the structural, elastic, electronic and thermodynamic properties of the rhombohedral topological insulator Bi2Se3 are investigated by the generalized gradient approximation with the Wu-Cohen (WC) exchange-correlation functional.
Abstract: The structural, elastic, electronic and thermodynamic properties of the rhombohedral topological insulator Bi2Se3 are investigated by the generalized gradient approximation (GGA) with the Wu–Cohen (WC) exchange-correlation functional. The calculated lattice constants agree well with the available experimental and other theoretical data. Our GGA calculations indicate that Bi2Se3 is a 3D topological insulator with a band gap of 0.287 eV, which are well consistent with the experimental value of 0.3 eV. The pressure dependence of the elastic constants Cij, bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio σ of Bi2Se3 are also obtained successfully. The bulk modulus obtained from elastic constants is 53.5 GPa, which agrees well with the experimental value of 53 GPa. We also investigate the shear sound velocity VS, longitudinal sound velocity VL, and Debye temperature ΘE from our elastic constants, as well as the thermodynamic properties from quasi-harmonic Debye model. We obtain t...
SIDI1
TL;DR: In this paper, structural, elastic and thermodynamic properties of Li2O and Rb2O have been made using FP-APW+lo method as implemented in the WIEN2k code.
TL;DR: In this article, Ho 3+ substituted cobalt-zinc ferrite with a chemical formula Co 0.7 Zn 0.3 Ho x Fe 2−x O 4 (0≤x≤0.1) were synthesized by sol-gel method.
TL;DR: In this article, the structural, thermodynamic, elastic, anisotropic and electronic properties of P2221-Si have been studied using first-principles calculations, and the elastic constants are satisfied with mechanical stability criteria.
TL;DR: In this paper, the structural, electronic, optical and thermodynamic properties of Mo2Ga2C were investigated using density functional theory (DFT) within the generalized gradient approximation (GGA).
Abstract: The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states (DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters (e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) have been calculated for the first time. The study of dielectric constant (e1) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values (DOS, Debye temperature, atomic mass etc.) suggests that the compound is less likely to be superconductor.
TL;DR: In this article, the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers' hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2 were investigated.
Abstract: First-principles computation on the basis of density functional theory (DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers' hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson's and Pugh's ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli (B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo2TiAlC2 is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo–C–Mo covalent bonding associated with a relatively weak Ti–C bond. The calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive one. The hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.