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Showing papers on "Debye model published in 2021"


Journal ArticleDOI
TL;DR: In this article, the structural, electronic, elastic, magnetic, and thermodynamic properties of two new Heusler alloys are studied based on the first principal calculation using the scheme of the generalized gradient approximation (GGA) of density function theory.
Abstract: The structural, electronic, elastic, magnetic, and thermodynamic properties of two new Heusler alloys Rh2MnZ (Z = Zr, Hf) are studied based on the first principal calculation using the scheme of the generalized gradient approximation (GGA) of density function theory. The investigation was carried out in ferromagnetic (FM), anti-ferromagnetic (AFM), and the non-magnetic (NM) phases of the Cu2MnAl-type structure (regular structure) and Hg2CuTi-type-structure (inverse structure). Both alloys were found to be more stable in the ferromagnetic phase of the Cu2MnAl-type structure. The equilibrium lattice parameter in this structure is equal to 6.39 Ǻ for Rh2MnZr and 6.35 Ǻ for Rh2MnHf. The electronic properties reveled the metallic nature of the Heusler Rh2MnZ (Z = Zr, Hf) alloys. The interpretation of the elastic properties confirmed the elastic stability of the two alloys in the studied structure with a good agreement between the resulting bulk modulus from the structural properties and that of resulting from the elastic properties. Other elastic parameters such as modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio (ν) and Pugh’s ratio B/G, and the Zener anisotropy parameter A showed that the Rh2MnZ (Z = Zr, Hf) alloys are slightly deformed. They show high rigidity, anisotropic, and little deformation and behave in ductile way. The magnetic properties confirmed the ferromagnetic state of both compounds with computed total magnetic moment equal to 4.76 μB for Rh2MnZr and 4.60 μB for Rh2MnHf. The thermodynamic parameters were evaluated with various temperatures between 0 and 1200 K and a pressure from 0 to 50 GPa using the quasi-harmonic Debye model.

118 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed first-principles study of physical parameters associated with the structural, electronic, optical and elastic properties of the ternary gallium-arsenides Sr3GaAs3 and Ba3GAs3 is presented.

94 citations


Journal ArticleDOI
TL;DR: In this paper, the authors have studied the pressure dependent structural, thermo-physical, electronic band structure, and superconducting state properties of NaSn2P2 in details for the first time via ab initio technique.
Abstract: NaSn2P2 is a recently discovered superconducting system belonging to a particular class of materials with van der Waals (vdW) structure. There is enormous interest in vdW compounds because of their intriguing electrical, optical, chemical, thermal, and superconducting state properties. We have studied the pressure dependent structural, thermo-physical, electronic band structure, and superconducting state properties of this quasi-two dimensional system in details for the first time via ab initio technique. The optical properties are also investigated for different electric field polarizations for the first time. Structural, electronic, and optical properties were explored via density functional theory (DFT) calculations. Thermal properties were investigated using the quasi-harmonic Debye model. NaSn2P2 is found to be mechanically stable in the pressure range 0–3.0 GPa. The elastic anisotropy indices point towards high level of mechanical and bonding anisotropy in NaSn2P2 consistent with its highly layered structure. The elastic constants, moduli, and Debye temperature (θD) show non-monotonic variation with pressure, particularly close to 1.0 GPa. The pressure dependent superconducting transition temperature, Tc, of NaSn2P2 is predicted to vary strongly with the pressure dependent variation of θD. The electronic energy dispersion curves, E(k), reveal high level of direction dependence; the effective masses of charge carries are particularly high for the out-of-plane (c-axis) charge transport. The optical parameters compliment the underlying electronic energy density of states features and are weakly dependent on the polarization of the incident electric field. The reflectivity of NaSn2P2 is very high in the visible region and remains quite high and non-selective over an extended energy range in the ultraviolet region. The absorption coefficient is also high in the mid-ultraviolet band. All these optical features render NaSn2P2 suitable for optoelectronic device applications.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the strain induced electronic properties, phonon dynamics and thermoelectric performance of ZrRhSb compound via density functional theory calculations. And they used the Boltzmann constant to predict the p-type semiconducting and indirect energy gap of 1.15 eV between the X and Γ symmetry points.

41 citations


Journal ArticleDOI
29 Jun 2021
TL;DR: A series of full-Heusler properties of rare earth Ag2YB (Y = Nd, Sm, Gd) are studied by linearized augmented plane waves with total potential (FP-LAPW) method as discussed by the authors.
Abstract: A series of full-Heusler based on rare earth Ag2YB (Y = Nd, Sm, Gd) are studied by linearized augmented plane waves with total potential (FP-LAPW) method. We have investigated the structural and elastic properties with generalized gradient approximation (GGA) using Perdew–Burke–Ernzehrof parameterization for electron exchange and correlation. We have found that our three compounds are stable in AlCu2Mn-type structure (FM) states that are ductile and anisotropic at equilibrium state. The lattice parameters, elastic constants, and their associated parameters are compared with other available experimental and theoretical results. The electronic and magnetic properties are studied with GGA and GGA + U approximations. Based on the quasi-harmonic Debye model, we have studied the variation of heat capacity and coefficient of thermal expansion as a function of temperature.

38 citations


Journal ArticleDOI
TL;DR: In this paper, first-principles calculations have been carried out to explore the mechanical properties, Vickers hardness, elastic anisotropy, thermal properties, and optical properties of predicted thermodynamically stable MAX compounds.

36 citations


Journal ArticleDOI
TL;DR: In this article, the structural, elastic, electronic and optical properties of a new layered perovskite-type oxyfluoride: CsSrNb2O6F were investigated.

31 citations


Journal ArticleDOI
TL;DR: In this paper, the structural, mechanical, thermal, and optical properties of Cr2CoZ (Z = Al, In) inverse-Heuslers for the first time using density functional theory were investigated.

30 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed investigation has been carried out on nanocrystalline particles of Mg-Mn co-substituted CdFe2O4 to estimate intrinsic strain through Williamson-Hall (W-H) analysis.
Abstract: Properties of materials greatly differ in nanoparticle form compared to their bulk counterpart. Strain mechanism, elastic properties and cation distribution play a major role as particle size decreased to nanoscale level and therefore it is necessary to evaluate these properties precisely through reliable methodology. In the present work, a detailed investigation has been carried out on nanocrystalline particles of Mg–Mn co-substituted CdFe2O4 to estimate intrinsic strain through Williamson-Hall (W–H) analysis. The results were compared with those obtained from Scherrer equation and Rietveld refinement. Bertuat method was used to estimate the cation distribution of spinel ferrite. Elastic properties such as, stiffness constant, Young's modulus, bulk modulus, rigidity modulus, Poisson's ratio and Debye temperature were studied by using the band positions of tetrahedral – A and octahedral – B sites observed through infrared spectra. The obtained results were discussed in the light of strain mechanism, elastic constants and substitution of Mg–Mn ions in the CdFe2O4.

29 citations


Journal ArticleDOI
TL;DR: In this article, the effects of pressure on the structural, elastic, magnetic, and thermodynamic properties of Mn2AlC and Mn2SiC MAX phases using density functional theory were investigated.

29 citations


Journal ArticleDOI
TL;DR: In this article, a brief overview of the physical properties of Nb2SC1-xBx (x = 0.0-1.0) MAX phase solid solutions via the calculations of elastic, electronic, thermal and optical properties using density functional theory (DFT).
Abstract: Inherent and modified characteristics of MAX phase materials are important for technological applications in different fields. From this point of view, the present article gives a brief overview of the physical properties of Nb2SC1-xBx (x = 0.0–1.0) MAX phase solid solutions via the calculations of elastic, electronic, thermal and optical properties using density functional theory (DFT). The substitutional effect of B at the C site on the physical properties of Nb2SC is also discussed. The increase of B-content (x) enhances the elastic constants (except C12 and C13) and moduli (except B), Debye temperature, melting point, and minimum and lattice thermal conductivity of Nb2SC1-xBx. Conversely, the machinability and dry lubricity decrease gradually with the increase of x. The ductility decreases with the increase of x, and when x > 0.2, Nb2SC1-xBx becomes completely brittle and the brittleness increase with further increase of x. All the compositions of Nb2SC1-xBx have potential to be used as thermal barrier coating (TBC) and high temperature structural materials. Moreover, the investigated optical parameters are discussed on the basis of electronic structures. Average reflectivity in the visible light region is more than 45%, which make Nb2SC1-xBx systems capable of reducing the solar heating. It is expected that this study will stimulate the MAX phase research community to further explore the characteristics of these materials via experiment and theory.

Journal ArticleDOI
TL;DR: A DFT study of the synthesized MAX phase Zr2SeC has been carried out for the first time to explore its physical properties for possible applications in many sectors.
Abstract: A DFT study of the synthesized MAX phase Zr2SeC has been carried out for the first time to explore its physical properties for possible applications in many sectors. The studied properties are compared with prior known MAX phase Zr2SC. The structural parameters (lattice constants, volume, and atomic positions) are observed to be consistent with earlier results. The band structure and density of states (DOS) are used to explore the metallic conductivity, anisotropic electrical conductivity, and the dominant role of Zr-d states to the electrical conductivity at the Fermi level. Analysis of the peaks in the DOS and charge density mapping (CDM) of Zr2SeC and Zr2SC revealed the possible variation of the mechanical properties and hardness among them. The mechanical stability has been checked using elastic constants. The values of the elastic constants, elastic moduli and hardness parameters of Zr2SeC are found to be lowered than those of Zr2SC. The anisotropic behavior of the mechanical properties has been studied and analyzed. Technologically important thermodynamic properties such as the thermal expansion coefficient (TEC), Debye temperature (ΘD), entropy (S), heat capacity at constant volume (Cv), Gruneisen parameter (γ) along with volume (V) and Gibbs free energy (G) are investigated as a function of both temperature (from 0 to 1600 K) and pressure (from 0 to 50 GPa). Besides, the ΘD, minimum thermal conductivity (Kmin), melting point (Tm), and γ have also been calculated at room temperature and found to be lowered for Zr2SeC compared to Zr2SC owing to their close relationship with the mechanical parameters. The value of the ΘD, Kmin, Tm, and TEC suggest Zr2SeC as a thermal barrier coating material. The optical properties such as dielectric constant (real and imaginary part), refractive index, extinction coefficient, absorption coefficient, photoconductivity, reflectivity, and loss function of Zr2SeC are computed and analyzed to reveal its possible applications.

Journal ArticleDOI
TL;DR: In this article, first-principles calculations were employed to investigate the elastic, thermal properties, and the anisotropies in elastic modulus, Debye temperature and thermal conductivity of the ternary nitrides β-M4AlN3 (M = V, Nb, Ta).

Journal ArticleDOI
TL;DR: In this article, the structural properties, elastic anisotropies, and thermal properties of hexagonal TMSi2 (TM = Cr, Mo, W) silicides are explored.
Abstract: In this study, the first-principles (DFT) is used to explore the structural properties, elastic anisotropies, and thermal properties of hexagonal TMSi2 (TM = Cr, Mo, W) silicides. The elastic properties of single-crystal and poly-crystal are acquired by using Voigt-Reuss-Hill approximations method. The hardness of TMSi2 silicides were calculated from the bulk B and shear moduli G; In addition, the results show that hexagonal TMSi2 silicide is not potentially super-hard materials. Meanwhile, in terms of their Poisson’s ratio, GH/BH and Cauchy pressures, TMSi2 silicides are brittle material. Elastic anisotropies of TMSi2 silicides are measured by using anisotropy index of elastic properties, 3D surface constructions of elastic moduli and their two-dimensional planar projections were used to indicate the elastic anisotropies of these TMSi2 silicides. The sequence of elastic anisotropy follows as WSi2 > MoSi2 > CrSi2. Finally, the sound velocities, Debye temperatures, thermal conductivity and their anisotropies of these silicides were discussed, the sound velocities and Debye temperature of these TMSi2 silicides are anisotropic in the [100] and [001] directions.

Journal ArticleDOI
TL;DR: In this article, the vanadium substitutions effect on physical properties of Zr2AlC MAX phase compounds have been studied using the first-principle method and the equilibrium ground states of properties were calculated and compared with available experimental and theoretical data.

Journal ArticleDOI
TL;DR: In this article, an approach to reduce the thermal conductivity of thermoelectric composite materials using acoustic impedance mismatch and the Debye model is presented. But the performance of the proposed approach is limited due to the high computational complexity of the model.
Abstract: We present a novel approach to reduce the thermal conductivity ( k ) in thermoelectric composite materials using acoustic impedance mismatch and the Debye model. Also, the correlation between interface thermal resistance ( R i n t ) and the particle size of the dispersed phase on the k of the composite is discussed. In particular, the k of an oxide composite, which consists of a natural superlattice Aurivillius phase (SrBi4Ti4O15) as a matrix and perovskite (La0.7Sr0.3MnO3) as a dispersed phase, is investigated. A significant reduction in k of composite, even lower than the k of the matrix when the particle size of La0.7Sr0.3MnO3 is smaller than the Kapitza radius ( a K ) is observed, depicting that R i n t dominates for particle size lower than a K due to increased surface to volume ratio. The obtained results have the potential to provide new directions for engineering composite thermoelectric systems with desired thermal conductivity and promising in the field of energy harvesting.

Journal ArticleDOI
TL;DR: The Fermi level gradually increases, moving towards and past the upper bound of the pseudogap, when the value of x goes from zero to unity, indicating that the structural stability reduces gradually when the amount of Si increases within the Ti3(Al1−xSix)C2 system.
Abstract: Recently, a series of high-purity Ti3(Al1−xSix)C2 solid solutions with new compositions (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been reported with interesting mechanical properties. Here, we have employed density functional theory for Ti3(Al1−xSix)C2 solid solutions to calculate a wider range of physical properties including structural, electronic, mechanical, thermal and optical. With the increase of x, a decrease of cell parameters is observed. All elastic constants and moduli increase with x. The Fermi level gradually increases, moving towards and past the upper bound of the pseudogap, when the value of x goes from zero to unity, indicating that the structural stability reduces gradually when the amount of Si increases within the Ti3(Al1−xSix)C2 system. In view of Cauchy pressure, Pugh’s ratio and Poisson’s ratio all compositions of Ti3(Al1−xSix)C2 are brittle in nature. Comparatively, low Debye temperature, lattice thermal conductivity and minimum thermal conductivity of Ti3AlC2 favor it to be a thermal barrier coating material. High melting temperatures implies that the solid solutions Ti3(Al1−xSix)C2 may have potential applications in harsh environments. In the visible region (1.8–3.1 eV), the minimum reflectivity of all compositions for both polarizations is above 45%, which makes them potential coating materials for solar heating reduction.

Journal ArticleDOI
TL;DR: In this paper, the electronic structure, elastic, optical and thermodynamic properties of cubic perovskite NaBaF3 under high pressure were investigated using the ab initio calculations, and the calculated lattice constant (a0) and bulk modulus (B0) at 0 GPa were determined to be 4.278 A and 53.555 GPa, respectively.
Abstract: The electronic structure, elastic, optical and thermodynamic properties of cubic perovskite NaBaF3 under high pressure were investigated using the ab initio calculations. The calculated lattice constant (a0) and bulk modulus (B0) at 0 GPa were determined to be 4.278 A and 53.555 GPa, respectively, which are consistent with previous reports. The elastic constants and bulk modulus at high pressure were calculated. According to Pugh’s crystal mechanical stability conditions, the phase transition point of NaBaF3 is found to be 68.8 GPa, which has not been reported by any previous paper. The band structure calculations reveal that cubic perovskite NaBaF3 is a direct band-gap material in the pressure range from 0 GPa to 60 GPa. The dielectric function ɛ(ω), absorption coefficient α(ω), reflectivity R(ω), transmittance T(ω), absorbance A(ω) and complex refractive index N(ω) at 0 GPa, 20 GPa, 40 GPa and 60 GPa were studied. It is found that the band gap increases with the increasing pressure, and the absorption spectra show blue shift. The Debye temperature at 300 K and the values of the relative volume, heat capacity, bulk modulus, thermal expansion coefficient, heat capacities, and relative Debye temperature with pressures and temperatures effect were investigated. Our results will provide theoretical guidance for the experimental investigations and industrial applications of NaBaF3 in future.

Journal ArticleDOI
TL;DR: In this article, the electronic structure, structural stability, mechanical, phonon, and optical properties of Zr2GaC and Hf 2GaC MAX phases have been investigated under high pressure using first-principles calculations.
Abstract: The electronic structure, structural stability, mechanical, phonon, and optical properties of Zr2GaC and Hf2GaC MAX phases have been investigated under high pressure using first-principles calculations. Formation enthalpy of competing phases, elastic constants, and phonon calculations revealed that both compounds are thermodynamically, mechanically, and dynamically stable under pressure. The compressibility of Zr2GaC is higher than that of Hf2GaC along the c-axis, and pressure enhanced the resistance to deformation. The electronic structure calculations reveal that M2GaC is metallic in nature, and the metallicity of Zr2GaC increased more than that of Hf2GaC at higher pressure. The mechanical properties, including elastic constants, elastic moduli, Vickers hardness, Poisson’s ratio anisotropy index, and Debye temperature, are reported with fundamental insights. The elastic constants C11 and C33 increase rapidly compared with other elastic constants with an increase in pressure, and the elastic anisotropy of Hf2GaC is higher than that of the Zr2GaC. The optical properties revealed that Zr2GaC and Hf2GaC MAX phases are suitable for optoelectronic devices in the visible and UV regions and can also be used as a coating material for reducing solar heating at higher pressure up to 50 GPa.

Journal ArticleDOI
23 Feb 2021
TL;DR: In this article, the electron-phonon interaction in type II Dirac semimetallic 1T-PdTe2 was determined by means of helium atom scattering, and the superconducting critical temperature was derived.
Abstract: We have determined the electron–phonon interaction in type II Dirac semimetallic 1T-PdTe2 by means of helium atom scattering. While 1T-PdTe2 is isostructural with 1T-PtTe2, only the former is superconductor. The difference can be traced to the substantially larger value of the electron–phonon coupling in 1T-PdTe2, λ = 0.58, obtained from the Debye-Waller attenuation of the He specular peak. With this value and the surface Debye temperature, ΘD = 106.2 K, we have figured out the superconducting critical temperature, Tc = 1.83 K given by the BCS theory, which is in good agreement with Tc = (1.95 ± 0.03) K obtained with low-temperature scanning tunneling microscopy. The value of the effective mass related to ΘD indicates that the large electron–phonon coupling in 1T-PdTe2 is due to coupling, not only with the zone-center optical mode O2 at 9.2 meV, as proposed in a recent theoretical study, but also with the zone-boundary acoustic mode LA. Our results suggest that the topological states of a Dirac cone play a negligible role on the onset of superconductivity.

Journal ArticleDOI
TL;DR: In this article, a detailed study of the recently predicted thermodynamically stable Zr3CdB4 MAX phase boride was performed and the electronic structure, mechanical and dynamical stability, elastic anisotropy, along with thermodynamic and optical properties were investigated for the first time.

Journal ArticleDOI
29 Oct 2021-Vacuum
TL;DR: In this paper, the tensile properties of Zr2AlX (X = C, N) were calculated by first-principles calculations based on density functional theory.

Journal ArticleDOI
TL;DR: In this article, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poisson's ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory.
Abstract: In the present study, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poisson's ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory. The estimated structural lattice parameters were consistent with the prior report. The mechanical and dynamical stability of these compounds have been established theoretically. The materials are brittle in nature and elastically anisotropic. The value of fracture toughness, KIC for the B6S and B6Se, are ∼ 2.07 MPam0.5, evaluating the resistance to limit the crack propagation inside the materials. Both B6S and B6Se compounds possess high hardness values in the range of 31–35 GPa and have the potential to be prominent members of the class of hard compounds. Strong covalent bonding and sharp peak at low energy below the Fermi level confirmed by partial density of states (PDOS) resulted in the high hardness. The profile of band structure as well as density of states assesses the indirect semiconducting nature of the titled compounds. The comparatively high value of Debye temperature (ΘD), minimum thermal conductivity (Kmin), lattice thermal conductivity (kph), low thermal expansion coefficient, and low density suggest that both boron-rich chalcogenides might be used as thermal management materials. Large absorption capacities in the mid-ultraviolet region (3.2–15 eV) of the studied materials and low reflectivity (∼16%) are significantly noted. Such favorable features give promise to the compounds under investigation to be used in UV surface-disinfection devices as well as medical sterilizer equipment applications. Excellent correlations are found among all the studied physical properties of these compounds.

Journal ArticleDOI
TL;DR: In this article, structural, magnetic, mechanical, and thermal properties of equiatomic quaternary Heusler alloys (EQHA) were examined by employing full potential linearized augmented plane wave (FP-LAPW) scheme.

Journal ArticleDOI
TL;DR: In this paper, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poissons ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory.
Abstract: In the present study, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poissons ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory The estimated structural lattice parameters were consistent with the prior report The mechanical and dynamical stability of these compounds have been established theoretically The materials are brittle in nature and elastically anisotropic The value of fracture toughness, KIC for the B6S and B6Se are ~ 207 MPam05, evaluating the resistance to limit the crack propagation inside the materials Both B6S and B6Se compounds possess high hardness values in the range 31-35 GPa, and have the potential to be prominent members of the class of hard compounds Strong covalent bonding and sharp peak at low energy below the Fermi level confirmed by partial density of states (PDOS) resulted in the high hardness The profile of band structure, as well as DOS, assesses the indirect semiconducting nature of the titled compounds The comparatively high value of Debye temperature ({\Theta}D), minimum thermal conductivity (Kmin), lattice thermal conductivity (kph), low thermal expansion coefficient, and low density suggest that both boron-rich chalcogenides might be used as thermal management materials Large absorption capacities in the mid ultraviolet region (32-15 eV) of the studied materials and low reflectivity (~16 %) are significantly noted Such favorable features give promise to the compounds under investigation to be used in UV surface-disinfection devices as well as medical sterilizer equipment applications Excellent correlations are found among all the studied physical properties of these compounds

Journal ArticleDOI
TL;DR: In this article, a series of Bi2Te2-xS1+x compounds were prepared by traditional melting-quenching-annealing process, and the results showed that the strong coupling of the phonon density of state contributed by Bi and Te(1) atoms results in the low avoided-crossing frequencies, sound velocities, Debye temperature and therefore the low lattice thermal conductivities.

Journal ArticleDOI
TL;DR: In this article, the in-plane thermal conductivity of monolayer and multilayer graphene was analyzed using experimental measurements, theoretical calculations and molecular dynamics simulations, and it was shown that the cross-plane phonon mean free path is several hundreds of nanometers instead of a few nanometers as predicted using classical kinetic theory.
Abstract: Graphene, due to its atomic layer structure, has the highest room temperature thermal conductivity k for all known materials. Thus, it is expected that graphene based materials are the best candidates for thermal management in next generation electronic devices. In this perspective, we first review the in-plane k of monolayer graphene and multilayer graphene obtained using experimental measurements, theoretical calculations and molecular dynamics (MD) simulations. Considering the importance of four-phonon scattering in graphene, we also compare the effects of three-phonon and four-phonon scattering on phonon transport in graphene. Then, we review phonon transport along the cross-plane direction of multilayer graphene and highlight that the cross-plane phonon mean free path is several hundreds of nanometers instead of a few nanometers as predicted using classical kinetic theory. Recently, hydrodynamic phonon transport has been observed experimentally in graphitic materials. The criteria for distinguishing the hydrodynamic from ballistic and diffusive regimes are discussed, from which we conclude that graphene based materials with a high Debye temperature and high anharmonicity (due to ZA modes) are excellent candidates to observe the hydrodynamic phonon transport. In the fourth part, we review how to actively control phonon transport in graphene. Graphene and graphite are often adopted as additives in thermal management materials such as polymer nanocomposites and thermal interface materials due to their high k. However, the enhancement of the composite's k is not so high as expected because of the large thermal resistance between graphene sheets as well as between the graphene sheet and matrix. In the fifth part, we discuss the interfacial thermal resistance and analyze its effect on the thermal conductivity of graphene based materials. In the sixth part, we give a brief introduction to the applications of graphene based materials in thermal management. Finally, we conclude our review with some perspectives for future research.

Journal ArticleDOI
TL;DR: In this paper, the structural, electronic and thermal transport characteristics of bilayer tetragonal graphene (TG) are systematically explored with a combination of first-principles calculations and machine-learning interatomic potential approaches.
Abstract: In this article, the structural, electronic and thermal transport characteristics of bilayer tetragonal graphene (TG) are systematically explored with a combination of first-principles calculations and machine-learning interatomic potential approaches. Optimized ground state geometry of the bilayer TG structure is predicted and examined by employing various stability criteria. Electronic bandstructure analysis confirmed that bilayer TG exhibits a metallic band structure similar to the monolayer T-graphene structure. Thermal transport characteristics of the bilayer TG structure are explored by analysing thermal conductivity, the Seebeck coefficient, and electrical conductivity. The electronic part of the thermal conductivity shows linearly increasing behaviour with temperature, however the lattice part exhibits the opposite character. The lattice thermal conductivity part is investigated in terms of the three phonon scattering rates and weighted phase space. On the other hand, the Seebeck coefficient goes through a transition from negative to positive values with increasing temperature. The Wiedemann–Franz law regarding electrical transport of the bilayer TG is verified and confirms the universal Lorentz number. Specific heat of the bilayer TG structure follows the Debye model at low temperature and constant behaviour at high temperature. Moreover, the Debye temperature of the bilayer TG structure is verified by ab initio calculations as well as fitting the specific heat data using the Debye model.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the quantum effect on the thermal transport of amorphous silicon using equilibrium molecular dynamics, the structure factor method and the Allen-Feldman theory.
Abstract: While it is well known that the vibrational modes are fully occupied and the quantum effect can be ignored only if the temperature is high enough, e.g., well above the Debye temperature of the systems, all vibrational modes are assumed to be fully occupied at any temperatures in classical molecular dynamics. Therefore, the thermal conductivity of crystals predicted by classical molecular dynamics at low temperatures, e.g., much lower than the corresponding Debye temperature, is unphysical. Even by applying the quantum corrections on the classical thermal conductivity of crystals, the results are still unreasonable since both the occupation and intrinsic scattering process of the vibrations are determined by the temperatures. However, the scattering picture in amorphous silicon is quite different from that in its corresponding crystal counterpart. How the quantum effect will affect the thermal transport in amorphous silicon is still unclear. Here, by systematically investigating thermal transport of amorphous silicon using equilibrium molecular dynamics, the structure factor method and the Allen–Feldman theory, we directly observe that all the vibrational modes are fully occupied at any temperatures and the quantum effect on the scattering process can be ignored. By assuming all the vibrational modes are fully occupied, the thermal conductivity calculated using the structure factor method and the Allen–Feldman theory agrees quite well with the results computed using Green–Kubo equilibrium molecular dynamics. By correcting the excitation state of the vibrations in amorphous silicon, the thermal conductivity calculated by the structure factor method and the Allen–Feldman theory can fully capture the experimentally measured temperature dependence. Our study proves that the quantum effect on the scattering process caused by the distribution functions for the amorphous materials in molecular dynamics simulations, i.e., Boltzmann distributions in molecular dynamics simulations vs Bose–Einstein distributions for the bosons, can be ignored, while the quantum effect on the excitation states of the vibrations are important and must be considered.

Journal ArticleDOI
TL;DR: In this paper, the mass and linear attenuation coefficients (MAC, LAC) of gamma-ray photons at the energy range from 0.015 to 15.MeV have been investigated using the Phy-X/PSD software program as well as the XCOM database program.
Abstract: Nd3+ doped lithium-zinc-phosphate glasses were synthesized by melt-quenching technique. FTIR spectra were recorded in the wavenumber range of 400–4000 cm−1. Elastic parameters such as Debye temperature and fractal bond connectivity were calculated. The results revealed that these parameters were influenced by the glass system's composition and dopant concentration. The mass and linear attenuation coefficients (MAC, LAC) of gamma-ray photons at the energy range from 0.015 to 15 MeV have been investigated using the Phy-X/PSD software program as well as the XCOM database program. Both MAC and LAC increase with the increase in the amount of Nd2O3. Also, the mean free path values and the half-value layer decrease while the density increases with the increase of the Nd2O3 content. Moreover, the fast neutron removal cross section was also presented and the results were compared with the concrete and commercial shielding glasses.