Component Of Thermal Conductivity Research Articles

First principles calculations of physical properties of the CeCu2Si2 material

Using local density approximation functional computations, LSDA (local spin density approximation) and mBJ (modified Becke-Johnson) for exchange-correlation interactions, we examined the combination CeCu2Si2, concentrating on its many physical properties. This work used the WC-GGA method to compute the elastic characteristics of CeCu2Si2 material, and the results indicate that unstrained CeCu2Si2 is more brittle. The density of states exhibits the metallic character of the chemical, in agreement with the inference made from the band structure. We also assessed several optical characteristics, such as real and imaginary optical conductivity, electronic energy loss, absorption coefficient, refractive index, and extinction coefficient. We also looked at the electronic components of thermal conductivity, electrical conductivity, Seebeck coefficient, and electronic conductivity. The compound's Seebeck coefficient values are negative, indicating p-type behavior. A thorough analysis of the data is presented, along with important details regarding the CeCu2Si2 compound's characteristics.

Thermal properties of In2O3 and α-Ga2S3 compounds

We investigate the thermal conductivity of In₂O₃ and α-Ga₂S₃ lattices using simulations based on the Boltzmann phonon transport equation (BTE) and first-principles calculations. The study employs a real-space finite displacement method to determine the second- and third-order interatomic force constants (IFCs), which are critical for solving the BTE iteratively. Our findings indicate that In₂O₃ and α-Ga₂S₃ exhibit relatively low thermal conductivities compared to other wide-bandgap semiconductors. At room temperature (300 K), the calculated isotropic thermal conductivity of cubic In₂O₃ is 16.2 Wm−1K⁻1. For monoclinic α-Ga₂S₃, the three principal components of thermal conductivity are 17.0, 20.7, and 15.2 W m⁻1 K⁻1, depending on the crystallographic direction. This low thermal conductivity is primarily attributed to significant phonon scattering via three-phonon processes. Furthermore, we estimate the phonon mean free path (MFP) to be approximately 56 nm for In₂O₃ and between 198 and 231 nm for α-Ga₂S₃, varying with crystal orientation. These findings offer valuable insights into the thermal transport properties of In₂O₃ and α-Ga₂S₃, highlighting their potential for thermoelectric applications while delineating the constraints these properties impose on their use in electronic devices.

DIW-Printed Thermal Management PDMS Composites with 3D Structural Thermal Conductive Network of h-BN Platelets and Al2O3 Nanoparticles.

Electronic devices play an increasingly vital role in modern society, and heat accumulation is a major concern during device development, which causes strong market demand for thermal conductivity materials and components. In this paper, a novel thermal conductive material consisting of polydimethylsiloxane (PDMS) and a binary filler system of h-BN platelets and Al2O3 nanoparticles was successfully fabricated using direct ink writing (DIW) 3D printing technology. The addictive manufacturing process not only endows the DIW-printed composites with various geometries but also promotes the construction of a 3D structural thermal conductive network through the shearing force during the printing process. Moreover, the integrity of the thermal conductive network can be optimized by filling the gaps between the BN platelets with Al2O3 particles. Resultingly, the configuration of the binary fillers is arranged by the shearing force during the DIW process, fabricating the thermal conductive network of oriented fillers. The DIW-printed BN/Al2O3/PDMS with 45 wt% thermal conductive binary filler can reach a thermal conductivity of 0.98 W/(m·K), higher than the 0.62 W/(m·K) of the control sample. In this study, a novel strategy for the thermal conductive performance improvement of composites based on DIW technology is successfully verified, paving a new way for thermal management.

Effect of Starting Powder Particle Size on the Thermoelectric Properties of Hot-Pressed Bi0.3Sb1.7Te3 Alloys.

P-type Bi0.3Sb1.7Te3 polycrystalline pellets were fabricated using different methods: melting and mechanical alloying, followed by hot-press sintering. The effect of starting powder particle size on the thermoelectric properties was investigated in samples prepared using powders of different particle sizes (with micro- and/or nano-scale dimensions). A peak ZT (350 K) of ~1.13 was recorded for hot-pressed samples prepared from mechanical alloyed powder. Moreover, hot-pressed samples prepared from ≤45 μm powder exhibited similar ZT (~1.1). These high ZT values are attributed both to the presence of high-density grain boundaries, which reduced the lattice thermal conductivity, as well as the formation of antisite defects during milling and grinding, which resulted in lower carrier concentrations and higher Seebeck coefficient values. In addition, Bi0.3Sb1.7Te3 bulk nanocomposites were fabricated in an attempt to further reduce the lattice thermal conductivity. Surprisingly, however, the lattice thermal conductivity showed an unexpected increasing trend in nanocomposite samples. This surprising observation can be attributed to a possible overestimation of the lattice thermal conductivity component by using the conventional Wiedemann-Franz law to estimate the electronic thermal conductivity component, which is known to occur in nanocomposite materials with significant grain boundary electrical resistance.

Improving inherent thermal conductivity of epoxy resins based on contribution components of thermal conductivity: A molecular dynamics study

The inherent thermal transport properties of epoxy resin are vital factors to be studied in applications. In the present work, we constructed the amorphous crosslinking structure, the step crosslinking structure and the ordered crosslinking structure based on molecular dynamics theory, and used the reverse nonequilibrium molecular dynamics (RNEMD) method to calculate the thermal conductivity (TC) of different structures. Based on the numerical verification of the reliability of the method, the contribution of bonding to the TC was enhanced by increasing the molecular arrangement orderliness to reduce phonon scattering, taking the composition of the TC contribution as the guide. Meanwhile, the contribution of non-bonding interaction to the TC was enhanced by using compression process to achieve TC increase in the epoxy resin intrinsic structure, followed by exploring the effect of cross-linking degree on the TC of different structures. The results showed that the TC of amorphous epoxy resin decreased with the increase of crosslinking degree, and the relative high-frequency VDOS increased, but the influence of crosslinking degree on TC was minor in the range. For amorphous epoxy resin four-sided pressurization varied in the range of 0–7 Gpa, the non-bond energy percentage increased in the range of 0–60%, and the increase of non-bond energy made its contribution to TC increased significantly. The epoxy resin achieved 215% improvement in intrinsic TC by changing the molecular arrangement orderliness. The ordered structure TC varied from 0.3 to 3.5 W/(m⋅K) in the pressure variation range of 0–7 GPa. As the structure becomes more ordered, the TC increased significantly with the degree of cross-linking. The study provided the theoretical basis for the realization of resin preparation and resin thermal property evaluation with regulated intrinsic TC.

Role of dual doping in zinc oxide for optimizing thermoelectric performance

In this study, we have investigated the effect of dual doping on the thermoelectric performance of zinc oxide (ZnO). Pure ZnO is a wide band-gap semiconductor with a very low carrier concentration in its intrinsic form. Doping ZnO by trivalent impurity ions is considered a viable approach to improve its electrical conductivity by enhancing the concentration of charge carriers in the material. However, the above enhancement in the carrier concentration can also increase the electronic component of the system's thermal conductivity, thereby limiting its thermoelectric performance. It is expected that the dual doping of ZnO can decrease its thermal conductivity without adversely affecting its electrical conductivity. To test the above hypothesis, we doped ZnO with four different pairs of dopants (In/B, In/Al, In/Ga, and In/Bi) and compared the thermoelectric performance of the resulting materials over the temperature range of 350 K–773 K. For the above comparison, Seebeck coefficient, electrical conductivity, and thermal conductivity of the samples were measured, and corresponding power factors (PF) and figure of merits (ZT) were determined. Among all the samples investigated in the study, the In/Bi-doped ZnO exhibited the highest ZT value of 0.37 at 773 K.

A new ternary molybdenum phospho-silicide Mo3Si2P: Phase equilibria, structural, electronic, transport and thermal properties

Here we report the successful preparation and systematical characterization of a novel molybdenum compound Mo3Si2P. As the first genuine ternary molybdenum phospho-silicide, it augments the Mo–Si–P family and may be served as an innovative archetype to develop exotic electronic states. The phase-equilibrium relation of Mo–Si–P system was studied, which defines the phase-stability region of Mo3Si2P, and a phase diagram that makes reviews on the abundant material and electronic physics in the system was established. Mo3Si2P crystallizes in a non-centrosymmetric orthorhombic structure (space group: Ama2) that appears as alternately stacking flat (Mo1)3P3 sheets and buckled (Mo2)3Si3 double-layers along the a-axis direction. The Bloch-Grüneisen-Mott model is employed to describe the T-dependent multiband metallic-conduction which is principally governed by electrons at high temperatures. The thermal-conductivity components of charge carrier and lattice vibration were extracted from κtotal by following the extended Wiedemann-Franz law. Poor thermoelectric performance is evidenced by very low thermoelectric power factor and figure-of-merit that are ascribed to small Seebeck coefficient and high thermal conductivity. Sommerfeld coefficient (γ) and Wilson ratio (RW) demonstrate that the electron correlation is extremely weak. First-principles calculations predict significant contribution from Mo-4 dx2−y2 orbital electrons to the Fermi surface of Mo3Si2P which shows different band fillings from Mo3Ge2P where dz2 electrons take the maximal occupation. Electron-phonon coupling parameter λep was calculated as 0.74, which reveals a medium interaction strength.

Computing the Lattice Thermal Conductivity of Small‐Molecule Organic Semiconductors: A Systematic Comparison of Molecular Dynamics Based Methods

AbstractWhile the Green‐Kubo and non‐equilibrium molecular dynamics methods have been compared quite extensively to calculate the thermal conductivity in inorganic compounds, there is currently a lack of comparison of these algorithms with the more recently developed approach‐to‐equilibrium molecular dynamics (AEMD) method for other types of materials such as organic semiconductors. To fill this gap, this article reports a theoretical description of thermal transport in single crystals made of terthiophene as prototypical system based on the three most popular molecular dynamics approaches. A systematic comparison of the computed values of thermal conductivity and its anisotropy is carried out and the strengths and weaknesses associated with each method are discussed. Although the three algorithms give essentially the same trends, this study points to the “AEMD” approach as the most suitable compromise between accuracy and computing cost. On the material aspects, the theoretical modeling yields an anisotropic character of the thermal transport in crystals whose out‐of‐plane thermal conductivity component is approximately twice larger than the in‐plane components. The AEMD approach is further used to investigate the influence of temperature on thermal transport in terthiophene. The trends are utterly rationalized by relying on the concepts of phonon mean free paths and phonon group velocities.

Thermophysical properties of the regolith on the lunar far side revealed by the in situ temperature probing of the Chang'E-4 mission.

Temperature probes onboard the Chang'E-4 (CE-4) spacecraft provide the first in situ regolith temperature measurements from the far side of the Moon. We present these temperature measurements with a customized thermal model and reveal the particle size of the lunar regolith at the CE-4 landing site to be ∼15μm on average over depth, which indicates an immature regolith below the surface. In addition, the conductive component of thermal conductivity is measured as ∼1.53×10-3W m-1 K-1 on the surface and ∼8.48×10-3W m-1 K-1 at a depth of 1 m. The average bulk density is ∼471kg m-3 on the surface and ∼824kg m-3 in the upper 30cm of the lunar regolith. These thermophysical properties provide important additional 'ground truth' at the lunar far side, which is critical for the future analysis and interpretation of global temperature observations.

Ultrahigh Electron Thermal Conductivity in T‐Graphene, Biphenylene, and Net‐Graphene (Adv. Energy Mater. 28/2022)

Thermal Transport In article number 2200657, Zhen Tong, Traian Dumitrică, Thomas Frauenheim, and co-workers study thermal transport in T-graphene, biphenylene, and net- graphene with a framework that combines the Boltzmann transport equation with ab initio computed three-phonon, four-phonon, and electron-phonon interaction lifetimes. They reveal for the first time a dominant electronic thermal conductivity component in these 2D carbon allotropes, of great interest for heat dissipation in microelectronics.

Feasibility of high performance in p‐type Ge1−xBixTe materials for thermoelectric modules

AbstractGeTe is a promising candidate for the fabrication of high‐temperature segments for p‐type thermoelectric (TE) legs. The main restriction for the widespread use of this material in TE devices is high carrier concentration (up to ∼ 1021 cm−3), which causes the low Seebeck coefficient and high electronic component of thermal conductivity. In this work, the band structure diagram and phase equilibria data have been effectively used to attune the carrier concentration and to obtain the high TE performance. The Ge1−xBixTe (x = 0.04) material prepared by the Spark plasma sintering (SPS) technique demonstrates a high power factor accompanied by moderate thermal conductivity. As a result, a significantly higher dimensionless TE figure of merit ZT = 2.0 has been obtained at ∼ 800 K. Moreover, we are the first to propose that application of the developed Ge1−xBixTe (x = 0.04) material in the TE unicouple should be accompanied by SnTe and CoGe2 transition layers. Only such a unique solution for the TE unicouple makes it possible to prevent the negative effects of high contact resistance and chemical diffusion between the segments at high temperatures.

Thermoelectric properties plus phonon and de Haas\u2013van Alphen frequencies of hole/electron-doped hbox {CeIn}_3

We investigate temperature, pressure, and localization dependence of thermoelectric properties, phonon and de Haas–van Alphen (dHvA) frequencies of the anti-ferromagnetic (AFM) CeIn_3 using density functional theory (DFT) and local, hybrid, and band correlated functionals. It is found that the maximum values of thermopower, power factor, and electronic figure of merit of this compound occur at low (high) temperatures provided that the 4f-Ce electrons are (not) localized enough. The maximum values of the thermopower, power factor, electronic figure of merit (conductivity parameters), and their related doping levels (do not) considerably depend on the localization degree and pressure. The effects of pressure on these parameters substantially depend on the degree of localization. The phonon frequencies are calculated to be real which shows that the crystal is dynamically stable. From the phonon band structure, the thermal conductivity is predicted to be homogeneous. This prediction is found consistent with the thermal conductivity components calculated along three Cartesian directions. In analogous to the thermoelectric properties, it is found that the dHvA frequencies also depend on both pressure and localization degree. To ensure that the phase transition at Néel temperature cannot remarkably affect the results, we verify the density of states (DOS) of the compound at the paramagnetic phase constructing a non-collinear magnetic structure where the angles of the spins are determined so that the resultant magnetic moment vanishes. The non-collinear results reveal that the DOS and whence the thermoelectric properties of the compound are not changed considerably by the phase transition. To validate the accuracy of the results, the total and partial DOSs are recalculated using DFT plus dynamical mean-field theory (DFT+DMFT). The DFT+DMFT DOSs, in agreement with the hybrid DOSs, predict the Kondo effect in this compound.

Влияние фотонной обработки на повышение термоэлектрической добротности твердого раствора Bi2Te3 − Bi2Se3

In the present work, the phase compositions, morphology, structure, and thermal conductivity of Bi2Te3 – хSeх-based semiconductor wafers before and after the photon treatment (PT) were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and laser flash methods. The semiconductor plates 10 × 10 × 2 mm in size were prepared by electric discharge cutting from the briquettes, synthesized by hot pressing of Bi2Te3 – хSeх powder. Then, the plates were annealed at 570 K in an argon atmosphere for 24 h. The PT was carried out in an Ar atmosphere by irradiation of gas-discharge xenon lamps with pulses of 1.0 and 1.4 s and energy density ranging from 125 to 175 J/cm2. As revealed, the PT initiates the formation of a thin surface layer with an inhomogeneous nanocrystalline structure and an arbitrary nanocrystals orientation. The volume of material manifests a large-block textured crystalline structure with the original elemental and phase compositions formed during the extrusion. Thereby, a gradient nanostructured region composed of nano-sized and large Bi2Te3 – хSeх crystals with tunneling contacts is formed in the process of PT. We revealed that the PT changes the material bandgap slightly, decreases the concentration of charge carriers, increasing their mobility. The scattering of carriers and photons on linear defects dominates in a wide temperature range in the studied samples. Thereby, the figure of merit rise s by 8 % after PT, due to a decrease in the phonon component of thermal conductivity.

Janus Al2STe monolayer: A prospective thermoelectric material

Two dimensional materials based on chalcogenides are showing exciting thermoelectric efficiency. Recent experimental synthesisation of several Janus monolayers inspire investigation of novel materials. In this paper, we study the thermoelectric performance of the novel Janus Al2STe monolayer using Density Functional theory. We found that Janus Al2STe monolayer is an indirect band gap semiconductor with an energy gap of 1.17 eV and is dynamically stable. The transport coefficients such as Seebeck coefficient, electrical conductivity, power factor, and electronic thermal conductivity are evaluated using BoltzTraP2 code based on Boltzmann transport theory within constant relaxation time approximation. The dependence of relaxation time on temperature has been approximated with the deformation potential theory. Further, the lattice component of thermal conductivity has been obtained using ShengBTE code. The calculated value of ZT shows that both n-type and p-type Janus monolayer have outstanding thermoelectric performance. From the evaluated results, we conclude that Janus Al2STe monolayer can be used as a propitious candidate in the fabrication of thermoelectric devices.

Effect of heat treatment on the galvanomagnetic properties of bulk nanostructured samples of Bi85Sb15 solid solution

Extruded bulk nanostructured samples of Bi85Sb15 solid solution from particles with average sizes ∼ 2.105; 950; 650; 380; 30 and 15 nm were obtained and investigated their galvanomagnetic properties in the range of ∼ 77-300 K. Were investigated samples that have not passed heat treatment, and the same samples that have passed heat treatment. It was found that the electrical and thermal properties of Bi85Sb15 solid solution samples significantly depend on the size of nanoparticles and post-extrusion heat treatment. Heat treatment leads to a decrease in the concentration of current carriers and to an increase in the mobility of current carriers and the total thermal conductivity of the samples under study, which is mainly due to the electronic component of thermal conductivity. The change in thermal parameters is satisfactorily explained by changes in occurring in the structure of samples during extrusion and heat treatment and correlates well with changes in the electrical parameters of these processes.

Integration of Thermal Core Profiling and Scratch Testing for the Study of Unconventional Reservoirs

Core analysis provides the essential information necessary for the characterization and development of hydrocarbon reservoirs. High core-scale heterogeneity and anisotropy, natural in unconventional reservoirs, complicate reservoir characterization and dictate the sampling methodology used. Continuous high-resolution thermal measurements with an optical scanner and scratcher along the core column can yield benefits in a sampling strategy. This article describes some features of the suggested integration of non-destructive thermal profiling with partially destructive scratch testing applied for the study of rocks from the Bazhenov Formation (West Siberia, Russia). The spatial variation in the unconfined compressive strength and thermal conductivity components parallel and perpendicular to bedding for more than 1000 samples are demonstrated and discussed on core and log scales. The relationships between these properties are established for different rock types composing the formation. The joint analysis allows specialists to correctly define multiscale heterogeneities and facies that would be difficult or impossible to observe with logging data analysis or geological description alone. The established relationships make it possible to partially replace the semi-destructive scratch test with non-destructive optical scanning, providing UCS estimation. One more important outcome of the present work is the lessons learned regarding how to organize future works. The integration of thermal core profiling and scratch testing data looks promising for unconventional reservoir characterization.

Thermoelectric properties of efficient thermoelectric materials on the basis of bismuth and antimony chalcogenides for multisection thermoelements

The following effective thermoelectric (TE) materials have been developed: Bi2Te2.8Se0.2 (0.14 wt%CdCl2), Bi0.5Sb1.5Тe3 (2 wt%Te and 0.14 wt% TeI4) obtained by zone melting; Bi2Te2.4Se0.6 (0.18 wt% CuBr) and Bi0.4Sb1.6Te3 (0.12 wt% PbCl2 and 1.50 wt% Te) obtained by extrusion; Bi2Te2.76Se0.24 (0.075 wt% Te and 0.026 wt% CdCl2) and Bi0.46Sb1.54Te3 (0.14 wt% Pb) obtained by rapid solidification. The elemental composition of TE materials was studied using the energy dispersive X-ray spectrometry. TE materials are designed for the manufacture of multisection thermoelements for thermoelectric generators (TEGs). In addition, TE materials obtained by zone melting can be used in the Peltier thermoelements. The electrical conductivity, Seebeck coefficient, thermal conductivity, thermal diffusivity, specific heat of TE materials in the temperature range of 300–600 K were investigated and an interpretation of their temperature dependences is provided. To obtain reliable data, the thermal conductivity was determined by two methods: (i) using the results of measuring the specific heat and thermal diffusivity; (ii) measuring the thermal conductivity by an absolute stationary method. The comparison of the results obtained by the mentioned methods showed that the discrepancy in the values of thermal conductivity does not exceed 8%, which correlates with the measurement error. The components of thermal conductivity were calculated and the mechanisms of heat transfer in TE materials were determined. The temperature dependences of dimensionless figure of merit ZT were defined. The operating temperatures for each material were found, in which ZT has the maximum values from 0.91 to 1.20. It was determined by the differential scanning calorimetry and thermogravimetric analysis that the materials investigated are thermally stable in the temperature range of 300–600 K.

Thermoelectric Properties and Thermal Stability of Nanostructured Thermoelectric Materials on the Basis of PbTe, GeTe, and SiGe

We have developed compositions and methods for obtaining effective medium-temperature nanostructured thermoelectric materials (TEMs): PbTe (doped by 0.2 wt % PbI2, 0.3 wt % Ni), GeTe (doped by 7.4 wt % Bi), high-temperature Si0.8Ge0.2 (doped by 1.7 wt % P) and Si0.8Ge0.2 (doped by 0.5 wt % B). Using scanning electron microscopy, the composition and structure of the materials are studied. The temperature dependence of the electrical conductivity and thermoelectric power of TEMs are explored. The thermal conductivity of TEMs are studied by the absolute stationary method. The components of thermal conductivity are determined. A decrease in thermal conductivity in nanostructured materials by 10–15% in comparison with the usual structure due to phonon heat transfer has been found. The obtained data are used to calculate the thermoelectric figure of merit (Z) and parameter ZТ. For nanostructured TEMs based on PbTe, GeTe, and n-type Si0.8Ge0.2, the temperature dependences of specific heat have been studied for the first time using differential scanning calorimetry (DSC). With the help of repeated DSC measurements, it has been found that nanostructured TEMs are thermally stable in the working temperature ranges. Thermogravimetric analysis is carried out and temperatures are determined at which a significant TEM sublimation occurs. The ranges of operating temperatures at which the investigated TEMs have the maximum efficiency and thermal stability have been determined. This is urgent in modeling multisectional thermoelements operating in a wide temperature range.

Mechanisms of Heat Transfer in Thermoelectric Materials

The analysis of methods for calculating the components of thermal conductivity of solid materials is carried out. The problems of using these methods are identified and their assessment is given from the point of view of obtaining reliable results. Experimental data on the temperature dependences of thermoelectric parameters of the main thermoelectric materials (TEMs) used for the manufacturing of Peltier and Seebeck thermoelements are presented. Using the obtained data, we calculated the main components of the thermal conductivity of TEMs (phonon, electronic, and bipolar) in the temperature range from 250 to 1200 K for solid solutions based on Bi, Sb, Pb, and Ge chalcogenides, as well as SiGe obtained by various methods of directional crystallization. The relationship between the mechanisms of heat transfer in TEMs and the temperature dependences of electrical conductivity and thermoelectric power has been established. It is shown that the use of nanostructured TEMs is promising for increasing the thermoelectric figure of merit.

Electron and heat transport in SnTe crystals with various vacancy concentrations in tin sublattice

SnTe single crystals with super-stoichiometric Sn up to 1.0 at.% were grown, their electrical conductivity thermo-e.m.f. and thermal conductivity χ coefficients, as well as the electrical properties of their contacts with Bi-Sn eutectic in the range 90–300 K have been studied. The electronic and lattice components of thermal conductivity as well as thermal resistance created by structural vacancies were determined. It was shown that the temperature dependences of the electrical conductivity and the thermo-e.m.f. coefficient of the samples are well explained by the model of two valence bands, and the thermal conductivity by phonon-phonon scattering. Excess tin atoms up to 0.05 at.% creating donor scattering phonon centers in SnTe crystals reduce thermal conductivity and electrical conductivity of samples, and above 0.05 at.% filling vacancies increase and of the samples. The contacts are ohmic and low resistance enough, and the current flows through them along metal shunts formed during the creation of the contact.