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The continuous updating and iteration of electronic devices brings about a significant accumulation of heat. It is urgent to enhance the thermal properties of polymer‐based composites to alleviate the heat dissipation problem in the microelectronics industry. In this paper, the hot drawing process was introduced to increase the crystallinity of ultra‐high molecular weight polyethylene (UHMWPE) fiber and improve its thermal conductivity. The ultra‐high molecular weight polyethylene fiber/epoxy resin (UHMWPE fiber/Epoxy) composites with high thermal conductivity were prepared by compositing UHMWPE fiber with epoxy resin under vacuum conditions. Due to the good crystallinity of the UHMWPE fiber (86%), an efficient thermal conduction path is provided for phonons in the axial direction along the fibers. The results show that the thermal conductivity of the composites reaches a maximum of 3.51 W/mK (in‐plane), which is 17.47 times higher than that of the epoxy resin (0.19 W/mK). The thermography pictures indicate that the composites have better heat transfer capacity with an increase in the draw ratio (λ). In addition, the composites also have the characteristics of low density and low electrical conductivity. These researches will provide a new idea for the preparation of all‐polymer composites with high thermal properties. Highlights: A hot drawing process was introduced to increase the crystallinity of UHMWPE fiber for improving thermal conductivity.High crystallinity facilitates the reduction of phonon scattering and the transmission of thermal energy by phonons.The obtained polymer composites exhibit an ultra‐high in‐plane thermal conductivity. [ABSTRACT FROM AUTHOR]

Thermal switches that switch the thermal conductivity (κ) of the active layers are attracting increasing attention as thermal management devices. For electrochemical thermal switches, several transition metal oxides (TMOs) are proposed as active layers. After electrochemical redox treatment, the crystal structure of the TMO is modulated, which results in the κ switching. However, the κ switching width is still small (<4 W m−1 K−1). In this study, it demonstrates that LaNiOx‐based solid‐state electrochemical thermal switches have a κ switching width of 4.3 W m−1 K−1. Fully oxidized LaNiO3 (on state) has a κ of 6.0 W m−1 K−1 due to the large contribution of electron thermal conductivity (κele, 3.1 W m−1 K−1). In contrast, reduced LaNiO2.72 (off state) has a κ of 1.7 W m−1 K−1 because the phonons are scattered by the oxygen vacancies. The LaNiOx‐based electrochemical thermal switch is cyclable of κ and the crystalline lattice of LaNiOx. This electrochemical thermal switch may be a promising platform for next‐generation devices such as thermal displays. [ABSTRACT FROM AUTHOR]

Rhombohedral GeSe is a promising p‐type thermoelectric material, noted for its low toxicity, environmental friendliness, and greater affordability compared with tellurides. However, its thermoelectric performance still requires further enhancement for practical applications. In this work, a highly competitive peak figure of merit (ZT) of 1.24 at 623 K for p‐type polycrystalline Ge0.895Cu0.005Se0.9(AgBiTe2)0.1, along with a high average ZT of 0.74 between 323 K and 623 K is reported. Comprehensive micro/nanostructural characterization reveals that alloying with AgBiTe2 and doping with Cu successfully induce dense point defects, secondary Ag2Te phases, and various nanoprecipitates in the GeSe matrix. These abundant crystalline and lattice defects result in strong phonon scattering, leading to an ultra‐low lattice thermal conductivity of 0.35 W m−1 K−1 at 623 K. Moreover, Cu doping enhances carrier mobility, promoting decoupling between carriers and phonons. This allows for low thermal conductivity and high power factor coexistence to achieve a high ZT. Additionally, with a temperature difference of 325 K, the theoretical energy conversion efficiency reaches up to 8.5%, indicating great potential for medium‐temperature device applications. This work suggests that Cu doping is an effective strategy for achieving high thermoelectric performance in rhombohedral GeSe‐based materials. [ABSTRACT FROM AUTHOR]

When a small atom is induced into a larger lattice, new phonon scattering modes are aroused and thermal conductivity is significantly reduced by increased anharmonicity. This effect, called “rattling,” has been reported in pyrochlores and some cage compounds, but not in α‐SiAlON. In this study, we reveal that in (Yb+Ca) co‐doped α‐SiAlON ceramics (YbaCabSi7.5Al4.5O1.5N14.5, x = a/[a+b]), the rattling effect plays a crucial role in reducing thermal conductivity. Samples with different Yb/Ca ratios (x = 0, 0.1, 0.2, 0.3…, 1.0) were sintered by spark plasma sintering (SPS) at 1600°C and their thermal diffusivity/conductivity were measured by the laser‐flash method. We found that substituting Ca2+ with smaller Yb3+ cations in Ca‐α‐SiAlON caused significant reduction in thermal conductivity. On the contrary, substituting Yb3+ with larger Ca2+ cations in Yb‐α‐SiAlON caused only slight reduction in thermal conductivity. A lowest thermal conductivity of 3.3 W/(m·K) was achieved, when x = 0.3 rather than x = 0.5 or 0.7. Further analysis of phonon scattering intensity confirmed that both intrinsic and extrinsic scatterings are enhanced in the sample of x = 0.3. This study demonstrates that by utilization of the rattling effect, α‐SiAlON, well‐known for its excellent mechanical properties, can be tuned to exhibit low thermal conductivity comparable to that of La2Zr2O7 and 8YSZ. [ABSTRACT FROM AUTHOR]

With the continuous development of high‐end electronic information technologies such as 5G communications, thermal management is an urgent issue in the electronic and circuit industries due to the miniaturization, functionalization and integration. Recently, polymer‐based composites with the fillers of hexagonal boron nitride (h‐BN) have been regarded as promising candidates resulting from their excellent thermal conductivity (TC), good insulation and remarkable comprehensive properties. However, the high surface inertness of h‐BN itself, incompatibility with matrix and other fillers and mismatch of phonon‐spectrum will bring about the matrix/filler and filler/filler interfacial thermal resistance (ITR), which will greatly decline the TC of the composites, and limit their thermal management ability. Therefore, how to design, regulate and improve the interfacial states in composites and eventually enhance the TC is a current challenge. Researchers have made great effort to reduce the ITR of the composites to improve their TC. However, a comprehensive summary and analysis of researches on the improvement methods of the interface states in composites in the past 3 years is still lacking. In this work, the commonly used mechanism models, and simulation methods for calculating and predicting TC was summarized. From perspectives of Synthesis of h‐BNNs, modification, orientation, bridging and three‐dimensional structures construction, we reviewed strategies for improving the interface states in composites, and focused on the ITR regulation and TC improvement. The improvement effects of various methods on TC were compared. The development trend of high TC composite materials was prospected. Highlights: Crystallinity, defect, size, flatness, thickness of hexagonal boron nitride nanosheets (BNNSs) affect interfacial thermal resistance (ITR).Nature of interaction between adjacent layers of BNNS need exploited.Interface and defect are root cause of extra phonon scattering.Shape, density, surface area, distribution and compatibility reduce ITR.Theory, model, simulation methods need developed on different levels. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) technology can effectively alleviate energy shortage and environmental pollution problems and has thus attracted extensive attention. In this work, we designed two unexplored two‐dimensional materials, Ba2ZnAs2 and Ba2ZnSb2, and investigated their stability, mechanical characteristics, and TE properties using first‐principles calculations and by solving the Boltzmann transport equation. We revealed that the two materials possess high stability and moderate cleavage energies of 0.84 and 0.76 J m−2. Moreover, they are indirect semiconductors with band‐gaps of 1.26 and 0.97 eV and show flat energy dispersion near the valence band maximum, resulting in a high p‐type Seebeck coefficient of approximately 0.72 and 0.29 mV K−1 at 300 K. Furthermore, they have significant anisotropic TE power factor along the a‐ and b‐axis, with maxima of 1.19 and 0.75 mW m−1 K−2 at 300 K. Owing to the strong coupling between the acoustic and optical phonons, as well as the low frequency for low‐lying phonons, the materials have high phonon scattering rates and low lattice thermal conductivities of 0.54/0.52 and 0.81/0.43 W mK−1 along the a‐/b‐axis. Ultimately, Ba2ZnAs2 and Ba2ZnSb2 can deliver high‐performance TE transport with high figures‐of‐merit of 0.32 and 0.19 at 300 K, which increase further to 1.67 and 0.91, respectively, at 700 K. [ABSTRACT FROM AUTHOR]

Bi6Cu2Se4O6 is considered as an ideal n‐type thermoelectric material to pair with p‐type BiCuSeO for preparing oxyselenide‐based thermoelectric devices, but its thermoelectric performance is limited by poor electrical conductivity. In this research, the reduced graphene oxide (rGO) nanosheets are introduced into Bi6Cu2Se3.6Cl0.4O6 matrix through liquid‐phase shear exfoliation to modify the microstructure. rGO can insert into matrix grains as intercalations, or embed into grain boundaries as wetting phase, and prompt grain alignment, which contributes to the significantly enhanced carrier mobility, thus leading to an improvement in electrical conductivity from ≈15 S cm−1 to ≈230 S cm−1 at 303 K. Whereafter, the effective donor dopant Nb is chosen to substitute Bi. The carrier concentration is increased without damaging the carrier mobility, resulting in a further improved electrical conductivity of ≈840 S cm−1 at 303 K. Lattice thermal conductivity is also suppressed owing to the intensive phonon scattering by point defects and grain boundaries. Ultimately, a record‐breaking peak ZT ≈0.5 (873 K) and average ZT ≈0.3 (303–873 K) can be achieved in Bi5.91Nb0.09Cu2Se3.6Cl0.4O6 + 0.5% rGO. The microstructure optimization method in this research effectively improves thermoelectric performance, and is anticipated to be applied in other thermoelectrics. [ABSTRACT FROM AUTHOR]

Thermal management becomes increasingly important in silicon gate‐all‐around (GAA) field‐effect transistor (FETs) for 3 nm technology node and beyond. The channel thermal conductivity significantly differs from bulk silicon. Precise determination of thermal conductivity is crucial for device evaluation and optimization. This study investigates the thermal conductivity of silicon nanowires, examining the complex interplay between size and channel orientation. The conventional nonequilibrium molecular dynamics (NEMD) method is used with the standard Stillinger–Weber potential at the atomic scale. The results indicate that the thermal conductivity of silicon nanowires along the [100] direction increases monotonically with both length (L) and cross‐sectional side length (D). Conversely, the [110] direction exhibits nonmonotonic variation in thermal conductivity with D, due to increased acoustic–optic phonon scattering. For GAA FET devices with a silicon nanowire channel of L = 20 nm and D = 5 nm, the NEMD calculations yield thermal conductivities of 10.8 W m·K−1 for the [100] direction and 25.3 W m·K−1 for the [110] direction. Subsequently, the self‐heating effect (SHE) in silicon nanowire GAA FETs by technology computer‐aided design with the modified channel conductivity is analyzed. The results suggest that silicon nanowires with the [110] transport direction are more suitable for device design. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) technology can effectively alleviate energy shortage and environmental pollution problems and has thus attracted extensive attention. In this work, we designed two unexplored two‐dimensional materials, Ba2ZnAs2 and Ba2ZnSb2, and investigated their stability, mechanical characteristics, and TE properties using first‐principles calculations and by solving the Boltzmann transport equation. We revealed that the two materials possess high stability and moderate cleavage energies of 0.84 and 0.76 J m−2. Moreover, they are indirect semiconductors with band‐gaps of 1.26 and 0.97 eV and show flat energy dispersion near the valence band maximum, resulting in a high p‐type Seebeck coefficient of approximately 0.72 and 0.29 mV K−1 at 300 K. Furthermore, they have significant anisotropic TE power factor along the a‐ and b‐axis, with maxima of 1.19 and 0.75 mW m−1 K−2 at 300 K. Owing to the strong coupling between the acoustic and optical phonons, as well as the low frequency for low‐lying phonons, the materials have high phonon scattering rates and low lattice thermal conductivities of 0.54/0.52 and 0.81/0.43 W mK−1 along the a‐/b‐axis. Ultimately, Ba2ZnAs2 and Ba2ZnSb2 can deliver high‐performance TE transport with high figures‐of‐merit of 0.32 and 0.19 at 300 K, which increase further to 1.67 and 0.91, respectively, at 700 K. [ABSTRACT FROM AUTHOR]

Thermoelectric cooling materials based on Bi2Te3 have a long history of unsurpassed performance near room temperature. Recently, research into price‐competitive Mg3(Bi, Sb)2‐based materials are focused on replacing traditional cooling materials. Here, the thermoelectric properties of Mg3.2Bi1.998−xSbxTe0.002Cu0.005 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) polycrystalline compounds are investigated. In all temperature regions, electrical resistivity and Seebeck coefficient are increased with Sb concentration. The electronic transport properties of Sb‐alloyed compounds are maximized by synergistically combined band engineering approaches such as band structure change caused by lattice strain, increased electronic density of states, and chemical potential shift, leading to exceptionally high‐power factor values of over 3.0 mW m−1 K−2 at room temperature. Furthermore, with increasing Sb content, thermal conductivity values are systematically reduced due to the promotion of alloy scattering of phonons and suppression of the bipolar contribution. Consequently, these multiple approaches significantly enhance thermoelectric performance, resulting in an enhancement of thermoelectric figure‐of‐merit zT above 1.1 at 348–423 K. Additionally, a zTavg of 1.1 is recorded at 300–450 K, making it an unrivaled value among the reported n‐type Mg3Bi2‐based thermoelectric materials. Overall, this work demonstrates that Mg3Bi2‐based materials are more promising for thermoelectric cooling applications compared to Bi2Te3‐based materials. [ABSTRACT FROM AUTHOR]

Nanomaterial phonon transport is crucial for miniaturized devices and superior thermophysical properties in condensed matter physics. Diamond nanosheets, applicable in nanoelectronics/optoelectronics, offer availability to explore dimensionality's impact on phonon transport. Raman spectroscopy is used to study the thermal conductivity (κ) of diamond nanosheets with a thickness below 100 nm. Results show a κ∼T−1$\kappa \sim {{T}^{ - 1}}$ law above 140 K, highlighting Umklapp phonon scattering. Despite the reduced thickness, κ (1100‐2000 W/mK) remains higher than metals and most semiconductors, showcasing diamonds' remarkable in‐plane heat transfer. Intriguingly, the research uncovers unique length‐dependent behavior κ∼log(L)$\kappa \sim {\mathrm{log}}( L )$, consistent with graphene, the two‐dimensional (2D) allotrope. This research offers insights into thermal transport in quasi‐2D nanosheets, with significant implications for nanoscale heat management and highly efficient thermal devices. [ABSTRACT FROM AUTHOR]

The main bottleneck in obtaining high‐performance thermoelectric (TE) materials is identified as how to decouple the strong interrelationship between electrical and thermal parameters. Herein, a precise interface modification approach based on the powder atomic layer deposition (ALD) technology is presented to enhance the performance of CuNi alloys. ZnO and Al2O3 layers as well as their combinations are deposited on the surface of powders, typically in 10–100 ALD cycles, and their effects on the TE performance of bulks is thoroughly investigated. The enhancement of the Seebeck coefficient, caused by the energy filtering effect, compensates for the electrical conductivity deterioration due to the low electrical conductivity of oxide layers. Furthermore, the oxide layers may significantly increase the phonon scattering. Therefore, to reduce the resistivity of coating layer, a multilayer structure is deposited on the surface of powders by inserting Al2O3 into ZnO. The accurate microstructure characterization shows that the Al atoms diffused into ZnO and realized the doping effect after pressing. Al diffusion has the potential to increase the electrical conductivity and complexity of coating layers. Compared to pure CuNi, zT increases by 128% due to the decrease in resistivity and stronger phonon scattering in phase boundaries. [ABSTRACT FROM AUTHOR]

Porous SiC ceramics with three different pore sizes (∼7, ∼45, and ∼98 μm) and two different porosities (∼54% and ∼63%) were prepared to investigate the effects of pore size on electrical and thermal properties of the porous ceramics. With an increase in pore size from ∼7 to ∼98 μm at the same porosity (∼54%), the electrical and thermal conductivities of the porous ceramics increased from ∼1.01 to ∼2.30 Ω−1·cm−1 and ∼14.3 to ∼26.2 W·m−1K−1, respectively. Similar trends have been obtained in the ceramics with ∼63% porosity. The porous SiC ceramic with larger pore size has smaller pore/strut interface area at the same porosity, which leads to less carrier scattering and phonon‐pore scattering at the pore/strut interfaces, resulting in higher electrical and thermal conductivities, respectively. These results suggest that the electrical and thermal properties of porous SiC ceramics can be successfully tuned by adjusting the pore size and porosity depending on the application. [ABSTRACT FROM AUTHOR]

In this article, a field‐plated and recessed gate III‐Nitride Nano‐HEMT developed on β‐Ga2O3 substrate is proposed and investigated for various performance characteristics over different temperatures. The 2DEG (Two Dimensional Electron Gas) dependence on temperature is critical for commercial utilization of GaN‐based HEMTs (high electron mobility transistors). Here, the temperature influence on 2DEG for proposed HEMT over the range of 300–400 K has been investigated. The results demonstrate that the 2DEG density of proposed HEMT reduces as temperature increases. It has been observed that phonon scattering results in a sharp decline in the mobility of 2DEG as temperature increases, which causes the electric field to decrease. It also exhibited that the cut‐off frequency decreased over the temperature changes from 300 to 400 K due to diminution in electron mobility. This research aims to contribute an extensive overview of proposed III‐Nitride Nano‐HEMT designed on a lattice‐matched substrate of β‐Ga2O3 to foster future research on the latest developments in this field. [ABSTRACT FROM AUTHOR]

Tuning the thermal transport properties of hybrid halide perovskites is critical for their applications in optoelectronics, thermoelectrics, and photovoltaics. Here, an effective strategy is demonstrated to modulate the thermal transport property of hybrid perovskites by halide alloying. A highly tunable thermal conductivity of mixed‐halide hybrid perovskites is achieved due to halide‐alloying and structural distortion. The experimental measurements show that the room temperature thermal conductivity of MAPb(BrxI1‐x)3 (x = 0─1) can be largely modulated from 0.27 ± 0.07 W m−1 K−1 (x = 0.5) to 0.47 ± 0.09 W m−1 K−1 (x = 1). Molecular dynamics simulations further demonstrate that the thermal conductivity reduction of hybrid halide perovskites results from the suppression of the mean free paths of the low‐frequency acoustic and optical phonons. It is found that halide alloying and the induced structural distortion can largely increase the scatterings of optical and acoustic phonons, respectively. The confined diffusion of MA+ cations in the octahedra cage is found to act as an additional thermal transport channel in hybrid perovskites and can contribute around 10–20% of the total thermal conductivity. The findings provide a strategy for tailoring the thermal transport in hybrid halide perovskites, which may largely benefit their related applications. [ABSTRACT FROM AUTHOR]

External pressure can significantly alter the transport coefficients, power factor, and figure of merit because of its direct influence on the electronic structure, electron–phonon, and phonon–phonon couplings. This study delves into the electronic and thermal transport properties of SnPS3${\rm SnPS}_3$ at external pressures up to 30 GPa using first‐principles calculations and Boltzmann transport theory. The electron–phonon relaxation time is computed within the electron–phonon‐averaged (EPA) approximation, enabling exploration beyond the constant relaxation time approximation. The first‐principles calculations reveal an indirect bandgap of 1.76 (without pressure) and 0.12 eV (30 GPa). The density functional perturbation theory calculations confirm the dynamic stability of SnPS3${\rm SnPS}_3$ at external pressure up to 30 GPa. The electronic transport properties are improved by more than one order of magnitude at 30 GPa, consistent with experimental observations. The Peierls–Boltzmann transport calculations demonstrate the room temperature lattice thermal conductivity of 0.22 (without pressure) and 7.4 Wm−1K−1${\rm Wm}^{-1}{\rm K}^{-1}$ (at 30 GPa). The results emanate that SnPS3${\rm SnPS}_3$ exhibits ZT$ZT$ of 0.71 at 900 K at a hole doping of 2×1020$\times 10^{20}$cm−3$\text{cm}^{-3}$ at zero pressure, which decreases with increasing pressure. The findings explore the effect of external pressure on both electronic and thermal transport properties of SnPS3${\rm SnPS}_3$, warranting further experimental exploration of thermal transport properties at higher pressures. [ABSTRACT FROM AUTHOR]

Bi2Te3‐based materials have drawn much attention from the thermoelectric community due to their excellent thermoelectric performance near room temperature. However, the stability of existing n‐type Bi2(Te,Se)3 materials is still low due to the evaporation energy of Se (37.70 kJ mol−1) being much lower than that of Te (52.55 kJ mol−1). The evaporated Se from the material causes problems in interconnects of the module while degrading the efficiency. Here, we have developed a new approach for the high‐performance and stable n‐type Se‐free Bi2Te3‐based materials by maximizing the electronic transport while suppressing the phonon transport, at the same time. Spontaneously generated FeTe2 nanoinclusions within the matrix during the melt‐spinning and subsequent spark plasma sintering is the key to simultaneous engineering of the power factor and lattice thermal conductivity. The nanoinclusions change the fermi level of the matrix while intensifying the phonon scattering via nanoparticles. With a fine‐tuning of the fermi level with Cu doping in the n‐type Bi2Te3–0.02FeTe2, a high power factor of ~41 × 10−4 Wm−1 K−2 with an average zT of 1.01 at the temperature range 300–470 K are achieved, which are comparable to those obtained in n‐type Bi2(Te,Se)3 materials. The proposed approach enables the fabrication of high‐performance n‐type Bi2Te3‐based materials without having to include volatile Se element, which guarantees the stability of the material. Consequently, widespread application of thermoelectric devices utilizing the n‐type Bi2Te3‐based materials will become possible. [ABSTRACT FROM AUTHOR]

The emergence of various topological semimetal states presents a novel opportunity for enhancing the efficiency of thermoelectric transport. This study introduces a recipe to improve the thermoelectric (TE) performance in topological materials containing single‐pair Weyl points (SP WPs) fermions and phonons. The recipe focuses on two key factors contributing to the enhancement of TE performance: the increase in the density of states to achieve a high power factor, and the introduction of additional phonon scattering to reduce the lattice thermal conductivity. The proposed recipe is confirmed in a half‐metallic SP WPs material BaNiIO6 through first‐principles methods. An enhanced density of states arises near the energy of the SP WPs in BaNiIO6, leading to a peak power factor connected to the complex Fermi surface due to the degeneracy of Weyl pockets in energy. Furthermore, it is shown that the SP WPs phonons in BaNiIO6 possess a high scattering rate and can likely contribute to the low lattice thermal conductivity, especially when two crossing points in SP WPs do not degenerate in frequency. The new recipe can be used for discovering high‐performance thermoelectric materials in the future by utilizing the transport advantages of degenerate‐in‐energy SP WPs fermions and non‐degenerate‐in‐frequency SP WPs phonons. [ABSTRACT FROM AUTHOR]

A new preparation process for silicon carbide (SiC) powder is developed. In the Si–(C) –PTFE–Ar system, the grain size and morphology of the product 3C–SiC were controlled by adding a carbon source (graphite) and changing the percentage of polytetrafluoroethylene (PTFE) (0%, 10%, and 20%). The experimental results showed that the SiC powders prepared using a molar ratio of 1:1 silicon powder to graphite, plus 20% PTFE have a uniform particle size distribution (∼130 nm), a lamellar structure made of spherical particle stacking, a small bandgap (1.80 eV), a high carrier concentration, and a large number of lattice defects. These properties are expected to increase the electrical conductivity of 3C–SiC and decrease its thermal conductivity, thus providing a promising feedstock preparation option for SiC thermoelectric materials. In addition, the mechanism of PTFE in the preparation of SiC reactions was studied in detail. [ABSTRACT FROM AUTHOR]

Manipulating thermal properties of materials can be interpreted as the control of how vibrations of atoms (known as phonons) scatter in a crystal lattice. Compared to a perfect crystal, crystalline solids with defects are expected to have shorter phonon mean free paths caused by point defect scattering, leading to lower lattice thermal conductivities than those without defects. While this is true in many cases, alloying can increase the phonon mean free path in the Cd‐doped AgSnSbSe3 system to increase the lattice thermal conductivity from 0.65 to 1.05 W m−1 K−1 by replacing 18% of the Sb sites with Cd. It is found that the presence of lone pair electrons leads to the off‐centering of cations from the centrosymmetric position of a cubic lattice. X‐ray pair distribution function analysis reveals that this structural distortion is relieved when the electronic configuration of the dopant element cannot produce lone pair electrons. Furthermore, a decrease in the Grüneisen parameter with doping is experimentally confirmed, establishing a relationship between the stereochemical activity of lone pair electrons and the lattice anharmonicity. The observed "harmonic" behavior with doping suggests that lone pair electrons must be preserved to effectively suppress phonon transport in these systems. [ABSTRACT FROM AUTHOR]

Thermoelectric materials are highly promising for waste heat harvesting. Although thermoelectric materials research has expanded over the years, bismuth telluride‐based alloys are still the best for near‐room‐temperature applications. In this work, a ≈38% enhancement of the average ZT (300−473 K) to 1.21 is achieved by mixing Bi0.4Sb1.6Te3 with an emerging thermoelectric material Sb2Si2Te6, which is significantly higher than that of most BiySb2−yTe3‐based composites. This enhancement is facilitated by the unique interface region between the Bi0.4Sb1.6Te3 matrix and Sb2Si2Te6‐based precipitates with an orderly atomic arrangement, which promotes the transport of charge carriers with minimal scattering, overcoming a common factor that is limiting ZT enhancement in such composites. At the same time, high‐density dislocations in the same region can effectively scatter the phonons, decoupling the electron‐phonon transport. This results in a ≈56% enhancement of the thermoelectric quality factor at 373 K, from 0.41 for the pristine sample to 0.64 for the composite sample. A single‐leg device is fabricated with a high efficiency of 5.4% at ΔT = 164 K further demonstrating the efficacy of the Sb2Si2Te6 compositing strategy and the importance of the precipitate‐matrix interface microstructure in improving the performance of materials for relatively low‐temperature applications. [ABSTRACT FROM AUTHOR]

Due to their amorphous‐like ultralow lattice thermal conductivity both below and above the superionic phase transition, crystalline Cu‐ and Ag‐based superionic argyrodites have garnered widespread attention as promising thermoelectric materials. However, despite their intriguing properties, quantifying their lattice thermal conductivities and a comprehensive understanding of the microscopic dynamics that drive these extraordinary properties are still lacking. Here, an integrated experimental and theoretical approach is adopted to reveal the presence of Cu‐dominated low‐energy optical phonons in the Cu‐based argyrodite Cu7PS6. These phonons yield strong acoustic‐optical phonon scattering through avoided crossing, enabling ultralow lattice thermal conductivity. The Unified Theory of thermal transport is employed to analyze heat conduction and successfully reproduce the experimental amorphous‐like ultralow lattice thermal conductivities, ranging from 0.43 to 0.58 W m−1 K−1, in the temperature range of 100–400 K. The study reveals that the amorphous‐like ultralow thermal conductivity of Cu7PS6 stems from a significantly dominant wave‐like conduction mechanism. Moreover, the simulations elucidate the wave‐like thermal transport mainly results from the contribution of Cu‐associated low‐energy overlapping optical phonons. This study highlights the crucial role of low‐energy and overlapping optical modes in facilitating amorphous‐like ultralow thermal transport, providing a thorough understanding of the underlying complex dynamics of argyrodites. [ABSTRACT FROM AUTHOR]

Due to their amorphous‐like ultralow lattice thermal conductivity both below and above the superionic phase transition, crystalline Cu‐ and Ag‐based superionic argyrodites have garnered widespread attention as promising thermoelectric materials. However, despite their intriguing properties, quantifying their lattice thermal conductivities and a comprehensive understanding of the microscopic dynamics that drive these extraordinary properties are still lacking. Here, an integrated experimental and theoretical approach is adopted to reveal the presence of Cu‐dominated low‐energy optical phonons in the Cu‐based argyrodite Cu7PS6. These phonons yield strong acoustic‐optical phonon scattering through avoided crossing, enabling ultralow lattice thermal conductivity. The Unified Theory of thermal transport is employed to analyze heat conduction and successfully reproduce the experimental amorphous‐like ultralow lattice thermal conductivities, ranging from 0.43 to 0.58 W m−1 K−1, in the temperature range of 100–400 K. The study reveals that the amorphous‐like ultralow thermal conductivity of Cu7PS6 stems from a significantly dominant wave‐like conduction mechanism. Moreover, the simulations elucidate the wave‐like thermal transport mainly results from the contribution of Cu‐associated low‐energy overlapping optical phonons. This study highlights the crucial role of low‐energy and overlapping optical modes in facilitating amorphous‐like ultralow thermal transport, providing a thorough understanding of the underlying complex dynamics of argyrodites. [ABSTRACT FROM AUTHOR]

The assembly of 2D materials via vertical stacking has shown great advantages in modern device design, while the interface formed by two 2D materials also provides a new opportunity to tune various physical properties. Herein, the impact of homogeneous stacking on the thermal conductivity of 2D SnSe, a promising thermoelectric material, has been elucidated by solving the phonon‐Boltzmann transport equation with the first‐principles approach. SnSe bilayer and trilayer stacks, involving diverse interfacial configurations, are constructed to reveal potential modulation of in‐plane lattice thermal conductivity. Compared to the single‐layer counterpart, the result demonstrates a reduced thermal transport capacity in both the SnSe bilayer and trilayer due to van der Waals interaction, and the SnSe bilayer could exhibit a greater potential for thermoelectric applications due to the significantly suppressed phonon transport. Moreover, the interface effect can be further verified by the stacking‐dependent behavior of thermal conductivity, while the reduced thermal conductivity in SnSe stacks can be attributed to the decreased phonon relaxation time caused by interlayer interactions, implying great potential to further promote 2D SnSe‐based thermoelectric applications by stacking modulation. [ABSTRACT FROM AUTHOR]

Herein, (14,14,14)‐graphyne (GY) supported by silicon substrate is chosen to be the research object. The results demonstrate that the increasing distance between substrate and supported materials (dsub‐sup) results in the enhancement of thermal conductivity (TC) of supported GY, and the TC of supported GY is even higher than that of free‐standing GY when dsub‐sup exceeds a certain value, which means substrate plays an abnormal promoting role in the thermal transport in supported materials (SM). This phenomenon breaks the traditional cognition that the increasing dsub‐sup can only lead to the TC of SM approaching that of free‐standing model. The related mechanism can be seen as the combined impact of weak interaction of long‐dsub‐sup substrate and tensile effect led by lattice mismatch between substrate and GY. Combining with phonon analysis, it can be observed that the influence of substrate shows a closer relationship with phonon scattering, i.e., the anharmonicity, especially the anharmonicity of out‐of‐plane direction. The anomalous promoting effect of long‐dsub‐sup can be also attributed to the weaker scattering of out‐of‐plane phonon, especially the reduced four‐order phonon scattering. This research provides a new idea to suppress the negative effect of substrate on heat dissipation in electronic devices. [ABSTRACT FROM AUTHOR]

An ab initio characterization of the impact of tert‐Butyl isocyanate (C5H9NO${\rm C}_5{\rm H}_9{\rm NO}$) functionalization on TaS2${\rm TaS}_2$ lattice thermal conductivity is presented. Such a system has been previously synthetized and experimentally charachterized, showing that the incorporation of covalently bonded C5H9NO${\rm C}_5{\rm H}_9{\rm NO}$ on bulk TaS2${\rm TaS}_2$ leads to a dramatic in‐plane lattice thermal conductivity decrease by more than two orders of magnitudes. To elucidate these experimental findings, detailed calculations of the phonon dispersion relations and scattering rates in TaS2${\rm TaS}_2$ are performed. The analysis is addressed to discern the impact of inter‐layer covalently bonded C5H9NO${\rm C}_5{\rm H}_9{\rm NO}$ molecules on these phonon properties, providing insights into the underlying mechanisms of the observed thermal conductivity decrease. Present calculations provide evidence that the observed lattice thermal conductivity reduction is attributed to two effects: i)$i)$ the increase of inter‐layer separation and ii)$ii)$ the presence of low‐frequency molecular optical modes. The first inhibits specific Van der Waals quasi‐acoustic inter‐layer vibrational modes contributing as much as ≈55%$\approx \!\! 55\%$ in bulk TaS2${\rm TaS}_2$. The second effect dramatically decreases the phonon group velocities as a consequence of phonon‐crossing phenomena among low‐frequency molecular modes and TaS2${\rm TaS}_2$ acoustic modes, eventually leading to a strong reduction of all phonon lifetimes. [ABSTRACT FROM AUTHOR]

Phonon statistics in a hybrid optomechanical system, where a mechanical resonator is quadratically coupled to a cavity and couples with another resonator via Coulomb interaction is studied. It is found that the conventional and unconventional phonon blockade can be both achieved at the same parameter regime, which is confirmed by analytical and numerical results. By analyzing the energy level structure, it is found that the anharmonicity of the system is the joint action of both the Coulomb interaction and the optomechanical coupling, where the nonlinearity introduced by the latter has a more significant effect on one branch of the conventional phonon blockade. In addition, the phonon blockade can be enhanced by introducing the mechanical parametric amplifier with optimal parameters, where the physical mechanism underlying comes from the multi‐pathway destructive interference. It is found that the phonon blockade is fragile toward thermal noise due to the weak quantum interference, which can be overcome by increasing the driving strength and applying the mechanical parametric amplifier with suitable parameters. This work may provide a way to manipulate the phonon blockade and can be helpful to the application of quantum information processing. [ABSTRACT FROM AUTHOR]

Finding parent thermoelectric materials with a high figure of merit is a direction that people pursue. However, the interplay and constraints among the Seebeck coefficient, electrical conductivity, and thermal conductivity pose formidable challenges. In this review, the decoupling effect of anisotropic electronic energy band and multi‐valley band structures are initially introduced on the Seebeck coefficient and electrical conductivity. Subsequently, an overview of how materials with a host‐guest structure enable the coexistence of high electrical conductivity and low thermal conductivity through unique transport mechanisms is provided. Finally, deliberating on approaches to achieve intrinsic low lattice thermal conductivity, encompassing low dimensionality, low phonon group velocities, and substantial anharmonicity. Moreover, a detailed analysis is conducted to dissect the physical mechanisms through which strong higher‐order anharmonicity restricts lattice thermal transport. It is believed that this review serves as a guiding resource for the quest for and design of efficient thermoelectric materials. [ABSTRACT FROM AUTHOR]

Lead‐free polycrystalline manganese telluride holds great potential in the development of waste heat recovery due to its fascinating physical properties. However, the poor thermoelectric (TE) performance in the p‐type MnTe alloys always results from their inferior carrier concentration, leading to low power factor and high thermal conductivity which restrict the overall thermoelectric performance. In this work, the problem is solved by decoupling its electrical and thermal transports through the hole donor Ge‐deficiency in MnTe + x mol.% GeTe (0 ≤ x ≤ 4) compounds. Intrinsically, extra GeTe in MnTe + x mol.% GeTe compound offers free charge carriers due to a narrow bandgap comparatively, realizing not only a full assessment of stimulated electrical performance but also an enhanced power factor. Moreover, benefiting from the nano‐precipitates and tweed microstructures, the lattice thermal conductivity effectively reduces due to the intensive phonon scattering accordingly. Ultimately, a maximum ZT of ≈1.2 at 873 K in the 3 mol.% GeTe doped MnTe sample is realized. [ABSTRACT FROM AUTHOR]

The creation of hierarchical nanostructures can effectively strengthen phonon scattering to reduce lattice thermal conductivity for improving thermoelectric properties in inorganic solids. Here, we use Zn doping to induce a remarkable reduction in the lattice thermal conductivity in SnTe, approaching the theoretical minimum limit. Microstructure analysis reveals that ZnTe nanoprecipitates can embed within SnTe grains beyond the solubility limit of Zn in the Zn alloyed SnTe. These nanoprecipitates result in a substantial decrease of the lattice thermal conductivity in SnTe, leading to an ultralow lattice thermal conductivity of 0.50 W m−1 K−1 at 773 K and a peak ZT of ~0.48 at 773 K, marking an approximately 45 % enhancement compared to pristine SnTe. This study underscores the effectiveness of incorporating ZnTe nanoprecipitates in boosting the thermoelectric performance of SnTe‐based materials. [ABSTRACT FROM AUTHOR]

The crystal structure and transport properties of GeBi2Te4 are investigated as a layered compound with potential applications as thermoelectric materials. A disordered arrangement of Ge and Bi atoms in a septuple‐layer structure is discovered through synchrotron radiation X‐ray diffraction and transmission electron microscopy. Neutron pair distribution function analysis revealed the presence of discordant Ge atoms with an off‐centering distance of 0.12 Å at 300 K. The thermal conductivity of GeBi2Te4 is very low due to the strong phonon scattering. This is a result of the three Einstein local oscillators coupled with the disordered arrangement of atoms. This study also explores further the structural characteristics of these materials and their associated phonon scattering processes. The effect of Sb substitution for Ge on the electrical transport properties of the sample is profound, resulting in a change from p‐type to n‐type conduction. An enhanced thermoelectric figure of merit (ZT) of 0.45 at 523 K in the in‐plane direction is obtained. This research provides valuable insights into the crystal structure and transport properties of GeBi2Te4, showcasing its promising role as a thermoelectric material with potential for near‐room‐temperature applications. [ABSTRACT FROM AUTHOR]

In this study, the strain‐induced effects on thermal and electrical transport properties of LaCuOSe are studied by combining first‐principles calculations with semi‐classical Boltzmann transport theory. The results show that external strain affects the crystal and electronic structures of LaCuOSe significantly. It is interesting to find that the electrical conductivity of n‐type LaCuOSe is improved by the tensile strain. In addition, the tensile strain also has positive effects on the Seebeck coefficient of p‐type doped LaCuOSe. Consequently, the power factor of p‐type doped LaCuOSe is enhanced by 18.2% under 10% tensile strain at 800 K. However, due to the obviously affected mechanical properties of LaCuOSe under external strain, the decreased Grüneisen constant and reduced Debye temperatures are resulted, and the lattice thermal conductivity of LaCuOSe at 300 K increases from 2.91 to 5.95 Wm/K with the tensile strain increasing from 0% to 10%. The sharply increased thermal conductivity finally results in the optimal ZT value of 0.076 and 0.417 for ideal p‐ and n‐type LaCuOSe at 800 K being reduced to 0.048 and 0.286 under 10% tensile strain, respectively. These results suggest that the thermoelectrical properties of LaCuOSe need to be further improved for its application under stress. [ABSTRACT FROM AUTHOR]

2D Janus materials have drawn great interest in recent years due to their energy applications including thermoelectricity (TE) and photocatalysis. In this work, density functional theory and Boltzmann transport equations are coupled to look into the thermoelectric properties of Sn2SeS$Sn_2SeS$ monolayer. Sn2SeS$Sn_2SeS$ is an indirect bandgap semiconductor with a bandgap of 0.88 eV. This monolayer is chemically as well as dynamically stable. The thermoelectric parameters such as the Seebeck coefficient, electrical conductivity, and thermal conductivity due to electrons and phonons are explored along the zigzag and armchair orientation. The high value of electrical conductivity and low‐value lattice thermal conductivity along the zigzag orientation yields the high value of ZT = 1.93. [ABSTRACT FROM AUTHOR]

Structural mosaic of rare-earth tri-tellurides (RTe3) inlaid with non-classical structural motifs like the 2D-polytelluride square nets has attracted immense attention owing to their enigmatic chemical bonding, unconventional structure, and harboring charge density wave (CDW) ground states. GdTe3, an archetypal RTe3, is a natural heterostructure of charged and van der Waals (vdW) layers, formed by intercalating vdW gap separated 2D square telluride nets … between the charged double corrugated slabs of n[GdTe]+. Here, we have investigated the evolution of structural distortions along with the electrical and thermal transport properties of GdTe3 across its CDW transition through X-ray pair distribution function analysis, thermal conductivity measurements, Raman spectroscopy and first principles theoretical calculations. The results reveal that the unusual structure of GdTe3 engenders a large anisotropic lattice thermal conductivity by concomitantly hampering the phonon propagation along parallel to the spark plasma sintering (SPS) pressing direction via chemical bonding hierarchy while facilitating phonon propagation along perpendicular to the SPS pressing direction through the metallic Te sheets and phason channel. The low lattice thermal conductivity is attributed to the strong vibrational anharmonicity caused by CDW-induced concerted local lattice distortions of both Gd-Te slab and Te square net, and the robust electron-phonon coupling. [ABSTRACT FROM AUTHOR]

As a highly promising thermoelectric material in the mid‐temperature region, pristine GeTe shows deteriorated thermoelectric properties due to the low Seebeck coefficient and the intrinsic high thermal conductivity. Herein, it is discovered that the introduction of strongly correlated d, f electrons by alloying rare‐earth atoms at Ge sites will increase the band effective mass and promote band convergency, which can largely improve the electric transport property. Moreover, the heavy atoms (Pb, Bi) doping induces optical phonon softening and the avoided crossing between acoustic and optical phonon branches, decelerating both optical and acoustic phonon velocities. The modulated composition wave from the fluctuated multi‐component distribution introduces a complicated hierarchical structure including point defects and nanoprecipitates, which provides all‐scale scattering sources for heat‐carrying phonons and results in low lattice thermal conductivity. Consequently, a high zT of 2.4 at 800 K can be obtained in the Ge0.86Pb0.09Bi0.03Ce0.005Te sample due to the combination of strong correlation for d, f electrons and the full‐spectrum scattering for phonons. This work provides an effective strategy to increase the thermoelectric performance of IV–VI compounds by combining the modulated band structure and the softening phonon dispersion. [ABSTRACT FROM AUTHOR]

Structural mosaic of rare-earth tri-tellurides (RTe3) inlaid with non-classical structural motifs like the 2D-polytelluride square nets has attracted immense attention owing to their enigmatic chemical bonding, unconventional structure, and harboring charge density wave (CDW) ground states. GdTe3, an archetypal RTe3, is a natural heterostructure of charged and van der Waals (vdW) layers, formed by intercalating vdW gap separated 2D square telluride nets … between the charged double corrugated slabs of n[GdTe]+. Here, we have investigated the evolution of structural distortions along with the electrical and thermal transport properties of GdTe3 across its CDW transition through X-ray pair distribution function analysis, thermal conductivity measurements, Raman spectroscopy and first principles theoretical calculations. The results reveal that the unusual structure of GdTe3 engenders a large anisotropic lattice thermal conductivity by concomitantly hampering the phonon propagation along parallel to the spark plasma sintering (SPS) pressing direction via chemical bonding hierarchy while facilitating phonon propagation along perpendicular to the SPS pressing direction through the metallic Te sheets and phason channel. The low lattice thermal conductivity is attributed to the strong vibrational anharmonicity caused by CDW-induced concerted local lattice distortions of both Gd-Te slab and Te square net, and the robust electron-phonon coupling. [ABSTRACT FROM AUTHOR]

The chemical reduction method is a simple and popular way to contrast the graphene network to improve the polymer matrix's thermal conductivity. And hybrid thermal conductive fillers composed of two or more mixed fillers through chemical synthesis usually have better thermal conductivity because of the synergistic effort. In this work, silicon carbide nanowires (SiC NWs) in graphene aerogels are synthesized with the chemical vapor deposition method, acting as bridges for phonon transmission between adjacent graphene sheets. The RGO/SiC NWs aerogel‐endowed EP composites have a high thermal conductivity of 3.79 W/mK at a filler loading of 5.5 wt%, and 4.23 W/mK at a filler loading of 7.5 wt%, which is 1895% and 2126% higher than pure EP resin, respectively. Finite element analysis (FEA) is utilized to analyze the heat conduction mechanism of composites at last. [ABSTRACT FROM AUTHOR]

Violet phosphorus (VP) is garnering attention for its appealing physical properties and potential applications in optoelectronics. A comprehensive investigation of the photodegradation and thermal effects of exfoliated VP on SiO2/Si substrates is presented. The degradation rate of VP is strongly influenced by the wavelength and exposure duration of light. Light illumination of VP above the bandgap leads to faster degradation, attributed to interactions with reactive oxygen species. Power‐dependent photoluminescence (PL) measurements at low temperature (T = 4 K) show neutral exciton (X0) and trion (T) intensities linearly increase with excitation power, while the energy difference between peak energies decreases. The T/X0 spectral weight ratio increases from 0.28 at 300 K to 0.69 at 4 K, suggesting enhanced T formation due to reduced phonon scattering. Temperature‐dependent Raman is used to investigate the phonon properties of VP. Tracking peak positions of 9 Raman modes with temperature, the linear first‐order temperature coefficient is obtained and found to be linear for all modes. The results provide a deeper understanding of VP's degradation behavior and implications for optoelectronic applications. [ABSTRACT FROM AUTHOR]

High energy‐conversion efficiency (ZT) of thermoelectric materials has been achieved in heavy metal chalcogenides, but the use of toxic Pb or Te is an obstacle for wide applications of thermoelectricity. Here, high ZT is demonstrated in toxic‐element free Ba3BO (B = Si and Ge) with inverse‐perovskite structure. The negatively charged B ion contributes to hole transport with long carrier life time, and their highly dispersive bands with multiple valley degeneracy realize both high p‐type electronic conductivity and high Seebeck coefficient, resulting in high power factor (PF). In addition, extremely low lattice thermal conductivities (κlat) 1.0–0.4 W m−1 K−1 at T = 300–600 K are observed in Ba3BO. Highly distorted O–Ba6 octahedral framework with weak ionic bonds between Ba with large mass and O provides low phonon velocities and strong phonon scattering in Ba3BO. As a consequence of high PF and low κlat, Ba3SiO (Ba3GeO) exhibits rather high ZT = 0.16–0.84 (0.35–0.65) at T = 300–623 K (300–523 K). Finally, based on first‐principles carrier and phonon transport calculations, maximum ZT is predicted to be 2.14 for Ba3SiO and 1.21 for Ba3GeO at T = 600 K by optimizing hole concentration. Present results propose that inverse‐perovskites would be a new platform of environmentally‐benign high‐ZT thermoelectric materials. [ABSTRACT FROM AUTHOR]

Bismuth sulfide (Bi2S3) is a promising thermoelectric material with earth‐abundant, low‐cost, and environment‐friendly constituents. However, it shows poor thermoelectric performance due to its extremely low electrical conductivity derived from the low electron concentration. Here, a high‐performance Bi2S3‐based material is reported to benefit from the Fermi level tuning by Ag and Cl co‐doping and defect engineering by introducing dense low‐angle grain boundaries. Both Ag and Cl act as donors in Bi2S3, upshifting the Fermi level. This increases the electron concentration without degrading the electron mobility, thereby obtaining improved electrical conductivity. The electron localization function (ELF) contour map indicates that interstitial Ag causes electron delocalization, showing higher electron mobility in Bi2S3. More importantly, dense low‐angle grain boundaries block phonon propagation, yielding an ultralow lattice thermal conductivity of 0.30 W m−1 K−1. Consequently, a record ZT value of ≈0.9 at 676 K is achieved in the Bi2Ag0.01S3‐0.5%BiCl3 sample. [ABSTRACT FROM AUTHOR]

Bismuth sulfide (Bi2S3) is a promising thermoelectric material with earth‐abundant, low‐cost, and environment‐friendly constituents. However, it shows poor thermoelectric performance due to its extremely low electrical conductivity derived from the low electron concentration. Here, a high‐performance Bi2S3‐based material is reported to benefit from the Fermi level tuning by Ag and Cl co‐doping and defect engineering by introducing dense low‐angle grain boundaries. Both Ag and Cl act as donors in Bi2S3, upshifting the Fermi level. This increases the electron concentration without degrading the electron mobility, thereby obtaining improved electrical conductivity. The electron localization function (ELF) contour map indicates that interstitial Ag causes electron delocalization, showing higher electron mobility in Bi2S3. More importantly, dense low‐angle grain boundaries block phonon propagation, yielding an ultralow lattice thermal conductivity of 0.30 W m−1 K−1. Consequently, a record ZT value of ≈0.9 at 676 K is achieved in the Bi2Ag0.01S3‐0.5%BiCl3 sample. [ABSTRACT FROM AUTHOR]

Anomalous thermal transport of Cs2NaYbCl6 double‐halide perovskite above room temperature is reported and rationalized. Calculations of phonon dispersion relations and scattering rates up to the fourth order in lattice anharmonicity have been conducted to determine their effective dependence on temperature. These findings show that specific phonon group velocities and lifetimes increase if the temperature is raised above 500 K. This, in combination with anharmonicity, provides the microscopic mechanism responsible for the increase in lattice thermal conductivity at high temperatures, contrary to the predictions of phonon transport theories based on solely cubic anharmonicity. The model accurately and quantitatively reproduces the experimental thermal conductivity data as a function of temperature. [ABSTRACT FROM AUTHOR]

Anomalous thermal transport of Cs2NaYbCl6 double‐halide perovskite above room temperature is reported and rationalized. Calculations of phonon dispersion relations and scattering rates up to the fourth order in lattice anharmonicity have been conducted to determine their effective dependence on temperature. These findings show that specific phonon group velocities and lifetimes increase if the temperature is raised above 500 K. This, in combination with anharmonicity, provides the microscopic mechanism responsible for the increase in lattice thermal conductivity at high temperatures, contrary to the predictions of phonon transport theories based on solely cubic anharmonicity. The model accurately and quantitatively reproduces the experimental thermal conductivity data as a function of temperature. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) reinforced polymer nanocomposites with high thermal conductivity show a promising prospect in thermal management of next‐generation electronic devices due to their excellent mechanical adaptability, outstanding processability, and superior flexibility. However, interfacial thermal resistance between individual CNT significantly hinders the further improvement in thermal conductivity of CNT‐reinforced nanocomposites. Herein, an interfacial welding strategy is reported to construct graphitic structure welded CNT (GS‐w‐CNT) networks. Notably, the obtained GS‐w‐CNT/polydimethylsiloxane (PDMS) nanocomposite with a GS loading of 4.75 wt% preserves a high thermal conductivity of 5.58 W m−1 K−1 with a 410% enhancement as compared to a pure CNT/PDMS nanocomposite. Molecular dynamics simulations are utilized to elucidate the effect of interfacial welding on the heat transfer behavior, revealing that the GS welding degree plays an important role in reducing both phonon scattering in the GS‐w‐CNT structure and interfacial thermal resistance at the interfaces between CNT. The unique welding strategy provides a new route to optimize the thermal transport performance in filler reinforced polymer nanocomposites, promoting their applications in next‐generation microelectronic devices. [ABSTRACT FROM AUTHOR]

Thermal processes play a crucial role in a variety of applications ranging from thermoelectrics, to thermal barrier coatings for turbines to memory devices, where materials with low thermal conductivity κ are essential for energy savings. By comparing two phase‐change materials, Ge2Sb2Te5$\left(\text{Ge}\right)_{2} \left(\text{Sb}\right)_{2} \left(\text{Te}\right)_{5}$ and Ga2Te3$\left(\text{Ga}\right)_{2} \left(\text{Te}\right)_{3}$, that have very similar thermal conductivities despite very different structures and bond strengths, it is argued that their phonon‐glass electron‐crystal properties stem from randomly oriented nonbonding lone–pair orbitals subtended at chalcogen atoms surrounding intrinsic vacancies. [ABSTRACT FROM AUTHOR]

Herein, the synthesis of high‐entropy wolframite oxide (CoCuNiFeZn)1‐xGaxWO4 through standard solid‐state route followed by spark plasma sintering and their structural, microstructural, and thermoelectric (TE) properties are investigated. X‐ray diffraction pattern followed by patterns matching refinement shows a monoclinic structure with the volume of the unit cell decreasing with increasing Ga content. The optical bandgap for these oxides shows a cocktail effect in high‐entropy configuration. The Seebeck coefficient indicates electrons as dominating charge carriers with a nondegenerate behavior. The electrical resistivity decreases with increasing temperature depicting a semiconducting nature. Thermal conductivity in high‐entropy samples (κ ≈ 2.1 W m−1 K−1 @ 300 K) is significantly lower as compared to MgWO4 (κ ≈ 11.5 W m−1 K−1 @ 300 K), which can be explained by the strong phonon scattering due to large lattice disorder in high‐entropy configuration. The TE figure of merit zT increases with Ga doping via modifying all three TE parameters positively. [ABSTRACT FROM AUTHOR]

Lattice thermal conductivity (κL) of the hexagon‐shaped nanocrystals cluster of Bi2Se3, prepared by the hot‐injection technique using nontoxic solvents, is studied. From the temperature‐dependent Raman spectra of Bi2Se3 nanocrystals, the average Debye temperature (θD) and Gruneisen parameter (γ) are calculated by adopting the bond‐order–length–strength correlation theory. The average room temperature κL of Bi2Se3 nanocrystals evaluated from the Slack model using θD and γ is ≈1.1 Wm−1K−1. The κL of Bi2Se3 nanocrystals is larger than out‐of‐plane κL (≈0.4 Wm−1K−1) but close to the in‐plane κL (≈1.4 Wm−1K−1) simulated using the Boltzmann transport equation for phonon with three‐phonon scatterings. Nanostructuring introduces grain boundaries in the Bi2Se3 that block the long mean free path of phonons physically, reduces the phonon mean free path, and decreases the κL. The anisotropic phonon scattering introduced by the weak van der Waals force between adjacent quintuple layers in the out‐of‐plane direction, in addition to the acoustic–optical phonon scattering and anharmonicity, hinders the efficient transport of thermal energy in the Bi2Se3 and results in a lower κL. By utilizing materials with anisotropic thermal conductivity, thermoelectric devices can be designed to preferentially conduct heat in specific directions while minimizing heat loss in others. [ABSTRACT FROM AUTHOR]

Herein, the synthesis of high‐entropy wolframite oxide (CoCuNiFeZn)1‐xGaxWO4 through standard solid‐state route followed by spark plasma sintering and their structural, microstructural, and thermoelectric (TE) properties are investigated. X‐ray diffraction pattern followed by patterns matching refinement shows a monoclinic structure with the volume of the unit cell decreasing with increasing Ga content. The optical bandgap for these oxides shows a cocktail effect in high‐entropy configuration. The Seebeck coefficient indicates electrons as dominating charge carriers with a nondegenerate behavior. The electrical resistivity decreases with increasing temperature depicting a semiconducting nature. Thermal conductivity in high‐entropy samples (κ ≈ 2.1 W m−1 K−1 @ 300 K) is significantly lower as compared to MgWO4 (κ ≈ 11.5 W m−1 K−1 @ 300 K), which can be explained by the strong phonon scattering due to large lattice disorder in high‐entropy configuration. The TE figure of merit zT increases with Ga doping via modifying all three TE parameters positively. [ABSTRACT FROM AUTHOR]

Since the lattice thermal conductivity of thermoelectric materials is a relatively independent parameter, exploring semiconductor materials with intrinsically low lattice thermal conductivity is an important direction in the field of thermoelectric research. Herein, a high figure of merit ZT of 1.23 at 873 K and an exceptionally low lattice thermal conductivity of 0.18 W m−1 K−1 are realized in the n‐type CuIn7Se11 compound for the first time. The weak In─Se chemical bonds induce strong coupling between acoustic phonon and optical phonon with low frequency, leading to low sound velocity. The highly disordered configuration of Cu, In, and vacancies at In2, In3, and M sites, in conjunction with atomic‐scale slips and flips intensify phonon scattering. All these result in an intrinsically low thermal conductivity of the CuIn7Se11 compound. DFT calculation reveals that the density of states at the bottom of the conduction band is mainly contributed by the coupling between 4p orbitals of Se atoms and 5s orbitals of In atoms, featuring with a small effective mass. This small effective mass of charge carrier renders the CuIn7Se11 compound high carrier mobility of 435 cm2 V−1 s−1 at 300 K. Consequently, the CuIn7Se11 compound possesses an extraordinary thermoelectric performance [ABSTRACT FROM AUTHOR]

The polycrystalline pellet of La2‐xSrxCuO4 with x = 0.04, has been sintered using the solid‐state reaction process. X‐ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) have been carried out for microstructural characterizations. The transport properties (electrical and thermal) of La2‐xSrxCuO4 for x = 0.04 have been investigated in the temperature range between 15 and 300 K with the aid of a closed‐cycle refrigerator (CCR). The DC four‐probe resistivity measurement confirms a decrease in resistivity with increasing temperature below 200 K. However, above 200 K, an increase in resistivity with temperature (metallic behaviour) has been noticed due to charge carrier localization. The Hall measurement conveys hole‐type conduction and phonon‐dominated mobility with carrier concentration ~1018/cm3, which lie somewhere between non‐degenerate and degenerate limit. The Seebeck coefficient also confirms hole type conduction and its temperature dependence can be explained in the light of the model applicable for mixed‐valence heavy fermions systems. The steady‐state method for thermal conductivity measurement has been employed. The plot of thermal conductivity (λ) as a function of temperature (T) shows a hump‐like structure at around 65 K, which may be attributed to an increase in the quasi‐particle mean free path. Further, the electronic and lattice (phononic) contributions to thermal conductivity have been separated using electrical conductivity data with the help of the Wiedemann‐Franz law. Our analysis confirms the phononic dominance in the thermal conductivity of the investigated sample. The figure of merit (ZT) estimated from the experimental data has a maximum value of 0.086 at 290 K and hence shows its inherent energy harvesting properties that can further be stored in a battery or capacitor. [ABSTRACT FROM AUTHOR]