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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]

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]

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]

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]

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]

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]

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]

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]

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]

Introducing nanostructures into bulk thermoelectric materials is an effective strategy for reducing lattice thermal conductivity (κlat). However, large numbers of hanging bonds emerge on account of lattice mismatch usually at the interfaces between nanostructures and matrix, thereby significantly deteriorating carrier mobility (µH) and seriously limiting thermoelectric performance. Here, utilizing the cointroduction of Gd‐Cu2Te into n‐type PbSe as a paradigm, the zT could be greatly improved. The conduction band flattening caused by Gd doping can successfully compensate for the small Seebeck coefficient in n‐type PbSe, thus achieving extraordinary electrical performance. Further advanced electron microscopy and X‐ray absorption fine structure spectra directly demonstrate that most of the Cu forms nanoscale Cu2Se precipitates, especially a unique semi‐coherent interface between the PbSe matrix and the Cu2Se nanoprecipitate is observed for the first time. Such nanoprecipitate accompanied by the semi‐coherent interface not only ensures higher µH as an excellent charge transfer mediator but also collectively scatters the heat‐carrying phonons over a wide frequency range to obtain the ultralow κlat, resulting in the prominent improvement of the ratio µH/κlat. The present finding represents an important step forward in electron–phonon decoupling via constructing semi‐coherent nanostructure and interface engineering, which should be applicable for other thermoelectric materials. [ABSTRACT FROM AUTHOR]

ZnO is a promising high‐temperature thermoelectric (TE) material due to its superior stability and earth abundance. However, the coupling relation between Seebeck coefficient and electrical conductivity on carrier concentration limits the optimum TE performance for most TE materials, especially ZnO. Herein, enhancement of TE performance is achieved via a stepwise optimization strategy composed of carrier concentration optimization and carrier filtering effect for fabricating robust ZnO‐based composite ceramics through a self‐developed specific high‐pressure synthesis followed by spark plasma sintering. Specifically, doping SnO2 provide substantial electrons to surge the carrier concentration. The subsequent compositing Si3N4 nanoparticles results in the unique reaction‐generated Zn2SiO4 nanoprecipitates with a larger bandgap and intrinsically low thermal conductivity, which introduce an excellent carrier filtering effect to increase the Seebeck coefficient by 57.7% at 300 K without compromising electrical conductivity much and enhance phonon scattering to cause an ultralow lattice thermal conductivity of 1.39 W m−1 K−1 achieving amorphous limits of ZnO (1.4±0.1 W m−1 K−1). Consequently, a high peak ZT (figure of merit) of 0.691 at 873 K is obtained, which is higher than that of previously reported ZnO‐based TE materials. This work demonstrates a feasible and effective strategy to fabricate high‐performance TE materials, especially those with inferior electrical conductivity. [ABSTRACT FROM AUTHOR]

Bismuth‐telluride‐based alloy is the sole thermoelectric candidate for commercial thermoelectric application in low‐grade waste heat harvest near room temperature, but the sharp drop of thermoelectric properties at higher temperature and weak mechanical strength in zone‐melted material are the main obstacles to its wide development for power generation. Herein, an effective approach is reported to improve the thermoelectric performance of p‐type Bi0.42Sb1.58Te3 hot‐pressed sample by incorporating Ag5SbSe4. A peak ZT of 1.40 at 375 K and a high average ZT of 1.25 between 300 and 500 K are achieved. Such outstanding thermoelectric performance originates from the synergistic effects of improved density‐of‐states effective mass, reduced bipolar thermal conductivity by the boosted carrier concentration, and suppressed lattice thermal conductivity by the induced phonon scattering centers including substitute point defects, dislocations, stress–strain clusters, and grain boundaries. Comprised of the p‐type Bi0.42Sb1.58Te3 + 0.10 wt% Ag5SbSe4 and zone‐melted n‐type Bi2Te2.7Se0.3, the thermoelectric module exhibits a high conversion efficiency of 6.5% at a temperature gradient of 200 K, indicating promising applications for low‐grade heat harvest near room temperature. [ABSTRACT FROM AUTHOR]

The atomic‐scale structure of cuprous selenide room temperature phase (α‐Cu2Se), which plays an important role in understanding the mechanism of its high thermoelectric performance, is still not fully determined. Here, direct observation with atomic‐scale resolution is realized to reveal the fine structure of α‐Cu2Se via spherical‐aberration‐corrected scanning transmission electron microscopy. It is observed to be an interesting self‐independent binary‐sublattice construction for Cu and Se in α‐Cu2Se, respectively, which shows a variety of ordered copper fluctuation structures are embedded in a rigid pseudo‐cubic Se sublattice. Ordering of Cu uses a variety of configurations with little energy difference, forming considerable amounts of "boundaries," which may lead to ultrastrong phonon scattering. Furthermore, density functional theory calculations indicate that the electronic structures are mainly determined by the rigid Se face‐centered cubic sublattice and not sensitive to the various copper fluctuations, which may guarantee the electron transfers with large carrier mobility. The self‐independent binary‐sublattice construction is speculated to enhance phonon scattering while still maintaining good electrical transport property. This study provides new critical information for further understanding the possible correlation between the specific structure and thermoelectric performance of α‐Cu2Se, as well as designing new thermoelectric materials. [ABSTRACT FROM AUTHOR]

Balancing the contradictory relationship between thermoelectric parameters, such as effective mass and carrier mobility, is a challenge to optimize thermoelectric performance. Herein, the exceptional thermoelectric performance is realized in GeTe through collaboratively optimizing the carrier and phonon transport via stepwise alloying Pb and CuSbSe2. The formation energy of Ge vacancy is efficiently bolstered by alloying Pb, which reduces carrier density and carrier scattering to maintain superior carrier mobility in GeTe. Additionally, CuSbSe2, acting as an n‐type dopant, further modulates carrier density and validly equilibrates carrier mobility and effective mass. Accordingly, the promising power factor of 45 µW cm−1 K−2 is achieved at 723 K. Meanwhile, point defects are found to significantly suppress phonons transport to descend lattice thermal conductivity by Pb and CuSbSe2 alloying, which barely impacts the carrier mobility. A combination with superior carrier mobility and lower lattice thermal conductivity, a maximum ZT of 2.2 is attained in Ge0.925Pb0.075Cu0.005Sb0.005TeSe0.01, which corresponds to a 100% promotion compared with that of intrinsic GeTe. This study provides a new indicator for optimizing carrier and phonon transport properties by balancing interrelated thermoelectric parameters. [ABSTRACT FROM AUTHOR]

Balancing the contradictory relationship between thermoelectric parameters, such as effective mass and carrier mobility, is a challenge to optimize thermoelectric performance. Herein, the exceptional thermoelectric performance is realized in GeTe through collaboratively optimizing the carrier and phonon transport via stepwise alloying Pb and CuSbSe2. The formation energy of Ge vacancy is efficiently bolstered by alloying Pb, which reduces carrier density and carrier scattering to maintain superior carrier mobility in GeTe. Additionally, CuSbSe2, acting as an n‐type dopant, further modulates carrier density and validly equilibrates carrier mobility and effective mass. Accordingly, the promising power factor of 45 µW cm−1 K−2 is achieved at 723 K. Meanwhile, point defects are found to significantly suppress phonons transport to descend lattice thermal conductivity by Pb and CuSbSe2 alloying, which barely impacts the carrier mobility. A combination with superior carrier mobility and lower lattice thermal conductivity, a maximum ZT of 2.2 is attained in Ge0.925Pb0.075Cu0.005Sb0.005TeSe0.01, which corresponds to a 100% promotion compared with that of intrinsic GeTe. This study provides a new indicator for optimizing carrier and phonon transport properties by balancing interrelated thermoelectric parameters. [ABSTRACT FROM AUTHOR]

Thermal conductivity, which measures the ease at which heat passes through a crystalline solid, is controlled by the nature of the chemical bonding and periodicity in the solid. This necessitates an in‐depth understanding of the crystal structure and chemical bonding to tailor materials with notable lattice thermal conductivity (κL). Herein, the nature of chemical bonding and its influence on the thermal transport properties (2–523 K) of all‐inorganic halide perovskite Cs3Bi2I9 are studied. The κL exhibits an ultralow value of ≈0.20 W m−1K−1 in 30–523 K temperature range. The antibonding states just below the Fermi level in the electronic structure arising from the interaction between bismuth 6s and iodine 5p orbitals, weakens the bond and causes soft elasticity in Cs3Bi2I9. First‐principles density functional theory (DFT) calculations reveal highly localized soft optical phonon modes originating from Cs‐rattling and dynamic double octahedral distortion of 0D [Bi2I9]3− in Cs3Bi2I9. These low energy nearly flat optical phonons strongly interact with transverse acoustic modes creating an ultrashort phonon lifetime of ≈1 ps. While the presence of extended antibonding states gives rise to soft anharmonic lattice; Cs rattling provides sharp localized optical phonon modes, which altogether result in strong lattice anharmonicity and ultralow κL. [ABSTRACT FROM AUTHOR]

Layered van der Waals (vdW) magnets are prominent playgrounds for developing magnetoelectric, magneto‐optic, and spintronic devices. In spintronics, particularly in spincaloritronic applications, low thermal conductivity (κ) is highly desired. Herein, by combining thermal transport measurements with density functional theory calculations, this study demonstrates low κ down to 1 W m−1 K−1 in a typical vdW ferromagnet Cr2Si2Te6. In the paramagnetic state, development of magnetic fluctuations way above Tc = 33 K strongly reduces κ via spin‐phonon scattering, leading to low κ ≈ 1 W m−1 K−1 over a wide temperature range, in comparable to that of amorphous silica. In the magnetically ordered state, emergence of resonant magnon‐phonon scattering limits κ below ≈2 W m−1 K−1, which will be three times larger if magnetic scatterings are absent. Application of magnetic fields strongly suppresses the spin‐phonon scattering, giving rise to large enhancements of κ. This study's calculations well capture these complex behaviors of κ by taking the temperature‐ and magnetic‐field‐dependent spin‐phonon scattering into account. Realization of low κ, which is easily tunable by magnetic fields in Cr2Si2Te6, may further promote spincaloritronic applications of vdW magnets. This study's theoretical approach may also provide a generic understanding of spin‐phonon scattering, which appears to play important roles in various systems. [ABSTRACT FROM AUTHOR]

Layered van der Waals (vdW) magnets are prominent playgrounds for developing magnetoelectric, magneto‐optic, and spintronic devices. In spintronics, particularly in spincaloritronic applications, low thermal conductivity (κ) is highly desired. Herein, by combining thermal transport measurements with density functional theory calculations, this study demonstrates low κ down to 1 W m−1 K−1 in a typical vdW ferromagnet Cr2Si2Te6. In the paramagnetic state, development of magnetic fluctuations way above Tc = 33 K strongly reduces κ via spin‐phonon scattering, leading to low κ ≈ 1 W m−1 K−1 over a wide temperature range, in comparable to that of amorphous silica. In the magnetically ordered state, emergence of resonant magnon‐phonon scattering limits κ below ≈2 W m−1 K−1, which will be three times larger if magnetic scatterings are absent. Application of magnetic fields strongly suppresses the spin‐phonon scattering, giving rise to large enhancements of κ. This study's calculations well capture these complex behaviors of κ by taking the temperature‐ and magnetic‐field‐dependent spin‐phonon scattering into account. Realization of low κ, which is easily tunable by magnetic fields in Cr2Si2Te6, may further promote spincaloritronic applications of vdW magnets. This study's theoretical approach may also provide a generic understanding of spin‐phonon scattering, which appears to play important roles in various systems. [ABSTRACT FROM AUTHOR]

Thermal transport in amorphous lithium‐sulfur (a‐LixS) is systematically investigated using molecular dynamics and the contributions from different types of heat carriers are quantitatively evaluated. In general, the thermal conductivity (TC) of a‐LixS changes largely by varying the concentration (x) of Li ions in a‐LixS. Interestingly, the TC of a‐LixS shows three distinct regimes of dependence on Li concentration. For low Li concentration (x = 0.4–1.2), the TC grows slowly, followed by a rapid increase in TC for medium Li concentration (x = 1.2–1.6), where the growth rate is three times that of the first regime, and finally, the TC is independent of Li concentration (x = 1.6–2.0). The TC enhancement in the first and second regimes is mainly attributed to propagating and non‐propagating vibrational modes in a‐LixS, respectively. In contrast, the stable thermal transport regime is governed by the competition between propagating and non‐propagating phonons. These investigations provide quantitative TC data of various polysulfides for shuttling analysis, and a fundamental understanding of the thermal transport mechanism of complex a‐LixS structures, which is beneficial for the rational design of thermal management of Li‐S batteries. [ABSTRACT FROM AUTHOR]

A unique strain‐mediated lattice rotation strategy is introduced via nanocompositing to upsurge the optimized limits in the composition‐to‐structural pathway on rationally engineering the efficient thermoelectric material. In this study, a special lattice rotation via strain engineering is realized to optimize the desired electronic and chemical environment for enhancing thermoelectric properties in n‐type Bi2S2Se. This approach results in a unique transport phenomenon to assist high‐energy electrons in transferring through the optimized transport channels, and appropriate structure disparity to significantly localize phonons. As a result, Sb over Cl doping in Bi2S2Se gently reduces Eg and introduces defect states in bandgap with shifting down the Fermi level, thus causing increase in carrier concentration, which contributes to a higher power factor of ≈7.18 µW cm−1 K−2 (at T = 773 K). Besides, a lower thermal conductivity of ≈0.49 W m−1 K−1 is driven through lattice strain and defect engineering. Consequently, an ultra‐high ZTmax = 1.13 (at T = 773 K) and a high ZTave = 0.54 (323 K‐773 K) are realized. This study not only leads to an extraordinary thermoelectric performance but also reveals a unique paradigm for electron transportation and phonon localization via lattice strain engineering. [ABSTRACT FROM AUTHOR]

The development of environmentally benign thermoelectric materials with high energy conversion efficiency (ZT) continues to be a long‐standing challenge. So far, high ZT has been achieved using heavy elements to reduce lattice thermal conductivity (κlat). However, it is not preferred to use such elements because of their environmental load and high material cost. Here a new approach utilizing hydride anion (H−) substitution to oxide ion is proposed for ZT enhancement in thermoelectric oxide SrTiO3 bulk polycrystals. Light element H− substitution largely reduces κlat from 8.2 W/(mK) of SrTiO3 to 3.5 W/(mK) for SrTiO3−xHx with x = 0.216. The mass difference effect on phonon scattering is small in the SrTiO3−xHx, while local structure distortion arising from the distributed Ti−(O,H) bond lengths strongly enhances phonon scattering. The polycrystalline SrTiO3−xHx shows high electronic conductivity comparable to La‐doped SrTiO3 single crystal because the H− substitution does not form a grain boundary potential barrier and thus suppresses electron scattering. As a consequence, SrTiO3−xHx bulk exhibits maximum ZT = 0.11 at room temperature and the ZT value increases continuously up to 0.22 at T = 657 K. The H− substitution idea offers a new approach for ZT enhancement in thermoelectric materials without utilizing heavy elements. [ABSTRACT FROM AUTHOR]

Dense point defects can strengthen phonon scattering to reduce the lattice thermal conductivity and induce outstanding thermoelectric performance in GeTe‐based materials. However, extra point defects inevitably enlarge carrier scattering and deteriorate carrier mobility. Herein, it is found that the interstitial Cu in GeTe can result in synergistic effects, which include: 1) strengthened phonon scattering, leading to ultralow lattice thermal conductivity of 0.48 W m−1 K−1 at 623 K; 2) weakened carrier scattering, contributing to high carrier mobility of 80 cm2 V−1 s−1 at 300 K; 3) optimized carrier concentration of 1.22 × 1020 cm−3. Correspondingly, a high figure‐of‐merit of ≈2.3 at 623 K can be obtained in the Ge0.93Ti0.01Bi0.06Te‐0.01Cu, which corresponds to a maximum energy conversion efficiency of ≈10% at a temperature difference of 423 K. This study systematically investigates the doping behavior of the interstitial Cu in GeTe‐based thermoelectric materials for the first time and demonstrates that the localized interstitial Cu is a new strategy to enhance the thermoelectric performance of GeTe‐based thermoelectric materials. [ABSTRACT FROM AUTHOR]

The soft and polar nature of quasi‐2D (PEA)2PbBr4 perovskite, and robust photo‐generated excitons lead exciton‐polaritons and exciton‐polarons as the important phenomena near the band edge for application in the lighting aspect. In this work, a convenient methodology is proposed based on the polariton resonant modes in temperature‐dependent (77 K to RT) spectroscopy, and investigate the effect of these quasi‐particles on refractive index dispersion. The large binding energy (≈335 meV) of quasi‐2D excitons is obtained by the reflectance measurements at 77 K. Stable exciton‐polaritons and exciton‐polarons are confirmed by energy dispersions and the observation of self‐trapped exciton‐polaron state, respectively. Furthermore, the large negative thermal‐optic coefficient due to damping effect of exciton‐phonon scattering is observed. The phenomenon is opposite to those observed in conventional semiconductors (e.g., Si, Ge, GaN, AlN, GaAs, AlAs, and ZnO etc.). The observed stable negative thermal‐optic coefficients from 160 K to RT indicate that the quasi‐2D perovskite can be used as a phase compensator for conventional semiconductor materials. [ABSTRACT FROM AUTHOR]

Composite engineering favors high thermoelectric performance by tuning the carrier and phonon transport. Herein, orthorhombic and rhombohedral dual‐phase GeSe are designed in situ by tailoring chemical bonds. Atom probe tomography verifies the coexistence of a covalently bonded orthorhombic phase and a metavalently bonded rhombohedral phase in GeSe‐InTe alloys. The production of the rhombohedral phase simultaneously increases the carrier concentration, the carrier mobility, the band degeneracy, and the density‐of‐states effective mass due to the reduced formation energy of cation vacancies and the improved crystal symmetry. These attributes are beneficial to a high‐power factor. In addition, the thermal conductivity can be significantly reduced due to the intrinsically strong lattice anharmonicity of the metavalently bonded phase, the interfacial acoustic phonon mismatch across different bonding mechanisms, and the phonon scattering at vacancy‐solute clusters. Moreover, the metavalently bonded phase embraces higher solubility of dopants that enables the further optimization of properties by Cd‐Ag doping, resulting in a zT of 0.95 at 773 K as well as enhanced strength and ductility in dual‐phase Ge0.94Cd0.03Ag0.03Se(InTe)0.15. This work indicates that in situ design of dual‐phase composites by tailoring chemical bonds is an effective method for enhancing the thermoelectric and mechanical properties of GeSe and other p‐bonded chalcogenides. [ABSTRACT FROM AUTHOR]

The lattice thermal conductivity (κph) of metals and semimetals is limited by phonon‐phonon scattering at high temperatures and by electron‐phonon scattering at low temperatures or in some systems with weak phonon‐phonon scattering. Following the demonstration of a phonon band engineering approach to achieve an unusually high κph in semiconducting cubic‐boron arsenide (c‐BAs), recent theories have predicted ultrahigh κph of the semimetal tantalum nitride in the θ‐phase (θ‐TaN) with hexagonal tungsten carbide (WC) structure due to the combination of a small electron density of states near the Fermi level and a large phonon band gap, which suppress electron‐phonon and three‐phonon scattering, respectively. Here, measurements on the thermal and electrical transport properties of polycrystalline θ‐TaN converted from the ε phase via high‐pressure synthesis are reported. The measured thermal conductivity of the θ‐TaN samples shows weak temperature dependence above 200 K and reaches up to 90 Wm−1K−1, one order of magnitude higher than values reported for polycrystalline ε‐TaN and δ‐TaN thin films. These results agree with theoretical calculations that account for phonon scattering by 100 nm‐level grains and suggest κph increase above the 249 Wm−1 K−1 value predicted for single‐crystal WC when the grain size of θ‐TaN is increased above 400 nm. [ABSTRACT FROM AUTHOR]

The good co‐existence of midgap state and valence band degeneracy is realized in Bi‐alloyed GeTe through the In‐Cd codoping to play different but complementary roles in the valence band structure modification. In doping induces midgap state and results in a considerably improved Seebeck coefficient near room temperature, while Cd doping significantly increases the Seebeck coefficient in the mid‐high temperature region by promoting the valence band convergence. The synergistic effects obviously increase the density of state effective mass from 1.39 to 2.65 m0, and the corresponding carrier mobility still reaches 34.3 cm2 V−1 s−1 at room temperature. Moreover, the Bi‐In‐Cd co‐alloying introduces various phonon scattering centers including nanoprecipitates and strain field fluctuations and suppresses the lattice thermal conductivity to a rather low value of 0.56 W m−1 K−1 at 600 K. As a result, the Ge0.89Bi0.06In0.01Cd0.04Te sample obtains excellent thermoelectric properties of zTmax ≈2.12 at 650 K and zTavg ≈1.43 between 300 and 773 K. This study illustrates that the thermoelectric performance of GeTe can be optimized in a wide temperature range through the synergy of midgap state and valence band convergence. [ABSTRACT FROM AUTHOR]

Synergetic optimization of electrical and thermal transport properties is achieved for SnTe‐based nano‐crystalline materials. Gd doping is able to suppress the Sn vacancy, which is confirmed by positron annihilation measurements and corresponding theoretical calculations. Hence, the optimal hole carrier concentration is obtained, leading to the improvement of electrical transport performance and simultaneous decrease of electronic thermal conductivity. In addition, the incremental density of states effective mass m* in SnTe is realized by the promotion of the band convergence via Gd doping, which is further confirmed by the band structure calculation. Hence, the enhancement of the Seebeck coefficient is also achieved, leading to a high power factor of 2922 µW m−1 K−2 for Sn0.96Gd0.04Te at 900 K. Meanwhile, substantial suppression of the lattice thermal conductivity is observed in Gd‐doped SnTe, which is originated from enhanced phonon scattering by multiple processes including mass and strain fluctuations due to the Gd doping, scattering of grain boundaries, nano‐pores, and secondary phases induced by Gd doping. With the decreased phonon mean free path and reduced average phonon group velocity, a rather low lattice thermal conductivity is achieved. As a result, the synergetic optimization of the electric and thermal transport properties contributes to a rather high ZT value of ≈1.5 at 900 K, leading to the superior thermoelectric performance of SnTe‐based nanoscale polycrystalline materials. [ABSTRACT FROM AUTHOR]

Temperature variation‐induced thermoelectric catalytic efficiency of thermoelectric material is simultaneously restricted by its electrical conductivity, Seebeck coefficient, and thermal conductivity. Herein, Bi2Te3 nanosheets are in situ grown on reduced graphene oxides (rGO) to generate an efficient photo‐thermoelectric catalyst (rGO‐Bi2Te3). This system exhibits phonon scattering effect and extra carrier transport channels induced by the formed heterointerface between rGO and Bi2Te3, which improves the power factor value and reduces thermal conductivity, thus enhancing the thermoelectric performance of 2.13 times than single Bi2Te3. The photo‐thermoelectric catalysis of rGO‐Bi2Te3 significantly improves the reactive oxygen species yields, resulting from the effective electron–hole separation caused by the unique thermoelectric field and heterointerfaces of rGO‐Bi2Te3. Correspondingly, the electrospinning membranes containing rGO‐Bi2Te3 nanosheets exhibit high antibacterial efficiency in vivo (99.35 ± 0.29%), accelerated tissue repair ability, and excellent biosafety. This study provides an insight into heterointerface design in photo‐thermoelectric catalysis. [ABSTRACT FROM AUTHOR]

Efficient thermoelectric (TE) conversion of waste heat to usable energy is a holy grail promising to address major societal issues related to energy crisis and global heat management. For these to be economical, synthesis of a solid‐state material with a high figure‐of‐merit (ZT) values is the key, with characterization methods quantifying TE and heat transport properties being indispensable for guiding the development of such materials. In the present study, a large enhancement of the TE power factor in Sb2Te3/MoS2 multilayer structures is reported. A new approach is used to simultaneously experimentally determine the values of in‐plane (kxy) and out‐of‐pane (kz) thermal conductivities for multilayer samples with characteristic layer thickness of few nanometres, essential for the quantification of the ZT, the key parameter for the TE material. Combining simultaneous enhancement in the value of in‐plane power factor (to (4.9 ± 0.4) × mWm−1 K−2) and reduction of the in‐plane value of the thermal conductivity (to 0.7 ± 0.1 Wm−1 K−1) for Sb2Te3/MoS2 multilayer sample led to high values of ZT of 2.08 ± 0.37 at room temperature. The present study, therefore, sets the foundation for a new methodology of exploiting the properties of 2D/3D interfaces for the development of novel fully viable thermoelectric materials. [ABSTRACT FROM AUTHOR]

Cationic doping is mainly used to improve the performance of rocksalt‐structured GeTe thermoelectric materials. However, its counterpart anionic doping is scarcely facilitated. Here, a comprehensive discussion is provided on doping at the anion site of rocksalt‐structured thermoelectric materials, surrounding its influence on bonding mechanisms, carrier and phonon transport characteristics, and thermoelectric figure‐of‐merit. To verify the viewpoint, a modified flux‐assist method is adopted to synthesize anionic Iodine (I) doped GeTe samples, which show comparably optimized electrical and thermal properties with that of cationic Antimony (Sb) or Bismuth (Bi) doped GeTe samples. Further combining cationic Bi and anionic I co‐doping, an enhanced figure‐of‐merit from 0.8 in pristine GeTe to 2.5 at 675 K can be realized in 8% (Bi and I) co‐doped GeTe, which corresponds to a maximum heat‐to‐electricity conversion efficiency of 14.6% under a temperature difference of 430 K. This study rationalizes the influence of anionic doping on the electrical and thermal properties of the rocksalt‐structured materials, which serves as an effective yet previously neglected strategy toward high‐performance GeTe thermoelectrics. [ABSTRACT FROM AUTHOR]

SnTe is an emerging Pb‐free thermoelectric compound that has drawn significant attention for clean energy conversion. Chemical doping is routinely used to tailor its charge carrier concentration and electronic band structures. However, the efficacy of dopants is often limited by their small solubility. For example, only 0.5% Ag can be incorporated into the SnTe matrix. Yet, significantly more Ag (>7%) can be dissolved if SnTe is alloyed with AgSbTe2. This large enhancement of solubility can be understood from a chemical bonding perspective. Both SnTe and AgSbTe2 employ metavalent bonding as identified by an unusual bond‐rupture in atom probe tomography. Density functional theory calculations show that upon Ag doping the energy offset of the upmost two valence bands decreases significantly. This induces band alignment in SnTe, which results in an enhanced power factor over a broad temperature range. Moreover, the increased concentration of point defects and associated lattice strain lead to strong phonon scattering and softening, contributing to an extremely low κL of 0.30 Wm−1K−1. These synergistic effects contribute to a peak ZT of 1.8 at 873 K and a record‐high average ZT of ≈1.0 between 400 and 873 K in Sn0.87Mn0.08Sb0.08Te–5%AgSbTe2 alloy. [ABSTRACT FROM AUTHOR]

Although the twisting strategy has provided great opportunities to tune the electronic and optical properties of materials, little research has been done on how twisting affects phonon properties. Using machine‐learning‐based interatomic potentials within DFT‐level quality and the perturbation theory to the fourth‐order anharmonicity, the phonon transport properties are studied and the phonon behaviors of layered material Bi2O2Se when twisting is applied. It is found that the phonons of Bi2O2Se exhibit hardening effects at finite temperature, and the intrinsic lattice thermal conductivity along the out‐of‐plane (in‐plane) direction is reduced to 3.21 (3.42) W/mK from 3.69 (4.55) W/mK at 300 K by including the four‐phonon scattering. When introducing the twisting between the layers, the out‐of‐plane thermal conductivity can be further reduced by 83% as compared to that of the twist‐free configuration. Such huge reduction of the thermal conductivity arises from the nearly flat acoustic phonon branches and the enhanced third‐ and fourth‐order phonon anharmonicity due to the strong coupling between the twisted layers. These findings unravel that twisting is an effective strategy for tuning phonon band structure and phonon‐phonon interactions, leading to ultralow lattice thermal conductivity of materials. [ABSTRACT FROM AUTHOR]

High aspect ratio metal nanostructures are commonly found in a broad range of applications such as electronic compute structures and sensing. The self‐heating and elevated temperatures in these structures, however, pose a significant bottleneck to both the reliability and clock frequencies of modern electronic devices. Any notable progress in energy efficiency and speed requires fundamental and tunable thermal transport mechanisms in nanostructured metals. In this work, time‐domain thermoreflectance is used to expose cross‐plane quasi‐ballistic transport in epitaxially grown metallic Ir(001) interposed between Al and MgO(001). Thermal conductivities ranges from roughly 65 (96 in‐plane) to 119 (122 in‐plane) W m−1 K−1 for 25.5–133.0 nm films, respectively. Further, low defects afforded by epitaxial growth are suspected to allow the observation of electron–phonon coupling effects in sub‐20 nm metals with traditionally electron‐mediated thermal transport. Via combined electro‐thermal measurements and phenomenological modeling, the transition is revealed between three modes of cross‐plane heat conduction across different thicknesses and an interplay among them: electron dominant, phonon dominant, and electron–phonon energy conversion dominant. The results substantiate unexplored modes of heat transport in nanostructured metals, the insights of which can be used to develop electro‐thermal solutions for a host of modern microelectronic devices and sensing structures. [ABSTRACT FROM AUTHOR]

The electron–phonon coupling (EPC) in semiconductors is typically much weaker than phonon–phonon scattering and its effect on lattice thermal conductivity κl has long been considered negligible. Herein, using first‐principle calculations, it is discovered that the EPC can be significant or even dominant over the intrinsic phonon–phonon scattering via doping in 2D semiconductor hexagonal boron phosphorus (h‐BP). Filling electron pocket till van Hove singularity gradually strengthens the EPC and consequently diminishes the room‐temperature κl by 25% and 80% for monolayer and bilayer h‐BP, respectively. Strikingly, at high doping levels, the EPC drives phonon transport in bilayer h‐BP to an anomalous regime where κl becomes nearly temperature (T) independent deviated from the intrinsic 1/T trend. This distinctive behavior is governed by the joint effects of horizontal mirror symmetry breaking, and weak phonon–phonon scattering stemming from the predominance of normal processes. Further considering electronic contributions, the abnormal T‐independent thermal conductivity is still reserved, thereby facilitating the experimental exploration of EPC effect on κl. This study unveils the exotic thermal transport phenomenon in one‐atom‐thick 2D semiconductors and offers a unique avenue to manipulate heat flow by externally controlling the EPC, which calls for future experimental verification. [ABSTRACT FROM AUTHOR]

Interfacial thermal resistance plays a critical role in heat dissipation, when the mean free paths of heat energy carriers approach or exceed the characteristic lengths of devices. Deep understanding on electron and phonon scattering, as well as their coupling behaviors are of importance for interfacial heat transport enhancement. In this work, complicated influential mechanisms of interface defects on phonon scattering are studied, from the aspects of both time‐domain thermoreflectance (TDTR) measurements and atomistic simulations. Particularly, this study focuses on the comprehensive influence of inelastic phonon scattering on interfacial thermal conductance (hK) of hexagonal and amorphous boron nitride (BN)/copper (Cu) interfaces with nonreactive and nondiffusive features. The TDTR results imply that the hK of Al/a‐BN/Cu is ≈80% higher than that of Al/h‐BN/Cu counterpart, with the comparable film thicknesses, grain sizes, and interface roughness. Although lower local strain near h‐BN/Cu interface can boost electron–phonon coupling, inelastic phonon scattering at a‐BN/Cu interface may greatly promote the interfacial heat transport. The authors believe multiple phonons scattering accompanied by high‐frequency phonons transformation to low‐frequency phonons within a‐BN may provide more phonon–phonon coupling channels at the a‐BN/Cu interface. The present findings may provide more insights to understand nanoscale heat transport mechanisms at metal/nonmetal interfaces. [ABSTRACT FROM AUTHOR]

The Seebeck coefficient and electrical conductivity are two central quantities to be optimized simultaneously in designing thermoelectric materials, and they are determined by the dynamics of carrier scattering. Here a new regime is uncovered where the presence of multiple electron bands with different effective masses, crossing near the Fermi level, leads to strong energy‐dependent carrier lifetimes due to intrinsic electron–phonon scattering. In this anomalous regime, electrical conductivity decreases with carrier concentration, Seebeck coefficient reverses sign even at high doping, and power factor exhibits an unusual second peak. The origin and magnitude of this effect is explained using a general simplified model as well as first‐principles Boltzmann transport calculations in recently discovered half‐Heusler alloys. General design rules for using this paradigm to engineer enhanced performance in thermoelectric materials are identified. [ABSTRACT FROM AUTHOR]

Alloying scattering of phonons is particularly effective in reducing the thermal conductivity. The alloying model considers the mass and strain fluctuations but the substitutional atoms are assumed to be positioned at the ideal lattice point, i.e., without lattice distortion. In the real case, the existence of the lattice distortion in the alloy is inevitable, and it should have an additional contribution to the phonon scattering. Such an effect, however, is usually ignored and can be partially ascribed to the difficulty of experimentally identifying and quantifying the lattice distortion. In this work, significant distortion of the crystal lattice is directly observed by the scanning transmission electron microscopy in YbCd2Sb2 with multiple elements alloying. These results show that the plane distance of adjacent Ytterbium atoms along the direction b fluctuates in the range between 0.34 and 0.46 nm, a distortion from ≈−11.7% to ≈16.0%. The lattice distortion plays a remarkable role in phonon scattering and substantially reduces the lattice thermal conductivity to ≈0.45 Wm–1 K–1 at 700 K. As a result, a peak zT of ≈1.4 is achieved in (Yb0.9Mg0.1)Cd1.2Mg0.4Zn0.4Sb2. These results indicate that tuning the lattice distortion can be a promising strategy for enhancing thermoelectric performance. [ABSTRACT FROM AUTHOR]

Alloying scattering of phonons is particularly effective in reducing the thermal conductivity. The alloying model considers the mass and strain fluctuations but the substitutional atoms are assumed to be positioned at the ideal lattice point, i.e., without lattice distortion. In the real case, the existence of the lattice distortion in the alloy is inevitable, and it should have an additional contribution to the phonon scattering. Such an effect, however, is usually ignored and can be partially ascribed to the difficulty of experimentally identifying and quantifying the lattice distortion. In this work, significant distortion of the crystal lattice is directly observed by the scanning transmission electron microscopy in YbCd2Sb2 with multiple elements alloying. These results show that the plane distance of adjacent Ytterbium atoms along the direction b fluctuates in the range between 0.34 and 0.46 nm, a distortion from ≈−11.7% to ≈16.0%. The lattice distortion plays a remarkable role in phonon scattering and substantially reduces the lattice thermal conductivity to ≈0.45 Wm–1 K–1 at 700 K. As a result, a peak zT of ≈1.4 is achieved in (Yb0.9Mg0.1)Cd1.2Mg0.4Zn0.4Sb2. These results indicate that tuning the lattice distortion can be a promising strategy for enhancing thermoelectric performance. [ABSTRACT FROM AUTHOR]

As an eco‐friendly oxide‐based thermoelectric material, Bi2O2Se exhibits considerable potential for practical device application, but its low electrical conductivity needs to be further improved to achieve higher thermoelectric performance. Here, a record‐high figure of merit, ZT of >0.7 at 773 K in the shear‐exfoliated nanostructured Bi2O2Se with graphite nanosheets as multifunctional secondary nanoinclusions, is achieved. The introduced graphite nanosheets regularize the arrangement of Bi2O2Se nanograins, strengthen the anisotropy, and act as the "expressway" to improve the electrical conductivity by simultaneously enhancing the electron carrier concentration and mobility of the hybrid materials, leading to a high power factor of ≈6.0 µW cm–1 K–2 at 773 K. Also, the liquid‐phase shear exfoliation refines both graphite and Bi2O2Se into nanosheets. Moreover, the as‐sintered hybrid bulk materials composed of these nanosheets possess dense grain and phase boundaries, as well as various lattice imperfections, such as lattice distortions and stacking faults formed by physical shearing, which can significantly scatter the phonons with different wavelengths and in turn contribute to a low thermal conductivity of only 0.63 W m–1 K–1 at 773 K, both contributing to a competitive ZT of ≈0.73 at this temperature, indicating the great potential for practical applications. [ABSTRACT FROM AUTHOR]

The structure–property link is inherent to materials. Hexagonal Ge4Se3Te phase, with special Ge–Ge cationic bonding and distinctive from other IV–VI compounds, reveals thermoelectric (TE) performance far below the common values for IV–VI compounds. Here, it is shown that its TE performance can be substantially enhanced by phase modulation: increasing sintering temperature from 573 to 773 K leads to the decomposition of hexagonal phase into a composite of orthorhombic and rhombohedral phases, which significantly improves TE performance at T≤ 550 K; Sb/Cd doping stabilizes the rhombohedral phase, compensates the hole concentration, and strengthens the phonon scattering, which further enhances the TE performance over the whole temperature range. The theoretical calculation reveals that the rhombohedral phase has a more favorable electronic band structure than the hexagonal phase for achieving higher electrical transport properties. The optimized TE performance is obtained in rhombohedral Ge0.90Sb0.08Cd0.02Se0.75Te0.25, with a zTmax of 1.36 at 778 K and zTave of 0.73 from 322 to 778 K, which are among the highest values in the Se‐rich side of Ge(Se, Te) system, and one order higher than those in the hexagonal phase. The study sheds light on the validity of phase modulation for TE performance optimization in Ge(Se, Te)‐based material systems. [ABSTRACT FROM AUTHOR]

The structure–property link is inherent to materials. Hexagonal Ge4Se3Te phase, with special Ge–Ge cationic bonding and distinctive from other IV–VI compounds, reveals thermoelectric (TE) performance far below the common values for IV–VI compounds. Here, it is shown that its TE performance can be substantially enhanced by phase modulation: increasing sintering temperature from 573 to 773 K leads to the decomposition of hexagonal phase into a composite of orthorhombic and rhombohedral phases, which significantly improves TE performance at T≤ 550 K; Sb/Cd doping stabilizes the rhombohedral phase, compensates the hole concentration, and strengthens the phonon scattering, which further enhances the TE performance over the whole temperature range. The theoretical calculation reveals that the rhombohedral phase has a more favorable electronic band structure than the hexagonal phase for achieving higher electrical transport properties. The optimized TE performance is obtained in rhombohedral Ge0.90Sb0.08Cd0.02Se0.75Te0.25, with a zTmax of 1.36 at 778 K and zTave of 0.73 from 322 to 778 K, which are among the highest values in the Se‐rich side of Ge(Se, Te) system, and one order higher than those in the hexagonal phase. The study sheds light on the validity of phase modulation for TE performance optimization in Ge(Se, Te)‐based material systems. [ABSTRACT FROM AUTHOR]

Substantial progress in improving the thermoelectric performance of CaMg2Bi2‐based materials has been made, yet existing reports barely discuss the effect of intrinsic Bi impurity on the transport properties. In this study, the first‐principles calculation shows that the Bi‐rich environment associated with Bi impurities facilitates the reduction of cation vacancy formation energy and then increases the carrier concentration. In addition, in the samples containing Bi impurity, a dynamic doping behavior caused by the redissolving of Bi second phase into the matrix with increasing temperature is identified experimentally, which force the carrier concentration to approach the optimal carrier concentration nH,opt, leading to a more than a 5 times enhancement of the figure‐of‐merit (ZT) compared to the single‐phase CaMg2Bi1.94. Moreover, by doping Ba and Yb on the Ca Site, orbital alignment is realized and phonon scattering is also enhanced. The synergistical optimization of electrical and thermal transportation brings a peak ZT of 1.24 at 873 K and a record ZTave of 0.86 (300–873 K) in (Ca0.5Yb0.25Ba0.25)0.995Na0.005Mg2Bi1.98 sample. [ABSTRACT FROM AUTHOR]

Alloyed lead‐free double perovskites display intense photoluminescence, are environmentally friendly, and their devices show long‐term operation. Thanks to these properties, which make them excellent warm white‐emitting materials, they have recently received great attention in lighting applications. An important factor to tune the optical properties of alloyed lead‐free double perovskites is the presence of self‐trapped excitons. Here, it is demonstrated that in lead‐free double perovskites, the strong electron–phonon coupling plays a crucial role in the generation of self‐trapped excitons. The strong electron–phonon coupling is confirmed by a large Huang–Rhys factor and by the presence of multiphonon transitions. In particular, sharp emission lines superimposed on the broad photoluminescence emission band of one of these samples (Cs2Ag0.6Na0.4InCl6 0.5%Bi) are observed; these are due to the strong coupling of longitudinal‐optical phonons with excited electronic states caused by the tetragonally distorted AgCl6 octahedrons. Such a strong coupling of longitudinal‐optical phonons to electrons can effectively modulate the photophysical properties of alloyed double perovskites, and its understanding is, thus, of paramount importance for the design of future optoelectronic devices. [ABSTRACT FROM AUTHOR]

2D beryllium polynitrides or beryllonitrene is a newly synthesized layered material displaying anisotropic Dirac cones and van Hove singularity (VHS) located only ≈0.5 eV above the Fermi level. Using the Boltzmann transport equation with many‐body effects and first‐principles calculations, it is uncovered that beryllonitrene has an in‐plane anisotropic room‐temperature phonon thermal conductivity (κph) of 78.6 and 98.8 W mK−1, and an electron thermal conductivity (κe) of 23.0 and 60.7 W mK−1, along the in‐plane directions. κph is dominated by the large heat capacity flexural acoustic (ZA) modes, which are susceptible to three‐phonon and four‐phonon scatterings but rather immune to scattering onto electrons. Filling the Dirac cones till VHS and above gradually enhances the phonon–electron coupling and monotonically decreases κph by up to 55%. Instead, κe displays unusual nonmonotonic variations with the increase in the carrier density and follows the electron density of states at corresponding Fermi levels. The results shed light on the thermal and electrical transport properties in beryllonitrene and reveal a thermal conductivity modulation mechanism that includes a 60% increase of κe upon filling of the Dirac cones until VHS. [ABSTRACT FROM AUTHOR]

ZnO is identified as a potentially attractive n‐type oxide thermoelectric material due to its abundance, nontoxicity, and a high degree of stability. However, working with ZnO is challenging due to its high thermal conductivity from its strong ionic bonds and low electrical conductivity due to its low charge concentrations. Here, it is demonstrated that the electrical and thermal transport properties of ZnO can be simultaneously improved via the successful doping of Al and ZnS coating. The ZnS coating in Al‐doped ZnO is observed and analyzed through microstructure and spectroscopic studies. The power factor for 1% ZnS‐coated Zn0.98Al0.02O is increased to ≈0.75 mW m−1 K−2 at 1073 K, 161% higher than pure ZnO. This enhancement in the power factor can be explained by the aliovalent Al3+ doping and modifications in intrinsic defects, leading to an increased carrier concentration. Interestingly, ZnS coating significantly reduces lattice thermal conductivity to ≈2.31 W m−1 K−1 at 1073 K for 2% ZnS‐coated Zn0.98Al0.02O, a 62% decrease over pure ZnO. This large reduction in lattice thermal conductivity can be elucidated based on coherent phonon scattering via Callaway's model. Overall, the figure of merit, zT, increases to 0.2 in 2% ZnS‐coated Zn0.98Al0.02O, which is 272% higher than pure ZnO at 1073 K. [ABSTRACT FROM AUTHOR]

Bi2S3‐based thermoelectric materials without toxic and expensive elements have a high Seebeck coefficient and intrinsic low thermal conductivity. However, Bi2S3 suffers from low electrical conductivity, which makes it a less‐than‐perfect thermoelectric material. In this work, halogen elements F, Cl, and Br from halogen acid are successfully introduced into the Bi2S3 lattice using a hydrothermal procedure to efficiently improve the carrier concentration. Compared with the pure sample, the electron concentration of the Bi2S3 sample treated with HCl is increased by two orders of magnitude. An optimal power factor of 470 µW m−1 K−2 for the Bi2S2.96Cl0.04 sample at 673 K is obtained. Density functional theory calculations reveal that an effective delocalized electron conductive network forms after Cl doping, which raises the Fermi level into the conduction bands, thus generating more free electrons and improving the conductivity of the Bi2S3‐based materials. Ultimately, an excellent ZT of ≈0.8 is achieved at 673 K for the Bi2S2.96Cl0.04 sample, which is one of the highest values reported for a state‐of‐the‐art Bi2S3 system. The energy conversion efficiency of the module reaches 2.3% at 673 K with a temperature difference of 373 K. This study offers a new method for enhancing the thermoelectric properties of Bi2S3 by adding halogen acid in the hydrothermal process for powder synthesis. [ABSTRACT FROM AUTHOR]

Urged by the increasing power and packing densities of integrated circuits and electronic devices, efficient dissipation of excess heat from hot spot to heat sink through thermal interface materials (TIMs) is a growing demand to maintain system reliability and performance. In recent years, graphene‐based TIMs received considerable interest due to the ultrahigh intrinsic thermal conductivity of graphene. However, the cooling efficiency of such TIMs is still limited by some technical difficulties, such as production‐induced defects of graphene, poor alignment of graphene in the matrix, and strong phonon scattering at graphene/graphene or graphene/matrix interfaces. In this study, a 120 µm‐thick freestanding film composed of vertically aligned, covalently bonded graphene nanowalls (GNWs) is grown by mesoplasma chemical vapor deposition. After filling GNWs with silicone, the fabricated adhesive TIMs exhibit a high through‐plane thermal conductivity of 20.4 W m−1 K−1 at a low graphene loading of 5.6 wt%. In the TIM performance test, the cooling efficiency of GNW‐based TIMs is ≈1.5 times higher than that of state‐of‐the‐art commercial TIMs. The TIMs achieve the desired balance between high through‐plane thermal conductivity and small bond line thickness, providing superior cooling performance for suppressing the degradation of luminous properties of high‐power light‐emitting diode chips. [ABSTRACT FROM AUTHOR]