Search

• This study presents, for the first time, the identification of an exceptional metallic material, KNaRb, characterized by an ultralow lattice thermal conductivity of 0.114 W/mK at room temperature, a value comparable to the lowest thermal conductivities reported for metals and metallic materials. • The contribution of phononic thermal conductivity to the overall thermal transport in KNaRb amounts to merely 0.66 %, markedly lower than the typical range observed in other metals and metallic systems. • The ultralow phononic thermal conductivity observed in KNaRb can be attributed to the loose bonding characteristics of Rb. In the domain of metallic systems, electronic thermal conductivity typically governs heat transfer, while lattice (phononic) thermal conductivity (LTC) remains non-negligible magnitude. This study introduces the exceptional metallic material, cubic half-Heusler-type KNaRb, via phonon Boltzmann transport equation (BTE) resolution and first-principles calculations. KNaRb exhibits an ultralow LTC of 0.114 W/mK at room temperature, comparable to the lowest reported for metallic materials, contributing merely 0.66 % to overall thermal transport. Analysis attributes KNaRb's low LTC to low group velocity and strong anharmonicity, originating from its loosely bonded electronic structure. Acoustic modes, primarily from Rb atoms, dominate thermal transport. Examination of mean square displacement and potential energy profiles reveals significant movement of loosely bonded Rb atoms within KNaRb, acting as intrinsic "rattlers," inducing pronounced phonon anharmonicity and ultrashort lifetimes. This study advances understanding of heat conduction in metals, offering insights into materials with extremely low lattice thermal conductivity for potential future applications. [ABSTRACT FROM AUTHOR]

The figure of merit of thermoelectric materials can be increased by suppressing the lattice thermal conductivity without degrading electrical properties. Phonons are the carriers for lattice thermal conduction, and their transport can be impeded by nanostructuring, owing to the recent progress in nanotechnology. The key question for further improvement of thermoelectric materials is how to realize ultimate structure with minimum lattice thermal conductivity. From spectral viewpoint, this means to impede transport of phonons in the entire spectral domain with noticeable contribution to lattice thermal conductivity that ranges in general from subterahertz to tens of terahertz in frequency. To this end, it is essential to know how the phonon transport varies with the length scale, morphology, and composition of nanostructures, and how effects of different nanostructures can be mutually adopted in view of the spectral domain. Here we review recent advances in analyzing such spectral impedance of phonon transport on the basis of various effects including alloy scattering, boundary scattering, and particle resonance.

Abstract Semiconductor InSe with wide bandgap and layered crystal structure is expected to be a promising thermoelectric material, and its excellent plasticity brings great potential applications in flexible and wearable thermoelectric devices. To advance its thermoelectric performance, this work systematically investigates the carrier and phonon transport properties in n‐type InSe. It is found that InSe compound presents an exceptional dynamic carrier transport property due to the amphoteric indium (In+ and In3+), which contributes to favorable temperature‐dependent increasing carrier concentration. More importantly, with S alloying in InSe, the carrier concentration can be further enhanced from ∼3.2 × 1013 cm–3 in InSe to ∼4.8 × 1015 cm–3 in InSe0.97S0.03 at 300 K, because S (χP ∼ 2.58) with larger Pauling electronegativity than Se (χP ∼ 2.55) can induce more In3+ state to increase carrier concentration in matrix. This boosted dynamic carrier transport property benefits an obviously enhanced power factor. Additionally, InSe compound presents intrinsically low thermal conductivity ∼1.6 W m–1 K–1 at 300 K due to low‐symmetry crystal structure and strong anharmonicity. This work indicates that the special dynamic carrier transport property and intrinsically low thermal conductivity in InSe make it as a worth‐expecting thermoelectric material.

The lattice thermal conductivity (LTC) of silicon nanowires (NWs) with diameters of 115, 56, 37 and 22 nm in the temperature range of 2–300 K for different pressures ranging from 0 to 10 GPa, was calculated by employing a modified Callaway model. Both longitudinal and transverse modes were explicitly considered within the model. A strategy is utilized to calculate the Debye and phonon group velocity in addition to the bulk modulus and it is derivative for different NW diameters from their related melting temperature under different pressures. The influence of the Gruneisen parameter, surface roughness and dislocation as structurally dependent parameters are successfully exploited to correlate the calculated values of LTC to that of the experimentally measured curves at various pressures including zero. The respective application of the Murnghan and Clapeyron equations for pressure-dependent lattice volume and melting temperature in the Callaway model produces results that tend to be systematically applicable by this model. The confinement and size effects of phonons and the role of pressure in the reduction of LTC are investigated. The peak value of LTC decreases with the increase of pressure for both bulk and its nanowires. [ABSTRACT FROM AUTHOR]

Filled skutterudite is currently one of the most promising intermediate-temperature thermoelectric (TE) materials, having good thermoelectric transport performance and excellent mechanical properties. For the preparation of high-efficiency filled skutterudite TE devices, it is important to have p- and n-type filled skutterudite TE materials with matching performance. However, the current TE properties of p-type Fe-based filled skutterudite materials are worse than n-type filled skutterudite materials. Therefore, how to obtain high-performance p-type Fe-based filled skutterudite materials is the key to preparation of high-efficiency skutterudite-based TE devices. This review summarizes some methods for optimizing the thermal transport performance of p-type filled skutterudite materials at the atomic-molecular and nano-mesoscopic scale that have been used in recent years. These methods include doping, multi-atom filling, and use of low-dimensional structure and of nanocomposite. In addition, the synergistic optimization methods of the electrical and thermal transport parameters and advanced preparation technologies of p-type filled skutterudite materials in recent years are also briefly summarized. These optimizational methods and advanced preparation technologies can significantly improve the TE properties of p-type Fe-based filled skutterudite materials. [ABSTRACT FROM AUTHOR]

The effect of uniaxial strain on the thermoelectric (TE) conversion efficiency of puckered monolayer arsenic antimonide (SbAs) is explored based on the density function and Boltzmann transport equation (BTE) theories. The lattice thermal conductivity (κl) can be sharply lowered through tensile strain. Taking a + 3.25% tensile strain as an example, κl along the armchair (AC) direction at 300 K decreases almost three times than that without a strain, which is ascribed to the low phonon group velocity, large Grüneisen parameter, and high three‐phonon scattering phase space. The carrier effective mass decreases in imposing tensile strain monolayer SbAs and slightly suppresses the Seebeck coefficient; however, the electrical conductivity is improved due to the small effective mass and long relaxation time. Thus, power factor increases by 3.4 times under a + 3.25% tensile at n=8.3×1011 cm−2 compared with a SbAs monolayer without strain. Thereafter, the figure of merit in an n‐type SbAs monolayer with a tensile strain of +3.25% is eight times as large as that in SbAs without strain at 300 K along the AC direction. Furthermore, the maximum TE figure of merit is 1.85 for an n‐type SbAs monolayer with +3.25% strain at 800 K. This study paves a way toward improving the TE performance through strain engineering in the TE field. [ABSTRACT FROM AUTHOR]

In this paper, the thermoelectric properties of p-type and n-type GeSe are studied systematically by using first principles and Boltzmann transport theory. The calculation includes electronic structure, electron relaxation time, lattice thermal conductivity and thermoelectric transport properties. The results show that GeSe is an indirect band gap semiconductor with band gap 1.34 eV. Though p-type GeSe has a high density of states near Fermi level, the electronic conductivity is relative low because there is no carrier transport pathway along the a-axis direction. For n-type GeSe, a charge density channel is formed near conduction band minimum, which improves the electrical conductivity of n-type GeSe along the a-axis direction. At 700 K, the optimal ZT value reaches 2.5 at 4 × 1019 cm−3 for n-type GeSe, while that is 0.6 at 1 × 1020 cm−3 for p-type GeSe. The results show n-type GeSe has better thermoelectric properties than p-type GeSe, indicating that n-type GeSe is a promising thermoelectric material in middle temperature.

Electronegative guests can be induced to fill the voids of skutterudite by doping electron donors in the framework of skutterudites. This method has been considered a promising method to improve thermoelectric properties. In this study, Se y Ni 0.3 Co 3.7 Sb 12 (y = 0, 0.025, 0.1, 0.125, 0.15) skutterudite compounds were prepared using a melt-quenching-annealing synthesis route and spark plasma sintering technology. The phase constituents, microstructure, thermoelectric properties, and thermal transport properties were investigated. Experimental results suggest that the charge compensation between Ni doping and Se filling has a positive effect on the formation of thermodynamically stable Se y Ni 0.3 Co 3.7 Sb 12 alloys. The existence of Se fillers in the voids reduces the lattice thermal conductivity. As the filling fraction of Se increases, the number of holes increases while the electron concentration decreases. The figure of merit (zT) of Se 0.15 Ni 0.3 Co 3.7 Sb 12 reaches a maximum of 0.81 at 823 K. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Buckled hexagonal CSe nanosheet made of earth-abundant elements is investigated for thermoelectric performance by employing the first-principle calculations and the Boltzmann transport theory. The buckled hexagonal CSe sheet is shown to be an indirect-gap semiconductor with a lattice constant of 3.07 Å and band gap of 1.51 eV. The maximum power factor of n-type (p-type) CSe sheet is 618 to 483 (9.87 to 7.42) mW m - 1 K - 2 at the temperatures from 300 to 700 K at the carrier concentration of about 1.17 × 10 13 ( 1.24 × 10 13 ) cm - 2 ). The lattice thermal conductivity of the buckled CSe sheet is in the range of 11.62 to 5.00 W m - 1 K - 1 , and the dimensionless figure of merit of n-type (p-type) CSe sheet is as high as 0.69 to 0.85 (0.18 to 0.40) at the temperatures from 300 to 700 K by choosing appropriate doping level. The high thermoelectric performance indicates that the buckled hexagonal CSe sheet is a promising n-type two-dimensional thermoelectric material. [ABSTRACT FROM AUTHOR]

Transition metal disulfides (TMDCs) have attracted extensive attention in recent years for their novel physical and chemical properties. Based on the first-principles calculations together with semi-classical Boltzmann transport theory, we explored the electronic structures and transport properties of van der Waals WSe2/WTe2 heterostructure. WSe2/WTe2 heterostructure has distinctive hexagon structure and isotropic thermal transport properties. To prove the accuracy of band structure, both Perdew–Burke–Eruzerhof (PBE) and Heyd–Scuseria–Ernzerhof (HSE06) have been used to calculate the band structures. We simulated the band structures under uniaxial and biaxial strains from −8% to +8% and found that all band gaps calculated by HSE06 are larger than results calculated by PBE. More importantly, it was found that when the biaxial strain reaches ±8%, it undergone semiconductor to metal and the dynamic stabilities of WSe2/WTe2 heterostructure have been predicted at the same time. We calculated the mobilities of electrons and holes and found that the mobility of holes is larger than that of electrons. The obtained lattice thermal conductivity (LTC) of WSe2/WTe2 heterostructure at room temperature (70.694 W/mK) is significantly higher than other transition metal tellurium and transition metal selenium, such as PdSe2 (2.91 W/mK) and PdTe2 (1.42 W/mK) monolayers. Our works further enrich studies on the strain dependence of electronic structures and predicted high LTC of WSe2/WTe2 heterostructure, which provide the theoretical basis for experiments in the future. [ABSTRACT FROM AUTHOR]

The rational synthesis of high‐performance thermoelectric (TE) materials guided by theoretical design is still in its infancy. Here by computationally exploiting the possibilities of materials' dopability and hence the electron–phonon transport/scattering, a new defective compound, AgGaTe2, with simultaneous Ag deficiency and isoelectronic substitution of In on Ga‐site (InGa) is predicted, and its high performance is then confirmed via experiments. Using density functional theory and density functional perturbation theory calculations, it is identified that controlled defects viz. Ag vacancy and In substitution in AgGaTe2 system can lead to extremely low lattice thermal conductivity (κL) of around 0.13 WK−1 m−1 at 850 K. This ultralow κL results from both the Ag vacancy that serves as a better rattler and the extra phonon scattering due to the defect induced internal lattice distortion (ψ). The synthesized compounds Ag0.85Ga1−xInxTe2 (x = 0–0.3) indeed achieve the extremely low κL (0.08 WK−1 m−1 for x = 0.15). As a result, the highest TE figure of merit (ZT) of 1.44 is obtained, which is the highest recorded value for silver‐based ternary chalcopyrite semiconductors to date. [ABSTRACT FROM AUTHOR]

Efficient and precise calculations of thermal transport properties and figures of merit, alongside a deep comprehension of thermal transport mechanisms, are essential for the practical utilization of advanced thermoelectric materials. In this study, we explore the microscopic processes governing thermal transport in the distinguished crystalline material Tl 9 SbTe 6 by integrating a unified thermal transport theory with machine learning-assisted self-consistent phonon calculations. Leveraging machine learning potentials, we expedite the analysis of phonon energy shifts, higher-order scattering mechanisms, and thermal conductivity arising from various contributing factors, such as population and coherence channels. Our finding unveils an exceptionally low thermal conductivity of 0.31 W m -1 K -1 at room temperature, a result that closely correlates with experimental observations. Notably, we observe that the off-diagonal terms of heat flux operators play a significant role in shaping the overall lattice thermal conductivity of Tl 9 SbTe 6 , where the ultralow thermal conductivity resembles that of glass due to limited group velocities. Furthermore, we achieve a maximum ZT value of 3.17 in the c -axis orientation for p -type Tl 9 SbTe 6 at 600 K and an optimal ZT value of 2.26 in the a -axis and b -axis direction for n -type Tl 9 SbTe 6 at 500 K. The crystalline Tl 9 SbTe 6 not only showcases remarkable thermal insulation but also demonstrates impressive electrical properties owing to the dual-degeneracy phenomenon within its valence band. These results not only elucidate the underlying reasons for the exceptional thermoelectric performance of Tl 9 SbTe 6 but also suggest potential avenues for further experimental exploration.

In this study, bismuthene was intercalated between bilayer Ti 2 CTx to induce significant modifications in its electronic and phonon structures, thereby enhancing its thermoelectric properties. First-principles calculations reveal that the insertion of bismuthene transforms the Ti 2 CO 2 system from a semiconductor into a metal and optimizes the thermoelectric properties of bilayer Ti 2 CO 2 by enhancing its power factor and reducing its lattice thermal conductivity. Under the first-principles calculation parameters used in this study, the ZT of the Ti 2 CO 2 system increased from 0.12 to 0.55. Conversely, for metallic bilayer MXenes, the introduction of bismuthene led to a substantial decrease in ZT (from 0.53 to 0.11 in the Ti 2 C system and from 0.07 to 0.05 in the Ti 2 CCl 2 system). This study investigates the physical mechanisms underlying the enhancement of thermoelectric properties from both electronic and phononic perspectives and provides theoretical insights into the development and application of MXene-based thermoelectric materials.

Zintl phases typically exhibit low lattice thermal conductivity, which are extensively investigated as promising thermoelectric candidates. While the significance of Zintl anionic frameworks in electronic transport properties is widely recognized, their roles in thermal transport properties have often been overlooked. This study delves into KCdSb as a representative case, where the [CdSb 4/4 ] - tetrahedrons not only impact charge transfer but also phonon transport. The phonon velocity and mean free path, are heavily influenced by the bonding distance and strength of the Zintl anions Cd and Sb, considering the three acoustic branches arising from their vibrations. Furthermore, the weakly bound Zintl cation K exhibits localized vibration behaviors, resulting in strong coupling between the high-lying acoustic branch and the low-lying optical branch, further impeding phonon diffusion. The calculations reveal that grain boundaries also contribute to the low lattice thermal conductivity of KCdSb through medium-frequency phonon scattering. These combined factors create a glass-like thermal transport behavior, which is advantageous for improving the thermoelectric merit of zT. Notably, a maximum zT of 0.6 is achieved for K 0.84 Na 0.16 CdSb at 712 K. The study offers both intrinsic and extrinsic strategies for developing high-efficiency thermoelectric Zintl materials with extremely low lattice thermal conductivity., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

The Mercury Sulphohalides have attracted significant attention in the fields of solar cells and thermoelectric applications. This study delves into the fundamental characteristics, including structural, elasticity, electronic behavior, phonon stability, optical properties, and transport features of AgHgSZ (Z = Br, I) through computational simulations based on Density Functional Theory (DFT) using WIEN2k software. Meticulous calculations of the phonon band structure ensure dynamic stability. The semiconductor nature with indirect band gaps (1.833 eV and 1.832 eV) for Mercury Sulphohalides (Br, I), as revealed by their band structures, suggests diverse photovoltaic and transport applications. Mechanical assessments show stable ductility for AgHgSBr and brittleness for AgHgSI, along with anisotropy and resistance to scratching. Optical properties exhibit anisotropy and significant UV absorption. Analysis of effective masses, exciton binding energy, and exciton Bohr radius suggests low exciton binding energy and classification under Mott-Wannier excitons. Positive thermopower results indicate holes as the predominant charge carriers in AgHgSBr and AgHgSI materials. Moreover, essential thermoelectric factors are examined, revealing the compounds' potential for thermoelectric applications. Notably, the figure of merit (ZT) at 300 K for AgHgSBr and AgHgSI are calculated to be 0.41 and 0.13, respectively. While these values are low at 300 K, they indicate promising potential for thermoelectric applications at higher temperatures. In summary, this investigation provides valuable understanding into the photovoltaic and thermoelectric properties of AgHgSZ (Z = Br, I) materials, potentially paving the way for further exploration in this domain., (© 2024. The Author(s).)

High entropy alloys (HEAs) are alloys composed of five or more primary elements in equal or nearly equal proportions of atoms. In the present study, the thermophysical properties of the CoCrFeNiCu high entropy alloy (HEA) were investigated by a molecular dynamics (MD) method at nanoscale. The effects of the content of individual elements on lattice thermal conductivity k were revealed, and the results suggested that adjusting the atomic content can be a way to control the lattice thermal conductivity of HEAs. The effects of temperature on p were revealed, and the results suggested that adjusting the atomic content can be a way to control the lattice thermal conductivity of HEAs. The effects of temperature on k p were investigated quantitively, and a power-law relationship of k p with T -0.419 was suggested, which agrees with previous findings. The effects of temperature and the content of individual elements on volumetric specific heat capacity C v were also studied: as the temperature increases, the C v of all HEAs slightly decreases and then increases. The effects of atomic content on C v varied with the comprising elements. To further understand heat transfer mechanisms in the HEAs, the phonon density of states (PDOS) at different temperatures and varying atomic composition was calculated: Co and Ni elements facilitate the high-frequency vibration of phonons and the Cu environment weakens the heat transfer via low-frequency vibration of photons. As the temperature increases, the phonon mean free path (MFP) in the equiatomic CoCrFeNiCu HEA decreases, which may be attributed to the accelerated momentum of atoms and intensified collisions of phonons. The present research provides theoretical foundations for alloy design and have implications for high-performance alloy smelting., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier Ltd.)

Surface and strain engineering are among the cheaper ways to modulate structure property relations in materials. Due to their compositional flexibilities, MXenes, the family of two-dimensional materials, provide enough opportunity for surface engineering. In this work, we have explored the possibility of improving thermoelectric efficiency of MXenes through these routes. The Janus MXenes obtained by modifications of the transition metal constituents and the functional groups passivating their surfaces are considered as surface engineered materials on which bi-axial strain is applied in a systematic way. We find that in the three Janus compounds Zr 2 COS, ZrHfCO 2 and ZrHfCOS, tensile strain modifies the electronic and lattice thermoelectric parameters such that the thermoelectric efficiency can be maximised. A remarkable reduction in the lattice thermal conductivity due to increased anharmonicity and elevation in Seebeck coefficient are obtained by application of moderate tensile strain. With the help of first-principles electronic structure method and semi-classical Boltzmann transport theory we analyse the interplay of structural parameters, electronic and dynamical properties to understand the effects of strain and surface modifications on thermoelectric properties of these systems. Our detailed calculations and in depth analysis lead not only to the microscopic understanding of the influences of surface and strain engineering in these three systems, but also provide enough insights for adopting this approach and improve thermoelectric efficiencies in similar systems., (© 2024 IOP Publishing Ltd.)

Materials with low intrinsic lattice thermal conductivity are crucial in the pursuit of high-performance thermoelectric (TE) materials. Here, the TE properties of PbBi 2 Te 4-x Se x (0 ≤ x ≤ 0.6) samples are systematically investigated for the first time. Doping with Se in PbBi 2 Te 4 can simultaneously reduce carrier concentration and increase carrier mobility. The Seebeck coefficient is significantly increased by doping with Se, based on the density functional theory calculation, it is shown to be due to the increased bandgap and electronic density of states. In addition, the lattice strain is enhanced due to the difference in the size of Se and Te atoms, and the multidimensional defects formed by Se doping, such as vacancies, dislocations, and grain boundaries, enhance the phonon scattering and reduce the lattice thermal conductivity by about 37%. Finally, by using Se doping to reduce carrier concentration and thermal conductivity, a large ZT max = 0.56 (at 574K) is achieved for PbBi 2 Te 3.5 Se 0.5 , which is around 64% larger than those of the PbBi 2 Te 4 pristine sample. This work not only demonstrates that PbBi 2 Te 4 is a potential medium temperature thermoelectric material, but also provides a reference for enhancing thermoelectric properties through defect and energy band engineering., (© 2024 Wiley‐VCH GmbH.)

Se-free n-type (Bi,Sb) 2 Te 3 thermoelectric materials, outperforming traditional n-type Bi 2 (Te,Se) 3 , emerge as a compelling candidate for practical applications of recovering low-grade waste heat. A 100% improvement in the maximum ZT of n-type Bi 1.7 Sb 0.3 Te 3 is demonstrated by using melt-spinning and excess Te-assisted transient liquid phase sintering (LPS). Te-rich sintering promotes the formation of intrinsic defects (Te Bi ), elevating the carrier concentration and enhancing the electrical conductivity. Melt-spinning with excess Te fine-tunes the electronic band, resulting in a high power-factor of 0.35 × 10 -3 W·m -1 K -2 at 300 K. Rapid volume change during sintering induces the formation of dislocation networks, significantly suppressing the lattice thermal conductivity (0.4 W·m -1 K -1 ). The developed n-type legs achieve a high maximum ZT of 1.0 at 450 K resulting in a 70% improvement in the output power of the thermoelectric device (7.7 W at a temperature difference of 250 K). This work highlights the synergy between melt-spinning and transient LPS, advancing the tailored control of both electronic and thermal properties in thermoelectric technology.

The lattice thermal conductivities (κlat) of Earth's lower mantle (LM) minerals is a crucial parameter in the study of deep Earth dynamics and its determination is also one of the grand challenges in condensed matter physics. Here, we review recent progress on theoretical and experimental studies for theκlatunder high pressure ( P ) and high temperature ( T ) condition up to 150 GPa and 4000 K. After the critical parameters necessary to obtain converged values of theκlatare summarized, the theoreticalκlatof the LM minerals, determined through various computational methodologies, is compiled along with experimental findings. Although significant scattering is found in the experimental results at LM P,T , the quantum anharmonic lattice dynamics theory combined with the phonon Boltzmann transport theory demonstrates a clear relationship in theκlatof the end-member LM phases, MgO, MgSiO 3 bridgmanite (Brg) and post-perovskite (PPv),κlatMgO>>κlatPPv>κlatBrg, and a discontinuous change in theκlatby ∼20%-50% expected across the Brg-PPv transition. Knowledge on the additional but geophysically important factors, such as the effects of iron solid solution, isotopic mass difference, and higher order crystal anharmonicity are also summarized in detail. Current problems and future perspectives are finally mentioned., (Creative Commons Attribution license.)

While lead sulfide shows notable thermoelectric properties, its production costs remain high, and its mechanical hardness is low, which constrains its commercial viability. Herein, we demonstrate a straightforward and cost-effective method to produce PbS nanocrystals at ambient temperature. By introducing controlled amounts of silver, we achieve p-type conductivity and fine-tune the energy band structure and lattice configuration. Computational results show that silver shifts the Fermi level into the valence band, facilitating band convergence and thereby enhancing the power factor. Besides, excess silver is present as silver sulfide, which effectively diminishes the interface barrier and enhances the Seebeck coefficient. Defects caused by doping, along with dislocations and interfaces, reduce thermal conductivity to 0.49 W m -1 K -1 at 690 K. Moreover, the alterations in crystal structure and chemical composition enhance the PbS mechanical properties. Overall, optimized materials show thermoelectric figures of merit approximately 10-fold higher than that of pristine PbS, alongside an average hardness of 1.08 GPa.

Discovering high thermal conductivity materials is essential for various practical applications, particularly in electronic cooling. The significance of two-dimensional (2D) materials lies in their unique properties that emerge due to their reduced dimensionality, making them highly promising for a wide range of applications. Hexagonal boron nitride (BN), both monolayer and bilayer forms, has garnered attention for its fascinating properties. In this work, we focus on bilayer boron phosphide (BP), which is isostructural to its BN analogue. The lattice thermal conductivity of both bilayer BN and BP have been calculated using ab-initio density functional theory, machine learning with the moment tensor potential method, and the temperature-dependent effective-potential method (TDEP). The TDEP approach gives more accurate results for both BN and BP materials. The lattice thermal conductivity of bilayer BP is lower than that of bilayer BN at room temperature, attributed to increased phonon anharmonicity. This study highlights the importance of understanding phonon scattering mechanisms in determining the thermal conductivity of 2D materials, contributing to the broader understanding and potential applications of these materials in future technologies., (© 2024 IOP Publishing Ltd.)

Room-temperature superconductivity has been attracting increasing attention in recent years. Recent studies have proved the potential of compressed H-rich materials for achieving room-temperature superconductivity. In this paper, we study the phononic thermal transport in the rare earth yttrium hydrides allotropes under 0, 50, and 300 GPa by using Boltzmann transport equation. We find that the lattice thermal conductivity of yttrium hydrides increases with the pressure among different allotropes, which is attributed to the increase of bond strength and the decrease of phonon-phonon scattering due to structural compression. Yttrium hydrides structure at high pressure of 300 GPa is the superconducting phase, and has high thermal conductivity around 1,360 Wm−1K−1 at room temperature. Comparison of phonon properties with existing high thermal conductivity materials further uncovers the origin for the observed high thermal conductivity. For the zero pressure allotrope, a large number of optical flat bands mix with the low-frequency acoustic phonons, which significantly increases the phonon scattering channel and effectively suppresses the phonon lifetime. As for yttrium hydrides allotropes under 50 and 300 GPa, there are two obvious band gaps in the phonon dispersion relation, and the band gap of the structure at 300 GPa is significantly wider. The occurrence of the band gap effectively inhibits the absorption and emission process of the three-phonon interactions, leading to the decrease of phonon scattering and thus the increase of the phonon lifetime and thermal conductivity at high pressure. Our work reveals the physical mechanism of the thermal transport behaviors in yttrium hydrides structures under different pressures.

Abstract Charge and thermal transport in a crystal is carried by free electrons and phonons (quantized lattice vibration), the two most fundamental quasiparticles. Above the Debye temperature of the crystal, phonon‐mediated thermal conductivity (κL) is typically limited by mutual scattering of phonons, which results in κL decreasing with inverse temperature, whereas free electrons play a negligible role in κL. Here, an unusual case in charge‐density‐wave tantalum disulfide (1T‐TaS2) is reported, in which κL is limited instead by phonon scattering with free electrons, resulting in a temperature‐independent κL. In this system, the conventional phonon–phonon scattering is alleviated by its uniquely structured phonon dispersions, while unusually strong electron‐phonon (e‐ph) coupling arises from its Fermi surface strongly nested at wavevectors in which phonons exhibit Kohn anomalies. The unusual temperature dependence of thermal conduction is found as a consequence of these effects. The finding reveals new physics of thermal conduction, offers a unique platform to probe e‐ph interactions, and provides potential ways to control heat flow in materials with free charge carriers. The temperature‐independent thermal conductivity may also find thermal management application as a special thermal interface material between two systems when the heat conduction between them needs to be maintained at a constant level.

Theoretical calculations on the lattice thermal conductivity (LTC) of the bulk bismuth (Bi) and nanowires (NWs) have been studied with diameters 98 nm, 115 nm and 327 nm in the 〈110〉 direction from temperature range of 0 to 300 K. Several size dependent parameters are estimated to correlate the value of LTC using the modified Morelli-Callaway model, including mass density, Umklapp, normal, boundary impurity, dislocation, and phonon-electron scattering rate. In a particular range of temperature, their effects are varied on the bell-shaped LTC. In accordance, Grüneisen parameter has been calculated for each case and the obtained values fitted with the experimental data of LTC. The result indicates that the impact of increasing the surface area to volume ratio is satisfied on the LTC for some Bi NWs. At a specific temperature, the LTC drops with the reduction of size of NWs. The effects of the variation in size on LTC are calculated and the obtained results are in good agreement with the experimental data.

Summary: Energy harvesting along with the thermoelectric materials has been investigated over recent decades with increased interest. This is not only due to their structural capability for demonstrating and integrating various new concepts to enhance the thermoelectric figure of merit but also high thermal stability, which is useful for thermoelectric devices. In the present investigation, we have used density functional theory combined with Boltzmann transport scheme to predict the properties of Co2XAl (X = Zr, Nb, Hf) Heuslers. The elastic parameters are simulated to determine the strength and ductile nature of these materials. Three different methods for exchange correlations are utilized to investigate the band profile for that modified Becke‐Johnson potential illustrates the better results than generalized gradient approximation and GGA + U functional. The band profile found to be n‐type (indirect band‐gap) for Co2NbAl and p‐type (direct band‐gap) for Co2ZrAl and Co2HfAl Heuslers near the Fermi level. The formation and cohesive energy approve the thermodynamic stability of these materials. The band occupation and density of states in the post DFT treatment are used to predict the relations among various transport properties. The most important lattice portion of thermal conductivity has been keenly determined by Slack's equation. The half‐metallic nature along with efficient thermoelectric parameters, including electrical conductivity, Seebeck coefficient, thermal conductivity, power factor, and zT suggest the likelihood of these materials to have a potential application in designing the shape of memory devices and imminent thermoelectric and energy harvesting materials. [ABSTRACT FROM AUTHOR]

Rare‐earth pyrochlore materials are promising thermal barrier coatings materials and fundamental understanding of their thermal transport is crucial for further improving its performance. In this work, using density functional theory (DFT) method, we calculated the intrinsic lattice thermal conductivities κl of Ln2Sn2O7 (Ln = La, Gd) and conducted a comprehensive analysis on the mode thermal conductivity, relaxation time, Grüneisen parameters, group velocity, and specific heat, respectively. It is shown that in pyrochlore‐type materials the number of the optical phonons is much larger than that of the acoustic phonon, and the thermal conductivity of acoustic phonons are suppressed, both of which increase the contribution ratio of optical phonons. Especially, through cumulative κl analysis, we found that the contribution of optical phonons is significant: the ratio of optical contribution is more than 50% and 64% in La2Sn2O7 and Gd2Sn2O7. This work provides a comprehensive picture illustrating the significant role of the optical phonons in the lattice thermal conduction in rare‐earth pyrochlore materials, and points out an avenue to obtain low thermal conductivity in complex structural thermal insulation materials. [ABSTRACT FROM AUTHOR]

A heat flow switching device was developed using semiconductors characterized by very small lattice thermal conductivity. We selected Ag2Ch (Ch = S, Se) which possesses semiconducting electron transport properties and very small lattice thermal conductivity, and tried to control their electron thermal conductivity using bias voltage. The samples were prepared by means of self-propagating high-temperature synthesis under vacuum atmosphere, and mechanically rolled into ribbons of 10µm in thickness. For making the capacitor-type device, amorphous Si and Mo were deposited on the rolled films using RF-sputtering. We compared thermal conductivity with and without bias voltage by means of the AC heating method. As a result, we succeeded in observing a 10% increase of heat flow in the capacitor type heat flow switching device. [ABSTRACT FROM AUTHOR]

Silicon-germanium (SiGe) alloys are prominent high-temperature thermoelectric (TE) materials used as a powering source for deep space applications. In this work, we employed rapid cooling rates for solidification by melt-spinning and rapid heating rates for bulk consolidation employing spark plasma sintering to synthesize high-performance p-type SiGe nano-alloys. The current methodology exhibited a TE figure-of-merit (ZT) ≈ 0.94 at 1123 K for a higher cooling rate of ∼3.0 × 107 K/s. This corresponds to ≈ 88% enhancement in ZT when compared with currently used radioisotope thermoelectric generators (RTGs) in space flight missions, ≈ 45% higher than pressure-sintered p-type alloys, which results in a higher output power density, and TE conversion efficiency (η) ≈ 8% of synthesized SiGe nano-alloys estimated using a cumulative temperature dependence (CTD) model. The ZT enhancement is driven by selective scattering of phonons rather than of charge carriers by the high density of grain boundaries with random orientations and induced lattice-scale defects, resulting in a substantial reduction of lattice thermal conductivity and high power factor. The TE characteristics of synthesized alloys presented using the constant property model (CPM) and CTD model display their high TE performance in high-temperature regimes along with wide suitability of segmentation with different mid-temperature TE materials. [ABSTRACT FROM AUTHOR]

Lattice thermal conductivity can be reduced by introducing point defect, grain boundary, and nanoscale precipitates to scatter phonons of different wave‐lengths, etc. Recently, the effect of electron–phonon (EP) interaction on phonon transport has attracted more and more attention, especially in heavily doped semiconductors. Here the effect of EP interaction in n‐type P‐doped single‐crystal Si has been investigated. The lattice thermal conductivity decreases dramatically with increasing P doping. This reduction on lattice thermal conductivity cannot be explained solely considering point defect scattering. Further, the lattice thermal conductivity can be fitted well by introducing EP interaction into the modified Debye–Callaway model, which demonstrates that the EP interaction can play an important role in reducing lattice thermal conductivity of n‐type P‐doped single‐crystal Si. [ABSTRACT FROM AUTHOR]

The presence of water in minerals generally alters their physical properties. Ringwoodite is the most abundant phase in the lowermost mantle transition zone and can host up to 1.5–2 wt% water. We studied high‐pressure lattice thermal conductivity of dry and hydrous ringwoodite by combining diamond‐anvil cell experiments with ultrafast optics. The incorporation of 1.73 wt% water substantially reduces the ringwoodite thermal conductivity by more than 40% at mantle transition zone pressures. We further parameterized the ringwoodite thermal conductivity as a function of pressure and water content to explore the large‐scale consequences of a reduced thermal conductivity on a slab's thermal evolution. Using a simple 1‐D heat diffusion model, we showed that the presence of hydrous ringwoodite in the slab significantly delays decomposition of dense hydrous magnesium silicates, enabling them to reach the lower mantle. Our results impact the potential route and balance of water cycle in the lower mantle. Plain Language Summary: The physical properties of minerals are determined by the interaction of atoms in the crystal lattice. Water can be incorporated into the crystal structure and alter its behavior. Ringwoodite is a high‐pressure mineral that can host large quantities of water and is expected to be abundant in the lower part of Earth's mantle transition zone, a region ranging from 520 to 660‐km depth. Here we studied ringwoodite thermal conductivity, describing how effectively heat is transported through solids. Based on our measurements we determined that water in ringwoodite significantly slows down heat propagation. We performed computer simulations to investigate the large‐scale implications of our findings. For this purpose, we modeled a cold oceanic plate, entirely made of ringwoodite, which is surrounded by warm mantle. The delayed heat transport is sufficient to maintain low temperatures in the inner part of the oceanic plate and potentially preserve the hydrous minerals for an extended period of time. Key Points: Ringwoodite thermal conductivity is reduced by 40% due to the presence of 1.73 wt% water in the crystal structureLower thermal conductivity of hydrous ringwoodite might delay the breakdown of hydrous phases hosted in a subducting slabHydrous ringwoodite acts as a heat propagation barrier, supporting preservation of hydrous minerals down to the lower mantle [ABSTRACT FROM AUTHOR]

Polycrystalline bulks of Hf-doped Cu0.01Bi2Te2.7Se0.3 are prepared via a conventional melt-solidification process and subsequent spark plasma sintering technology, and their thermoelectric performances are evaluated. To elucidate the effect of Hf-doping on the thermoelectric properties of n-type Cu0.01Bi2Te2.7Se0.3, electronic and thermal transport parameters are estimated from the measured data. An enlarged density-of-states effective mass (from ~0.92 m0 to ~1.24 m0) is obtained due to the band modification, and the power factor is improved by Hf-doping benefitting from the increase in carrier concentration while retaining carrier mobility. Additionally, lattice thermal conductivity is reduced due to the intensified point defect phonon scattering that originated from the mass difference between Bi and Hf. Resultantly, a peak thermoelectric figure of merit zT of 0.83 is obtained at 320 K for Cu0.01Bi1.925Hf0.075Te2.7Se0.3, which is a ~12% enhancement compared to that of the pristine Cu0.01Bi2Te2.7Se0.3. [ABSTRACT FROM AUTHOR]

Self‐consistent ab‐initio calculations with highly precise spin‐polarized, density functional theory have been performed for the first time, to investigate the electronic structure, magnetism, transport, elasto‐mechanical, and thermophysical properties of newly tailored Mn‐based full‐Heuslers. The cohesive and ground‐state energy calculations in ferromagnetic, nonmagnetic, and antiferromagnetic states confirm the stability of materials in face‐centered ferromagnetic configuration. The spin‐based band structure analysis is well defined by modified Becke‐Johnson potential with the occurrence of half‐metallic character along the Fermi level. Estimation of elastic parameters is used to check the mechanical stability and nature of forces occurring in materials, where we see the alloys display ductile nature along with a Debye temperature of 398.75 K for Mn2NbAl, 337.53 K for Mn2NbGa, and 360.52 K for Mn2NbIn. Furthermore, within the solution of Boltzmann theory, thermoelectric efficient parameters address its applications in energy harvesting and solid‐state device applications. Thermodynamic potentials have been keenly predicted by implementing quasi harmonic Debye model to descript its stability at high temperature and pressure varying conditions. The prediction of ground state and thermodynamic properties from extensive first‐principles calculations could be beneficial for its future experimental insights with intriguing applications. Hence, the overall theme from the current study creates an application stand in spintronics, power generation, as well as green energy sources for future technologies. [ABSTRACT FROM AUTHOR]

Charge and thermal transport in a crystal is carried by free electrons and phonons (quantized lattice vibration), the two most fundamental quasiparticles. Above the Debye temperature of the crystal, phonon‐mediated thermal conductivity (κL) is typically limited by mutual scattering of phonons, which results in κL decreasing with inverse temperature, whereas free electrons play a negligible role in κL. Here, an unusual case in charge‐density‐wave tantalum disulfide (1T‐TaS2) is reported, in which κL is limited instead by phonon scattering with free electrons, resulting in a temperature‐independent κL. In this system, the conventional phonon–phonon scattering is alleviated by its uniquely structured phonon dispersions, while unusually strong electron‐phonon (e‐ph) coupling arises from its Fermi surface strongly nested at wavevectors in which phonons exhibit Kohn anomalies. The unusual temperature dependence of thermal conduction is found as a consequence of these effects. The finding reveals new physics of thermal conduction, offers a unique platform to probe e‐ph interactions, and provides potential ways to control heat flow in materials with free charge carriers. The temperature‐independent thermal conductivity may also find thermal management application as a special thermal interface material between two systems when the heat conduction between them needs to be maintained at a constant level. [ABSTRACT FROM AUTHOR]

In thermal barrier coating materials, there are several conventional routes to suppress the lattice thermal conductivity in order to improve the thermal insulation efficiency, such as doping, increasing the mass of unit cells, or using complex lattice structures. However, in spite of the fact that the mass of unit cell of La 2 Sn 2 O 7 is much larger than that of La 2 Zr 2 O 7 and these two pyrochlores have very similar crystal structure, the thermal conductivity of the former is much higher. By comparing the phonon spectra, phonon density of states and Grüneisen parameter of each phonon mode calculated using first-principles methods, it is found that the La 2 Zr 2 O 7 has stronger anharmonicity than La 2 Sn 2 O 7 because of the anharmonic potential of La atoms in the (111) plane. The difference between La potentials of the two pyrochlores is attributed to the fact that the electron cloud around Zr atoms is more easily polarized than that around Sn by the displacement of La atoms, which induces stronger long-range interaction and decreases the potential energy of La. These results provide intuitive insights towards the interplay between the electronic structure, anharmonicity and lattice thermal conductivity of rare-earth pyrochlores. [ABSTRACT FROM AUTHOR]

Recent progress in theoretical mineral physics based on the ab initio quantum mechanical computation method has been dramatic in conjunction with the rapid advancement of computer technologies. It is now possible to predict stability, elasticity, and transport properties of complex minerals quantitatively with uncertainties that are comparable to or even smaller than those attached in experimental data. These calculations under in situ high-pressure (P) and high-temperature conditions are of particular interest because they allow us to construct a priori mineralogical models of the deep Earth. In this article, we briefly review recent progress in studying high-P phase relations, elasticity, thermal conductivity, and rheological properties of lower mantle minerals including silicates, oxides, and some hydrous phases. Our analyses indicate that the pyrolitic composition can describe Earth's properties quite well in terms of density and P- and S-wave velocity. Computations also suggest some new hydrous compounds that could persist up to the deepest mantle and that the postperovskite phase boundary is the boundary of not only the mineralogy but also the thermal conductivity. ▪ The ab initio method is a strong tool to investigate physical properties of minerals under high pressure and high temperature. ▪ Calculated thermoelasticity indicates that the pyrolytic composition is representative to the chemistry of Earth's lower mantle. ▪ Simulations predict new dense hydrous phases stable in the whole lower mantle pressure and temperature condition. ▪ Calculated lattice thermal conductivity suggests a heat flow across the core mantle boundary no greater than 10 TW. [ABSTRACT FROM AUTHOR]

Boron-based 2D materials are of current interest. However, graphene-like geometry is unstable for B due to the electron deficiency, which can be stabilized by introducing H, F and Cl. Here, using density functional theory combined with phonon Boltzmann transport equation, we perform systematic studies on how the functionalization changes the lattice thermal conductivity (LTC). We find that when going from hydrogenation to fluorination and chlorination, the LTC along zigzag direction changes from 367.6 to 211.3 and 43.0 W/(m·K), while the corresponding values in armchair direction are 279.6, 198.9, and 41.6 W/(m·K), respectively. These huge differences imply the sensitivity of LTC to functionalization, which can be attributed to the enhanced anharmonicity as revealed by analyzing group velocity, Gruneisen parameter, anharmonic scattering rates, and three-phonon scattering space. [ABSTRACT FROM AUTHOR]