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So far, the method of optimizing the thermoelectric properties of skutterudite CoSb 3 is usually to achieve a breakthrough in high-properties thermoelectric merit by selecting excellent doping atoms and determining a reasonable percentage of atoms. In this study, we achieved the preparation of small atomic radius Al-filled Co 4 Sb 11.5 Te 0.5 compounds by high-temperature and high-pressure (HTHP) synthesis methods. The thermoelectric properties of the samples Al x Co 4 Sb 11.5 Te 0.5 were optimized from two dimensions: synthesis pressures (1.0 GPa, 1.5 GPa, 2.0 GPa) and Al filling concentration (x = 0.1, 0.2, 0.3, 0.5), ultimately achieving effective decoupling of electron-phonon transport properties. The experimental results show that Al doping can optimize the electrical transport properties of materials effectively, rapid synthesis method of HTHP can introduce abundant grain boundaries, diversification of grain sizes, a large number of dislocations and widely distributed nano second phase, etc. These microstructures in bulk materials form a multi-scale phonon scattering network in situ, which can effectively scatter phonons and reduce the lattice thermal conductivity effectively. After optimizing the synthesis pressure and Al filling concentration through orthogonal transformation, the sample Al 0.3 Co 4 Sb 11.5 Te 0.5 prepared at a synthesis pressure of 1.5 GPa obtained a minimum lattice thermal conductivity value of 0.88 W m−1 K−1, a maximum power factor of 40.96 μ W cm−1 K−2 and a maximum zT value of 1.18 at 773.15 K. [ABSTRACT FROM AUTHOR]

Heat is produced by all machinery, including microprocessors and jet engines, as well as by industrial processes that produce goods from steel to food. There is still a strong desire for alternative energy sources in this day of ecologically conscious and sustainable energy needs. The recovery of heat from waste heat into beneficial electrical energy provides a simple energy source with enormous potential. Thermoelectrics is one of the popular technologies, which can convert heat into electricity, making them useful for power generation. Tin telluride (SnTe), a significant type of newly developed thermoelectric material, has drawn a lot of attention due to its low toxicity and environmentally friendly characteristics. Here, we synthesize Bi/Se co-doped SnTe (Sn 1-x Bi x Te 0.97 Se 0.03 (x = 0, 0.02, 0.04, 0.06)) samples by employing the solid-state metathesis route. The results of this work suggest that the combined action of cationic and anionic substitution of Bi and Se to SnTe matrix could potentially modify the microstructure and band structure of SnTe, thereby effectively improving its electronic, mechanical, and thermal transport properties. In line with the experimental findings, the samples show degenerate semiconducting electronic transport behaviour throughout the temperature range. The maximum Seebeck coefficient is found to be ∼84 μV/K and the total thermal conductivity is reduced to 1.6 W/mK at 573 K in a 6 % Bi-doped sample, which is 2.2 times less than the pristine sample. The Sn 0.94 Bi 0.06 Te 0.97 Se 0.03 sample has a maximum ZT of approximately 0.23 at 573 K, which is three times higher than the pristine sample because of the combined regulation of cation-anion co-doping and an elevated power factor of 936 μW/K2m in Sn 0.96 Bi 0.04 Te 0.97 Se 0.03 sample at 573 K, which is 1.82 times higher than that of pristine SnTe. Considering these findings, it appears that Bi-Se co-doped SnTe is a promising material for thermoelectric applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Cu 3 SbSe 4 is recognized for its abundant elemental availability, cost-effectiveness, and non-toxic properties, making it a promising candidate for thermoelectric applications at medium temperatures. This study explored the preparation of Bi/Fe, Ag/Fe, and Ag/Bi double-doped Cu 3 SbSe 4 ceramics using vacuum melting and cold isostatic pressing techniques. The focus was on examining the influence of these dopants on the microstructural and thermoelectric performances of Cu 3 SbSe 4. The analysis revealed the presence of Cu 3 SbSe 4 and Cu 2− x Se phases in the doped samples. Double doping optimized the carrier concentration, increased the effective mass, and significantly enhanced the electrical conductivity from 12.45 to 64.01 S cm−1. Notably, the power factor of the Cu 2.85 Ag 0.15 Sb 0.985 Bi 0.015 Se 4 sample reached 649.1 μWm−1K−2 at 573 K. Furthermore, the thermal conductivity was significantly reduced to 0.73 W/mK. The maximum ZT value of the Cu 2.85 Ag 0.15 Sb 0.985 Bi 0.015 Se 4 sample was 0.47 at 573 K. These breakthrough results demonstrate that dual doping markedly enhances the thermoelectric properties of the Cu 3 SbSe 4 system. [ABSTRACT FROM AUTHOR]

Thermoelectric energy conversion technology is considered as one of the most promising solutions for recovering waste heat generated by fossil fuel combustion. As typical types of thermoelectric materials in the middle and high‐temperature range (500–900 K), binary IV‐VI (IV = Ge, Sn, Pb; VI = Se, Te) compounds are extensively studied. Lately, the obtained high‐performance thermoelectric solid solutions between IV‐VI and I‐V‐VI2 (I = Li, Na, K, Ag, Cu; V = Sb, Bi; VI = S, Se, Te) compounds have brought those complex chalcogenides back to the central point of thermoelectric community due to the emerging rich physical phenomena. Profiting from this effective approach, unveiling the underlying mechanism and understanding of alloying effect on the transport properties of these solid solutions becomes particularly significant. This review presents the latest progress in designing high‐performance IV‐VI/I‐V‐VI2 solid solutions and the underlining physical mechanisms, in which detailed discussion about the role of I‐V‐VI2 compounds play in optimizing individual properties of IV‐VI materials is made. This comprehensive review highlights the multiple effects of I‐V‐VI2 alloying on thermoelectric properties of IV‐VI compounds and will drive the related research interests aiming at developing new‐generation thermoelectric compounds in this family. [ABSTRACT FROM AUTHOR]

Systematic empirical relations were established for the nanosize-dependent surface roughness, $\varepsilon (D)$ ϵ (D) , dislocations, $N_D\lpar D \rpar$ N D (D) , and effective length to examine their effects on the temperature-dependent lattice thermal conductivity (LTC) within the framework of the Morelli-Callaway model for In0.53Ga0.47As alloy films with thicknesses ranging from 10 to 70 and 1400 nm, the latter representing the material's bulk state. The results were analyzed for film thicknesses of 2, 5, 200, and 500 nm, under the assumption that electrons and impurities are unaffected by nanosize, while a small alloy parameter significantly and sensitively alters the LTC curve in medium and high-temperature regions. According to these new findings, and considering phonon scattering processes, the LTC's temperature dependence is sufficiently reduced at the nanoscale and fits well with the available reported experimental findings. It was also discovered that the LTC's peak maximum value and its corresponding temperature are influenced by the film's dislocation concentration, surface roughness, and thickness. Unravelling the complex interplay between nanosize-dependent dislocation and surface roughness concentrations becomes critical for a thorough knowledge when examining the delicate nuances of LTC in In0.53Ga0.47As nanofilms. Finally, the Morelli-Callaway-based model has been modified to calculate LTC for nanofilms without fitting parameters, provided their related bulk state values are known. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) oxides are paid great attention due to their good thermal stability, but the high lattice thermal conductivity (κ L) largely impedes their further development. In this paper, a Hollandite-type structure and multiple dopants in K x Ti 8 O 16 -based oxides are studied to seek for an ultralow κ L. Benefited from the complex crystal structure, a relatively low κ L (2.13 W m−1 K−1 at 373 K) is obtained in K 1.78 Ti 8 O 16. The Ba dopant can make the [TiO 6 ] octahedra undistorted and increase the Ti3+ amount, leading to a doubled power factor. Meanwhile, the dual-doping effect of Ba and Nb dopants can further decrease the κ L to 0.85 W m−1 K−1. Thus, a competitive zT value of 0.18 is obtained in Ba 1.15 Ti 7.2 Nb 0.8 O 16 at 1073 K. This work demonstrates that the TE performance of Hollandite-type oxides deserves to be further studied and a complex crystal structure can be designed to achieve a high zT value. [ABSTRACT FROM AUTHOR]

A geometrical approach is constructed to explain the dependence of lattice thermal conductivity (LTC) in InAs/GaAs multi-layered superlattice structures (SLs). The Morelli–Callaway model is applied to calculate the LTC of InAs/GaAs SLs with the assumption of InAs+GaAs thickness as a grain boundary and the total layer thickness as the sample size. Calculations gave a systematically conventional temperature dependence of LTC for nine different samples depending on their number of layers and the InAs and GaAs layer thicknesses having their ratio from 0.13 to 0.295. The dependence of LTC for both peak values at the low and room temperature were examined according to sample size, number of layers and layer thickness ratio. A new relation is examined for the assessment of the grain boundary effects. The best dependence of LTC was obtained by introducing the effects of the layer thickness ratio (InAs/GaAs) and the sample size D in the form [D/(InAs/GaAs)] which gave a systematic mathematical fitting equation. [ABSTRACT FROM AUTHOR]

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 [CdSb4/4]− 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 K0.84Na0.16CdSb at 712 K. The study offers both intrinsic and extrinsic strategies for developing high‐efficiency thermoelectric Zintl materials with extremely low lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Doping is a key method employed in semiconductor technology for tuning the carrier‐density‐dependent electrical properties. In thermoelectric materials, which are typically heavily doped semiconductors, more impact factors are needed to be considered due to the heavy dose doping compared to normal semiconductors beyond carrier concentration optimization, such as band structure modification, carrier scattering mechanism and even thermal transport property. In this review, the doping effect determined by the intrinsic band features and vice versa the influence of dopants on band structure is first illustrated; and then introduce the approaches to overcoming the dilemma in effective doping caused by the temperature‐dependent optimal carrier concentration. Second, the strategies including rational vacancy design, proper selection of dopants and lattice purification toward high efficient doping and weakened carrier scattering strength are reviewed. Third, the recent discovery of the effect of dopant on thermal transport is highlighted covering the dopant‐induced local lattice distortion and exceptional strong electron‐phonon coupling. Finally, a perspective is given for the doping strategies to further boost the performance of thermoelectric materials. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature 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.)

Thermal and mechanical properties play a key role in optimizing the performance of nanoelectronic devices. In this study, the lattice thermal conductivity (κ L) and elastic constants of Si nanosheets at different sheet thicknesses were determined using recently developed machine learning interatomic potentials (MLIPs). A Si nanosheet with a minimum thickness of 10 atomic layers was used for model training to predict the properties of sheets with greater thicknesses. The training dataset was efficiently constructed using stochastic sampling of the Born-Oppenheimer potential energy surface. Density functional theory calculations were used to extract the MLIP, which served as the basis for further analysis. The moment tensor potential method was used to obtain the MLIP in this study. The results showed that, at sub-6 nm sheet thickness, the thermal conductivity dropped to ~7% of its bulk value, whereas some stiffness tensor components dropped to ~3% of the bulk values. These findings contribute to the understanding of heat transport and mechanical behavior of ultrathin Si nanosheets, which is crucial for designing and optimizing nanoelectronic devices. The technological implications of the extracted parameters on nanosheet field-effect transistor performance at advanced technology nodes were evaluated using TCAD device simulations. [ABSTRACT FROM AUTHOR]

Abstract 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.

As a typical liquid-like thermoelectric material, Cu2 Se not only has good electrical transport performance, but also has low lattice thermal conductivity. Nanoengineering is an effective method to achieve high thermoelectric properties for thermoelectrics. However, nanoscale Cu2 Se particles are extremely easy to be oxidized in the process of synthesizing, thus affecting its thermoelectric performance. In order to study the effect of powder reduction on the thermoelectric performance of Cu2 Se, nano-sized Cu2 Se powders were synthesized by hydrothermal method. Hydrogen argon mixed gas ( hydrogen volume fraction of 5%) and pure argon were used to purge the powders, respectively. Cu2 Se bulk materials with density above 95% were prepared by spark plasma sintering. The results show that the oxygen content of Cu2 Se bulk is significantly reduced after powder reduction, and there is a 41% decrease in thermal conductivity at 800 K, with a 16% increase in ZT value. [ABSTRACT FROM AUTHOR]

Thermoelectric materials are widely researched for their energy conversion capabilities in the fields of power generation and refrigeration. And a superior thermoelectric conversion efficiency requires an excellent power factor and low thermal conductivity. Herein, a remarkable thermoelectric figure of merit（ZT） ∼ 2.6 at 673 K is realized in GeTe with 20% addition of CuSbSe2. Multiple synergistic effects of CuSbSe2 alloying collectively contribute to the excellent thermoelectric performance in GeTe. CuSbSe2 alloying effectively tunes ultrahigh carrier density of GeTe to the optimum. The introduction of Cu, Sb, and Se atoms create numerous point defects that scatter high‐frequency phonons. Additionally, surplus CuSbSe2 facilitates the formation of copper‐selenium phases, which embed at grain boundaries and generate interfaces after sintering. Combining the planar defects evolved from Ge vacancies, multi‐dimension defects effectively scatter multiple frequency phonons. An extraordinarily low lattice thermal conductivity of 0.3 Wm−1 K−1 at 673 K is obtained, approaching the theoretical estimation predicted by Cahill model. Eventually, the peak conversion efficiency of 7.4% is obtained in segmented device with ΔT of 419 K. The commingled effects of CuSbSe2 in GeTe further open up an elitist route to designing high‐performance materials. [ABSTRACT FROM AUTHOR]

Thermoelectric materials are important in waste heat utilization and clean energy development due to environmental and energy issues. In advanced thermoelectric applications, two-dimensional nanomaterials offer substantial advantages due to their exceptional bending stiffness and natural flexibility. The first-principles study has been used to predict the electronic structures and thermoelectric transport characteristics of BiOClBr, BiOClI, and BiOBrI monolayers. The results indicate that the three monolayers are semiconductors with an indirect band gap and high stability. The Seebeck coefficient and electrical conductivity are efficiently enhanced by the valence band valley and high carrier mobility. Moreover, a small phonon group velocity, short phonon relaxation time, large Grüneisen parameter, and phonon scattering phase space are responsible for the low lattice thermal conductivities of 1.66 (BiOClBr), 0.98 (BiOClI), and 1.51 W m–1 K–1 (BiOBrI) at 300 K. Under n-type doping, BiOClBr and BiOClI monolayers have optimal ZT values of 2.30 and 4.35 at 300 K and up to 4.78 and 7.83 at 700 K, respectively. For the BiOBrI monolayer with p-type doping, the optimal ZT values are 5.98 at 300 K and 10.01 at 700 K, which outperform some previously published Bi-based thermoelectric materials, suggesting that the three monolayers are promising Bi-based candidate thermoelectric materials. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) semiconductors are widely regarded as promising contenders for the next generation of optoelectronics and microelectronics, rendering the development of novel 2D semiconductors a focal point in current research. In this study, our attention is directed towards the non-van der Waals material Cu6GeWS8, where we have successfully predicted a stable 2D monolayer, designated as 2D Cu6GeWS8. This monolayer exhibits a direct bandgap of 1.709 eV, which maintains its robustness under biaxial strain ranging from −4% to 3%. Remarkably, the monolayer Cu6GeWS8 showcases high hole mobility and demonstrates a moderate optical absorption coefficient across the visible and ultraviolet spectra. Notably, our investigation reveals that the monolayer Cu6GeWS8 possesses an exceptionally low lattice thermal conductivity of 0.593 W m−1 K−1 at room temperature. These findings underscore the excellent physical characteristics of the predicted monolayer Cu6GeWS8, positioning it as a promising candidate for advanced low-dimensional devices. [ABSTRACT FROM AUTHOR]

In a recent breakthrough in the field of two-dimensional (2D) nanomaterials, the first synthesis of a single-atom-thick gold lattice of goldene has been reported through an innovative wet chemical removal of Ti3C2 from the layered Ti3AuC2. Inspired by this advancement, in this communication and for the first time, a comprehensive first-principles investigation using a combination of density functional theory (DFT) and machine learning interatomic potential (MLIP) calculations has been conducted to delve into the stability, electronic, mechanical and thermal properties of the single-layer and free-standing goldene. The presented results confirm thermal stability at 700 K as well as remarkable dynamical stability of the stress-free and strained goldene monolayer. At the ground state, the elastic modulus and tensile strength of the goldene monolayer are predicted to be over 226 and 12 GPa, respectively. Through validated MLIP-based molecular dynamics calculations, it is found that at room temperature, the goldene nanosheet can exhibit anisotropic tensile strength over 9 GPa and a low lattice thermal conductivity around 10 ± 2 W/(m.K), respectively. We finally show that the native metallic nature of the goldene monolayer stays intact under large tensile strains. The combined insights from DFT and MLIP-based results provide a comprehensive understanding of the stability, mechanical, thermal and electronic properties of goldene nanosheets. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature 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.)

Abstract 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 [CdSb4/4]− 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 K0.84Na0.16CdSb at 712 K. The study offers both intrinsic and extrinsic strategies for developing high‐efficiency thermoelectric Zintl materials with extremely low lattice thermal conductivity.

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

Higher manganese silicide (HMS) is a promising thermoelectric (TE) semiconductor that operates effectively at medium temperatures. It is characterized by its abundance, environmental friendliness, and desirable impact resistance properties. To enhance the TE properties of HMS, this study employs isoelectronic anion and cation codoping, combined with embedded quantum dot (QD) techniques. The introduction of element doping and nanoinclusions, such as Mn 0.96 Re 0.04 (Si 0.96 Ge 0.04) 1.79 +1.5%Ag 2 Pt QDs sample, leads to an approximately 85% increase in electrical conductivity. This boost is attributed to the adjustment of the band structure through Re, Ge, and Ag element doping and the charge transfer facilitated by MnSi, Si, and Pt precipitates. Furthermore, the enhanced PF of 1.85 × 10−3 W m−1 K−2 at 773 K is approximately 29% higher than that of pure HMS. Simultaneously, the increase in point defects hampers the improvement of lattice thermal conductivity (κ l) by intensively scattering short-wave phonons. This effect is complemented by the precipitation of Si, MnSi, Ag, and Pt nanoparticles, which increases the density of grain boundaries, enhances medium-wave phonon scattering, and substantially reduces κ l to 1.45 W m–l K−1 (at 773 K), ∼30% lower than that of pure HMS. The figure of merit of the sample containing 1.5%Ag 2 Pt QDs at 823 K attains a value of 0.69, which is ∼52% and ∼19% higher than that of pure HMS and Re-Ge-double-doped samples, respectively. The incorporation of isoelectronic codoping, along with the integration of metastable QDs, is demonstrated as an effective strategy for enhancing TE properties. [ABSTRACT FROM AUTHOR]

Strain engineering has been proved to be an effective approach to modulate various physical properties in two-dimensional (2D) materials with flexible structures. In this work, based on first-principles calculations, the impact of in-plane biaxial tensile strain on lattice thermal conductivity of bilayer MoSe2, involving different stacking modes, has been systematically investigated by iteratively solving phonon Boltzmann transport equation. Simultaneously, potential regulations of interfacial anharmonic effect in phonon transport via in-plane strain can also be clarified through a comparative study between the monolayer and bilayer cases. Our results indicate that thermal transport in both the monolayer and bilayer MoSe2 is governed by low-frequency phonon branches, and the bilayer exhibits a notably reduced thermal transport capacity due to interlayer interaction existing in van der Waals homogeneous stacks. As the in-plane tensile strain is applied, a significant suppression in thermal transport capacity per layer can be further achieved in both the monolayer and bilayer cases, implying great potential for effective thermal management in 2D MoSe2 via strain engineering. Besides, the role of homogeneous interface in phonon transport of bilayer MoSe2 can also be regulated by the exerted in-plane tensile strain, which slows the decline in thermal conductivity with strain and leads to a larger thermal sheet conductance in the strained bilayer compared to the monolayer. [ABSTRACT FROM AUTHOR]

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

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 kp 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 kp were investigated quantitively, and a power-law relationship of kp 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 Cv were also studied: as the temperature increases, the Cv of all HEAs slightly decreases and then increases. The effects of atomic content on Cv 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.

The high lattice thermal conductivity of half-Heuslers (HHs) restricts the further enhancement of their thermoelectric figure-of-merit (ZT). In this study, multiscale scattering centers, such as point defects, dislocations, and nanoprecipitates, are synchronously introduced in a n-type ZrNiSn-based HH matrix through Nb doping and Hf substitution. The lattice thermal conductivity is substantially decreased from 4.55 (for the pristine ZrNiSn) to 1.8 W·m−1·K−1 at 1 123 K via phonon scattering over a broad wavelength range through the adjustment of multiscale defects. This value is close to the theoretically estimated lowest thermal conductivity. The power factor (PF) is enhanced from 3.25 (for the pristine ZrNiSn) to 5.01 mW·m−1·K−2 for Zr0.66Hf0.30Nb0.04NiSn at 1 123 K owing to the donor doping and band regulation via Nb doping and Hf substitution. This can be ascribed to the synergistic interaction between the lowering of the lattice thermal conductivity and retention of the high PF. Consequently, a ZT value of as high as 1.06 is achieved for Zr0.66Hf0.30Nb0.04NiSn at 1 123 K. This work demonstrates that these actions are effective in jointly manipulating the transport of electrons and phonons, thereby improving the thermoelectric performance through defect engineering.

Without a profound knowledge of technological growth and future perspectives of materials their physical properties cannot be explained. Heusler compounds belong to class of prominent materials with special characteristics which ultimately land them as multifunctional materials. The results of this work stem the investigations of structural phase stability, elasto-mechanical and thermoelectric properties of Co2AgAl and Co2PdAl full Heuslers with the density functional theory (DFT). This theory is successfully executed in Boltzmann transport theory and WIEN2k program package to obtain the desired results. The generalised-gradient approximation (GGA) scheme and Tran Blaha modified Becke-Johnson (TB-mBJ) potential are embraced to compute the ground state properties. The approximations approves both compounds ideal for thermoelectric as well as for elasto-mechanical applications. The computation for mechanical parameters such as Young's modulus, Shear modulus, Pugh's ratio elastic constants and Poisson's ratio are investigated. The mechanical tolerance ultimately revealed that both compounds Co2AgAl and Co2PdAl are stable with ductile nature and exhibit low rigidity. The thermodynamic parameters like Seebeck coefficient, thermal conductivity electrical conductivity, lattice thermal and electronic conductivity, power factor (ɳ) and electrical figure of merit (zT) have been computed within relaxation time approximation as a function of high temperature. [ABSTRACT FROM AUTHOR]

The primary objective of this study is to investigate the influence of spin-orbit coupling and atom type on the electronic, optical, and thermoelectric properties of LuXNi2Sn2 (X = V, Nb, and Ta) double-half Heusler alloys. To achieve this, calculations were performed using the full potential linearized augmented plane wave method within the framework of density functional theory. Both full relativistic and scalar relativistic calculations were employed. The exchange-correlation interactions in this study were modeled using the PBEsol version of the generalized gradient approximation when calculating the structural ground state parameters. For the analysis of electronic, optical, and thermoelectric properties, the modified Becke–Johnson potential was employed. The modified Becke–Johnson potential was specifically chosen for its capability to improve the description of band gaps, particularly for systems with small band gaps, such as the LuXNi2Sn2 (X = V, Nb, and Ta) double-half Heusler materials examined in this study. This potential offers a more accurate representation of the electronic properties, enabling a more reliable analysis of the optical and thermoelectric characteristics of the materials under investigation. The examined LuXNi2Sn2 (X = V, Nb, and Ta) materials exhibit semiconductor behaviour, with band gaps smaller than 0.4 eV that can be controlled by varying the "X" atom. The charge carriers, specifically holes and electrons, exhibit light effective masses, indicating high mobility. Furthermore, these compounds exhibit low thermal expansion coefficients and satisfy the criteria for thermodynamic stability. In terms of optical properties, they display substantial absorption coefficients in the ultraviolet (UV) light region, high optical conductivity, and high reflectivity in the visible light region. Considering their favourable power factor and figure of merit characteristics, the LuXNi2Sn2 (X = V, Nb, and Ta) materials possess the potential to be promising candidates for thermoelectric applications. [ABSTRACT FROM AUTHOR]

By performing the density functional theory-based first principle calculations, we investigated electronic and transport properties of pure NaYX (X=C,Ge) and by applying uniaxial strain of NaYX (X=C,Ge) HH compounds. NaYX (X=C,Ge) HH compounds obey Born-Huang stability criteria. The formation energy and phonon dispersion support their chemical and dynamical stability. Our electronic band structure calculations show that NaYC,NaYGe is a direct band gap semiconductor having an energy band gap of 0.52eV and 0.57eV. After applying strain in NaYX (X=C,Ge) also has direct band gap but position of VBM and CBM is changed. We have calculated the transport properties of NaYX (X=C,Ge) Seebeck coefficient, electrical conductivity, electronic thermal conductivity by using constant relaxation time (10fs). Lattice thermal conductivity k l of NaYX (X=C,Ge) compounds were obtained with Slack's equation designed to compute k l within the experimental range. At temperature 1200 K, the k l for NaYC and NaYGe are 9.20 W m - 1 K - 1 , 5.97 W m - 1 K - 1 respectively We find that both n-type and p-type NaYX (X=C,Ge) are suitable for thermoelectric applications. Application of uniaxial strain has a significant impact on the electronic structure and transport properties. Among the investigated compounds, p-type NaYGe emerges as the better material in view of thermoelectric performance. [ABSTRACT FROM AUTHOR]

Mg2X (X = Si, Ge or Sn) based alloys are considered as promising candidates in the middle to high temperature range thermoelectric applications due to their low cost, nontoxicity and abundance of constituent elements. However, they exhibit relatively higher thermal conductivity compared to other thermoelectric materials. In this study, we present a simple synthetic method for a Mg2 + xSi0.5Sn0.5Sb0.075 material with a heterogeneous microstructure that reduces thermal conductivity. By controlling the amount of excess Mg during synthesis, a heterogeneous microstructure due to the formation of secondary phases was obtained. This heterogeneous microstructure reduced the thermal conductivity through phonon scattering, leading to an improved thermoelectric efficiency, particularly at high temperatures. [ABSTRACT FROM AUTHOR]

Searching for new materials with intrinsically low lattice thermal conductivity is crucial for the exploration of high‐performance thermoelectric materials. Herein, the layered compound GeBi2Se4 with intrinsically low lattice thermal conductivity is discovered, and its thermoelectric performance optimization is accelerated by machine learning. The ultralow lattice thermal conductivity of 0.53 W m−1 K−1 at room temperature for the GeBi2Se4 sample can be ascribed to the large anharmonicity and miscellaneous crystal defects. By alloying tellurium (Te) at the selenium (Se) site, the lattice thermal conductivity is further reduced due to the alloy scattering effect and chemical bond softening while the density‐of‐states effective mass of electrons is significantly increased. Finally, the best n‐type thermoelectric GeBi2Se1.9Te2.1 sample with a dimensionless figure of merit zT of 0.56 at 460 K is screened out by machine learning and verified by experiments, which increases by 140% in comparison with the pristine GeBi2Se4. [ABSTRACT FROM AUTHOR]

Recently, the 2D van der Waals (vdW) layered MA2Z4 series has attracted a lot of attention. Among these 2D materials, MoSi2P4 and WSi2P4 monolayers each demonstrate strong environmental stability, a moderate band gap, and considerable carrier mobility. The lattice thermal transport properties in MoSi2P4 and WSi2P4 monolayer structures have been investigated using first-principles calculations. Due to the gap present in the phonon energy band structure of the WSi2P4 monolayer within the middle frequency range, the specific heat capacity, phonon group velocity, and phonon relaxation time of the WSi2P4 monolayer structure are smaller than those of the MoSi2P4 monolayer structure. This makes the lattice thermal conductivity of the WSi2P4 monolayer lower than that of the MoSi2P4 monolayer. The MoSi2P4 structure has a lattice thermal conductivity of 28 W/mK at 300 K. The WSi2P4 structure has a lattice thermal conductivity of 14.5 W/mK in the x -direction and 15 W/mK in the y -direction. The results suggest that the MoSi2P4 and WSi2P4 monolayers can be potentially used as nanoelectronics devices for thermal transport applications. [ABSTRACT FROM AUTHOR]

The discovery of compounds with low thermal conductivity and the understanding of their microscopic mechanisms are of great challenges and scientific significance. Herein, we report a unique ternary sulfide compound, Cu3BiS3, in which all Cu atoms are coordinated within a two‐dimensional [CuS3] triangle plane. This local coordination leads to efficient out‐of‐plane phonon scattering and an ultralow thermal conductivity. Through DFT phonon spectrum calculations and analyses, we reveal that the lowest vibration frequency decreases from 2 THz for high‐dimensional [CuS4] tetrahedral coordinated Cu atoms in CuBiS2 (CN=4, with an average Cu−S bond length of 2.328 Å) to 1.5 THz for low‐dimensional [CuS3] triangular coordinated Cu atoms in Cu3BiS3 (CN=3, with a shorter Cu−S bond length of 2.285 Å). This is due to the out‐of‐plane thermal vibration of the Cu atoms in the latter. Consequently,Cu3BiS3 exhibits one of the lowest values of κlat (0.32 W/m K) among its peer, with a 36 % reduction compared to CuBiS2 (0.50 W/m K). This groundbreaking discovery highlights the significant role of 2D local coordination in reducing thermal conductivity through characteristic out‐of‐plane phonon scattering, while also contributing to a large Grüneisen parameter (2.06) in Cu3BiS3. [ABSTRACT FROM AUTHOR]

The binary compound Mg3Sb2 (also written as MgMg2Sb2) exhibits a much lower lattice thermal conductivity ( κ L ) than its ternary analog CaMg2Sb2, despite its relatively low mass density and simple crystalline structure. Here, we perform a comparative first-principles study of the lattice dynamics in MgMg2Sb2 and CaMg2Sb2 based on the density functional theory, together with the self-consistent phonon theory and the Boltzmann transport theory. We show that the modest anharmonicity of CaMg2Sb2 renders the three-phonon processes dominant, and the temperature dependence of κL approximately follows the T − 1 relationship. In contrast, the strong quartic anharmonicity of MgMg2Sb2 leads to the ultralow κL and weak temperature dependence, in agreement with the experimental observations. A comprehensive analysis reveals that the κ L s in the two compounds are mainly carried by the acoustic phonons associated with the Sb atoms, and the different behaviors of κ L result from the chemical bond changes around Sb atoms, which bond more covalently with the Mg atoms than the Ca atoms and thus lead to high-order anharmonicity in MgMg2Sb2. These results give us insights into the understanding of the anomalous thermal transport in thermoelectric materials. [ABSTRACT FROM AUTHOR]

The rapid evolution in materials science has resulted in a significant interest in high-entropy alloys (HEAs) for their unique properties. This study focuses on understanding both quaternary and quinary body-centered cubic (BCC) of 12 refractory-based HEAs, and on analysis of their electronic structures, lattice distortions, mechanical, and thermal properties. A comprehensive assessment is undertaken by means of density functional theory (DFT)-based first principles calculations. It is well known that multiple constituents lead to notable lattice distortions, especially in quinary HEAs. This distortion, in turn, has significant implications on the electronic structure that ultimately affect mechanical and thermal behaviors of these alloys such as ductility, lattice thermal conductivity, and toughness. Our in-depth analysis of their electronic structures revealed the role of valence electron concentration and its correlation with bond order and mechanical properties. Local lattice distortion (LD) was investigated for these 12 HEA models. M1 (WTiVZrHf), M7 (TiZrHfW), and M12 (TiZrHfVNb) have the highest LD whereas the models M3 (MoTaTiV), M5 (WTaCrV), M6 (MoNbTaW), and M9 (NbTaTiV) have the less LD. Furthermore, we investigated the thermal properties focusing on Debye temperature (ΘD), thermal conductivity (κ), Grüneisen parameter (γα), and dominant phonon wavelength (λdom). The NbTaTiV(M9) and TiVNbHf(M10) models have significantly reduced lattice thermal conductivities (κL). This reduction is due to the mass increase and strain fluctuations, which in turn signify lattice distortion. The findings not only provide an understanding of these promising materials but also offer guidance for the design of next-generation HEAs with properties tailored for potential specific applications. [ABSTRACT FROM AUTHOR]

Reducing lattice thermal conductivity (κl) that reflects the material’s heat-carrying capacity through lattice phonon vibrations is crucial for optimizing the figure of merit (zT). Using density functional theory (DFT) and density functional perturbation theory (DFPT), present work considers the structural, electronic, magnetic, and phonon properties of the XNiSn (X=Ti, Zr, Hf ) half Heusler (hH) compounds. TiNiSn, ZrNiSn, and HfNiSn are identified as semiconductors with indirect band gaps of 0.43 eV, 0.47 eV and 0.39 eV, respectively, exhibiting dynamical stability. The temperature- dependent κl of hH XNiSn are compared using Slack’s model with two approaches for analyzing phonon velocity: elastic constants from quasi- harmonic approximation (QHA) as implemented in the Thermo_pw code and slope of phonon bands based on DFPT. At room temperature, TiNiSn, ZrNiSn and HfNiSn have κl values of 28.61 Wm−1K−1, 34.61 Wm−1K−1 and 29.85 Wm−1K−1 respectively using phonon velocity from slopes of phonon bands based on DFPT. These values show deviation of 1.48%, 6.29%, and 5.82% to those κl values 29.01 Wm−1K−1’, 36.79 Wm−1K−1 and 31.59 Wm−1K−1 for TiNiSn, ZrNiSn and HfNiSn respectively using QHA.

The effect of pressure and temperature on acoustic and thermodynamic properties of cubic CsNbO3 (CNO) has been demonstrated using first principles method. The high values of velocity, impedance, and sound intensity exhibit CNO's potential acoustic applications. CNO is found thermodynamically unstable at 0 GPa, though it becomes stable at 20 GPa. The high Debye, melting temperatures, heat capacity, low thermal expansion coefficient, and thermal conductivity substantiate the compound can be used as thermal management material. The low value of the Gruneisen parameter corresponding to low anharmonicity proclaims higher lattice thermal conductivity of the material. The monotonic decline of lattice thermal conductivity with temperature is observed in CNO. The significant response of enthalpy, entropy, free energy, constant pressure heat capacity, and constant volume heat capacity with pressure and temperature have also been analyzed, which can be supportive for future investigations of CNO through experiments and theories.

Tin selenide materials have attracted much attention due to the intrinsic low thermal conductivity. However, the further application of SnSe materials is limited due to the poor electrical conductivity. Herein, a two-step doping process is employed on p-type polycrystalline SnSe materials to enhance the thermoelectric properties. It is found that the Sn0·98Ag0.01Ga0.01Se sample achieves a high ZT value of 1.53 at 823 K and a quite competitive ZTave value of 1.04 from 673 to 823 K. This is attributed to the associations of point defects, AgSn′, GaSn·, and Ga0, and nano-precipitates, SnGa4Se7, Ag9GaSe6 and AgGa1+δ. In those defects, AgSn′ acts as an accepter, which can conduce to enhancing the hole carrier concentration. Ga element doping astonishingly play dual-roles, in that it both faultlessly maintains the electrical transport properties and effectively decreases the thermal conductivity through the associations with the point defects, GaSn·, and Ga0, and nano-precipitates, SnGa4Se7, Ag9GaSe6 and AgGa1+δ. The method paves the way for achieving high thermoelectric properties in SnSe materials by the point defects engineering and nano-precipitates.

Mg3Sb2 has attracted intensive attention as a typical Zintl-type thermoelectric material. Despite the exceptional thermoelectric performance in n-type Mg3Sb2, the dimensionless figure of merit (zT) of p-type Mg3Sb2 remains lower than 1, which is mainly attributed to its inferior electrical properties. Herein, we synergistically optimize the thermoelectric properties of p-type Mg3Sb2 materials via codoping of Cd and Ag, which were synthesized by high-energy ball milling combined with hot pressing. It is found that Cd doping not only increases the carrier mobility of p-type Mg3Sb2, but also diminishes its thermal conductivity (κtot), with Mg2.85Cd0.5Sb2 achieving a low κtot value of ∼0.67 W m−1 K−1 at room temperature. Further Ag doping elevates the carrier concentration, so that the power factor is optimized over the entire temperature range. Eventually, a peak zT of ∼0.75 at 773 K and an excellent average zT of ∼0.41 over 300 − 773 K are obtained in Mg2.82Ag0.03Cd0.5Sb2, which are ∼240% and ∼490% higher than those of pristine Mg3.4Sb2, respectively. This study provides an effective pathway to synergistically improve the thermoelectric performance of p-type Mg3Sb2 by codoping Cd and Ag, which is beneficial to the future applications of Mg3Sb2-based thermoelectric materials.

ABSTRACTThe thermoelectric properties of a new type of Pr2-xSrxFeCrO6 double perovskite were investigated at higher temperature after its sol-gel synthesis. The XRD results validate the single-phase orthorhombic structure, and the crystallite sizes meet the morphological measurements. XPS examination, which formed the defect sites in these oxides, confirmed the varied oxidation states of constituents. The temperature-dependent electrical conductivity (σ) was poor in the original Pr2FeCrO6 composition, but after substituting Sr on the Pr-site, a significant rise in σ with two semiconductors and one metal transition was observed. A positive Seebeck coefficient confirmed the presence of a p-type charge carrier in the entire composition, and the charge transport mechanism was driven by the SPH model. Thermal conductivity increases in all doped samples, while it decreases in pristine compounds over the broad analyzed temperature range. Thermal expansion coefficient increased after doping in oxygen-deficient compound. The PrSrFeCrO6 compound had the maximum ZT (0.105), which was 3.9 times higher than that of the pristine compound.

Mg3(BixSb1−x)2 (0 ≤ x ≤ 1) nanocomposites are a highly appealing class of thermoelectric materials that hold great potential for solid-state cooling applications. Tuning of the lattice thermal conductivity is crucial for improving the thermoelectric properties of these materials. Hereby, we investigated the lattice thermal conductivity of Mg3(BixSb1−x)2 nanocomposites with varying Bi content (x = 0.0, 0.25, 0.5, 0.75, and 1.0) using first-principles calculations. This study reveals that the lattice thermal conductivity follows a classical inverse temperature-dependent relationship. There is a significant decrease in the lattice thermal conductivity when the Bi content increases from 0 to 0.25 or decreases from 1.0 to 0.75 at 300 K. In contrast, when the Bi content increases from 0.25 to 0.75, the lattice thermal conductivity experiences a gradual decrease and reaches a plateau. For the nanohybrids (x = 0.25, 0.5, and 0.75), the distribution patterns of the phonon group velocity and phonon lifetime are similar, with consistent distribution intervals. Consequently, the change in lattice thermal conductivity is not pronounced. However, the phonon group speed and phonon lifetime are generally lower compared to those of the pristine components with x = 0 and x = 1.0. Our results suggest that the lattice thermal conductivity is sensitive to impurities but not to concentrations. This research provides valuable theoretical insights for adjusting the lattice thermal conductivity of Mg3(BixSb1−x)2 nanocomposites. [ABSTRACT FROM AUTHOR]