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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 (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]

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]

In this study, Yb x Co 4 Sb 12 and In x Yb 0.3 Co 4 Sb 12 bulk materials were fabricated via microwave synthesis combined with spark plasma sintering. Based on ytterbium single filling, indium was further filled into the voids of CoSb 3. Carrier concentration and mobility were regulated as 1.6–1.8 × 1020 cm-³ and ∼30 cm2V−1S−1, respectively, resulting in an improved power factor of ∼4900 μWm−1K−2. The phonon-resonant scattering, caused by indium and ytterbium double filling, was combined with other phonon scattering mechanisms such as nano-inclusion, dislocation, and grain boundary segregation, which resulted in a significantly decreased lattice thermal conductivity of 0.72–2.08 Wm−1K−1. Owing to the improvements in carrier concentration and phonon transport, excellent thermoelectric performance, reflected by ZT = 1.38 at 773 K, was achieved in In 0.4 Yb 0.3 Co 4 Sb 12. • Indium and ytterbium double-filled skutterudite was successfully synthesized by microwave heating for the first time. • The carrier concentration was adjusted to a optimum range. • The power factor was greatly increased. • Multiple phonon scattering mechanisms result in an extremely low lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

Mg 3 Sb 2 has attracted intensive attention as a typical Zintl-type thermoelectric material. Despite the exceptional thermoelectric performance in n-type Mg 3 Sb 2 , the dimensionless figure of merit (zT) of p-type Mg 3 Sb 2 remains lower than 1, which is mainly attributed to its inferior electrical properties. Herein, we synergistically optimize the thermoelectric properties of p-type Mg 3 Sb 2 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 Mg 3 Sb 2 , but also diminishes its thermal conductivity (κ tot), with Mg 2.85 Cd 0.5 Sb 2 achieving a low κ tot 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 Mg 2.82 Ag 0.03 Cd 0.5 Sb 2 , which are ∼240% and ∼490% higher than those of pristine Mg 3.4 Sb 2 , respectively. This study provides an effective pathway to synergistically improve the thermoelectric performance of p-type Mg 3 Sb 2 by codoping Cd and Ag, which is beneficial to the future applications of Mg 3 Sb 2 -based thermoelectric materials. [ABSTRACT FROM AUTHOR]

[Display omitted] Nanograins and pores, as two common microstructural defects, are capable to impede phonon transport. However, thus far, the stability of nanograins at elevated temperature and the feasibility of porosity in boosting the figure of merit ZT are still concerned in thermoelectrics. Herein, we report that a specifically designed microstructure mainly consisting of ultrafine grains within the nanocrystalline regime and randomly distributed pores in α-MgAgSb gives rise to an ultralow lattice thermal conductivity ∼0.46 W m−1 K−1 at 300 K that breaks the limit of the estimated minimum value. Associated with a slightly deteriorated electrical performance, an unprecedented performance, ZT ∼0.94 at 300 K and ZT ave ∼1.16, are realized. Benefiting from optimized α-MgAgSb in this work and Mg 3.2 (Bi, Sb) 2 material to fabricate a Peltier module, we can achieve a high maximum temperature difference ΔT max ∼52 K and a maximum coefficient of performance COP ∼8.3 at hot-side temperature T h = 300 K, outperforming these previously reported non-Bi 2 Te 3 modules. This is, to our knowledge, the first demonstration of high performance thermoelectric modules mediated by the utilization of ultrafine grains and nanoporous structures, which provides a swift pathway to accelerate the wide employment of thermoelectric cooling technology in modern society. [ABSTRACT FROM AUTHOR]

We fabricate Bi 1−x-y Pb y Cu 1−x SeO (x = 0, 0.03, 0.06, y = 0, 0.10) samples via 4 min-microwave synthesis combined with 5 min-spark plasma sintering. The phase composition, microstructure, valence, and electrical and thermal transport properties of the samples are investigated at 298–873 K. Pb doping provides impurity carriers and increases the concentration to 0.9–3.0 × 1020 cm-³. Bi and Cu vacancy could provide a carrier transport channel to reduce carrier scattering probability, leading to improved mobility. Twin crystals, stacking faults, and grain boundary segregation are observed in Bi 0.87 Pb 0.10 Cu 0.97 SeO on scanning transmission electron microscopy. Bi and Cu vacancy increase the sample point defects in Pb-doped or undoped samples which results in a decrease in lattice thermal conductivity. The lattice thermal conductivity of Bi 0.87 Pb 0.10 Cu 0.97 SeO is decreased to an extremely low value of 0.13 Wm−1 K−1 and a maximum ZT value of 1.09 is achieved at 873 K. [ABSTRACT FROM AUTHOR]

Van der Waals heterostructures (vdWHs) have attracted considerable interest owing to their outstanding performances. In this study, we investigated the structural, electronic, optical, phonon transport, and thermoelectric properties of BAs-MXY vdWHs (MXY=TiSO, TiSeO, ZrSO, ZrSeO, HfSO, and HfSeO) using the density functional theory and Boltzmann transport equation. The stability of the designed vdWHs is verified based on their thermal, mechanical, and dynamic properties. Band structures explored using PBE and HSE06 functionals revealed that most vdWHs are indirect band semiconductors. The BAs-MXY vdWHs can effectively harness incident radiation. An increase in the Seebeck coefficient and electrical conductivity and a decrease in the thermal conductivity are observed with respect to temperature owing to the softening mode of phonons. The improved dimensionless figure of merit (ZT) indicates the possibility of designing BAs-MXY vdWHs for optoelectronic and thermoelectric applications. [Display omitted] • The electronic, optical, phonon transport, and thermoelectric properties of BAs-MXY vdWHs (MXY=TiSO, TiSeO, ZrSO, ZrSeO, HfSO, and HfSeO) are explored. • The stability of the designed vdWHs is verified by thermal, mechanical, and dynamic properties. • The designed heterostructures have better absorption in the visible region than in the ultraviolet region. • The Seebeck coefficient and electrical conductivity increased, while the thermal conductivity decreased with temperature. [ABSTRACT FROM AUTHOR]

Recently, CdX (X = Se, Te) materials have garnered notable interest owing to their great application potential for high-efficiency solar cells, fiber optic communication systems, and nanoelectronic devices. The performance of optoelectric devices is significantly influenced by the thermal conductivity. In this study, a combination of machine-learning methods and first-principles calculations is utilized to investigate the phonon thermal transport properties of CdSe and CdTe, as well as to give deep insights into the phonon behavior in heat transfer. It is found that acoustic phonons dominate the lattice thermal conductivity (κ) in CdSe, while optical phonons contribute around 50 % to the κ value in CdTe. There are strikingly strong four-phonon scattering phenomena in both materials, which result in 55 % and 66 % reduction in κ values for CdSe and CdTe, respectively. Further analysis shows that the mid-frequency phonons play an important role in amplifying the four-phonon scattering. Its special frequency positions permit an unusually large number of four-phonon scattering processes to occur and cause large scattering of low-frequency phonons. This mechanism differs from earlier proposed features regarding large acoustic-optical gaps, bunching of acoustic branches and four-phonon Fermi resonance, which implies strong four-phonon anharmonicity. Thus, the present work opens up new prospects in the exploration and design of innovative thermoelectric material, which provides a more thorough understanding of the four-phonon scattering mechanisms in crystalline solids. • The optical phonons located in the mid-frequency range amplifying the four-phonon scattering. • The acoustic phonons of CdSe dominates its k , while the second optical branch of CdTe dominates its k. • Heavy-atom compression frequencies that greatly enhance the four-phonon scattering process for low-frequency phonons. [ABSTRACT FROM AUTHOR]

Skutterudite (CoSb 3) is a kind of promising environment-friendly medium-temperature thermoelectric material. Indium-filled CoSb 3 has been widely studied, but its bipolar effect, which is commonly generated between 600 and 700 K, seriously hinders the increase of Seebeck coefficient and zT value. The zT value not only directly reflects the overall thermoelectric performance of the material, but also reflects the thermoelectric conversion efficiency of the device. In this work, In filled and Fe, Se double doped CoSb 3 materials were successfully prepared by high-temperature and high-pressure synthesis method (HPHT), with a significant shorten synthesis time of 30 mins for each sample. This research has shown that after Se doping via HPHT synthesis method, the bipolar effect of In-filled CoSb 3 was significantly suppressed, thus the temperature limitations of electrical transport performance has been overcome. Through the further microstructure analysis, it was found that the crystal structure of sample In 0.5 Fe 0.01 Co 3.99 Sb 11.91 Se 0.09 has the characteristics of multiple grain sizes and complex defect types. And these two microscopic morphological characteristics resulted in the sample obtaining a minimum lattice thermal conductivity of 0.94 Wm−1K−1 at a test temperature of 773.15 K. Through synergistic optimization of synthesis methods and element substitution, the maximum zT value of 1.21 of the sample In 0.5 Fe 0.01 Co 3.99 Sb 11.91 Se 0.09 has been found at 773.15 K. • The processing time of samples can be reduced from a few days to half an hour. • The minimum lattice thermal conductivity of 0.94 Wm−1K−1 was obtained for In 0.5 Fe 0.01 Co 3.99 Sb 11.91 Se 0.09 at 773.15 K. • The maximum zT value of In 0.5 Fe 0.01 Co 3.99 Sb 11.91 Se 0.09 at 773.15 K reached 1.21. [ABSTRACT FROM AUTHOR]

Low lattice thermal conductivity is one of the key factor for excellent thermoelectric performance of materials. In this work, we have systematically studied the thermoelectric properties of Ag 2 GeX 3 (X = S, Se, Te) by first-principles calculations in combination with Boltzmann transport theory. In terms of phonon transmission performance, due to the low frequency of acoustic phonons, strong coupling between low-frequency optical phonons and acoustic phonons, and relatively strong anharmonicity, Ag 2 GeX 3 (X = S, Se, Te) exhibits extremely low lattice thermal conductivity of 0.30 Wm−1K−1, 0.28 Wm−1K−1 and 0.65 Wm−1K−1 at room temperature, respectively. At the same time, Ag 2 GeX 3 (X = S, Se, Te) also exhibits good electrical transport performance. The appropriate band gap and high slope of electronic density of states (DOS) near the Fermi level result in a large Seebeck coefficient of the materials. As a result, the optimal ZT values of p(n)-type Ag 2 GeX 3 (X = S, Se, Te) are 1.4(1.2), 2.2(0.7), and 0.9(0.7) at 800 K, respectively. These results demonstrate outstanding thermoelectric performance of Ag 2 GeSe 3 for energy conversion applications. • The optimal ZT values of p(n)-type Ag 2 GeX 3 (X = S ,Se and Te) are 1.4(1.2), 2.2(0.7), and 0.9(0.7) at 800 K, respectively. • These results demonstrate outstanding thermoelectric performance of Ag 2 GeSe 3 for energy conversion applications. • This article reveals the source of low lattice thermal conductivity of Ag 2 GeX 3 (X = S, Se, Te). [ABSTRACT FROM AUTHOR]

Monolayer metal iodides are garnering widespread attention due to their ultralow lattice thermal conductivity and their potential applications in the field of thermoelectrics. Here, we utilized first-principles calculations and Boltzmann transport theory to thoroughly investigate the thermoelectric behavior of monolayer InI. Results indicate that this material functions as a direct bandgap semiconductor and features an exceptionally low lattice thermal conductivity of 0.27 W m−1K−1 at 300 K, a result of its low group velocities and short phonon lifetimes. Furthermore, transport coefficients were calculated with enhanced precision through the Wannier interpolation method, incorporating the HSE06 hybrid functional and spin-orbit coupling (SOC) effects. Remarkably, the maximum thermoelectric figure of merit (ZT) values for monolayer InI demonstrate substantial growth with increased temperatures, surging from 0.31 at 300 K to 1.20 at 450 K for p-type, and escalating from 0.26 at 300 K to 0.72 at 450 K for n-type. These promising low-temperature thermoelectric properties exhibited by monolayer InI suggest its suitability for integration into the production of thermoelectric devices. • Monolayer InI is a direct bandgap semiconductor with a bandgap of 2.73 eV. • Monolayer InI has an ultra-low lattice thermal conductivity of 0.27 W m⁻1K⁻1 at 300 K. • Transport coefficients were evaluated using the Wannier interpolation method with HSE06 hybrid functional and SOC effects. • The ZT value of monolayer InI increases obviously with temperature, reaching 1.20 for p-type and 0.72 for n-type at 450 K. [ABSTRACT FROM AUTHOR]

The electronic, optical, elastic, and thermal transport properties of half-Heusler-derived (HHD) Ti 2 FeNiSb 2 are comprehensively characterized via density functional theory. The stability of HHD Ti 2 FeNiSb 2 is evaluated by the phonon dispersion, formation energy, and phase separation, and its elastic constants meet the mechanically stable conditions. HHD Ti 2 FeNiSb 2 is predicted to be an indirect nonmagnetic semiconductor with a bandgap of 0.94 (PBE) eV and 1.75 (HSE06) eV. To further understand the electronic structures, the atomic orbital projection of the electronic band structure is systematically studied and discussed. The band structures and bandgap can be sensitively tuned by the strain. The calculated elastic and optical properties indicate that Ti 2 FeNiSb 2 has good ductility and hardness, and the optical property calculations reveal its excellent potential for harvesting solar energy. Using the elastic properties, the minimum lattice thermal conductivity is evaluated by the Slack, Clarke, and Cahill models. Based on the Slack model, the lattice thermal conductivity is 5.93 W/mK at 300 K; this value is consistent with the experimental value. [ABSTRACT FROM AUTHOR]

A glassy zeolitic imidazolate framework-62 (g -ZIF-62) is used to composite with GeTe for effectively enhancing the mid-frequency phonon scattering to decrease the thermal conductivity of GeTe. After compositing, g -ZIF-62 distributes at the grain boundary of GeTe, leading to reduced lattice thermal conductivity (κ l) of 0.31 W m–1 K–1 at 673 K, which is close to the theoretical amorphous limit of GeTe. Meanwhile, the introduction of g -ZIF-62 refrains the hall mobility and electrical conductivity, thus leading to minimized electrical thermal conductivity (κ e). Accordingly, such g -ZIF-62 compositing can solely increase the ZT (dimensionless figure of merit) of GeTe of around 32 % at 723 K, even though the other parameters are not technically optimized for improving thermoelectric properties of GeTe. This study suggests that compositing g -ZIF-62 with GeTe can effectively strengthen the mid-frequency phonon scattering to decrease κ l and κ e of GeTe, providing a reasonable way to enhance the ZT of the thermoelectric materials. • We composited g -ZIF-62 into GeTe and studied its influence on TE performance. • Realize the preferential distribution of g -ZIF-62 at grain boundaries of GeTe. • Approach ultra-low lattice thermal conductivity of 0.31 W m–1 K–1 at 673 K. [ABSTRACT FROM AUTHOR]

Carbide materials find extensive application as tool materials due to their exceptional properties, encompassing high hardness, wear resistance, and robust strength. Exhibiting diverse bonding characteristics, carbides constitute a pivotal material class in modern-day technologies. The structural and energetic attributes of grain boundaries play a vital role in understanding the properties of polycrystalline materials, necessitating an examination of the grain boundary regime. In this study, metal carbide grain boundaries, specifically the Kingery type Σ3 (111) grain boundaries in TiC, TaC, and WC, were systematically investigated utilizing density functional theory calculations. The scrutiny comprehends their structural, electronic, mechanical, and thermal properties. Results show that the investigated grain boundaries are energetically stable. The calculated electronic properties further unveil the presence of metallic behavior. Dynamic stability was observed at 0 K for Σ3 (111) grain boundaries constructed from the L1 0 cubic lattice structure in TiC, while phonon softening was observed for the Σ3 (111) grain boundaries structures in TaC and WC. Thermodynamic properties, including Helmholtz free energy, heat capacity, and entropy, were thoroughly scrutinized. Mechanical properties suggest the ductile behavior with significant metallic nature of considered grain boundary systems. The study extended to thermal properties, examining the lattice thermal conductivity (κ L) of the considered grain boundary systems. It was observed that the Σ3 (111) grain boundary in TiC significantly increases the thermal conductivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Several experimental studies have been conducted on the thermoelectric properties of cementitious materials, but a detailed inspection of the intrinsic properties of their main ingredients is still missing. This work focuses on the thermoelectric properties of portlandite and tobermorite, two mineral components found in Ordinary Portland Cement pastes. To this end, atomistic simulations were carried out to predict the thermoelectric properties of cement-based materials. The methodology is based on the density functional theory approach together with GW-quasiparticle and Boltzmann transport equation methods. As expected, the undoped minerals have low thermal conductivity. However, both the Seebeck coefficient and the electrical conductivity can be dramatically increased by appropriate carrier doping. In fact, an enhanced figure of merit of Z = 0.6 at 650 K and 0.79 at 600 K is observed for portlandite and tobermorite. Therefore, our results confirm that there are still much promising prospects for enhancing the characteristics of concrete materials for energy harvesting. • Proposed the calculation of thermal conductivity of cement composite with slack model. • Significantly improved the ZT of portlandite and tobermorite-11 by carrier doping. • Doping one atom of silicon with aluminum achieves ZT = 0.5 at 600 K. [ABSTRACT FROM AUTHOR]

Understanding the microscopic dynamics of the fundamental energy carriers in condensed matter under extreme pressure conditions can reveal insights into unique physical phenomena that are otherwise not easily discernible at ambient conditions. Here, by utilizing a combination of machine learning interatomic potential (MLP)-based molecular dynamics simulations to calculate phonon thermal conductivity and parameter-free first-principles calculations of electron–phonon coupling and electronic thermal conductivity, we show that (contrary to typical elemental metals) the phonon contribution to the total thermal conductivity in iridium can be increased from 18% at ambient conditions to 40% at 60 GPa hydrostatic pressure conditions. The strength of electron–phonon scattering, as quantified by the mass enhancement parameter, decreases monotonically with pressure resulting in an increase in the lifetime of electrons around the Fermi energy. This consequently leads to a monotonic increase in the electron thermal conductivity from 134 W m−1 K−1 at ambient to 177 W m−1 K−1 at 60 GPa. Similarly, the phonon thermal conductivity has a relatively higher increase from 30 W m−1 K−1 at ambient to 120 W m−1 K−1 at 60 GPa. This is attributed to considerable phonon hardening and increase in the group velocity of the heat carrying phonons with pressure. Along with the pronounced phonon contributions to the total thermal conductivity, we also show that the temperature dependence of the phonon thermal conductivity at ambient pressure is dictated by higher-order phonon interactions (beyond the typical three-phonon processes) in iridium. • Lattice contribution to thermal conductivity in iridium increases from 18% at 0 GPa to 40% at 60 GPa. • Higher-order phonon scattering (beyond three-phonons) dictates the lattice contribution. • Electron-phonon coupling decreases with increasing pressure in iridium. [ABSTRACT FROM AUTHOR]

The charge density plot along 110 plane of the AGeO 3 (A = Mg, Cd) compounds. [Display omitted] • Transport properties and thermodynamic properties of AGeO 3 (A = Mg, Cd) perovskites have been performed by FP-LAPW method. • The MgGeO 3 and CdGeO 3 alloys have a gap of 3.368 and 2.555 eV, respectively, making them indirect band gap semiconductors. • The lattice thermal conductivity magnitudes for MGeO 3 and CdGeO 3 are 7.47 W/mK and 21.55 W/mK, respectively, at 300 K. • The thermodynamic parameters, such as heat capacity, entropy, and Debye temperature, were also computed. In this manuscript, transport properties like thermoelectric and thermodynamic properties of AGeO 3 (A = Mg, Cd) perovskites have been performed in detail along with effect of chemical potential on various thermoelectric parameters. Furthermore, we present the electronic effects and thermodynamic stability of these materials. The MgGeO 3 and CdGeO 3 alloys have a gap of 3.368 and 2.555 eV, respectively, making them indirect band gap semiconductors. Furthermore, using a constant relaxation time approximation and semiclassical Boltzmann theory, the thermoelectric (TE) properties of both materials have been studied. The lattice thermal conductivity magnitudes for MGeO 3 and CdGeO 3 are 7.47 W/mK and 21.55 W/mK, respectively, at 300 K. Power Factor (PF) has been measured at approximately 0 chemical potential, or approximately 14 (1011 W/K2 ms) at 1200 K, 7.5 (1011 W/K2 ms) at 700 K, and 3.5 (1011 W/K2 ms) at 300 K for both MgGeO 3 and CdGeO 3. At room temperature, the electrical conductivities of MgGeO 3 and CdGeO 3 were measured to be 1.43 × 1015W/mK and 1.08 × 1015W/mK, respectively. Over a broad temperature range (0–1200 K), the thermodynamic parameters, such as heat capacity, entropy, thermal expansion, and Debye temperature, were also computed and discussed. [ABSTRACT FROM AUTHOR]

The inorganic double perovskites (DPs) Cs 2 SbAuX 6 (X = Cl, Br, I) are an emerging applicant for solar cells, optoelectronic, and thermoelectrics to acquire clean energy. Therefore, the present research thoroughly addresses the mechanical, thermodynamic, optical, and thermoelectric characteristics by modified Becke and Johnson potential of Trans and Balaha (TB-mBJ) and BoltzTraP code. The structural stability is narrated from the tolerance factor and thermodynamic stability by formation energy. Born criteria assure the mechanical existence of cubic structures. The Cs 2 SbAu(Cl/Br) 6 is ductile, and Cs 2 SbAuI 6 has brittle behavior with a metallic nature. The band structures analysis reports the narrow band gaps for Cl/Br and the zero band gap for I-based DPs. The optical properties are studied by dielectric constants, absorption bands, refractive index, and other dependent optical parameters. Lastly, thermoelectric characteristics regarding Seebeck coefficient, electrical conductivity, power factor, thermal conductivity, and figure of merit in the temperature range 200–600K are analyzed. ZT's significant value at room temperature makes them potential candidates for thermoelectric generators. • Double perovskites are emerging Aspirant for solar cells. • The large value of efficiency of conversion light energy into electrical energy. • The absorption bands exist visible to infrared region. • The large figure of merit at room temperature. [ABSTRACT FROM AUTHOR]

Despite the increasing attention on two-dimensional (2D) metal iodides in recent years for their appropriate bandgaps and exceptional optical properties, there is limited understanding of their intriguing thermal transport properties. Here, the strain-tunable mechanic, electronic, and transport properties of the monolayer CaI 2 are calculated in detail by combining first-principles calculations with Boltzmann transport theory. We have checked its thermal, dynamic, and mechanical stability by computing ab -initio molecular dynamics, phonon spectra and elastic constants, respectively. The calculation results from the PBE-GGA and HSE06 methods indicate that the monolayer CaI 2 is an indirect semiconductor, with band gaps of 3.92 eV and 5.12 eV, respectively. Additionally, the effective masses and Fermi velocities for both holes and electrons are also obtained, which indicates that the monolayer CaI 2 owns the excellent electronic transport property. These mechanical constants and electronic parameters are also highly sensitive to the external strain. The calculated real lattice thermal conductivity of the monolayer CaI 2 at 300 K is about 1.01 W/mK, which is rather low among 2D materials, implying its potential application in heat insulation materials or thermal insulation material. With the biaxial tensile strain increasing, its lattice thermal conductivity would further decrease. The difference in lattice thermal conductivities between 0 % and 2 % strain, as well as between 4 % and 6 % strain, is much smaller than that between 2 % and 4 % strains. Subsequently, the group velocities, phonon scattering rates, and cumulative lattice thermal conductivities of the monolayer CaI 2 are discussed under the different strains. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strong EPI significantly reduces thermal conductivity in the C 3 B monolayer. • The reduction of κ induced by EPI is closely related to electron DOS. • The electronic band structure of C 3 B exhibits multivalley characteristics. • Unusual phenomenon of large el-ph scattering with low el-ph strength is uncovered. • The B atoms of C 3 B break structural symmetry and induce mass disorder scattering. Recently, the two-dimensional semiconductor C 3 B monolayer has attracted much attention owing to its excellent physical, optical, and electronic properties. In this work, the origin of electron-phonon interaction (EPI) on the thermal properties of C 3 B by n -type and p -type doping is systematically investigated via first-principles calculations to provide fundamental knowledge for the thermal management the C 3 B-based electronic devices. The carrier concentrations for the largest reduction of the lattice thermal conductivity (κ) appear at 4 × 1014 cm−2 for n -type and 9 × 1014 cm−2 for p -type, which is closely related to the electron density of states (DOS). The boron (B) atoms break the structural symmetry and induce mass disorder scattering, which renders C 3 B more prone to the influence of EPI. Moreover, the electronic band structure in the C 3 B monolayer exhibits multivalley characteristics, which leads to an intervalley scattering. It is worth noting that the anisotropy in the C 3 B monolayer can be significantly enhanced by EPI. Additionally, an abnormal phenomenon of strong electron-phonon scattering but low electron-phonon coupling strength is found in C 3 B monolayer, which indicates that large electron-phonon coupling strength is sufficient but not necessary for strong electron-phonon scattering. [ABSTRACT FROM AUTHOR]

[Display omitted] Structural, electronic, lattice dynamics, optical, elastic, and thermoelectric features of Indium based Perovskite InGeX 3 (X = F, Cl) are studied by using WIEN2k code within density functional theory DFT. A level of the Boltzmann transport theory is used to derive electronic transport coefficients together with anticipated electronic relaxation times. These compounds exhibit stability and are cubic with the space group Pm-3m 221, according to the structural analysis. The band structure having the 2.15 eV and 1.29 eV band gap and density of state (DOS) are calculated for electronic characteristics, indicating that both compounds are semiconducting. For the analysis of elastic characteristics, elastic constants, bulk modulus (49.99, 22.69), Poisson's ratio (0.343, 0.261), anisotropy factor (0.52, 0.59), and Pugh's ratio (2.87, 1.75) are examined. The ductile nature of the compounds is described by Pugh's ratio, and the ionic nature can be ascertained by evaluating the Cauchy pressure. In the energy range of 0–10 eV, optical features like reflectivity, optical conductivity, refractive index, extinction coefficient and absorption coefficient are computed. These compounds broad-range absorption in the UV spectrum suggests that they could be good optoelectronic device candidates. The transport feature like Seebeck coefficient, thermal and lattice conductivity, power factor, electrical conductivity, and figure of merit zT (0.99, 0.98) can be calculated against temperature. The chemical potential against an excellent thermoelectric property of InGeX 3 (X = F, Cl) have high figure of merit due to high Seebeck and electrical conductivity. These predicted outcomes indicated that both compounds are suitable candidates for thermoelectric applications. Such compounds can replace with other renewable energy sources in thermoelectric devices because of their powerful thermoelectric response. [ABSTRACT FROM AUTHOR]

• 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 unique transport properties make CuInTe 2 emerge as a promising thermoelectric material. However, the intrinsically low carrier concentration and high lattice thermal conductivity of CuInTe 2 limit its thermoelectric performance. In this work, firstly, we investigate the influence of excess Te on the electrical and thermal transport properties of CuInTe 2. The results suggest that excess Te can act as both electron acceptors and phonon scattering centers, which simultaneously optimizes the carrier concentration and impedes the propagation of high-frequency phonons. Furthermore, the substitutional Ag/Cu defects integrated with excess Te lead to a further reduction in lattice thermal conductivity. DFT calculations indicate that the substitution of Ag for Cu can reduce phonon group velocity and intensify the acoustic phonon scattering, which agrees well with our experimental data. Finally, a high zT value of 1.03 is obtained @840 K for sample Cu 0.8 Ag 0.2 InTe 2.2. This study demonstrates a facile but effective approach to boost the thermoelectric performance of chalcopyrite compounds. [Display omitted] • Excess Te optimizes the carrier concentration and impedes the propagation of high-frequency phonons. • The introduction of Ag on Cu sites results in a further reduction in lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

• Many locally nano-domains exist in the high pressured NaCl-type SnTe binary compounds. • The domain phases are the CuPt and CuAu-I-type variants evolved from the NaCl-type matrix phase. • The formations of the domain phase are related to locally off-stoichiometric of SnTe and strong inner-stress in the lattices. • The domain phase can inhibit the phonon relaxation time by orders of magnitude over a wide phonon frequency range. • The domain phase benefits to a wide frequency phonon scattering network and thus a low lattice thermal conductivity. The phonon transport is intensively related to microstructure defects. Herein, a unique high-pressure sintering technology (GPa-level) was applied to modify the microstructure of pristine SnTe. There are many nano-domains exist in the high pressured NaCl-type SnTe binary compounds. The fast Fourier transform images show the domain phases have two sets of reflections with comparable intensity and exhibit doublet periodicities of special lattice planes, which demonstrates the domain phases are the CuPt and CuAu-I-type variants evolved from the NaCl-type matrix phase. An in-depth investigation indicates the constructions of the domain phase are related to locally off-stoichiometric of SnTe and the introduced strong inner-stress during high pressure sintering process. Additionally, a calculation of the phonon transport discloses the nano-domains restrict the phonon relaxation time by orders of magnitude over a wide phonon frequency range. As a result, a wide frequency phonon scattering network can be established to lower the lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

Filled CoSb 3 -based skutterudites are promising middle-temperature thermoelectric materials. However, p-type skutterudites containing electropositive fillers require additional charge compensation by doping atoms at the framework, which leads to enhanced carrier scattering. In this work, p-type filled CoSb 3 materials with electronegative guest Cl were successfully prepared by high-pressure high-temperature (HPHT) process. A high filling fraction of Cl in void sites reaching ∼23% was obtained without charge compensation. Cl filler exhibited p-type electron acceptor behavior and can increase hole concentration of pristine CoSb 3 to a magnitude of 1019 cm−3. As the content of Cl rose, abnormal spinal morphology and fine nano grain were observed in Cl-filled skutterudites. In turn, lattice thermal conductivity of Cl 0.6 Co 4 Sb 12 sample significantly reduced by 46% when compared to pristine CoSb 3 at room temperature due to enhanced scattering of point defect, rattler, and grain boundary. In sum, HPHT process looks promising for using Cl as additional p-type dopant candidate to yield significantly enhanced phonon scattering. [ABSTRACT FROM AUTHOR]

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]

The quenching process effectively reduces Ge enrichment, while the introduction of Bi to GeTe efficiently regulates the carrier concentration to the optimal level. Moreover, the incorporation of AgCuTe alloying, with its capacity to lower the Ge enrichment and introduce the secondary phase Cu 2 Te, significantly decreases the lattice thermal conductivity to the amorphous level. Ultimately, the (Ge 0.94 Bi 0.06 Te) 0.98 (AgCuTe) 0.02 sample demonstrates a remarkable peak ZT value of approximately 2.27 at 773 K. [Display omitted] • The quenching process reduces Ge's enrichment, leading to reduced thermal conductivity. • AgCuTe alloying introduces Cu 2 Te and regulates the ratio of Ge/Te. • The (Ge 0.94 Bi 0.06 Te) 0.98 (AgCuTe) 0.02 sample exhibits a peak ZT of ∼2.27 at 773 K. Germanium telluride (GeTe) exhibits substantial potential as a thermoelectric material well-suited for mid-temperature applications. The presence of a significant amount of off-stoichiometric Ge leads to the formation of Ge precipitates and vacancies, which exert a pronounced influence on the electrical and thermal transport properties of GeTe. In this study, a heat treatment process is initially applied to alleviate Ge enrichment within pristine GeTe, resulting in the achievement of a uniform distribution of Ge precipitates throughout the matrix. Subsequently, we coarsely optimize the carrier concentration through Bi counter-doping, thereby attaining the desired range for optimal performance. Notably, we finely adjust the Ge/Te ratio through AgCuTe alloying, effectively modulating Ge precipitation, reducing lattice thermal conductivity, and enhancing the thermoelectric performance of GeTe. Consequently, the synthesized sample (Ge 0.94 Bi 0.06 Te) 0.98 (AgCuTe) 0.02 exhibits a peak ZT value of approximately 2.27 at 773 K, with an average ZT value of approximately 1.38 within the temperature range of 323 to 773 K, making this material as a prominent candidate for medium-temperature thermoelectric applications. [ABSTRACT FROM AUTHOR]

In the current study, the novel pristine compounds of both VEC 18 (NiVAl & NiAlSb) and VEC 19 (NiVSn) materials have been synthesized employing arc-melting and hot-pressed at 1073 K. The measured carrier concentration for all the compounds was found ∿ 1020-1021 cm−3. Further, NiAlSb, NiVAl, and NiVSn half-Heusler (HH) compounds exhibited n-type semiconductor behaviour, with maximum Seebeck coefficients (S) of −50.2 μV/K, −40.5 μV/K, and −14.5 μV/K at 723 K. As a result of the measured S and electrical conductivity, the estimated power factor for NiVSn (0.20 mWm−1K−2), NiAlSb (0.41 mWm−1K−2), and NiVAl (0.65 mWm−1K−2) at 723 K. The NiVSn lattice thermal conductivity ( κ l) was reduced to ∿ 79.80 % and 76.71 % as compared to NiAlSb and NiVAl compounds. Despite having reduced κ l , low zT exhibited for NiVSn compound mainly due to nominal S. The reduced κ l was mainly attributed to weak chemical bonding results from lower group velocity of phonon, leading to a higher anharmonicity effect in the lattice. Therefore, NiVSn of VEC 19-based compound can be considered as a potential candidate material for TE applications other than traditional 18-VEC HH compounds. The thermoelectric performance of the novel HH compounds is suitably corroborated with the structural and microstructural investigations. [Display omitted] • Novel NiVAl, NiAlSb (VEC-18) and NiVSn (VEC-19) HH compounds were synthesized employing arc melting and hot press at 1073 K. • The maximum power factor of 0.65mWm−1K−2 for NiVAl is ∿30 % more than conventional TiCoSb. • The lattice anharmonicity significantly reduced κ L ∿79.8 % for NiVSn of 19 VEC as compared to NiAlSb of 18 VEC. • The power factor of novel NiVSn of 19 VEC can be enhanced by Band engineering approach. [ABSTRACT FROM AUTHOR]

High-efficiency thermoelectric materials require two essential characteristics; low lattice thermal conductivity (κ l) and high power factor (PF). Although group-III chalcogenides exhibit extremely high PF , their high κ l hinders their practical applications. Through first-principles calculations, we have discovered that the LiMTe 2 (M = Al, Ga, and In) monolayers, which have a similar structure stacking as the group-III chalcogenides, simultaneously possess the two key characteristics mentioned above. The κ l values of the LiMTe 2 monolayers are as low as 1.4−2.0 W m −1 K − 1 at room temperature. Detailed analysis of bonding characteristics and phonon scattering rates suggests that the ultralow κ l can be mainly attributed to the strong bond anharmonicity, which is a result of the cooperative endeavor of bond heterogeneity (coexistence of strong covalent bonds and weak ionic bonds) and the existence of lone-pair electrons. Additionally, the "pudding-mold" type of the conduction band near the Fermi level contributes to the high power factor of LiMTe 2 monolayers. Therefore, the ZT values of n -type doped LiMTe 2 monolayers exceed 1 at T = 800 K and carrier conentration of 1.71 × 1012 – 3.32 × 1012 cm − 2, indicating the great potential of the 2D LiMTe 2 -family under n -type doping as high-temperature thermoelectric materials. The current work suggests that increasing bond complexity and the introduction of lone-pair electrons are strategic pathways for designing high-performance thermoelectric materials. [Display omitted] • The lattice thermal conductivities of LiMTe 2 (M = Al, Ga, and In) monolayers are as low as 1.4−2.0 W m−1 K−2 at 300 K. • The bonding heterogeneity and lone-pair electrons is responsible for their low lattice thermal conductivity. • The "pudding-mold" type of conduction band near the Fermi level results in high power factors. • The n -type doped LiMTe 2 monolayers are promising high-temperature thermoelectric materials. [ABSTRACT FROM AUTHOR]

We present a detailed study on the phonon thermal transport and thermoelectric (TE) properties of gold monochalcogenide AuX (X = S, Se, Te) monolayers via first-principles calculations and the Boltzmann transport theory. At room temperature, the calculated lattice thermal conductivity (κ l) values in the x -direction (y -direction) were determined to be 12.66 (3.59), 6.06 (1.23), and 3.02 (0.40) W/(m·K) for the AuS, AuSe, and AuTe monolayers, respectively. The analysis of scattering matrix elements and anharmonic scattering rates suggested that the presence of strong bond anharmonicity leads to low κ l values. This anharmonicity was induced by the nonlinear electrostatic repulsive force between lone-pair electrons (LPEs) surrounding the chalcogen atom and adjacent bonding electron. Furthermore, the AuS monolayer exhibited the highest bond anharmonicity among the three monolayers. This can be attributed to the reduced strength of the electrostatic repulsive force when electronegativity decreased from S to Se and Te. Although the AuS monolayer exhibited the strongest bond anharmonicity, its κ l was still the largest, demonstrating that among the factors that influence κ l , harmonic factors have a greater effect than anharmonic parameters. When the atomic mass was increased, the phonon frequencies, phonon group velocities, and κ l decreased. Benefiting from low κ l induced by LPEs, the maximum ZT values of p -type doped AuSe and AuTe monolayers exceeded 1.0 and 2.0 at T = 800 K, respectively. These results not only confirmed that the introduction of LPEs can reduce the lattice thermal conductivity and enhance the TE performance of 2D materials, but also demonstrated the promising potential of the 2D AuX family for applications in high-temperature TE devices. [Display omitted] • The harmonic factors dominate over the anharmonic parameters in determining the κ l of AuX monolayers. • The lone-pair electrons lead to strong bond anharmonicity, which greatly suppresses the lattice thermal conductivity. • The maximum ZT values of p -type doped AuSe and AuTe monolayers exceeded 1.0 and 2.0 at T = 800 K, respectively. [ABSTRACT FROM AUTHOR]

In the present work electronic, structural and thermoelectric properties of newly designed layered rare-earth metal germanide halides such as Y 2 GeX 2 (X = Cl, Br, I) are investigated. These materials are indirect band gap semiconductors with narrow band gap 0.30 eV for Y 2 GeCl 2 ,0.36 eV for Y 2 GeBr 2 , and 0.41 eV for Y 2 GeI 2 respectively. First principles method along with Boltzmann transport equations (BTE) is utilized together to analyse the thermoelectric properties. These materials are dynamically and mechanically stable. Thermoelectric coefficients such as electrical conductivity, seebeck coefficient and thermal conductivity are computed and put together to ultimately get the Figure of merit (ZT). Y 2 GeI 2 has highest figure of merit (ZT) of 0.42 with Seebeck coefficient 532.12 VK − 1 , electrical conductivity 8.6 × 1 0 5 Sm − 1 and has lowest lattice thermal conductivity value of 5.55 Wm − 1 K − 1 among three materials, which is necessary to achieve high figure of merit. The computed value of Figure of merit 0.07, 0.22 and 0.42 for Y 2 GeCl 2 , Y 2 GeBr 2 and Y 2 GeI 2 accordingly, shows that these materials can be considered as good candidates for energy harvesting in thermoelectric applications. [ABSTRACT FROM AUTHOR]

A comprehensive study was carried out on MXAs compounds (M = Ni and Pd; X = Lu and Sc) within the framework of Density functional theory (DFT) based on projected augmented waves to determine their viability as thermopower generator. The electronic properties were computed and the results predicted that NiLuAs, NiScAs and PdScAs compounds are semicondutors with indirect bandgaps of 0.48 eV 0.50 ev and 0.44 eV respectively while PdLuAs compound is predicted to be semi-metallic in nature. The computed elastic constants were observed to satisfy the general criteria for stability for cubic symmetry. The corresponding mechanical properties revealed that all the compounds are ductile and anisotropic. The computed phonon dispersion also affirmed the dynamical stability of the compounds as evident in the absence of imaginary frequencies in the entire Brillouin zone for all the compounds. The thermodynamic properties were reported. The electrical conductivity, seebeck coefficient and thermal conductivity calculated further verified that MXAs compounds are promising candidates for efficient thermoelectric materials. The P -type PdScAs compound was predicted to be the most efficient thermoelectric materials with highest zT of 0.75 at temperature of 300–500 K. The NiLuAs and NiScAs compounds record zT of 0.52 and ≈0.60 for the P -type and N -type respectively while PdLuAs compound has zT of 0.42 at 1000 K. Our results demonstrate that these compounds are prospective materials for thermoelectric applications. [Display omitted] • The compounds investigated are NiLuAs, NiScAs, PdLuAs and PdScAs half-Heusler compounds with Valence Electron Count (VEC) of 18. • The electronic properties showed that NiLuAs, NiScAs and PdScAs compounds are semiconductors with narrow energy gap of 0.48 eV 0.50 eV and 0.44 eV while PdLuAs compound is semi-metallic in nature. • The computed elastic and dynamical properties revealed these compounds are mechanically and dynamically stable in cubic configuration. Hence, they can be experimentally synthesized for practical application. • The lattice thermal conductivity is computed using modified Debye-Callaway model and results showed the decrease in the lattice thermal conductivity with respect to temperature is more in PdLuAs and least in NiScAs compounds. • The other thermoelectric parameters were computed using constant relaxation semi-classical Boltzmann theory. The P -type PdScAs was predicted as the compound with the highest figure of merit at every temperature. [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]

Nanoparticles in thermoelectric alloys has been considered as one of the most important ingredients to enhance their thermoelectric figure of merit zT mainly by reducing the lattice thermal conductivity due to intensified phonon scattering. However, the scattering mechanism of phonon with respect to wavelengths, which provides the comprehensive design rules for nanocomposites with enhanced zT , has not been fully understood. Here, we report a critical role of nanoparticles for the lattice thermal conductivity reduction from the theoretical and experimental analysis of the temperature-dependent thermal and electronic transport properties of p -type Ag/Cu nanoparticles-embedded Bi 0.5 Sb 1.5 Te 3 with respect to their electronic, bipolar, and lattice thermal conductivities. It was found that the introduction of the Ag/Cu nanoparticles reduced the lattice thermal conductivity through the additional phonon scattering based on the changeover between the Rayleigh and geometrical scatterings, indicating the indispensability of nanoparticles to scatter phonons that cannot be scattered effectively by either point defects or grain boundaries. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Thermal physical properties of inorganic borates are important in application of optical device working under high temperature. Herein, we investigate the temperature-dependent thermoelasticity, thermal expansion(α), and lattice thermal conductivity(κ) of simple orthohomibic LaBO 3 with a two dimension like crystal structure though first principles for the first time. The calculated rate of temperature-dependent second elastic constant C 11 is significantly larger than that of C 22 and C 33 , and the theoretical slopes of corresponding bulk, shear, and Young's moduli in the range of 300–900 K are −0.0289 GPa•K−1, −0.0156 GPa•K−1, and −0.0398 GPa•K−1, respectively. The predicted α is positive and increases with the rise of temperature. The anisotropic ratio α c / α a or α c / α b is approximately 2 at 300 K, which might be attributed to the difference of elastic compliance S 12 and S 13. Besides, the anisotropic lattice thermal conductivity κ a , κ b and κ c of LaBO 3 is predicted to be 1.43, 1.40 and 0.80 W/m-K at 300 K via Debye-Callaway model. Most importantly, the atomic projected Grüneisen parameters γ reveal that asymmetrical LaO 9 polyhedra in the crystal lattice dominate the thermal expansion and lattice thermal conductivity. Our results indicate that LaBO 3 has good thermal physical properties working under high temperature. [Display omitted] • The thermophysical property of LaBO 3 was predicted by first-principles calculation. • The thermal expansion coefficients along c direction are much larger than those of a and b directions. • The anisotropic lattice thermal conductivity is predicted by Debye-Callaway model. • The lattice thermal conductivity along c direction is smaller than that of a and b directions. • The projected atomic Grüneisen parameters suggest that LaO 9 polyhedron charge the thermophysical properties in LaBO 3. [ABSTRACT FROM AUTHOR]

We applied the density functional theory formalism to compute the lattice thermal conductivity, transport and thermoelectric properties of Rb 2 LiTlF 6 double perovskite in the cubic phase. To gain some insights on lattice related dynamic behaviour of this material, we determined its phonon lifetimes and Grüneisen parameters within the considered frequency range. This quaternary compound has a very low value of lattice thermal conductivity, with the predicted value of 0.687 W/mK at 300 K. The highest value of dimensionless figure of merit was determined to be 5.73 × 10−3 at 800 K when hole concentration is 1020 cm−3, this low ZT value could be attributed to the wide band gap nature of this compound. Our results will serve as a benchmark for future experimental and theoretical research on lattice and thermoelectric properties of this material. • Lattice dynamics. • Transport properties. • Thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]

The lattice thermal conductivity of the CdO monolayer was investigated by density functional theory in combination with Boltzmann transport theory and it was estimated about 3.346 Wm−1K−1 at T = 300 K. Comparing this result with the one reported for the bulk CdO, it was revealed that the lattice thermal conductivity of the monolayer is lower than the bulk CdO. The lower lattice thermal conductivity of the CdO monolayer was attributed to the lower phonon lifetime and phonon group velocity in comparison to the bulk counterpart. Considering the lower lattice thermal conductivity of the monolayer, higher thermoelectric efficiency was estimated in comparison with the reported efficiency for the bulk CdO. At T = 900 K, the maximum zT = 0.76 can be found in p-type for the hole concentrations of 7.2 × 1012 cm−2. • The phonon dispersion of CdO monolayers were investigated with considering Born effective charges. • The contribution of phonon frequency to the k lat , group velocity, and phonon lifetime were investigated. • Thermoelectric efficiency of the CdO monolayer was investigated. [ABSTRACT FROM AUTHOR]

Bismuth sulphide is one of the promising thermoelectric material due to its low thermal conductivity, less toxicity, and abundance in nature. This work analyzed an Al-substituted Bi 2 S 3 compounds for mid-temperature thermoelectric applications prepared by hydrothermal route. The combination of stacking faults and point defects significantly improved the phonon scattering, resulting in decreased thermal conductivity in (x = 0.10) Al substituted sample with the value of 0.498 Wm−1K−1 at 623 K. Also, it simultaneously contributes to the enhancement in carrier concentration of −2.15 × 1019 cm−3, resulting the increased electrical conductivity of 10,142 Sm-1 at 563 K. Further, x = 0.025 Al substitution in Bi 2-x Al x S 3 leads to a high power factor of 338 Wm−1K-2 and a low phonon thermal conductivity of 0.578 μWm−1K−1, leading to a maximum zT of 0.30 at 623 K. [Display omitted] • Al substituted Bi 2 S 3 were prepared by the one-pot hydrothermal method followed by Hot press. • The isovalant substitution of Al significantly improves the electrical transport properties by carrier tuning. • Stacking faults and dislocations enhance the multiple phonon scattering results in decreased lattice thermal conductivity. • The (x = 0.025) substituted Bi 2-x Al x S 3 sample achieved a maximum zT of 0.30 at 623 K. [ABSTRACT FROM AUTHOR]

Ternary chalcostibite CuSbSe 2 compound is known for low thermal conductivity. However, the poor electrical properties severely limit its thermoelectric performance. In this study, the Mn-doped CuSb 1- x Mn x Se 2 (x = 0–0.04) samples were synthesized by vacuum melting with spark plasma sintering, and their thermoelectric properties were characterized. The results indicate that the impurity phase Cu 3 SbSe 3 will be generated when Mn content x > 0.02, and the carrier concentration and mobility were optimized significantly for the Mn-doped compounds, thus enhancing the electrical transport performance. In terms of results, the PF increases from 1.3 × 102 to 2.18 × 102 µW m−1 K−2 at 673 K. Point defects and the second phase enhance phonon scattering and lead to a lower lattice thermal conductivity for CuSb 1- x Mn x Se 2 compounds, the κ l decreases from 0.39 to 0.26 W m−1 K−1 at 673 K. As a consequence, a maximum figure of merit ZT of ∼0.53 was achieved at 673 K for CuSb 0.97 Mn 0.03 Se 2 , which is 140 % higher than the intrinsic CuSbSe 2. • Optimization of carrier concentration and mobility improved electric conductivity. • Phonon transport was suppressed resulting in a 32 % decrease for κ l. • The ZT increased by 1.4 times compared with the intrinsic CuSbSe 2. [ABSTRACT FROM AUTHOR]

Using full electron-phonon interactions and the Boltzmann transport equation, the phonon scattering channel and electrical properties of graphene are investigated under anharmonic phonon renormalization (APRN). After the anharmonic phonon renormalization is considered, both phonon frequency and three-phonon phase space become small with the temperature. Meanwhile, the APRN has a greater effect on the acoustic branch and little effect on the optical branch. When three-phonon scattering is considered, the corresponding thermal conductivity is 3518 W/mK (300 K), 1900 W/mK (500 K), and 1122 W/mK (800 K), respectively. After four-phonon scattering is considered, the thermal conductivity of graphene decreases to 1844 W/mK at 300 K, 900 W/mK at 500 K, and 600 W/mK at 800 K, respectively. For three-phonon scattering, the primary scattering channels include ZA + TA → ZO, TA + TA → ZA, LA + LA → ZO, ZA/TA → TA + LA, LA/ZO → ZO + TA, TO → ZA + LA and LO → ZO + LA. About the four-phonon scattering channel, the main contributions originate from X + ZA → ZA + ZA, X + ZA/ZO → ZA + ZO, and X + TA → LA + ZO. The anharmonic phonon renormalization enlarges the strength of electron-phonon coupling, leading to the increase of n-type electric resistance from 24 Ω to 26 Ω at room temperature. This work gives insight into the phonon scattering channel and electrical property via anharmonic phonon renormalization in which normal processes dominate the ph-ph scattering. [Display omitted] 1. The effect of anharmonic phonon renormalization on the thermal/electrical properties of graphene is investigated. 2. When considering the renormalization effect, phonon frequency/phase space become small with the temperature. 3. The anharmonic phonon renormalization has a greater effect on acoustic branch and little effect on optical branch. 4. The primary scattering channels include A + A → A/O, A/O → A/O + A and X + ZA/TA/ZO → ZA/LA + ZA/ZO. • For the four-phonon scattering channel, the main contributions originate from X + ZA/TA/ZO → ZA/LA + ZA/ZO. 5. The anharmonic phonon renormalization enlarges the electron-phonon coupling matrix and electric resistance. [ABSTRACT FROM AUTHOR]

• Cu doping in Cs 2 Cu x Ag 1-x BiBr 6 perovskites alters electronic structure, affecting thermoelectric properties. • The introduction of Cu dopants narrows the band gap and influences the carrier concentration in the material. • Enhanced thermoelectric performance, including improved zT values, observed at specific Cu doping levels. • Temperature-dependent analysis reveals varied peak zT values for different compositions, suggesting tailored applications. This study focuses on examining the thermoelectric properties of Cs 2 Cu x Ag 1-x BiBr 6 perovskites and investigates the influence of lattice thermal conductivity on their thermoelectric performance. To achieve this, the study utilizes a combination of first-principles calculations and Boltzmann transport theory. The calculated structural properties, obtained through the generalized Perdew-Burke-Ernzerhof approximation (GGA-PBE), closely align with both experimental and theoretical data for lattice constants and bulk modulus. The electronic properties were assessed using the TB-mBJ (Tran-Blaha-modified Becke-Johnson) method, indicating relatively small band gaps within the range of 1.146 eV for Cs 2 CuBiBr 6 and 2.072 eV for Cs 2 AgBiBr 6. The materials exhibit significant Seebeck coefficients and controllable lattice thermal conductivity between 0.067 and 0.662 W/mK at room temperature, with the relaxation time being determined using the Drude model. The study revealed that the most significant zT values, approximately 0.80, were observed when x = 0.5 in the Cs 2 Cu x Ag 1-x BiBr 6 perovskite material. This indicates that these perovskites possess the ability to efficiently and inexpensively convert heat into electrical energy. Consequently, these findings propose the potential of Cs 2 Cu x Ag 1-x BiBr 6 perovskites as a favorable option for real-world thermoelectric applications. The study further highlights the importance of utilizing lattice thermal conductivity to enhance the overall thermoelectric performance of such materials. [ABSTRACT FROM AUTHOR]