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Thermoelectric transport properties of Janus monolayers M2P2S3Se3 (M = Zn and Cd) are investigated by the first-principles based transport theory. The Zn2P2S3Se3 and Cd2P2S3Se3 monolayers are indirect-gap semiconductors. The high polarizability of M-Se/S bonds in the MS3Se3 distorted octahedrons leads to anharmonic phonon behavior, which produces an intrinsic lattice thermal conductivity (κl) as low as 1.06 and 1.99 W m−1 K−1 at 300 K for Zn2P2S3Se3 and Cd2P2S3Se3 monolayers, respectively. The lower κl of the Zn2P2S3Se3 monolayer is mainly attributed to more pronounced flat modes of the phonon dispersion in a frequency range of 1–1.7 THz caused by the softer Zn–Se/S bonds. The polar optical phonon scattering of carriers surprisingly plays a dominant role in carrier transport of both the monolayers, which greatly suppresses the electrical conductivity and thereby the power factor by about an order of magnitude. The predicted figure of merit (zT) increases monotonically with the temperature at the optimal carrier density, and at the operating temperature of 1200 K, it reaches an optimal value of 0.86 at an optimal electron density of ∼ 1.5 × 1 0 13 cm−2 for the n-type Zn2P2S3Se3 monolayer and 0.30 at an optimal electron density of ∼ 7 × 1 0 12 cm−2 for the n-type Cd2P2S3Se3 monolayer. [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]

Incorporating nano-dispersions into thermoelectric (TE) materials is an effective approach to enhance the TE properties. Herein, the TE performance of Cu2Se thin film is significantly enhanced by incorporating highly dispersed SnSe nano-inclusions. The high power factor (PF, ∼11.0 μW cm−1 K−2, 310 K) at near room temperature is achieved mainly due to the enhanced energy filtering effect that originated from the potential barrier difference. The total thermal conductivity is decreased owing to the simultaneously reduced electrical conductivity and enhanced phonon scattering. As a result, a high zT value (∼0.59 at 375 K) is achieved, which is about 12 times of pristine Cu2Se film. Remarkably, the calculated average zT values of Cu2Se/SnSe films from 310 to 375 K greatly exceed those of the pristine Cu2Se film, as well as the most state-of-the-art studies. High room-temperature PF and average zT value are crucial for expanding the practical application of Cu2Se at near room temperature. This work provides a feasible strategy to optimize the zT values of some other TE films by introducing nano-dispersions. [ABSTRACT FROM AUTHOR]

The film thickness, temperature, substrate and doping dependence of the phonon energy ω and damping γ , as well as the electrical conductivity, of pure and Sr-doped LaMnO3 thin films near the phase transition temperature T N are investigated using a microscopic model and the Green's function technique. Due to the strong spin–phonon interaction, there appears a kink at T N in the temperature dependence of ω (T) and γ (T) . The softening and hardening of the ω = 495 cm−1 (A1g) and ω = 614 cm−1 (B2g) modes is explained by the different sign of the anharmonic spin–phonon interaction constant R. The damping increases with T for both cases because it is proportional to R 2 . ω decreases whereas γ increases with an increasing Sr concentration. This is due to the strain caused by the difference between the ionic radii of the La and Sr ions. The film thickness dependence is also considered. ω and γ increase strongly with the decreasing film thickness. The electrical conductivity is enhanced after the doping of the LMO thin films with Sr, which could be used for energy storage applications. The observed results are in good qualitative agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Thermoelectric devices are both solid-state heat pumps and energy generators. Having a reversible process without moving parts is of high importance for applications in remote locations or under extreme conditions. Yet, most thermoelectric devices have a rather limited energy conversion efficiency due to the natural competition between high electrical conductivity and low thermal conductivity, both being essential conditions for achieving a high energy conversion efficiency. Heavy-fermion compounds YbT2Zn20 (T = Co, Rh, Ir) have been reported to be potential candidate materials for thermoelectric applications at low temperatures. Motivated by this result, we applied chemical substitution studies on the transition metal site in order to optimize the charge carrier concentration as well as promote more efficient phonon scatterings. Here, we present the latest investigation on the Ni-doped specimens YbCo2−xNixZn20, where enhanced thermoelectric figure of merit values have been obtained. [ABSTRACT FROM AUTHOR]

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

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

Half-Heusler alloys (HHs) as medium- and high-temperature thermoelectric materials have attracted increasing considerable attention, owing to their excellent mechanical properties and thermal stability. Nonetheless, the intercoupling between the Seebeck coefficient and electrical conductivity, and their high thermal conductivity limit the furthermore enhancement of their thermoelectric properties. This review systemically summarizes and analyses the various current strategies for improving thermoelectric properties, such as manipulating band structure, optimizing electron and phonon transports, and constructing high configurational entropy, etc. Moreover, the possible deficiencies of the existing electric-phonon transport mechanisms are highlighted and discussed, which aiming to provide a meaningful guide for future efforts to accelerate the development of HHs. Finally, based on current research, a new potential future for the integration of single crystal technology and high-entropy effect is introduced for HHs. [ABSTRACT FROM AUTHOR]

To our knowledge, this is the first study to successfully synthesise high-temperature-phase copper selenide (β -Cu 2 Se) at room temperature using rapid microwave hybrid heating (MHH). Controlling the starting Cu/Se ratio is the critical parameter for adjusting the content of α - and β -phases in the as-synthesised sample. The relatively low Cu composition causes impurities to form in the Cu 3 Se 2 phase, deteriorating the thermoelectric (TE) properties of the Cu 2 Se material. The β phase formation at room temperature promotes electrical conductivity. The thermal conductivities of the Cu 2.0 Se samples were 0.5–0.8 Wm−1K−1 at 303–673 K. A strong electronic-phonon interaction may potentially couple electronic thermal conductivity (κ e) and lattice thermal conductivity (κ L), resulting in incomplete separability of κ L and κ e in the β -Cu 2.0 Se sample. The Cu 2.0 Se exhibited a ZT value of 0.65 at 523 K because of its considerably lowered thermal conductivity. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) materials have attracted considerable interest for their potential and the figure of merit ZT serves as a crucial metric for evaluating TE performance. Chalcogenide materials, such as tellurium (Te) and selenium (Se), have been favored for high-performance TE applications. However, their toxic nature raises concerns, demanding exploration of non-toxic alternatives suitable for human-contacting devices. This study focused on antimony trioxide (Sb 2 O 3) due to its high Seebeck coefficient and explored the potential of layered double hydroxide (LDH) materials as a non-toxic alternative for efficient TE materials. Composites of Sb 2 O 3 nanowires integrated with 2D CaAl-LDH were synthesized to reduce thermal conductivity and improve TE performance. The composites displayed enhanced electrical conductivity, resulting in a significantly improved power factor. The introduction of CaAl-LDH facilitated the charge carrier transport paths, leading to better electrical performance. Furthermore, the composites exhibited reduced thermal conductivity due to phonon scattering at the heterointerfaces between Sb 2 O 3 and CaAl-LDH. As a result, the Sb 2 O 3 /CaAl-LDH_70 composite achieved a maximal ZT value of 0.0485 at 473 K, demonstrating promising potential for LDH-based composites as environmentally friendly TE materials. These findings contribute to sustainable energy conversion technologies, ensuring progress towards more efficient and biocompatible TE materials. [ABSTRACT FROM AUTHOR]

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

Bi2Se3 alloys are promising thermoelectric materials for use at near room temperature. In this study, we investigated the thermoelectric transport properties of Co-doped Bi2Se3, Bi2−xCoxSe3 (x = 0 , 0.03, 0.06, 0.09, and 0.12) polycrystalline alloys. The electrical conductivity of Bi2Se3 increased with Co doping as the electron concentration increased. The power factor increased by 83% (1.17 mW/mK2) with the Co doping compared with 0.64 mW/mK2 for pristine Bi2Se3 at room temperature. The density-of-states effective mass significantly increased to 0.30 m 0 (free electron mass) by high Co doping of x =0.12 compared to 0.14 m 0 for pristine Bi2Se3. The total thermal conductivity of the Co-doped samples increased owing to the increase in electronic thermal conductivity, despite the systematic decrease in the lattice thermal conductivity caused by Co doping due to additional phonon scattering. Nevertheless, an enhancement in z T was observed for all the Co-doped samples. The maximum z T value of 0.39 in highly Co-doped Bi1.88Co0.12Se3 is observed at 520K, which is 18% higher than that of pristine Bi2Se3. The z T value of the Co-doped sample could be further increased with the decrease in carrier concentration, which could be attained with the decrease in total thermal conductivity owing to the decreased electronic thermal conductivity while maintaining a high power factor originating from the increased effective mass. [ABSTRACT FROM AUTHOR]

SnTe is the most widely studied p-type thermoelectric (TE) alternative to PbTe. In this study, we prepared a nanostructured SnTe bulk material via spark plasma sintering from a precursor synthesized by a chemical precipitation process without using organic molecules. The sintered sample comprised tiny grains (100–300 nm) with high-density grain boundaries. Eventually, because the material would contain no impurities acting as scattering nodes of charge carriers, the material exhibited a relatively high electrical conductivity of 7.07 × 105 Sm−1 at 310 K. The material demonstrated low lattice thermal conductivity (0.87 Wm−1K−1 at 764 K), which can be owing to the increasing phonon scattering at grain boundaries. The maximum ZT was 0.31 at 764 K in the measured temperature range. This study provides a method for the design of phase-pure and surfactant-free SnTe thermoelectric materials that exhibit low lattice thermal conductivity and high carrier mobility using a chemical synthetic approach. [ABSTRACT FROM AUTHOR]

Different amounts of TiC particles between 1 and 7.5 vol% were coated on spray-dried B 4 C granules with a simple dry particle coating method, then spark plasma sintered at 2200 °C under vacuum, forming 3D-segregated network structures (SNS) of in-situ TiB 2 between 1 and 9 vol% , to improve the thermoelectric (TE) performance of B 4 C. With the in-situ TiB 2 -SNS, a maximum ZT of 8.02×10−2 was achieved with 2 vol% TiB 2 -SNS at 923 K by simultaneous improvement of electrical conductivity due to the electrically conductive network of TiB 2 and reduction of thermal conductivity due to the increased phonon scattering, improving the ZT of monolithic B 4 C by an impressive ≈ 120%. Higher quantities of TiC addition proved inefficient in improving the TE performance; by forming 9 vol% TiB 2 , ≈ 945% increase in electrical conductivity was achieved; however, the Seebeck coefficient was affected negatively, causing a drastic decrease in the ZT value. [ABSTRACT FROM AUTHOR]

We demonstrated the systematic investigation of the graphene addition on the microstructural behaviour and concurrent thermoelectric properties of water-atomized p-type BiSbTe (BST)- based alloy using mechanical ball milling, and followed through the spark plasma sintering to fabricate a bulk compact specimen. X-ray diffraction results confirm the single phase of BST. The fracture surface of both specimen exhibits the homogenous distribution of grains with irregular shapes in a random alignment. The graphene in the BST provides an extra carrier transport leading to an increment in the carrier concentration (n) resulting in higher electrical conductivity (σ) for the BST + Graphene composite. The interface between two-dimensional (2D) graphene and bulk BST provides a larger degree of phonon scattering leading to a maximum reduced thermal conductivity (к) of 0.8 W m−1K−1 compared to pristine- BST (0.9 W m−1K−1) results in a maximum figure of merit (ZT) 1.1 at 400 K. [ABSTRACT FROM AUTHOR]

Tin sulfide (SnS), as a low-cost and eco-friendly thermoelectric (TE) material, exhibits relatively poor phonon and charge transport capacities when the long-range ordered layered crystal structure is broken by the grain boundaries of polycrystalline. Nevertheless, doping and compositing are effective strategies for improving the electrical and thermal conductivity. Herein, utilizing the composite powders synthesized via Cu-doped SnS nanosheets grown in-situ on the surface of Cu-doped SnS nanofibers, we design a homogeneous nanofibers composited Cu-doped SnS polycrystalline bulk to boost its TE performance. Comparing with pure phase SnS, Cu doping can effectively increase the carrier concentration and mobility of SnS, realizing an increase of electrical conductivity from 4.11 S·cm−1 to 31.57 S·cm−1. Simultaneously, quite a number of fiber/matrix composite interfaces for phonon scattering are formed due to incorporating of composite nanofibers, which significantly reduce the lattice thermal conductivity of Cu-doped SnS polycrystalline bulk. The results show that thermal conductivity reduced as low as 0.64 W·m−1 K−1 at 324 K when the additive amount of nanofibers was fix at 2 wt%. Ultimately, the power factor and ZT value are markedly enhanced at low and medium temperature ranges (300–500 K) compared with SnS polycrystalline bulk without fiber incorporation. This provides an effective strategy for optimizing the thermoelectric performance of SnS-based polycrystalline. [Display omitted] • In-situ growth of SnS-based nanofiber composite thermoelectric materials synthesized using a simple approach. • Cu doping increased the carrier concentration and increased the conductivity from 4.11 S·cm−1 to 31.57 S·cm−1. • The composite SnS fibers reduced the thermal conductivity from 1.38 W·m−1·K−1. to 0.64 W m−1·K−1. [ABSTRACT FROM AUTHOR]

Sb2Te3 alloys are promising thermoelectric materials because of their outstanding electrical transport properties in the midtemperature range of 500–700 K, while codoping with multiple elements has been successful to improve their thermoelectric performance. In this study, enhanced thermoelectric properties with a maximum thermoelectric figure of merit of 0.97 are reported for singly and lightly Pb-doped Sb2Te3 polycrystalline alloys (Sb2– x Pb x Te3). Very light Pb doping in the range 0.005 ≤ x ≤ 0.0125 in the Sb2– x Pb x Te3 alloys yielded significantly improved carrier transport properties and increased electrical conductivity while the Seebeck coefficient is decreased moderately, since the density-of-state effective mass is improved much. As a result, power factor for the Pb-doped Sb2Te3 is largely increased up to 3.7 mW/mK2 at 300 K. The lattice thermal conductivity decreased considerably owing to the additional point defect phonon scattering by the Pb despite slight doping. Consequently, a maximum thermoelectric figure of merit of 0.97 was obtained for Sb1.9875Pb0.0125Te3 (x = 0.0125) at 600 K, which is the highest reported value for singly doped Sb2Te3-based alloys. A maximum energy conversion efficiency was calculated to be 9.0% for a temperature difference of 350 K, which is higher than that for other singly or codoped Sb2Te3 alloys. [ABSTRACT FROM AUTHOR]

We investigated the Ruddlesden‐Popper series CaO(CaMnO3)m with m = 1, 2, 3, ∞, to study the impact of the varying amounts of CaO layers on their thermoelectric properties. Previous studies showed that highly dense samples are difficult to obtain due to the refractory nature of these materials. In this study, we managed to obtain dense pellets during a classical hot‐pressing step, if and only if the samples were subjected to extended ball‐milling prior to pressing, resulting in crystallite sizes of 30–35 nm after hot‐pressing. The sample with the largest amount of CaO layers (m = 1) had the lowest electrical and thermal conductivity, and the highest Seebeck coefficient, as predicted. Ultimately the perovskite CaMnO3 (m = ∞, no CaO layers) exhibited the best thermoelectric properties. [ABSTRACT FROM AUTHOR]

In this study, by utilizing the first-principles calculation coupled with the Boltzmann transport theory, we comprehensively study the thermoelectric (TE) properties of the Sb2C monolayer. The calculated results show that the Sb2C monolayer owns an inherent ultra-low lattice thermal conductivity of 0.88 W m−1 K−1 at 300 K, which originates from small phonon group velocities, large Grüneisen parameters, and short phonon lifetimes. The Sb2C monolayer also exhibits excellent electrical transport properties mainly due to the degeneration of the bottom conduction bands, which increases the Seebeck coefficient of the n-type doped samples and thus yields a larger power factor. Based on the extremely low lattice thermal conductivity and superior electrical transport performance, a large ZT value of 2.71 for the n-type doped Sb2C monolayer at 700 K is obtained. Our results quantify Sb2C monolayers as promising candidates for building outstanding thermoelectric devices. [ABSTRACT FROM AUTHOR]

High-performance thermoelectric (TE) properties of pristine Sn-based colusites are investigated theoretically. A recent experimental article [Bourgès et al., J. Am. Chem. Soc. 140, 2186 (2018)] showed how structural disordering reduced the lattice thermal conductivity in Cu 26 V 2 Sn 6 S 32 and improved the TE figure of merit (ZT). In this article, it is observed that low energy soft optical phonons and the vacancy defect play a crucial role in reducing thermal conductivity. An ultra-low lattice thermal conductivity 0.35 Wm − 1 K − 1 is observed in Cu 26 V 2 Sn 6 Se 32. It is seen that mass variance perturbation and number of vacancies are important to tune the thermal and electrical properties. Though the electrical conductivity decreases with the number of vacant sites, the Seebeck coefficient enhances due to the reduction in carrier concentration. The detailed study of thermoelectric properties of Cu 26 V 2 Sn 6 Se 32 with Se vacancies points to enhanced ZT values of 0.34 at 300 K, which is ∼ 15 times greater than ZT of Cu 26 V 2 Sn 6 S 32. A maximum ZT of 1.68 at 755 K is predicted for Cu 26 V 2 Sn 6 Se 32 with Se vacancies, which is the highest to date reported for Sn-based colusites. [ABSTRACT FROM AUTHOR]

Higher manganese silicide (HMS) is a naturally abundant, environmentally friendly, and mechanically robust P-type thermoelectric (TE) semiconductor. Isoelectronic doping elements Re and Ge are used to partially occupy cation (Mn) and anion (Si) sites, respectively. Compared with the single Re-doped strategy, TE performance is further improved in the isoelectronic double-doped Mn 0.96 Re 0.04 (Si 0.96 Ge 0.04) 1.79 composition. The electrical conductivity (∼54.2 × 103 S m–1 at 823 K) is double that of pure HMS (∼26.1 × 103 S m–1), whereas the power factor increases from ∼1.42 × 10–3 W m–1 K–2 to ∼1.80 × 10–3 W m–1 K–2 due to the increase in carrier concentration caused by the decreased band gap (from 0.82 eV to 0.74 eV), as well as the embedding of the Si, Ge nanodispersions with low work functions. Furthermore, the substitution of Re and Ge increases the amounts of lattice defects, and the presence of nanoscale Ge precipitates cause the broadband phonon-scattering effect in the HMS matrix. Finally, the lattice thermal conductivity at 673 K decreases from ∼2.18 W m–1 K–1 to ∼1.60 W m–1 K–1. The zT value at 823 K increases by ∼36% from 0.45 to 0.61. The strategy of cation and anion double doping can effectively improve the TE properties of materials, which has significance for the optimization of other materials. [ABSTRACT FROM AUTHOR]

The phonon-drag effect is useful for improving the thermoelectric performance, especially the Seebeck coefficient. Therefore, the phonon and electron transport properties of Si single crystals at different carrier densities were investigated, and the relationship between these properties and the phonon-drag effect was clarified. Phonon transport properties were determined using nanoindentation and spot-periodic heating radiation thermometry. The electron transport properties were determined based on the electrical conductivity of Si. The diffusive Seebeck coefficient derived from the electron transport properties was in good agreement with previous reports. However, the value of the phonon-drag Seebeck coefficient derived from the phonon transport properties is very low. This phenomenon suggests that phonons with a normal mean free path (MFP) do not contribute to the increase in the Seebeck coefficient; however, phonons with a long MFP and low frequency increase the Seebeck coefficient via the phonon-drag effect. Moreover, the phonon-drag effect was sufficiently pronounced even at 300 K and in the heavily doped region. These features are key in designing thermoelectric materials with enhanced performance derived from the phonon-drag effect. [ABSTRACT FROM AUTHOR]

The experimental data of the temperature dependence of the electrical conductivity σ(T) and the Hall coefficient RH(T) on single crystal samples of n-type CdS reported in literature are reviewed and have been critically analysed including hopping conduction in an impurity band. It is shown that the experimental data of σ(T) and RH(T) reported in almost previous studies can be simultaneously fitted using a common set of the values of material parameters for calculating free-electron conduction, i.e. the conduction and the density-of-state effective mass of electrons, the acoustic-phonon deformation potential, the Fröhlich coupling constant and the piezoelectric coupling coefficient, whereas wide ranges of values for these material parameters had been adopted in different studies. The correct assignment of impurity conduction mechanisms in n-type CdS single crystals is presented. In addition, reasonable explanations are given for unresolved enigmas regarding impurity pairing, unexpected large Hall mobility at low temperatures, and the effect of electric field on hopping Hall mobility. [ABSTRACT FROM AUTHOR]

The electrical conductivity (σ), thermoelectric power (α), Hall coefficient (RH), and thermal conductivity (κ) of unmodified and 0.5 wt % ZrO2-modified extruded samples of the Bi0.85Sb0.15 solid solution have been measured in the range ~77–300 K at a magnetic field strength of up to ~74 × 104 A/m. The results demonstrate that the addition of 0.5 wt % ZrO2 to Bi0.85Sb0.15 reduces the phonon component of its thermal conductivity, leading to an increase in its thermoelectric figure of merit (Z) to ~6.4 × 10–3 K–1. The use of the modified material is expected to considerably improve parameters of related low-temperature thermoelectric converters. At ~77 K, in both the unmodified and ZrO2-modified Bi0.85Sb0.15 solid solutions heat is transported largely by lattice vibrations. [ABSTRACT FROM AUTHOR]

Ti2−xNiCoSnSb (x = 0.125, 0.250, 0.375, and 0.500) half Heusler (HH) high-entropy thermoelectric alloys were synthesized by the arc melting—ball milling—spark plasma sintering route. The impact of secondary phase content on the thermoelectric properties in these alloys was examined. Ni-rich intermetallic (Ni3Sn2, Ni3Sn4) compounds were observed; the intermetallic content increased for lower Ti content, e.g., Ti1.5NiCoSnSb. A Ni-rich full Heusler (FH) secondary phase was also observed. These results were consistent with first-principles calculations that show that the formation enthalpy of Ti1.5NiCoSnSb was higher than that of Ti2NiCoSnSb and the full Heusler (FH) TiNi2Sn phase. In lower Ti content samples, the electrical conductivity increased, and lattice thermal conductivity decreased at the expense of thermopower owing to higher FH and the Ni3Sn2 phase content. Ti1.5NiCoSnSb exhibited lower lattice thermal conductivity of 3.5 W/mK, compared to 5.4 W/mK at 823 K for Ti2NiCoSnSb due to increased phonon scattering at HH/Ni3Sn2 interfaces. But considering the decreasing power factor with lower Ti content, the maximum ZT obtained in Ti1.875NiCoSnSb (0.171 at 973 K) was only marginally higher than the value for Ti2NiCoSnSb. Further, compositional tuning is hence necessary to maximize the power factor. [ABSTRACT FROM AUTHOR]

Based on the first-principles calculations, the electronic structure and transport properties of BiMChO (M=Cu and Ag, Ch=S, Se, and Te) superlattices have been studied. They are all semiconductors with indirect band gaps. The increased band gap and decreased band dispersion near the valence band maximum (VBM) lead to the lowest electrical conductivity and the lowest power factor for p-type BiAgSeO/BiCuSeO. The band gap value of BiCuTeO/BiCuSeO decreases because of the up-shifted Fermi level of BiCuTeO compared with BiCuSeO, which would lead to relatively high electrical conductivity. The converged bands near VBM can produce a large effective mass of density of states (DOS) without explicitly reducing the mobility µ for p-type BiCuTeO/BiCuSeO, which means a relatively large Seebeck coefficient. Therefore, the power factor increases by 15% compared with BiCuSeO. The up-shifted Fermi level leading to the band structure near VBM is dominated by BiCuTeO for the BiCuTeO/BiCuSeO superlattice. The similar crystal structures bring out the converged bands near VBM along the high symmetry points Γ - X and Z - R . Further studies show that BiCuTeO/BiCuSeO possesses the lowest lattice thermal conductivity among all the superlattices. These result in the ZT value of p-type BiCuTeO/BiCuSeO increasing by over 2 times compared with BiCuSeO at 700 K. [ABSTRACT FROM AUTHOR]

In this research work, for the first time, the thermal transport properties of the natural Azerbaijani bentonites (Gobu and Atyali) as well as their Multi-Walled Carbon NanoTube/Gobu and Multi Walled Carbon Nano Tube/Atyali ceramic composites were investigated, their application abilities were studied, and the initial mechanism for explaining the thermal properties of these nanocomposites was studied. A laser flash technique was used to determine the thermal conductivity and thermal diffusivity of the prepared nanocomposites. The nanocomposites were prepared by an irreversible dispersion method that was developed by our research group. The highest thermal conductivity and thermal diffusivity were observed for 16% MWCNT-containing nanocomposites. The highest values of thermal conductivity and thermal diffusivity are κ = 1.3 W·(m·K−1) at T = 498 K, a = 1.539 × 10–6 m2·s−1 at T = 543 K for Gobu/x MWCNT (x = 16%) and κ = 0.97 W·(m·K−1) at T = 473 K, a = 1.013 × 10–6 m2·s−1 at T = 300 K for Atyali/x MWCNT (x = 16%) ceramic composites, respectively, and are mostly limited by phonon scattering within the bundles, by MWCNT and natural bentonite ceramic matrix interfaces, formed structure types of MWCNT networks. Experimental results prove that the cross-bar structure of MWCNTs inside Atyali matrices affects thermal conductivity negatively in comparison to the horizontally aligned structure of MWCNTs inside Gobu matrices. The electrical conductivity of these ceramic nanocomposites was significantly increased (for Gobu/x MWCNT (x = 16%) − 284 S·m−1 and for Atyali/x MWCNT 89.8 S·m−1). As these nanocomposites are electrically and thermally conductive at the same time, they can potentially be used as non-corrosive electrodes for electrolysis processes, as substrates like coolers for electronic devices with less heat release, and as heating elements for coveralls and for heating apartments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag intercalated Bi 2 Se 3 samples were synthesised by hydrothermal method followed by cold pressing technique. • HRTEM images and IFFT pattern confirms the presence of stacking faults. • The slight fermi energy shift towards conduction band significantly improved the electrical conductivity. • Low lattice thermal conductivity of 0.3 W/mK obtained at 543 K by various scattering mechanism. • The peak zT of 0.3 was attained at 543 K due to the synergy of enhanced power factor and low lattice thermal conductivity. Bismuth Selenide is a Tellurium free topological insulator in V-VI compounds with an excellent thermoelectric performance from room temperature to mid-temperature region. Herein, hydrothermally prepared polycrystalline Bi 2 Ag x Se 3 nanostructures have been reported for thermoelectric application. The crystal structure identification and morphology with the elemental presence were analyzed by XRD (X-ray diffraction), HR-SEM with EDS (High resolution scanning electron microscope with energy dispersive X-ray), and HR-TEM (High-resolution transmission electron microscope) measurements. The reduced lattice thermal conductivity and enhanced electrical transport properties synergistically boost the thermoelectric properties through the highly-dense stacking faults with the presence of dislocations. The IFFT (Inverse Fast Fourier Transform) pattern reveals the existence of stacking faults and dislocations. These highly dense stacking faults and dislocations act as active phonon scattering centers, which can contribute to effective phonon scattering results in extremely low lattice thermal conduction of 0.3 W/mK at 543 K. On the other hand, the involvement of phonon–phonon scattering primarily reduced the lattice thermal conductivity at elevated temperatures. In addition, phonon-carrier scattering was less compared to phonon–phonon scattering at elevated temperature region. Moreover, the enhancement of electrical conductivity and controlled reduction of the Seebeck coefficient plays a vital role in achieving the maximum power factor of 335 μW/mK2 at 543 K due to the energy filtering effect. The synergistic combination of low thermal conduction and the maximum power factor helps to achieve the high peak zT of 0.3 at 543 K. [ABSTRACT FROM AUTHOR]

Many thermoelectric materials benefit from complex microstructures. Grain boundaries (GBs) in nanocrystalline thermoelectrics cause desirable reduction in the thermal conductivity by scattering phonons, but often lead to unwanted loss in the electrical conductivity by scattering charge carriers. Therefore, modifying GBs to suppress their electrical resistivity plays a pivotal role in the enhancement of thermoelectric performance, zT. In this work, different characteristics of GB phases in Ti‐doped NbFeSb half‐Heusler compounds are revealed using a combination of scanning transmission electron microscopy and atom probe tomography. The GB phases adopt a hexagonal close‐packed lattice, which is structurally distinct from the half‐Heusler grains. Enrichment of Fe is found at GBs in Nb0.95Ti0.05FeSb, but accumulation of Ti dopants at GBs in Nb0.80Ti0.20FeSb, correlating to the bad and good electrical conductivity of the respective GBs. Such resistive to conductive GB phase transition opens up new design space to decouple the intertwined electronic and phononic transport in thermoelectric materials. [ABSTRACT FROM AUTHOR]

Here, we report a series of (Sr 1/3 Ba 1/3 Ca 1/3)TiO 3 -based oxides with different La-Nb doping levels synthesized by solid-state reaction and graphite-burial sintering method. The results indicate that La-Nb co-doping significantly enhances the electrical conductivity by increasing carrier concentration, leading to a remarkable improvement in power factor (∼1665 μW/(m·K2) at 773 K). Additionally, the lattice thermal conductivity is reduced due to the enhanced phonon scattering caused by point defects and pores. As a result, a peak ZT value of 0.36 at 773 K is achieved for the 5% La-10% Nb co-doped sample, 200% higher compared to the un-doped sample. This work highlights the promising potential of the (Sr 1/3 Ba 1/3 Ca 1/3)TiO 3 -based oxides as environmentally-friendly thermoelectric materials. [ABSTRACT FROM AUTHOR]

In this work, we design and synthesize a hybrid structure consisting of Sn-incorporated Cu3SbSe4 and a second phase CuSe, that is, (Cu3Sb1 − xSnxSe4)(CuSe)y (x = 0–0.04, y = 0.3–0.08), and explore the role of each phase on the improvement of the thermoelectric (TE) performance. In the Cu3Sb1 − xSnxSe4 phase, the element Sn residing at the Sb site provides p-type holes while at the same time increasing the point defects and crystal structure distortion. The presence of the second phase CuSe, which is in situ formed within the Cu3Sb1 − xSnxSe4 matrix, not only improves the electrical conductivity but also increases the phonon scattering on the phase boundaries. As a result, the hybrid structure allows the improvement in TE performance with the highest ZT value of 0.37 at ∼600 K for the samples at x = 0.02–0.03 and y = 0.11–0.09, which is about 42% higher than that of pristine Cu3SbSe4. This work reveals us a new method of improving TE performance, that is, through organizing a hybrid structure in Cu3SbSe4-based composites. [ABSTRACT FROM AUTHOR]

Sulfides and selenides of copper and silver have been intensively studied, particularly as potentially efficient thermoelectrics. Ag 3 CuS 2 (jalpaite) is a related material. However very little is known about its physical properties. It has been found that the compound undergoes several structural phase transitions, having the tetrahedral structural modification I4 1 /amd at room temperature. In this work, its band structure, phonon spectrum and thermoelectric properties were studied theoretically and experimentally. Seebeck coefficient, electrical conductivity and thermal conductivity were measured in a broad temperature range from room temperature to 600 K. These are the first experimental data on transport properties of jalpaite. Ab initio calculations of the band structure and Seebeck coefficient were carried out taking into account energy dependence of the relaxation time typical for the scattering of charge carriers by phonons. The results of the calculations qualitatively agree with the experiment and yield large values of the Seebeck coefficient characteristic for lightly doped semiconductor. The influence of intrinsic defects (vacancies) on the transport properties was studied. It was shown that the formation of silver vacancies is the most probable and leads to an increase of hole concentration. Using the temperature dependent effective potential method, the phonon spectrum and thermal conductivity at room temperature were calculated. The measurements yield low lattice thermal conductivity value of 0.5 W/(m K) at 300 K, which is associated with the complex crystal structure of the material. The calculated room temperature values of the lattice thermal conductivity were also small (0.14–0.2 W/(m K)). [ABSTRACT FROM AUTHOR]

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

The electron and phonon thermal transport behavior of Ag + doped KSr 2 Nb 5 O 15 were discussed by using the first-principles calculations. The band gap was reduced after Ag+ doping, and the electrons near the Fermi level had stronger transition capability, which effectively increased the carrier concentration and electrical conductivity and reduced the thermal conductivity, thereby improving the ZT of the doped KSr 2 Nb 5 O 15 from 0.6298 to 0.7214 (1200 K) under ideal conditions. In addition, the solid-state reaction method was used to prepare Ag nanoparticle added KSr 2 Nb 5 O 15 samples, and their thermoelectric performance was tested. The experimental results and the calculated results showed a good consistent trend in which Ag improved the thermoelectric properties of KSr 2 Nb 5 O 15. When the amount of addition of nanosized Ag was 20 wt%, the power factor and ZT of the material were the highest at 1073 K, which were 0.228 mW/(K2·m) and 0.1090, respectively. This research shows how to improve the thermoelectric performance of KSr 2 Nb 5 O 15 ceramics and broaden their temperature range for application. [Display omitted] [ABSTRACT FROM AUTHOR]

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

This study investigates Ga‐doped n‐type PbTe thermoelectric materials and the dynamic phase conversion process of the second phases via Cu2Se alloying. Introducing Cu2Se enhances its electrical transport properties while reducing its lattice thermal conductivity (κlat) via weak electron–phonon coupling. Cu2Te and CuGa(Te/Se)2 (tetragonal phase) nanocrystals precipitate during the alloying process, resulting in Te vacancies and interstitial Cu in the PbTe matrix. At room temperature, Te vacancies and interstitial Cu atoms serve as n‐type dopants, increasing the carrier concentration and electrical conductivity from ≈1.18 × 1019 cm−3 and ≈1870 S cm−1 to ≈2.26 × 1019 cm−3 and ≈3029 S cm−1, respectively. With increasing temperature, the sample exhibits a dynamic change in Cu2Te content and the generation of a new phase of CuGa(Te/Se)2 (cubic phase), strengthening the phonon scattering and obtaining an ultralow κlat. Pb0.975Ga0.025Te‐3%CuSe exhibits a maximum figure of merit of ≈1.63 at 823 K, making it promising for intermediate‐temperature device applications. [ABSTRACT FROM AUTHOR]

Aluminum nitride, with its high thermal conductivity and insulating properties, is a promising candidate as a thermal dissipation material in optoelectronics and high-power logic devices. In this work, we have shown that the thermal conductivity and electrical resistivity of AlN ceramics are primarily governed by ionic defects created by oxygen dissolved in AlN grains, which are directly probed using 27Al NMR spectroscopy. We find that a 4-coordinated AlN3O defect (ON) in the AlN lattice is changed to intermediate AlNO3, and further to 6-coordinated AlO6 with decreasing oxygen concentration. As the aluminum vacancy (VAl) defect, which is detrimental to thermal conductivity, is removed, the overall thermal conductivity is improved from 120 to 160 W/mK because of the relatively minor effect of the AlO6 defect on thermal conductivity. With the same total oxygen content, as the AlN3O defect concentration decreases, thermal conductivity increases. The electrical resistivity of our AlN ceramics also increases with the removal of oxygen because the major ionic carrier is VAl. Our results show that to enhance the thermal conductivity and electrical resistivity of AlN ceramics, the dissolved oxygen in AlN grains should be removed first. This understanding of the local structure of Al-related defects enables us to design new thermal dissipation materials. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have being actively studied on the account of their large density‐of‐state effective mass and low lattice thermal conductivity. Herein, thermoelectric and electrical transport properties of MoSe2–MoTe2 system are investigated. A series of Mo(Se1−xTex)2 (x = 0,.25,.5,.75, and 1) polycrystalline samples was synthesized by conventional solid‐state reaction. Single hexagonal phase was identified for each sample without secondary phase, confirming the formation of complete solid solutions between MoSe2 and MoTe2. The electrical conductivity and magnitude of the Seebeck coefficient increased simultaneously with increasing Te content x at high temperatures, with the power factor following the same trend. As results, the MoTe2 sample exhibited the maximum power factor of.014 mW/(m K2) at 823 K. The lattice thermal conductivities of the alloyed samples (x =.25,.5, and.75) significantly decreased compared to MoSe2 and MoTe2 owing to point defect phonon scattering via anion substitution, which is verified by the Debye–Callaway model. A maximum zT of.0044 was obtained for MoTe2 sample at 773 K; however, the calculated quality factor B values of the samples with x =.75 and 1 at 773 K were almost identical, suggesting that a further enhancement of zT can be achieved by optimizing an nH of the Mo(Se0.25Te0.75)2 sample. [ABSTRACT FROM AUTHOR]

In this paper, thermoelectric (TE) properties of n- type InSb 1-x Bi x (x = 0.00, 0.02, 0.05 and 0.10) polycrystalline samples, synthesized by single-step vacuum melting reaction, have been studied in the temperature range of 300–623 K. P-XRD confirms the phase purity and preferred orientation of (220) plane. FE-SEM back-scattered electron (BSE) micrographs reveal surface morphology and phase homogeneity, and elemental mapping with EDS is used to identify the chemical composition. The elemental existence and oxidation state of In3+, Sb3+, and Bi3+ in InSb 1-x Bi x are rechecked through XPS analysis. With Bi substitution, the electrical conductivity of InSb increases, whereas Seebeck coefficient starts decreasing. However, the maximum Seebeck coefficient, S of −241 μV/K at 423 K, was achieved for the composition of InSb 0.98 Bi 0.02. Interestingly, a huge reduction in lattice thermal conductivity, κ lattice from ∼17.5 W/mK (InSb) to 13.1 W/mK (InSb 0.9 Bi 0.10) at 300 K is observed due to increased phonon scattering from mass-fluctuation and created point defects. Further, the maximum thermoelectric figure of merit, zT was achieved as ∼0.56 at 623 K with higher Vickers micro-hardness values of ∼140 H V for the composition of InSb 0.98 Bi 0.02 which is notably higher than the recently reported InSb based materials. [ABSTRACT FROM AUTHOR]

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

Nanostructured materials remarkably improve the overall properties of thermoelectric devices, mainly due to the increase in the surface-to-volume ratio. This behavior is attributed to an increased number of scattered phonons at the interfaces and boundaries of the nanostructures. Among many other materials, nanostructured Si was used to expand the power generation compared to bulk crystalline Si, which leads to a reduction in thermal conductivity. However, the use of nanostructured Si leads to a reduction in the electrical conductivity due to the formation of low dimensional features in the heavily doped Si regions. Accordingly, the fabrication of hybrid nanostructures based on nanostructured Si and other different nanostructured materials constitutes another strategy to combine a reduction in the thermal conductivity while keeping the good electrical conduction properties. This review deals with the properties of Si-based thermoelectric devices modified by different nanostructures and hybrid nanostructured materials. [ABSTRACT FROM AUTHOR]

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

Copper antimony selenide (Cu3SbSe4), a ternary Cu-based material, is a promising p-type thermoelectric material. In this study, the morphology of Cu3SbSe4 particles was controlled using the shape of Se during the synthesis process. To this end, Se particles with a size of 20 μm were exfoliated to form nanosheets through an ultrasonication process without the oxidation of Se. The variation in the morphology of Cu3SbSe4 nanoparticles and nanosheets affected their grain size, thus affecting their electrical conductivity and lattice thermal conductivity owing to the phonon and electron scattering at the interface of the grains. By combining the effects of the morphological variation with the electrical and lattice thermal conductivity, the Cu3SbSe4 synthesized using Se nanosheets exhibited improved thermoelectric performance. The synthesized Cu3SbSe4 nanosheets achieved a maximum thermoelectric figure of merit value of 0.40, which was 1.41 times higher than that of Cu3SbSe4 nanoparticles. [ABSTRACT FROM AUTHOR]

Sinnerite Cu 6 As 4 S 9 has been identified as a promising material for optoelectronic applications, with potential for other energy-related applications; however, knowledge of the electrical and thermal properties as well as the mechanisms underlying transport in sinnerite is lacking. We present an investigation of the synthesis, structural, thermal and electrical transport properties of stoichiometric and Sn-doped Cu 6 As 4 S 9. Sinnerite has a triclinic lattice structure, with highly distorted local atomic coordination environments that, in part, results in its complex structure and bonding. Our results and analyses indicate As 4 s 2 lone pair-induced distortions and strong lattice anharmonicity that leads to a relatively short phonon mean free path, resulting in intrinsically very low thermal conductivity. The electrical resistivity for both compositions, Cu 6 As 4-x Sn x S 9 (x = 0, 0.2), are relatively high and varies little with temperature, typical of degenerate semiconductors. An increase in mobility and electrical conductivity was obtained by Sn doping in Cu 6 As 3.8 Sn 0.2 S 9. This work demonstrates an effective route to synthesize bulk sinnerite as well as advances the knowledge of the properties of sinnerite, as this and other ternary chalcogenides continue to be of interest for potential technologically significant applications. [Display omitted] • Polycrystalline sinnerites were successfully synthesized by ball milling and solid-state annealing. • The thermal conductivity is intrinsically low (< 1 Wm−1K−1) due to the unique structure and bonding. • The mobility and electrical conductivity increase and the thermal conductivity decreases with Sn doping. • The thermoelectric properties improved by 60% with Sn doping. [ABSTRACT FROM AUTHOR]

To improve the incompatibility between thermal conduction and electromagnetic wave absorption properties, 3D interconnected CNF/Co composites as a multifunctional filler were fabricated with magnetic/dielectric dual loss and phonon/electron co-transfer via a straightforward sol-gel and annealing route. Results show that the CNF/Co composites produced at a high Co2+ concentration (c) exhibit low defects, small S BET , large electrical conductivity, and high Co content. The optimal comprehensive properties of CNF/Co composites are achieved at c = 0.8 M. Besides, the CNF/Co composites bear a large thermal conductivity (3.61 W/mK) at a low load (15 wt%) due to the enhanced phonon/electron co-transfer in 3D interconnected CNF frameworks and decreased phonon scattering. Moreover, the CNF/Co composites demonstrate tunable electrical conductivity (σ = 7.53 ×10−5 ∼ 1.22 ×10−2 S/cm) and significant enhancements in electromagnetic wave absorption properties (4.53 GHz/mm, 2.4 mm thickness, 35% load), outperforming most other previously reported materials. The significant enhancements could be attributed to the high attenuation and excellent impedance matching caused by magnetic/dielectric dual-loss Co and 3D interconnected porous frameworks. The exceptional electromagnetic wave absorption properties and thermal conduction endow the 3D interconnected CNF/Co composites with prospective application as a multifunctional filler in modern electronics. 3D interconnected CNF/Co composites were synthesized via a straightforward sol-gel and annealing route, exhibiting a synchronous enhancement in heat conductance and EMW absorption. [Display omitted] • A facile synthesis of 3D interconnected CNF/Co composites. • Optimizing the composition, structure, and properties of the composites. • A synchronous enhancement in heat conductance and EMW absorption. • Revealing the mechanism of synchronous enhancement. [ABSTRACT FROM AUTHOR]

In this work, the thermoelectric (TE) performances of n -type Bi 2 Te 2.7 Se 0.3 with the addition of pyrite CoSe 2 were studied. The findings reveal an in-situ reaction between Bi 2 Te 2.7 Se 0.3 and CoSe 2 during the SPS process, resulting in the formation of a secondary phase, CoTe 2 , which refined the microstructure of Bi 2 Te 2.7 Se 0.3. Consequently, the electrical conductivity and Seebeck coefficient of Bi 2 Te 2.7 Se 0.3 were simultaneously optimized, attaining a higher power factor of 30.2 μW cm−1 K−2 at room temperature. Additionally, due to the reduced average sound velocity and phonon mean free path, the lattice thermal conductivity of Bi 2 Te 2.7 Se 0.3 was suppressed by the incorporation of CoSe 2. Furthermore, the bipolar thermal conductivity also experienced slight suppression at elevated temperatures. Ultimately, a substantial figure of merit of 0.85 was achieved at 423 K for n -type Bi 2 Te 2.7 Se 0.3 with the addition of 3 mol% CoSe 2. • In-situ generated the layered CoTe 2 increases the texture degree of Bi 2 Te 2.7 Se 0.3 grains. • The σ and S of Bi 2 Te 2.7 Se 0.3 were improved simultaneously by CoSe 2 addition, leading to a higher PF. • Both the κ latt and κ bip of Bi 2 Te 2.7 Se 0.3 has been inhibited by CoSe 2 addition. [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]

Many thermoelectrics are polar materials, where the long-range interaction plays a non-negligible role; however, its effect on the electrical transport property of thermoelectric materials is yet to be fully investigated. In this work, we demonstrate the importance of long-range interaction on the electrical transport property and the electron–phonon scattering mechanism in thermoelectric Mg2Si. We find that agreement between experimental and theoretical electrical conductivities can be significantly improved after considering the long-range interaction. In addition, we also demonstrate the importance of long-range interaction for studying the effect of band convergence on thermoelectric properties. [ABSTRACT FROM AUTHOR]

Thermoelectric generators are solid-state energy-converting devices that are promising alternative energy sources. However, during the fabrication of these devices, many waste scraps that are not eco-friendly and with high material cost are produced. In this work, a simple powder processing technology is applied to prepare n-type Bi2Te3 pellets by cold pressing (high pressure at room temperature) and annealing the treatment with a canning package to recycle waste scraps. High-pressure cold pressing causes the plastic deformation of densely packed pellets. Then, the thermoelectric properties of pellets are improved through high-temperature annealing (500 ∘ C) without phase separation. This enhancement occurs because tellurium cannot escape from the canning package. In addition, high-temperature annealing induces rapid grain growth and rearrangement, resulting in a porous structure. Electrical conductivity is increased by abnormal grain growth, whereas thermal conductivity is decreased by the porous structure with phonon scattering. Owing to the low thermal conductivity and satisfactory electrical conductivity, the highest ZT value (i.e., 1.0) is obtained by the samples annealed at 500 ∘ C. Hence, the proposed method is suitable for a cost-effective and environmentally friendly way. [ABSTRACT FROM AUTHOR]

Doping is one of the possible ways to significantly increase the thermoelectric properties of many different materials. It has been confirmed that by introducing bismuth atoms into Mg sites in the Mg2Si compound, it is possible to increase career concentration and intensify the effect of phonon scattering, which results in remarkable enhancement in the figure of merit (ZT) value. Magnesium silicide has gained scientists’ attention due to its nontoxicity, low density, and inexpensiveness. This paper reports on our latest attempt to employ ultrafast self-propagating high-temperature synthesis (SHS) followed by the spark plasma sintering (SPS) as a synthesis process of doped Mg2Si. Materials with varied bismuth doping were fabricated and then thoroughly analyzed with the laser flash method (LFA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with an integrated energy-dispersive spectrometer (EDS). For density measurement, the Archimedes method was used. The electrical conductivity was measured using a standard four-probe method. The See-beck coefficient was calculated from measured See-beck voltage in the sample subjected to a temperature gradient. The structural analyses showed the Mg2Si phase as dominant and Bi2Mg3 located at grain boundaries. Bismuth doping enhanced ZT for every dopant concentration. ZT = 0.44 and ZT=0.38 were obtained for 3wt% and 2wt% at 770 K, respectively [ABSTRACT FROM AUTHOR]