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

Compatible p‐ and n‐type materials are necessary for high‐performance GeTe thermoelectric modules, where the n‐type counterparts are in urgent need. Here, it is reported that the p‐type GeTe can be tuned into n‐type by decreasing the formation energy of Te vacancies via AgBiTe2 alloying. AgBiTe2 alloying induces Ag2Te precipitates and tunes the carrier concentration close to the optimal level, leading to a high‐power factor of 6.2 µW cm−1 K−2 at 423 K. Particularly, the observed hierarchical architectural structures, including phase boundaries, nano‐precipitates, and point defects, contribute an ultralow lattice thermal conductivity of 0.39 W m−1 K−1 at 423 K. Correspondingly, an increased ZT of 0.5 at 423 K is observed in n‐type (GeTe)0.45(AgBiTe2)0.55. Furthermore, a single‐leg module demonstrates a maximum η of 6.6% at the temperature range from 300 to 500 K. This study indicates that AgBiTe2 alloying can successfully turn GeTe into n‐type with simultaneously optimized thermoelectric performance. [ABSTRACT FROM AUTHOR]

In high-level radioactive waste disposal, a heat-generating waste canister is generally encased with a layer of bentonite-based buffer material acting as an engineered barrier to limit water percolation and radionuclide release. The low thermal conductivity of bentonite (~0.5 W/m∙K) combined with a high thermal loading waste package may result in a high surface temperature on the package that can potentially impact the structural integrity of the package itself as well as the surrounding buffer material. We show here that the thermal conductivity of bentonite can be effectively enhanced by embedding copper wires/meshes across the buffer layer to form fully connected high heat conduction pathways. A simple calculation based on Rayleigh's model shows that a required thermal conductivity of 5 W/m∙K for effective heat dissipation can be achieved simply by adding ~1 vol % of copper wires/meshes into bentonite. As a result, the peak surface temperature on a large waste package such as a dual-purpose canister can be reduced by up to 300°C, leading to a significant reduction in the surface storage time for waste cooling and therefore the overall cost for direct disposal of such waste packages. Because of the ensured full thermal percolation across the buffer layer, copper wires/meshes turn out to be much more effective than any other materials currently suggested (such as graphene or graphite) in enhancing the thermal conductivity of buffer material. Furthermore, the embedded copper wires/meshes can help reinforce the mechanical strength of the buffer material, thus preventing the material from a potential erosion by a possible intrusion of dilute groundwater. [ABSTRACT FROM AUTHOR]

Thermoelectric properties of Cu2Sn1−2xZnxFexS3 (x = 0–0.1) doped with Zn and Fe as acceptor at Sn-site were investigated. With increased doping, the primary phase was observed to change from cation-ordered monoclinic phase to cation-disordered cubic and tetragonal phases. Favored by the growth of carrier concentration, and as well the enhanced DOS effective mass caused by Fe-doping, an optimal power factor ~ 12 μWcm−1 K−2 was obtained with x = 0.1 at 773 K. Meanwhile, the lattice thermal conductivity in the dual-doped samples was found to be further lower than that in the singly doped counterparts due to cations disordering and bond softening. These led to a maximal dimensionless figure of merit, ZT ~ 0.7 (x = 0.05), synergistically. Moreover, the magnetoelectronic coupling induced by Fe was observed to influence the carrier concentration sensitively, while little affecting the carrier's mobility and effective mass. [ABSTRACT FROM AUTHOR]

Crystal structure and thermoelectric properties of Nb5+- and Ln3+-(rare earth: La3+, Nd3+, Sm3+, and Gd3+) doped SrO(SrTiO3)n (n=1,2) ceramics, which were fabricated by conventional hot-pressing, were measured to clarify the effects of Ti4+- and Sr2+-site substitution on the thermoelectric properties. The thermal conductivities are very close between the n=1 and 2 phases either doped with Nb5+ or Ln3+ and decreased by ¿60% at room temperature and ¿30% at 1000 K as compared to that of SrTiO3, which is likely due to an enhanced phonon scattering at the SrO/(SrTiO3)n (n=1,2) interfaces. The density of states effective mass md* (1.8¿2.4 m0) and consequently the Seebeck coefficient |S| in Nb5+-doped samples are fairly smaller than those reported for SrTiO3, which probably resulted from a deterioration of DOS due to the formation of the singly degenerate a1g (Ti 3dxy) orbital as the conduction band bottom, which should be induced by the distortion of TiO6 octahedra in (SrTiO3)n layers. However, in the Ln3+-doped SrO(SrTiO3)2, the TiO6 octahedra were found to be restored, in contrast to the Nb5+-doped, with a gradually increasing O¿Ti¿O bond angle in the (100) plane at high temperatures, which would lead to the formation of triply degenerate Ti 3d-t2g (dxy, dyz, and dxz) orbitals to cause a significant enhancement in md* (¿7.5 m0 at 1000 K) and consequently in |S|. Accordingly, the maximum dimensionless figure of merit ZT¿0.24 obtained in 5%-Gd3+-doped SrO(SrTiO3)2 at 1000 K is about... [ABSTRACT FROM AUTHOR]

Polycrystalline samples of Ca0.9-xSrxYb0.1MnO3-δ (x=0, 0.025. 0.05, 0.1, and 0.2) were prepared by a conventional solid-state reaction and their thermoelectric properties were evaluated at 303–973 K. Each of the samples consisted of a single phase with an orthorhombic structure. All the samples showed a metallic conductivity and their electrical resistivity was markedly affected by the distortion of the MnO6 octahedron. The Seebeck coefficient of all the samples was negative, indicating that the predominant carriers were electrons over the entire temperature range examined. The highest power factor achieved (0.22 mW m-1 K-2 at 773 K) was shown by the sample with x=0.1. The thermal conductivity was affected by both the crystal distortion and the difference in mass between the Ca2+ and Sr2+ ions. The highest dimensionless figure of merit obtained was 0.09 at 973 K for the sample with x=0.1; this is a result of its low electrical resistivity and its moderate Seebeck coefficient and thermal conductivity. [ABSTRACT FROM AUTHOR]

Eco-friendly thiospinel-type CuCo2S4 material has been investigated as a potential thermoelectric material. The temperature, T, dependence of electrical resistivity, ρ, of CuCo2S4 shows a metallic conductivity (∂ρ/∂T > 0) and a strong degenerate state, in the range of 323–723 K. Besides a high carrier concentration consistent with the metallic nature, its Hall mobility is still unexpectedly estimated to be 8.5 cm2 V−1 s−1 at room temperature. The positive Seebeck coefficient S confirms a p-type carrier conduction. Similar to most of the transition-metal spinel chalcogenides, the S value is very low, 12–36 μV K−1 at 323–723 K. As a result, a relatively low power factor PF&!thinsp; ∼ 0.35 mW m−1 K−2 was obtained at 723 K. Due to the dominant role of electronic thermal conductivity, the total thermal conductivity к was high and increases with a linear dependence on T. However, the intrinsic lattice conductivity кl was relatively low, ranging from 1.48 W m−1 K−1 at 323 K to 0.57 W m−1 K−1 at 723 K. It follows there is a T−1 dependence indicative of Umklapp type phonon–phonon interaction. Importantly, the intrinsically low кl in CuCo2S4 is attributed to multiple mechanisms, mainly including the large unit cell with primarily octahedral coordination, the high distortion and complexity of the structure, and additional interfacial thermal resistance. [ABSTRACT FROM AUTHOR]

Layer-structured AgCrSe 2 has attracted much attention for thermoelectrics for its low lattice thermal conductivity, however, the intrinsic electrical transport properties are poor. Here, remarkable effects of an exfoliation-restacking process were demonstrated for a series of Ag-deficient Ag 1- x CrSe 2 bulk ceramics by comparison. An effectively increased crystallographic orientation together with a reduction of grain size was obtained in such processed samples compared to that for the simply Ag-deficient ones. Electrical conductivity was significantly improved due to the increase in carrier mobility, while Seebeck coefficient was affected little with the unchanged carrier concentration and effective mass, leading to an optimal power factor of 7.3 μWcm−1K−2 at 773 K with x = 0.06; Meanwhile, lattice thermal conductivity was further reduced due to the enhanced phonon scattering by grain boundaries. Ultimately, a maximal ZT of ∼0.79 was achieved with x = 0.06 at 773 K, which stands among the tops so far for AgCrSe 2 -based thermoelectric materials. These results demonstrated a remarkable effectiveness of shear-exfoliation and restacking on tuning the thermoelectric performance of AgCrSe 2 -like layered superionic compounds. [Display omitted] • Shear-exfoliation and restacking process promoted the micro-texturing degree obviously with reduced grainsize for AgCrSe 2 ; • Electrical conductivity and power factor were further improved with increased carrier mobility due to micro-texturing; • Lattice thermal conductivity was further suppressed due to the reduced grainsize; • A record high ZT value of ~0.79 at 773 K was realized by the microstructural manipulation based on Ag deficiency. [ABSTRACT FROM AUTHOR]

This study reports on the successful synthesis and on the properties of polycrystalline AgPb mSnSe2+ m ( m = ∞, 100, 50, 25) samples with a rock salt structure. Between ≈160 and ≈400 K, the dominant scattering process of the carriers in this system changes from acoustic phonon scattering in PbSe to ionized impurity scattering in AgPb mSnSe2+, the Seebeck coefficient is enhanced by boosting the scattering factor, the electric conductivity is improved by the increase of the concentration of holes coupled to a limited degradation of their mobility, and the total thermal conductivity is reduced by suppressing bipolar thermal conductivity. Therefore, ZT of AgPb m, which synergistically optimizes electrical and thermal transport properties. Thanks to the faint amount of AgSnSe2, the Seebeck coefficient is enhanced by boosting the scattering factor, the electric conductivity is improved by the increase of the concentration of holes coupled to a limited degradation of their mobility, and the total thermal conductivity is reduced by suppressing bipolar thermal conductivity. Therefore, ZT of AgPb mSnSe2+ m ( m = 50) reaches 1.3 at 889 K. The mechanism suggested in this study opens new paths to improve the thermoelectric performances of other families of materials. [ABSTRACT FROM AUTHOR]

The effects of excess SrO on the thermoelectric properties of n-type SrTiO3 have been investigated through a comparative study of different polycrystalline ceramic samples. These include Gd-doped SrTiO3 with varying SrO, nominally in the form of Ruddlesden-Popper phase of SrO(SrTiO3)n with n = 5, 10, and 20, and previously reported analogues with n = 1, 2, and ∞ (i.e., stoichiometric SrTiO3). As compared with stoichiometric SrTiO3, with increasing SrO excess (i.e., decreasing n value), the electrical conductivity is found to decrease more substantially than the thermal conductivity, while the Seebeck coefficient remains almost unaffected with n in the range of 5-20. [ABSTRACT FROM AUTHOR]

Layered metal sulfides (MS)1+x(TiS2)2 (M = Pb, Sn, Bi) with alternative stacking of MS layers and TiS2 layers (a natural superlattice) have been proposed as thermoelectric materials. In this paper, various nanoscale stacking faults have been found in these materials, including the translational disorder in (SnS)1.2(TiS2)2 and the staging disorder in (BiS)1.2(TiS2)2. The lattice thermal conductivities along the layers are systematically and significantly reduced by these stacking faults which are only a few unit cells apart, without deteriorating the electron mobility, demonstrating a 'phonon-blocking, electron-transmitting' scenario. [ABSTRACT FROM AUTHOR]

Thermal conductivity is one of the key parameters in the figure of merit of thermoelectric materials. Over the past decade, most progress in thermoelectric materials has been made by reducing their thermal conductivity while preserving their electrical properties. The phonon scattering mechanisms involved in these strategies are reviewed here and divided into three groups, including (i) disorder or distortion of unit cells, (ii) resonant scattering by localized rattling atoms and (iii) interface scattering. In addition, we propose construction of a 'natural superlattice' in thermoelectric materials by intercalating an MX layer into the van der Waals gap of a layered TX2 structure which has a general formula of (MX)1+x (TX2)n (M = Pb, Bi, Sn, Sb or a rare earth element; T = Ti, V, Cr, Nb or Ta; X = S or Se and n = 1, 2, 3). We demonstrate that one of the intercalation compounds (SnS)1.2(TiS2)2 has better thermoelectric properties compared with pure TiS2 in the direction parallel to the layers, as the electron mobility is maintained while the phonon transport is significantly suppressed owing to the reduction in the transverse phonon velocities. [ABSTRACT FROM AUTHOR]

As a Te-free alternative to Bi 2 Te 3 , BiSe exhibits attractive near-room-temperature thermoelectric potential as an n-type material, yet its excessive electrical conductivity limits practical applications. To enhance the overall thermoelectric performance, we devise a rational triple optimization process to boost the figure of merit, ZT , of polycrystalline BiSe up to 0.84 at 475 K, a current record-high value. The shear exfoliation process introduces increased Bi vacancies and denser grain boundaries in the sintered polycrystalline material. This modification effectively reduces excessive electron carrier concentration and carrier scattering. Consequently, this reduction in excessive electrical conductivity, which previously leads to low Seebeck coefficients and high electronic thermal conductivity, is mitigated. As a result, there is a significant increase in the Seebeck coefficient and an optimization of the power factor. Subsequent equivalent substitution by Sb doping at Bi sites (Sb Bi) widens the bandgap, while secondary Sn doping at Bi sites (Sn Bi) achieves acceptor doping, further reducing electrical conductivity and enhancing the Seebeck coefficient to improve the power factor. Moreover, this triple optimization process systematically introduces various crystal and lattice defects, effectively scattering phonons of different wavelengths to lower the lattice thermal conductivity, ultimately resulting in a remarkable 235 % increase in ZT. This work offers new insights into effectively enhancing the performance of layered thermoelectric materials. [Display omitted] [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]

In this study, we delved into the thermoelectric characteristics of TiS 2 - x mol% CoSe 2 composites, with x varying from 0 to 3. The incorporation of a modest quantity of CoSe 2 prominently enhanced the grain orientation of TiS 2. Nevertheless, a subsequent increase in CoSe 2 content led to a rapid deterioration of the TiS 2 grain orientation. The electrical conductivity σ exhibited an initial surge followed by a decline upon the addition of CoSe 2. Conversely, the absolute Seebeck coefficient | S | initially decreased and then rose. Notably, the power factor PF of TiS 2 peaked at 14.4 μWcm−1K−2 upon the inclusion of 2 mol% CoSe 2 , marking a substantial 1.7-fold enhancement compared to pristine TiS 2. Furthermore, the thermal conductivity κ of TiS 2 was effectively suppressed by the addition of CoSe 2. Consequently, TiS 2 - 2 mol% CoSe 2 achieved a ZT max value of 0.59 at 673 K, representing a noteworthy 1.8-fold increase over pristine TiS 2. • The σ and S of TiS2 were improved simultaneously by CoSe2 addition, leading to a higher PF. • The κ of TiS2 was suppressed by compositing with CoSe2. • The ZTmax of TiS2 has been improved to 0.59 at 673 K. [ABSTRACT FROM AUTHOR]

Diamond-like Cu 2 SnSe 3 has drawn intensive attention as an excellent environmentally-friendly p-type thermoelectric material. In this study, the effects of Co-doping at Sn site on its thermoelectric properties were investigated. Results revealed an effective increase in carrier concentration and enhancement of density-of-states (DOS) effective mass m * due to the role of Co as acceptor and probably the contribution of its d states in the valence bands. Consequently, a remarkable power factor of up to 9.55 μW cm−1 K−2 has been achieved at 823 K. In addition, lattice thermal conductivity was strongly suppressed due to the intensified phonon scattering and softening of bonding as revealed by the sound velocity analysis. Ultimately, a maximal ZT of 0.97 at 823 K and an average ZT of ∼ 0.7 have been achieved in Cu 2 Sn 0.88 Co 0.12 Se 3 , almost double that of the pristine one. ● Co-doping in Cu 2 SnSe 3 caused a maximal PF of 9.5 μWcm−1K−2 with increased hole concentration and carrier effective mass. ● Lattice thermal conductivity was reduced by intensified phonon scattering and bond softening induced by Co‐doping. ● A maximal ZT value of 0.97 at 823 K has been achieved by 12% Co-doping, almost double that of the pristine one. [ABSTRACT FROM AUTHOR]

Abstract: We report the thermal conductivity of bulk Nd2/3−x Li3x TiO3 (0.047

The substitutional doping of magnesium into the host layers (TiS2), calcium and strontium into phonon barrier layers (BiS) was attempted to improve the thermoelectric performance of (BiS)1.2(TiS2)2 misfit layer sulfides by decreasing the carrier concentration. The substitutional doping did reduce the carrier concentration; however, the Seebeck coefficient decreased slightly due to the decrease in the effective mass of carrier electrons. Meanwhile, the lattice thermal conductivity was increased by the formation of an ordered or commensurate structure. [ABSTRACT FROM AUTHOR]

Abstract: Glass-like thermal conductivity is observed in (La1− x Yb x )2Zr2O7 (1/6⩽ x ⩽1/3), which exhibits great potential as a high-temperature thermal barrier coating material. In the pyrochlore-type La2Zr2O7, the large 16c-site La3+ is weakly bonded by its surrounding 48f-site oxygen ions, and substitution of La3+ with smaller and heavier Yb3+ gives rise to a large atomic displacement parameter (ADP) of Yb3+ which behaves as a “rattler”, as evidenced by the X-ray diffraction refinement. The localized “rattling” of Yb3+ in the cation sublattice significantly scatters the heat-carrying phonons and lowers the thermal conductivity close to the amorphous limit in combination with the intrinsic oxygen vacancies in the anion sublattice. In contrast, substituting Yb3+ with the larger La3+ in Yb2Zr2O7 does not result in as remarkable a decrease in the thermal conductivity as in Yb-doped La2Zr2O7 due to the absence of rattling atoms. In this study, a resonant phonon scattering is proposed as a new approach to reduce the thermal conductivity of oxides which are important in various thermal engineering applications. [Copyright &y& Elsevier]

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]

Micro-texturing engineering has been taken to manipulate the thermoelectric performance of (PbS) 1.18 (TiS 2) 2 via an exfoliation-restacking approach coupled with spark plasma sintering. The resultant polycrystalline material showed remarkably promoted (00 l) texturing together with a noticeable reduction in grain size, leading to prominently prior transport properties along the in-plane direction. Particularly, the electrical conductivity was much improved due to the increased carrier mobility without affecting carrier concentration and DOS effective mass, which gave rise to a maintained Seebeck coefficient and consequently a high power factor of 8.8–11.4 μW·cm−1·K−2 in the range of 323 – 773 K. Despite the slightly increased thermal conductivity due to electronic component and the limited suppression of phonon transport, a record-high ZT value of 0.52 has been achieved with an increase by ∼20% compared to that of the pristine one, demonstrating the significant effectiveness of exfoliation-restacking on boosting the thermoelectric performance for misfit layered materials. [Display omitted] • Prominently (00 l)-textured (PbS) 1.18 (TiS 2) 2 ceramic with refined grains was obtained by an exfoliation-restacking process. • In-plane carrier mobility was improved without changing carrier density, yielding a peak power factor of 11.4 μWcm−1K−2. • A record-high ZT (0.52) for TiS 2 -based misfit compounds has been achieved. [ABSTRACT FROM AUTHOR]

In the present work, the thermoelectric properties of S-doped Bi 2 O 2- x S x Se at the temperatures from 320 to 793 K have been studied. The results show that the solubility limit of S is around x = 0.01 and S-doping is helpful to the sintering and grain growth of Bi 2 O 2 Se. Moreover, S-doping reduces the band gap of Bi 2 O 2- x S x Se remarkably as x rises. As a result, a thousand times promotion of electrical conductivity at x = 0.02 is obtained, leading to a nearly 3 times increase of power factor at 787 K. By virtue of the intrinsically low thermal conductivity, a peak ZT of 0.29 at 793 K with an average of 0.21 has been achieved for Bi 2 O 1.98 S 0.02 Se, which is nearly 3 and 6 times larger than that of the pristine one. This study indicates that a small amount of S substitution for O could improve the thermoelectric properties of Bi 2 O 2 Se effectively. [ABSTRACT FROM AUTHOR]

In the present work, an artificial designed composition defects coupled with liquid-phase mechanical exfoliation (LME) was introduced to improve the thermoelectric performance of Bi 2 O 2 Se. The results indicate that non-stoichiometric of Bi 2 O 2 Se with LME could induce high grain orientation. Moreover, the electrical conductivity of Bi 2 O 2- x Se 1+ x with LME have been greatly improved due to both higher carrier concentration and holes mobility. In contrast, a relatively low thermal conductivity had been retained. Finally, A high ZT peak of around 0.54 at 773 K was obtained for the sample Bi 2 O 1.96 Se 1.04 with LME, which is a new ZT record of Bi 2 O 2 Se based thermoelectrics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Owing to the high near-room-temperature thermoelectric performance, Bi 2 Te 2.7 Se 0.3 (BTS)-based semiconductors have gained significant attention and acted as n-type materials in practical thermoelectric devices. To achieve higher thermoelectric performance in polycrystalline BTS, in this work, we employ SnSe as multifunctional micro/nanoinclusions via co-shear-exfoliating SnSe and BTS ingots and sintering the as-achieved hybrid powders into bulk materials. Experimental results indicate that the 2D-structured SnSe reduces the average size of shear-exfoliated BTS powders, leading to strengthened anisotropy of the as-sintered bulk materials, which can significantly improve the carrier mobility and in turn, the electrical conductivity. As well, introducing p-type SnSe into n-type BTS enhances the bipolar temperature of BTS, leading to higher Seebeck coefficients at higher temperatures, which contributes to a boosted power factor of >32 μW cm−1 K−2 at 448 K. Besides, the introduced SnSe micro/nanoinclusions with intrinsic low lattice thermal conductivities suppress the overall thermal conductivity of the hybrid bulk materials by providing denser phase boundaries in the matrix, and in turn strengthen the phonon scattering, which contributes to a competitive figure-of-merit ZT of ∼1.04 at 448 K and a high average ZT of 0.92, indicating the great potential for applying to practical devices. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the thermoelectric properties of PbSe- x %FeSe 2 (x = 0, 0.25, 0.5, 0.75, 1, 3, 5) alloys are investigated. The results show that FeSe 2 can partly dissolve into the lattice of PbSe to introduce extra holes, which will offset the electron content and reduce the electrical conductivity. Accordingly, the absolute Seebeck coefficient is greatly improved by reducing the electron content. In addition, owing to the reduced electronic thermal conductivity, decreased interatomic force and increased lattice anharmonicity by FeSe 2 alloying, the thermal conductivity of PbSe-0.5 %FeSe 2 is suppressed successfully. Thanks to the improved PF and suppressed κ by FeSe 2 alloying, a larger ZT of 0.53 at 323 K and 1.1 at 773 K with an average ZT of 0.9 are obtained in PbSe-0.5 %FeSe 2. • FeSe 2 can partly dissolve into the lattice of PbSe to introduce extra holes. • FeSe 2 alloying can weaken the interatomic force and enhance the anharmonicity. • FeSe 2 alloying can improve the PF and suppress the κ of PbSe. [ABSTRACT FROM AUTHOR]

In this study, the effects of MoS 2 addition on the thermoelectric properties of Bi 2 O 2 Se were investigated. The results show that the introduction of MoS 2 can improve the efficiency of the liquid assisted shear exfoliation process, increase the porosity and inhibit the grain growth of Bi 2 O 2 Se. Accordingly, the electrical conductivity decreases first and then increases with the increase of the MoS 2 content. Besides, the absolute Seebeck coefficient | S | of the composite sample rises first and then decreases with the increase of the MoS 2 content due to the offset effect between |S| and σ. In addition, the enhanced phonon scattering combined with the increased porosity by MoS 2 addition significantly inhibited the lattice thermal conductivity of Bi 2 O 2 Se. Finally, a ZT max of 0.55 for 0.3 mol%MoS 2 /Bi 2 O 2 Se at 773 K was obtained. Schematic diagram of MoS 2 /Bi 2 O 2 Se nanocomposites prepared by shear exfoliation process. [Display omitted] • MoS 2 addition improve efficiency of the liquid assisted shear exfoliation process. • The TE performance of Bi 2 O 2 Se was further boosted by MoS 2 addition. • A new nanocomposite technology was introduced for layered materials. [ABSTRACT FROM AUTHOR]

In this work, the thermoelectric properties of Bi 2 O 2 Se by Bi 2 Te 2.7 Se 0.3 addition through liquid assisted shear exfoliation- restacking (LASE-R) process were studied. The results show that the Bi 2 Te 2.7 Se 0.3 can alloy with Bi 2 O 2 Se and reduce the band gap, which introduce more electrons and improve the electrical conductivity of Bi 2 O 2 Se. Moreover, Bi 2 Te 2.7 Se 0.3 addition act as a liquid phase sintering aids here, which can promote crystal growth and increase the sintering density of Bi 2 O 2 Se. Owing to the offset effect between |S| and σ , the absolute Seebeck coefficient | S | of all samples drops first and then rises with the increase of Bi 2 Te 2.7 Se 0.3 content. Thus, the power factor is effectively improved. In addition, the lattice thermal conductivity is also suppressed to the nearly minimum theoretical limit, which should be attributed to the enhanced phonon-scattering by alloying. Therefore, a high figure of merit of 0.7 at 772 K was achieved for Bi 2 O 2 Se- 0.3 mol% Bi 2 Te 2.7 Se 0.3. ● The σ of Bi 2 O 2 Se has been improved by Bi 2 Te 2.7 Se 0.3 addition. ● The κ l of Bi 2 O 2 Se is restricted to the minimum theoretical limit. ● A competitive high zT value of 0.7 has been achieved for Bi 2 O 2 Se. [ABSTRACT FROM AUTHOR]

This study reports on the successful synthesis and on the properties of polycrystalline AgPb mSnSe2+ m ( m = ∞, 100, 50, 25) samples with a rock salt structure. Between ≈160 and ≈400 K, the dominant scattering process of the carriers in this system changes from acoustic phonon scattering in PbSe to ionized impurity scattering in AgPb mSnSe2+ m, which synergistically optimizes electrical and thermal transport properties. Thanks to the faint amount of AgSnSe2, the Seebeck coefficient is enhanced by boosting the scattering factor, the electric conductivity is improved by the increase of the concentration of holes coupled to a limited degradation of their mobility, and the total thermal conductivity is reduced by suppressing bipolar thermal conductivity. Therefore, ZT of AgPb mSnSe2+ m ( m = 50) reaches 1.3 at 889 K. The mechanism suggested in this study opens new paths to improve the thermoelectric performances of other families of materials. [ABSTRACT FROM AUTHOR]

In this study, the thermoelectric properties of Bi 2 O 2 Se- x %AgSnSe 2 composites via liquid assisted shear exfoliation- restacking (LASE-R) method were investigated. The results show that Ag can diffuse into Bi 2 O 2 Se to further improve the electron content and the electrical conductivity. Meanwhile, the absolute Seebeck coefficient gets a little deterioration with an increase in the electron content and the effective mass. Besides, the rest AgSnSe 2 can further reduce the lattice thermal conductivity of Bi 2 O 2 Se through enhanced interfaces and mass fluctuation scattering of the phonons by compositing with AgSnSe 2. Finally, a ZT max of 0.58 for Bi 2 O 2 Se-1%AgSnSe 2 was obtained, which is 1.24 times that of Bi 2 O 2 Se. • It is the first time to study the effects of AgSnSe 2 addition with LASE-R process. • The σ of Bi 2 O 2 Se- x %AgSnSe 2 composites was improved by the diffusion of Ag • The κ l of Bi 2 O 2 Se was inhibited successfully by compositing with AgSnSe 2. [ABSTRACT FROM AUTHOR]

In this study, the thermoelectric properties of TiS 2 - x mol%SnSe (x = 0, 0.5, 1 and 2) composites prepared with liquid-assisted shear exfoliation (LASE) process were investigated. Results show that the carrier mobility of composites can be improved owing to the enhanced texturing degree via LASE process, and the carrier concentration can be increased together with SnSe addition due to charge transfer. Therefore, high power factors optimally to ~16.4 μW cm−1 K−2 can be obtained, which is almost 67% and 40% higher than that of the pristine and the LASE TiS 2 , respectively. Unexpectedly, lattice thermal conductivity was increased probably due to the enhanced heterophase electrostatic force between TiS 2 and SnSe phase induced by charge transfer. As a result of compromise, a modest ZT maximum of ~0.48 at 673 K was obtained for TiS 2 -1 mol%SnSe. • Power factor (PF) largely enhanced by charge transfer and texturing after incorporating SnSe via liquid-shear exfoliation. • Lattice thermal conductivity (κ l) increased unexpectedly with SnSe addition, accompanied by increased phonon velocities. • Maximal ZT of 0.48 obtained at 673 K in TiS 2 -1mol%SnSe due to the offset between high PF and increased κ with SnSe addition. [ABSTRACT FROM AUTHOR]

• Seven groups of TiNiSn powders, which contained a wide range of particle sizes were fabricated. • Energy filtering effect leads to an increase in the Seebeck coefficient and power factor. • Lattice thermal conductivity has decreased largely due to the grain boundary scattering. • Significant improvement has been achieved in the thermoelectric properties of intrinsic TiNiSn. [Display omitted] Half-Heusler compounds MNiSn (M = Ti, Zr, Hf) have attracted increasing attentions in the field of thermoelectrics, since their constituent elements are non-toxic and abundant. Meanwhile, it possesses good thermal stability as well as high mechanical strength. Herein, a substantial enhancement to the thermoelectric performance of intrinsic TiNiSn is achieved by passing the pulverized powders through the sieve prior to sintering. The Seebeck coefficient has increased sharply owing to the energy filtering effect, which is induced by the reduction in the average grain sizes, combined with a slightly decreased electrical conductivity, leading to a significant improvement in power factor. Moreover, the lattice thermal conductivity can be further reduced via the enhancement of the grain boundary scattering. Consequently, a maximum figure-of-merit (zT) value of 0.84 at 820 K is achieved for un-doped TiNiSn. This work indicates that the grain boundary engineering may serve as an effective method for improving the thermoelectric performance of other half-Heusler compounds. [ABSTRACT FROM AUTHOR]

• Stepwise carrier concentration optimization of Bi 2 GeTe 4 thermoelectric materials. • Ge vacancy-engineering transfer Bi 2 GeTe 4 into highly degenerated semiconductor. • Carrier concentration optimization leads to high power factor of 4.2 μW cm−1 K−2. • Approaching a record-high zT value of ∼ 0.22 at 423 K in Bi 2 Ge 1.45 Te 4. Bi 2 GeTe 4 is a promising near room-temperature thermoelectric candidate with a low lattice thermal conductivity. Carrier concentration of intrinsic Bi 2 GeTe 4 changes dramatically with tiny Ge content adjustment, leading to a challenge in carrier concentration optimization. To overcome this challenge, we firstly introduce excessive Ge into Bi 2 GeTe 4 to shift the Fermi level deep into the conduction band and transfer Bi 2 GeTe 4 into a highly degenerate n-type semiconductor. Secondly, the embedded p-type Bi 2 Ge 2 Te 5 secondary phase induces further optimization of the Fermi level and carrier concentration. Finally, the power factor of the as-synthesized Bi 2 GeTe 4 -based material is significantly increased from ∼ 0.08 μW cm−1 K−2 to ∼ 4.2 μW cm−1 K−2 at 423 K when increasing the nominal Ge content (x) of Bi 2 Ge x Te 4 from 1 to 1.45. Correspondingly, a high figure-of-merit of ∼ 0.22 at 423 K is achieved in Bi 2 GeTe 4 -based thermoelectric materials. This result indicates our viable stepwise strategy can be used to optimize carrier concentration and achieve high thermoelectric performance of the n-type Bi 2 GeTe 4. [ABSTRACT FROM AUTHOR]

• The sintering density of Bi 2 O 2 Se has been improved by W-doping. • Both the electron concentration and the mobility of Bi 2 O 2 Se have been improved. • The power factor of Bi 2 O 2 Se has been improved. • A peak ZT of 0.62 has been achieved for Bi 1.98 W 0.02 O 2 Se at 773 K. In this study, W-doping with the shear exfoliation- restacking process was used to optimize the thermoelectric properties of Bi 2 O 2 Se. It is noted that W-doping with the shear exfoliation- restacking process can synergistically improve carrier concentration and mobility, thus a higher electrical conductivity was obtained. In addition, total thermal conductivity of Bi 1.98 W 0.02 O 2 Se was restricted to 0.6 Wm−1 K−1 at 770 K. Consequently, a maximum ZT value of Bi 1.98 W 0.02 O 2 Se is raised to 0.62 at 773 K. The results show that the thermoelectric properties of Bi 2 O 2 Se can be further optimized by W-doping with the shear exfoliation-restacking process. [ABSTRACT FROM AUTHOR]

• The grain orientation of Bi 2 O 2 Se has been improved. • Both the electron concentration and the mobility of Bi 2 O 2 Se have been improved. • The power factor of Bi 2 O 2 Se has been greatly improved. Ti-doping with the shear exfoliation-restacking process could be helpful to the preferential grain orientation of Bi 2 O 2 Se. Therefore, the electron concentration and mobility were synergistically improved, thus a high electrical conductivity and high power factor have been obtained. [Display omitted] Bi 2 O 2 Se is a potential medium-temperature n -type thermoelectric material owing to its lower lattice thermal conductivity and larger Seebeck coefficient. However, very low electrical conductivity of pristine polycrystalline Bi 2 O 2 Se hinders further enhancement of its thermoelectric performance. In this work, the thermoelectric properties of Bi 2 O 2 Se were investigated by Ti-doping with the shear exfoliation- restacking process. The results show that both the electron content and mobility can be further improved by Ti-doping with the shear exfoliation-restacking process, thus a higher electrical conductivity can be obtained. (e.g., 368 S cm−1 of Bi 1.99 Ti 0.01 O 2 Se at room temperature) On the other hand, the thermal conductivity of Bi 1.99 Ti 0.01 O 2 Se is suppressed to 0.84 Wm−1 K−1 at 772 K. Finally, the ZT peak of Bi 1.99 Ti 0.01 O 2 Se is raised to 0.56, which is 1.2 times of that of un-doped sample. The results show that the thermoelectric properties of Bi 2 O 2 Se can be further optimized by Ti doping with the shear exfoliation-restacking process. [ABSTRACT FROM AUTHOR]

• Attapulgite served as a donor in Cu2Sn0.8Co0.2S3, enabling manipulation of hole concentration and electrical transport. • High power factors are maintained, accompanied with a 50% reduction in electronic thermal conductivity. • Record-high ZT close to 1 has been achieved in Cu 2 Sn 0.8 Co 0.2 S 3 embedded with 0.2 wt% attapulgite. [Display omitted] Mohite-type Cu 2 SnS 3 has merged as a promising environmentally-friendly thermoelectric candidate. When heavily hole-doped, it exhibits a large power factor (PF) by virtue of a high electrical conductivity (σ), which results in an undesired high electronic thermal conductivity (κ e) that limits the ZT value. In the present work, nanocomposites of Co-doped Cu 2 Sn 0.8 Co 0.2 S 3 embedded with fibrous in-situ-dehydrated attapulgite (D-ATT) nanorods are prepared, and the effect of D-ATT on the thermoelectric properties are investigated. Results show that, with the incorporation of D-ATT, σ is lowered effectively as expected as a primary result of charge compensation caused by a donor effect of D-ATT, which gives rise to an optimal reduction of κ e by 50% in the studied temperature range, accompanied with an enhanced Seebeck coefficient (S) and high PF s maintained at ~9.4 μW cm−1 K−2 at 773 K. Meanwhile, the lattice thermal conductivity is strongly suppressed due to the intensified phonon scattering with ATT addition, leading to an ultralow value of 0.27 W m−1 K−1 at 773 K. Finally, a maximal ZT of ~1.0 has been achieved in the sample with 0.2 wt% D-ATT at 773 K, which stands a new record for Cu 2 SnS 3 -based TE materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Double perovskite Pr 2 CoFeO 6 has developed as a new thermoelectric oxide. • Sr-doping lowers the Fermi level into the valence band of Pr 2 CoFeO 6. • Unique micro/nanostructures suppress lattice thermal conductivity to 0.58 W m−1 K−1. • Carrier concentration is optimized to induce a power factor of ~ 46 μW m−1 K−2. • A ZT of 0.05 is experimentally obtained and a high ZT of > 0.2 is predicted. Owing to their excellent thermal stability, non-toxicity, and low cost, oxide-based thermoelectric materials have considerably expanded research interests and industrial application. Here, we, for the first time, report a new-type Pr 2 CoFeO 6 oxide-based thermoelectric materials from both theoretical and experimental aspects. Our first-principles calculation results indicate that Pr 2 CoFeO 6 is a p-type semiconductor with narrow bandgap. The experimental thermoelectric evaluation shows that pristine Pr 2 CoFeO 6, synthesized by a combination of sol–gel method and conventional sintering, has a peak figure of merit, ZT of 0.015 at 773 K with a high positive Seebeck coefficient of 250 μV K−1 and very low thermal conductivity of 0.7 W m−1 K−1 at this temperature. Further Sr2+ doping on Pr-sites (Pr3+) enhances the carrier concentration from 4.03 × 1014 cm−3 to 5.22 × 1017 cm−3, contributing to an improved power factor up to 46 μW m−1 K−2. Besides, Sr-doping induces point defects in the matrix and further suppresses the thermal conductivity to 0.58 W m−1 K−1, leading to a promising ZT up to 0.05 at 673 K in Pr 1.8 Sr 0.2 CoFeO 6 , which is significantly improved by 233% compared to pristine Pr 2 CoFeO 6. We also predict that a high ZT of > 0.2 can be achieved by the optimization of carrier density, band engineering, and energy filtering, which is comparable to many other oxide-based thermoelectric materials. [ABSTRACT FROM AUTHOR]

In this study, Sb-doping with the procedure of shear exfoliation was adopted in order to improve the thermoelectric performance of Bi 2 O 2 Se. It is found that Sb-doping could further increase the electron concentration and mobility, leading to a high electrical conductivity. (e.g., 517 S cm−1 of Bi 1.96 Sb 0.04 O 2 Se at room temperature) Besides, thermal conductivity had been inhibited to 0.6 Wm-1 K−1 at 770 K for the sample Bi 1.99 Sb 0.01 O 2 Se. Finally, a peak ZT of around 0.59 at 773 K was achieved for the sample Bi 1.98 Sb 0.02 O 2 Se, which is about 1.8 times larger than that of un-doped one. The results indicate that Sb-doping with the procedure of shear exfoliation could optimize the thermoelectric performance of Bi 2 O 2 Se noticeably. • Sb-doping with the procedure of shear exfoliation could improve the thermoelectric performance of Bi 2 O 2 Se effectively. [ABSTRACT FROM AUTHOR]

In this study, the thermoelectric properties of Zn-doped CuInSe 2.02 (CuIn 1-x Zn x Se 2.02 , x = 0, 0.01, 0.02, 0.03, 0.05, 0.07) at the temperatures from 323 K to 773 K have been investigated. The results indicate that small amount of Zn substitution for In could increase the electrical conductivity and Seebeck coefficient simultaneously, lead to a high power factor of 0.21 mW m−1 K−2 for CuIn 0.98 Zn 0.02 Se 2.02 at 430 K. In addition, the thermal conductivity of Zn-doped CuInSe 2.02 bulk materials have a slight suppression. Thus, the CuIn 0.98 Zn 0.02 Se 2.02 achieves the highest peak ZT of 0.18 at 773 K due to the synergistically optimized electrical and thermal transport properties, which is twice larger than that of pristine CuInSe 2.02. The present work indicates that the substitution of In by Zn would be a promising means to improve thermoelectric properties of CuInSe 2.02. • Small amount of Zn substitution for In could increase the electrical conductivity and Seebeck coefficient. • Change the electrical conduction mechanism of CuInSe2 from two-charge carrier behavior to hole dominated behavior. • The CuIn 0.98 Zn 0.02 Se 2.02 achieves the highest peak ZT of 0.18, which is twice larger than that of pristine CuInSe 2.02. [ABSTRACT FROM AUTHOR]