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Optimizing thermoelectric conversion efficiency requires the compromise of electrical and thermal properties of materials, which are hard to simultaneously improve due to the strong coupling of carrier and phonon transport. Herein, a one-pot approach realizing simultaneous second phase and Cu vacancies modulation is proposed, which is effective in synergistically optimizing thermoelectric performance in copper sulfides. Multiple lattice defects, including nanoprecipitates, dislocations, and nanopores are produced by adding a refined ratio of Sn and Se. Phonon transport is significantly suppressed by multiple mechanisms. An ultralow lattice thermal conductivity is therefore obtained. Furthermore, extra Se is added in the copper sulfide for optimizing electrical transport properties by inducing generating Cu vacancies. Ultimately, an excellent figure of merit of ~1.6 at 873 K is realized in the Cu1.992SSe0.016(Cu2SnSe4)0.004 bulk sample. The simple strategy of inducing compositional and structural modulation for improving thermoelectric parameters promotes low-cost high-performance copper sulfides as alternatives in thermoelectric applications. It is hard to simultaneously improve electrical and thermal properties of materials due to the strong coupling of carrier and phonon transport. Here, the authors propose a one-pot modulation strategy for simultaneously adjusting carrier and phonon transport in copper sulfids. [ABSTRACT FROM AUTHOR]

The recent growing energy crisis draws considerable attention to high‐performance thermoelectric materials. n‐type bismuth telluride is still irreplaceable at near room temperature for commercial application, and therefore, is worthy of further investigation. In this work, nanostructured Bi2Te3 polycrystalline materials with highly enhanced thermoelectric properties are obtained by alkali metal Na solid solution. Na is chosen as the cation site dopant for n‐type polycrystalline Bi2Te3. Na enters the Bi site, introducing holes in the Bi2Te3 matrix and rendering the electrical conductivity tunable from 300 to 1800 Scm–1. The solid solution limit of Na in Bi2Te3 exceeds 0.3 wt%. Owing to the effective solid solution, the Fermi level of Bi2Te3 is properly regulated, leading to an improved Seebeck coefficient. In addition, the scattering of both charge carriers and phonons is modulated, which ensured a high‐power factor and low lattice thermal conductivity. Benefitting from the synergistic optimization of both electrical and thermal transport properties, a maximum figure of merit (ZT) of 1.03 is achieved at 303 K when the doping content is 0.25 wt%, which is 70% higher than that of the pristine sample. This work disclosed an effective strategy for enhancing the performance of n‐type bismuth telluride‐based alloy materials. [ABSTRACT FROM AUTHOR]

• The thermoelectric properties of natural chalcopyrite were investigated for the first time. • The TE properties of chalcopyrite were highly enhanced by vacuum annealing. • The natural chalcopyrite is a promising thermoelectric material. This paper focuses on the thermoelectric properties of natural chalcopyrite and provides methods for optimizing its thermoelectric properties. Natural chalcopyrite shows obvious anisotropic thermoelectric properties. Although the thermoelectric properties of natural chalcopyrite are low, they are found to be significantly enhanced by vacuum annealing. Natural chalcopyrite was proven to be feasible and potential thermoelectric materials. [ABSTRACT FROM AUTHOR]

Digenite (Cu 1.8 S) as a low-cost, low-toxicity thermoelectric material attracts more and more attention due to its excellent electrical transport. In this paper, the Bi 2 S 3 and Bi 2 S 3 @Bi core-shell were introduced to Cu 1.8 S bulk prepared by mechanical alloying (MA) and spark plasma sintering (SPS) technique. The core-shell structural nanorods were synthesized by a hydrothermal method using Bi 2 S 3 nanorods as the template. The effects of adding Bi 2 S 3 on the thermoelectric properties of Cu 1.8 S were investigated in detail at the temperature between 323 K and 723 K. The power factor of Cu 1.8 S was enhanced by introducing Bi 2 S 3 @Bi core-shell nanorods due to improved Seebeck coefficient. A maximum thermoelectric figure of merit ( ZT ) value of 0.77 was attained at 723 K due to optimized thermal transport properties and to the maintained electrical transport properties, which is 2.4 times higher than that of the pristine Cu 1.8 S (0.32 at 723 K). [ABSTRACT FROM AUTHOR]

Nanostructuring is a conventional approach to decrease thermal conductivity, nevertheless, the effect of grain boundaries on scattering phonon is limited. Herein, a new approach of constructing complex nanostructures is proposed. The copper sulfides-based nanocomposites with high thermoelectric properties and phase stability were fabricated by combining with solid-state reaction and spark plasma sintering techniques. The main phase of Cu 12 Sb 4 S 13 and Cu 1.96 S with complex nanostructures is obtained by introducing CoSb 3 additive to Cu 1.8 S matrix. Hole concentration in p-type composites is tailored by regulating Cu vacancies concentration and Co3+ doping in Cu+ sites, resulting in the significantly enhanced Seebeck coefficient and carrier thermal conductivity reduction. Furthermore, an ultralow thermal conductivity of 0.47 W m−1 K−1 at 773 K is achieved due to the tuned carrier concentration and the enhanced phonons scattering by continuous nanopores, extra phase interfaces and nanoprecipitates. The record high ZT of 1.6 is achieved at 773 K in Cu-S based thermoelectric material system for the composite specimen, namely Cu 1.8 S-5 wt.% CoSb 3. Our result provides a new strategy to construct complex nanostructures and realize spontaneous composition regulation in improving TE performance of copper sulfide-based materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• The Cu 1.8 S-Ru composites were fabricated by MA and SPS technology. • The power factor has been overall increased for the Cu 1.8 S. • Alloying with Ru is beneficial for improving the stability of Cu 1.8 S material. • A conversion efficiency of 1.0% is achieved at a ΔT of 480 K in Cu 1.8 S-1% Ru sample. • The Cu 1.8 S-1% Ru bulk obtains the average Vickers hardness of 1.22 GPa. Cu 1.8 S (digenite), a copper sulfide with natural Cu deficiencies, possesses excellent conductivity, low-cost, as well as environmentally friendly features. It has thus recently attracted heightened attention. However, the thermoelectric performance of pristine Cu 1.8 S is poor, and the related mechanical properties have not been deeply investigated, which hinders this material from becoming a candidate for commercial applications. This work proposes an effective approach to synergistically improve the comprehensive performance of polycrystalline Cu 1.8 S-based bulk materials for use in practical applications. Cu 1.8 S- x Ru (x = 0.005, 0.01, 0.02) bulk composites were successfully fabricated by combining mechanical alloying and spark plasma sintering technology. Benefiting from the overall optimized power factor and thermal conductivity by the regulated carrier concentration and enhanced phonon scattering effect from the incorporation of multiscale lattice defects, a peak figure of merit of 1.0 at 773 K was achieved in the Cu 1.8 S-1% Ru bulk specimen. In addition, the introduction of ruthenium could enhance the thermal stability of Cu 1.8 S materials by suppress the Cu ions motion. A conversion efficiency of 1.0% at a temperature difference of 480 K was obtained for the single-leg TE module. Finally, the excellent average Vickers hardness of 1.22 GPa for the Cu 1.8 S-1%Ru bulk composite was higher than that of other state-of-art TE materials. Compositing with ruthenium might be an approach worth promoting to synergistically improve the thermoelectric and mechanical performance of other materials. [ABSTRACT FROM AUTHOR]

• The Cu 1.8 S-AgCl composites were fabricated by MA and SPS technology. • Multiple lattice defects are introduced in the Cu 1.8 S-AgCl composites. • The lattice of Cu 1.8 S material has been softened by introducing Ag+. • A record ZT of 1.5 is achieved at 773 K in Cu 1.8 S-1% AgCl specimen. Digenite received extensive attention in recent years owing to the good electrical and thermal stability as well as the characteristics of the environmental benignity and low cost. The major task of Cu 1.8 S material is to further optimize the thermoelectric performance by means of the Seebeck coefficient improvement and thermal conductivity reduction. In this study, the Cu 1.8 S based bulk material with the extraordinary high thermoelectric performance was obtained through alloying with AgCl, in which the Seebeck coefficient has been improved by carefully regulating the excessive hole carrier concentration. Besides, the FESEM, EDS and XPS results reveal that multiple phonon scattering centers have been introduced, and the liquid-like Ag+/Cu+ ions result in the chemical lattice softening and thus the weakened sound velocity. These advantageous factors cause the drastically decreased thermal conductivity as well as the remarkably optimized thermoelectric properties in Cu 1.8 S specimen with 1 wt% AgCl, achieving a record zT value of 1.5 at 773 K, among the currently optimum performance in Cu 1.8 S system materials. [ABSTRACT FROM AUTHOR]

SnSe materials have garnered significant interest due to the intrinsic low thermal conductivity. However, its limited electrical conductivity hinders their practical implementation. This study achieved a high ZT value of 1.40 at 773 K in the samples of n-type polycrystalline SnSe 0.95 + x wt% SmCl 3 + y wt% ErCl 3 (x = 0, 0.75, 1.0, 1.25, and 1.5; y = 0, 0.0675, 0.125, and 0.25) since (SmCl 3 , ErCl 3) co-doping decoupled the electrical-thermal transport properties. First, the released electron carrier concentration due to SmCl 3 doping enhanced the electrical transport properties. The SnSe 0.95 + 1.25 wt% SmCl 3 sample exhibited a high power factor of 563 μWm−1K−2 at 773 K. Then, the lattice thermal conductivity markedly decreased with further ErCl 3 doping due to the high-density dislocations and coherent boundary, resulting in effective the phonon scattering. Additionally, the special microtopography was conducive to the decreased lattice thermal conductivity. Therefore, the SnSe 0.95 + 1.25 wt% SmCl 3 + 0.125 wt% ErCl 3 sample achieved a low lattice thermal conductivity value of 0.28 Wm−1K−1 at 773 K. Simultaneously, the (SmCl 3 , ErCl 3) co-doped samples maintained the electrical transport properties than the SmCl 3 -doped samples. Consequently, the SnSe 0.95 + 1.25 wt% SmCl 3 + 0.125 wt% ErCl 3 sample obtained a peak ZT value of 1.40 at 773 K and a competitive average ZT value of 0.37 from 323 to 773 K, and a theoretically calculated conversion efficiency reached 7.2%, which can be applied in the deep space for power generation. This strategy can be utilized to optimize the thermoelectric performance of other thermoelectrical material systems. [ABSTRACT FROM AUTHOR]

InGaO 3 (ZnO) m (m = 1, 2, 3, 4, and 5) ceramics are a series of n-type oxide thermoelectric materials with layered structures and low thermal conductivities. Herein, InGaO 3 (ZnO) m (m = 1, 2, 3, 4, and 5) ceramics were fabricated by spark plasma sintering (SPS). Two different trends in the thermoelectric properties of the InGaO 3 (ZnO) m (m = 1, 2, 3, 4, and 5) ceramics were observed depending on the odevity of the m value. The InGaO 3 (ZnO) sample exhibited a relatively high electrical conductivity and was therefore selected for vacuum annealing to further improve the electrical transport performance. Oxygen vacancy defects were introduced to the matrix during the annealing procedure, which improved the thermoelectric performance. A maximum ZT of 0.45 was obtained at 973 K for the InGaO 3 (ZnO) sample with a 96 h vacuum annealing treatment, which is 30 times higher than that of the pristine sample. [ABSTRACT FROM AUTHOR]

The recent growing energy crisis draws considerable attention to high‐performance thermoelectric materials. n‐type bismuth telluride is still irreplaceable at near room temperature for commercial application, and therefore, is worthy of further investigation. In this work, nanostructured Bi2Te3 polycrystalline materials with highly enhanced thermoelectric properties are obtained by alkali metal Na solid solution. Na is chosen as the cation site dopant for n‐type polycrystalline Bi2Te3. Na enters the Bi site, introducing holes in the Bi2Te3 matrix and rendering the electrical conductivity tunable from 300 to 1800 Scm–1. The solid solution limit of Na in Bi2Te3 exceeds 0.3 wt%. Owing to the effective solid solution, the Fermi level of Bi2Te3 is properly regulated, leading to an improved Seebeck coefficient. In addition, the scattering of both charge carriers and phonons is modulated, which ensured a high‐power factor and low lattice thermal conductivity. Benefitting from the synergistic optimization of both electrical and thermal transport properties, a maximum figure of merit (ZT) of 1.03 is achieved at 303 K when the doping content is 0.25 wt%, which is 70% higher than that of the pristine sample. This work disclosed an effective strategy for enhancing the performance of n‐type bismuth telluride‐based alloy materials. [ABSTRACT FROM AUTHOR]

The decrease in lattice thermal conductivity is one of the most effective methods for enhancing thermoelectric properties. Achieving lattice thermal conductivity close to the theoretical limit is extremely difficult while maintaining an impressive power factor. By introducing ultrafine bismuth sulfide nanograins, strong phonon scattering was generated by associated multiscale lattice defects to further gain a low lattice thermal conductivity of 0.244 W/m/K approaching Clarke's limitation of 0.242 W/m/K. Simultaneously, the electrical conductivity was increased by S diffusion and suppression of the antisite defects, and a high power factor was maintained to produce an improved ZT peak of 1.2 at 473 K for the Bi 2 Te 2.7 Se 0.3 + 1 wt % Bi 2 S 3 #2 sample. This sample was used to fabricate a small device with a p-leg, and the direct conversion efficiency reached 4.39%. Inverse changes in hardness and Young's modulus in conjunction with Bi 2 S 3 content are first reported in thermoelectric materials, which has potential assistance in synchronously improving their mechanical and thermoelectric properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Digenite (Cu 1.8 S) is a subject of increasing interest as a potential p-type thermoelectric material because of its element abundance, low cost and environmental friendliness. However, its thermoelectric properties are limited by high thermal conductivity. In this work, the Cu 1.8 S with x wt% Bi 2 Te 3 (x = 0, 0.5, 1, 3, 5) samples were prepared by combining mechanical alloying (MA) and spark plasma sintering (SPS) technology. The results reveal that Bi 2 Te 3 addition can effectively optimize the thermoelectric properties of Cu 1.8 S materials by tuning the carrier concentration and introducing nanoprecipitates. As a result, the optimal Cu 1.8 S +1 wt% Bi 2 Te 3 sample presents an excellent performance, with relatively high ZT value of 1.1 (at 773 K), which is approximately 2.4 times that of pure Cu 1.8 S. • Cu 1.8 S + x wt% Bi 2 Te 3 (x = 0, 0.5, 1, 3, 5) bulk samples were prepared by mechanical alloying method (MA) and spark plasma sintering (SPS). • A ZT peak reaches 1.1 at 773 K for Cu 1.8 S + 1 wt% Bi 2 Te 3 sample, which is 2.4 times higher than that of pristine. • The average ZT reaches 0.32 in the temperature range from 323 K to 773 K, which is twice of that in undoped Cu 1.8 S sample. [ABSTRACT FROM AUTHOR]

Polycrystalline SnSe thermoelectric materials have received extensive interests owing to the low thermal conductivity and available mechanical properties. However, the low electrical conductivity seriously hinders its application. In this work, stemming from the introducing of Hf and Cl substitution, they released more electrons. Owing to the improved carrier concentration, a high electrical conductivity of 33 S cm−1 for the SnSe 0.95 +1 wt%HfCl 4 sample was obtained at 773 K, about 5 times as much as that of the SnSe 0.95 sample. Thus, a peak power factor of 553.8 μW m−1 K−2 of SnSe 0.95 +3 wt%HfCl 4 sample at 773 K was obtained. Meanwhile, the phonon scattering was enhanced due to the decrease of grain size, the lattice thermal conductivity was suppressed. The pretty low κ l of 0.33 W m−1 K−1 was obtained at 773 K for the SnSe 0.95 +4 wt%HfCl 4 sample. Consequently, the peak ZT value of ∼1.1 was achieved for SnSe 0.95 +3 wt%HfCl 4 sample at 773 K. • (Hf, Cl) co-doping in polycrystalline SnSe bulk samples were fabricated via melting method and combined with the spark plasma sintering (SPS) method. • Due to the introduced Hf and Cl substitution, the more electronic was released, a high electrical conductivity of 33 S cm−1 for the SnSe 0.95 +1 wt%HfCl 4 sample was obtained at 773 K. • Owing to the decreased grain size and the enhanced phonon scattering, a low κ l of 0.33 Wm−1 K−1 was obtained at 773 K for the SnSe 0.95 +4 wt%HfCl 4 sample. [ABSTRACT FROM AUTHOR]

Both single crystal and polycrystalline SnSe have been widely investigated due to their superior thermoelectric properties in the medium temperature range. Due to its poor mechanical properties and complex and time-consuming synthesis process, single crystal SnSe is difficult to apply commercially. In this work, n-type polycrystalline SnSe with high thermoelectric properties was fabricated by LaCl 3 doping via the melting method combined with the spark plasma sintering (SPS) technique. Surprisingly, it was found that the different doping processes affect the electrical behavior of LaCl 3 -doped polycrystalline SnSe. The sample of LaCl 3 -doped SnSe was p-type when ball milling and the SPS technique were employed in our previous work, and the sample was n-type when the melting method and SPS were employed in this work. The doping mechanism was investigated in detail in this work. [Display omitted] • LaCl 3 -doped SnSe was fabricated via the melting method and SPS. • The dopant atom position in SnSe lattice depends on the synthesis process. • Power factor of 562 ​μWm−1K−2 ​at 773 ​K was achieved in n-type polycrystalline SnSe. • The highest ZT of 0.85 ​at 773 ​K was achieved in SnSe 0.95 +1 ​wt% LaCl 3 at 773 ​K. [ABSTRACT FROM AUTHOR]

• Bi 2 Te 3 +1 wt% Ru bulk sample was prepared by hand milling and SPS using commercial Bi 2 Te 3 ingot. • A ZT peak reaches 0.93 at 150 °C for Bi 2 Te 3 +1 wt% Ru sample which is 45.3% higher than that of pristine. • Vickers hardness reaches 2.38 GPa for Bi 2 Te 3 +1 wt% Ru sample which is the highest in Bi 2 Te 3 system. Recently, researchers have been exploring the optimization of the thermoelectric properties of composite materials. Composite technology with many successful cases of enhancement in thermoelectric properties have been confirming effectively to optimize thermoelectric materials. In this study, Ru nano-micro composite particles were successfully introduced in commercial bismuth telluride (Bi 2 Te 3) as second phase to simultaneously optimize the thermoelectric and mechanical properties. In a Bi 2 Te 3 sample containing 1 wt% Ru (+1 wt% Ru), the ZT peak was measured to be 0.93 (at 150 °C) and the maximum Vickers hardness was measured to be 2.38 GPa. These values exceeded the values of a pure sample by 45.3% and 36%, respectively. The average ZT of the +1 wt% Ru sample at 50–200 °C was 0.86, which is comparable with the Bi 2 Te 3-x Se x system. By varying the Ru content, the components, microstructure, thermoelectric and mechanical properties of Bi 2 Te 3 were manipulated and their interdependence demonstrated. The extent to which the thermoelectric and mechanical properties of Bi 2 Te 3 can be optimized, via Ru compositing and nano-Bi 2 Te 3 producing, is related by the complex nano-micro composite structure. The superior thermoelectric properties of composite materials hold great the commercial value and may reduce the input of raw materials. [ABSTRACT FROM AUTHOR]