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Cu 1.97 Se- x wt. % In 2 O 3 (x = 0–1) bulk composites are fabricated by combining high-temperature melting and spark plasma sintering technology. The doping of In3+in Cu vacancies tunes the carrier concentration and modifies the band structure of Cu 1.97 Se. Additionally, excessive In 2 O 3 particles benefit the construction of multiple lattice defects to strengthen phonon scattering and suppress the long-range migration of Cu ions, resulting in obviously reduced thermal conductivity and improved service stability. Ultimately, a peak ZT value of 1.43 is obtained at 873 K for the Cu 1.97 Se-0.5 wt. % In 2 O 3 bulk specimen, which is almost 150% higher than that of pristine sample. The thermoelectric conversion efficiency and mechanical properties of the composites sample are also measured. The results suggest that Cu 1.97 Se-based nanocomposites offer potential for use in power generation device assembly. [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-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]

• PbBr 2 doped n -type polycrystalline SnSe that forms multi-nanoprecipitates. • The carrier concentration increased to 1.79 × 1019 cm−3 at room temperature. • The thermal conductivity decreased to 0.32 Wm−1K−1 at 773 K. • A ZT peak reaches 1.1 at 773 K along the parallel to SPS pressure direction. Both p - and n -type SnSe single crystals have been reported to possess high thermoelectric performances, thus highlighting the possibility for commercialization. Polycrystalline SnSe that has better mechanical properties however possesses inferior thermoelectric properties compared to single crystal SnSe. In this work, n -type polycrystalline SnSe 0.95 + x wt% PbBr 2 (x = 0, 0.5, 1, and 1.5) samples were synthesized by combining mechanical alloying and spark plasma sintering technology. The effects of PbBr 2 doping on thermoelectric performance of SnSe were studied in detail. The results show that the carrier concentration was dramatically increased from 2.51 × 1017 cm−3 in pure SnSe 0.95 to 1.79 × 1019 cm−3 in SnSe 0.95 + 1.5 wt% PbBr 2 , further resulting in an enhanced electrical conductivity. Multi-nanoprecipitates are present in the samples, including SnO, SnPb and SnBr x O y , which possibly affect the Seebeck coefficient and the lattice thermal conductivity. A peak ZT value of 1.1 was obtained at 773 K for the SnSe 0.95 + 1.0 wt% PbBr 2 sample. This work highlights that PbBr 2 is an effective dopant to improve the TE performance of n -type polycrystalline SnSe. [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]

Copper Sulfide as a type of environmentally friendly and low-cost thermoelectric material has attracted extensive attention in the last few years. However, the thermoelectric performance and stability of pristine copper sulfides are poor because of the excessive hole concentration and Cu-ion migration behavior in the high temperature, which are the key reason why this material system can't become the candidate of commercial application. In this paper, carbon nanotubes (CNTs) were coated with CuO by ultrasonic spraying pyrolysis, and then waiting to be compounded with Cu 1.8 S material. A series of copper sulfide-based composites were produced by combining with solid-state reaction (SSR) and spark plasma sintering (SPS) technique. The effect of dispersing CNT/CuO on optimizing thermoelectric properties of copper sulfide was investigated in detail in the temperature range from 323 K to 773 K. Carrier concentration of copper sulfides was tuned by carefully regulating Cu vacancies, resulting in the significantly improved Seebeck coefficient. Meanwhile, the thermal conductivity was drastically decreased owing to the introduced pores and weakened contribution from electrical conductivity. A maximum thermoelectric figure of merit (ZT) value of 1.05 was obtained at 773 K for the copper sulfide-based bulk composite, namely Cu 1.8 S-5 wt. % CNT/CuO, which was twice as higher as the pristine Cu 1.8 S specimen. This bulk composite also exhibits a relatively stable thermoelectric performance in the cycling test. • Copper sulfide and CNT/CuO composites were fabricated by SSR and SPS. • The S values of the composites were enhanced from 102 μVK-1–206 μVK-1 compared to the pristine sample. • A peak ZT reached 1.05 at 773 K for the Cu1.8S bulk sample with 5 wt% CNT/CuO. • The stability of composites was improved compared to the pristine sample. [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]