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Thermoelectric Mg3+δ(Sb, Bi)2 Zintls have attracted significant attention because of their high‐performing, eco‐friendly, and cost‐effective features, but their thermoelectric properties still need improvement for application to practical devices. Here an outstanding ZT of ≈1.87 at 773 K and a high average ZT of ≈1.2 in n‐type Y‐doped Mg3.2Sb1.5Bi0.49Se0.01 are reported, both of which rank as top values among the reported literature. First‐principles calculations indicate that substituting the Mg site with Y shifts the Fermi level into the conduction band and simultaneously narrows the bandgap, both strengthening the n‐type semiconducting feature and boosting the electron carrier density of Mg3.2Sb1.5Bi0.49Se0.01. A high power factor of ≈21.4 µW cm–1 K–2 is achieved at 773 K in Mg3.18Y0.02Sb1.5Bi0.49Se0.01, benefiting from the rationally tuned carrier density of ≈7.7 × 1019 cm–3 at this temperature. In addition, the doped Ys act as point defects to cause significant lattice distortions and strains, confirmed by comprehensive micro/nanostructure characterizations. These lattice imperfections suppress the lattice thermal conductivity to ≈0.41 W m–1 K–1 at 773 K, leading to such a high ZT. Furthermore, a high energy conversion efficiency of ≈13.8% is predicted by a temperature gradient of 450 K, indicating a great potential to be applied to practical devices for mid‐temperature applications. [ABSTRACT FROM AUTHOR]

Ag2Se is an attractive candidate for room temperature thermoelectric applications because of its extremely low thermal conductivity, large power factor, and excellent mechanical properties. However, its performance is difficult to be improved effectively by doping other atoms. The traditional synthesis processes have the disadvantages of low yield, complex steps, and long period. In this study, the Ag2Se1+x samples were rapidly synthesized by the melting method via changing the ratio of Ag and Se. The carrier concentration and mobility of Ag2Se are optimized by adding excess Se, which could regulate non-stoichiometric defects in the process of synthesis. A high Seebeck coefficient of ∼136.0 μV K−1, a large power factor of ∼3000.0 μW m−1 K−2, and the maximum figure of merit (ZT) of ∼1.02 of the Ag2Se1.015 sample have been achieved at 375 K. The ZT value is 2.3 times than that of the pristine sample (Ag2Se). The mechanical properties of the molting sample are comparable to state-of-the-art thermoelectric materials. Finally, the highest ZT value of the material is predicted by factor B. This work provides an idea for further optimizing Ag2Se-based and other non-stoichiometric thermoelectric semiconductors by a slight excess of Se. Moreover, the fast synthesis technology can significantly save time and energy, which manifests great advantages to the wholesale manufacturing industry. [ABSTRACT FROM AUTHOR]

SiGe‐based thermoelectric (TE) materials are well‐known for high‐temperature utilization, but rarely relevant in the low temperature region. Here a Ge quantum dots (QDs) and Sn precipitation SiGeSn hybrid film are constructed via ultrafast high temperature annealing (UHA) of a treated P‐ion implantation SiGeSn film on Si/SiO2 substrate. Combining the modulation doping effect dominated by Sn precipitates and the energy filtering effect caused by Ge QDs, the optimized SiGe films achieve a giant power factor as high as 91 µW cm−1 K−2 @300 K, room temperature, while maintaining low thermal conductivity. This strategy on film construction provides a novel insight for TE materials with striking performance. [ABSTRACT FROM AUTHOR]

In this study, we report a power factor (PF) value as high as 1950 μW m−1 K−2 for B-ion implanted thermoelectric Si1-x-yGexSny ternary alloy films at ambient temperature by radio frequency sputtering followed by a short-term rapid thermal annealing heat treatment. The record high PF value was realized by modulation doping of Sn in the Si1-x-yGexSny film. It was found that using metallic Sn as nanoparticles and Si1-x-yGexSny as the matrix leads to a large enhancement of the carrier concentration and a very small decrease in carrier mobility. As a result, the electrical conductivity and power factor of the modulation doped Si1-x-yGexSny alloy were greatly improved. The findings of this study present emerging opportunities for the modulation of Si integration thermoelectrics as wearable devices charged by body temperature. [ABSTRACT FROM AUTHOR]

Recently, Ag8SnSe6-based materials, belonging to the family of argyrodite compounds, have been considered as promising thermoelectric candidates due to their intrinsically ultralow lattice thermal conductivity. However, their thermoelectric properties have been rarely investigated because of the intrinsic low carrier concentration. In this work, polycrystalline Ag8SnSe6 bulk materials were successfully synthesized by a bottom-up method by using hydrothermally synthesized Ag8SnSe6 nanocrystals as the precursors. The carrier concentration and mobility of Ag8SnSe6 are successfully enhanced by introducing additional Sn, which should manipulate the self-defects and improve the crystallinity. Thanks to the synergistic optimization of crystal and composition engineering, a maximum ZT value of about 1.22 is achieved for Ag8Sn1.005Se6 at 715 K, which is about 11% higher than that of the pristine sample, and the average ZT is also improved from about 0.65 to about 0.87. This study indicates that crystal engineering and composition engineering play an important role in the thermoelectric properties of Ag8SnSe6 and may provide guidance to improve the thermoelectric performance of other argyrodite compounds. [ABSTRACT FROM AUTHOR]

Strontium titanite (SrTiO 3 ), which is an experimentally-friendly thermoelectric material, could be a promising candidate for thermoelectric power generation applications. The theorectical study indicates the co-doping of La and Nb could enhance the thermoelectric performance, however, the thermoelectric figure of merits ( ZT s) of SrTiO 3 are still low because the co-doping process at nano-scale is experimentally difficult to control. Here we report a high performance SrTiO 3 with La-Nb co-doping, which are prepared by a combination of hydrothermal method and high-efficiency sintering. Nano-scale co-doping is successfully modulated by hydrothermal method, and nano-inclusions precipitate during sintering process, to form complex microstructures. In this case, the electrical and thermal transport properties are optimized simultaneously by doping concentration and dopants type, resulting in a record-high ZT >0.6 at 1000−1100 K in the 10 mol% La and 10 mol% Nb doped SrTiO 3 bulk materials. The nano-scale modulation doping and microstructure controlling approach validated in the present study should be also applicable for other thermoelectric materials. [ABSTRACT FROM AUTHOR]

By using the parent monomers, 3,4-ethylenedioxythiophene and aniline, a series of nanocomposites consisting of different mass ratios of polyaniline (PANI) to poly(3,4-ethylenedioxythiophene) (PEDOT) have been successfully prepared in hydrochloric acid solution through oxidative polymerization, then redoped with p-toluenesulfonic acid ( p-TSA). Firstly, PEDOT nanoparticles were fabricated via chemical oxidation polymerization in reverse (water-in-oil) microemulsions. Then, PANI-doped PEDOT nanoparticles were formed by oxidative polymerization of aniline to form PANI/PEDOT nanofibers. The resulting nanostructured components were characterized by scanning electron microscopy (SEM) and a series of spectroscopic methods. The presence of PEDOT increased the room-temperature electrical conductivity of the PANI/PEDOT nanocomposites by more than two orders of magnitude in comparison with the parent PANI. Moreover, the PANI/PEDOT nanocomposites showed better thermoelectric properties than PANI. Different concentrations of p-TSA also affected the electrical conductivity and Seebeck coefficient of the nanocomposites. With increasing temperature, both the electrical conductivity and Seebeck coefficient increased. [ABSTRACT FROM AUTHOR]

One-step molten salt synthesis process was introduced to fabricate nano to micrometer sized powders in which effects of synthesis temperature, oxide-to-flux ratios and raw materials on the generation of powders were examined. 100 nm or above sized pure particles were obtained at relatively lower temperature of 900C. Micro-sized rhombohedral crystals with a maximum size of approximately 12 m were obtained from or strontium source with 1:1 O/S ratio. Controlled crystal size and morphology of Nb-doped particles are prepared by using this method to confirm the performance of thermoelectric properties. The Seebeck coefficient obtained is significantly high when compared with the reported data, and the high ratio of nano particles in the sample has a positive effect on the increase of Seebeck coefficient too, which is likely due to the energy filtering effect at large numbers of grain boundaries resulting from largely distributed structure. [ABSTRACT FROM AUTHOR]

Lead-free and eco-friendly GeTe shows promising mid-temperature thermoelectric applications. However, a low Seebeck coefficient due to its intrinsically high hole concentration induced by Ge vacancies, and a relatively high thermal conductivity result in inferior thermoelectric performance in pristine GeTe. Extrinsic dopants such as Sb, Bi, and Y could play a crucial role in regulating the hole concentration of GeTe because of their different valence states as cations and high solubility in GeTe. Here we investigate the thermoelectric performance of GeTe upon Sb doping, and demonstrate a high maximum zT value up to 1.88 in Ge0.90Sb0.10Te as a result of the significant suppression in thermal conductivity while maintaining a high power factor. The maintained high power factor is due to the markable enhancement in the Seebeck coefficient, which could be attributed to the significant suppression of hole concentration and the valence band convergence upon Sb doping, while the low thermal conductivity stems from the suppression of electronic thermal conductivity due to the increase in electrical resistivity and the lowering of lattice thermal conductivity through strengthening the phonon scattering by lattice distortion, dislocations, and twin boundaries. The excellent thermoelectric performance of Ge0.90Sb0.10Te shows good reproducibility and thermal stability. This work confirms that Ge0.90Sb0.10Te is a superior thermoelectric material for practical application. [ABSTRACT FROM AUTHOR]

Abstract SnSe 2 is regarded as an attractive thermoelectric material for its structural and chemical analogy to SnSe that is claimed with the highest ZT in single crystal. In this study, the pure and Cl-doped SnSe 2 polycrystals (3%, 6%, 9% and 12% molar Cl content) were fabricated in four steps that are hydrothermal synthesis, heating purification, diffusion doping, and spark plasma sintering. The phase structure, lamellar morphology and crystallite orientation were studied for the synthesized SnSe 2 powder and the sintered pellets. The structural evolution was traced from the SnSe 2 hexagonal plates of powders to the (001) oriented grains in pellets. The Cl doping into SnSe 2 was verified by phase composition, lattice parameter, element distribution, and chemical valance. The doped Cl increased both the carrier concentration and the mobility. The anisotropic thermoelectric properties of SnSe 2 bulk materials were investigated as functions of temperature from 50 °C to 300 °C and the doping amount, respectively. The Seebeck coefficient was less anisotropic than the electrical and thermal conduction. The grain orientation influenced the anisotropy of the electrical and thermal conductivity at a similar ratio. The power factors were less dependent on temperature with an optimum in-plane 1.06 mW m−1 K−2 and out-of-plane 0.41 mW m−1 K−2. The highest ZT s of 0.3 were attained at 300 °C in both directions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Long-range ordered structure formed in α-Cu 2 Se by compositional off-stoichiometry. • Power factor of 856.59 ± 119.92 μWm−1K−2 obtained at 303 K in flexible α-Cu 2 Se film. • α-Cu 2 Se film with optimal length shows a high output power density of 2.92 μWcm−2K−2. The solution-process method can be easily realized without expensive and complicated equipment, which provides the possibility for cost-effective application of flexible thermoelectric films. Nonetheless, the reported output properties of solution-processed Cu 2 Se based films are not satisfactory due to the absence of effective compositional adjustment and optimal length. In this work, a series of solution-processed nylon-supported flexible Cu 2+x Se films have been fabricated. The excess Cu not only fills the vacancies, but also transforms the β -Cu 2 Se with disordered Cu atoms into long-range ordered lamellar α -Cu 2 Se, thereby reducing the carrier concentration and improving the carrier mobility of the films. As a result, a high power factor of 856.59 ± 119.92 μW m−1 K−2 has been achieved in the Cu 2.20 Se film at 303 K. In addition, by numerical simulation, the ideal length of single Cu 2.20 Se film was calculated to be 2 mm. With an actual temperature difference of 6.6 K, a maximum output power density of 2.918 μW cm−2 K−2, which is superior to those of other p-type flexible thermoelectric films, is realized in the single Cu 2.20 Se film. This work provides a feasible idea to promote the output performance of solution-processed flexible thermoelectric films. [ABSTRACT FROM AUTHOR]

• A record power factor of ∼5503 μW m−1 K−1 at 673 K in Zr-doped GeTe. • The enhanced interaction between the Te 5s2 lone pair and the antibonding orbital. • Simultaneous band sharpening in valence band and flattening in conduction band. • A theoretical maximum power density of ∼12.2 W cm−2 at Δ T = 500 K. Lead-free GeTe-based thermoelectric (TE) materials are most promising candidates to replace the environmentally harmful PbTe for TE application at middle temperature range, where high power factor (PF) is significantly important for high power generation if the cost of heat source is low enough. In this study, we report for the first time that the PF of GeTe can be greatly enhanced by tailoring the interaction between Te 5s2 lone pair and antibonding orbitals, which is induced by the hybridization of Zr 4d2 electrons with antibonding orbitals. As a result, the contribution of Ge 4s2 electrons to the valence band is promoted, leading to the band sharpening at the valence band maximum in rhombohedral phase, and simultaneous band sharpening at the valence band maximum and band flattening at the conduction band minimum in cubic phase. Lower band effective mass m b * effectively increases the carrier mobility to a very high value of ∼121 cm−2 V−1 s−1 (300 K), and the Seebeck coefficient is improved by the reduced detrimental effect of minority carrier in cubic phase, enhancing the maximum PF up to a record value of ∼5503 μW m−1 K−1. With the assistance of reduced thermal conductivity, a peak zT of ∼1.9 is achieved at 673 K, which is one of the highest values among single doped GeTe. This work provides a new guidance to enhance the TE performance of GeTe-based materials. [ABSTRACT FROM AUTHOR]

Due to the exhaustion of rare metal resources and the hazard of toxic material to the environment, development of cost-effective, nontoxic, and earth-abundant thermoelectric materials has become more urgent. This study introduces a nontoxic, earth abundant n-type iron-based cost-effective Fe–2.3C–Si–5Mn–7V–8Cr thermoelectric material that is prepared by a simple melting method. Significant increase in both electrical conductivity and Seebeck coefficient are achieved by several heat treatment processes to optimize the distribution and grain size of VC, Cr 23-x Fe x C 6 typed chromium carbide as well as base matrix. As a result, the power factor of the sample that is normalized at 1150 °C is about 0.75 mWm −1 K −2 in maximum value, which is 2.6 times larger than that (0.29 mWm −1 K −2 ) of as-cast sample. The highest ZT value of the sample that is normalized at 1150 °C is 0.028 at 868 K, which is 4.3 times larger than that of as-cast sample (0.0065 at 964 K) in present study, indicating that a proper heat treatment process would remarkably enhance ZT value. This research provides extremely valuable data for the future researches on thermoelectric alloys. [ABSTRACT FROM AUTHOR]