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MgAgSb alloy has attracted wide attention due to its inherent low thermal conductivity, excellent thermoelectric (TE) properties, and environmental friendliness. Although the TE performance has been deeply investigated for the temperature range over 300–700 K, while cryogenic range has seldom report. In this study, a systematic investigation on cryogenic TE performance of α-MgAgSb has been performed. α-MgAgSb alloy has been synthesized by ordinary ball milling followed spark plasma sintering process and then further regulated by heat treatment. The power factor of MgAgSb alloy after 10 days of heat-treating increased by 230%, which is attributed to the reduction of the impurity phase and the improvement of the crystallinity achieved by the optimization of heat treatment. The total thermal conductivity decreased by 18% to 1.15 W m−1 K−1, and the maximum ZT reached 0.264 at 173 K, which is 300% enhancement to untreated one. The ZTavg reached to 0.45 over 173–298 K, located at the pinnacle among cryogenic TE materials. In addition, the ZTeng value of 0.23 related to the highest device conversion efficiency of 5.2% demonstrates good device potential. This work reveals that the purity and the cryogenic TE properties of α-MgAgSb alloy can be effectively improved by heat-treating, and demonstrates the greatly potential of MgAgSb materials in the field of liquefied natural gas's cold energy recovery. [ABSTRACT FROM AUTHOR]

Bi-based YbMg2Bi1.98 Zintl compounds represent promising thermoelectric materials. Precise composition and appropriate doping are of great importance for this complex semiconductor. Here, the influence of Zn substitution for Mg on the microstructure and thermoelectric properties of p-type YbMg1.85−xZnxBi1.98 (x = 0, 0.05, 0.08, 0.13, 0.23) was investigated. Polycrystalline samples were prepared using induction melting and densified with spark plasma sintering. X-ray diffraction confirmed that the major phase of the samples possesses the trigonal CaAl2Si2-type crystal structure, and SEM/EDS indicated the presence of minor secondary phases. The electrical conductivity increases and the lattice thermal conductivity decreases with more Zn doping in YbMg1.85−xZnxBi1.98, whereas the Seebeck coefficient has a large reduction. The band gap decreases with increasing Zn concentration and leads to bipolar conduction, resulting in an increase in the thermal conductivity at higher temperatures. Figure of merit ZT values of 0.51 and 0.49 were found for the samples with x = 0 and 0.05 at 773 K, respectively. The maximum amount of Zn doping is suggested to be less than x = 0.1. [ABSTRACT FROM AUTHOR]

Silicon–germanium (SiGe) alloy has become one of the representative high-temperature thermoelectric (TE) materials due to its advantages of stability, non-toxicity, oxidation resistance, and high mechanical strength. However, the high thermal conductivity and expensive Ge greatly limit the enhancement of zT value and its application. In this paper, n-type Si90Ge10P2Znx nanocomposites were prepared by ball milling and spark plasma sintering. By adjusting the Zn content and sintering time, multiple phonon-scattering centers, such as Zn precipitates, nano-pores, and layered structures, have been introduced into the SiGe matrix. The thermal conductivity was significantly reduced to 2.59 W m−1 K−1 without deteriorate power factor (PF), thus leading to a high zT value of 1.23 at 873 K. At 323–873 K, the average zT value (zTavg) also reached 0.6, increased by approximately 25% in comparison to the reported value using the same ratio of Si90Ge10. Compared with the conventional radioisotope TE generator with Si80Ge20 composition, the zTavg value increased by nearly 30% with only half of Ge, giving strong impetus to the application of SiGe-based TE materials. [ABSTRACT FROM AUTHOR]

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]

As the first-generation semiconductor, silicon (Si) exhibits promising prospects in thermoelectric (TE) convention application with the advantages of un-toxic, abundant, robust, and compliant to the integrated circuit. However, Si-based TE materials are always implemented for high-temperature application and deficient at room temperature (RT) ambience. This study displays an N-type Si1−x−yGexSny thin film by carrying out the strategy of metallic modulation doping for enhancing its power factor (PF). It was distinct to observe the extra carriers poured from the precipitated Sn particles without prominent degradation of mobility while sustaining appreciable thermal conductivity. The PF of 12.21 μ W c m − 1 K − 2 and zT of 0.27 were achieved at 125 °C, which illustrated the significant potential for implementation at near RT ambiance. [ABSTRACT FROM AUTHOR]

Strontium titanate (SrTiO3) is a thermoelectric material with large Seebeck coefficient that has potential applications in high-temperature power generators. To simultaneously achieve a low thermal conductivity and high electrical conductivity, polycrystalline SrTiO3 with a multi-scale architecture was designed by the co-doping with lanthanum, cerium, and niobium. High-quality nano-powders were synthesized via a hydrothermal method. Nano-inclusions and a nano/micro-sized second phase precipitated during sintering to form mosaic crystal-like and epitaxial-like structures, which decreased the thermal conductivity. Substituting trivalent Ce and/or La with divalent Sr and substituting pentavalent Nb with tetravalent Ti enhanced the electrical conductivity without decreasing the Seebeck coefficient. By optimizing the dopant type and ratio, a low thermal conductivity of 2.77 W⋅m−1⋅K−1 and high PF of 1.1 mW⋅m−1⋅K−2 at 1000 K were obtained in the sample co-doped with 5-mol% La, 5-mol% Ce, and 5-mol% Nb, which induced a large ZT of 0.38 at 1000 K. [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]

With excellent high-temperature stability (up to 1000 K) and favorable electrical properties for thermoelectric application, TiNiSn-based half-Heusler (HH) alloys are expected to be promising thermoelectric materials for the recovery of waste heat in the temperature ranging from 700 K to 900 K. However, their thermal conductivity is always relatively high (5-10 W/mK), making it difficult to further enhance their thermoelectric figure-of-merit (ZT). In the past decade, introducing nano-scale secondary phases into the HH alloy matrix has been proven to be feasible for optimizing the thermoelectric performance of TiNiSn. In this study, a series of TiNiSn-based alloys have been successfully synthesized by a simple solid-state reaction. The content and composition of the heterogeneous phase (TiNi2Sn and Sn) is accurately regulated and, as a result, the thermal conductivity successfully reduced from 4.9 W m−1 K−1 to 3.0 Wm−1 K−1 (750 K) due to multi-scale phonon scattering. Consequently, a ZT value of 0.49 is achieved at 750 K in our TiNiSn-based thermoelectric materials. Furthermore, the thermal stability of TiNiSn alloys is enhanced through reducing the Sn substance phase. [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]