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Recently, Cu2MnSnSe4 alloys and similar compounds have drawn immense attention due to their low intrinsic thermal conductivity. However, their inferior electrical properties hinder their industrial applications. Herein, Cu2MnSn1−xInxSe4 alloys are successfully synthesized and the thermoelectric transport properties are investigated. The results reveal that In doping significantly enhances the electrical properties by reducing electrical resistivity by 4.3 times at maximum temperature. As a consequence, the power factor value is enhanced to 665 μW K−2 m−1 for the sample with 7.5% In concentration which is about 2.2 times higher than the pristine sample. Eventually improved dimensionless figure of merit of 0.33 has been obtained for 5% sample. [ABSTRACT FROM AUTHOR]

Cu-based quaternary chalcogenide compounds have been thermoelectric topic of interest among researchers, especially in recent years, due to their intrinsically low thermal conductivity. Recently plenty of work is done on thermoelectric properties of Cu2ZnSnSe4-based alloys emphasizing on importance of Cu2ZnSnSe4-based alloys in thermoelectric power generation. In this study, we report the effect of annealing temperature on microstructure and thermoelectric properties of Cu2.1Zn0.9SnSe4 alloys. Cu2.1Zn0.9SnSe4 compounds were synthesized by high-temperature melting followed by annealing at four different temperatures (600 °C, 650 °C, 700 °C and 725 °C). X-ray diffraction combined with Raman spectroscopy confirmed the presence of Cu2ZnSnSe4 phase along with ZnSe and CuSe secondary phases. The increased annealing temperature critically affected the microstructure of Cu2.1Zn0.9SnSe4 alloys. Successive increase in annealing temperature subsequently increases the average grain size from 7.3 for 600 sample to 12.1 μm for 725 °C sample by shifting grain size distribution toward higher range. Increased grain size results in reduced carrier scattering and decreases the electrical resistivity eventually improving power factor and maximum power factor of about 400 μWk−2 m−1 is obtained for 725 °C sample. Besides, the increased annealing temperature resulted in increased thermal conductivity attributing increased grain size resulting in low phonon scattering. 725 °C sample shows highest power factor and moderate thermal conductivity among all the samples which resulted in highest value of figure of merit for 725 °C sample of about 0.1 at 673 K. [ABSTRACT FROM AUTHOR]

Lead telluride (PbTe) is an excellent thermoelectric material in the intermediate temperature zone and has been applied to deep space exploration, waste heat recovery and other fields. However, the low thermoelectric conversion efficiency of the n-type PbTe alloys limits its applications. Here, the thermoelectric performances have been enhanced in n-type PbTe alloys through trace bismuth (Bi) and iodine (I) co-doping. The Pb1−xBixTe1−xIx (x = 0.00%, 0.05%, 0.10%, 0.20% and 0.50%) alloys are synthesized in the single phase compounds by a stepwise synthesis method. The carrier concentration has reached an optimal concentration range within the order of 1019 cm−3. The highest absolute Seebeck coefficient of 244 μV/K is obtained for 0.05% doped alloy at 730 K. The highest absolute Seebeck coefficient leads to high power factor for 0.05% doped, especially in low- and middle-temperature range. The highest power factor ∼25 μW K−2 cm−1 has been obtained at 329 K. Complex micro-scale grain boundaries and point defects strongly increase the phonon scattering and then lead to the lowest lattice thermal conductivity of 0.64 W mK−1 at 674 K for x = 0.50%, which is 26% lower than that of pristine PbTe. As a result, the highest figure of merit, zT ∼ 0.9 has been determined in 0.20% doped samples at 725 K. Moreover, the highest average figure of merit, zTave ∼ 0.7 has been achieved in 0.05% doped samples in the 323–723 K temperature range, which is about two or three times higher than reported for single Bi or I doped PbTe samples. [ABSTRACT FROM AUTHOR]

Lead-free tin telluride (SnTe) has been viewed as one promising solid thermoelectric material for recovering waste heat in recent years. In this work, SnTe alloys doped with excessive In and Sb have been synthesized by melting, quenching and spark plasma sintering. The Seebeck coefficient has been enhanced by synergistic effect based on resonant levels and increased carrier effective mass especially at low and middle temperature range, and then, the power factor is enlarged. With the reduced electrical and lattice thermal conductivity via co-doping, the total thermal conductivity is decreased. Intrinsic point defect and more grain boundaries lead to reduction in the lattice thermal conductivity through the co-doping. In addition, as the doping level is near the solubility limit, the 200–600 nm, In-rich precipitations have been detected in Sn0.848Sb0.14In0.012Te alloy, which can further reduce the lattice thermal conductivity. Thus, the lowest lattice thermal conductivity of 0.96 W m−1 K−1 is obtained at 800 K. Finally, the maximum figure of merit zT of ~ 0.8 at 800 K has been obtained for Sn0.848Sb0.14In0.012Te alloy, and a relative high average zT of ~ 0.45 in 300–800 K is achieved due to the zT improvement in the low and middle temperature range which indicated that SnTe is a promising candidate for the thermoelectric application. [ABSTRACT FROM AUTHOR]

Al–Ga based alloys are important on-line hydrogen supply materials under harsh working conditions. Up to now, the activation mechanism is still unclear, especially the reason why In or Sn is indispensable to the alloys' performance is unknown. Here, we elaborately designed and implemented the simulation and validation experiments to unveil the role of indium and tin in the alloys. In simulation experiments, we conducted the penetration of liquid metals (LMs) into Al sheets to analyze its influence on Al's microstructure and the effects of In or Sn on Ga's distribution. We found that the activation effects of In and Sn are different. Subsequently, the validation experiments confirmed the above conclusion that In favors inducing deeper and wider cracks inside the alloy compared with Sn, thus making the alloy easier to break during hydrolysis and ensuring higher yields. Moreover, we found that Sn facilitated the reaction rate, which was explained by experiments and the theoretical calculation. Finally, a novel Al matrix embrittlement mechanism based on low-melting-point phases was proposed for Al–Ga based alloys, which provided a reference for the interpretation of material properties and precise material design. In addition, we gave suggestions for sample selection in actual working conditions. [Display omitted] • Improved mechanism is proposed to guide the application of Al alloys in H 2 supply. • Penetration simulation experiments were used to explored the role of In and Sn. • In and Sn can enhance Al alloys' performance through Al matrix embrittlement. • In and Sn's different effect on Ga's distribution affects Al alloys' performance. • The law that In favors H 2 yield while Sn favors reaction rate is confirmed. [ABSTRACT FROM AUTHOR]

For the purpose of investigating the effect of Zn replacement of In3Sn on the hydrogen production performance of Al-rich alloy ingots, Al-Ga-In3Sn alloys with various Zn dosages (0–5 wt.%) were prepared by a traditional melting and casting technique. The phase compositions and microstructures were characterized using X-ray diffractometer (XRD) and scanning electron microscope (SEM) with an Energy Dispersed X-ray system (EDS). The SEM results indicate that, with a small amount of Zn instead of In3Sn, the number and total area of grain boundary (GB) phases will decrease gradually, and the average single GB area will eventually stabilize. The distribution of Zn in the alloy is similar to that of Ga, and an area with high Zn content appeared in the high-Zn-doped sample. The melting behaviors of Al with other metals were measured by DSC. The reaction of these alloys and water were investigated at different temperatures. Compared with Al-Ga-In3Sn alloy, low addition of Zn changed the composition of GB phase and increased the maximum hydrogen production rate. The reason for the changes in the hydrolysis reaction of Al with the addition of Zn was discussed. [ABSTRACT FROM AUTHOR]

• SnTe-NaSbSe 2 alloys based on colloid synthesis are detailed for the first time. • The Seebeck coefficient are significantly optimized at the same time. • κ L of 0.38 W m−1 K−1 below the amorphous limit of Debye–Cahill is achieved. • The ZT reaches up to 1.15 at 823 K for (SnTe) 0.85 (NaSbSe 2) 0.15. Ternary I-V-VI 2 colloidal NaSbSe 2 nanocrystals are herein used to improve the performance of lead-free SnTe thermoelectric materials. We showcase a versatile bottom-up engineering approach to produce nanocrystal-based SnTe-NaSbSe 2 alloys from the rapid hot press of colloidal nanocrystal building blocks. The incorporation of NaSbSe 2 nanocrystals significantly enhances the Seebeck coefficient of SnTe. The band convergence and simultaneous increasing band gap of SnTe-NaSbSe 2 alloys are certified by the first-principles density functional theory calculations. Besides, defect engineering generated by the incorporation of NaSbSe 2 nanocrystals such as Sn vacancies, substitution point defects, dense dislocations, and strains generated by the NaSbSe 2 nanoparticles incorporation result in a dramatic reduction of the lattice thermal conductivity below the amorphous limit of pure SnTe, down to 0.38 W m−1 K−1. As a consequence, power factors enhance up to 1.77 mW m−1 K−2, which is ∼193 % higher than that of the pristine SnTe, and thermoelectric figures of merit up to 1.15 at 823 K for (SnTe) 0.85 (NaSbSe 2) 0.15 are achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Cu 2.1 Mn 0.9 SnSe 4 samples are rapidly synthesized by ball-milling method. • The formation energy of V Cu is modified by compression and tension lattice strain. • The lattice strain shortens the phonon relaxation time and suppresses the κ L. • A lowest κ L (0.57 W m−1 K−1 at 673 K) close to the amorphous limit is obtained. • A record high zT (0.48 at 673 K) in Cu 2 MnSnSe 4 -based alloys is achieved. Quaternary Cu 2 MnSnSe 4 alloys with low intrinsic thermal conductivity are identified as promising middle-temperature thermoelectric materials. However, zT is depressed by the poor electrical performance. To overcome this issue, here, a series of Cu 2.1 Mn 0.9 SnSe 4 samples are prepared by ball-milling method which appears as a time-saving technique and lattice strain variation is observed by changing the annealing time (x = 0, 1, 2, 3, 4 days). The vacancy defects concentration of Cu, with lowest vacancy defects formation energy, is changed with the competition between compression and tension-strain state, consistent with the first principles calculations, which optimizes the carrier transport. As a result, about 4 times increment of the carrier mobility is found. Moreover, the lattice strain of several nanometers is observed with TEM analysis, which scatters phonon strongly. A lowest κ L value of 0.57 W m−1 K−1 at 673 K is obtained for x = 3 sample, which is close to the amorphous limit. The interactive effect of enhanced mobility and strong scattering of phonons, contributing to a record zT ∼ 0.48 at 673 K for x = 3 sample. Lattice strain engineering is an effective tactic to simultaneously optimize the electrical and thermal transport. [ABSTRACT FROM AUTHOR]

[Display omitted] • The manipulation of grain boundary scattering increases the carrier mobility. • Pb doping enhances SOC, leading to the enlarging band gap and the decreasing effective mass. • Strong stress flied fluctuation and attenuated bipolar diffusion effectively decrease the thermal conduction. Owing to the strong anharmonicity and large band degeneracy number, the metastable cubic SnSe exhibits promising thermoelectic (TE) performances theoretically and attracts extense attentions. Experimentally, ABX 2 compounds alloying can effectively stabilize the cubic structure. However, newly emerging shortcomings like low carrier mobilitys and tiny band gaps hinder further optimizations of their TE properties. In this work, the carrier transport mechanism on the typical cubic Sn 0.5- x Pb x (AgSb) 0.25 Se sample is innovatively investigated, revealing that the pristine grain boundary scattering near room temperature changes to a mixed scattering of acoustic phonons and alloys due to the grain growth. Combined with the reduced effective mass by Pb doping, a significant improvement is realized in the mobility, leading to an increased power factor PF (∼7 W cm−1K−2) and a relatively high PF ave (5.6 W cm−1K−2). What's more, Pb doping also makes a big contribution in the reduction of thermal transports: on the one hand, enhancing the high-frequancy phonons scattering via strong mass fluctuation and stress flied fluctuation; on the other hand, enlarging the band gap by enhanced spin–orbit coupling effect, suppressing the bipolar diffusion at elevated temperatures. Resultantly, a small lattice and bipolar contributed thermal conductivity (κ l + κ bi) of 0.58 W m−1K−1 is obtained near 850 K in Sn 0.38 Pb 0.12 (AgSb) 0.25 Se sample, only 59 % of the pristine Sn 0.5 (AgSb) 0.25 Se sample. Finally, an improved TE figure of merit zT value of 0.8 and a zT ave value of 0.47 are obtained. [ABSTRACT FROM AUTHOR]

Al-Ga-In-(Sn) alloys with different indium (In) content were prepared by the traditional high-temperature melting technique. The compositions and microstructures of alloys are studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). We found that free indium presented in alloys plays vital role in morphology transformation of grain boundary (GB) phase particles and associated hydrogen production performance of alloys. As In dosage increasing, the numerous irregular bar-like particles instead of granular particles (mainly composed of In 3 Sn) were observed in alloys with GB phase which mainly composed of free indium (combined with XRD and EDS analysis). Meanwhile, the content and distribution of aluminum (Al) contained in GB phase particles have been somewhat neglected by the wider researchers. In this work, we provide a comprehensive study in relevant fields how Al atoms can contribute to morphology transformation process of GB phase particles. The hydrogen production performance tests were completed by gas mass flowmeter at 40 °C. The results show that the hydrogen release rate of the as-cast alloys gets significantly decreased with the increase of In dosage in alloys, which enables applications of effective on-demand hydrogen supply. • Free indium in alloys reduce the H 2 release rate compared with In 3 Sn. • Free indium leads to a morphology transformation of particles. • Al content of GB phase particles is increase as In dosage increasing. • Morphology transformation process relates to the distribution of Al in particles. [ABSTRACT FROM AUTHOR]

The Mg-bearing Al-Ga-In-Sn alloy with more stable hydrogen generation rate during hydrolysis reaction was synthesized, which is great suitable for the on-board hydrogen supply applications. The test results show that the hydrogen release rate of the Mg-bearing alloys could be effectively controlled. In particular, when the Mg dosage is 0.5 wt.%, the average hydrogen generation rate can even be reduced to 2.1 ml/min·g, while the total energy conversion efficiency of Al has not been affected and still reaches to nearly 100%. Further analysis shows that the reduction of hydrogen production rate during the Al-water reaction process is closely related to the changes of the phase compositions and the microstructure of grain boundary phase (GB-phase) particles in these alloys. Moreover, the electrochemical tests further clarify the reactivity of the alloys with different Mg dosage. • Mg-doping reduces the H 2 release rate but achieves 100% energy conversion. • Mg 2 Sn and In starts to appear in GB-phase particles with Mg doping. • Mg 2 Sn and In simple substance do not co-exist in the same GB-phase particle. • Mg-doping results in a morphology change of particles from stereoscopic to linear. • The average H 2 rate even reduced to 2.1 ml/min when Mg dosage is 0.5 wt%. [ABSTRACT FROM AUTHOR]

Alloy 5(Al-2.5Ga-4.46In-1.54Sn-1.5Al 2 O 3) shows a relatively stable hydrogen production rate, which is suitable for providing hydrogen source for proton exchange membrane fuel cells online. This has a wide range of applications, such as on-board hydrogen supply, field emergency power supply, etc. • The effect of Al 2 O 3 addition on the phase composition and microstructure of alloys were investigated. • Alloys with stable hydrogen production rates in all Al 2 O 3 -added formulations have also been investigated, and this demonstrates potential applications in proton exchange membrane fuel cells. • The addition of Al 2 O 3 alloys could improve hydrogen production rate of Al-Ga-In-Sn alloys. • The addition of Al 2 O 3 promotes the growth of dendrites and tertiary dendrites were observed in the Al 2 O 3 -added alloys for the first time. Al 2 O 3 -added Al-Ga-In-Sn alloys were prepared using a smelting and casting method. As the Al 2 O 3 is added, the Al grain will be refined. With the refinement of the Al grain, the size of grain boundary particle decreases slightly, and under these circumstances, the reaction rate of Al-water is improved. Al-2.5Ga-5.58In-1.92Sn-1.0Al 2 O 3 alloys exhibit maximum rate of hydrogen production. Alloys with stable hydrogen production rates in all Al 2 O 3 -added formulations have also been investigated, and this demonstrates potential applications in proton exchange membrane fuel cells. The reasons for the changes in the microstructure and Al-water reaction with the Al 2 O 3 addition was supposed. [ABSTRACT FROM AUTHOR]