Development Of Thermoelectric Materials Research Articles

The growth evolution of SnSe-doped SnTe alloy by in-situ selenization substitution method

In the era of increasing environmental pollution and energy crisis, the development of thermoelectric materials to achieve the reuse of waste heat energy is of great significance. SnTe, as an environmentally friendly thermoelectric material, its high electronic-thermal conductivity and coupled high electrical conductivity originated from intrinsic high carrier hole concentration leads to the unsatisfactory thermoelectric properties. With a lot of research going on to optimize thermoelectric performance by decoupling the thermo-electrical contradiction, the entropy engineering strategy, which can independently modulate lattice thermal conductivity is proved to be feasible by increasing the internal configurational entropy through doping. However, due to the uncontrollable growth microscopic process and the perturbation of film quality, the desired precise phase doping remains a challenge. In this work, we report an instantiation of the entropy increase of SnSe-doped SnTe alloy thin films prepared by two-step magnetron sputtering and selenization method. The microstructure and physical properties of thin films were investigated for replaying and controlling the growth evolution of in-situ selenization substitution. When the reaction temperature and duration were adjusted to 300℃ and 30 mins respectively, the desired pure phase doping was obtained. This work provides a new method of doping modification of SnTe materials, and the product as a new functional material expands the thermoelectric material library. In particular, it has positive reference significance for the development of synthesis controllability and structure establishment of complex polycrystalline materials.

3D-printed Bi2Te3-based Thermoelectric Generators for Energy Harvesting and Temperature Response.

Thermoelectric generators (TEGs) are environmentally friendly energy harvesting technologies that hold great promise in the field of self-powered electronics and sensing. However, the current development of thermoelectric (TE) devices has largely lagged behind the development of thermoelectric materials, especially in the preparation of thermoelectric components with customizable shapes and excellent properties, which largely limits their practical applications. These issues can be effectively addressed by using 3D printing technology. Here, we print multiple p-type thermoelectric legs (pins) consecutively with this simple technique, and the printed TEGs have excellent thermal potential (288 μV K-1 at room temperature) and excellent temperature response properties, which exhibited an output voltage of 127.94 mV at a temperature difference (ΔT) of 40 K. The 3D-printed thermoelectric generator enables the collection of thermal energy. In addition, the device has excellent temperature sensing characteristics, and this temperature signal to electrical signal conversion is very rapid, which enables temperature sensing alarms in a wide temperature domain. Combining these features, an energy harvesting and electrical alarm concept for home-scale applications is proposed, which is expected to provide a diverse research idea for the application of next-generation thermoelectric devices.

Simultaneous realization of high power factor and low thermal conductivity in medium-entropy La-doped (Sr1/3Ba1/3Ca1/3)1-xLaxTiO3 oxides with porous structure

Some studies have proven the effectiveness of high-entropy alloying in reducing lattice thermal conductivity; however, the synchronous degradation in carrier mobility limits the thermoelectric properties of high-entropy materials. Herein, we present a series of medium-entropy oxides (Sr1/3Ba1/3Ca1/3)1-xLaxTiO3 (x = 0.05, 0.1, 0.15) with different levels of La doping, breaking the trade-off between carrier and phonon transport. The medium-entropy design helps keep the carrier mobility at a moderate level while modulating the carrier concentration through La3+ doping, thereby yielding a peak power factor value of 1842 μW/(m⋅K2) at 773 K. Meanwhile, the incorporation of nano-micro-porous structure and medium entropy effect leads to a significant reduction in lattice thermal conductivity, reaching 2.3 W/(m⋅K) at 1073 K. Consequently, a ZTmax value of 0.67 is obtained for the MEP-10La sample at 1073 K, which is one of the state-of-the-art ZT values reported for the SrTiO3-based materials. The present work provides a viable approach for the development of thermoelectric materials with enhanced performance.

The extreme high cooling capacity thermoelectric cooler optimal design for kilowatts scale thermoelectric air-conditioner of high-speed railway carriage

In recent 20 years, the rapidly development of thermoelectric materials promotes thermoelectric s application in large scale cooling area, i.e. air-conditioner. To provide quiet working environment for the driver of high-speed railway, a kilowatt scale air-conditioner was designed. Firstly, a novel thermoelectric cooler with maximum cooling capacity of 450 W was designed with 199 thermoelectric elements, and the cooling performance were investigated under different cold and hot side heat exchange capacity. Second, the hot and cold side heat exchangers were optimized adopting genetic algorithm. Finally, a high coefficient of performance (COP) thermoelectric air conditioning (TEAC) system was designed for high-speed railway locomotive. The TEAC system comprising 16 TECs achieved a cooling capacity of 2342 W with a COP of 0.5 in cooling mode, and meets one 1HP TEAC requirements. The temperature field inside the locomotive was uniform and exhibited a linear correlation with the supplied air temperature. This research demonstrates the utility of high-power TEAC in high-speed railway carriages, providing valuable insights for the application of TEAC technology.

Thermoelectric Properties of Porous SiC/SiO2/C Composite from Carbonized Cryptomeria japonica Wood

Electric power generation by thermoelectric material utilizing radiated heat of from roof’s house, engine and others is potential clean energy in tropical areas such as Indonesia. In this study, thermoelectric materials such as silicon carbide (SiC/SiO2/C) composites were developed from carbonized Cryptomeria japonica wood infiltrated ethyl silicate-40 by sintering at 1400, 1600 and 1800 ºC for 30 min under N2 atmosphere. This study aimed to examine the morphology, microstructure and thermoelectric properties of porous SiC/SiO2/C composites. SiC/SiO2/C composites sintered at 1600 ºC with low value of thermal conductivity was potential for the development of thermoelectric material. The oxidation of SiC/SiO2/C composite sintered at 1600 °C which removed parts of residual silica and carbon, transformed the composite exhibiting p-type semiconductor with low values of Seebeck coefficient of to that exhibiting n-type semiconductor with high values Seebeck coefficient. A maximum of figure of merit of 6.25 x 10--5 K-1 was obtained at 140 ºC in the oxidized SiC/SiO2/C composite sintered at 1600 °C. The comparatively high figure of merit indicates the potentiality the material for thermoelectric purpose.

Prediction of lattice thermal conductivity with two-stage interpretable machine learning

Thermoelectric and thermal materials are essential in achieving carbon neutrality. However, the high cost of lattice thermal conductivity calculations and the limited applicability of classical physical models have led to the inefficient development of thermoelectric materials. In this study, we proposed a two-stage machine learning framework with physical interpretability incorporating domain knowledge to calculate high/low thermal conductivity rapidly. Specifically, crystal graph convolutional neural network (CGCNN) is constructed to predict the fundamental physical parameters related to lattice thermal conductivity. Based on the above physical parameters, an interpretable machine learning model–sure independence screening and sparsifying operator (SISSO), is trained to predict the lattice thermal conductivity. We have predicted the lattice thermal conductivity of all available materials in the open quantum materials database (OQMD) (https://www.oqmd.org/). The proposed approach guides the next step of searching for materials with ultra-high or ultra-low lattice thermal conductivity and promotes the development of new thermal insulation materials and thermoelectric materials.

Realizing Plain Optimization of the Thermoelectric Properties in BiCuSeO Oxide via Self-Substitution-Induced Lattice Dislocations.

Seeking new strategies to tune the intrinsic defect and optimize the thermoelectric performance via no or less use of external doped elements (i.e., plain optimization) is an important method to realize the sustainable development of thermoelectric materials. Meanwhile, creating dislocation defects in oxide systems is quite challenging because the rigid and stiff ionic/covalent bonds can hardly tolerate the large strain energy associated with dislocations. Herein, taking BiCuSeO oxide as an example, the present work reports a successful construction of dense lattice dislocations in BiCuSeO by self-doping of Se at the O site (i.e., SeO self-substitution), and achieves plain optimization of the thermoelectric properties with only external Pb doping. Owing to the self-substitution-induced large lattice distortion and the potential reinforcement effect by Pb doping, high-density (about 3.0×1014 m-2) dislocations form in the grains, which enhances the scattering strength of mid-frequency phonon and results in a substantial low lattice thermal conductivity of 0.38 W m-1 K-1 at 823 K in Pb-doped BiCuSeO. Meanwhile, PbBi doping and Cu vacancy markedly improve the electrical conductivity while maintaining a competitively high Seebeck coefficient, thereby contributing to a highest power factor of 942 μW m-1 K-2. Finally, a remarkably enhanced zT value of 1.32 is obtained at 823 K in Bi0.94Pb0.06Cu0.97Se1.05O0.95 with almost compositional plainification. The high-density dislocation structure reported in this work will also provide a good inspiration for the design and construction of dislocations in other oxide systems.

Comparison between thermoelectric generator and organic Rankine cycle for low to medium temperature heat source: A Techno-economic analysis

With the fast development of thermoelectric materials, the thermoelectric generator is on the edge of broader commercial application. The objective of this work is to investigate the tech-economic feasibility of the thermoelectric generator (TEG) for power generation from low to medium temperature heat sources in contrast to organic Rankine cycle (ORC). Off-the-shelf TEG and ORC products’ specification are reviewed and two typical models are chosen for analysis. In the techno-economic analysis, technical constraints such as output power and efficiency; the economic metrics, such as net present value, internal rate of return and payback period are considered as evaluation indicators. The comparison results in this study can provide insights of today and outlook of the future for the waste heat recovery and geothermal industry.

Thermoelectric Silver-Based Chalcogenides.

Heat is abundantly available from various sources including solar irradiation, geothermal energy, industrial processes, automobile exhausts, and from the human body and other living beings. However, these heat sources are often overlooked despite their abundance, and their potential applications remain underdeveloped. In recent years, important progress has been made in the development of high-performance thermoelectric materials, which have been extensively studied at medium and high temperatures, but less so at near room temperature. Silver-based chalcogenides have gained much attention as near room temperature thermoelectric materials, and they are anticipated to catalyze tremendous growth in energy harvesting for advancing internet of things appliances, self-powered wearable medical systems, and self-powered wearable intelligent devices. This review encompasses the recent advancements of thermoelectric silver-based chalcogenides including binary and multinary compounds, as well as their hybrids and composites. Emphasis is placed on strategic approaches which improve the value of the figure of merit for better thermoelectric performance at near room temperature via engineering material size, shape, composition, bandgap, etc. This review also describes the potential of thermoelectric materials for applications including self-powering wearable devices created by different approaches. Lastly, the underlying challenges and perspectives on the future development of thermoelectric materials are discussed.

Cu-Ni-Based Alloys from Nanopowders as Potent Thermoelectric Materials for High-Power Output Applications

A new approach for the development of thermoelectric materials, which focuses on a high-power factor instead of a large figure of merit zT, has drawn attention in recent years. In this context, the thermoelectric properties of Cu-Ni-based alloys with a very high electrical conductivity, a moderate Seebeck coefficient, and therefore a high power factor are presented as promising low-cost alternative materials for applications aiming to have a high electrical power output. The Cu-Ni-based alloys are prepared via an arc melting process of metallic nanopowders. The heavy elements tin and tungsten are chosen for alloying to further improve the power factor while simultaneously reducing the high thermal conductivity of the resulting metal alloy, which also has a positive effect on the zT value. Overall, the samples prepared with low amounts of Sn and W show an increase in the power factor and figure of merit zT compared to the pure Cu-Ni alloy. These results demonstrate the potential of these often overlooked metal alloys and the utilization of nanopowders for thermoelectric energy conversion.

Intrinsically low thermal conductivity of tetragonal-structured PbSe2

Designing new compounds with earth-abundant constituent elements and intrinsically low thermal conductivity are crucial to the development of thermoelectric materials. In this letter, the tetragonal-structured PbSe 2 with extremely low thermal conductivity was prepared by two-step ball milling and high pressure synthesis method. Density functional theory calculation shows that the low thermal conductivity of PbSe 2 is originated from its weak interatomic bonding strength and high lattice vibration anharmonicity. We also found that the carrier concentration of PbSe 2 can be tuned effectively by Ag doping in Pb site, which leads to an enhanced figure of merit. These results indicate that PbSe 2 is a potential candidate as a thermoelectric material. • Tetragonal structured PbSe 2 was synthesized by a high-pressure method. • PbSe 2 behaves an extremal low thermal conductivity. • The carrier concentration and ZT of PbSe 2 was enhanced effectively by Ag doping.

Soft Organic Thermoelectric Materials: Principles, Current State of the Art and Applications.

The enormous demand for waste heat utilization and burgeoning eco-friendly wearable materials has triggered huge interest in the development of thermoelectric materials that can harvest low-cost energy resources by converting waste heat to electricity efficiently. In particular, due to their high flexibility, nontoxicity, cost-effectivity, and promising applicability in various fields, organic thermoelectric materials are drawing more attention compared with their toxic, expensive, heavy, and brittle inorganic counterparts. Organic thermoelectric materials are approaching the figure of merit of the inorganic ones via the construction and optimization of unique transport pathways and device geometries. This review presents the recent development of the interdependence and decoupling principles of the thermoelectric efficiency parameters as well as the new achievements of high performance organic thermoelectric materials. Moreover, this review also discusses the advances in the thermoelectric devices with emphasis on their energy-related applications. It is believed that organic thermoelectric materials are emerging as green energy alternatives rivaling their conventional inorganic counterparts in the efficient and pure electricity harvesting from waste heat and solar thermal energy.

Novel two-dimensional beta-XTe (X = Ge, Sn, Pb) as promising room-temperature thermoelectrics.

In this paper, we designed novel low-symmetry two-dimensional (2D) structures based on conventional XTe (X = Ge, Sn, Pb) thermoelectrics with large average atomic mass. The first-principles calculations combined with Boltzmann transport theory show that the beta-XTe exhibit good stability, high electron carrier mobility, and ultralow ΚL. The subsequent analyses show that the ultralow ΚL stems from the coexistence of resonant bonding, weak bonding, and lone-pair electrons in beta-XTe, which leads to large anharmonicities. On the other hand, the lowest energy conduction band of beta-GeTe and beta-SnTe show the convergence of the low-lying Ʃ band, which is the source of the high-power factor in the two systems. The calculated maximum ZT of beta-XTe (X = Ge, Sn, Pb) are 3.08, 1.60, and 0.57 at 300K, respectively, which is significantly greater than that of the previously reported high-symmetry 2D alpha-XTe and the commercial thermoelectrics. We hope that this work can provide important guidance for the development of thermoelectric materials.

New Developments in Thermoelectric Materials Based on the Thermomagnetic Effects

New Developments in Thermoelectric Materials Based on the Thermomagnetic Effects

A record high average ZT over a wide temperature range in a Single-layer Sb2Si2Te6

Conversion of waste heat into usable energy requires development of thermoelectric materials with high efficiency in a wide temperature range. Using first principles theory and Boltzmann transport theory, we show that the thermoelectric performance of the p-type single-layer Sb2Si2Te6 has a high figure of merit ZT of 2.62 at 900 K and a record high average ZT of ~1.93 (corresponding the conversion efficiency of ~23.2%) in the temperature range of 300‐900 K. These values are significantly higher than the recently measured average ZT of ~0.57 in the temperature range of 310–823 K [Luo et al., Joule 4, 159–175 (2020)] in layered bulk Sb2Si2Te6. We attribute the large enhancement of ZT in the single layer material to the increase in the thermoelectric power factor resulting from the complex Fermi surface. Our work reveals the great potential of a single-layer Sb2Si2Te6 for wide-temperature-range thermoelectric applications.

Thermoelectric degrees of freedom determining thermoelectric efficiency

SummaryFor over half a century, the development of thermoelectric materials has based on the dimensionless figure of merit , assuming that the efficiency is mainly determined by this single parameter. Here, we show that the thermoelectric conversion efficiency is determined by three independent parameters, , τ, and β, which we call the three thermoelectric degrees of freedom (DoFs). is the well-defined mean of the traditional under nonzero temperature differences. The two additional parameters τ and β are gradients of material properties and crucial to evaluating the heat current altered by nonzero Thomson heat and asymmetric Joule heat escape. Each parameter is a figure of merit. Therefore, increasing one of the three DoFs leads to higher efficiency. Our finding explains why the single-parameter theory is inaccurate. Further, it suggests an alternative direction in material discovery and device design in thermoelectrics, such as high τ and β, beyond .

Low-cost seebeck power measurement system for characterization of thermoelectric junctions and modules

Development of thermoelectric materials and devices requires performance testing to assess improvements as compared against known control samples. Traditionally, this has been done by measuring the figure of merit. However, another important parameter for materials evaluation is the power output of a single P-N junction pair, typically performed by applying current to the circuit and measuring the Peltier temperature difference output. This approach often leads to errors due to contact resistive heating across interfaces within a device. An alternative approach is to evaluate a thermoelectric couple as a Seebeck generator that requires expensive meters ($20 k-$30 k) to measure milli-volt and milli-amp outputs. In order to enable materials evaluation without the need to use full device modules that are costly and time intensive to fabricate and test, this paper describes the development of low-cost (~$200) measurement circuit and shows data that validates the milli-volt and milli-amp outputs from a single thermoelectric couple.

Significant enhancement in thermoelectric power with Iso-electronic doping in c-axis oriented MoTe2 nano bulk sheets

The search for techniques to enhance thermoelectric power as well as figure of merit is indispensable in the development of thermoelectric materials. In this work, iso-electronic substitution of Tellurium with 9% Sulfur in MoTe2 nano-bulk sheets showed an 88% room temperature enhancement in thermopower combined with a 13% increase in power factor with a negative temperature coefficient of resistivity below 80 K. To correlate the results, a two-band model was successfully applied to temperature variation of both thermopower and resistivity. The results ascribe the thermopower enhancement to the formation of a narrow sulfur impurity band, which causes, a considerable percentage of the holes to pop-up to the valence band maximum and get localized around the S2-cores, resulting in a sharp depletion in hole density available for transport. The application of the two-carrier model to the field dependent magneto resistance, supports the above proposed reduction in hole density. Our results shed light on doping induced thermopower tuning, leading to more efficient thermo-electrics.

Optimization of Power and Efficiency in a segmented legs STEG using the Taguchi method

In the recent times, many researchers have concentrated on the development of thermoelectric materials with higher values of figure of merits to enhance the conversion efficiency. It have been observed in some of the previous studies that the figure of merit and hence, the performance of thermoelectric modules can be enhanced using the module with segmented legs of two or more thermoelectric materials. In this study, the application of segmented thermoelectric modules in a solar assisted thermoelectric generator have been presented. PbTe and BiTe alloys are used in the segmented module. Except the figure of merit, the performance of thermoelectric generator is also dependent on temperatures across modules, load resistance and various design parameters such as leg geometries, cross sectional area of legs etc. So, Taguchi method of optimization was employed using five factors and five levels design to optimize the power and conversion efficiency. The power and efficiencies are mathematically calculated at different combinations according to L25 orthogonal array. The maximum power output is predicted up to 31.52 W and conversion efficiency up to 14.61% using The Taguchi analysis. Analysis of Variance method is also used to analyze general linear model which results into the estimation of contribution percentages of each factor on the power and efficiency.

Thermoelectric Performance of the Half-Heusler Phases RNiSb ( R=Sc,Dy,Er,Tm,Lu ): High Mobility Ratio between Majority and Minority Charge Carriers

Deeper understanding of electrical and thermal transport is critical for further development of thermoelectric materials. Here we describe the thermoelectric performance of a group of rare-earth-bearing half-Heusler phases determined in a wide temperature range. Polycrystalline samples of $\mathrm{Sc}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Dy}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Er}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$, and $\mathrm{Lu}\mathrm{Ni}\mathrm{Sb}$ are synthesized by arc melting and densified by spark plasma sintering. They are characterized by powder x-ray diffraction and scanning electron microscopy. The physical properties are studied by means of heat-capacity and Hall-effect measurements performed in the temperature range from 2 to 300 K, as well as electrical-resistivity, Seebeck-coefficient, and thermal-conductivity measurements performed in the temperature range from 2 to 950 K. All the materials except $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$ are found to be narrow-gap intrinsic $p$-type semiconductors with rather light charge carriers. In $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$, the presence of heavy holes with large weighted mobility is evidenced by the highest power factor among the series ($17\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ at 700 K). The experimental electronic relaxation time calculated with the parabolic band formalism is found to range from $0.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ to $2.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ s. In all the materials studied, the thermal conductivity is between 3 and $6\phantom{\rule{0.2em}{0ex}}{\mathrm{W m}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ near room temperature (i.e., smaller than in other pristine $d$-electron half-Heusler phases reported in the literature). The experimental observation of the reduced thermal conductivity appears fully consistent with the estimated low sound velocity as well as strong point-defect scattering revealed by Debye-Callaway modeling. Furthermore, analysis of the bipolar contribution to the measured thermal conductivity yields abnormally large differences between the mobilities of $n$-type and $p$-type carriers. The latter feature makes the compounds examined excellent candidates for further optimization of their thermoelectric performance via electron doping.