Performance Of Thermoelectric Materials Research Articles

Thermoelectric performance of Ag2GeX3 (X = S, Se, Te) with intrinsically low lattice thermal conductivity: A first principles study

Low lattice thermal conductivity is one of the key factor for excellent thermoelectric performance of materials. In this work, we have systematically studied the thermoelectric properties of Ag2GeX3 (X = S, Se, Te) by first-principles calculations in combination with Boltzmann transport theory. In terms of phonon transmission performance, due to the low frequency of acoustic phonons, strong coupling between low-frequency optical phonons and acoustic phonons, and relatively strong anharmonicity, Ag2GeX3 (X = S, Se, Te) exhibits extremely low lattice thermal conductivity of 0.30 Wm−1K−1, 0.28 Wm−1K−1 and 0.65 Wm−1K−1 at room temperature, respectively. At the same time, Ag2GeX3 (X = S, Se, Te) also exhibits good electrical transport performance. The appropriate band gap and high slope of electronic density of states (DOS) near the Fermi level result in a large Seebeck coefficient of the materials. As a result, the optimal ZT values of p(n)-type Ag2GeX3 (X = S, Se, Te) are 1.4(1.2), 2.2(0.7), and 0.9(0.7) at 800 K, respectively. These results demonstrate outstanding thermoelectric performance of Ag2GeSe3 for energy conversion applications.

Achieving High Isotropic Figure of Merit in Cd and in Codoped Polycrystalline SnSe.

Here, we combined Cd and In codoping with a simple hydrothermal synthesis method to prepare SnSe powders composed of nanorod-like flowers. After spark plasma sintering, its internal grains inherited well the morphological features of the precursor, and the multiscale microstructure included nanorod-shaped grains, high-density dislocations, and stacking faults, as well as abundant nanoprecipitates, resulting in an ultralow thermal conductivity of 0.15 W m-1 K-1 for the synthesized material. At the same time, Cd and In synergistically regulated the electrical conductivity and Seebeck coefficient of SnSe, leading to an enhanced power factor. Among them, Sn0.94Cd0.03In0.03Se achieved a peak ZT of 1.50 parallel to the pressing direction, representing an 87.5% improvement compared with pure SnSe. Notably, the material possesses isotropic ZT values parallel and perpendicular to the pressing direction, overcoming the characteristic anisotropy in thermal performance observed in previous polycrystalline SnSe-based materials. Our results provide a new strategy for optimizing the performance of thermoelectric materials through structural engineering.

Mesoscopic combinatorial design of anisotropic graphitic carbon with ordered porous frameworks for thermoelectric conversion

The incorporation of carbon materials can effectively enhance the performance of thermoelectric materials. By optimizing the thermoelectric properties of the carbon scaffold, it is possible to further improve the thermoelectric performance of the prepared carbon-based composites. To elevate the thermoelectric performance of the carbon scaffold, this work introduces a novel mesoscopic design strategy, utilizing natural flake graphite to create a three-dimensional ordered porous framework. Highly controllable anisotropic conductivity and thermal conductivity of the porous graphite skeleton were achieved, by combining sizable sodium chlorine templates (37.5–250 μm) with a natural flake graphite matrix (50–150 μm). A porous graphite with high electrical conductivity and low thermal conductivity along the vertical axis was obtained by carefully regulating the parameters. The sample demonstrated exceptional thermoelectric conversion performance, achieving a thermoelectric power factor of 12.2 μW m−1 K−2 and a figure of merit value of 28.3 × 10−4. Furthermore, the thermoelectric property of the samples could be greatly improved by adding a small amount of ferric chloride, with a thermoelectric power factor reaching 41.9 × 10−4 and a thermoelectric figure of merit reaching 81.4 μW m−1 K−2. This work provides an effective scheme for the mesoscopic regulation of porous graphite carbon structures and offers a new strategy for enhancing the performance of thermoelectric generators.

Unconventional anomalous Hall effect in Zintl thermoelectric Eu[formula omitted]ZnSb[formula omitted

The outstanding performance of thermoelectric materials is intimately related to complicated electronic band structures that may comprise topological linear dispersion bands. In this work, the exotic magnetism and magneto-transport properties of thermoelectric Eu2ZnSb2 single crystal are investigated. Temperature- and field-dependent magnetization reveal an antiferromagnetic (AFM) ground state and highly localized magnetic moments of Eu2+ ions. The longitudinal resistivity [ρxx(T)] and magnetoresistivity (MR) unveil the coexistence of underlying ferromagnetic (FM) and AFM fluctuations. Furthermore, an unconventional anomalous Hall effect (UAHE) for both above and below the AFM phase transition temperature (TN) is observed, which is suggested to be caused by the vacancy-induced Weyl bands and strong magnetic fluctuations. Our work is benefit for understanding the exotic band structures and thermoelectric properties in Eu2ZnSb2.

The Remarkable Role of Indium in Synergistically Optimizing Carrier Concentration and Phase Distribution of AgCuTe-Based Materials.

Carrier regulation has proven to be an effective approach for optimizing the thermoelectric performance of materials. One common method to adjust the carrier concentration is through element doping. In the case of AgCuTe-based materials, it tends to form with cation vacancies, resulting in a high hole concentration and complex phase composition at low temperatures, which also hinders material stability. However, this also offers additional opportunities to manipulate the carrier concentration. In this study, the improved performance of AgCuTe through indium doping is reported, which leads to a reduction in hole concentration. In combination with a significant increase in the effective mass of the carriers, the enhanced Seebeck coefficient is also realized. Particularly, a notable improvement in power factor is observed in the hexagonal phase near room temperature. Furthermore, a lower electron thermal conductivity is achieved, contributing to an average figure of merit value of ≈1.21 (between 523 and 723K). Additionally, the presence of indium inhibits the formation of the second phase and ensures a homogeneous phase distribution, which reduces the instability arising from phase transition. This work significantly enhances the potential of AgCuTe-based materials for low to medium-temperature applications.

Nanoscale fabrication of heterostructures in thermoelectric SnTe.

Enhancing the performance of thermoelectric materials is demanded to develop strategies for introducing multidimensional microstructures into materials to induce full-scale phonon scattering while ensuring electrical transport performance. Herein, a previously unreported rhombohedral h-SnTe (R3̄m) has been achieved in the nanoscale dimension by the electron beam irradiation of β-SnTe (Fm3̄m) materials. The h-SnTe structure contains interlayer van der Waals gaps and exhibits metallic behavior evaluated by density-functional theory calculations, which coherently appears in the narrow-band semiconductor β-SnTe matrix. Our results provide a strategy for modifying the properties of SnTe-based thermoelectric materials and designing nanostructured chalcogenide heterostructures via electron beam irradiation.

Effects of isotropic strain on the structure and transport properties of half-Heusler alloy BiBaK: a first-principles investigation.

In this study, using density functional and Boltzmann transport theories, we systematically investigated the effects of tensile and compressive strains on the elastic properties, phonon dispersion relation, electronic structure, and transport properties of the half-Heusler compound BiBaK. We calculated the elastic constants and phonon dispersion curves for BiBaK, which demonstrated its mechanical and thermodynamic stability, respectively, under different isotropic strains. Further, calculations showed that the electronic structure and energy bandgap of BiBaK changed with the application of isotropic strain. A high power factor and low thermal conductivity are key to improving the performance of thermoelectric materials. The figure of merit of BiBaK is 0.6 when it is unstrained and reaches a maximum value of 0.93 at -9% compressive strain and a temperature of 1200 K, indicating that under isotropic compressive strain, BiBaK compounds are efficient thermoelectric materials for high-temperature applications.

ALD-Based Interface Engineering for Improving Electrical Conductivity of Nanoporous Thermoelectric Materials

The way to improve the performance of thermoelectric materials is to break the strong correlation between electrical conductivity and thermal conductivity. Combining porous structures with atomic layer deposition (ALD) is a promising strategy to solve this problem. The porous structure introduced into thermoelectric materials effectively lowers the lattice thermal conductivity, greatly increasing performance. However, the formation of nanopores is accompanied by a decrease in electrical conductivity. Here, we create nanoporous Bi0.4Sb1.6Te3 powder formed through selective dissolution from the mixture of KCl and Bi0.4Sb1.6Te3 powder. We propose a strategy to control carrier concentration by ALD of ZnO on nanoporous Bi0.4Sb1.6Te3 powder, thereby improving electrical conductivity and lowering thermal conductivity. Even after spark plasma sintering, ZnO is conformally formed at the nanoporous Bi0.4Sb1.6Te3 grain boundaries. The electrical conductivity increases from 651.72 S/cm to 724.52 S/cm by interfacial reaction of ZnO and Bi0.4Sb1.6Te3. In addition, ZnO inhibits grain growth and creates numerous grain boundaries to lower the lattice thermal conductivity of the porous structure. As a result, the ZT of the nanoporous Bi0.4Sb1.6Te3 deposited with ZnO is increased by 46%. This study demonstrates that ALD is an effective method for improving the conductivity of nanoporous thermoelectric materials.

Optimization of segmented thermoelectric power generators from waste heat while considering the influence of temperature on materials

Thermoelectric technology is commonly used in waste heat utilization of automotive internal combustion engines and widely combined with solar energy units to form solar thermoelectric generator systems. The structure of the Thermoelectric Generator (TEG) needs to be optimized in order to obtain better performance for wider applications. In this paper, the influence of temperature on the height of PN-type thermoelectric arms was analyzed using an improved one-dimensional heat conduction model with the calculus method. At the same time, both the calculation formula of the maximum output power and the calculation formula of various size parameters of the TEG was derived when the influence of temperature on the performance of thermoelectric materials has been considered. In addition, the relationships among different size parameters were derived to obtain the maximum efficiency. The relationships include the most commonly used classical optimization relationship, that is, when the Seebeck coefficient, thermal conductivity and resistivity are averaged, the relationship is consistent with the classical optimization relationship. By considering the impact of temperature on the performance of thermoelectric materials, an improved calculation formula of the figure of merit (Z) was also given. The new optimization formula was compared with the classical optimization method by taking the maximum output power as the optimization index. In the case study, the temperatures of the cold end and the hot end were set at 330 K and 700 K, respectively. PbTe and PbSe were used as the materials with intermediate temperature, and Bi2Te3 was used as the material with low temperature. Through theoretical analysis, it is found that the maximum output power of the new optimization formula can be higher than that of the classical optimization formula.

Enhancement of electrical conductivity and lateral photovoltaic sensitivity via mechanical bending in flexible Cr:In2O3 films

Functional oxide thin film materials have drawn extensive attention due to their rich tunable properties. Here, we deposited Cr-doped In2O3 thin films on flexible mica substrates and investigated the tunable effect of bending strain on their electrical transport and lateral photovoltaic properties. By applying mechanical bending with different curvature, a range of bending strains from compressive (-0.084%) to tensile (0.083%) in the Cr-doped In2O3 thin films was achieved. As the bending strain increased, the lateral photovoltage based on the thermoelectric effect and the electrical conductivity significantly increased. The flexoelectric effect induced by bending strain plays a key role in the mechanical bending tunable effect. In the Cr:In2O3 thin films, bending strain simultaneously increased both the electrical conductivity and the Seebeck coefficient, while reducing the thermal conductivity, highlighting its potential value in enhancing the performance of thermoelectric materials.

POWER FACTOR OF Bi2Te3 AND Sb2Te3 ENHANCED BY HIGH DENSITY AND HARDNESS

The power factor is an indicator of the performance of thermoelectric materials. Many researchers improved the thermoelectric conversion efficiency of materials by various techniques such as doping, substitution, and decreasing particle size for dense samples. We present Bi2Te3 and Sb2Te3 materials prepared by hot pressing method at 673 K for 2 h in Ar atmosphere. Bulk samples were investigated for their crystalline structure, hardness, and power factor by XRD, micro-Vickers hardness, and ZEM-3, respectively. The Seebeck coefficient, electrical resistivity, and power factor of n- Bi2Te3 and p- Bi2Te3 bulk samples were higher than literature data in the same temperature range of 325 to 475 K. The higher power factor value of Bi2Te3 and Bi2Te3 bulk samples of this study have resulted from the high density and high micro-Vickers hardness of the samples.

Pressure-induced remarkable four-phonon interaction and enhanced thermoelectric conversion efficiency in CuInTe2

Hydrostatic pressure (P) has been regarded as an effective approach to improve the performance of thermoelectric materials. Although a positive correlation between its thermoelectric performance and pressure has been demonstrated experimentally for CuInTe2, the underlying physical mechanism remains unclear. Herewith, we investigate the inherent mechanism of hydrostatic pressure-induced electron-thermal transport properties and thermoelectric conversion efficiency for CuInTe2. It is demonstrated that the pressure limits the thermal transport behavior of heat-carrying phonons by changing phonon dispersion, where the broadening of the low-lying phonon bandwidth caused by the compression promotes the dominance of the four-phonon (4ph) scattering mechanism, especially at high temperatures. In addition, the power factor has achieved a huge net increase through the convergence of the valence band edge despite the presence of strong coupling between electron transport parameters. Such bidirectional optimization gives rise to a remarkable enhancement of thermoelectric conversion efficiency. Our work highlights the significant effect of pressure-induced 4ph interaction in CuInTe2, which brings deeper insights into the behavior of thermoelectric materials under extreme pressure environments.

Large Mobility Enables Higher Thermoelectric Cooling and Power Generation Performance in n-type AgPb18+xSbTe20 Crystals.

The room-temperature thermoelectric performance of materials underpins their thermoelectric cooling ability. Carrier mobility plays a significant role in the electronic transport property of materials, especially near room temperature, which can be optimized by proper composition control and growing crystals. Here, we grow Pb-compensated AgPb18+xSbTe20 crystals using a vertical Bridgman method. A large weighted mobility of ∼410 cm2 V-1 s-1 is achieved in the AgPb18.4SbTe20 crystal, which is almost 4 times higher than that of the polycrystalline counterpart due to the elimination of grain boundaries and Ag-rich dislocations verified by atom probe tomography, highlighting the significant benefit of growing crystals for low-temperature thermoelectrics. Due to the largely promoted weighted mobility, we achieve a high power factor of ∼37.8 μW cm-1 K-2 and a large figure of merit ZT of ∼0.6 in AgPb18.4SbTe20 crystal at 303 K. We further designed a 7-pair thermoelectric module using this n-type crystal and a commercial p-type (Bi, Sb)2Te3-based material. As a result, a high cooling temperature difference (ΔT) of ∼42.7 K and a power generation efficiency of ∼3.7% are achieved, revealing promising thermoelectric applications for PbTe-based materials near room temperature.

Ultrahigh Thermoelectric Performance of ZnO-CdO Thin Films

Zinc oxide (ZnO) is emerging as a promising n-type thermoelectric material (TE) for power harvesting due to its high melting point and large Seebeck coefficient. However, the TE performance of ZnO is limited by high thermal conductivity and low carrier mobility. Adding or doping a divalent element such as cadmium oxide (CdO) can lower the thermal conductivity and enhance the carrier concentration of ZnO. In this paper, the thermoelectric transport properties of ZnO-CdO nanocrystalline thin films are investigated by varying the Zn/Cd ratio at temperatures ranging from room temperature (RT) to 423 K. The electrical conductivity, carrier concentration and mobility of ZnO were enhanced by increasing the Cd concentration. The maximum power factor of 2.75 × 10−4 W m−1 K−2 was obtained at 423 K for the Zn/Cd = 1:3 sample. The thermal conductivity was dominated by lattice thermal conductivity in which Umklapp scattering occurs between anharmonic phonons. The thermal conductivity of ZnO decreased significantly with increasing Cd concentration. The highest estimated figure of merit (ZT) of 0.59 was found at 413 K for the Zn/Cd = 1:3 sample, which is 223 times greater than for ZnO, indicating that the film is efficient in energy generation.

Bulk and Surface Electrical Properties of BiSb on Flat and Ion‐Beam Nano‐Patterned InP Substrates

One route to the improvement of thermoelectric material performance is nanostructuring. Herein, BiSb thin films are grown by molecular‐beam epitaxy on two types of InP(001) substrate: flat epiready wafer, and nano‐patterned by ion bombardment and annealing (IBA). The effects of IBA on InP substrate are presented, and the structural and electrical properties of the BiSb films are measured. BiSb films on flat substrates are highly textured with (003) orientation, while films on IBA‐patterned substrates are less well ordered with mainly (012) orientation. A simple calculation method for nonplanar Hall measurements is proposed to explain the electrical conduction in rough films. The effects of BiSb film texture, roughness, and thickness on carrier density and mobility are provided. Sheet carrier density is independent of thickness at 77 K, which suggests conduction via surface states. Topological protection of such states may support nano‐patterning as a route to reducing thermal conductivity while maintaining electrical conductivity.

Additive Manufacturing of Colloidal Nanocrystals for Flexible Thermoelectric Generators

2D Chalcogenides, a narrow gap layered semiconductor and a topological insulator has been reported to have excellent room temperature thermoelectric performances. Alloying and nanostructuring of the material have been widely studied for reducing the lattice thermal conductivity (ΚL) of the materials to enhance the thermoelectric figure of merit (ZT). But the performance of printed thermoelectric devices is significantly low compared to bulk counterparts due to low density and porosity, here we report interface engineering and Nano inclusion in the crystals as an effective way to increase the performance of thermoelectric materials. This work demonstrates the scalable solvothermal synthesis of crystalline nanomaterials with engineered defects and interface engineering to improve the thermoelectric performance of the colloidal nano-inks. The engineered nanomaterials are transformed into devices using multiple additive manufacturing methods including Screen printing, Aerosol Jet Printing, Plasma Jet Printing, and Direct Writing. The low-cost scalable additive manufacturing methods and interface engineering developed in this work demonstrate a significant advance in the field of high-performing low-cost thermoelectric generators, advancing the commercial viability of the technology for energy harvesting, sensing, and cooling applications.

Device‐Level Optimization of n‐Type Mg3(Sb, Bi)2‐Based Thermoelectric Modules toward Applications: A Perspective

AbstractIn recent decades, improvements in thermoelectric material performance have made it more practical to generate electricity from waste heat and to use solid‐state devices for refrigeration. However, despite the development of successful strategies to enhance the figure‐of‐merit zT, optimizing devices for large‐scale applications remains challenging. High zT values do not guarantee excellent device performance, and maintaining high zT over a wide temperature range is difficult. Thus, device‐level structural optimization is crucial for maximizing overall energy conversion efficiency. Proper interfacial and structure design strategies, including contact layer selection, multi‐stage optimization, and size matching for the n‐ and p‐type thermoelectric legs, are necessary for advancing device performance. Additionally, thermal stability issues, device assembly techniques, mechanical properties, and manufacturing costs are crucial considerations for large‐scale applications. To achieve actual applications, the thermoelectric community must look beyond simply aiming for high zT values. This article focuses on modules based on n‐type Mg3(Sb, Bi)2, one of the most promising commercially available thermoelectric materials, and discusses the influence of various parameters on the modules and on the corresponding device‐level optimization strategies.

AgCl Addition to Chalcopyrite Compound for Ultra-Low Thermal Conductivity in Realizing High ZT Thermoelectric Materials.

Optimizing the performance of thermoelectric materials by reducing its thermal conductivity is crucial to enhance its thermoelectric efficiency. Novel thermoelectric materials like the CuGaTe2 compound are hindered by high intrinsic thermal conductivity, which negatively impacts its thermoelectric performance. In this paper, we report that the introduction of AgCl by the solid-phase melting method will influence the thermal conductivity of CuGaTe2. The generated multiple scattering mechanisms are expected to reduce the lattice thermal conductivity while maintaining sufficient good electrical properties. The experimental results were supported by first-principles calculations confirming that the doping of the Ag will decrease the elastic constants, bulk modulus, and shear modulus of CuGaTe2, which makes the mean sound velocity and Debye temperature of Ag-doped samples lower than those of CuGaTe2, indicating the lower lattice thermal conductivity. In addition, the Cl elements within the CuGaTe2 matrix escaping during the sintering process will create holes of various sizes within the sample. These combined effects of holes and impurities will induce phonon scattering, which further reduces the lattice thermal conductivity. Based on our findings, we conclude that the introduction of AgCl into CuGaTe2 has shown a lower thermal conductivity without compromising the electrical performance, resulting in an ultra-high ZT value of 1.4 in the (CuGaTe2)0.96(AgCl)0.04 sample at 823 K.

Recent advances, challenges, and perspective of copper‐based liquid‐like thermoelectric chalcogenides: A review

AbstractAs a group of emerging liquid‐like thermoelectric materials for waste heat recovery into useful energy, di‐chalcogenides Cu2(S, Se, Te) have been considered as superionic thermoelectric materials. Due to their highly disordered degree of Cu‐ion in the crystal lattice, Cu2(S, Se, Te) compounds can exhibit ultralow thermal conductivity, and in the meantime, their rigid sublattice can decently maintain the electrical performance, making them distinct from other state‐of‐the‐art thermoelectric materials. This review summarizes the well‐designed strategies to realize the impressive performance in thermoelectric materials and their modules by linking the adopted approaches such as defect engineering, interfaces, nano‐porous inclusions, thin films, dislocations, nano‐inclusions, and polycrystalline bulks etc., with the moderate design of the device. Some recent reports are selected to outline the fundamentals, underlined challenges, outlooks, and future development of Cu2(S, Se, Te) liquid‐like thermoelectric materials. We expect that this review covers the needs of future researchers in choosing some potential materials to explore thermoelectricity and other efficient energy conversion technologies.image

Concentration anomalies of galvanomagnetic properties of (Bi1-хSbх)2Te3 solid solutions based on Sb2Te3 in the (Bi1-хSbх)2Te3 system

Today, solid solutions based on antimony and bismuth tellurides are among the most widely used materials for the p-legs of thermoelectric converters used at room temperature and below. This paper presents the results of a study of galvanomagnetic properties (electrical conductivity σ, Hall coefficient RH, Hall mobility of charge carriers μH) of thermoelectric solid solutions (Bi1-хSbх)2Te3 in the range of compositions close to pure antimony telluride (x = 1 – 0.96) at temperatures T = 80 K and T = 300 K. The study was carried out on cast polycrystalline samples obtained by the method of crystallization from the melt followed by long-term annealing in vacuum at a temperature of T = 650 K. Galvanomagnetic properties were measured by the standard dc-method, the experimental cell was cooled with liquid nitrogen. The measurement error of RH and σ did not exceed ± 5%. It is shown that the introduction of the first portions of Bi2Te3 leads to a sharp decrease in σ, which is associated with a high degree of disorder of the crystal lattice. In the range of compositions x = 0.99 – 0.9825, the concentration dependences of σ(x) and μH(x) revealed anomalous growth of σ and μH. The presence of concentration anomalies is associated with the transition from dilute to concentrated solid solutions. An assumption is made about the percolation nature of the phase transition. Within the framework of the problem of spheres of percolation theory, within the framework of the task of spheres of the theory of percolation the radius of the deformation sphere of an impurity atom (Bi) is estimated. The obtained value is consistent with the short-range potential of the impurity. It is shown that the position of the anomalies in the σ(x) and μH(x) dependences does not change with the decrease in temperature down to 80K. Thus, the observation of concentration anomalies of the properties for the solid solution (Bi1-xSbx)2Te3 is another confirmation of the hypothesis about the universal nature of the behavior of solid solutions at a low impurity concentration. The detected anomalies must be taken into account when developing methods for increasing the thermoelectric performance of materials by creating solid solutions and doping.