Charge transfer engineering to achieve extraordinary power generation in GeTe-based thermoelectric materials

Atomic-scale interface strengthening unlocks efficient and durable Mg-based thermoelectric devices

Solid-state thermoelectric technology presents a compelling solution for converting waste heat into electrical energy. However, its widespread application is hindered by long-term stability issues, particularly at the electrode-thermoelectric material interface. Here we address this challenge by constructing an atomic-scale direct bonding interface. By forming robust chemical bonds between Co and Sb atoms, we develop MgAgSb/Co thermoelectric junctions with a low interfacial resistivity (2.5 µΩ cm2), high bonding strength (60.6 MPa) and high thermal stability at 573 K. This thermally stable and ohmic contact interface enables MgAgSb-based thermoelectric modules to achieve a conversion efficiency of 10.2% at a temperature difference of 287 K and to exhibit negligible degradation over 1,440 h of thermal cycling. Our findings underscore the critical role of atomic-scale interface engineering in advancing thermoelectric semiconductor devices, enabling more efficient and durable thermoelectric modules.

Discovery of a p-Type Thermoelectric Material in the [Bi2]m[Bi2Q3]n Family through the Regulation of Carrier Concentration

In recent years, many potential n-type near-room-temperature thermoelectric materials belonging to the [Bi2]m[Bi2Q3]n family have been discovered, whereas new p-type thermoelectric materials are relatively rare. In this study, Sb is doped based on n-type Bi0.6Sb0.4Te by adjusting the carrier concentration and then transforms the materials into p-type thermoelectric materials. A novel p-type near-room-temperature thermoelectric material, Bi0.45Sb0.55Te, is discovered in this family. With an increase in doping concentration of Sb, leads to a significant decrease in the bipolar diffusion thermal conductivity. Moreover, when the doping concentration is >50%, the lattice thermal conductivity increases with Sb doping, which is mainly due to the transformation of the host and guest atoms. Furthermore, based on the excessive Bi and Se atoms doping of Bi0.45Sb0.55Te, the ZT value at room temperature can reach approximately 0.44, making Bi0.47Sb0.55TeSe0.05 become a potential room-temperature p-type thermoelectric material.

Chemical modulation and defect engineering in high-performance GeTe-based thermoelectrics

Thermoelectric technology plays an important role in developing sustainable clean energy and reducing carbon emissions, offering new opportunities to alleviate current energy and environmental crises. Nowadays, GeTe has emerged as a highly promising thermoelectric candidate for mid-temperature applications, due to its remarkable thermoelectric figure of merit (ZT) of 2.7. This review presents a thorough overview of the advancements in GeTe thermoelectric materials, meticulously detailing the crystal structure, chemical bonding characteristics, band structure, and phonon dynamics to elucidate the underlying mechanisms that contribute to their exceptional performance. Moreover, the phase transition in GeTe introduces unique degrees of freedom that enable multiple pathways for property optimization. In terms of electrical properties, noticeable enhancement can be realized through strategies such as band structure modulation, carrier concentration engineering, and vacancy engineering. For phonon transport properties, by incorporating defect structures with varying dimensions and constructing multi-scale hierarchical architectures, phonons can be effectively scattered across different wavelengths. Additionally, we provide a summary of current research on devices and modules of GeTe. This review encapsulates historical progress while projecting future development trends that will facilitate the practical application of GeTe in alignment with environmentally sustainable objectives.

Multifunctional microwave absorption materials: construction strategies and functional applications

The widespread adoption of wireless communication technology, especially with the introduction of artificial intelligence and the Internet of Things, has greatly improved our quality of life. However, this progress has led to increased electromagnetic (EM) interference and pollution issues. The development of advanced microwave absorbing materials (MAMs) is one of the most feasible solutions to solve these problems, and has therefore received widespread attention. However, MAMs still face many limitations in practical applications and are not yet widely used. This paper presents a comprehensive review of the current status and future prospects of MAMs, and identifies the various challenges from practical application scenarios. Furthermore, strategies and principles for the construction of multifunctional MAMs are discussed in order to address the possible problems that are faced. This article also presents the potential applications of MAMs in other fields including environmental science, energy conversion, and medicine. Finally, an analysis of the potential outcomes and future challenges of multifunctional MAMs are presented.

Defect Engineering Advances Thermoelectric Materials

Defect engineering is an effective method for tuning the performance of thermoelectric materials and shows significant promise in advancing thermoelectric performance. Given the rapid progress in this research field, this Review summarizes recent advances in the application of defect engineering in thermoelectric materials, offering insights into how defect engineering can enhance thermoelectric performance. By manipulating the micro/nanostructure and chemical composition to introduce defects at various scales, the physical impacts of diverse types of defects on band structure, carrier and phonon transport behaviors, and the improvement of mechanical stability are comprehensively discussed. These findings provide more reliable and efficient solutions for practical applications of thermoelectric materials. Additionally, the development of relevant defect characterization techniques and theoretical models are explored to help identify the optimal types and densities of defects for a given thermoelectric material. Finally, the challenges faced in the conversion efficiency and stability of thermoelectric materials are highlighted and a look ahead to the prospects of defect engineering strategies in this field is presented.

Bi2Te3/Carbon Nanotube Hybrid Nanomaterials as Catalysts for Thermoelectric Hydrogen Peroxide Generation

Harnessing waste heat from environmental or industrial sources presents a promising approach to eco-friendly and sustainable chemical synthesis. In this study, we introduce a thermoelectrocatalytic (TECatal) system capable of utilizing even small amounts of heat for hydrogen peroxide (H2O2) production. We developed a nanohybrid structure, combining carbon nanotubes (CNTs) and Bi2Te3 nanoflakes (Bi2Te3/CNTs), through a one-pot synthesis method. Bi2Te3, as a thermoelectric (TE) material, generates charge carriers under a temperature gradient via the Seebeck effect, enabling them to participate in surface redox reactions. However, the rapid recombination of these charge carriers greatly limits the TECatal activity. In the Bi2Te3/CNTs nanohybrid system, the introduction of CNTs substantially enhances the efficiency of H2O2 production, as the strong bonding between CNTs and Bi2Te3, along with the excellent conductivity of CNTs, facilitates charge carrier separation and transport, as confirmed by TE electrochemical tests. This study underscores the significant potential of thermoelectric nanomaterials for converting waste heat into green chemical synthesis.

Boosting the Thermoelectric Properties of Ge0.94Sb0.06Te via Trojan Doping for High Output Power

GeTe stands as a promising lead-free medium-temperature thermoelectric material that has garnered considerable attention in recent years. Suppressing carrier concentration by aliovalent doping in GeTe-based thermoelectrics is the most common optimization strategy due to the intrinsically high Ge vacancy concentration. However, it inevitably results in a significant deterioration of carrier mobility, which limits further improvement of the zT value. Thus, an effective Trojan doping strategy via CuScTe2 alloying is utilized to optimize carrier concentration without intensifying charge carrier scattering by increasing the solubility of Sc in the GeTe system. Because of the high doping efficiency of the Trojan doping strategy, optimized hole concentration and high mobility are obtained. Furthermore, CuScTe2 alloying leads to band convergence in GeTe, increasing the effective mass m* in (Ge0.84Sb0.06Te0.9)(CuScTe2)0.05 and thus significantly improving the Seebeck coefficient throughout the measured temperature range. Meanwhile, the achievement of the ultralow lattice thermal conductivity (κL ∼ 0.34 W m-1 K-1) at 623 K is attributed to dense point defects with mass/strain-field fluctuations. Ultimately, the (Ge0.84Sb0.06Te0.9)(CuScTe2)0.05 sample exhibits a desirable thermoelectric performance of zTmax ∼ 1.81 at 623 K and zTave ∼ 1.01 between 300 and 723 K. This study showcases an effective doping strategy for enhancing the thermoelectric properties of GeTe-based materials by decoupling phonon and carrier scattering.

Doping strategy in metavalently bonded materials for advancing thermoelectric performance

Metavalent bonding is a unique bonding mechanism responsible for exceptional properties of materials used in thermoelectric, phase-change, and optoelectronic devices. For thermoelectrics, the desired performance of metavalently bonded materials can be tuned by doping foreign atoms. Incorporating dopants to form solid solutions or second phases is a crucial route to tailor the charge and phonon transport. Yet, it is difficult to predict if dopants will form a secondary phase or a solid solution, which hinders the tailoring of microstructures and material properties. Here, we propose that the solid solution is more easily formed between metavalently bonded solids, while precipitates prefer to exist in systems mixed by metavalently bonded and other bonding mechanisms. We demonstrate this in a metavalently bonded GeTe compound alloyed with different sulfides. We find that S can dissolve in the GeTe matrix when alloyed with metavalently bonded PbS. In contrast, S-rich second phases are omnipresent via alloying with covalently bonded GeS and SnS. Benefiting from the reduced phonon propagation and the optimized electrical transport properties upon doping PbS in GeTe, a high figure-of-merit ZT of 2.2 at 773 K in (Ge0.84Sb0.06Te0.9)(PbSe)0.05(PbS)0.05 is realized. This strategy can be applied to other metavalently bonded materials to design properties beyond thermoelectrics.

Lattice Softening and Band Convergence in GeTe-Based Alloys for High Thermoelectric Performance

GeTe-based alloys have been studied as promising TE materials in the midtemperature range as a lead-free alternate to PbTe due to their nontoxicity. Our previous study on GeTe1-xIx revealed that I-doping increases lattice anharmonicity and decreases the structural phase transition temperature, consequently enhancing the thermoelectric performance. Our current work elucidates the synergistic interplay between band convergence and lattice softening, resulting in an enhanced thermoelectric performance for Ge1-ySbyTe0.9I0.1 (y = 0.10, 0.12, 0.14, and 0.16). Sb doping in GeTe0.9I0.1 serves a double role: first, it leads to lattice softening, thereby reducing lattice thermal conductivity; second, it promotes a band convergence, thus a higher valley degeneracy. The presence of lattice softening is corroborated by an increase in the internal strain ratio observed in X-ray diffraction patterns. Doping also introduces phonon scattering centers, further diminishing lattice thermal conductivity. Additionally, variations in the electronic band structure are indicated by an increase in density of state effective mass and a decrease in carrier mobility with Sb concentration. Besides, Sb doping optimizes the carrier concentration efficiently. Through a two-band modeling and electronic band structure calculations, the valence band convergence due to Sb doping can be confirmed. Specifically, the energy difference between valence bands progressively narrows upon Sb doping in Ge1-ySbyTe0.9I0.1 (y = 0, 0.02, 0.05, 0.10, 0.12, 0.14, and 0.16). As a culmination of these effects, we have achieved a significant enhancement in zT for Ge1-ySbyTe0.9I0.1 (y = 0.10, 0.12, 0.14, and 0.16) across the entire range of measured temperatures. Notably, the sample with y = 0.12 exhibits the highest zT value of 1.70 at 723 K.

High-performance Mg3Sb2-based thermoelectrics with reduced structural disorder and microstructure evolution

Mg3Sb2-based thermoelectrics show great promise for next-generation thermoelectric power generators and coolers owing to their excellent figure of merit (zT) and earth-abundant composition elements. However, the complexity of the defect microstructure hinders the advancement of high performance. Here, the defect microstructure is modified via In doping and prolonged sintering time to realize the reduced structural disorder and microstructural evolution, synergistically optimizing electron and phonon transport via a delocalization effect. As a result, an excellent carrier mobility of ~174 cm2 V-1 s-1 and an ultralowκ l a t of ~0.42 W m-1 K-1 are realized in this system, leading to an ultrahigh zT of ~2.0 at 723 K. The corresponding single-leg module demonstrates a high conversion efficiency of ~12.6% with a 425 K temperature difference, and the two-pair module of Mg3Sb2/MgAgSb displays ~7.1% conversion efficiency with a 276 K temperature difference. This work paves a pathway to improve the thermoelectric performance of Mg3Sb2-based materials, and represents a significant step forward for the practical application of Mg3Sb2-based devices.

Reducing Domain Density Enhances Conversion Efficiency in GeTe

Incorporating dilute doping and controlled synthesis provides a means to modulate the microstructure, defect density, and transport properties. Transmission electron microscopy (TEM) and geometric phase analysis (GPA) have revealed that hot-pressing can increase defect density, which redistributes strain and helps prevent unwanted Ge precipitates formation. An alloy of GeTe with a minute amount of indium added has shown remarkable TE properties compared to its undoped counterpart. Specifically, it achieves a maximum figure-of-merit zT of 1.3 at 683 K and an exceptional TE conversion efficiency of 2.83% at a hot-side temperature of 723 K. Significant zT and conversion efficiency improvements are mainly due to domain density engineering facilitated by an effective hot-pressing technique applied to lightly doped GeTe. The In-GeTe alloy exhibits superior TE properties and demonstrates notable stability under significant thermal gradients, highlighting its promise for use in mid-temperature TE energy generation systems.

Realizing a Superior Conversion Efficiency of ≈11.3% in the Group IV-VI Thermoelectric Module

GeTe-based materials exhibit superior thermoelectric performance, while the development of power generation devices has mainly been limited by the challenge of designing the interface due to the phase transition in GeTe. In this work, via utilizing the low-temperature nano-Ag sintering technique and screening suitable Ti-Al alloys, a reliable interface with excellent connection performance has been realized. The Ti-Al intermetallic compounds effectively inhibit the diffusion process at Ti-34Al/Ge0.9Sb0.1Te interface. Thus, the thickness of the interfacial reaction layer only increases by ≈2.08 µm, and the interfacial electrical contact resistivity remains as low as ≈15.2 µΩ cm2 even after 30 days of isothermal aging at 773 K. A high conversion efficiency of ≈11.3% has been achieved in the GeTe/PbTe module at a hot-side temperature of 773 K and a cold-side temperature of 300 K. More importantly, the module's performance and the reliability of the interface remain consistently stable throughout 50 thermal cycles and long-term aging. This work promotes the application of high-performance GeTe materials for thermoelectric power generation.

Unraveling electronic origins for boosting thermoelectric performance of p-type (Bi,Sb)2Te3

P-type Bi2-xSbxTe3 compounds are crucial for thermoelectric applications at room temperature, with Bi0.5Sb1.5Te3 demonstrating superior performance, attributed to its maximum density-of-states effective mass (m*). However, the underlying electronic origin remains obscure, impeding further performance optimization. Herein, we synthesized high-quality Bi2-xSbxTe3 (00 l) films and performed comprehensive angle-resolved photoemission spectroscopy (ARPES) measurements and band structure calculations to shed light on the electronic structures. ARPES results directly evidenced that the band convergence along the [Formula: see text]-[Formula: see text] direction contributes to the maximum m* of Bi0.5Sb1.5Te3. Moreover, strategic manipulation of intrinsic defects optimized the hole density of Bi0.5Sb1.5Te3, allowing the extra valence band along [Formula: see text]-[Formula: see text] to contribute to the electrical transport. The synergy of the above two aspects documented the electronic origins of the Bi0.5Sb1.5Te3's superior performance that resulted in an extraordinary power factor of ~5.5 milliwatts per meter per square kelvin. The study offers valuable guidance for further performance optimization of p-type Bi2-xSbxTe3.

Metavalently bonded tellurides: the essence of improved thermoelectric performance in elemental Te

Elemental Te is important for semiconductor applications including thermoelectric energy conversion. Introducing dopants such as As, Sb, and Bi has been proven critical for improving its thermoelectric performance. However, the remarkably low solubility of these elements in Te raises questions about the mechanism with which these dopants can improve the thermoelectric properties. Indeed, these dopants overwhelmingly form precipitates rather than dissolve in the Te lattice. To distinguish the role of doping and precipitation on the properties, we have developed a correlative method to locally determine the structure-property relationship for an individual matrix or precipitate. We reveal that the conspicuous enhancement of electrical conductivity and power factor of bulk Te stems from the dopant-induced metavalently bonded telluride precipitates. These precipitates form electrically beneficial interfaces with the Te matrix. A quantum-mechanical-derived map uncovers more candidates for advancing Te thermoelectrics. This unconventional doping scenario adds another recipe to the design options for thermoelectrics and opens interesting pathways for microstructure design.

Simultaneously Enhanced Thermoelectric and Mechanical Performance in SnSe-Based Nanocomposites Produced via Sintering SnSe and KCu7S4 Nanomaterials

Both thermoelectric and mechanical properties are important to the practical applications of thermoelectric materials. Herein, we develop a strategy for alloying KCu7S4 to improve the dimensionless figure of merit (zT), compressive strength, and Vickers hardness of polycrystalline SnSe. Through chemical synthesis and particle mixing in solutions, powders with SnSe nanoparticles and KCu7S4 nanowires are produced, and the subsequent spark plasma sintering triggers the reaction between the two chalcogenides, resulting in the formation of Cu2SnSe3 nanoparticles and substitution of Cu and S in the SnSe matrix. The composition tuning and secondary phase formation effectively enhance the power factor and diminish the lattice thermal conductivity, leading to a maximum zT of 1.13 at 823 K for the optimal sample, which is improved by 135% over that of SnSe. Simultaneously, the compressive strength and hardness are also enhanced, as exemplified by a high compressive strength of 135 MPa that is enhanced by ∼81% compared to that of SnSe. The current study demonstrates effective composite and composition design toward enhanced thermoelectric and mechanical performance in polycrystalline SnSe.