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Valley anisotropy is a favorable electronic structure feature that could be utilized for good thermoelectric performance. Here, taking advantage of the single anisotropic Fermi pocket in p-type Mg 3 Sb 2 , a feasible strategy utilizing the valley anisotropy to enhance the thermoelectric power factor is demonstrated by synergistic studies on both single crystals and textured polycrystalline samples. Compared to the heavy-band direction, a higher carrier mobility by a factor of 3 is observed along the light-band direction, while the Seebeck coefficient remains similar. Together with lower lattice thermal conductivity, an increased room-temperature zT by a factor of 3.6 is found. Moreover, the first-principles calculations of 66 isostructural Zintl phase compounds are conducted and 9 of them are screened out displaying a p z -orbital-dominated valence band, similar to Mg 3 Sb 2 . In this work, we experimentally demonstrate that valley anisotropy is an effective strategy for the enhancement of thermoelectric performance in materials with anisotropic Fermi pockets. Valley anisotropy is proposed theoretically to benefit the electrical transport of thermoelectric materials but it lacks experimental demonstration. Here, the authors demonstrate how to utilize the single anisotropic Fermi pocket in p-type Mg 3 Sb 2 to enhance its thermoelectric properties.

Solid-state thermoelectric technology offers a promising solution for converting waste heat to useful electrical power. Both high operating temperature and high figure of merit zT are desirable for high-efficiency thermoelectric power generation. Here we report a high zT of ∼1.5 at 1,200 K for the p -type FeNbSb heavy-band half-Heusler alloys. High content of heavier Hf dopant simultaneously optimizes the electrical power factor and suppresses thermal conductivity. Both the enhanced point-defect and electron–phonon scatterings contribute to a significant reduction in the lattice thermal conductivity. An eight couple prototype thermoelectric module exhibits a high conversion efficiency of 6.2% and a high power density of 2.2 W cm −2 at a temperature difference of 655 K. These findings highlight the optimization strategy for heavy-band thermoelectric materials and demonstrate a realistic prospect of high-temperature thermoelectric modules based on half-Heusler alloys with low cost, excellent mechanical robustness and stability. Thermoelectric materials could be used to convert waste heat into useful electricity, but the ideal substance needs to both optimize the electrical power factor and suppress thermal conductivity. Here, the authors report a high figure of merit of 1.5 at 1,200 K in the p -type half-Heusler alloy FeNbSb.

Applying a temperature gradient in a magnetic material generates a voltage that is perpendicular to both the heat flow and the magnetization. This phenomenon is the anomalous Nernst effect (ANE), which was long thought to be proportional to the value of the magnetization. However, more generally, the ANE has been predicted to originate from a net Berry curvature of all bands near the Fermi level ( E F ). Subsequently, a large anomalous Nernst thermopower ( S yx A ) has recently been observed in topological materials with no net magnetization but a large net Berry curvature [Ω n ( k )] around E F . These experiments clearly fall outside the scope of the conventional magnetization model of the ANE, but a significant question remains. Can the value of the ANE in topological ferromagnets exceed the highest values observed in conventional ferromagnets? Here, we report a remarkably high S yx A -value of ~6.0 µV K −1 in the ferromagnetic topological Heusler compound Co 2 MnGa at room temperature, which is approximately seven times larger than any anomalous Nernst thermopower value ever reported for a conventional ferromagnet. Combined electrical, thermoelectric, and first-principles calculations reveal that this high-value of the ANE arises from a large net Berry curvature near the Fermi level associated with nodal lines and Weyl points. Energy conversion: Heat- recovery magnets identified Thermoelectric devices that convert heat into electricity may benefit from the unusual temperature sensitivity of cobalt–manganese–gallium (Co 2 MnGa) ferromagnets. When one end of a magnetized metal is made hot and the other cold, redistribution of electrons creates an electric voltage perpendicular to the temperature gradient. Satya N. Guin from the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany, and colleagues now report how certain class of material can boost the electrical power produced from “waste heat” source using transverse thermoelectric effect. When the team applied magnetic fields to Co 2 MnGa and characterized its transverse electrical response to temperature gradient, they saw voltage generation several times higher than expected. Computer simulations indicated that the crystal geometry distorted the energy levels available to electron making it easier for electrons to move when thermally excited. We report a high anomalous Nernst thermopower ( S y x A ) -value of ~6.0 µV K −1 at room temperature in the ferromagnetic topological Heusler compound Co 2 MnGa. The measured value is seven-times larger than any anomalous Nernst thermopower value ever reported for a conventional ferromagnet. The high anomalous Nernst effect originates from a large net Berry curvature near the Fermi level associated with nodal lines and Weyl points.

Chemical doping is one of the most important strategies for tuning electrical properties of semiconductors, particularly thermoelectric materials. Generally, the main role of chemical doping lies in optimizing the carrier concentration, but there can potentially be other important effects. Here, we show that chemical doping plays multiple roles for both electron and phonon transport properties in half-Heusler thermoelectric materials. With ZrNiSn-based half-Heusler materials as an example, we use high-quality single and polycrystalline crystals, various probes, including electrical transport measurements, inelastic neutron scattering measurement, and first-principles calculations, to investigate the underlying electron-phonon interaction. We find that chemical doping brings strong screening effects to ionized impurities, grain boundary, and polar optical phonon scattering, but has negligible influence on lattice thermal conductivity. Furthermore, it is possible to establish a carrier scattering phase diagram, which can be used to select reasonable strategies for optimization of the thermoelectric performance. Chemical doping plays an important role in tuning carrier concentration of materials, but its influence on other aspects of electrical properties is less known. Here, the authors find that chemical doping brings strong screening effects to ionized impurities, grain boundary, and polar optical phonon scattering.

Low-cost thermoelectric materials with simultaneous high performance and superior plasticity at room temperature are urgently demanded due to the lack of ever-lasting power supply for flexible electronics. However, the inherent brittleness in conventional thermoelectric semiconductors and the inferior thermoelectric performance in plastic organics/inorganics severely limit such applications. Here, we report low-cost inorganic polycrystalline Mg 3 Sb 0.5 Bi 1.498 Te 0.002 , which demonstrates a remarkable combination of large strain (~ 43%) and high figure of merit zT (~ 0.72) at room temperature, surpassing both brittle Bi 2 (Te,Se) 3 (strain ≤ 5%) and plastic Ag 2 (Te,Se,S) and organics ( zT  ≤ 0.4). By revealing the inherent high plasticity in Mg 3 Sb 2 and Mg 3 Bi 2 , capable of sustaining over 30% compressive strain in polycrystalline form, and the remarkable deformability of single-crystalline Mg 3 Bi 2 under bending, cutting, and twisting, we optimize the Bi contents in Mg 3 Sb 2- x Bi x ( x  = 0 to 1) to simultaneously boost its room-temperature thermoelectric performance and plasticity. The exceptional plasticity of Mg 3 Sb 2- x Bi x is further revealed to be brought by the presence of a dense dislocation network and the persistent Mg-Sb/Bi bonds during slipping. Leveraging its high plasticity and strength, polycrystalline Mg 3 Sb 2- x Bi x can be easily processed into micro-scale dimensions. As a result, we successfully fabricate both in-plane and out-of-plane flexible Mg 3 Sb 2- x Bi x thermoelectric modules, demonstrating promising power density. The inherent remarkable plasticity and high thermoelectric performance of Mg 3 Sb 2- x Bi x hold the potential for significant advancements in flexible electronics and also inspire further exploration of plastic inorganic semiconductors. Authors realize simultaneous high thermoelectric performance and high plasticity in Mg-based semiconductors at room temperature, demonstrating their great potential for use in flexible thermoelectrics.

Aliovalent doping is a way to optimize the electrical properties of semiconductors, but its impact on the phonon structure and propagation is seldom considered properly. Here we show that aliovalent doping can be much more effective in reducing the lattice thermal conductivity of thermoelectric semiconductors than the commonly employed isoelectronic alloying strategy. We demonstrate this in the heavy-band NbFeSb system, finding that a reduction of 65% in the lattice thermal conductivity is achieved through only 10% aliovalent Hf doping, compared with the four times higher isoelectronic Ta alloying. We show that aliovalent doping introduces free charge carriers and enhances screening, leading to the softening and deceleration of optical phonons. Moreover, the heavy dopant can induce the avoided crossing of acoustic and optical phonon branches, decelerating the acoustic phonons. These results highlight the significant role of aliovalent dopants in regulating the phonon structure and suppressing the phonon propagation of semiconductors.Aliovalent doping affects the electrical properties of semiconductors, but its effect on phonons is unclear. Now, strong softening and deceleration of phonons, causing a significant reduction in lattice thermal conductivity, is reported for Hf-doped NbFeSb.

The intrinsic structural disorder dramatically affects the thermal and electronic transport in semiconductors. Although normally considered an ordered compound, the half-Heusler ZrNiSn displays many transport characteristics of a disordered alloy. Similar to the (Zr,Hf)NiSn based solid solutions, the unsubstituted ZrNiSn compound also exhibits charge transport dominated by alloy scattering, as demonstrated in this work. The unexpected charge transport, even in ZrNiSn which is normally considered fully ordered, can be explained by the Ni partially filling interstitial sites in this half-Heusler system. The influence of the disordering and defects in crystal structure on the electron transport process has also been quantitatively analyzed in ZrNiSn 1- x Sb x with carrier concentration n H ranging from 5.0×10 19 to 2.3×10 21  cm −3 by changing Sb dopant content. The optimized carrier concentration n H ≈ 3–4×10 20  cm −2 results in ZT ≈ 0.8 at 875K. This work suggests that M NiSn ( M = Hf, Zr, Ti) and perhaps most other half-Heusler thermoelectric materials should be considered highly disordered especially when trying to understand the electronic and phonon structure and transport features.

Wearable thermoelectric generators (TEGs), which can convert human body heat to electricity, provide a promising solution for self‐powered wearable electronics. However, their power densities still need to be improved aiming at broad practical applications. Here, a stretchable TEG that achieves comfortable wearability and outstanding output performance simultaneously is reported. When worn on the forehead at an ambient temperature of 15 °C, the stretchable TEG exhibits excellent power densities with a maximum value of 13.8 µW cm−2 under the breezeless condition, and even as high as 71.8 µW cm−2 at an air speed of 2 m s−1, being one of the highest values for wearable TEGs. Furthermore, this study demonstrates that this stretchable TEG can effectively power a commercial light‐emitting diode and stably drive an electrocardiogram module in real‐time without the assistance of any additional power supply. These results highlight the great potential of these stretchable TEGs for power generation applications. A stretchable thermoelectric generator (TEG) is fabricated, which exhibits both outstanding output performance and comfortable wearability for human body heat harvesting. The stretchable TEGs are enough for driving an electrocardiogram module in real time without the assistance of an additional power supply.

Hierarchical scattering is suggested as an effective strategy to enhance the figure of merit zT of heavy‐band thermoelectric materials. Heavy‐band FeNbSb half‐Heusler system with intrinsically low carrier mean free path is demonstrated as a paradigm. An enhanced zT of 1.34 is obtained at 1150 K for the Fe1.05Nb0.75Ti0.25Sb compound with intentionally designed hierarchical scattering centers.

The introduction of magnetism into a solid material might significantly modulate its electronic transport behavior, thereby serving as a means to tune the thermoelectric properties that have attracted considerable research attention in recent years. In this review, an introduction to recent studies on the interplay of magnetism and the thermoelectric Seebeck and Nernst effects is given. Concerning the Seebeck effect, the influence of superparamagnetic nanoparticles on the electronic and phonon transport of conventional nonmagnetic thermoelectric materials, as well as the spin‐related thermoelectric transport phenomenon in magnetic materials, are discussed. Then, the Nernst effect‐related transverse thermoelectric transport properties in nonmagnetic and magnetic topological materials are summarized, followed by a short introduction to the Nernst devices. Last, a further outlook on this new research direction is offered.