4 research outputs found

    Defect Engineering for High-Performance n‑Type PbSe Thermoelectrics

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    Introducing structural defects such as vacancies, nanoprecipitates, and dislocations is a proven means of reducing lattice thermal conductivity. However, these defects tend to be detrimental to carrier mobility. Consequently, the overall effects for enhancing ZT are often compromised. Indeed, developing strategies allowing for strong phonon scattering and high carrier mobility at the same time is a prime task in thermoelectrics. Here we present a high-performance thermoelectric system of Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)­Se<sub>1–<i>y</i></sub>Te<sub><i>y</i></sub> (□ = vacancy; <i>y</i> = 0–0.4) embedded with unique defect architecture. Given the mean free paths of phonons and electrons, we rationally integrate multiple defects that involve point defects, vacancy-driven dense dislocations, and Te-induced nanoprecipitates with different sizes and mass fluctuations. They collectively scatter thermal phonons in a wide range of frequencies to give lattice thermal conductivity of ∼0.4 W m<sup>–1</sup> K<sup>–1</sup>, which approaches to the amorphous limit. Remarkably, Te alloying increases a density of nanoprecipitates that affect mobility negligibly and impede phonons significantly, and it also decreases a density of dislocations that scatter both electrons and phonons heavily. As <i>y</i> is increased to 0.4, electron mobility is enhanced and lattice thermal conductivity is decreased simultaneously. As a result, Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)­Se<sub>0.6</sub>Te<sub>0.4</sub> exhibits the highest ZT ∼ 1.5 at 823 K, which is attributed to the markedly enhanced power factor and reduced lattice thermal conductivity, in comparison with a ZT ∼ 0.9 for Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)Se that contains heavy dislocations only. These results highlight the potential of defect engineering to modulate electrical and thermal transport properties independently. We also reveal the defect formation mechanisms for dislocations and nanoprecipitates embedded in Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)­Se<sub>0.6</sub>Te<sub>0.4</sub> by atomic resolution spherical aberration-corrected scanning transmission electron microscopy

    High-Power-Density Skutterudite-Based Thermoelectric Modules with Ultralow Contact Resistivity Using Fe–Ni Metallization Layers

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    Most reported thermoelectric modules suffer from considerable power loss due to high electrical and thermal resistivity arising at the interface between thermoelectric legs and metallic contacts. Despite increasing complaints on this critical problem, it has been scarcely tackled. Here we report the metallization layer of Fe–Ni alloy seamlessly securing skutterudite materials and metallic electrodes, allowing for a minimal loss of energy transferred from the former. It is applied to an 8-couple thermoelectric module that consists of n-type (Mm,Sm)<sub><i>y</i></sub>Co<sub>4</sub>Sb<sub>12</sub> (ZT<sub>max</sub> = 0.9) and p-type DD<sub><i>y</i></sub>Fe<sub>3</sub>CoSb<sub>12</sub> (ZT<sub>max</sub> = 0.7) skutterudite materials. It performs as a diffusion barrier suppressing chemical reactions to produce a secondary phase at the interface. Consequent high thermal stability of the module results in the lowest reported electrical contact resistivity of 2.2–2.5 μΩ cm<sup>2</sup> and one of the highest thermoelectric power density of 2.1 W cm<sup>–2</sup> for a temperature difference of 570 K. Employing a scanning transmission electron microscope equipped with an energy-dispersive X-ray spectroscope detector, we confirmed that it is negligible for atomic diffusion across the interface and resulting formation of a detrimental secondary phase to energy transfer and thermal stability of the thermoelectric module

    Extraordinary Off-Stoichiometric Bismuth Telluride for Enhanced n‑Type Thermoelectric Power Factor

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    Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (<i>ZT</i>) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (Bi<sub>2</sub>Te<sub>3</sub>) that violates phase equilibrium, namely, phase-pure n-type K<sub>0.06</sub>Bi<sub>2</sub>Te<sub>3.18</sub>. Incorporated potassium and tellurium in Bi<sub>2</sub>Te<sub>3</sub> far exceed their solubility limit, inducing simultaneous increase in the electrical conductivity and the Seebeck coefficient along with decrease in the thermal conductivity. Consequently, a high power factor of ∼43 μW cm<sup>–1</sup> K<sup>–2</sup> and a high <i>ZT</i> > 1.1 at 323 K are achieved. Our current synthetic method can be used to produce a new family of materials with novel physical and chemical characteristics for various applications

    Enhancing p‑Type Thermoelectric Performances of Polycrystalline SnSe via Tuning Phase Transition Temperature

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    SnSe emerges as a new class of thermoelectric materials since the recent discovery of an ultrahigh thermoelectric figure of merit in its single crystals. Achieving such performance in the polycrystalline counterpart is still challenging and requires fundamental understandings of its electrical and thermal transport properties as well as structural chemistry. Here we demonstrate a new strategy of improving conversion efficiency of bulk polycrystalline SnSe thermoelectrics. We show that PbSe alloying decreases the transition temperature between <i>Pnma</i> and <i>Cmcm</i> phases and thereby can serve as a means of controlling its onset temperature. Along with 1% Na doping, delicate control of the alloying fraction markedly enhances electrical conductivity by earlier initiation of bipolar conduction while reducing lattice thermal conductivity by alloy and point defect scattering simultaneously. As a result, a remarkably high peak <i>ZT</i> of ∼1.2 at 773 K as well as average <i>ZT</i> of ∼0.5 from RT to 773 K is achieved for Na<sub>0.01</sub>(Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>)<sub>0.99</sub>Se. Surprisingly, spherical-aberration corrected scanning transmission electron microscopic studies reveal that Na<sub><i>y</i></sub>Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Se (0 < <i>x</i> ≤ 0.2; <i>y</i> = 0, 0.01) alloys spontaneously form nanoscale particles with a typical size of ∼5–10 nm embedded inside the bulk matrix, rather than solid solutions as previously believed. This unexpected feature results in further reduction in their lattice thermal conductivity
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