Thermoelectric technology enables the harvest of waste heat and its direct conversion into electricity. The conversion efficiency is determined by the materials figure of merit
Here we show a maximum
...of ~2.8 ± 0.5 at 773 kelvin in n-type tin selenide (SnSe) crystals out of plane. The thermal conductivity in layered SnSe crystals is the lowest in the out-of-plane direction two-dimensional (2D) phonon transport. We doped SnSe with bromine to make n-type SnSe crystals with the overlapping interlayer charge density (3D charge transport). A continuous phase transition increases the symmetry and diverges two converged conduction bands. These two factors improve carrier mobility, while preserving a large Seebeck coefficient. Our findings can be applied in 2D layered materials and provide a new strategy to enhance out-of-plane electrical transport properties without degrading thermal properties.
Microstructure engineering is an effective strategy to reduce lattice thermal conductivity (κl) and enhance the thermoelectric figure of merit (zT). Through a new process based on melt‐centrifugation ...to squeeze out excess eutectic liquid, microstructure modulation is realized to manipulate the formation of dislocations and clean grain boundaries, resulting in a porous network with a platelet structure. In this way, phonon transport is strongly disrupted by a combination of porosity, pore surfaces/junctions, grain boundaries, and lattice dislocations. These collectively result in a ≈60% reduction of κl compared to zone melted ingot, while the charge carriers remain relatively mobile across the liquid‐fused grains. This porous material displays a zT value of 1.2, which is higher than fully dense conventional zone melted ingots and hot pressed (Bi,Sb)2Te3 alloys. A segmented leg of melt‐centrifuged Bi0.5Sb1.5Te3 and Bi0.3Sb1.7Te3 could produce a high device ZT exceeding 1.0 over the whole temperature range of 323–523 K and an efficiency up to 9%. The present work demonstrates a method for synthesizing high‐efficiency porous thermoelectric materials through an unconventional melt‐centrifugation technique.
The melt‐centrifugation technique is demonstrated to be able to decrease the thermal conductivity while preserving the good electrical properties. By introducing a unique porous structure with microscale dislocation, ≈60% reduction in lattice thermal conductivity compared to conventional zone melted ingots is achieved. Such a method paves a new way for top‐down introduction of large porosity and dense dislocations in bulk materials.
Recent findings about ultrahigh thermoelectric performance in SnSe single crystals have stimulated related research on this simple binary compound, which is focused mostly on its polycrystalline ...counterparts, and particularly on electrical property enhancement by effective doping. This work systematically investigated the thermoelectric properties of polycrystalline SnSe doped with three alkali metals (Li, Na, and K). It is found that Na has the best doping efficiency, leading to an increase in hole concentration from 3.2 × 1017 to 4.4 × 1019 cm–3 at room temperature, accompanied by a drop in Seebeck coefficient from 480 to 142 μV/K. An equivalent single parabolic band model was found adequate to capture the variation tendency of Seebeck coefficient with doping levels within a wide range. A mixed scattering of carriers by acoustic phonons and grain boundaries is suitable for numerically understanding the temperature-dependence of carrier mobility. A maximum ZT of ∼0.8 was achieved in 1% Na- or K-doped SnSe at 800 K. Possible strategies to improve the mobility and ZT of polycrystals were also proposed.
Display omitted
Piezoelectric materials are an important functional material in the modern world because they are capable of converting electrical energy into mechanical energy and vice versa. ...Lead-free potassium sodium niobate (KNN)-based piezoelectric materials have been intensively researched in the past decade for only one purpose: to replace the less environmentally friendly lead-based piezoelectric materials in commercial products. In this review, the historical research evolution of KNN-based piezoelectric ceramics is highlighted. Meanwhile, to evaluate the technology transfer status, we emphasize on the analysis of the patents applied within the past five years, as well as certain practical applications of KNN-based materials. This paper concludes with the prediction of remaining challenges and opportunities for adopting the lead-free KNN-based piezoelectric ceramics in practical applications.
P-type SnS compound and SnS
Se
solid solutions were prepared by mechanical alloying followed by spark plasma sintering (SPS) and their thermoelectric properties were then studied in different ...compositions (x = 0.0, 0.2, 0.5, 0.8) along the directions parallel (//) and perpendicular (⊥) to the SPS-pressurizing direction in the temperature range 323-823 Κ. SnS compound and SnS
Se
solid solutions exhibited anisotropic thermoelectric performance and showed higher power factor and thermal conductivity along the direction ⊥ than the // one. The thermal conductivity decreased with increasing contents of Se and fell to 0.36 W m
K
at 823 K for the composition SnS
Se
. With increasing selenium content (x) the formation of solid solutions substantially improved the electrical conductivity due to the increased carrier concentration. Hence, the optimized power factor and reduced thermal conductivity resulted in a maximum ZT value of 0.64 at 823 K for SnS
Se
along the parallel direction.
Bi2Te3 thermoelectric materials are utilized for refrigeration for decades, while their application of energy harvesting requires stable thermoelectric and mechanical performances at elevated ...temperatures. This work reveals that a steady zT of ≈0.85 at 200 to 300 °C can be achieved by doping small amounts of copper iodide (CuI) in Bi2Te2.2Se0.8–silicon carbide (SiC) composites, where SiC nanodispersion enhances the flexural strength. It is found that CuI plays two important roles with atomic Cu/I dopants and CuI precipitates. The Cu/I dopants show a self‐tuning behavior due to increasing solubility with increasing temperatures. The increased doping concentration increases electrical conductivity at high temperatures and effectively suppresses the intrinsic excitation. In addition, a large reduction of lattice thermal conductivity is achieved due to the “in situ” CuI nanoprecipitates acting as phonon‐scattering centers. Over 60% reduction of bipolar thermal conductivity is achieved, raising the maximum useful temperature of Bi2Te3 for substantially higher efficiency. For module applications, the reported materials are suitable for segmentation with a conventional ingot. This leads to high device ZT values of ≈0.9–1.0 and high efficiency up to 9.2% from 300 to 573 K, which can be of great significance for power generation from waste heat.
High device ZT and efficiency can be achieved by segmenting a Bi2Te2.79Se0.21 ingot and a Cu/I‐doped Bi2Te2.2Se0.8 sample. By extending the use of Bi2Te3 to higher temperatures, the overall efficiency is increased to 9.2%, which rivals that of mid temperature materials (hot side temperature ≈675–900 K), making Bi2Te3 competitive for waste‐heat power generation applications.
Developing high-efficiency materials with earth-abundant and low-toxicity elements has become a popular trend in the field of thermoelectrics. Among these compounds, oxides and sulfides, the lighter, ...cheaper and green analogies of tellurides, have been extensively investigated and summarized as well defined classes. Nonetheless, the vast family of selenides with better electrical performance, lower thermal conductivity and higher thermoelectric efficiency have not been specially discussed. Here in this review, we present recent advances in binary and multinary selenide thermoelectric materials, covering traditional PbSe, liquid-like Cu2Se, layered SnSe, diamond-like and disordered multinary compounds. The features of selenides are discussed based on both environmental concerns and from the perspective of chemical bonding, transport properties and performance. Emphasis is put on the “composition-structure-processing-performance” relationship, and some interesting issues are addressed. Finally, challenges for thermoelectric selenides are discussed, and possible optimization strategies are also suggested. Keywords: Thermoelectric materials, Selenides, Transport properties
Nanoporous architecture has long been predicted theoretically for its proficiency in suppressing thermal conduction, but less concerned as a practical approach for better thermoelectric materials ...hitherto probably due to its technical challenges. This article demonstrates a study on nanoporous PbSe–SiO2 composites fabricated by a facile method of mechanical alloying assisted by subsequent wet‐milling and then spark plasma sintering. Owing to the formation of random nanopores and additional interface scattering, the lattice thermal conductivity is limited to a value as low as 0.56 W m−1 K−1 at above 600 K, almost the same low level achieved by introducing nanoscale precipitates. Besides, the room‐temperature electrical transport is found to be dominated by the grain‐boundary potential barrier scattering, whose effect fades away with increasing temperatures. Consequently, a maximum ZT of 1.15 at 823 K is achieved in the PbSe + 0.7 vol% SiO2 composition with >20% increase in average ZT, indicating the great potential of nanoporous structuring toward high thermoelectric conversion efficiency.
Nanoporous thermoelectric composites are fabricated by a facile milling method, where nanosized SiO2 particles help to create randomly distributed nanopores throughout PbSe matrix. The existence of nanoporous structure significantly lowers the thermal conductivity with a low plateau above 600 K, eventually benefiting the thermoelectric efficiency of PbSe at moderate temperatures.
AgBiSe2 and AgSbSe2, two typical examples of Te-free I–V–VI2 chalcogenides, are drawing much attention due to their promising thermoelectric performance. Both compounds were synthesized via melting ...and consolidated by spark plasma sintering. The role of annealing on the transport properties of polymorphous AgBiSe2 and monophase AgSbSe2 was studied. Annealing has a greater impact on AgBiSe2 than AgSbSe2, which is ascribed to the temperature dependent phase transition of AgBiSe2. Unannealed AgBiSe2 shows p–n switching, but annealed AgBiSe2 exhibits n-type semiconducting behavior over the whole measurement temperature range. By performing high-temperature Hall measurements, we attribute this intriguing variation to the change in the amount of Ag vacancies and mid-temperature rhombohedral phase after annealing. Both AgBiSe2 and AgSbSe2 exhibit low thermal conductivity values, which are ∼0.40–0.50 W m−1 K−1 for AgSbSe2 and ∼0.45–0.70 W m−1 K−1 for AgBiSe2, respectively. The maximum ZT value of AgBiSe2 is enhanced from 0.18 to 0.21 after annealing. Pristine AgSbSe2 presents a ZT value as high as 0.60 at 623 K, although slight deterioration emerges after annealing.
The Altay Orogenic Belt in Xinjiang, China, is characterized by numerous pegmatite veins, among which Kaluan pegmatite potentially hosts an ultra-large lithium spodumene deposit. Since the discovery ...of lithium deposits in this region, the formation of pegmatites has been a focal point in mineral deposit studies. Previous research has primarily focused on the geological and geochemical aspects, lacking indirect geophysical evidence regarding the genetic link between the pegmatite veins and the deep-seated granitic basement. This paper utilizes four audio-magnetotelluric (AMT) profile datasets to inverse the electrical structure characteristics of the area. To obtain reliable AMT inversion results, following preprocessing of the raw data, the Bahr decomposition method was employed to estimate the two-dimensional (2D) deviation for all measurement points. In addition, the Groom-Bailey (GB) multisite multifrequency decomposition method was used to estimate the azimuth angle of the electrical axis in the study area. Data processing results indicate that the shallow subsurface in this area exhibits favorable 2D characteristics, making it suitable for 2D inversion studies. Lastly, impedance tensor data were rotated to align with the direction of the electrical axis, and inversion was performed using the transverse magnetic polarization mode data. In the conclusion of this paper, we have integrated the results of resistivity measurements from rock specimens, magnetic anomaly, geological cross-sections, and existing geochemical research findings to comprehensively explore the geological conditions of pegmatite formation in the study area. The research findings of this study indicate that the pegmatite veins of the Kaluan lithium deposit typically develop above the deep-seated granitic basement and are controlled by both surface and subsurface fault structures. Meanwhile, isotopic studies in geochemistry reveal a strong affinity between the granitic rocks and the pegmatites in terms of provenance. Based on this comprehensive analysis, it can be inferred that a close genetic relationship exists between the Kaluan pegmatite veins and the deep-seated granitic basement, as well as the fault structures.
PDF
