Enhanced Thermoelectric Performance of p-Type Mg3Sb2 for Reliable and Low-Cost all-Mg3Sb2-Based Thermoelectric Low-Grade Heat Recovery

Bi₂Te₃-based devices have long dominated the commercial market for thermoelectric cooling applications, but their narrow operating temperature range and high cost have limited their possible applications for conversion of low-grade heat into electric power. The recently developed n-type Mg₃Sb₂-based compounds exhibit excellent transport properties across a wide temperature range, have low material costs, and are nontoxic, so it would be possible to substitute the conventional Bi₂Te₃ module with a reliable and low-cost all-Mg₃Sb₂-based thermoelectric device if a good p-type Mg₃Sb₂ material can be obtained to match its n-type counterpart. In this study, by comprehensively regulating the carrier concentration, carrier mobility, and lattice thermal conductivity, the thermoelectric performance of p-type Mg₃Sb₂ is significantly improved through Na and Yb doping in Mg_1.8Zn_1.2Sb₂. Moreover, p- and n-type Mg₃Sb₂ are similar in terms of their coefficients of thermal expansion and their good performance stability, thus allowing the construction of a reliable all-Mg₃Sb₂-based unicouple. The decent conversion efficiency (≈5.5% at the hot-side temperature of 573 K), good performance stability, and low cost of this unicouple effectively promote the practical application of Mg₃Sb₂-based thermoelectric generators for low-grade heat recovery.     

High‐Performance N‐type Mg3Sb2 towards Thermoelectric Application near Room Temperature

Se‐doped Mg_3.2Sb_1.5Bi_0.5‐based thermoelectric materials are revisited in this study. An increased ZT value ≈ 1.4 at about 723 K is obtained in Mg_3.2Sb_1.5Bi_0.49Se_0.01 with optimized carrier concentration ≈ 1.9 × 10¹⁹ cm^?3. Based on this composition, Co and Mn are incorporated for the manipulation of the carrier scattering mechanism, which are beneficial to the dramatically enhanced electrical conductivity and power factor around room temperature range. Combined with the lowered lattice thermal conductivity due to the introduction of effective phonon scattering centers in Se&Mn‐codoped sample, a highest room temperature ZT value ≈ 0.63 and a peak ZT value ≈ 1.70 at 623 K are achieved for Mg_3.15Mn_0.05Sb_1.5Bi_0.49Se_0.01, leading to a high average ZT ≈ 1.33 from 323 to 673 K. In particular, a remarkable average ZT ≈ 1.18 between the temperature of 323 and 523 K is achieved, suggesting the competitive substitution for the commercialized n‐type Bi₂Te₃‐based thermoelectric materials.     

High-Density Frenkel Defects as Origin of N-Type Thermoelectric Performance and Low Thermal Conductivity in Mg3Sb2-Based Materials

Mg₃Sb₂-based intermetallic compounds with exceptionally high thermoelectric performance exhibit unconventional n-type dopability and anomalously low thermal conductivity, attracting much attention to the underlying mechanisms. To date, investigations have been limited to first-principle calculations and thermodynamic analysis of defect formation, and detailed experimental analysis on crystal structure and phonon modes has not been achieved. Here, a synchrotron X-ray diffraction study clarifies that, against a previous view of a simple crystal structure with a small unit cell, Mg₃Sb₂ is inherently a heavily disordered material with Frenkel defects, charge-neutral defect complexes of cation vacancies and interstitials. Ionic charge neutrality preserved in Mg₃Sb₂ is responsible for exotic n-type dopability, which is unachievable for other Zintl phase materials. The thermal conductivity of Mg₃Sb₂ exhibits deviation from the standard T⁻¹ temperature dependency with strongly limited phonon transport due to a strain field. Inelastic X-ray scattering measurement reveals enhanced phonon scattering induced by disorder. The results will draw renewed attention to crystal defects and disorder as means to explore new high-performance thermoelectric materials.     

Rational Manipulation of Epitaxial Strains Enabled Valence Band Convergence and High Thermoelectric Performances in Mg3Sb2 Films

Strain engineering is demonstrated to effectively regulate the functionality of materials, such as thermoelectric, ferroelectric, and photovoltaic properties. As the straightforward approach of strain engineering, epitaxial strain is usually proposed for rationally manipulating the electronic structure and performances of thermoelectric materials, but has rarely been verified experimentally. In this study, tunable and large epitaxial strains are demonstrated, as well as the resulting valence band convergence can be achieved in the Mg₃Sb₂ epi-films with the choice of substrates. The large epitaxial strains up to 8% in Mg₃Sb₂ films represent one of the most striking results in strain engineering. The angle-resolved photoemission spectroscopy measurements and the theoretical calculations reveal the vital role of epitaxial strain in tuning the crystal field splitting and the band structure of Mg₃Sb₂. Benefiting from the appropriate manipulation of the crystal field effect via in-plane compressive strain, the valence band convergence is unambiguously discovered in the strained Mg₃Sb₂ film grown on InP(111) substrate. As a result, a state-of-the-art thermoelectric power factor of 0.94 mWm⁻¹K⁻² is achieved in the strain-engineered Mg₃Sb₂ film, well exceeding that of the strain-relaxed Mg₃Sb₂. The work paves the way for effectively manipulating epitaxial strain and band convergence for Mg₃Sb₂ and other thermoelectric films.     

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

In 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.     

On Intensifying Carrier Impurity Scattering to Enhance Thermoelectric Performance in Cr‐Doped CeyCo4Sb12

The beneficial effect of impurity scattering on thermoelectric properties has long been disregarded even though possible improvements in power factor have been suggested by Ioffe more than a half century ago. Here it is theoretically and experimentally demonstrated that proper intensification of ionized impurity scattering to charge carriers can benefit the thermoelectric figure of merit (ZT) by increasing the Seebeck coefficient and decreasing the electronic thermal conductivity. The optimal strength of ionized impurity scattering for maximum ZT depends on the Fermi level and the density of states effective mass. Cr‐doping in Ce_yCo₄Sb₁₂ progressively increases the strength of ionized impurity scattering, and significantly improves the Seebeck coefficient, resulting in high power factors of 45 μW cm^?1 K^?2 with relatively low electrical conductivity. This effect, combined with the increased Ce‐filling fraction and thus decreased lattice thermal conductivity by charge compensation of Cr‐dopant, gives rise to a maximum ZT of 1.3 at 800 K and a large average ZT of 1.1 between 500 and 850 K, ≈30% and ≈20% enhancements as compared with those of Cr‐free sample, respectively. Furthermore, this study also reveals that carrier scattering parameter can be another fundamental degree of freedom to optimize electrical properties and improve thermal‐to‐electricity conversion efficiencies of thermoelectric materials.     

The Role of Ionized Impurity Scattering on the Thermoelectric Performances of Rock Salt AgPbmSnSe2+m

This study reports on the successful synthesis and on the properties of polycrystalline AgPb_mSnSe_2+m (m = ∞, 100, 50, 25) samples with a rock salt structure. Between ≈160 and ≈400 K, the dominant scattering process of the carriers in this system changes from acoustic phonon scattering in PbSe to ionized impurity scattering in AgPb_mSnSe_2+m, which synergistically optimizes electrical and thermal transport properties. Thanks to the faint amount of AgSnSe₂, the Seebeck coefficient is enhanced by boosting the scattering factor, the electric conductivity is improved by the increase of the concentration of holes coupled to a limited degradation of their mobility, and the total thermal conductivity is reduced by suppressing bipolar thermal conductivity. Therefore, ZT of AgPb_mSnSe_2+m (m = 50) reaches 1.3 at 889 K. The mechanism suggested in this study opens new paths to improve the thermoelectric performances of other families of materials.     

Bi2Te3热电材料研究现状

Bi2Te3热电材料是半导体材料,室温下具有良好的热电特性,能够实现热能和电能的相互转化,应用前景十分广阔。Bi2Te3热电材料的转换效率低是影响其应用的瓶颈之一,目前世界范围内的研究热点主要集中在如何提高热电材料的能量转换效率上。综述了热电材料的种类、国内外关于Bi2Te3热电薄膜的制备方法和性能研究,对多种典型制备方法进行分析对比,探讨了影响Bi2Te3热电薄膜质量的因素及机制。结合Bi2Te3热电薄膜在温差发电和热电制冷方面的应用,如果微型热电制冷器实现与大功率LED芯片集成封装,那么芯片级低温散热问题有望解决。     

Sb2Te3热电薄膜磁控溅射制备工艺

Sb2Te3基半导体合金是目前性能较好的热电半导体材料.将材料低维化处理可以获得较块状材料更大的热电优值.通过磁控溅射工艺制备低维Sb2Te3薄膜,并通过AFM、XRD和XPS测试方法对薄膜的成分、薄膜表面以及原子偏析进行表征.通过退火工艺去除薄膜应力,观察退火工艺前后薄膜表面形貌的变化以及退火温度对薄膜表面质量的影响.试验结果表明通过磁控溅射工艺所制备出的Sb2Te3薄膜为非晶态,随着溅射功率增大,薄膜的表面粗糙度增大.退火可使薄膜变为晶态,但是表面粗糙度增大.较大或较小溅射功率下所制备的薄膜其合金成分与合金靶材有较大偏差.     

High-Efficiency Thermoelectric Module Based on High-Performance Bi0.42Sb1.58Te3 Materials

Bismuth-telluride-based alloy is the sole thermoelectric candidate for commercial thermoelectric application in low-grade waste heat harvest near room temperature, but the sharp drop of thermoelectric properties at higher temperature and weak mechanical strength in zone-melted material are the main obstacles to its wide development for power generation. Herein, an effective approach is reported to improve the thermoelectric performance of p-type Bi_0.42Sb_1.58Te₃ hot-pressed sample by incorporating Ag₅SbSe₄. A peak ZT of 1.40 at 375 K and a high average ZT of 1.25 between 300 and 500 K are achieved. Such outstanding thermoelectric performance originates from the synergistic effects of improved density-of-states effective mass, reduced bipolar thermal conductivity by the boosted carrier concentration, and suppressed lattice thermal conductivity by the induced phonon scattering centers including substitute point defects, dislocations, stress–strain clusters, and grain boundaries. Comprised of the p-type Bi_0.42Sb_1.58Te₃ + 0.10 wt% Ag₅SbSe₄ and zone-melted n-type Bi₂Te_2.7Se_0.3, the thermoelectric module exhibits a high conversion efficiency of 6.5% at a temperature gradient of 200 K, indicating promising applications for low-grade heat harvest near room temperature.     

Mn1/3Sb2/3对压电陶瓷材料性能的影响

研究了Pb(Mn1/3Sb2/3)y(Zn1/3Nb2/3)0.16(Zr,Ti)0.84-yO3(系压电陶瓷的主要特性，讨论了（Mn1/3Sb2/3)现代量变化对材料性能的影响。通过测试材料的介电损耗tanδ介电常数ε、机电耦合系数kp和机械品质因数Qm，判断出Mn1/3Sb2/3在PMZN系材料中的最佳取代范围。     

Tailoring Interfacial Charge Transfer for Optimizing Thermoelectric Performances of MnTe-Sb2Te3 Superlattice-Like Films

Interfacial charge transfer has a vital role in tailoring the thermoelectric performance of superlattices (SLs), which, however, is rarely clarified by experiments. Herein, based on epitaxially grown p-type (MnTe)_x(Sb₂Te₃)_y superlattice-like films, synergistically optimized thermoelectric parameters of carrier density, carrier mobility, and Seebeck coefficient are achieved by introducing interfacial charge transfer, in which effects of hole injection, modulation doping, and energy filtering are involved. Carrier transport measurements and angle-resolved photoemission spectroscopy (ARPES) characterizations reveal a strong hole injection from the MnTe layer to the Sb₂Te₃ layer in the SLs, originating from the work function difference between MnTe and Sb₂Te₃. By reducing the thickness of MnTe less than one monolayer, all electronic transport parameters are synergistically optimized in the quantum-dots (MnTe)_x(Sb₂Te₃)₁₂ superlattice-like films, leading to much improved thermoelectric power factors (PFs). The (MnTe)_0.1(Sb₂Te₃)₁₂ obtains the highest room-temperature PF of 2.50 mWm⁻¹K⁻², while the (MnTe)_0.25(Sb₂Te₃)₁₂ possesses the highest PF of 2.79 mWm⁻¹K⁻² at 381 K, remarkably superior to the values acquired in binary MnTe and Sb₂Te₃ films. This research provides valuable guidance on understanding and rationally tailoring the interfacial charge transfer of thermoelectric SLs to further enhance thermoelectric performances.     

Mg3+δSbxBi2−x Family: A Promising Substitute for the State‐of‐the‐Art n‐Type Thermoelectric Materials near Room Temperature

The Bi₂Te_3?xSe_x family has constituted n‐type state‐of‐the‐art thermoelectric materials near room temperature (RT) for more than half a century, which dominates the active cooling and novel heat harvesting application near RT. However, the drawbacks of a brittle nature and Te‐content restricts the possibility for exploring potential applications. Here, it is shown that the Mg_3+δSb_xBi_2?x family ((ZT)_avg = 1.05) could be a promising substitute for the Bi₂Te_3?xSe_x family ((ZT)_avg = 0.9–1.0) in the temperature range of 50–250 °C based on the comparable thermoelectric performance through a synergistic effect from the tunable bandgap using the alloy effect and the suppressible Mg‐vacancy formation using an interstitial Mn dopant. The former is to shift the optimal thermoelectric performance to near RT, and the latter is helpful to partially decouple the electrical transport and thermal transport in order to get an optimal RT power factor. The positive temperature dependence of the bandgap suggests this family is also a superior medium‐temperature thermoelectric material for the significantly suppressed bipolar effect. Furthermore, a two times higher mechanical toughness, compared with the Bi₂Te_3?xSe_x family, allows for a promising substitute for state‐of‐the‐art n‐type thermoelectric materials near RT.     

Sodium‐Mediated Epitaxial Growth of 2D Ultrathin Sb2Se3 Flakes for Broadband Photodetection

As an important member of group VA–VIA semiconductors, 2D Sb₂Se₃ has drawn widespread attention thanks to its outstanding optoelectronic properties as compared to the bulk material. However, due to the intrinsic chain‐like crystal structure, the controllable synthesis of ultrathin 2D planar Sb₂Se₃ nanostructures still remains a huge challenge. Herein, for the first time, the crystal structure limitation is overcome and the successful structural evolution of 2D ultrathin Sb₂Se₃ flakes (as thin as 1.3 nm), by introducing a sodium‐mediated chemical vapor deposition (CVD) growth method, is realized. The formation of 2D planar geometry is mainly attributed to the preferential growth of (010) plane with the lowest formation energy. The thickness‐dependent band structure of 2D Sb₂Se₃ flakes shows a wide absorption band from UV to NIR region (300–1000 nm), suggesting its potential application in broadband photodetection. Strikingly, the Sb₂Se₃ flakes–based photodetector demonstrates excellent performance such as broadband response varying from UV to NIR region, high responsivity of 4320 mA W^?1, fast response time (τ_rise ≈ 13.16 ms and τ_decay ≈ 9.61 ms), and strong anisotropic ratio of 2.5@ 532 nm, implying promising potential application in optoelectronics.     

Interplay between Structural and Thermoelectric Properties in Epitaxial Sb2+xTe3 Alloys

In recent years strain engineering is proposed in chalcogenide superlattices (SLs) to shape in particular the switching functionality for phase change memory applications. This is possible in Sb₂Te₃/GeTe heterostructures leveraging on the peculiar behavior of Sb₂Te₃, in between covalently bonded and weakly bonded materials. In the present study, the structural and thermoelectric (TE) properties of epitaxial Sb_2+xTe₃ films are shown, as they represent an intriguing option to expand the horizon of strain engineering in such SLs. Samples with composition between Sb₂Te₃ and Sb₄Te₃ are prepared by molecular beam epitaxy. A combination of X‐ray diffraction and Raman spectroscopy, together with dedicated simulations, allows unveiling the structural characteristics of the alloys. A consistent evaluation of the structural disorder characterizing the material is drawn as well as the presence of both Sb₂ and Sb₄ slabs is detected. A strong link exists among structural and TE properties, the latter having implications also in phase change SLs. A further improvement of the TE performances may be achieved by accurately engineering the intrinsic disorder. The possibility to tune the strain in designed Sb_2+xTe₃/GeTe SLs by controlling at the nanoscale the 2D character of the Sb_2+xTe₃ alloys is envisioned.     

Si-Bi2Te3光热耦合电源器件的结构设计与性能

空间近日等强辐照造成的高温严重影响光伏电池的转化效率,同时造成辐射能量的浪费.以单晶Si光伏电池和Bi2Te3热电电池为基本单元,构建Si-Bi2 Te3光热耦合电源器件模型.采用有限元分析法分析特定辐射条件下Si-Bi2Te3光热耦合电源器件的热分布情况,并结合光伏电池与热电电池的温度特性进一步计算了器件的转化效率.结果显示,Bi2Te3热电池的存在一定程度上降低了Si光伏电池的工作温度,在空间环境下Si-Bi2Te3光热耦合电源器件的转化效率相对于单一的Si光伏电池有2％ ～3％的提高.最后讨论了该器件Si光伏电池和Bi2Te3热电池的功率输出方式.     

Analysis of Nanostructuring in High Figure‐of‐Merit Ag1–xPbmSbTe2+m Thermoelectric Materials

Thermoelectric materials based on quaternary compounds Ag_1?xPb_mSbTe_2+m exhibit high dimensionless figure‐of‐merit values, ranging from 1.5 to 1.7 at 700 K. The primary factor contributing to the high figure of merit is a low lattice thermal conductivity, achieved through nanostructuring during melt solidification. As a consequence of nucleation and growth of a second phase, coherent nanoscale inclusions form throughout the material, which are believed to result in scattering of acoustic phonons while causing only minimal scattering of charge carriers. Here, characterization of the nanosized inclusions in Ag_0.53Pb₁₈Sb_1.2Te₂₀ that shows a strong tendency for crystallographic orientation along the {001} planes, with a high degree of lattice strain at the interface, consistent with a coherent interfacial boundary is reported. The inclusions are enriched in Ag relative to the matrix, and seem to adopt a cubic, 96 atom per unit cell Ag₂Te phase based on the Ti₂Ni type structure. In‐situ high‐temperature synchrotron radiation diffraction studies indicated that the inclusions remain thermally stable to at least 800 K.     

High‐efficiency Sb2S3‐based hybrid solar cell at low light intensity: cell made of synthesized Cu and Se‐doped Sb2S3

Cu‐doped (as p‐doped) and Se‐doped (as n‐doped) Sb₂S₃ were synthesized from undoped Sb₂S₃ using a newly developed technique, simple colloidal synthesis method. X‐ray diffraction measurements detected no peaks related to any of the Cu and Se compounds in Cu and Se‐doped samples. Energy dispersive X‐ray analysis, however, confirmed the presence of Cu and Se ions in the doped samples. Diffuse reflectance spectroscopy revealed the optical band gap energy changes because of doping effect, as reported for both the p‐type and the n‐type material. The valence‐band X‐ray photoelectron spectroscopy data showed a significant shift in the valence band to higher (Se‐doped; +0.53 eV) and a shift to lower (Cu‐doped; −0.41 eV) binding energy, respectively, when compared with the undoped sample. We report here on an inexpensive solar cell designed and made entirely of a synthesized material (indium tin oxide/p‐doped Sb₂S₃ + polyaniline (PANI)/amorphous/undoped Sb₂S₃ + PANI/n‐doped Sb₂S₃ + PANI/PANI/electrolyte (0.5 M KI + 0.05 M I₂)/Al). The cell has a high efficiency of 8% to 9% at a very low light intensity of only 5% sun, which makes it particularly suitable for indoor applications. As found, the cell performance at the intensity of 5% sun is governed by high shunt resistance (R_SH) only, which satisfies standard testing conditions. At higher light intensities (25% sun), however, the cell exhibits lower but not insignificant efficiency (around 2%) governed by both the series (R_S) and the R_SH. Minimal permeability in the UV region (up to 375 nm) and its almost constant value in the visible and the NIR region at low light intensity of 5% sun could be the reasons for higher cell efficiency. Copyright © 2015 John Wiley & Sons, Ltd.     

晶界杂质和缺陷行为与BaTiO_3基陶瓷的PTCR效应

钛酸钡陶瓷中，高温下晶格失氧使晶粒内部氧匮乏。在氧化气氛中烧成，晶界则是富氧环境。缺陷或杂 质在晶界上进一步氧化，产生晶粒中并不存在的缺陷种类。杂质和缺陷在晶界上与晶粒内部有不同的行为。某些在 晶界上被氧化成高价态的缺陷和杂质，在晶粒中不能存在，而在晶界上以亚稳态形式存在。它们在铁电相变点跃迁 回低价稳态，产生电子陷阱，使材料电阻率迅速增大，形成ＰＴＣＲ效应。     

Sb2S3/TiO2纳米管异质结阵列的制备和光电性能

结合水热法和阳极氧化法合成了Sb2S3/TiO2纳米管异质结阵列,采用场发射扫描电子显微镜、X射线衍射谱表征了异质结阵列的形貌和晶体结构.暗态下的电流-电压曲线表明Sb2S3/TiO2纳米管异质结阵列具有整流效应.相比于纯的TiO2纳米管阵列,Sb2S3/TiO2纳米管异质结阵列的光电性能有了显著地提升:在AM1.5标准光强作用下,光电转换效率从0.07％增长到0.40％,表面光电压响应范围从紫外光区拓宽至可见光区.结合表面光电压谱和相位谱,分析了Sb2S3/TiO2纳米管异质结阵列中光生载流子的分离和传输性能.