铁-镍双掺杂方钴矿的合成与热电性能

采用微波加热合成结合放电等离子体烧结制备了铁-镍双掺杂方钴矿Co_(3.8-x)Fe_xNi_(0.2)Sb_(12) (x=0.05, 0.10, 0.15, 0.20)块体材料,并对其物相组成、晶粒尺寸、元素分布、热电性能等进行了系统研究。X射线衍射分析表明,样品X射线衍射峰与单相CoSb_3相符;场发射扫描电镜分析表明,样品晶粒尺寸为1～3μm、平均尺寸为1～2μm,各元素均匀分布;电性能分析表明,Ni/Fe双掺杂对电输运性能有进一步改善,最高功率因子为2.667×10~3μW·(m·K~2)~(-1);热性能分析表明,Fe掺杂对晶格热导率影响较小,晶格热导率与晶粒尺寸有关,主要热输运机制为晶界散射,Co_(3.65)Fe_(0.15)Ni_(0.2)Sb_(12)的最小晶格热导率为2.8 W·(m·K)~(-1)。Co_(3.7)Fe_(0.1)Ni_(0.2)Sb_(12)在773 K获得最大热电优值0.50,显著高于传统方法制备的Ni/Fe单掺杂或者双掺杂样品。     

Microstructure and Thermoelectric Properties of Yb-Filled Skutterudites Prepared by Rapid Solidification

Single-phase nanostructured bulk Yb_0.2Co₄Sb₁₂ skutterudites have been prepared by combining a melt spinning technique with spark plasma sintering. The effects of a pre-annealing process on the microstructure and phase composition of ribbon samples and bulk materials are investigated. After the pre-annealing process, average grain size increases from 200 nm to 300 nm for ribbon samples and from 250 nm to 350 nm for bulk materials, and nearly single-phase skutterudites have formed. Because of the nanostructure, the thermal conductivity of bulk skutterudites notably decreases 25% at 800 K. As␣a result, the ZT values are improved compared with starting material prepared by the traditional method.     

提高热电材料优值的方法研究(英文)

热电材料是一种将热能与电能进行互相转换的功能材料,其转换效率取决于材料的热电优值Z.详细讨论了当前提高热电材料优值的几种途径:向晶格掺入杂质元素改变晶格结构;发展纳米技术制备纳米薄膜、纳米线材或纳米颗粒;制备方钴矿型化合物、功能梯度材料、准晶材料和Half-Heusler合金等新型热电材料.     

Effect of Y-filling on thermoelectric properties of CoSb3

The CoSb3 and Y0.18Co4Sb12 compounds were synthesized by a metallurgical route. Their bulk materials were prepared by the hot-pressed process under vacuum. Thermoelectric properties of the samples were measured by the thermoelectric measurement system and the laser flash diffusivity apparatus. The carrier type conversion of hot-pressed CoSb3 was found at about 530 K, while the conversion was missed for the Y0.18Co4Sb12 sample. Electrical conductivity of the Y0.18Co4Sb12 sample increased due to the increase of carrier concentration, and its thermal conductivity decreased due to the enhancement of phonon scattering. The value of ZT, figure of merit, for the Y0.18Co4Sb12 sample was obviously enhanced due to positive contribution of the electrical conductivity and the thermal conductivity.     

Synthesis of Nanocomposites with Improved Thermoelectric Properties

Bulk thermoelectric materials are of interest for commercial application in both power generation and Peltier refrigeration. Various synthesis approaches have been developed by our group for high performance bulk thermoelectric materials, such as solvo- or hydrothermal synthesis for nanopowders, hot-pressing, and spark plasma sintering for nanostructured bulk materials, and rapid solidification for metal silicides. In this article we report some of our recent results in the development of high ZT thermoelectric materials, including Bi₂Te₃-Sb₂Te₃ nanocomposites and CoSb₃ micro/nanocomposites prepared by a powder blending route, and GeTe-AgSbTe₂ and Mg₂Si-Mg₂Sn nanocomposites prepared by an in situ route. The results show various possibilities for improved microstructures and therefore enhanced properties of bulk thermoelectric materials through optimization of the preparation processing based on simple synthesis routes. A high ZT of approximately 1.5 has been obtained in both Bi₂Te₃-Sb₂Te₃ and GeTe-AgSbTe₂ nanocomposites. Further ZT enhancement of the materials should be possible through the control of the nanopowder morphology during synthesis and the hindering of␣grain growth during sintering, as well as through the optimization of composition and doping.     

Super-fast preparation of Nd-filled p-type skutterudite compounds with enhanced thermoelectric properties

P-type filled skutterudite materials have been gained considerable research interest in recent years due to their promising thermoelectric power generation applications at intermediate temperature. Herein, we systematically investigated the influence of Nd filling on the thermoelectric properties of Nd_xFe₂Co₂Sb₁₂ (x=0.4, 0.5 0.6, 0.7 and 0.8). Nd-filled skutterudites are synthesized using a simple and time-saving induction melt spinning technique followed by spark plasma sintering. The results show that Nd-filling leads to the significant reduction in the lattice thermal conductivity and enhancement of power factor over the entire temperature range. The most marked reduction in the lattice thermal conductivity is achieved with the value of 0.76 W/m K for x=0.7 sample, due to strengthened phonon scattering. Meanwhile, the highest ZT=0.98 is attained at 740 K for Nd_0.7Fe₂Co₂Sb₁₂. The rapid synthesis procedure provides an effective pathway for the fabrication of thermoelectric materials with high performance.     

Synthesis and Thermoelectric Properties of “Nano-Engineered” CoSb<Subscript>3</Subscript> Skutterudite Materials

Because of their good electrical transport properties, skutterudites have been widely studied as potential next-generation thermoelectric (TE) materials. One of the main obstacles to further improving their thermoelectric performance has been reducing their relatively high thermal conductivity. To some extent, this hindrance has been partially resolved by filling the voids found in the skutterudite structure with so-called “rattling” atoms. It has been predicted that reducing the dimensionality in a TE material would have a positive effect in enhancing its thermoelectric properties, for example increasing the thermopower and reducing the thermal conductivity. Introducing nanoparticles into the skutterudite materials could therefore have favorable effects on their electrical properties and should also reduce lattice thermal conductivity by introducing extra scattering centers throughout the sample. Nanoparticles may also be used in conjunction with void filling for further reduction of the thermal conductivity of skutterudites. Cobalt triantimonide (CoSb₃) samples with different amounts of embedded nanoparticles have been grown, and the electrical and thermal transport properties for these composites have been measured from 10 K to 650 K. The synthetic techniques and electrical and thermal transport data are discussed in this paper.     

Unveiling the Correlation between the Crystalline Structure of M‐Filled CoSb3 (M = Y,K, Sr) Skutterudites and Their Thermoelectric Transport Properties

Skutterudite‐type pnictides based on CoSb₃ are promising semiconductor materials for thermoelectric applications. An exhaustive structural characterization by synchrotron X‐ray powder diffraction of different M‐filled CoSb₃ (M = Y, K, Sr, La, Ce, Yb) skutterudites, with a panoply of M atoms with very different chemical nature, allows to better understand the effects of filling from a crystallo‐chemical point of view. These analyses focus on the correlation of chemical and structural features with the enhanced thermoelectric properties displayed by certain families of filled‐CoSb₃ skutterudites. These are mainly determined by Sb positional parameters, yielding Oftedal plots that depend on the filling fraction, ionic state, and atomic radius of the filler. Together with the distortion of [Sb₄] rings and [CoSb₆] octahedra present in the skutterudite structure, these results are linked to the band‐convergence concept and its influence on the thermoelectric transport properties. Here, the structural changes observed in the different chemical compositions are relevant to understand the improved thermoelectric performance of single partially filled n‐type skutterudites.     

n型填充方钴矿热电材料的快速制备研究

如何有效控制方钴矿基热电材料的制备成本成为其商业化应用的瓶颈。本课题组采用一种简单并且可放量的方法来制备n型填充方钴矿热电材料。该法由感应熔融淬、火和放电等离子烧结(SPS)组成, 制备周期(少于30 min)远小于传统制备方法: 电阻炉熔融(超过24 h),退火(1 w)和SPS。该法同传统制备工艺相当, 制备的方钴矿块体材料具有相对均匀的物相成份和组织结构, 以及良好的热电性能, 这得益于将经历感应熔融、淬火冷凝工艺形成的Sb/CoSb/CoSb₂包晶偏析结构破坏, 能同时实现快速反应和致密化。良好的热电性能和较少的生产周期及能耗, 使该法有望发展成为具有潜在应用前景的填充方钴矿热电材料工业化制备工艺。     

Thermal Expansion Studies of Selected High-Temperature Thermoelectric Materials

Radioisotope thermoelectric generators (RTGs) generate electrical power by converting the heat released from the nuclear decay of radioactive isotopes (typically plutonium-238) into electricity using a thermoelectric converter. RTGs have been successfully used to power a number of space missions and have demonstrated their reliability over an extended period of time (tens of years) and are compact, rugged, radiation resistant, scalable, and produce no noise, vibration or torque during operation. System conversion efficiency for state-of-practice RTGs is about 6% and specific power ≤5.1 W/kg. A higher specific power would result in more onboard power for the same RTG mass, or less RTG mass for the same onboard power. The Jet Propulsion Laboratory has been leading, under the advanced thermoelectric converter (ATEC) project, the development of new high-temperature thermoelectric materials and components for integration into advanced, more efficient RTGs. Thermoelectric materials investigated to date include skutterudites, the Yb₁₄MnSb₁₁ compound, and SiGe alloys. The development of long-lived thermoelectric couples based on some of these materials has been initiated and is assisted by a thermomechanical stress analysis to ensure that all stresses under both fabrication and operation conditions will be within yield limits for those materials. Several physical parameters are needed as input to this analysis. Among those parameters, the coefficient of thermal expansion (CTE) is critically important. Thermal expansion coefficient measurements of several thermoelectric materials under consideration for ATEC are described in this paper. The stress response at the interfaces in material stacks subjected to changes in temperature is discussed, drawing on work from the literature and project-specific tools developed here. The degree of CTE mismatch and the associated effect on the formation of stress is highlighted.