Microstructures and Thermoelectric Properties of Melt-Spun Zn x Sb3 Ribbons

Melt-spun Zn _x Sb₃ ribbons were fabricated with weight compositions of x = 3.6, 3.9, and 4.2 through a single-wheel process and were annealed for 2 h at 673 K. The microstructures of the ribbons were investigated using transmission electron microscopy, together with energy-dispersive x-ray analysis. The main structure consisted of β-Zn₄Sb₃ phase, which mainly coexisted with ZnSb phase for x < 4 and with Zn phase for x > 4. The analyzed composition of the β-Zn₄Sb₃ phase deviated from the stoichiometric composition of 4:3 for all the ribbons. Nanosized voids and zinc inclusions were randomly distributed throughout the β-Zn₄Sb₃ phase. The thermoelectric characteristics of the ribbons were revealed by measuring the Seebeck coefficient, electrical conductivity, power factor, dimensionless figure of merit, and thermal conductivity. The power factor and dimensionless figure of merit increase with increasing x and temperature because either the electrical conductivity or Seebeck coefficient increases.     

Thermoelectric Properties of Indium-Added Skutterudites In x Co4Sb12

The high-temperature thermoelectric properties of In _x Co₄Sb₁₂ (0.05 ≤ x ≤ 0.40) skutterudite compounds were investigated in this study. The phase states of the samples were identified by x-ray diffraction analysis and field-emission scanning electron microscopy at room temperature. InSb and CoSb₂ were found as secondary phases in samples with x = 0.10 to 0.40. The filling limit of In into the CoSb₃ cages of In _x Co₄Sb₁₂ was in the range 0.05 < x < 0.10. The electrical resistivity, Seebeck coefficient, and thermal conductivity of the In _x Co₄Sb₁₂ samples were measured from room temperature to 773 K. The Seebeck coefficient of all samples was negative. Reduction of the thermal conductivity by In addition resulted in a high thermoelectric figure of merit (ZT) of 0.67 for In_0.35Co₄Sb₁₂ at 600 K.     

Structural and Thermoelectric Properties of Bi1−x Sb x Nanoalloys Prepared by Mechanical Alloying

Bi_1?x Sb _x nanoparticles were prepared by mechanical alloying and compacted using different techniques. The influence of the composition as well as the pressing conditions on the thermoelectric performance was investigated. A strong dependence of the thermoelectric properties on the composition was found, which deviates from the behavior of single crystals. The results indicate a significant change in the band structure of the material induced by the reduced size. The influence of the pressing conditions on the thermoelectric properties also showed composition dependence. The results show that the compacting method has to be chosen carefully.     

Thermoelectric Properties of In0.2Ce0.1Co4Sb12.3 Ribbons Prepared by the Rapid-Quenching Technique

Semiconductors - The results of investigations of the thermoelectric properties of In0.2Ce0.1Co4Sb12.3 compound prepared by the rapid-quenching technique are presented. In the process of...     

Thermoelectric Properties of Skutterudites Co4−x Ni x Sb11.9−y Te y Se0.1

CoSb₃-based skutterudites with substitution of Ni atoms for Co, and substitution of Te and Se atoms for Sb were successfully prepared by solid-state reaction and spark plasma sintering. According to x-ray diffraction analysis the major phase of all the samples had a CoSb₃-type structure, although back-scattered electron images showed that small amounts of impurity phases were present in all the samples. The temperature-dependent transport properties were characterized over the temperature range 300–800 K for all the samples. It was found that appropriate substitution with Ni, Te, and Se effectively improved the power factor and reduced the thermal conductivity. As a result, Ni, Te, and Se-tri-doped CoSb₃ materials with enhanced thermoelectric figures of merit, ZT, were obtained. The highest ZT was greater than 1.1 at high temperature.     

Fabrication of Zn4Sb3 Bulk Thermoelectric Materials Reinforced with SiC Whiskers

SiC whiskers have been incorporated into Zn₄Sb₃ compound as reinforcements to overcome its extremely brittle nature. The bulk samples were prepared by either hot-extrusion or hot-pressing techniques. The obtained products containing 1 vol.% to 5 vol.% SiC whiskers were confirmed to exhibit sound appearance, high density, and fine-grained microstructure. Mechanical properties such as the hardness and fracture resistance were improved by the addition of SiC whiskers, as a result of dispersion strengthening and microstructural refinement induced by a pinning effect. Furthermore, crack deflection and/or bridging/pullout mechanisms are invoked by the whiskers. Regarding the thermoelectric properties, the Seebeck coefficient and electrical resistivity values comparable to those of the pure compound are retained over the entire range of added whisker amount. However, the thermal conductivity becomes large with increasing amount of SiC whiskers because of the much higher conductivity of SiC relative to the Zn₄Sb₃ matrix. This results in a remarkable degradation of the dimensionless figure of merit in the samples with addition of SiC whiskers. Therefore, the optimum amount of SiC whiskers in the Zn₄Sb₃ matrix should be determined by balancing the mechanical properties and thermoelectric performance.     

Thermoelectric Properties of Sb2Te3-Based Nanocomposites with Graphite

Semiconductors - Antimony-telluride-based nanocomposite samples containing different weight fractions of graphite (Sb2Te3 + x% graphite, where x = 0.0, 0.5, 1.0, and 2.5%) are synthesized and...     

High-Temperature Thermoelectric Properties of Compounds in the System Zn x In y O x+1.5y

Based on results obtained utilizing combinatorial chemistry techniques to screen the thermoelectric power factor of materials in the system Zn _x In _y O _x+1.5y , several multiphase candidates were down-selected and investigated in terms of their thermoelectric response from room temperature to 1050°C. While the screening experiments suggested that peaks in the power factor occur at relatively high indium oxide content, only the thermoelectric properties of zinc-oxide-rich homologous layered phases in the system (In₂O₃)(ZnO) _k have been well documented, since the phases where k < 3 cannot be easily formed. In the present study, indium-oxide-rich materials in the system In₂O₃–(In₂O₃)(ZnO)₃ were fabricated and their figures of merit were determined. The results suggest that the indium-oxide-rich phases have improved figures of merit, especially at elevated temperatures, relative to the best performing k phases by combining the high power factor of In₂O₃ and the low thermal conductivity of (In₂O₃)(ZnO) _k .     

Microwave Synthesis and Characterization of the Series Co1−x Fe x Sb3 High Temperature Thermoelectric Materials

The use of microwave energy for materials processing has a major potential and real advantages over conventional heating such as (1) time and energy savings, (2) rapid heating rates (volumetric heating vs. conduction), (3) considerably reduced processing time and temperature, (4) fine microstructures and hence improved mechanical properties and better product performance, and (5) finally lower environmental impact. In this study, we investigated the use of microwave-assisted synthesis to synthesize a series of Co_1?x Fe _x Sb₃ using this novel approach, which gave high quality materials with little or no impurities in a fraction of the time needed for conventional synthesis. X-ray diffraction analysis was used to examine the structure and the lattice parameters of the samples, while scanning electron microscopy with energy dispersive x-ray spectroscopy was used to study the morphology of the compounds. The samples were sintered by spark plasma sintering, and the highest ZT of 0.33 was obtained for x = 0.2 at 700 K.     

p型方钴矿化合物BayFeCo3Sb12的热电性能研究

用两步固相反应法合成了单相的p型BayFeCo3Sb12化合物,并系统地研究了Ba不同填充分数对方钴矿化合物热电性能的影响:化合物载流子浓度强烈地依赖于填充原子的填充分数,随Ba填充分数y的增加,载流子浓度及电导率降低;塞贝克系数随温度T的上升而增加,比CoSb3的塞贝克系数有一定程度的提高,尤其是在中温部分有大幅度提高,得到的最大塞贝克系数由CoSb3的107μVK-1提高到Ba1.0FeCo3Sb12的235μVK-1晶格热导率随Ba的填充分数y的增加而进一步下降,Ba08FeCo3Sb12甚至降到2.2 Wm1K1;Ba08FeCo3Sb12化合物显示最大热电性能指数,在850K左右其最大无量纲热电性能指数ZT值达0.75.     

Effects of Second Phase Yb5Sb3 on the Thermoelectric Properties of YbAl3

The compound YbAl₃ exhibits a very high power factor but also rather a large thermal conductivity, leading to a low figure of merit. The second phase Yb₅Sb₃ was introduced in the YbAl₃ matrix to reduce its thermal conductivity. The composites (YbAl₃)_1?x (Yb₅Sb₃) _x with x = 0, 0.01, 0.05, 0.10, and 0.20 were synthesized by high frequency induction melting, annealing treatment, and spark plasma sintering. The thermoelectric properties of the composites were evaluated. The composites are of n-type conduction. The pure YbAl₃ obtained in this work shows a high power factor of 11,500 μW m^?1 K^?2 but also a high thermal conductivity of 19.6 W m^?1 K^?1. However, the existence of Yb₅Sb₃ compound in the YbAl₃ matrix enhances the electrical resistivity and the absolute Seebeck coefficient of the composite, but significantly reduces its thermal conductivity in the temperature range considered, thereby enhancing the figure of merit. The highest ZT value of 0.23 may be obtained in the sample (YbAl₃)_0.95(Yb₅Sb₃)_0.05 at room temperature, which is apparently higher than that of pure YbAl₃.     

Thermoelectric properties of Ce x Nd y Co4Sb12 skutterudites

Experimental results of studying the thermoelectric properties of Co₄Sb₁₂, Ce_0.1Nd_0.5Co₄Sb₁₂, and Ce_0.5Nd_0.1Co₄Sb₁₂ prepared by induction melting are presented. The thermoelectric figure of merit ZT of the studied Co₄Sb₁₂ is approximately two times higher than ZT of unfilled skutterudites prepared by the conventional solid-phase synthesis method. The figure of merit of Ce_0.1Nd_0.5Co₄Sb₁₂ and Ce_0.5Nd_0.1Co₄Sb₁₂ appears lower than ZT of Co₄Sb₁₂ due to the presence of an impurity phase of metal antimony in the first two samples. It is assumed that the thermoelectric properties of filled skutterudites can be significantly improved by optimizing the induction melting method.

     

Electrodeposition of Sb x Te y Thermoelectric Films from Dimethyl Sulfoxide Solution

The electrochemical behaviors of nonaqueous dimethyl sulfoxide solutions containing Te^IV and Sb^III were investigated using cyclic voltammetry. On this basis, Sb _x Te _y thermoelectric films were prepared by the potentiodynamic electrodeposition technique from nonaqueous dimethyl sulfoxide solution, and the composition, morphology, and thermoelectric properties of the films were analyzed. Sb _x Te _y thermoelectric films prepared under different potential ranges all possessed smooth morphology. After annealing treatment at 200°C under N₂ protection for 4?h, all the deposited films showed p-type semiconductor properties. Sb_1.87Te_3.13 thermoelectric film, which most closely approached the stoichiometry of Sb₂Te₃ and possessed the highest Seebeck coefficient, could be potentiodynamically electrodeposited in the potential range of ?200?mV to ?600?mV.     

Synthesis and Thermoelectric Properties of In and Pr Double-Filled Skutterudites In x Pr y Co4Sb12

Double-filled skutterudites In _x Pr _y Co₄Sb₁₂, which are currently being investigated for potential applications as thermoelectric materials, have been successfully prepared by inductive melting and annealing. Our results showed that In and Pr double filling effectively improves both electrical conductivity and Seebeck coefficient compared with pristine or single-filled CoSb₃, giving rise to a respectable power factor. The largest power factor, 2.33 m Wm^?1 K^?2, was achieved at 609 K for In_0.05Pr_0.05Co₄Sb₁₂; this value is approximately three times that for In _x Co₄Sb₁₂ (x ≤ 0.3) skutterudites. These results imply that In and Pr double filling are better than In single filling for efficient improvement of the thermoelectric properties of CoSb₃ skutterudite.     

Effect of Nanostructuring on the Thermoelectric Properties of Co0.97Pd0.03Sb3

We synthesized n-type CeO₂/Co_0.97Pd_0.03Sb₃ composites with nanometric grain sizes (200 nm to 300 nm) by spark plasma sintering in order to promote phonon scattering at grain boundaries. Powdered samples were initially obtained by ball milling Co_0.97Pd_0.03Sb₃ together with x vol.% (x = 0, 0.5, 1, 2) of CeO₂ nanoparticles. This additive slows down the grain size growth of the skutterudite matrix which occurs during sintering, thereby contributing to phonon scattering. The nanostructured samples display reduced Hall electron concentration compared with that of the reference Co_0.97Pd_0.03Sb₃ because of Fe contamination by the steel balls and vials. However, the electronic transport properties are nearly identical to those of Co_0.98Pd_0.02Sb₃, which allows for comparison with this latter compound. The lattice thermal conductivity is strongly decreased in nano-Co_0.97Pd_0.03Sb₁₂ (?40% at 300 K). This results in an enhanced (+32%) ZT value peaking at 0.65 at 650 K in nano-Co_0.97Pd_0.03Sb₁₂ + 2% CeO₂ when compared with micro-Co_0.98Pd_0.02Sb₃.     

Thermoelectric Properties of SnO<Subscript>2</Subscript> Ceramics Doped with Sb and Zn

Polycrystalline SnO₂-based samples (Sn_0.97−x Sb_0.03Zn _x O₂, x = 0, 0.01, 0.03) were prepared by solid-state reactions. The thermoelectric properties of SnO₂ doped with Sb and Zn were investigated from 300 K to 1100 K. X-ray diffraction (XRD) analysis revealed all XRD peaks of all the samples as identical to the rutile structure, except for the x = 0.03 sample, which had a small amount of Zn₂SbO₄ as a secondary phase. We found that the power factor of the x = 0.03 sample was significantly improved due to the simultaneous increase in the electrical conductivity and the Seebeck coefficient. A power factor value of ∼2 × 10⁻⁴ W m⁻¹ K⁻² was obtained for the x = 0.03 sample at 1060 K, 126% higher than that for the undoped sample.