The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Lidong Chen - One of the best experts on this subject based on the ideXlab platform.
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electrode interface optimization advances conversion efficiency and stability of thermoelectric devices
Nature Communications, 2020Co-Authors: Jing Chu, X. Shi, Ruiheng Liu, Shengqiang Bai, Qihao Zhang, Jian Huang, Jincheng Liao, Xugui Xia, Chao Wang, Lidong ChenAbstract:Although the CoSb3-based skutterudite thermoelectric devices have been highly expected for wide uses such as waste heat recovery and space power supply, the limited long-term service stability majorly determined by the degradation of electrode interface obstructs its applications. Here, we built up an effective criterion for screening barrier layer based on the combination of negative interfacial reaction energy and high activation energy barrier of Sb migration through the formed interfacial reaction layer. Accordingly, we predicted niobium as a promising barrier layer. The experimental results show the skutterudite/Nb joint has the slowest interfacial reaction layer growth rate and smallest interfacial electrical resistivity. The fabricated 8-pair skutterudite module using Nb as barrier layer achieves a recorded conversion efficiency of 10.2% at hot-side temperature of 872 K and shows excellent stability during long-time aging. This simple criterion provides an effective guidance on screening barrier layer with bonding-blocking-conducting synergetic functions for thermoelectric device integration. Long-term service stability of thermoelectric devices is one of the major obstacles for their application. Here, the authors combine interfacial reaction energy and Sb migration activation energy barrier as a criterion to determine the interfacial reliability for skutterudite thermoelectric devices.
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scanning laser melting for rapid and massive fabrication of filled Skutterudites with high thermoelectric performance
Journal of Materials Chemistry, 2018Co-Authors: Fan Chen, Ruiheng Liu, Zheng Yao, Yunfei Xing, Shengqiang Bai, Lidong ChenAbstract:Skutterudite-based thermoelectric materials have great potential for use in waste heat recovery, but the conventional melting–quench–annealing process is not suitable for large-scale fabrication. In this study, we developed a rapid fabrication technique that combines scanning laser melting and spark plasma sintering to synthesize bulk n-type and p-type filled Skutterudites. The kinetics process and microstructure evolution during the scanning laser melting and annealing were systematically investigated. Due to fast solidification in scanning laser melting, the peritectic segregation size of precursor resultants is confined to several microns, which leads to great shortening of the fabrication period of filled Skutterudites. The as-synthesized n-type and p-type filled Skutterudites achieve excellent dimensionless figures of merit: ZT ∼ 1.23 at 850 K for Yb0.4Co4Sb12.1; ZT ∼ 1.09 at 700 K for In0.5Co4Sb12.1; ZT ∼ 0.79 at 750 K for Ce0.95Fe3CoSb12.1, which are among the highest values of single filled Skutterudites. The shortened processing period and enhanced thermoelectric performance make this novel synthesis method suitable for industrial-level large-scale fabrication of skutterudite-based thermoelectric materials.
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skutterudite with graphene modified grain boundary complexion enhances zt enabling high efficiency thermoelectric device
Energy and Environmental Science, 2017Co-Authors: Peng An Zong, Riley Hanus, Jeffrey G Snyder, Qihao Zhang, Maxwell Dylla, Yunshan Tang, Jingcheng Liao, Lidong ChenAbstract:Skutterudite materials are widely considered for thermoelectric waste heat recovery. While the skutterudite structure effectively scatters the high frequency phonons, grain-boundary engineering is needed to further reduce the thermal conductivity beyond simply decreasing grain size. Here, we show that reduced graphene oxide (rGO) increases the grain boundary thermal resistivity by a factor of 3 to 5 compared to grain boundaries without graphene. Wrapping even micron sized grains with graphene leads to such a significant reduction in the thermal conductivity that a high thermoelectric figure of merit zT = 1.5 was realized in n-type YbyCo4Sb12, while a zT of 1.06 was achieved in p-type CeyFe3CoSb12. A 16 leg thermoelectric module was made by using n- and p-type skutterudite–graphene nanocomposites that exhibited conversion efficiency 24% higher than a module made without graphene. Engineering grain boundary complexions with 2-D materials introduces a new strategy for advanced thermoelectric materials.
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enhanced thermoelectric performance in rare earth filled Skutterudites
Journal of Materials Chemistry C, 2016Co-Authors: Pengfei Qiu, X. Shi, Jeffrey G Snyder, Bo B Iversen, Haozhi Duan, Jikun Chen, Lidong ChenAbstract:A series of rare-earth filled Skutterudites are successfully fabricated by using a non-equilibrium synthesis approach involving super-cooling and high pressure sintering. The filler filling fractions are significantly improved to realize optimum carrier concentrations and hugely suppressed lattice thermal conductivity, thereby leading to significantly enhanced zT.
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defect enhanced void filling and novel filled phases of open structure Skutterudites
Chemical Communications, 2015Co-Authors: Yuting Qiu, X. Shi, Wenqing Zhang, Lidong Chen, David J Singh, Jihui YangAbstract:We report the design of novel filled CoSb3 skutterudite phases based on a combination of filling and Sb-substituted Ga/In defects. Ga/In doped skutterudite phases with Li-, Nd-, and Sm-fillings can be formed via this strategy, which can have relatively wider ranges of carrier concentration than other conventional filled skutterudite phases.
Gerda Rogl - One of the best experts on this subject based on the ideXlab platform.
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study of thermal stability of n type Skutterudites sr0 07ba0 07yb0 07co4sb12 by differential thermal analysis and knudsen effusion method
Calphad-computer Coupling of Phase Diagrams and Thermochemistry, 2021Co-Authors: Frantisek Zelenka, Gerda Rogl, Jakub Stradal, Pavel Brož, Jan Vřesťal, Jiři Bursik, Adela Zemanova, P RoglAbstract:Abstract With a high figure of merit, ZT, described in detail in the introduction, multi-filled CoSb3 Skutterudites attract attention for their use as thermoelectric materials. In this work, the thermal and phase stability of n-type Skutterudites, Sr0.07Ba0.07Yb0.07Co4Sb12, prepared by ball milling, hot pressing and high-pressure torsion or by combinations thereof, with ZT values of about 1.4, have been studied via differential thermal analysis and Knudsen effusion method. The results from evaporation of antimony, strontium, barium and ytterbium as the volatile elements and those from phase transformation measurements are presented. The information, supported by microstructure investigation and measurement of diffusion profiles, is summarized and the long-term operation stability of the studied bulk and nano-structured thermoelectrics is evaluated. Almost no strontium, barium and ytterbium evaporation and only a slight evaporation of antimony demonstrate a long-term operation stability of the bulk and nano-structured thermoelectrics investigated.
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nanostructuring as a tool to adjust thermal expansion in high zt Skutterudites
Acta Materialia, 2018Co-Authors: Gerda Rogl, A Grytsiv, Jiri Bursik, S Puchegger, Viktor Soprunyuk, W Schranz, Xinlin Yan, E BauerAbstract:Abstract Although filled Skutterudites have a high figure of merit, ZT, it is still an aim to further improve their thermoelectric behavior. One successful route is to homogeneously disperse nanoparticles into the skutterudite matrix and thereby to reduce the lattice thermal conductivity without disturbing the electrical conductivity and the Seebeck coefficient. In this work Ta0.8Zr0.2B was dispersed into n-type (Mm,Sm)yCo4Sb12 powder by ball-milling or high energy ball-milling prior to hot-pressing. Structural and physical properties, covering also the low temperature range, were studied and compared with the recently investigated impact of nano Ta0.8Zr0.2B on p-type Skutterudites. ZT was enhanced by 16%. As for thermoelectric applications good mechanical properties are important, we investigated the influence of Ta0.8Zr0.2B nanoparticles, added to (Mm,Sm)yCo4Sb12, on the hardness, elastic moduli and fracture toughness and found an enhancement of all three mechanical properties. It is well known that p-type Skutterudites generally have a higher thermal expansion coefficient than their n-type counterpart. We show that dispersed borides in both n-type (Mm,Sm)yCo4Sb12 and p-type DD0.7Fe3CoSb12 can level out this discrepancy.
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Skutterudites a most promising group of thermoelectric materials
Green and Sustainable Chemistry, 2017Co-Authors: Gerda Rogl, P RoglAbstract:Abstract The current review summarizes and discusses the latest research activities (after 2014) on p- and n-type skutterudite thermoelectrics.
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attempts to further enhance zt in Skutterudites via nano composites
Journal of Alloys and Compounds, 2017Co-Authors: Gerda Rogl, E Bauer, Andriy Grytsiv, F Failamani, Markus Hochenhofer, P RoglAbstract:Abstract Skutterudites are known as excellent thermoelectric p- and n-type materials and have already achieved good efficiencies for the conversion of heat to electricity, but nevertheless researchers try to further enhance the figure of merit, ZT. In the present work the aim was to mix p- and n-type skutterudite powders with additives in order to produce an evenly dispersed distribution of sub micron grains, preferable small nano-particles, which enhance the scattering of the heat carrying phonons of different wavelengths and reduce thermal conductivity without changing electrical resistivity and Seebeck coefficient. Various quantities of three groups of materials (a) nonmetallic oxides (Al 2 O 3 ), (b) metallic oxides (Cu 2 O and La 1.85 Sr 0.15 CuO 4 ) and (c) metallic borides (Fe 2.25 Co 0.75 B and Ta 0.8 Zr 0.2 B) were added to industrially produced p-type (DD y Fe 3 CoSb 12 ) and n-type ((Mm,Sm) y Co 4 Sb 12 ) skutterudite powders. First the influence of pre-sieving and various ball milling conditions before hot pressing were studied, using Al 2 O 3 as additive. As a consequence of these studies pre-sieved powders and high-energy ball milling were used for all following experiments. The goal, to enhance ZT was not reached with Al 2 O 3 and Cu 2 O. La 1.85 Sr 0.15 CuO 4 was successful for the n-type, Fe 2.25 Co 0.75 B for the p-type Skutterudites, although ZT-enhancement was small, but with Fe 2.25 Co 0.75 B the maximum ZT could be shifted to lower temperatures, a valuable information for device production. Much better results in respect to ZT values were gained with adding 0.5, 1.0 and 1.5 wt.% Ta 0.8 Zr 0.2 B to p-type DD y Fe 3 CoSb 12 . In this series it was possible to enhance ZT (from ZT ∼ 1.2 to ZT ∼ 1.3) as well as to significantly increase the thermal-electrical conversion efficiency η. In addition, we found that all boride additives enhanced the hardness, elastic moduli and fracture resistance.
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in doped multifilled n type Skutterudites with zt 1 8
Acta Materialia, 2015Co-Authors: Gerda Rogl, A Grytsiv, E Bauer, S Puchegger, Kunio Yubuta, Ch Raju, Rc C Mallik, P RoglAbstract:Abstract In this paper we maximize the thermoelectric (TE) figure of merit, ZT , of n-type Skutterudites, (In, Sr, Ba, Yb) y Co 4 Sb 12 , via three different routes: (i) find the optimum fraction of In as fourth filler (ii) check the influence of powder particle, grain, and crystallite size on the TE properties and (iii) check thermal stability. Filled n-type (Sr, Ba, Yb) y Co 4 Sb 12 was mixed in three different proportions with In 0.4 Co 4 Sb 12 , ball milled (regular or high-energy (HB) ball milling) and hot-pressed. Particle size analyses and SEM pictures of the broken surfaces of the hot pressed samples document that only HB produces uniform particles/grains with average crystallite sizes ∼100 nm, proven by transmission electron microscopy. X-ray Rietveld refinements combined with EDX indicate that in all cases indium entered the icosahedral voids of the skutterudite. Temperature dependent physical properties of all three regularly ball-milled samples show that increasing In-content infers an increasing electrical resistivity, increasing Seebeck coefficient but a decreasing total thermal conductivity. Although ZT (823 K) is in the same range as for the sample without In, the ZT values in the whole temperature range are higher and consequently the TE-conversion efficiency, η is at least 10% higher. Annealing the samples at 600 °C for three days shows minor changes in structure and thermoelectric properties, indicating TE stability. The HB sample, due to uniformly small particles, equally sized grains and crystallites, exhibits a high power factor (4.4 mW/m K −2 at 730 K) and a very low thermal conductivity leading to an outstanding high ZT = 1.8 at 823 K ( η max = 17.5%).
Jihui Yang - One of the best experts on this subject based on the ideXlab platform.
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dynamic process of the resonant phonon scattering in fully filled Skutterudites
Physical Review B, 2018Co-Authors: Yancheng Wang, Jihui Yang, Jiong Yang, Wenqing Zhang, Hongliang Yang, Wujie QiuAbstract:The dynamics of the phonon scattering caused by the guest-host interactions in fully filled Skutterudites $(\mathrm{Yb},\phantom{\rule{0.16em}{0ex}}\mathrm{La},\phantom{\rule{0.16em}{0ex}}\mathrm{Ba})\mathrm{F}{\mathrm{e}}_{4}\mathrm{S}{\mathrm{b}}_{12}$ are studied by ab initio molecular dynamics. The characteristics of filler vibrations are found to be the origin of ultralow lifetimes for the filler-dominant modes. Under the phonon-phonon interaction diagram, the large amplitudes of the filler vibrations and the coupling between filler and framework phonon modes greatly increase the strength of phonon scatterings. The lattice thermal conductivities for the three Skutterudites, however, are all overestimated comparing with the experimental results. The introduction of the resonant scattering is thus necessary to account for the deviations. Furthermore, by applying the wavelet-based analysis to the resonant scattering process, the time-frequency power spectrum shows clearly that the time-varying localized motions of the fillers periodically absorb the heat-carrying lattice phonons and emit them. This process is the origin of the resonant scattering mechanism in Skutterudites, and strongly interferes with the propagation of phonons near the frequency range of the fillers.
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high performance n type ybxco4sb12 from partially filled Skutterudites towards composite thermoelectrics
Npg Asia Materials, 2016Co-Authors: Shanyu Wang, James R. Salvador, Jiong Yang, Ping Wei, Bo Duan, Jihui YangAbstract:The filling fraction limit (FFL) of Skutterudites, that is, the complex balance of formation enthalpies among different species, is an intricate but crucial parameter for achieving high thermoelectric performance. In this work, we synthesized a series of YbxCo4Sb12 samples with x=0.2–0.6 and systemically studied the FFL of Yb, which is still debated even though this system has been extensively investigated for decades. Our combined experimental efforts of X-ray diffraction, microstructural and quantitative compositional analyses clearly reveal a Yb FFL of ~0.29 in CoSb3, which is consistent with previous theoretical calculations. The excess Yb in samples with x>0.35 mainly form metallic YbSb2 precipitates, significantly raising the Fermi level and thus increasing the electrical conductivity and decreasing the Seebeck coefficient. This result is further corroborated by the numerical calculations based on the Bergman’s composite theory, which accurately reproduces the transport properties of the x>0.35 samples based on nominal Yb0.35Co4Sb12 and YbSb2 composites. A maximum ZT of 1.5 at 850 K is achieved for Yb0.3Co4Sb12, which is the highest value for a single-element-filled CoSb3. The high ZT originates from the high-power factor (in excess of 50 μW cm-K−2) and low lattice thermal conductivity (well below 1.0 W m-K−1). More importantly, the large average ZTs, for example, ~1.05 for 300–850 K and ~1.27 for 500–850 K, are comparable to the best values for n-type Skutterudites. The high thermoelectric and thermomechanical performances and the relatively low air and moisture sensitivities of Yb make Yb-filled CoSb3, a promising candidate for large-scale power generation applications. Reducing the amount of rare-earths filling in nanovoids of a popular thermoelectric crystal could improve large-scale energy recovery. Minerals known as Skutterudites are being investigated as additions to electric vehicles and power-generation stations because they convert heat gradients into electricity at temperatures up to 600 degrees Celsius. To improve the energy conversion efficiency, rare-earth metals such as ytterbium (Yb) are usually incorporated into the skutterudite framework. Jihui Yang from the University of Washington in the US and co-workers have now determined the optimal filling ratio of Yb in these materials. X-ray and microscopy techniques showed that overloading Yb past its thermodynamic equilibrium led to metallic precipitates that negatively impacted performance. When a slightly lower-than-equilibrium fill ratio was used, however, thermoelectric conversion efficiencies approached the best values recorded for Skutterudites filled with a single element. High thermoelectric figure of merit ZT of 1.5 and a high average ZT >1.0 between 300 and 850 K can be achieved for Yb-filled CoSb3, which are superior to those of any single-element-filled skutterudite and comparable to the best in this class of materials. The long-term debate about the Yb-filling fraction limit in CoSb3 is clarified to be ~0.29, and the excess Yb mainly forms metallic YbSb2 precipitates. The transport properties of the x >0.35 samples with YbSb2 precipitates are quantitatively reproduced by the Bergman’s composite theory, providing new understanding of the role of Yb in CoSb3.
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defect enhanced void filling and novel filled phases of open structure Skutterudites
Chemical Communications, 2015Co-Authors: Yuting Qiu, X. Shi, Wenqing Zhang, Lidong Chen, David J Singh, Jihui YangAbstract:We report the design of novel filled CoSb3 skutterudite phases based on a combination of filling and Sb-substituted Ga/In defects. Ga/In doped skutterudite phases with Li-, Nd-, and Sm-fillings can be formed via this strategy, which can have relatively wider ranges of carrier concentration than other conventional filled skutterudite phases.
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thermoelectric properties of ni doped cefe4sb12 Skutterudites
Journal of Applied Physics, 2012Co-Authors: Pengfei Qiu, Jihui Yang, Jiong Yang, Xiangyang Huang, W Zhang, X. Shi, Lidong Chen, Rui Liu, David J SinghAbstract:We have prepared Ni-doped p-type Skutterudites CeyFe4−xNixSb12 and systematically studied their thermoelectric properties. The lattice parameters of these Skutterudites are found to be sensitive to both the Ni content and Ce-filling fraction. With increasing Ni content, the electrical conductivity decreases and the Seebeck coefficient increases, consistent with the expected decrease in hole concentration due to the extra electrons introduced by Ni. All Ni-doped samples possess similar band gap values. We also find that the Ni-doped CeyFe4−xNixSb12 system has electrical transport properties similar to those of Co-doped CeyFe4−xCoxSb12 system at a similar nominal hole concentration based on a simple charge counting. We do, however, find a pronounced bi-polar phenomenon in thermal conductivity that rapidly increases for Ni-doped samples when temperature is above 600 K. Importantly, Ni-doped samples have higher dimensionless thermoelectric figures of merit values than CeFe4Sb12 over the entire temperature ran...
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realization of high thermoelectric performance in n type partially filled Skutterudites
Journal of Materials Research, 2011Co-Authors: X. Shi, Jiong Yang, Wenqing Zhang, Lidong Chen, Shengqiang Bai, Jihui YangAbstract:Skutterudites are among the most exciting thermoelectric (TE) materials that could be used for various intermediate temperature applications. This study summarized our recent work on n-type partially filled Skutterudites. By combining theoretical and experimental approaches, we revealed the underlying mechanism of void filling in the intrinsic lattice voids in CoSb3. With that, the electronegativity selection rule is established for the current stable filled Skutterudites and further used for the discovery of a few novel filled CoSb3 compounds. The correlation between the thermal/electrical transport properties and impurity fillers in n-type partially filled Skutterudites was also carefully investigated. Our results provide fundamental understanding to how those filler impurities affect electronic structures and lattice dynamics. Based on these basic understanding on transport mechanisms and sophisticated strategy in materials synthesis, TE figure of merit for n-type materials were continually increased from 1.1 to 1.4 and then to 1.7 for single-, double-, and triple-filled Skutterudites.
Ctirad Uher - One of the best experts on this subject based on the ideXlab platform.
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thermoelectric properties of Skutterudites
2021Co-Authors: Ctirad UherAbstract:Abstract Thermoelectricity has made much progress during the past dozen years or so with new prospective materials being discovered and the established thermoelectric structures have much improved. In this chapter, I describe key developments in an important class of materials called Skutterudites, having great potential as mid-temperature power-generating thermoelectrics for applications such as waste heat recovery and its conversion to electricity. I review the basic structural forms of Skutterudites, mention how they are synthesized, and discuss their electronic and phonon properties. The bulk of the thermoelectric Skutterudites are n- and p-type structures of composition RT4X12, where R is an electropositive filler, such as alkali metals, alkaline-earth, and rare-earth elements, occupying structural voids of the [T4X12] framework, where T stands for transition metal and X for a pnicogen element (X = P, As, Sb). Recently, the family of Skutterudites has been augmented by the discovery of Skutterudites with electronegative fillers, and Skutterudites having an entirely new [Pt4Ge12] framework, avoiding rather volatile pnicogen elements. I will describe improvements achieved in the thermoelectric performance of Skutterudites and briefly mention where we stand in making commercially available modules based on Skutterudites.
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ultra fast synthesis and thermoelectric properties of te doped Skutterudites
Journal of Materials Chemistry, 2014Co-Authors: Tao Liang, Yonggao Yan, Gang Zheng, Qiang Zhang, Hang Chi, Xinfeng Tang, Ctirad UherAbstract:The self-propagating-high-temperature-synthesis (SHS) technique is applied here for the first time to synthesize CoSb3 thermoelectric materials. Mixtures of Co and Sb powders were compacted into pellets which were ignited from one end. A single-phase skutterudite material was obtained in a very short period of time using the SHS process which is maintained by the heat released from the chemical reaction of Co with Sb. Thermodynamic parameters and kinetics of the SHS reaction are investigated. The ignition temperature, adiabatic temperature, and the propagation speed of the combustion wave in the synthesis of CoSb3 are 723 K, 861 K, and 1.25 mm s−1, respectively. Using the SHS technique followed by Plasma Activated Sintering (PAS), we synthesized high performance bulk Skutterudites of composition CoSb2.85 Te0.15 with a ZT of 0.98 at 820 K, one of the highest ZT values for an unfilled form of Skutterudites. Compared with the samples synthesized by the traditional methods, the synthesis time is shortened from the typical several days to less than 20 minutes. Our work opens a new avenue for ultra-fast, low cost, mass production fabrication of skutterudite-based materials, which may also be universally applicable for the synthesis of other thermoelectric materials.
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realization of high thermoelectric performance in p type unfilled ternary Skutterudites fesb2 xte1 x via band structure modification and significant point defect scattering
Acta Materialia, 2013Co-Authors: Gangjian Tan, Yonggao Yan, Hang Chi, Xinfeng Tang, Shanyu Wang, Wei Liu, W Wongng, Ctirad UherAbstract:Abstract FeSb2Te, a ternary derivative of binary CoSb3, displays anomalous electrical and thermal transport properties because of considerable modifications in the band structure induced by Fe and significant mixed valence state (namely Fe2+ and Fe3+) scattering of phonons. The substitution of Te for Sb generates more holes without notably affecting the band structure, while markedly improving the electrical conductivity and retaining a high Seebeck coefficient due to the enhanced density of states, thereby leading to dramatically increased power factors. Furthermore, the heat carrying phonons are strongly scattered with increasing x value because of the formation of solid solutions between two end members: □FeSb2Te and □FeSb3 (where □ can be viewed as a vacancy). Consequently, high thermoelectric figures of merit were achieved in the FeSb2+xTe1−x compounds, with the largest ZT value reaching ∼0.65 for the sample with x = 0.2. This is the highest value among all p-type unfilled Skutterudites and is comparable with some filled compositions. Prospects for further improving the performance of p-type FeSb2Te-based Skutterudites are discussed.
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thermoelectric properties of p type ybxlayfe2 7co1 3sb12 double filled Skutterudites
Intermetallics, 2013Co-Authors: Lina Zhou, X. Shi, Ctirad Uher, Pengfei Qiu, Lidong ChenAbstract:Abstract Filling two or multiple atoms into the cages of a skutterudite crystal is a successful way to enhance the thermoelectric figure of merit in n-type partially filled Skutterudites. Here we use La–Yb double filling to improve the thermoelectric performance of p-type Skutterudites YbxLayFe2.7Co1.3Sb12 (x + y = 0.85, x = 0, 0.09, 0.17, 0.25, 0.34, 0.42, 0.85). The samples are synthesized by directly melting the raw materials followed by a long time annealing process. X-ray diffraction measurement confirms the skutterudite structure of the samples. By increasing the filling fraction of Yb, the lattice thermal conductivity is gradually depressed and reaches the lowest value of 0.9 W m−1 K−1 at high temperatures. At the same time, the Seebeck coefficient decreases while the electrical conductivity increases. The maximum power factor around 27 μW cm−1 K−2 for samples Yb0.17La0.68Fe2.7Co1.3Sb12 and Yb0.25La0.60Fe2.7Co1.3Sb12 is achieved at 600 K and 700 K, respectively. Sample Yb0.25La0.60Fe2.7Co1.3Sb12 has the maximum thermoelectric figure of merit 0.99 at 700 K, which is among the highest values among p-type filled Skutterudites.
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microstructure and thermoelectric properties of cosb2 75ge0 25 xtex prepared by rapid solidification
Acta Materialia, 2012Co-Authors: Xinfeng Tang, Xianli Su, Han Li, Guoyu Wang, Xiaoyuan Zhou, Qingjie Zhang, Ctirad UherAbstract:Abstract Since the vibration modes of the pnicogen rings in CoSb 3 -based Skutterudites fall within the range of frequencies of heat-carrying phonons, disruption of the rings by doping should have a strong influence on heat transport in this material. To test the premise, single-phase double-doped CoSb 2.75 Ge 0.25− x Te x ( x = 0.125–0.20) compounds were synthesized by combining melt spinning with a spark plasma sintering method. Following the melt-spinning process, the side of the ribbons contacting the copper drum is featureless and reflects its amorphous nature while the free surface of the ribbons is composed of 30–80 nm grains. After spark plasma processing the average grain size of the bulk samples is about 200 nm. High-resolution transmission electron microscopy images show an in situ nanostructure consisting of circular, 15 nm diameter dots of Te- and Ge-enriched skutterudite phase embedded in the skutterudite matrix. Transport properties were measured from 2 to 800 K as a function of Te and Ge content on the pnicogen (Sb) rings and the results were correlated with the structural data. Double-doping on pnicogen rings with Ge and Te, and using melt-spinning processing, results in binary skutterudite compounds that possess an impressive figure of merit of ZT ∼ 1.1 at 750 K.
Jiong Yang - One of the best experts on this subject based on the ideXlab platform.
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dynamic process of the resonant phonon scattering in fully filled Skutterudites
Physical Review B, 2018Co-Authors: Yancheng Wang, Jihui Yang, Jiong Yang, Wenqing Zhang, Hongliang Yang, Wujie QiuAbstract:The dynamics of the phonon scattering caused by the guest-host interactions in fully filled Skutterudites $(\mathrm{Yb},\phantom{\rule{0.16em}{0ex}}\mathrm{La},\phantom{\rule{0.16em}{0ex}}\mathrm{Ba})\mathrm{F}{\mathrm{e}}_{4}\mathrm{S}{\mathrm{b}}_{12}$ are studied by ab initio molecular dynamics. The characteristics of filler vibrations are found to be the origin of ultralow lifetimes for the filler-dominant modes. Under the phonon-phonon interaction diagram, the large amplitudes of the filler vibrations and the coupling between filler and framework phonon modes greatly increase the strength of phonon scatterings. The lattice thermal conductivities for the three Skutterudites, however, are all overestimated comparing with the experimental results. The introduction of the resonant scattering is thus necessary to account for the deviations. Furthermore, by applying the wavelet-based analysis to the resonant scattering process, the time-frequency power spectrum shows clearly that the time-varying localized motions of the fillers periodically absorb the heat-carrying lattice phonons and emit them. This process is the origin of the resonant scattering mechanism in Skutterudites, and strongly interferes with the propagation of phonons near the frequency range of the fillers.
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high performance n type ybxco4sb12 from partially filled Skutterudites towards composite thermoelectrics
Npg Asia Materials, 2016Co-Authors: Shanyu Wang, James R. Salvador, Jiong Yang, Ping Wei, Bo Duan, Jihui YangAbstract:The filling fraction limit (FFL) of Skutterudites, that is, the complex balance of formation enthalpies among different species, is an intricate but crucial parameter for achieving high thermoelectric performance. In this work, we synthesized a series of YbxCo4Sb12 samples with x=0.2–0.6 and systemically studied the FFL of Yb, which is still debated even though this system has been extensively investigated for decades. Our combined experimental efforts of X-ray diffraction, microstructural and quantitative compositional analyses clearly reveal a Yb FFL of ~0.29 in CoSb3, which is consistent with previous theoretical calculations. The excess Yb in samples with x>0.35 mainly form metallic YbSb2 precipitates, significantly raising the Fermi level and thus increasing the electrical conductivity and decreasing the Seebeck coefficient. This result is further corroborated by the numerical calculations based on the Bergman’s composite theory, which accurately reproduces the transport properties of the x>0.35 samples based on nominal Yb0.35Co4Sb12 and YbSb2 composites. A maximum ZT of 1.5 at 850 K is achieved for Yb0.3Co4Sb12, which is the highest value for a single-element-filled CoSb3. The high ZT originates from the high-power factor (in excess of 50 μW cm-K−2) and low lattice thermal conductivity (well below 1.0 W m-K−1). More importantly, the large average ZTs, for example, ~1.05 for 300–850 K and ~1.27 for 500–850 K, are comparable to the best values for n-type Skutterudites. The high thermoelectric and thermomechanical performances and the relatively low air and moisture sensitivities of Yb make Yb-filled CoSb3, a promising candidate for large-scale power generation applications. Reducing the amount of rare-earths filling in nanovoids of a popular thermoelectric crystal could improve large-scale energy recovery. Minerals known as Skutterudites are being investigated as additions to electric vehicles and power-generation stations because they convert heat gradients into electricity at temperatures up to 600 degrees Celsius. To improve the energy conversion efficiency, rare-earth metals such as ytterbium (Yb) are usually incorporated into the skutterudite framework. Jihui Yang from the University of Washington in the US and co-workers have now determined the optimal filling ratio of Yb in these materials. X-ray and microscopy techniques showed that overloading Yb past its thermodynamic equilibrium led to metallic precipitates that negatively impacted performance. When a slightly lower-than-equilibrium fill ratio was used, however, thermoelectric conversion efficiencies approached the best values recorded for Skutterudites filled with a single element. High thermoelectric figure of merit ZT of 1.5 and a high average ZT >1.0 between 300 and 850 K can be achieved for Yb-filled CoSb3, which are superior to those of any single-element-filled skutterudite and comparable to the best in this class of materials. The long-term debate about the Yb-filling fraction limit in CoSb3 is clarified to be ~0.29, and the excess Yb mainly forms metallic YbSb2 precipitates. The transport properties of the x >0.35 samples with YbSb2 precipitates are quantitatively reproduced by the Bergman’s composite theory, providing new understanding of the role of Yb in CoSb3.
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theoretical study of the filling fraction limit of fe substituted ba filled skutterudite bayfe4xco4 4xsb12
Key Engineering Materials, 2012Co-Authors: Zhuo Chen, Jiong YangAbstract:Theoretical study of the filling fraction limit (FFL) of the Fe-substituted Ba-filled skutterudite was carried out via first principle method calculations. The lattice constant of BayFe4xCo4-4xSb12 increases with the Ba filling fraction under fixed Fe content while it does not simply increases with Fe content under fixed Ba filling fraction. The FFL is determined by the competition between the formation of filled skutterudite phases and the corresponding secondary phases. The FFL of Ba in the Fe-substituted CoSb3 Skutterudites increases monotonically from 37.5% with Fe content of 0 to 100% with Fe content of ~50%. The most stable composition of the BayFe4xCo4-4xSb12is expected to be BayFe2.8Co1.2Sb12.
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thermoelectric properties of ni doped cefe4sb12 Skutterudites
Journal of Applied Physics, 2012Co-Authors: Pengfei Qiu, Jihui Yang, Jiong Yang, Xiangyang Huang, W Zhang, X. Shi, Lidong Chen, Rui Liu, David J SinghAbstract:We have prepared Ni-doped p-type Skutterudites CeyFe4−xNixSb12 and systematically studied their thermoelectric properties. The lattice parameters of these Skutterudites are found to be sensitive to both the Ni content and Ce-filling fraction. With increasing Ni content, the electrical conductivity decreases and the Seebeck coefficient increases, consistent with the expected decrease in hole concentration due to the extra electrons introduced by Ni. All Ni-doped samples possess similar band gap values. We also find that the Ni-doped CeyFe4−xNixSb12 system has electrical transport properties similar to those of Co-doped CeyFe4−xCoxSb12 system at a similar nominal hole concentration based on a simple charge counting. We do, however, find a pronounced bi-polar phenomenon in thermal conductivity that rapidly increases for Ni-doped samples when temperature is above 600 K. Importantly, Ni-doped samples have higher dimensionless thermoelectric figures of merit values than CeFe4Sb12 over the entire temperature ran...
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p type Skutterudites rxmyfe3cosb12 r m ba ce nd and yb effectiveness of double filling for the lattice thermal conductivity reduction
Intermetallics, 2011Co-Authors: Ruiheng Liu, Jiong Yang, X. Shi, Lidong Chen, Xihong Chen, Ctirad UherAbstract:Abstract Ab-initio calculations of the resonant modes and frequencies for a number of possible fillers in p-type R Fe 3 CoSb 12 and R Fe 4 Sb 12 were carried out. The results indicate that, although the exact values of fillers’ resonant frequencies in p-type Skutterudites are somewhat different from those in n-type Co-based Skutterudites, the Einstein-like resonant modes of the fillers are similar to those in n-type materials. Experimentally, several pairs of the fillers were selected and double-filled p-type skutterudite compounds R x M y Fe 3 CoSb 12 ( R , M = Ba, Ce, Nd, and Yb) were successfully synthesized. The reduction in the lattice thermal conductivity was realized by extending the range of resonant frequencies. As a result, enhanced ZT values above unity were achieved in these double-filled p-type Skutterudites.