• Title, Summary, Keyword: Skutterudite

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Process Development for Enhancement of High Temperature Thermoelectric Properties in a p-Type Skutterudite (P-형 Skutterudite 소재의 고온 열전물성 제어를 위한 공정 개발)

  • Liu, Peng Ju;Nou, Chang Wan;Choi, Soon-Mok
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.33 no.6
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    • pp.495-499
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    • 2020
  • Power factor improvement at high temperatures has been a major research topic for the development of skutterudite thermoelectric materials. Here, we attempted to optimize the process parameters for manufacturing skutterudite materials, especially for p-type systems. We focused on the effect of aging time variation to maximize the high-temperature performance of the Ce-filled Fe3CoSb12 skutterudite system. The optimized aging time was concluded to be a key parameter for the formation of single-phase nanostructures in this p-type skutterudite system. The optimized condition was effective in reducing the bipolar effect at high temperature ranges by increasing the carrier concentration in the p-type system. To confirm the conclusions, the electrical conductivity, Seebeck coefficient, and power factor were measured. The results matched well with the microstructure and with those of an XRD analysis performed for the system.

Thermoelectric Properties of Skutterudite CoSb3 Fabricated by Mechanical Alloying Process (기계적 합금화에 의해 제조된 Skutterudite CoSb3의 열전특성)

  • Choi Moon-Kwan;Cho Hyoung-Won;Ur Soon-Chul;Kim Il-Ho
    • Korean Journal of Materials Research
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    • v.14 no.11
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    • pp.802-806
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    • 2004
  • Skutterudite $CoSb_3$ powders were produced by mechanical alloying (MA) of elemental powders using a nominal stoichiometric composition. Annealing of MA powders under specific condition led to a complete phase transformation to a semiconducting ${\delta}-CoSb_3$. Single phase $CoSb_3$ was successfully produced by vacuum hot pressing using MA powders without subsequent annealing. Phase transformations during mechanical alloying and hot pressing were systematically investigated using XRD and SEM. Thermoelectric properties as a function of temperature were evaluated for the hot pressed specimens and compared with results of analogous studies.

Sn Filling Effects on the Thermoelectric Properties of CoSb3 Skutterudites (Skutterudite CoSb3의 열전특성에 미치는 Sn의 충진효과)

  • Jung, Jae-Yong;Ur, Soon-Chul;Kim, Il-Ho
    • Korean Journal of Materials Research
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    • v.16 no.9
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    • pp.529-532
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    • 2006
  • Sn-filled $Co_8Sb_{24}$ skutterudites were synthesized by the encapsulated induction melting process. Single ${\delta}-phase$ was successfully obtained by subsequent annealing and confirmed by X-ray diffraction analysis. Temperature dependences of Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed the p-type conductivity of the Sn-filled $Co_8Sb_{24}$. Electrical resistivity increased with increasing temperature, which shows that the Sn-filled $Co_8Sb_{24}$ skutterudite is a highly degenerate semiconductor. Thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. Thermoelectric figure of merit was enhanced by Sn filling and its optimum filling content was considered to be $z{\leq}0.5$ in the $Sn_zCo_8Sb_{24}$ system.

Research for Controlled Thermal Conductivity of p-Type Skutterudite Materials (P-type Skutterudite 열전소재의 열전도도 제어 연구)

  • Son, Geon Sik;Choi, Soon Mok
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.29 no.11
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    • pp.671-675
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    • 2016
  • Skutterudite materials show PGEC (phonon glass electron crystal) characteristics which is an optimal strategy for designing high performance thermoelectric materials. Now two methods are in parallel to control thermal conductivity of skutterudites, a rattler-atoms doping method and a process for nanostructured bulk materials. Amount of rattler atoms in p-type skutterudite are depends on a Fe/Co ratio of matrix, and the optimal Fe/Co ratio has been reported about from 3:1 to 3.5:0.5 in $R(Fe,Co)_4Sb_{12}$ structure. In this paper, our discussion for rattler doping research was concentrated on double-rattler systems and DD-doped systems in p-type skutterudites. A melt spinning precess combined with high energy ball milling were suggested as a strategy for nanostructured bulk materials with PGEC (phonon glass electron crystal) characteristics in p-type skutterudites.

Thermoelectric Properties of Sb Deficiency N-Type Skutterudite Co4Sb12 (Sb가 결핍된 N형 Skutterudite Co4Sb12의 열전 특성)

  • Tak, Jang-Yeul;Van Du, Nguyen;Jeong, Min Seok;Lee, NaYoung;Nam, Woo Hyun;Seo, Won-Seon;Cho, Jung Young
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.32 no.6
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    • pp.496-500
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    • 2019
  • In this study, we investigate the effect of an Sb-deficiency on the thermoelectric properties of double-filled n-type skutterudite ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$). Samples were prepared by encapsulated induction melting, consecutive long-time annealing, and finally spark plasma sintering processes. The Sb-deficient sample contained a $CoSb_2$ secondary phase. Both the double-filled n-type skutterudite pristine and Sb-deficient samples showed metallic behavior in electrical conductivity with increasing temperature. The carrier concentration of the Sb-deficient sample decreased compared with that of the pristine sample. Due to a decrease in carrier concentration, the Sb deficient sample showed decreased electrical conductivity and an increased Seebeck coefficient compared with the conductivity and coefficient of the pristine sample. Furthermore, the Sb deficient sample showed an increase in the power factor (${\sigma}{\cdot}S^2$); the power factor maximum shifted to athe lower temperature side than ones of the pristine sample. As a result, the Sb-deficient sample represents an improved average figure of merit (ZT) and a $ZT_{max}$ temperature lower than that of the pristine sample. Therefore, we propose that Sb-deficient double-filled n-type skutterudite thermoelectric material ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$) be used in the 573~673 K temperature range.

Thermoelectric Properties of Skutterudite FexCo4-xSb12 Synthesized by Mechanical Alloying Process (기계적 합금화에 의한 Skutterudite계 FexCo4-xSb12의 합성 및 열전특성)

  • Kwon, Joon-Chul;Kim, Il-Ho;Ur, Soon-Chul
    • Journal of Korean Powder Metallurgy Institute
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    • v.12 no.5
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    • pp.357-361
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    • 2005
  • Fe-doped skutterudite $CoSb_3$ with a nominal composition of $Fe_{x}Co_{4-x}Sb_{12}(0\;{\le}\;x\;{\le}\;2.5)$ has been synthesized by mechanical alloying (MA) of elemental powders, followed by hot pressing. Phase transformations during mechanical alloying and hot pressing were systematically investigated using XRD. Single phase skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase in the form of marcasite structure $FeSb_2$ was found to exist in case of $x\;{\ge}\;2$, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe contents were evaluated for the hot pressed specimens. Fe substitution up to x=1.5 with Co in $Fe_{x}Co_{4-x}Sb_{12}$ appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at 525K in this study.

Synthesis and Thermoelectric Properties of Skutterudite CoSb3 (Skutterudite CoSb3의 합성 및 열전특성)

  • Kim I. H.;You S. W.;Park J. B.;Lee J. I.;Ur S. C.;Jang K. W.;Choi G. S.;Kim J. S.;Kim H. J.
    • Korean Journal of Materials Research
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    • v.15 no.10
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    • pp.667-670
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    • 2005
  • Binary skutterudite $CoSb_3$ compounds were prepared by the arc melting and hot pressing processes and their thermoelectric properties were investigated in the range from 300 to 600 K. Annealing effect was correlated to phase transformation and homogenization. Thermoelectric properties of the arc-melted and hot-pressed $CoSb_3$ were discussed and compared. Undoped intrinsic $CoSb_3$ prepared by the arc melting showed p-type conduction, while it showed metallic behavior with increasing measuring temperature. However, hot pressed specimens showed n-type conduction, possibly due to Sb evaporation. Thermoelectric properties were remarkably improved by annealing In vacuum and they were closely related to phase transformation.

Thermoelectric Properties of Binary Skutterudite CoSb3 Prepared by Encapsulated Induction Melting (밀폐유도용해로 제조된 2원계 Skutterudite CoSb3의 열전특성)

  • You, Sin-Wook;Jung, Jae-Yong;Ur, Soon-Chul;Kim, Il-Ho
    • Korean Journal of Materials Research
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    • v.16 no.5
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    • pp.312-317
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    • 2006
  • Binary skutterudite $CoSb_3$ compounds were prepared by the encapsulated induction melting (EIM) process, and their thermoelectric, microstructural and mechanical properties were examined. Single-phase ${\delta}-CoSb_3$ was successfully produced by the EIM and subsequent heat treatment at 773 K-873 K for 24 hours in vacuum. Seebeck coefficient increased with increasing heat treatment temperature up to 673 K, showing the positive signs in the range of measuring temperature. However, the samples heat-treated at 773 K-873 K showed negative Seebeck coefficient from room temperature to 400 K, while it showed positive signs above 400 K. Electrical resistivity decreased with increasing temperature, showing typical semiconducting conductivity. Thermal conductivity decreased drastically with increasing heat-treatment temperature. This is closely related with the phase transition to ${\delta}-CoSb_3$.

Thermoelectric Properties of Nano Structured $CoSb_3$ Synthesized by Mechanical Alloying

  • Ur, Soon-Chul;Kwon, Joon-Chul;Choi, Moon-Kwan;Kweon, Soon-Yong;Hong, Tae-Whan;Kim, Il-Ho;Lee, Young-Geun
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • pp.665-666
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    • 2006
  • Undoped $CoSb_3$ powders were synthesized by mechanical alloying (MA) of elemental powders using a nominal stoichiometric composition. Nano-structured, single-phase skutterudite $CoSb_3$ was successfully produced by vacuum hot pressing (VHP) using MA powders without subsequent annealing. Phase transformations during synthesis were investigated using XRD, and microstructure was observed using SEM and TEM. Thermoelectric properties in terms of Seebeck coefficient, electrical conductivity, thermal conductivity and figure of merit(ZT) were systematically measured and compared with the results of analogous studies. Lattice thermal conductivity was reduced owing to increasing phone scattering in nano-structured MA $CoSb_3$, leading to enhancement in the thermoelectric figure of merit. MA associated with VHP technique offers an alternative potential processing route for the process of skutterudite.

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