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        검색결과 88

        1.
        2024.09 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        We conducted a study on excessive doping of the Cr and In elements in Bi-Sb-Te materials satisfying the Hume- Rothery rule, and investigated the resulting electrical and thermal properties. From X-ray diffraction (XRD) results, we confirmed the formation of a single phase even with excessive doping. Through analysis of electrical properties, we observed the highest enhancement in electrical characteristics at y = 0.2, suggesting that the appropriate ratio of Bi-Sb significantly influences this enhancement. Using the Callaway-von Baeyer (CvB) model to assess scattering due to point defects, we calculated the experimental point defect scattering factor (ΓCvB.exp), which was notably high due to the substantial differences in volume and atomic weight between the substituted (Cr, In) and original (Bi, Sb) elements. Additionally, we conducted a single parabolic band (SPB) modeling analysis of materials with compositions y = 0.1 and 0.2, where, despite a decrease in densityof- states effective mass (md *) during the enhancement process from y = 0.1 to 0.2, a sharp increase in non-degenerate mobility (μ0) led to an 88 % increase in weighted mobility (μw). Furthermore, analyzing zT with respect to nH revealed a 51 % increase in zT at a composition of y = 0.2. This study confirmed a significant reduction in lattice thermal conductivity with the co-doping strategy, and with further compositional studies to improve electrical properties, we anticipate achieving high zT.
        4,000원
        2.
        2024.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The development of thermoelectric (TE) materials to replace Bi2Te3 alloys is emerging as a hot issue with the potential for wider practical applications. In particular, layered Zintl-phase materials, which can appropriately control carrier and phonon transport behaviors, are being considered as promising candidates. However, limited data have been reported on the thermoelectric properties of metal-Sb materials that can be transformed into layered materials through the insertion of cations. In this study, we synthesized FeSb and MnSb, which are used as base materials for advanced thermoelectric materials. They were confirmed as single-phase materials by analyzing X-ray diffraction patterns. Based on electrical conductivity, the Seebeck coefficient, and thermal conductivity of both materials characterized as a function of temperature, the zT values of MnSb and FeSb were calculated to be 0.00119 and 0.00026, respectively. These properties provide a fundamental data for developing layered Zintl-phase materials with alkali/alkaline earth metal insertions.
        4,000원
        3.
        2024.04 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The n-type Bi2-xSbxTe3 compounds have been of great interest due to its potential to achieve a high thermoelectric performance, comparable to that of p-type Bi2-xSbxTe3. However, a comprehensive understanding on the thermoelectric properties remains lacking. Here, we investigate the thermoelectric transport properties and band characteristics of n-type Bi2-xSbxTe3 (x = 0.1 – 1.1) based on experimental and theoretical considerations. We find that the higher power factor at lower Sb content results from the optimized balance between the density of state effective mass and nondegenerate mobility. Additionally, a higher carrier concentration at lower x suppresses bipolar conduction, thereby reducing thermal conductivity at elevated temperatures. Consequently, the highest zT of ~ 0.5 is observed at 450 K for x = 0.1 and, according to the single parabolic band model, it could be further improved by ~70 % through carrier concentration tuning.
        4,000원
        4.
        2022.06 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Magnesium-antimonide is a well-known zintl phase thermoelectric material with low band gap energy, earthabundance and characteristic electron-crystal phonon-glass properties. The nominal composition Mg3.8-xZnxSb2 (0.00 ≤ x ≤ 0.02) was synthesized by controlled melting and subsequent vacuum hot pressing method. To investigate phase development and surface morphology during the process, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out. It should be noted that an additional 16 at. % Mg must be added to the system to compensate for Mg loss during the melting process. This study evaluated the thermoelectric properties of the material in terms of Seebeck coefficient, electrical conductivity and thermal conductivity from the low to high temperature regime. The results demonstrated that substituting Zn at Mg sites increased electrical conductivity without significantly affecting the Seebeck coefficient. The maximal dimensionless figure of merit achieved was 0.30 for x = 0.01 at 855 K which is 30% greater than the intrinsic value. Electronic flow properties were also evaluated and discussed to explain the carrier transport mechanism involved in the thermoelectric properties of this alloy system.
        4,000원
        5.
        2022.03 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Zintl phase Mg3Sb2 is a promising thermoelectric material in medium to high temperature range due to its low band gap energy and characteristic electron-crystal phonon-glass behavior. P-type Mg3Sb2 has conventionally exhibited lower thermoelectric properties compared to its n-type counterparts, which have poor electrical conductivity. To address these problems, a small amount of Sn doping was considered in this alloy system. P-type Mg3Sb2 was synthesized by controlled melting, pulverizing, and subsequent vacuum hot pressing (VHP) method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate phases and microstructure development during the process. Single phase Mg3Sb2 was successfully formed when 16 at.% of Mg was excessively added to the system. Nominal compositions of Mg3.8Sb2-xSnx (0 ≤ x ≤ 0.008) were considered in this study. Thermoelectric properties were evaluated in terms of Seebeck coefficient, electrical conductivity, and thermal conductivity. A peak ZT value ≈ 0.32 was found for the specimen Mg3.8Sb1.994Sn0.006 at 873 K, showing an improved ZT value compared to intrinsic one. Transport properties were also evaluated and discussed.
        4,000원
        6.
        2021.08 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Zintl compound Mg3Sb2 is a promising candidate for efficient thermoelectric material due to its small band gap energy and characteristic electron-crystal phonon-glass behavior. Furthermore, this compound enables fine tuning of carrier concentration via chemical doping for optimizing thermoelectric performance. In this study, nominal compositions of Mg3.8Sb2-xTex (0 ≤ x ≤ 0.03) are synthesized through controlled melting and subsequent vacuum hot pressing method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are carried out to investigate phase development and surface morphology during the process. It should be noted that 16 at. % of excessive Mg must be added to the system to compensate for the loss of Mg during melting process. Herein, thermoelectric properties such as Seebeck coefficient, electrical conductivity, and thermal conductivity are evaluated from low to high temperature regimes. The results show that Te substitution at Sb sites effectively tunes the majority carriers from holes to electrons, resulting in a transition from p to n-type. At 873 K, a peak ZT value of 0.27 is found for the specimen Mg3.8Sb1.99Te0.01, indicating an improved ZT value over the intrinsic value.
        4,000원
        7.
        2018.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Nanoparticles of PbTe are prepared via chemical reaction of the equimolar aqueous solutions of Pb(CH3COO)2 and Te at 120°C. The size of the obtained particles is 100 nm after calcination in a hydrogen atmosphere. Dense specimens for the thermoelectric characterization are produced by spark plasma sintering of prepared powders at 400°C to 500°C under 80 MPa for 5 min. The relative densities of the prepared specimens reach approximately 97% and are identified as cubic based on X-ray diffraction analyses. The thermoelectric properties are evaluated between 100°C and 300°C via electrical conductivity, Seebeck coefficient, and thermal conductivity. Compared with PbTe ingot, the reduction of the thermal conductivities by more than 30% is verified via phonon scattering at the grain boundaries, which thus contributes to the increase in the figure of merit.
        4,000원
        8.
        2017.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spark plasma sintering (SPS). To examine the influence of the milling atmosphere on the microstructure and thermo-electric (TE) properties, a p-type Bi-Sb-Te composite powder is mechanically alloyed in the presence of argon and air atmospheres. The oxygen content increases to 55% when the powder is milled in the air atmosphere, compared with argon. All grains are similar in size and uniformly, distributed in both atmospheric sintered samples. The Seebeck coefficient is higher, while the electrical conductivity is lower in the MA (Air) sample due to a low carrier concentration compared to the MA (Ar) sintered sample. The maximum figure of merit (ZT) is 0.91 and 0.82 at 350 K for the MA (Ar) and MA (Air) sintered samples, respectively. The slight enhancement in the ZT value is due to the decrease in the oxygen content during the MA (Ar) process. Moreover, the combination of mechanical alloying and SPS process shows a higher hardness and density values for the sintered samples.
        4,000원
        9.
        2017.08 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        In this work, the effects of hydrogen reduction on the microstructure and thermoelectric properties of (GeTe)0.85(AgSbTe2)0.15 (TAGS-85) were studied by a combination of gas atomization and spark plasma sintering. The crystal structure and microstructure of TAGS-85 were characterized by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The oxygen content of both powders and bulk samples were found to decrease with increasing reduction temperature. The grain size gradually increased with increasing reduction temperature due to adhesion of fine grains in a temperature range of 350 to 450 °C. The electrical resistivity was found to increase with reduction temperature due to a decrease in carrier concentration. The Seebeck coefficient decreased with increasing reduction temperature and was in good agreement with the carrier concentration and carrier mobility. The maximum power factor, 3.3 × 10−3 W/mK2, was measured for the non-reduction bulk TAGS-85 at 450 °C.
        4,000원
        10.
        2017.08 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        V-substituted SrTiO3 thermoelectric oxide materials were fabricated by the conventional solid state reaction method. From X-ray diffraction pattern analysis, it can be clearly seen that almost every vanadium atom incorporated into the SrTiO3 provided charge carriers. The electrical conductivity σ, Seebeck coefficient S, and thermal conductivity k were investigated in a high temperature regime above 1000 K. The addition of vanadium significantly reduced the thermal conductivity and enhanced the Seebeck coefficient, as well as the electrical conductivity, thus enhancing the ZT value. A maximum ZT value of 0.084 at 673 K was observed for the sample with 1.0 mole% of vanadium substitution. In this study, the reason for the enhanced thermoelectric properties via vanadium addition was also investigated.
        4,000원
        11.
        2017.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this work, p-type Bi−Sb−Te alloys powders are prepared using gas atomization, a mass production powder preparation method involving rapid solidification. To study the effect of the sintering temperature on the microstructure and thermoelectric properties, gas-atomized powders are consolidated at different temperatures (623, 703, and 743 K) using spark plasma sintering. The crystal structures of the gas-atomized powders and sintered bulks are identified using an X-ray diffraction technique. Texture analysis by electron backscatter diffraction reveals that the grains are randomly oriented in the entire matrix, and no preferred orientation in any unique direction is observed. The hardness values decrease with increasing sintering temperature owing to a decrease in grain size. The conductivity increases gradually with increasing sintering temperature, whereas the Seebeck coefficient decreases owing to increases in the carrier mobility with grain size. The lowest thermal conductivity is obtained for the bulk sintered at a low temperature (603 K), mainly because of its fine-grained microstructure. A peak ZT of 1.06 is achieved for the sample sintered at 703 K owing to its moderate electrical conductivity and sustainable thermal conductivity.
        4,000원
        12.
        2016.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        4,000원
        13.
        2016.08 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Graphene oxide (GO) powder processed by Hummer's method is mixed with p-type Bi2Te3 based thermoelectric materials by a high-energy ball milling process. The synthesized GO-dispersed p-type Bi2Te3 composite powder has a composition of Bi0.5Sb1.5Te3 (BSbT), and the powder is consolidated into composites with different contents of GO powder by using the spark plasma sintering (SPS) process. It is found that the addition of GO powder significantly decreases the thermal conductivity of the pure BSbT material through active phonon scattering at the newly formed interfaces. In addition, the electrical properties of the GO/BSbT composites are degraded by the addition of GO powder except in the case of the 0.1 wt% GO/BSbT composite. It is found that defects on the surface of GO powder hinder the electrical transport properties. As a result, the maximum thermoelectric performance (ZT value of 0.91) is achieved from the 0.1% GO/BSbT composite at 398 K. These results indicate that introducing GO powder into thermoelectric materials is a promising method to achieve enhanced thermoelectric performance due to the reduction in thermal conductivity.
        4,000원
        14.
        2016.04 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The recent rise in applications of thermoelectric materials has attracted interest in studies toward the fabrication of thermoelectric materials using mass production techniques. In this study, we successfully fabricate n-type Bi2Te2.7Se0.3 material by a combination of mass production powder metallurgy techniques, gas atomization, and spark plasma sintering. In addition, to examine the effects of hydrogen reduction in the microstructure, the thermoelectric and mechanical properties are measured and analyzed. Here, almost 60% of the oxygen content of the powder are eliminated after hydrogen reduction for 4 h at 360°C. Micrographs of the powder show that the reduced powder had a comparatively clean surface and larger grain sizes than unreduced powder. The density of the consolidated bulk using as-atomized powder and reduced atomized powder exceeds 99%. The thermoelectric power factor of the sample prepared by reduction of powder is 20% better than that of the sample prepared using unreduced powder.
        4,000원
        15.
        2016.04 KCI 등재 구독 인증기관 무료, 개인회원 유료
        P-type ternary Bi0.5Sb1.5Te3 alloys are fabricated via mechanical alloying (MA) and spark plasma sintering (SPS). Different ball sizes are used in the MA process, and their effect on the microstructure; hardness, and thermoelectric properties of the p-type BiSbTe alloys are investigated. The phases of milled powders and bulks are identified using an X-ray diffraction technique. The morphology of milled powders and fracture surface of compacted samples are examined using scanning electron microscopy. The morphology, phase, and grain structures of the samples are not altered by the use of different ball sizes in the MA process. Measurements of the thermoelectric (TE) transport properties including the electrical conductivity, Seebeck coefficient, and power factor are measured at temperatures of 300- 400 K for samples treated by SPS. The TE properties do not depend on the ball size used in the MA process.
        4,000원
        16.
        2015.08 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Bi2Te3 related compounds show the best thermoelectric properties at room temperature. However, n-type Bi2Te2.7Se0.3 showed no improvement on ZT values. To improve the thermolectric propterties of n-type Bi2Te2.7Se0.3, this research has Cu-doped n-type powder. This study focused on effects of Cu-doping method on the thermoelectric properties of n-type materials, and evaluated the comparison between the Cu chemical and mechanical doping. The synthesized powder was manufactured by the spark plasma sintering(SPS). The thermoelectric properties of the sintered body were evaluated by measuring their Seebeck coefficient, electrical resistivity, thermal conductivity, and hall coefficient. An introduction of a small amount of Cu reduced the thermal conductivity and improved the electrical properties with Seebeck coefficient. The authors provided the optimal concentration of Cu0.1Bi1.99Se0.3Te2.7. A figure of merit (ZT) value of 1.22 was obtained for Cu0.1Bi1.9Se0.3Te2.7 at 373K by Cu chemical doping, which was obviously higher than those of Cu0.1Bi1.9Se0.3Te2.7 at 373K by Cu mechanical doping (ZT=0.56) and Cu-free Bi2Se0.3Te2.7 (ZT=0.51).
        4,000원
        17.
        2015.02 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        The porous Mg3Sb2 based compounds with 60~70% of relative density were prepared by powder compaction at room temperature and reactive liquid phase sintering at 1023 K for 4hrs. The stoichiometric Mg3Sb2 compounds were synthesized from elemental Sb and Mg powder in the mixing range of 61~63 at% Mg. The increased scattering effect due to the micro-pores reduced the mobility of the charge carrier and the phonon, which caused the electrical conductivity and the thermal conductivity to decrease, respectively. But the scattering effect was greater for the electrical conductivity than for the thermal conductivity. Excess Mg alloyed in the Mg3Sb2 compounds decreased the electrical conductivity, but had no effect on the thermal conductivity. On the other hand, the large increase of the Seebeck coefficient was the result of a decrease in the charge carrier density due to the excess Mg. Dimensionless figure of merit of the porous Mg3Sb2 compound reached a maximum value of 0.28 at 61 at% Mg. The obtained value was similar to that of Mg3Sb2 compounds having little pores.
        4,000원
        18.
        2013.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Carbon nanotube-dispersed bismuth telluride matrix (CNT/Bi2Te3) nanopowders were synthesized by chem- ical routes followed by a ball-milling process. The microstructures of the synthesized CNT/Bi2Te3 nanopowders showed the characteristic microstructure of CNTs dispersed among disc-shaped Bi2Te3 nanopowders with as an average size of 500 nm in-plane and a few tens of nm in thickness. The prepared nanopowders were sintered into composites with a homogeneous dispersion of CNTs in a Bi2Te3 matrix. The dimensionless figure-of-merit of the composite showed an enhanced value compared to that of pure Bi2Te3 at the room temperature due to the reduced thermal conductivity and increased electrical conductivity with the addition of CNTs.
        4,000원
        19.
        2013.02 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Mg3-xZnxSb2 powders with x = 0-1.2 were fabricated by mechanical alloying in a planetary ball mill with a speed of 350 rpm for 24 hrs and then hot pressed under a pressure of 70 MPa at 773 K for 2 hrs. It was found that there were systematic shifts in the X-ray diffraction peaks of Mg3Sb2 (x = 0) toward a higher angle with increasing Zn for both the powder and the bulk sample and finally the phase of Mg1.86Zn1.14Sb2 was formed at the Zn content of x = 1.2. The Mg3-xZnxSb2 compounds had nano-sized grains of 21-30 nm for the powder and 28-66 nm for the hot pressed specimens. The electrical conductivity of hot pressed Mg3-xZnxSb2 increased with increasing Zn content and temperature from 33 Sm-1 for x = 0 to 13,026 Sm-1 for x = 1.2 at 323 K. The samples for all the compositions from x = 0 to x = 1.2 had positive Seebeck coefficients, which decreased with increasing Zn content and temperature, which resulted from the increased charge carrier concentration. Most of the samples had relatively low thermal conductivities comparable to the high performance thermoelectric materials. The dimensionless figure of merit of Mg3-xZnxSb2 was directly proportional to the Zn content except for the compound with Zn = 1.2 at high temperature. The Mg3-xZnxSb2 compound with Zn = 0.8 had the largest value of ZT, 0.33 at 723 K.
        4,000원
        20.
        2012.06 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        Bismuth antimony telluride (BiSbTe) thermoelectric materials were successfully prepared by a spark plasma sintering process. Crystalline BiSbTe ingots were crushed into small pieces and then attrition milled into fine powders of about 300 nm ~ 2μm size under argon gas. Spark plasma sintering was applied on the BiSbTe powders at 240, 320, and 380˚C, respectively, under a pressure of 40 MPa in vacuum. The heating rate was 50˚C/min and the holding time at the sintering temperature was 10 min. At all sintering temperatures, high density bulk BiSbTe was successfully obtained. The XRD patterns verify that all samples were well matched with the Bi0.5Sb1.5Te3. Seebeck coefficient (S), electric conductivity (σ) and thermal conductivity (k) were evaluated in a temperature range of 25~300˚C. The thermoelectric properties of BiSbTe were evaluated by the thermoelectric figure of merit, ZT (ZT = S2σT/k). The grain size and electric conductivity of sintered BiSbTe increased as the sintering temperature increased but the thermal conductivity was similar at all sintering temperatures. Grain growth reduced the carrier concentration, because grain growth reduced the grain boundaries, which serve as acceptors. Meanwhile, the carrier mobility was greatly increased and the electric conductivity was also improved. Consequentially, the grains grew with increasing sintering temperature and the figure of merit was improved.
        4,000원
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