• 한국분말재료학회지
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• 제24권5호
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• pp.357-363
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• 2017

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.

• 한국재료학회지
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• 제10권3호
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• pp.246-252
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• 2000

기계적 합금화 공정을 이용하여 제조한 $Bi_2(Te_{0.85}Se_{0.15})_3$ 가압소결체의 가압소결온도에 따른 열전특성을 분석하였다. $Bi_2(Te_{0.85}Se_{0.15})_3$ 가압소결체는 $300^{\circ}C$에서 $550^{\circ}C$ 범위의 가압소결온도에 무관하게 n형 전도를 나타내었다. $Bi_2(Te_{0.85}Se_{0.15})$ 합금분말을 (50% $H_2+50%$ Ar) 분위기에서 환원처리시, 분말 표면의 산화층 제거 및 과잉 Te 공격자의 소멸에 기인한 전자 농도의 감소로 가압소결체의 Seebeck 계수가 양의 값으로 변화하였다. $450^{\circ}C$ 이상의 온도에서 가압소결시 가압소결온도의 증가에 따라 $Bi_2(Te_{0.85}Se_{0.15})$ 합금의 성능지수가 증가하였으며, $550^{\circ}C$에서 가압소결시 $1.92{\times}10^{-3}/K$의 최대성능지수를 얻을 수 있었다.

• 한국분말재료학회지
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• 제24권2호
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• pp.141-146
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• 2017

$Bi_2Te_3$ powders are recovered by wet chemical reduction for waste n-type thermoelectric chips, and the recovered particles with different morphologies are prepared using various surfactants such as cetyltrimethylammonium bromide (CTAB), sodium dodecylbenzenesulfonate (SDBS), and ethylenediaminetetraacetic acid (EDTA). When citric acid is added as the surfactant, the shape of the aggregated particles shows no distinctive features. On the other hand, rod-shaped particles are formed in the sample with CTAB, and sheet-like particles are synthesized with the addition of SDBS. Further, particles with a tripod shape are observed when EDTA is added as the surfactant. The growth mechanism of the particle shapes depending on the surfactant is investigated, with a focus on the nucleation and growth phenomena. These results help to elucidate the intrinsic formation mechanism of the rod, plate, and tripod structures of the $Bi_2Te_3$ recovered by the wet reduction process.

• 한국분말재료학회지
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• 제24권2호
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• pp.115-121
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• 2017

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.

• 열처리공학회지
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• 제31권3호
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• pp.126-134
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• 2018

In this research, we produced polycrystalline n-type $Bi_2Te_{2.7}Se_{0.3}$ powder using water atomization. To obtain full benefit through water atomized powder, we have implemented spark plasma sintering and hot extrusion for powder compaction. The microstructure and thermoelectric properties were investigated and compared. The average grain size of SPS and extruded bulks were 3.08 and $3.86{\mu}m$ respectively. The extruded material microstructure contains layered grains with less grain boundaries and its counter-part SPS displays dense packed grains with high grain boundaries. Among both bulks, extrusion sample exhibited high power factor (PF) of $2.96{\times}10^{-3}Wm^{-1}K^{-2}$ which is 38% higher than SPS ($2.14{\times}10^{-3}$) bulk sample. Due to variations in grain size and grain boundaries, the SPS bulk shows low thermal conductivity than extruded bulk. However, the extruded bulk sample exhibited a peak ZT of 0.69 at 400 K, which is 19% higher than SPS bulk sample, due to its higher power factor.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2004년도 International Symposium on Powder Materials and Processing
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• pp.107-108
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• 2004

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2003년도 international symposium on advanced powder metallurgy
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• pp.121-122
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• 2003

• 마이크로전자및패키징학회지
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• 제18권4호
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• pp.55-61
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• 2011

n형 $Bi_2(Te_{0.9}Se_{0.1})_3$ 분말을 기계적 합금화 공정으로 제조하고 텅스텐 분말을 분산시켜 $550^{\circ}C$에서 30분간 가압소결 후, 텅스텐 함량에 따른 열전특성을 분석하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체의 상온 출력인자는 $21.9{\times}10^{-4}$ $W/m-K^2$ 이었으며, 1 vol% 텅스텐 분말의 분산에 의해 상온 출력인자가 $30.5{\times}10^{-4}$ $W/m-K^2$로 증가하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체는 상온에서 0.52의 무차원 성능지수를 나타내었으며, 1 vol% 텅스텐 분말의 분산에 의해 무차원 성능지수가 0.95로 크게 향상되었다.

• 한국재료학회지
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• 제33권7호
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• pp.295-301
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• 2023

Thermoelectric (TE) energy harvesting, which converts available thermal resources into electrical energy, is attracting significant attention, as it facilitates wireless and self-powered electronics. Recently, as demand for portable/wearable electronic devices and sensors increases, organic-inorganic TE films with polymeric matrix are being studied to realize flexible thermoelectric energy harvesters (f-TEHs). Here, we developed flexible organic-inorganic TE films with p-type Bi_0.5Sb_1.5Te₃ powder and polymeric matrices such as poly(3,4-eethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and poly (vinylidene fluoride) (PVDF). The fabricated TE films with a PEDOT:PSS matrix and 1 wt% of multi-walled carbon nanotube (MWCNT) exhibited a power factor value of 3.96 µW·m^-1·K^-2 which is about 2.8 times higher than that of PVDF-based TE film. We also fabricated f-TEHs using both types of TE films and investigated the TE output performance. The f-TEH made of PEDOT:PSS-based TE films harvested the maximum load voltage of 3.4 mV, with a load current of 17.4 µA, and output power of 15.7 nW at a temperature difference of 25 K, whereas the f-TEH with PVDF-based TE films generated values of 0.6 mV, 3.3 µA, and 0.54 nW. This study will broaden the fields of the research on methods to improve TE efficiency and the development of flexible organic-inorganic TE films and f-TEH.

• 한국분말재료학회지
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• 제17권2호
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• pp.136-141
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• 2010

Bismuth-telluride based $(Bi_{0.2}Sb_{0.8})_2Te_3$ thermoelectric powders were fabricated by two-step planetary milling process which produces bimodal size distribution ranging $400\;nm\;{\sim}\;2\;{\mu}m$. The powders were reduced in hydrogen atmosphere to minimize oxygen contents which cause degradation of thermoelectric performance by decreasing electrical conductivity. Oxygen contents were decreased from 0.48% to 0.25% by the reduction process. In this study, both the as-synthesized and the reduced powders were consolidated by the spark plasma sintering process at $350^{\circ}C$ for 10 min at the heating rate of $100^{\circ}C/min$ and then their thermoelectric properties were investigated. The sintered samples using the reduced p-type thermoelectric powders show 15% lower specific electrical resistivity ($0.8\;m{\Omega}{\cdot}cm$) than those of the as-synthesized powders while Seebeck coefficient and thermal conductivity do not change a lot. The results confirmed that ZT value of thermoelectric performance at room temperature was improved by 15% due to high electric conductivity caused by the controlled oxygen contents present at bismuth telluride materials.