• Journal of Powder Materials
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• v.23 no.2
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• pp.120-125
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• 2016

P-type ternary $Bi_{0.5}Sb_{1.5}Te_3$ 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.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.911-917
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• 2002

0.5 at% $Na_2$Te-doped ($Pb_{0.7}Sn_{0.3}$)Te and ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ powders were fabricated by mechanical alloying process. 0.5 at% Na$_2$Te-doped ($Pb_{0.7}Sn_{0.3}$)Te powders were charged at one end of mold and ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ powders were charged at the other end of a mold. Then these powders were hot-pressed to form p-type ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ functional gradient materials with the segment ratios (the ratio of ($Pb_{0.7}Sn_{0.3}$)Te to ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ ) of 1:2, 1:1, and 2:1. Power generation characteristics of the ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ were measured. When the temperature difference ΔT at both ends of the specimen was larger than $300^{\circ}C$, the ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ with the segment ratios of 1:2 and 1:1 exhibited larger output power than those of the ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ and 0.5 at% $Na_2$ Te-doped ($Pb_{0.7}Sn_{0.3}$)Te alloys. The maximum output power of the ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ predicted with the measured Seebeck coefficient and the estimated electrical resistivity was in good agreement with the measured maximum output power.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1223-1224
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• 2006

The p-type $(Bi_{0.2}Sb_{0.8})_2Te_3/(Pb_{0.7}Sn_{0.3})$Te functional gradient material (FGM) was fabricated by hot-pressing the mechanically alloyed $(Bi_{0.2}Sb_{0.8})_2Te_3$ and the 0.5 at% $Na_2Te-doped$ $(Pb_{0.7}Sn_{0.3})Te$ powders. Also, the n-type $Bi_2(Te_{0.9}Se_{0.1})_3/PbTe$ FGM was processed by hot-pressing the mechanically alloyed $Bi_2(Te_{0.9}Se_{0.1})_3$ and the 0.3 wt% Bi-doped PbTe powders. With ${\Delta}T$ larger than $300^{\circ}C$, the p-type $(Bi_{0.2}Sb_{0.8})_2Te_3/(Pb_{0.7}Sn_{0.3})Te$ FGM exhibited larger thermoelectric output power than those of the $(Bi_{0.2}Sb_{0.8})_2Te_3$ and the 0.5 at% $Na_2Te-doped$ $(Pb_{0.7}Sn_{0.3})Te$ alloys. For the n-type $Bi_2(Te_{0.9}Se_{0.1})_3/PbTe$ FGM, the thermoelectric output power superior to those of the $Bi_2(Te_{0.9}Se_{0.1})_3$ and the 0.3 wt% Bi-doped PbTe was predicted at ${\Delta}T$ larger than $300^{\circ}C$.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.3080-3087
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• 2023

Thermoelectric (TE) materials working in radioisotope thermoelectric generators are irradiated by neutrons throughout its service; thus, investigating the neutron irradiation stability of TE devices is necessary. Herein, the influence of neutron irradiation with fluences of 4.56 × 10¹⁰ and 1 × 10¹³ n/cm² by pulsed neutron reactor on the electrical and thermal transport properties of n-type Bi₂Te_2.7Se_0.3 and p-type Bi_0.5Sb_1.5Te₃ thermoelectric alloys prepared by cold-pressing and molding is investigated. After neutron irradiation, the properties of thermoelectric materials fluctuate, which is related to the material type and irradiation fluence. Different from p-type thermoelectric materials, neutron irradiation has a positive effect on n-type Bi₂Te_2.7Se_0.3 materials. This result might be due to the increase of carrier mobility and the optimization of electrical conductivity. Afterward, the effects of p-type and n-type TE devices with different treatments on the output performance of TE devices are further discussed. The positive and negative effects caused by irradiation can cancel each other to a certain extent. For TE devices paired with p-type Bi_0.5Sb_1.5Te₃ and n-type Bi₂Te_2.7Se_0.3 thermoelectric legs, the generated power and conversion efficiency are stable after neutron irradiation.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.311-352
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• 1996

Peltier 효과를 이용한 열전소자는 열응담 감도가 좋고 선택적 냉각이 가능하며 무소음, 무진동 및 소형화의 장점으로 각종 전자부품의 국부냉각소자로 응용되고 있다. 또한 최근 냉매의 사용없이 냉각이 가능한 열전재료를 이용한 자동차나 가정용 에어컨 및 냉장고 등의 각종 냉방시스템의 개발도 크게 주목을 받고 있다. 기존의 Bi2Te3계 단결정 열전재료는 성능지수는 우수하나, 기계적 취약성에 기인하여 소자가공시 수율 저하가 가장 큰 문제점으로 지적되고 있다. 이와 같은 문제점을 해결하기 위해 최근 단결정에 비해 기계적 강도가 우수한 다결정 열전재료의 제조공정에 관한 연구가 활발히 이루어지고 있으며, 그 일환으로 기계적 합금화법을 이용한 열전재료의 제조공정이 연구되고 있다. 원료금속이 고 에너지 볼-밀 내에서의 연쇄적인 파괴와 압접에 의해 합금분말로 변화되는 기계적 합금화 공정은 상온공정으로 이를 사용하여 다결정 열전재료를 제조시 기존의 다결정 열전재료의 제조공정인 "용해 및 분쇄법'과 비교하여 제조단가를 낮출 수 있는 장점이 있다. 본 연구에서는 전자냉각소자용 열전재료로서 상온부근에서 성능지수가 가장 우수한 p형 (Bi,Sb)2Te3 및 n형 Bi2(Te,Se)3 합금분말을 기계적 합금화 공정으로 제조하여 분말 특성을 분석하였으며, 가압소결 후 열전특성의 변화거동을 연구하였다. 순도 99.99% 이상인 Bi, Sb, Te, Se granule을 (Bi1-xSbx)2Te3 및 Bi2(Te1-ySey)3 조성에 맞게 칭량하여 불과 분말의 무게비 5:1로 강구와 함께 공구강 vial에 장입 후, Spex mixer/mill을 이용하여 기계적 합금화 하였다. 기계적 합금화 공정으로 제조한 분말에 대한 X-선 회절분석과 시차 열분석으로 합금화 정도를 분석하였다. (Bi1-xSbx)2Te3 및 Bi2(Te1-ySey)3 합금분말을 10-5 torr의 진공중에서 300℃∼550℃의 온도로 30분간 가압소결하였다. 가압소결체의 파단면에서의 미세구조를 주사전자현미경으로 관찰하였으며, 상온에서 가압소결체의 열전특성을 측정하였다. (Bi1-xSbx)2Te3의 기계적 합금화에 요구되는 공정시간은 Sb2Te3 함량에 따라 증가하여 x=0.5 조성에서는 4 시간 45분, x=0.75 조성에서는 5 시간, x=1 조성에서는 6 시간 45분의 vibro 밀링이 요구되었다. n형 Bi2(Te1-ySey)3 합금분말의 제조에 요구되는 밀링시간 역시 Bi2Se3 함량 증가에 따라 증가하였으며 Bi2(Te0.95Se0.05)3 합금분말의 제조에는 2시간, Bi2(Te0.9Se0.1)3 및 Bi2(Te0.85Se0.15)3 합금분말의 형성에는 3시간의 bivro 밀링이 요구되었다. 기계적 합금화로 제조한 p형 (Bi0.2Sb0.8)2Te3 및 n형 Bi2(Te0.9Se0.1)3 가압 소결체는 각기 2.9x10-3/K 및 2.1x10-3/K 의 우수한 성능지수를 나타내었다.

• Journal of Powder Materials
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• v.24 no.2
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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.

• Journal of Powder Materials
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• v.24 no.2
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• pp.108-114
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• 2017

We fabricate fine (<$20{\mu}m$) powders of $Bi_{0.5}Sb_{1.5}Te_3$ alloys using a large-scale production method and subsequently consolidate them at temperatures of 573, 623, and 673 K using a spark plasma sintering process. The microstructure, mechanical properties, and thermoelectric properties are investigated for each sintering temperature. The microstructural features of both the powders and bulks are characterized by scanning electron microscopy, and the crystal structures are analyzed by X-ray diffraction analysis. The grain size increases with increasing sintering temperature from 573 to 673 K. In addition, the mechanical properties increase significantly with decreasing sintering temperature owing to an increase in grain boundaries. The results indicate that the electrical conductivity and Seebeck coefficient ($217{\mu}V/K$) of the sample sintered at 673 K increase simultaneously owing to decreased carrier concentration and increased mobility. As a result, a high ZT value of 0.92 at 300 K is achieved. According to the results, a sintering temperature of 673 K is preferable for consolidation of fine (<$20{\mu}m$) powders.