• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.40-45
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• 2016

Recently, $Bi_2Te_3$-based alloys are the best thermoelectric materials near to room temperature, so it has been researched to achieve increased figure of merit(ZT). Ternary compounds such as Bi-Te-Se and Bi-Sb-Te have higher thermoelectric property than binary compound Bi-Te and Sb-Te, respectively. Compared to DC plating method, pulsed electrodeposition is able to control parameters including average current density, and on/off pulse time etc. Thereby the morphology and properties of the films can be improved. In this study, we electrodeposited n-type ternary Cu-doped $Bi_2(Te-Se)_3$ thin film by modified pulse technique at room temperature. To further enhance thermoelectric properties of $Bi_2(Te-Se)_3$ thin film, we optimized Cu doping concentration in $Bi_2(Te-Se)_3$ thin film and correlated it to electrical and thermoelectric properties. Thus, the crystal, electrical, and thermoelectric properties of electrodeposited $Bi_2(Te-Se)_3$ thin film were characterized the XRD, SEM, EDS, Seebeck measurement, and Hall effect measurement, respectively. As a result, the thermoelectric properties of Cu-doped $Bi_2(Te-Se)_3$ thin films were observed that the Seebeck coefficient is $-101.2{\mu}V/K$ and the power factor is $1412.6{\mu}W/mK^2$ at 10 mg of Cu weight. The power factor of Cu-doped $Bi_2(Te-Se)_3$ thin film is 1.4 times higher than undoped $Bi_2(Te-Se)_3$ thin film.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.49-54
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• 2010

The n-type $Bi_2(Te,Se)_3$ powders were fabricated by melting/grinding method and were hot-pressed in order to compare thermoelectric properties of the hot-pressed specimens with those of the $Bi_2(Te,Se)_3$ ingot. Effects of mechanical milling treatment of the $Bi_2(Te,Se)_3$ powders on thermoelectric characteristics of a hot-pressed specimen were also examined. The hot-pressed $Bi_2(Te,Se)_3$ exhibited power factors of $27.3{\sim}32.3{\times}10^{-4}W/m-K^2$ which were superior to $24.2{\times}10^{-4}W/m-K^2$ of the ingot. The $Bi_2(Te,Se)_3$, hot-pressed after mechanical milling treatment of the powders, possessed a non-dimensional figure-of-merit of 1.02 at $100^{\circ}C$ and exhibited extrinsic-intrinsic transition at $130^{\circ}C$.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.62-66
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• 2003

The preparation of n-type thermoelectric material of Bi₂ Te/sub 2.55/Se/sub 0.45/ doped with CuBr₂ was carried out using a vertical gradient freezing method. With this method, unidirectional solidified Bi₂Te/sub 2.55/Se/sub 0.45/ has been obtained. XRD analysis demonstrated that Bi₂/sub 2.55/Se/sub 0.45/ 5 ingot has grown with prefer orientation of (0 1 5) face. Seebeck coefficient and electrical conductivity were measured as functions of temperature in the range of 373 K to 523 K on the sample which prepared via VGF method.

• Korean Journal of Materials Research
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• v.8 no.5
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• pp.408-412
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• 1998

Thermoelectric properties of Bi$_{2}$(Te$_{1-x}$Se$_{ x}$)$_{3}$(0.05$\leq$x$\leq$0.25) prepared by mechanical alloying and hot pressing, were investigated. Contrary to the p-type behavior of single crystals, the hot-pressed Bi$_{2}$(Te$_{1-x}$Se$_{ x}$)$_{3}$ exhibited ntype conduction without addition of donor dopant. When $Bi_2(Te_{0.85}Se_{0.15})_3$powders were annealed in (50% $H_2$ + 50% Ar) atmosphere, the hot-pressed specimen exhibited a positive Seebeck coefficient due to the reduction of the electron concentration by removal of the oxide layer on the powder surface and annealing-out of the excess Te vacancies. Among the Bi$_{2}$(Te$_{1-x}$Se$_{ x}$)$_{3}$fabricated by mechanical alloying and hot pressing, $Bi_2(Te_{0.85}Se_{0.15})_3$ exhibited a maximum figure-of-merit of 1.92 $\times$ $lO^{-3}$/K.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.349-354
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• 1999

The temperature dependences of the Hall coefficient, carrier mobility, electrical resistivity, Seebeck coefficient, thermal conductivity, and figure-of-merit of the undoped and $CdI_2$-doped 90% $Bi_2Te_3-10% Bi_2Se_3$, single crystals, grown by the Bridgman method, have been characterized at temperatures ranging from 77K to 600K. The saturated carrier concentration and degenerate temperature of the undoped 90% $Bi_2Te_3-10% Bi_2Se_3$ single crystal are $5.85\times10_{18}cm^{-3}$ and 127K, respectively. The scattering parameter of the 90% $Bi_2Te_3-10% Bi_2Se_3$ single crystal is determined to b -0.23, and the electron mobility to hole mobility ratio ($\mu_e/\mu_h)$ is 1.45. The bandgap energy at 0K of the 90% <$Bi_2Te_3-10% Bi_2Se_3$ single crystal is 0.200 eV. Adding $CdI_2$as a donor dopant, a maximum figure-of-merit of $3.2\times10^{-3}/K$$CdI_2$-doped specimen.

• 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.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.40-49
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• 1997

$Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ thermoelectric matcrials havc 11et:n fahricxted hy mechanical alloying and hot pressing methods. Microstructure and thermoelectric properties of the hot 11resseii $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ have been investigated Lvith variations of hot pressing temperature and dopmt atltiition Formation of $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ alloy powders was completed by mechanical alloying of the as-mixed Ri. Te, arid Sc grmules of ~3.6mm size for 3 hours at ball-to-material weight ratio of 5 : 1. Figure of merit of $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ was markedly incrcwieti hy hot pressing at temperatures above $450^{\circ}C$, and value of $1.9{\times}10^{-3}/K$ was obtained for the specimen hot pressed at $550^{\circ}C$. With addition of 0.015 wt% Ri as acceptor dopant, figure of merit ol $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ hot pressed $550^{\circ}C$$2.1{\times}10^{-3}/K$.

• 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 $300^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.135-139
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• 2015

$Bi_2Te_3-Bi_2Se_3$ alloy which is typical n-type thermoelectric material were grown by traveling heater method (THM) technique. We investigate the effect of the composition of $100-x(Bi_2Te_3)-x(Bi_2Se_3)$ and doping of n-type dopants such as $SbI_3$ and $CdCl_2$. Maximum figure of merit of $Bi_2Te_3-Bi_2Se_3$ alloy was observed with $CdCl_2$ 0.1 wt% (Z: $2.73{\times}10^{-3}/K$) and $SbI_3$ 0.05 wt% (Z: $2.29{\times}10^{-3}/K$). Deviation along the length of $Bi_2Te_3-Bi_2Se_3$ ingot grown by THM method is low, which indicates that the ingot is very homogenized. Also we observed the close relationship of between anisotropy ratio and dopant in the $90(Bi_2Te_3)-10(Bi_2Se_3)$ alloys. And we confirmed the fact that anisotropy ratio exerts thermoelectric performance in $Bi_2Te_3$ based n-type thermoelectric material.

• Proceedings of the Korean Vacuum Society Conference
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• 1995.02a
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• pp.67-67
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• 1995