반응성 액상 소결법으로 제조한 다공성 Mg₃Sb₂계 화합물의 열전물성

장경욱,김인기,김일호,Jang, Kyung-Wook,Kim, In-Ki,Kim, Il-Ho 한국재료학회 2015 한국재료학회지 Vol.25 No.2

The porous $Mg_3Sb_2$ 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 $Mg_3Sb_2$ 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 $Mg_3Sb_2$ 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 $Mg_3Sb_2$ compound reached a maximum value of 0.28 at 61 at% Mg. The obtained value was similar to that of $Mg_3Sb_2$ compounds having little pores.

단상 하프-브릿지 PWM 컨버터의 고 역률 제어

장경욱(Kyung-wook Jang),이제현(Je-hyun Lee),최주희(Joo-hee choi),김민상(Min-sang Kim) 대한전기학회 2013 대한전기학회 학술대회 논문집 Vol.2013 No.7

Bi - Sb 합금의 자기 - 열전특성

장경욱(Kyung-Wook Jang),이동희(Dong-Hi Lee) 한국자기학회 1996 한국자기학회 학술연구발표회 논문개요집 Vol.6 No.2

냉간 압축 성형한 Mg₃Sb₂ 열전재료의 고상 반응 소결

김인기,장경욱,오한준,Kim, In-Ki,Jang, Kyung-Wook,Oh, Han-Jun 한국결정성장학회 2014 韓國結晶成長學會誌 Vol.24 No.4

상온 압축 성형 후 고상 반응 소결 공정을 통하여 $Mg_3Sb_2$ 소결체를 제조하고자 하였다. Mg과 Sb의 성분의 몰비와 반응온도에 따른 결정상의 변화를 조사하였다. 773~843 K에서 얻어진 고상반응 소결체들은 전형적인 $Mg_3Sb_2$ 결정상을 형성하였으나 소결체의 위치에 따라 약간 다른 상적 구성을 보였다. 소결체 하단 부위에서 전형적으로 얻어지는 결정상이 얻어졌으며 823 K 온도에서는 Mg : Sb = 3.15 : 1.85 조성일 때, 843 K 온도에서는 Mg의 몰 수가 3.10 이상인 모든 조성에서 ${\alpha}-Mg_3Sb_2$ 상과 정확히 일치하는 결정상이 얻어졌다. 미량 남아있는 Mg 성분은 응고 후 냉각 시 ${\alpha}-Mg_3Sb_2$ 상으로부터 석출된 것으로 보인다. We intended to prepare $Mg_3Sb_2$ compound bodies through solid state reactive sintering after cold-pressing mixtures of elementary Mg and Sb powders and investigated the crystal phases of the sintered bodies according to Mg/Sb mole ratios and reaction temperatures. The $Mg_3Sb_2$ bodies sintered at the temperatures of 773~843 K showed typical crystalline phases of $Mg_3Sb_2$ compounds, but their diffraction angles in XRD patterns were slightly different along with the vertical axis of the bodies obtained. All the bottom parts of the sintered $Mg_3Sb_2$ bodies were composed of the typical crystalline phases of $Mg_3Sb_2$ compounds and their diffraction angles were completely in accord with those of the ${\alpha}-Mg_3Sb_2$ phase, when Mg : Sb = 3.15 : 1.85 at 823 K, or when the Mg moles were greater than or equal to 3.10 at 843 K. It was considered that the slightly remaining Mg phases were formed by precipitation from ${\alpha}-Mg_3Sb_2$ phases during the solidification process of liquid phase.

기계적 합금법으로 제조한 Mg_3-xZn_xSb₂의 열전물성

김인기,장경욱,김일호,Kim, In-Ki,Jang, Kyung-Wook,Kim, Il-Ho 한국재료학회 2013 한국재료학회지 Vol.23 No.2

$Mg_{3-x}Zn_xSb_2$ 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 $Mg_3Sb_2$ (x = 0) toward a higher angle with increasing Zn for both the powder and the bulk sample and finally the phase of $Mg_{1.86}Zn_{1.14}Sb_2$ was formed at the Zn content of x = 1.2. The $Mg_{3-x}Zn_xSb_2$ 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 $Mg_{3-x}Zn_xSb_2$ 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 $Mg_{3-x}Zn_xSb_2$ was directly proportional to the Zn content except for the compound with Zn = 1.2 at high temperature. The $Mg_{3-x}Zn_xSb_2$ compound with Zn = 0.8 had the largest value of ZT, 0.33 at 723 K.

Ar-Kr 혼합가스를 이용한 OLED용 Al 전극 제작

김상모,장경욱,이원재,김경환,Kim, Sang-Mo,Jang, Kyung-Wook,Lee, Won-Jae,Kim, Kyung-Hwan 한국반도체디스플레이기술학회 2007 반도체디스플레이기술학회지 Vol.6 No.4

As preparing electrode for the OLED with the sputtering process, in order to be lower damage of the bottom organic layer and increase the life-time of the OLED, we prepared Al electrode for that by using Facing Targets Sputtering (FTS) system. Al electrode directly deposited on the cell (LiF/EML/HTL/Bottom electrode). Deposition condition was the working gas (Ar, Kr and Ar+Kr) and working gas pressure (1 and 6 mTorr). The film thickness and I-V curve of Al/cell were evaluated by a $\acute{a}$-step profiler and a semiconductor parameter (HP4156A) measurement. The thin film surface image was observed by a Atomic Force Microscope (AFM). In result, in comparison with about 11 [V] of the turn-on voltage of Al/cell with using the pure Ar gas, when Al thin film was deposited using the Ar-Kr mixture gas, the surface morphology was improved in some region and the turn-on voltage of Al/cell could be decreased to about 7 [V].

$Bi_{0.5}Sb_{1.5}Te_{3}/Bi_{2}Te_{2.4}Se_{0.6}$계 박막형 열전발전 소자의 제작과 작동 특성

김일호,장경욱,Kim Il-Ho,Jang Kyung-Wook 한국진공학회 2006 Applied Science and Convergence Technology Vol.15 No.2

[ $Bi_{0.5}Sb_{1.5}Te_{3}/Bi_{2}Te_{2.4}Se_{0.6}$ ]계 박막형 열전발전 소자에 의해 volt 단위의 비교적 고전압에서 microwatt 수준의 출력을 발생시킬 수 있었다. 최대 출력은 온도차와 2차 함수적인 관계가 있었고, 주어진 온도차에서 판형 모듈의 적층수에 비례하여 증가하였다. 판형 모듈의 적층수와 직렬/병렬 연결 조합의 변화에 의해 출력 전압과 전류를 조절할 수 있었다. 온도차에 대한 개회로 전압과 폐회로 전류의 변화는 직선성을 보였다. 개회로 전압은 직렬 연결의 경우 판형 모듈의 수에 의존하였지만, 병렬 연결의 경우에는 의존하지 않았다. 반면, 폐회로 전류는 직렬연결의 경우 판형 모듈의 적층수와 무관하게 일정한 값을 나타내었고, 병렬 연결의 경우 판형 모듈의 적층수에 비례하여 증가하였다. Microwatt power level at relatively high voltage(order of volt) was produced by $Bi_{0.5}Sb_{1.5}Te_{3}/Bi_{2}Te_{2.4}Se_{0.6}$ thin film thermoelectric generators, and maximum output power varied with temperature difference in the square-law relation. Output voltage and current were possible to control by changing the way of electrical connection as well as the number of stacking plate-modules. Variation of open circuit voltage and short circuit current with temperature difference showed a linear relationship. There were, however, some differences in variations; open circuit voltage were dependent on the number of plate-module when connected in series, but it was not for parallel connection. On the other hand, short circuit current showed the opposite behavior to the case of open circuit current.

N형 $Bi_2Te_{2.4}Se_{0.6}$ 박막의 열전 특성에 미치는 두께 및 열처리 효과

김일호,장경욱,Kim Il-Ho,Jang Kyung-Wook 한국진공학회 2005 Applied Science and Convergence Technology Vol.14 No.3

순간 증착법으로 제조한 n형 $Bi_2Te_{2.4}Se_{0.6}$ 박막에 대하여 유효 평균 자유 행로 모델을 적용하여 박막의 두께가 열전 특성에 영향을 미치지 않는 임계 두께를 구하였다. 또한 열처리 전후 전자 농도 및 이동도의 변화를 조사하여 열처리에 의한 열전 특성의 변화를 역구조 결함과 관련하여 설명하였다. Seebeck 계수와 전기 비저항 모두 두레의 역수와 직선적인 관계를 보였으며, 이로부터 구한 평균 자유 행로는 $5120\AA$이었다. 열처리에 의해 전자의 이동도가 증가하였지만, 역구조 결함의 감소로 인해 운반자의 전자 농도가 현저히 감소하여, 결국 전기전도도가 감소하고 Seebeck 계수가 증가하였다 473k에서 1시간 동안 열처리한 Seebeck 계수와 전기전도도는 각각 $-200\;\mu V/k$와 $510\omega^{-1}cm^{-1}$이었다 또한, 열처리에 의해 열전 성능 인자가 상당히 향상되어 $20\times10^{-4}\;W/(mK^2)$를 나타내었다. The effective mean free path model was adopted to examine the thickness effect on the thermoelectric properties of flash-evaporated n-type $Bi_2Te_{2.4}Se_{0.6}$ thin films. Annealing effects on the electron concentration and mobility were also studied, and their variations were analyzed in conjunction with antisite defects. Seebeck coefficient and electrical resistivity versus inverse thickness showed a linear relationship, and the mean free path was found to be $5120\AA$ Electron mobility was increased by annealing treatment and electron concentration was decreased considerably due to reduction of antisite defects, so that electrical conductivity was decreased and Seebeck coefficient was increased. When annealed at 473k for 1 hour, Seebeck coefficient and electrical conductivity were $-200\;\mu V/k\;and\;510\omega^{-1}cm^{-1}$, respectively. Therefore, the thermoelectric power factor was improved to be $20\times10^{-4}\;W/(mK^2)$.

Al 양극산화피막에서 Mn전착에 관한 임피던스 연구

오한준,장경욱,지충수,Oh, Han Jun,Jang, Kyung Wook,Chi, Choong Soo 대한화학회 1999 대한화학회지 Vol.43 No.1

황산용액에서 제조된 Al양극 산화피막 내부로 여러 주파수의 교류전압을 통하여 1 g/L $KMnO_4$ 용액내에서 Mn금속을 전착시켰다. 이때 Al 산화피막 내부로 전착되는 Mn금속의 변화와 산화피막의 특성변화를 임피던스를 통하여 조사했다. 낮은 교류전압의 주파소로 Mn전착된 피막의 임피던스 스펙트럼은 황산에서 제조된 산화피막의 임피던스 스펙트럼과 차이를 나타냈으며, 특히 등가회로에서는 Mn전착의 영향을 나타내는 파라미터인 저항과 축전용량이 추가로 첨가되었다. 또한 Mn전착은 기공성의 산화피막 내부로 진행되는 것으로 나타났다. 또한 기공성의 산화피막의 경우는 저주파를 부하하여 Mn전착시킬 경우 비전도성의 피막성장에 의해 전하이동저항이 높게 나타났다. 이러한 Al산화피막의 특성은 전도도의 구배를 나타내는 파라미터인 Young 임피던스를 통하여 관찰되었다. The Al oxide layer formed in 1M $H_2SO_4$ solution and the influence of applied frequency for electrodeposition of Mn on Al oxide layer were characterized using by impedance spectroscopy. Mn compounds were electrodeposited at the base of pores during deposition with applied low frequency voltage. For the Mn deposited oxide layer at 6OHz and 5Hz in 1 g/L $KMnO_4$ solution, in equivalent circuit for interpretation, the resistance ($R_2$) and capacitance ($C_2$) were considered to be due to deposition of Mn on base of pore. The electrochemical behavior of barrier layer and porous oxide layer on Al have been characterized by capacitance ($C_b$) and Young capacitance ($C_Y$) in equivalent circuit model.

고/액 계면에서의 Peltier 열 측정 및 결정성장에의 응용 II : 측정과 응용

김일호,장경욱,이동희,Kim, Il-Ho,Jang, Kyung-Wook,Lee, Dong-Hi 한국재료학회 1999 한국재료학회지 Vol.9 No.11

$\textrm{Bi}_{2}\textrm{Te}_{3}$의 고/액 계면을 통하여 전류밀도와 방향을 달리 하면서 통전시켰을 때 발생하는 고상, 액상 및 고/액 계면에서의 미소 온도변화를 측정하였다. 이 냉각(가열) 효과는 전류밀도, 통전방향 및 시간에 따라 다르게 나타났으며, 온도변화에 미치는 Peltier 열, Thomson 열 및 Joule 열의 영향을 이론 및 실험에 의해 각각 분류하였다. $\textrm{Bi}_{2}\textrm{Te}_{3}$의 고/액상간의 Peltier 계수는 -1.10$\times\textrm{10}^{-1}$V이었으며, 고상과 액상의 Thomson 계수는 각각 7.31\times\textrm{10}^{-4}V/K와 5.77\times\textrm{10}^{-5}V/K이었다. 직류를 통전하면서 Bi$_2$Te$_3$결정을 성장한 결과, 고상에서 액상으로 통전한 경우, Peltier 냉각에 의한 온도구배의 상승으로 방향성이 향상된 결정을 얻을 수 있었지만, 전류의 방향을 반대로 하면, 결정성 향상에 별 도움을 주지 못하였다. Thermoelectric effects on the temperature changes at the solid- and liquid-phase and its interface were studied by using the unidirectional solidification of $\textrm{Bi}_{2}\textrm{Te}_{3}$. Cooling or heating effects measured with current density. polarity and current passing time were quite different. By separating sole Peltier, Thomson and Joule heat theoretically and experimentally, the Peltier coefficient at the solid/liquid interface of $\textrm{Bi}_{2}\textrm{Te}_{3}$ was -1.10$\times\textrm{10}^{-1}$V, and the Thomson coefficients of solid- and liquid-phase were 7.31\times\textrm{10}^{-4}V/K, 5.77\times\textrm{10}^{-5}V/K, respectively. When D.C. passed from solid-phase to liquid-phase during the crystal growth of $\textrm{Bi}_{2}\textrm{Te}_{3}$ the crystal with more directionality was obtained owing to increase of the temperature gradient in liquid by the Peltier cooling. But in reverse current direction, the crystallinity was not changed significantly.