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Fe/Co 비율 제어를 통한 P형 Nd-Fe-Co-Sb계 Skutterudite 소재의 열전특성 향상
남우현(Woo Hyun Nam),조중영(Jung Young Cho) 한국환경에너지공학회 2023 한국열환경공학회 학술대회지 Vol.2023 No.2
본 연구는 Fe/Co 비율 제어를 통한 P 형 Nd-Fe-Co-Sb계 skutterudite 합금의 열전 특성 향상에 대해 보고한다. 유도 용해 및 급속 응고법을 통해 분말을 제작한 후 방전 플라즈마 소결법 (903 K, 50 MPa, 15 min)으로 Ndo_9fe4-~oxSb12(x = 0.5, 0.75, 1, 1.25, 1.5) 소결체를 합성하였다. 소결체의 XRD 분석을 통해 skutterudite 단일상이 형성되었으며, Fe/Co 비율 조절에 따른 주요 회절 피크의 이동을 통해 Co가 Fe 자리로 효과적으로 치환된 것을 확인하였다. Co 치환량 중가에 따른 캐리어 농도 감소로 전기전도도는 감소하고 제벡계수는 중가하는 경향을 보였으며, 캐리어 농도 최적화에 따라 X = 0.75 샘플에서 최대출력인자(28.9 x 10-4 wm-1K-2 @ 769 K)를 얻었다. 또한, 열전도도는 Co 치환량 중가에 따른 전자 전도 기여분의 저하로 감소하는 경향을 보였다 결과적으로 Fe/Co 비율 조절을 통해 p 형 skutterudite 소재의 전기적 및 열적특성을 동시에 제 어하여 열전성능이 향상되는 것을 확인하였으며. X = 0.75 샘플(Nd0.9Fe3.25CO0.7Sb12.2)에서 1.0(@ 769 K)의 최대 열전성능지수를 보였다.
남우현(Woo Hyun Nam),신원호(Weon Ho Shin),조중영(Jung Young Cho),서원선(Won-Seon Seo) 한국세라믹학회 2019 세라미스트 Vol.22 No.2
Thermoelectric energy conversion has attracted much attention because it can convert heat into electric power directly through solid state device and vice versa. Current research is aimed at increasing the thermoelectric figure of merit (ZT ) by improving the power factor and reducing the thermal conductivity. Although there have been significant progresses in increasing ZT of material systems composed of Bi, Te, Ge, Pb, and etc. over the last few decades, their relatively high cost, toxicity, and the scarcity have hindered further development of thermoelectrics to expand practical applications. In this paper, we review the current status of research in the fields of nanostructured thermoelectric materials with eco-friendly and low cost elements, such as skutterudites and oxides, for mid-high temperature applications, highlighting the strategies to improve thermoelectric performance.
남우현(Woo Hyun Nam),조중영(Jung Young Cho) 한국세라믹학회 2021 세라미스트 Vol.24 No.2
To solve the global energy problems, investigating renewable and environmentally friendly energy resources has considerable significance. Thermoelectric materials and modules have gained considerable attention because they can directly convert waste heat into electric power while leaving no environmental pollution. The performance of the thermoelectric materials can be determined using the dimensionless figure of merit, ZT. However, trade-off relationships between the thermoelectric parameters (electrical conductivity, Seebeck coefficient, and thermal conductivity) have hindered significant improvement of ZT over the decades. Therefore, independent control of the charge and phonon transports is of great importance. In this respect, CoSb3–based skutterudites showing PGEC (phonon-glass electron-crystal) properties are considered to be promising thermoelectric materials for mid-temperature power generation. In this paper, we review the current status of research in the fields of CoSb3-based thermoelectric materials and modularization techniques.
남우현,박영남,김희철,정성원,채성수,서영록,류경환,이원수,신임희,김정범 대한우울조울병학회 2008 우울조울병 Vol.6 No.2
Objectives:The Clinically Useful Depression Outcome Scale (CUDOS) was developed as a brief, clinically useful, reliable, and valid self-report questionnaire for the evaluation of depression outcome. This study aimed to standardize Korean version of the CUDOS (CUDOS-K). Method:The CUDOS was translated into Korean in due process. The subjects were 70 patients, who were undergoing either inpatient or outpatient treatment for major depressive disorder diagnosed by DSM-IV criteria, and 50 normal controls. The subjects, both depressed and normal control, were also administered CUDOS-K, Hamilton Depression Rating Scale-17 (HDRS-17), Korean Version of Center for Epidemiological Studies Depression Scale (CES-D), The Patient Health Questionnaire Nine-item Screener (PHQ-9), and Clinical Global Impression-Severity (CGI-S). Results:The CUDOS-K had high internal consistency (Cronbach’s α=.911) and high split-half reliability (Spearman-Brown formula=.949). The correlation coefficients between the CUDOS-K and CGI-S, HDRS-17, CES-D, and PHQ-9 were respectively high. To identify factor structure of the CUDOS-K, factor analysis was performed. There were five factors above eigen value 1.0, which explained 71.635% of variances. Conclusion:These results suggests that the CUDOS-K is reliable and valid self-report questionnaire for the outcome measurement of depressive symptoms, and it could be a valuable additions to routine clinical practice for the evaluation of depressive symptoms.
고에너지 볼 밀링이 Skutterudite계 CoSb3의 열전 및 전하 전송 특성에 미치는 영향
남우현,이정용,임영수,맹은지,이순일,서원선 한국전기전자재료학회 2015 전기전자재료학회논문지 Vol.28 No.12
본 연구에서는 고에너지 볼 밀링 공정이 In0.2Yb0.1Co4Sb12의 열전 및 전하 전송 특성에 미치는 영향에 대해 알아보았다. 볼 밀링 시간을 5, 10, 20분으로 조절하여 분말을 분쇄하였으며, 분쇄된 분말은 방전 플라즈마 소결법을 이용하여 소결되었다. 볼 밀링의 효과로 인해 소결체는 나노 및 마이크로 크기를 가지는 결정립으로 이루어져 있는 것을 미세구조 관찰을 통해 알아내었다. 고에너지 볼 밀링으로 인한 샘플의 구조적 변형이 충진 원자의 충진량을 감소시키기 때문에, 볼 밀링 시간이 증가할수록 소결체의 캐리어 농도는 감소하였다. 또한 볼 밀링으로 인한 결정립계 영역의 증가로 전자의 결정립계 산란이 증대되어 이동도도 감소하였다. 결과적으로 전기적 특성의 악화로 인해 소결체의 파워펙터 또한 볼 밀링의 시간이 증가할수록 감소하는 경향을 나타내었다. In this study, we investigate the effect of high-energy ball milling on thermoelectric transport properties in double-filled CoSb3 skutterudite (In0.2Yb0.1Co4Sb12). In0.2Yb0.1Co4Sb12 powders are milled using high-energy ball milling for different periods of time (0, 5, 10, and 20 min), and the milled powders are consolidated into bulk samples by spark plasma sintering. Microstructure analysis shows that the high-energy ball milled bulk samples are composed of nano- and micro-grains. Because the filling fractions are reduced in the bulk samples due to the kinetic energy of the high-energy ball milling, the carrier concentration of the bulk samples decreases with the ball milling time. Furthermore, the mobility of the bulk samples also decreases with the ball milling time due to enhanced grain boundary scattering of electrons. Reduction of electrical conductivity by ball milling has a decisive effect on thermoelectric transport in the bulk samples, power factor decreases with the ball milling time.
Pb(Bi1-xSnx)2Te4 (0≤x≤1) 화합물의 열전수송특성 연구
남우현,임영수 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.8
In this study, the effect of Sb incorporation on the thermoelectric transport properties of tetradymite-type Pb(Bi2-xSbx)Te4 (0≤x≤1) compounds is presented. PbBi2Te4 (x = 0) possesses a high electron concentration of ~1.6×1020/cm3 at room temperature and exhibits n-type degenerate semiconductor behavior, in which electrical conductivity decreases and negative Seebeck coefficient increases almost linearly with increasing temperature. For x = 0.5, the electron concentration decreased to ~5.5×1019/cm3 and n-type semiconductor characteristics was observed. When the Sb content increased to x = 1, the majority charge carrier was found to be hole (p ~ 3.3×1019/cm3), thus a change in polarity from n-type to p-type semiconductor was observed. It was suggested that the change in polarity with Sb incorporation observed in this study is due to the formation of a p-type antisite defect, which is formed because the electronegativity of Sb is closer to that of Te than that of Bi. Due to the decrease in charge concentration with the increase in Sb content, it was possible to increase the power factor near room temperature for x = 0.5. However, the overall output factor decreased with increasing x. These results are expected to be helpful in efforts to improve the thermoelectric properties of tetradymite-type homologous compounds through antisite defect control.