Sb가 결핍된 N형 Skutterudite Co₄Sb₁₂의 열전 특성

탁장렬,정민석,이나영,남우현,서원선,조중영,Tak, Jang-Yeul,Van Du, Nguyen,Jeong, Min Seok,Lee, NaYoung,Nam, Woo Hyun,Seo, Won-Seon,Cho, Jung Young 한국전기전자재료학회 2019 전기전자재료학회논문지 Vol.32 No.6

In this study, we investigate the effect of an Sb-deficiency on the thermoelectric properties of double-filled n-type skutterudite ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$). Samples were prepared by encapsulated induction melting, consecutive long-time annealing, and finally spark plasma sintering processes. The Sb-deficient sample contained a $CoSb_2$ secondary phase. Both the double-filled n-type skutterudite pristine and Sb-deficient samples showed metallic behavior in electrical conductivity with increasing temperature. The carrier concentration of the Sb-deficient sample decreased compared with that of the pristine sample. Due to a decrease in carrier concentration, the Sb deficient sample showed decreased electrical conductivity and an increased Seebeck coefficient compared with the conductivity and coefficient of the pristine sample. Furthermore, the Sb deficient sample showed an increase in the power factor (${\sigma}{\cdot}S^2$); the power factor maximum shifted to athe lower temperature side than ones of the pristine sample. As a result, the Sb-deficient sample represents an improved average figure of merit (ZT) and a $ZT_{max}$ temperature lower than that of the pristine sample. Therefore, we propose that Sb-deficient double-filled n-type skutterudite thermoelectric material ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$) be used in the 573~673 K temperature range.

용융방사법으로 제작된 Cu1.98Se의 열전특성

탁장렬,임영수 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.7

Cu2Se exhibits very low thermal conductivity and the origin is known to be the "liquid-like" behavior of Cu ions around the sub-lattice of Se. Due to its very high ZT, research interest in the thermoelectric properties of this material has been increasing rapidly. However, most studies have used a conventional melting process, and, to the best of our knowledge, the melt-spinning process has not yet been employed to fabricate the Cu2Se compound. Herein, we report the thermoelectric properties of Cu1.98Se compounds prepared by melt-spinning. Depending on the cooling rate, we could control the microstructure of the melt-spun Cu1.98Se ribbons successfully. The melt-spun ribbons were consolidated using a hot press, and the thermoelectric properties of the compounds were characterized. Although the electrical conductivity of the compound decreased as compared with the Cu1.98Se compound prepared by the conventional method, an increase in Seebeck coefficient led to an improved power factor in the compound prepared by melt-spinning. Furthermore, a reduction in thermal conductivity due to the reduced contribution of electronic to total conductivity resulted in the enhancement of ZT values in the Cu1.98Se compound.

Sb가 결핍된 N형 Skutterudite Co4Sb12의 열전 특성

탁장렬,Nguyen Van Du,정민석,이나영,남우현,서원선,조중영 한국전기전자재료학회 2019 전기전자재료학회논문지 Vol.32 No.6

In this study, we investigate the effect of an Sb-deficiency on the thermoelectric properties of double-filled n-type skutterudite (In0.05Yb0.15Co4Sb12-x). Samples were prepared by encapsulated induction melting, consecutive long-time annealing, and finally spark plasma sintering processes. The Sb-deficient sample contained a CoSb2 secondary phase. Both the double-filled n-type skutterudite pristine and Sb-deficient samples showed metallic behavior in electrical conductivity with increasing temperature. The carrier concentration of the Sb-deficient sample decreased compared with that of the pristine sample. Due to a decrease in carrier concentration, the Sb deficient sample showed decreased electrical conductivity and an increased Seebeck coefficient compared with the conductivity and coefficient of the pristine sample. Furthermore, the Sb deficient sample showed an increase in the power factor (σ⋅S2); the power factor maximum shifted to athe lower temperature side than ones of the pristine sample. As a result, the Sb-deficient sample represents an improved average figure of merit (ZT) and a ZTmax temperature lower than that of the pristine sample. Therefore, we propose that Sb-deficient double-filled n-type skutterudite thermoelectric material (In0.05Yb0.15Co4Sb12-x) be used in the 573~673 K temperature range. 본 연구는 이중 충진 된 n 형 Skutterudite에서 Sb 결핍 조성을 합성하여 열전 특성을 알아보았다. 밀폐유도용해 및 스파크 플라즈마 소결 공정에 의해 샘플을 제조 하였다. 이중 충진 된 n 형 skutterudite pristime 샘플과 Sb가 결핍된 샘플은 모두 온도가 증가함에 전도도가 낮아지는 금속 거동의 전기 전도성을 보여 주었다. 또한, 캐리어 농도 감소로 진성 반도체의 영향이 더 낮은 온도 대역부터 나타났으며, 이러한 결과로 파워 펙터의 최대치는 증가하고, 파워 펙터 최대치의 온도 또한 낮아졌다. 열전도도는 소폭 감소하였으며, 이로 인한 열전 성능 지수 (ZT)가 평균적으로 증가하였다. 결과적으로, Sb 결핍 샘플은 pristine 샘플 보다 평균 성능 지수 (ZT) 를 향상시켰고, ZTmax 온도를 낮추었다. 우리는 본 연구를 통하여, 573 K ~ 673 K 온도 범위에서 사용할 열전 재료로 Sb 결핍된 n형 CoSb3 를 제안한다.

Grain 크기 조절을 통한 n-Type Bi2Te3 열전 소재 특성 향상

이나영,예성욱,Rahman Jamil Ur,탁장렬,조중영,서원선,신원호,남우현,노종욱 한국마이크로전자및패키징학회 2021 마이크로전자 및 패키징학회지 Vol.28 No.4

The enhancement of thermoelectric figure of merit was achieved by the simple processes of sieving and high energy ball milling, respectively, which are enable to reduce the grain size of n-type Bi2Te3 thermoelectric materials. By optimizing the grain size, the electrical conductivities and thermal conductivities were controlled. In this study, spark plasma sintering was employed for hindering the grain growth during the sintering process. The thermoelectric figure of merit was measured to be 0.78 in the samples with 30 min high energy ball milling process. Notably, this value was 40 % higher than that of pristine Bi2Te3 sample. This result shows the properties of thermoelectric materials can be readily controlled by optimization of grain size via simple ball milling process. 본 연구에서는 체가름과 고에너지 볼 밀링 공정이 n-type Bi2Te3 열전 재료의 전기적 및 열적 수송 특성에 미치는 영향을 검토하였다. 입자 크기가 감소한 분말의 특성을 유지하기 위하여 짧은 시간 안에 소결이 가능한 방전 플라즈마 소결 공정 (spark plasma sintering, SPS)을 진행하였다. 그 결과, 밀링 처리를 진행한 소결체의 열전 성능지수가 향상되었으며, 30분동안 고에너지 볼 밀링 공정을 거친 샘플이 425 K에서 0.78의 최대 열전 성능지수를 가지는 것을 확인하였다. 이는 손쉬운 공정을 이용하여 결정립 크기 감소를 통한 phonon의 격자 산란을 효과적으로 유도한 결과이다. 동시에 n-type Bi2Te3에서 anti-site defect와 같은 결함을 제어함으로써 캐리어 농도를 증가시킬 수 있음을 본 연구를 통하여 확인하였다.

매트랩/시뮬링크 simulation model을 이용한 열전 모듈의 효율 예측

이나영,예성욱,Rahman Jamil Ur,탁장렬,조중영,서원선,신원호,Walter Commerell,남우현,노종욱 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.11

Development new high-performance thermoelectric materials for more efficient power generation systems and eco-friendly refrigerating systems has been challenging. Over the past few decades, thermoelectric studies have been focused on increasing the thermoelectric properties of materials. However, for conventional applications, developing of thermoelectric devices or modules with lower cost and simpler fabrication processes is also important. Simulation models that can predict the thermoelectric efficiency of modules using the thermoelectric properties of materials are needed for this purpose. In this study, we developed a simple model for calculating the efficiency of thermoelectric modules using MATLAB/Simulink. In this model, the temperature difference between the hot source and heat sink was fixed to ensure the precise comparisons of thermoelectric efficiency. The electric resistivity and Seebeck coefficient of thermoelectric materials was used in order to predict the efficiency of the thermoelectric modules. Then, the efficiency of the thermoelectric modules was verified using measured values which had been reported in prior experimental works. In this study, the simulated values were higher than the real thermoelectric effiency values. To address this, the simulations should consider the thermal resistance or electric contact resistance between the thermoelectric materials and electrodes.