• Journal of Powder Materials
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• v.30 no.2
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• pp.123-129
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• 2023

High-temperature and high-pressure post-processing applied to sintered thermoelectric materials can create nanoscale defects, thereby enhancing their thermoelectric performance. Here, we investigate the effect of hot isostatic pressing (HIP) as a post-processing treatment on the thermoelectric properties of p-type Bi_0.5Sb_1.5Te_3.0 compounds sintered via spark plasma sintering. The sample post-processed via HIP maintains its electronic transport properties despite the reduced microstructural texturing. Moreover, lattice thermal conductivity is significantly reduced owing to activated phonon scattering, which can be attributed to the nanoscale defects created during HIP, resulting in an ~18% increase in peak zT value, which reaches ~1.43 at 100℃. This study validates that HIP enhances the thermoelectric performance by controlling the thermal transport without having any detrimental effects on the electronic transport properties of thermoelectric materials.

• Korean Journal of Materials Research
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• v.7 no.5
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• pp.374-380
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• 1997

열전재료 분말을 AI관에 진공봉입하고 형틀가입한 후 소결하는 새로운 방법으로 n형 B $i_{2}$T $e_{2.4}$S $e_{0.6}$를 제조하여 소결조건에 따른 소결성과 열전특성을 조사.분석하였다. AI은 소결시 열전재료와 반응하지 않아 보호 용기로 적합하였으며, 평균입도 195$\mu\textrm{m}$의 분말을 사용하여 성형압 280 MPa, 온도 400에서 50$0^{\circ}C$에서 소결할 경우 성능지수는 1.9x $10^{-3}$K였다.다.

• Korean Journal of Materials Research
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• v.33 no.7
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• pp.295-301
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• 2023

Thermoelectric (TE) energy harvesting, which converts available thermal resources into electrical energy, is attracting significant attention, as it facilitates wireless and self-powered electronics. Recently, as demand for portable/wearable electronic devices and sensors increases, organic-inorganic TE films with polymeric matrix are being studied to realize flexible thermoelectric energy harvesters (f-TEHs). Here, we developed flexible organic-inorganic TE films with p-type Bi_0.5Sb_1.5Te₃ powder and polymeric matrices such as poly(3,4-eethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and poly (vinylidene fluoride) (PVDF). The fabricated TE films with a PEDOT:PSS matrix and 1 wt% of multi-walled carbon nanotube (MWCNT) exhibited a power factor value of 3.96 µW·m^-1·K^-2 which is about 2.8 times higher than that of PVDF-based TE film. We also fabricated f-TEHs using both types of TE films and investigated the TE output performance. The f-TEH made of PEDOT:PSS-based TE films harvested the maximum load voltage of 3.4 mV, with a load current of 17.4 µA, and output power of 15.7 nW at a temperature difference of 25 K, whereas the f-TEH with PVDF-based TE films generated values of 0.6 mV, 3.3 µA, and 0.54 nW. This study will broaden the fields of the research on methods to improve TE efficiency and the development of flexible organic-inorganic TE films and f-TEH.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.17-21
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• 2017

Horizontal thin-film thermoelectric cooler has been simulated using a commercial software (ANSYS Workbench Thermal-electric). The thermoelectric cooler consists of thin-film n-type $Bi_2Te_3$, p-type $Sb_2Te_3$ thermoelectric elements, and Au electrode, respectively. The hot spot was placed under the center of device which represents Joule heating. Numerical analysis was conducted by geometric variable, and a maximum temperature difference of $13^{\circ}C$ was obtained. As from the simulation parameters, we presented an optimized design for high efficiency cooling.

• Proceedings of the Korea Crystallographic Association Conference
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• 2007.11a
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• pp.38-38
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• 2007

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.11a
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• pp.43-43
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• 2004

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1323-1330
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• 2021

This work reported the radiation shielding characteristic of the bismuth titanium vanadium sodium tellurite glass system. The density of the specially-developed glass samples was increased from 2.21 to 4.01 g/cm³ with the addition of Bi₂O₃, despite the fact the molar volume is decease within 85.43-54.79 cm³/mol. The WinXcom program was used to approximate the effect of Bi₂O₃ on the gamma radiation shielding parameters of bismuth titanium vanadium sodium tellurite glasses. The ㎛ values decrease with the increase of Bi₂O₃ concentration. The computed data shows that the glass sample with 20 mol.% of Bi₂O₃ content has the greatest radiation attenuation performance in comparison to other selected glasses. The Bi₂O₃-TiO₂-V₂O₅-Na₂O-TeO₂ glass system shows excellent neutron shielding material with high long-term light transmittance and discharge resistance and could be potentially used as transparent radiation-resistant shielding glass applications.

• Archives of Metallurgy and Materials
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• v.64 no.2
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• pp.551-557
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• 2019

The dispersion of nanoparticles in the host matrix is a novel approach to enhance the thermoelectric performance. In this work, we incorporate the TiC (x = 0, 1 and 2 wt.%) nanoparticles into a p-type Bi_0.5Sb_1.5Te₃ matrix, and their effects on microstructure and thermoelectric properties were systematically investigated. The existence of TiC contents in a base matrix was confirmed by energy dispersive X-ray spectroscopy analysis. The grain size decreases with increasing the addition of TiC content due to grain boundary hardening where the dispersed nanoparticles acted as pinning points in the entire matrix. The electrical conductivity significantly decreased and the Seebeck coefficient was slightly enhanced, which attributes to the decrease in carrier concentration by the addition of TiC content. Meanwhile, the lowest thermal conductivity of 0.97 W/mK for the 2 wt.% TiC nanocomposite sample, which is ~16% lower than 0 wt.% TiC sample. The maximum figure of merit of 0.90 was obtained at 350 K for the 0 wt.% TiC sample due to high electrical conductivity. Moreover, the Vickers hardness was improved with increase the addition of TiC contents.

• Archives of Metallurgy and Materials
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• v.66 no.3
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• pp.803-808
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• 2021

The influence of nano dispersion on the thermoelectric properties of Bi₂Te₃ was actively investigating to wide-spread thermoelectric applications. Herein this report, we have systematically controlled the microstructure of Bi_0.5Sb_1.5Te₃ (BST) alloys through the incorporation of carbon nanofiber (CNF), and studied their effect on thermoelectric properties, and mechanical properties. The BST/x-CNF (x-0, 0.05, 0.1, 0.2 wt.%) composites powder was fabricated using high energy ball milling, and subsequently consolidated the powder using spark plasma sintering. The identification of CNF in bulk composites was analyzed in Raman spectroscopy and corresponding CNF peaks were recognized. The BST matrix grain size was greatly reduced with CNF dispersion and consistently decreased along CNF percentage. The electrical conductivity was reduced and Seebeck coefficient varied in small-scale by embedding CNF. The thermal conductivity was progressively diminished, obtained lattice thermal conductivity was lowest compared to bare sample due to induced phonon scattering at interfaces of secondary phases as well as highly dense fine grain boundaries. The peak ZT of 0.95 achieved for 0.1 wt.% dispersed BST/CNF composites. The Vickers hardness value of 101.8 Hv was obtained for the BST/CNF composites.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.3
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• pp.329-335
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• 2008

This paper proposes a miniaturized half-circular-slot UWB antenna. Using an analysis of the neld patterns, we show that the original circular-slot UWB antenna operates on a series of multi-pole radiation based on $TE_n$ modes, and a perfect magnetic wall exists along an axis of symmetry on the antenna. Using the perfect magnetic wall we designed and fabricated the miniaturized UWB antenna on RF-60A substrate with t=0.64mm, ${\varepsilon}_r=6.15\;and\;tan\;{\delta}=0.0025$, which not only has the half size of the original but also maintains UWB characteristics. The measured gain of the miniaturized antenna is $-2.1{\sim}4.3dBi$, which is comparable with the gain, $-2.7{\sim}3.1dBi$, of the original circular-slot UWB antenna. The radiation pattern is also similar to that of the original antenna.