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방전 플라즈마 소결법에 의한 ZnS 나노입자의 소결과 광학적 특성
김창일,김유비,여서영,홍연우,윤지선,박운익,정영훈,조정호,백종후,Kim, Chang-Il,Kim, You-Bi,Yeo, Seo-Yeong,Hong, Youn-Woo,Yun, Ji-Sun,Park, Woon-Ik,Jeong, Young-Hun,Cho, Jeong-Ho,Paik, Jong-Hoo 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.6
Zinc sulphide (ZnS) nanoparticles were fabricated by hydrothermal synthesis at $180^{\circ}C$ for 12 h. Two kinds of ZnS powder (hydrothermal synthesized ZnS and commercial ZnS) were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) for phase and microstructure, respectively. The XRD patterns showed that all ZnS nanoparticles have a sphalerite (cubic) structure. The nanoparticles of two different ZnS powders were sintered by spark plasma sintering. The sintered ZnS were analyzed by XRD, SEM, and FT-IR. We found that the transmittance of the infrared region is highly dependent on the density and crystal structure of sintered ZnS and the purity of the starting ZnS powder.
ZnO-Zn<sub>2</sub>BiVO<sub>6</sub>-Co<sub>3</sub>O<sub>4</sub> 세라믹스의 액상소결과 전기적 특성
홍연우,김유비,백종후,조정호,정영훈,윤지선,박운익,Hong, Youn-Woo,Kim, You-Bi,Paik, Jong-Hoo,Cho, Jeong-Ho,Jeong, Young-Hun,Yun, Ji-Sun,Park, Woon-Ik 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.2
This study focuses on the effects of doping $Zn_2BiVO_6$ and $Co_3O_4$ on the sintering and electrical properties of ZnO; where, ZZ consists of 0.5 mol% $Zn_2BiVO_6$ in ZnO, and ZZCo consists of 1/3 mol% $Co_3O_4$ in ZZ. As ZnO was sintered at about $800^{\circ}C$, the liquid phases, which are composed of $Zn_2BiVO_6$ and $Zn_2BiVO_6$-rich phases, were found to be segregated at the grain boundaries of sintered ZZ and ZZCo, respectively, which demonstrates that $V_o^{\cdot}$(0.33~0.36 eV) are formed as dominant defects according to the analysis of admittance spectroscopy. As $Co_3O_4$ is doped to ZZ, the resistivity of ZnO decreases to ~38%, while donor density ($N_d$), interface state density ($N_t$), and barrier height (${\Phi}_b$) increase twice higher than those of ZZ, according to C-V characteristics. This result harbingers that ZZCo and its derivative compositions will open the gate for ZnO to be applied as more progressive varistors in the future, as well as the advantageous opportunity of manufacturing ZnO chip varistors at lower sintering temperatures below $900^{\circ}C$.
ZnO-Zn<sub>2</sub>BiVO<sub>6</sub>-Co<sub>3</sub>O<sub>4</sub> 바리스터의 전류-전압 및 임피던스의 온도 특성
홍연우 ( Youn Woo Hong ),김유비 ( You Bi Kim ),백종후 ( Jong Hoo Paik ),조정호 ( Jeong Ho Cho ),정영훈 ( Young Hun Jeong ),윤지선 ( Ji Sun Yun ),박운익 ( Woon Ik Park ) 한국센서학회 2016 센서학회지 Vol.25 No.6
This study introduces the characteristics of current-voltage (I-V) and impedance variance for ZnO-Zn<sub>2</sub>BiVO<sub>6</sub>-Co<sub>3</sub>O<sub>4</sub> (ZZCo), which is sintered at 900℃, according to temperature changes. ZZCo varistor demonstrates dramatic improvement of non-linear coefficient, α = 66, with lower leakage current and higher insulating resistivity than those of ZZ (ZnO-Zn<sub>2</sub>BiVO<sub>6</sub>) from the aspect of I-V curves. While both systems are thermally stable up to 125℃, ZZCo represents a higher grain boundary activation energy with 1.05 eV and 0.94 eV of J-E-T and from IS & MS, respectively, than that of ZZ with 0.73 eV and 0.82 eV of J-E-T and from IS & MS, respectively, in the region above 180℃. It could be attributed to the formation of V<sub>O</sub> (0.41~0.47 eV) as dominant defect in two systems, as well as the defect-induced capacitance increase from 781 pF to 1 nF in accordance with increasing temperature. On the other hand, both the grain boundary capacitances of ZZ and ZZCo are shown to decrease to 357 pF and 349 pF, respectively, while the resistances systems decreased exponentially, in accordance with increasing temperature. So, this paper suggests that the application of newly formed liquid phases as sintering additives in both Zn<sub>2</sub>BiVO<sub>6</sub> and the ZZCo-based varistors would be helpful in developing commercialized devices such as chips, disk-type ZnO varistors in the future.
소결온도가 ZnO-Co3O4-Cr2O3의 결함과 전기적 특성에 미치는 영향
홍연우 ( Youn Woo Hong ),김유비 ( You Bi Kim ),이영진 ( Young Jin Lee ),김세기 ( Sei Ki Kim ),백종우 ( Jong Hoo Paik ),조만호 ( Man Ho Jo ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.12
The defects and origin of the good varistor properties in the ZnO-Co3O4-Cr2O3 system were investigated by admittance spectroscopy, I-V characteristics, and impedance and modulus spectroscopy. Two kinds of defects were detected, but (0.27 eV) was identified as a major donor level by admittance spectroscopy. The ZnO grain resistivity of ~0.4 Ωcm was calculated but somewhat increased with sintering temperature. J-E characteristics with varistor behavior was seen in this system while the nonlinear coefficient α changed from 9 to 92 with sintering temperature. The single potential barrier of 0.64-1.01 eV at the grain boundary region was confirmed by impedance and modulus spectroscopy. The origin of a good varistor behavior in ZnO-Co3O4-Cr2O3 would be due to the formation and stabilization of a double Schottky barrier by the redox reaction of Co ions and the existence of small Cr ions in the grain boundaries.
HP 및 SPS법에 의한 ZnS의 소결과 소결체의 광학적 특성
홍연우 ( Youn Woo Hong ),김유비 ( You Bi Kim ),이영진 ( Young Jin Lee ),김세기 ( Sei Ki Kim ),백종후 ( Jong Hoo Paik ),김진호 ( Jin Ho Kim ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.12
The sintering behaviors of commercial ZnS nanopowders (purity 99.999%) processed with the two different sintering techniques of hot pressing (HP) and spark plasma sintering (SPS) and optical properties of sintered material are investigated here. The results are compared between the two different sintering techniques in terms of the sintering parameters (density, microstructure, X-ray diffraction pattern) and the optical properties (infrared transmission in the range of 2~20 μm) of the sintered ZnS ceramics. The maximum density was obtained at 950℃ irrespective of the sintering method. The wurtzite (hexagonal) phase causes birefringence due to optical anisotropy which begins at a temperature of more than 920℃. The optimized optical properties were found to be ZnS ceramics sintered with HP at 950℃ and with SPS at 90 0℃. However, contamination from the graphite mold and its influence on the optical properties were confirmed to be very serious, especially in HP and SPS. In the SPS method, the optical properties by light scattering were found in this study to worsen considerably due to the refractive index differences among the ZnS, carbon impurities, and pores.