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포스터 발표 - 무기재료분과 / 전기화학분과 / 촉매분과 : 수열결정화를 이용한 PSZT 분말제조 및 소결
오정강,서경원,이기정 ( J . K . Oh,K . W . Seo,K . J . Lee ) 한국공업화학회 1997 한국공업화학회 연구논문 초록집 Vol.1990 No.3
N/A PSZT preparation by hydrothermal synthesis was studied for effect of morphology, crystal structure, particle diameter and size distribution with variation of mineralizer(KOH) and mole ratio of raw materials. Dielectric constant of sintered materials from prepared powders measured 1000∼3000 with 120Hz∼100kHz. Addition of Sr prevent crystal structure and inclease of particle diameter. In case of Zr/Ti=0.40/0.60, Tetragonal and in case of Zr/Ti=0.60/0.40, rhombohedral was showed. Increase of Zr declease particle diameter to Phase boundary but suddenly inclease a more Zr. ICP data show addition as wanted mole ratio.
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오정강,서경원,이기정 ( J . K . Oh,K . W . Seo,K . J . Lee ) 한국공업화학회 1997 한국공업화학회 연구논문 초록집 Vol.1997 No.0
N/A PSZT preparation by hydrothermal synthesis was studied for effect of morphology, crystal structure, particle diameter and size distribution with variation of mineralizer(KOH) and mole ratio of raw materials. Dielectric constant of sintered materials from prepared powders measured 1000∼3000 with 120Hz∼100kHz. Addition of Sr prevent crystal structure and inclease of particle diameter. In case of Zr/Ti=0.40/0.60, Tetragonal and in case of Zr/Ti=0.60/0.40, rhombohedral was showed. Increase of Zr declease particle diameter to Phase boundary but suddenly inclease a more Zr. ICP data show addition as wanted mole ratio.
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오정강,서경원 한국공업화학회 1998 응용화학 Vol.2 No.2
The effects of reaction period, concentration of feedstock and mixing rate on particle diameter and size distribution in preparation of BaTiO₃ powder under hydrothermal conditions have been studied. Experimental results showed that the particle size became smaller with its narrow distribution as the reaction period and mixing rate increased and the concentration of feedstock decreased in contrast with the results based on classical nucleation and growth models. After scrutinizing these experimental results, multiple reaction model that combins transformation and dissolution-precipitation was proposed.
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오정강,서경원,Oh, Jung Kang,Seo, Kyung Won 한국공업화학회 1999 공업화학 Vol.10 No.4
In Preparing $BaTiO_3$ powder under hydrothermal conditions, effects of reaction period feedstock concentration and mixing rate on crystallinity, mean size and size distribution of particles were studied. Experimental results showed that the particle size became smaller with its narrow distribution as the reaction period and mixing rate increased, but feedstock concentration decreased in contrast with the results based on the classical nucleation-growth model. From these results, $BaTiO_3$ particles seem to be prepared hydrothermally through a multiple reaction procedure that includes dissolution, precipitation, hydrolysis-condensation, aggregation, diffusion and transformation. 수열합성법을 이용한 $BaTiO_3$ 미세분말제조시 반응시간, 출발물질농도와 교반속도 등이 입자의 결정성, 평균입경과 입도분포에 미치는 영향을 조사하였다. 실험결과 기존의 핵생성-입자성장 모델과는 상이하게도 반응시간과 교반속도가 증가할수록 또는, 출발물질의 농도가 감소할수록 입자크기는 감소하였으며, 입도분포도 좁았다. 이로부터 $BaTiO_3$ 결정입자는 수열합성시 용해, 가수분해-축합반응, 침전, 응집, 확산, 전이 등의 복합적인 반응경로를 거치는 것으로 판단되었다.
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Ga 증기압 변화에 따른 GaN 박막의 누선전류 원인에 관한 연구
박병권,오정은,이상태,황지원,김문덕,김송강 한국물리학회 2016 새물리 Vol.66 No.11
We have investigated the origin of the leakage current in GaN films grown on AlN/Si(111) substrates by using plasma-assisted molecular beam epitaxy with various gallium fluxes. Scanning electron microscopy images revealed that the GaN film grown under a N-rich condition showed large hexagonal defects and a roughened surface. On the contrary, a flat surface with pinholes was obtained for the GaN film grown under a Ga-rich condition. Rocking-curve measurement of X-ray diffraction revealed that line-defect density decreased with increasing Ga flux. Electrical defect levels related with line (0.46 eV) and point (0.77 eV) defects were found by using deep-level transient spectroscopy. Moreover, line-defect density in the GaN film grown under a Ga-rich condition is almost constant compared to GaN films grown under N-rich or N/Ga$\sim$1 conditions. The experimental results indicated that lateral growth can be induced during the initial stage grown under a Ga-rich condition, it might be suppressed the threading dislocation. We believed that out experimental results provide the helpful information to understand and suppressing the defects during the initial growth state. 본 연구에 사용된 GaN 박막은 Ga 증기압을 달리하여 AlN/Si(111) 기판 위에 플라즈마-도움 분자선 켜쌓기 (plasma-assisted molecular beam epitaxy) 법으로 성장되었다. N 과잉 영역에서 성장된 GaN 박막은 거친 표면과 큰 육각형의 결함을 Ga 과잉 영역에서 성장된 시료는 평탄한 표면과 핀홀들이 있는 표면이 관측되었다. 고분해능 X-선 회절기의 흔듦 곡선 측정을 통하여 전파 전위 종류에 따른 선결함 밀도를 측정하였으며, 그 결과 Ga 증기압이 증가할수록 선결함 밀도는 감소하였다. Ga 증기압이 다른 세 시료에 대하여 깊은 결함 과도 분광 (deep level transient spectroscopy)을 측정하였을 때 선결함 (0.46 eV)과 점결함 (0.77 eV)에 관련된 결함 준위들을 관측하였다. 결함 농도를 비교하였을 때 Ga-과잉 영역에서 성장된 GaN 박막의 선결함 밀도는 N 과잉과 N/Ga$\sim$1 영역에서 성장된 시료에 비해 증가율이 매우 적음을 확인하였다. 이는 Ga 과잉 영역에서 초기 성장 시 수평 방향 성장을 빠르게 유도함으로써 기판으로부터 전이되는 결함을 억제할 수 있음을 보여 준다. 이러한 현상의 이해를 통하여 GaN박막 성장 시 결함을 억제하기 위한 초기 성장에 대하여 유용한 정보를 제공할 것으로 보인다.
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서경원,오정강 한국화학공학회 1999 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.37 No.1
KOH용액을 광화제로 첨가하여 80-200℃의 수열반응으로부터 평균입자크기가 0.5㎛이하인 입방정의 BaTiO₃결정분말을 제조하였다. 실험결과 0.2 M의 KOH를 첨가하였을 때는 아나타제(TiO₂)와 비정질의 혼합상이 생성되었으며 0.8 M이상의 KOH용액을 첨가하였을 때는 안정한 BaTiO₃ 결정분말이 합성되었다. 광화제 첨가장이 증가함에 따라 Ba(OH)^+와 Ti(OH)^(4-x)_x의 상대과포화도가 증가하여 핵생성속도가 증가하였고, 이로 인해 크기가 작은 결정입자가 순간적으로 많이 생성되어 평균입자크기가 작아지고 입도분포폭이 좁아졌다. 또한, 반응온도가 높을수록 Ba(OH)^+와 Ti(OH)^(4-x)_x의 축합반응이 촉진되어 용액내에 수산화물이 감소하기 때문에 BaTiO₃ 결정의 응집률이 감소하였으며, 결정성장속도가 증가하여 입자크기가 커졌다. Crystalline BaTiO₃ powder of cubic phase, the mean particle size of which was 0.5 ㎛, was prepared by hydrothermal synthesis at temperature between 80 and 200 ℃ with KOH as a mineralizer. A mixed phase of anatase and amorphous was formed with 0.2 M KOH, but a stable phase of BaTiO₃ crystal powder was obtained when the concentration of KOH was 0.8 M and above. As the concentration of the mineralizer increased, the relative supersaturations of Ba (OH)^+ and Ti(OH)^(4-x)_x were enhanced. A lot of crystal powder were, therefore, formed instantaneously due to an increase in nucleation rate, and consequently, the mean particle size was reduced and the size distribution became narrower. As the reaction temperature increased, condensation reaction between Ba(OH)^+ and Ti(OH)^(4-x)_x was accelerated, which led to a decrease in hydroxide concentration, so that agglomeration of powder was abated. However, the particle size became larger due to an increase in the crystal growth rate.
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