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BaZrO<sub>3</sub>의 부피 변화가 프로톤 전도 에너지 장벽에 미치는 영향
정용찬,김대희,김병국,김영철,Jeong, Yong-Chan,Kim, Dae-Hee,Kim, Byung-Kook,Kim, Yeong-Cheol 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.5
We studied the energy barrier for proton conduction with volume variation in $BaZrO_3$ using a first principles study to investigate an optimum volume for the proton conduction. The volume increase of $BaZrO_3$ was expected to decrease the energy barrier for proton rotation and to increase that for proton transfer, and these trends could be extrapolated when the volume was decreased. However, the energy barriers for the proton transfer with the volume decrease were increased, while all the other energy barriers varied as expected. We could explain this unexpected behavior by the bent Zr-O-Zr structure, when the volume was decreased.
Zn-doped BaZrO3에서의 멀티-프로톤 전도와 상호작용
정용찬 ( Yong Chan Jeong ),김대희 ( Dae Hee Kim ),김병국 ( Byung Kook Kim ),김영철 ( Yeong Cheol Kim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.12
Migration and interaction of multi-protons in a zinc-doped barium zirconate (Zn-doped BaZrO3) super cell were investigated using a density functional theory. O ions in the super cell form interconnected octahedrons with Zr or Zn ions positioned in their centers and Ba ions positioned among the eight octahedrons. When one proton was added to the super cell, the energy barrier of 0.80 eV for proton transfer from the first to second nearest O ion sites from the Zn ion reached its highest value. When two protons were added to the super cell, the two protons preferred the first nearest O ions from the Zn ion. The two protons were accommodated by pushing the neighboring Zn ion further away from the center of the octahedron. Energy barriers for proton transfer from the Zn-octahedron to the neighboring Zr-octahedron were spread in the range of 0.36 ~ 1.02 eV.
Y-doped BaZrO<sub>3</sub>에서의 산소 공공과 프로톤의 이동
김대희,정용찬,박종성,김병국,김영철,Kim, Dae-Hee,Jeong, Yong-Chan,Park, Jong-Sung,Kim, Byung-Kook,Kim, Yeong-Cheol 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.6
We studied the transfer of oxygen vacancy and proton in Y-doped BaZr$O_3$ (BYZ) using density functional theory (DFT). An oxygen vacancy was generated in the $2{\times}2{\times}2$ BYZ superstructure by replacing two Zr atoms with two Y atoms to satisfy the charge neutrality condition. The O vacancy transfer between the first and second nearest O atom sites from a Y atom showed the lowest activation energy barrier of 0.42 eV, compared to the other transfers between first and first, and second and second in the superstructure. Two protons were inserted in the structure by adding a proton and hydroxyl that were supplied by the dissociation of a water molecule. The two protons bonded to the first and second nearest O atoms were energetically the most favorable. The activation energy barrier for a proton transfer in the structure was 0.51 eV, when either proton transferred to its neighbor O atom. This value was well matched with the experimentally determined one.
비화학양론적 Na<sup>+</sup>β-alumina를 위한 Mg 원자의 치환: 제일원리 계산
김대현,김대희,정용찬,서화일,김영철,Kim, Dae-Hyun,Kim, Dae-Hee,Jeong, Yong-Chan,Seo, Hwa-Il,Kim, Yeong-Cheol 한국재료학회 2010 한국재료학회지 Vol.20 No.2
$Na^+$ ion conductivity can be improved by the substitution of an Mg atom for an Al atom to form a nonstoichiometric $Na^+$ $\beta$-alumina. We performed a first principles study to investigate the most stable substitution site of an Mg atom and the resulting structural change of the nonstoichiometric $Na^+$ $\beta$-alumina. Al atoms were classified as four different layers in the spinel block that are separated by conduction planes in the nonstoichiometric $Na^+$ $\beta$-alumina. The substitution of an Mg atom for an Al atom at a tetragonal site was more favorable than that at an octahedral site. The substitution in the spinel block was more favorable than that close to the conduction plane. This result was well explained by the volume changes of the polyhedrons, by the standard deviation of the Mg-O distance, and by the comparison with bulk MgO structure. Our result indicates that the most preferable site for the Mg atom was the tetrahedral site at the spinel block in the nonstoichiometric $Na^+$ $\beta$-alumina.
류혜연 ( Hye Yeon Ryu ),정용찬 ( Yong Chan Jeong ),이수정 ( Soo Jung Lee ) 한국소년정책학회 2020 少年保護硏究 Vol.33 No.2
The Juvenile Investigation system has its role as a standard data of judicial judgment that can help young offenders to be protected, educated, and civilized. Additionally, by taking advantage of the recidivism risk assessment at the time of investigation, it is possible to predict the tendency of re-offense and the effects that can help preventing crimes in advance. Although the rate of recidivism is steadily increased, the Juvenile Investigation system is not changed but maintained its state as before. The purpose of this paper is not only to study the contents of the juvenile investigation system and its current situation in South Korea and abroad, but examine a few different types of programs related to recidivism risk and its current situation as well. It turned out that the investigation system which was supposed to be carried out sufficiently in various stages of the judicial system that actually has not enough rate of conduct due to the problem of lacked investigators and some other reasons. Even though there are professional investigation tools that have been verified enough, such tools were not being used properly and enough. At the end, it is concluded that what we need to pursue is proper intervention of experts, adequate training for investigators, and accurate usage of the tools.
물 분자의 해리에 의한 Si (001)-c(4×2) 표면에서의 수산화기의 균일한 분포
이수경,오현철,김대희,정용찬,백승빈,김영철,Lee, Soo-Kyung,Oh, Hyun-Chul,Kim, Dae-Hee,Jeong, Yong-Chan,Baek, Seung-Bin,Kim, Yeong-Cheol 한국재료학회 2010 한국재료학회지 Vol.20 No.9
Adsorption of a water molecule on a Si (001) surface and its dissociation were studied using density functional theory to study the distribution of -OH fragments on the Si surface. The Si (001) surface was composed of Si dimers, which buckle in a zigzag pattern below the order-disorder transition temperature to reduce the surface energy. When a water molecule approached the Si surface, the O atom of the water molecule favored the down-buckled Si atom, and the H atom of the water molecule favored the up-buckled Si atom. This is explained by the attractions between the negatively charged O of the water and the positively charged down-buckled Si atom and between the positively charged H of the water and the negatively charged up-buckled Si atom. Following the adsorption of the first water molecule on the surface, a second water molecule adsorbed on either the inter-dimer or intra-dimer site of the Si dimer. The dipole-dipole interaction of the two adsorbed water molecules led to the formation of the water dimer, and the dissociation of the water molecules occurred easily below the order-disorder transition temperature. Therefore, the 1/2 monolayer of -OH on the water-terminated Si (001) surface shows a regular distribution. The results shed light on the atomic layer deposition process of alternate gate dielectric materials, such as $HfO_2$.