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Sol-gel 방법에 의한 $LaAlO_3$ 박막의 제조
김혜진,김병주,이희균,홍계원,Kim, H.J.,Kim, B.J.,Lee, H.G.,Hong, G.W. 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
Lanthanum aluminate($LaAlO_3$) film has been prepared on single crystal and metal substrates by dip coating method. Lanthanum acetate and aluminum were prepared via ligand exchange starting from lanthanum nitrate hexahydrate and aluminum nitrate hexahydrate in acetate glacial acetic acid solution after being refluxed. Coating solution was obtained by diluting the gel with methanol and 2-methoxyethanol to adjust the total cation concentration to 0.67 M. Precursor coated film was prepared by dip-coating with a speed of 25 mm/min on various substrates such as $LaAlO_3$ (001), MgO(001), $SrTiO_3$(001) single crystal, LMO/MgO/Ni-alloy. Thin films have been obtained by heat treating the precursor film at various temperatures from $600^{\circ}C{\sim}900^{\circ}C$ and various heating rate from $0.83^{\circ}C/min{\sim}1.25^{\circ}C/min$ under $Ar/O_2$ mixture containing 1000ppm oxygen. The films have been characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). XRD analysis for the prepared film showed that $LaAlO_3$ thin films with a preferred orientation of (100) plane parallel to substrate surface were obtained at $800^{\circ}C(1.11\;^{\circ}C/min)$ on LMO/MgO/Ni-alloy substrate, but the intensity decreased with the increase of heat treatment temperature.
IBAD 기판을 적용한 산화물 전구체 MOD 공정에 의한 YBCO Coated Conductor의 제조
김영국,유재무,고재웅,허순영,홍계원,이희균,정형식,Kim Y. K.,Yoo J. M.,Ko J. W.,Heo S. Y.,Hong G. W.,Lee H. G.,Chung H. S. 한국초전도학회 2005 Progress in superconductivity Vol.6 No.2
YBCO coated conductors have been fabricated with a newly developed oxide-precursor-based MOD process. The precursor solution was synthesized with low cost YBCO powders as starting materials and YBCO coated conductors have been deposited on IBAD substrate ($CeO_2$/IBAD-YSZ/SS). YBCO coated conductor prepared by dip coating shows transport $I_c$ of 15A/cm-w at 77 K. Microstructural and crystallographic analyses indicate that YBCO layer was grown in epitaxy with substrate and exhibited well-developed dense microstructure. Also discussed are processing and analysis of YBCO coated conductor by slot-die web coating method. It was shown that this oxide-based MOD process provides a low cost route to coated conductor with high $J_c$.
전자빔 증발법에 의한 박막형 고온초전도체의 $CeO_2$ 버퍼층 증착 연구
이종범,박신근,김혜진,문승현,이희균,홍계원,Lee, J.B.,Park, S.K.,Kim, H.J.,Moon, S.H.,Lee, H.G.,Hong, G.W. 한국초전도학회 2010 Progress in superconductivity Vol.11 No.2
The properties of buffer layer for thermal and chemical stability in coated conductor is a very important issue. $CeO_2$ has desirable thermal and chemical stability as well as good lattice match. In this study, $CeO_2$ was deposited by electron beam deposition. The MgO(001) single crystal and LMO buffered IBAD substrate(LMO/IBAD-MgO/$Y_2O_3/Al_2O_3$/Hastelloy) were used as substrates, which have $\Delta\phi$ values of ${\sim}8.9^{\circ}$. The epitaxial $CeO_2$ films was deposited with high deposition rate of $12{\sim}16\;{\AA}/sec$. During deposition, the change of oxygen partial pressure(${\rho}O_2$) does not cause change in c-axis texture. In case of $CeO_2$ on MgO single crystal, the substrate temperature was optimized at $750^{\circ}C$ with superior $\Delta\phi$ and $\Delta\omega$ value. Otherwise, In case of LMO buffered IBAD substrate, It was optimized at $650^{\circ}C$ with increasing its deposition thickness of $CeO_2$, which was finally obtained with best $\Delta\phi$ value of $5.5^{\circ}$, $\Delta\omega$ value of $2^{\circ}$ and Ra value of 2.2 nm.
화학적인 용액 코팅방법에 의한 박막형 고온초전도체에 사용되는 SUS310 금속모재의 평탄화 연구
이종범,이현준,김병주,권병국,김선진,이종수,이철영,문승현,이희균,홍계원,Lee, J.B.,Lee, H.J.,Kim, B.J.,Kwon, B.K.,Kim, S.J.,Lee, J.S.,Lee, C.Y.,Moon, S.H.,Lee, H.G.,Hong, G.W. 한국초전도학회 2011 Progress in superconductivity Vol.12 No.2
The properties of $2^{nd}$ generation high temperature superconducting wire, coated conductor strongly depend on the quality of superconducting oxide layer and property of metal substrate is one of the most important factors affecting the quality of coated conductor. Good mechanical and chemical stability at high temperature are required to maintain the initial integrity during the various process steps required to deposit several layers consisting coated conductor. And substrate need to be nonmagnetic to reduce magnetization loss for ac application. Hastelloy and stainless steel are the most suitable alloys for metal substrate. One of the obstacles in using stainless steel as substrate for coated conductor is its difficulties in making smooth surface inevitable for depositing good IBAD layer. Conventional method involves several steps such as electro polishing, deposition of $Al_2O_3$ and $Y_2O_3$ before IBAD process. Chemical solution deposition method can simplify those steps into one step process having uniformity in large area. In this research, we tried to improve the surface roughness of stainless steel(SUS310). The precursor coating solution was synthesized by using yttrium complex. The viscosity of coating solution and heat treatment condition were optimized for smooth surface. A smooth amorphous $Y_2O_3$ thin film suitable for IBAD process was coated on SUS310 tape. The surface roughness was improved from 40nm to 1.8 nm by 4 coatings. The IBAD-MgO layer deposited on prepared substrate showed good in plane alignment(${\Delta}{\phi}$) of $6.2^{\circ}$.
치환형 합금원소가 첨가된 용융 철-삼원계에서 질소의 확산계수의 예측에 대한 연구
이재영,홍계원,남인탁,조정완 대한금속재료학회(대한금속학회) 1982 대한금속·재료학회지 Vol.20 No.5
R.B. McLellan에 의해 제안된 침입형과 치환형 원소가 포함된 철 삼원계에 대한 quasi-chemical model을 침입형 원자간의 interaction energy(εii)가 0 이라고 가정하여 변형하였다. 이 model을 이용하여 철 삼원계에서의 치환형 합금원소와 침입형 합금원소 사이의 interaction energy (Δε)를 치환형 합금원소의 첨가에 의한 침입형 원소의 용해도의 변화로부터 구하였고, 이로부터 철 삼원계에서 치환형 합금원소가 첨가됨에 의한 침입형 원소의 확산계수의 변화를 예측하는 방법을 제시하였다. 용융철에서 합금원소가 첨가됨에 따른 질소의 확산계수의 변화는 발표된 실험값과 잘 일치하였다. The first-order approximated quasi-chemical model of Fe-base ternary system containing interstitial and substitutional solutes suggested by R. B. McLellan have been modified for dilute solid solutions with assumption that the interaction energy (εii) between interstitial solutes is zero. The interaction energy (Δε) between substitutional and interstitial atom and the diffusivities of interstitial elements in various substitutional compositions of Fe base system are calculated using published solubility of the system and diffusivity of Fe-interstitial binary data with above model. The nitrogen diffusivities in liquid Fe base binary alloys predicted by the above model with the assumption of ε_(NN)=0 agree with experimental results with some accommodation factor.