• Progress in Superconductivity
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• 제9권2호
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• pp.167-172
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• 2008

We fabricated $YBa_2Cu_3O_{7-x}$(YBCO) films on (00l) $LaAlO_3$ substrates prepared by metal organic deposition(MOD) method using trifluoroacetate(TFA) solution. The films with various thicknesses were prepared by repeating the dip-coating and calcining processes. The effects of film thickness on phase formation, microstructures, and critical properties were evaluated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microstructure and resultant critical current($I_C$) and critical current density($J_C$) varied remarkably with film thickness: The ($I_C$) value increased from 39 to 160 A/cm-width as the number of coatings increased from one to four, while the corresponding $J_C$ was measured to be in the range of $0.84-1.21\;MA/cm^2$. Both the $I_C$ and $J_C$ decreased when an additional coating was applied due to microstructural degradation, indicating that the optimum thickness is in the range of $1.1-1.8\;{\mu}m$. The possible cause for the decrease in the $I_C$ and $J_C$ value for film thicker than $1.8\;{\mu}m$ include non-uniform thickness, increased surface roughness, and the poor formability of the YBCO phase and texture arising from the insufficient heat treatment time with respect to the increased thickness.

• 한국전기전자재료학회논문지
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• 제19권5호
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• pp.467-476
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• 2006

We fabricated the YBCO films on LAO substrate using the TFA-MOD method and evaluated the effects of heat treatment temperature and film thickness on the microstructure, degree of texture, and critical properties. The calcining and firing were peformed at the temperature range of $370^{\circ}C-460^{\circ}C\;and\;750^{\circ}C-800^{\circ}C$, respectively. For the films fired at $775^{\circ}C$ after calcining at $400^{\circ}C-430^{\circ}C$showed highest critical temperature (Tc-onset) of 89.5 K and critical current (Ic) of 40A/cm-width which corresponds to critical current density (Jc) of $1.8MA/cm^2$. The highest critical properties are probably attributed to the formation of purer YBCO phase, stronger biaxial texture, and higher oxygen content, according to the XRD, pole-figure, SEM, Raman analysis. From the multi-coated films, the Ic increased from 39 to 169 A/cm-width as the coating repeated to four times, while the corresponding Jc was measured from once to be in the range of $0.8-1.2MA/cm^2$. Both Ic and Jc degraded as the coating repeated further, indicating that the optimum thickness is in the range of $1.0{\mu}m-1.7{\mu}m$.

• 한국초전도ㆍ저온공학회논문지
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• 제9권2호
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• pp.19-22
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• 2007

We report the phase and microstructure evolutions of metal trifluoroacetate (TFA) precursor films in the TFA-MOD process of YBCO films on the LAO (100) substrates. It was confirmed that the precursor films were decomposed into $Y_2O_3$, $BaF_2$, and CuO nanoparticles after the initial heat treatment up to 400$^{\circ}C$. After a subsequent heat treatment at higher temperatures ranging from 700 to 850$^{\circ}C$ for 2 h, these nano-sized phases are converted into YBCO films. High Jc(77K, sf)-YBCO thin films (over 2 MA/$cm^2$) were successfully fabricated with firing temperatures ranging from 775 to 850$^{\circ}C$ for 2 h, where films were composed of dense microstructures with large grains.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1247-1248
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• 2006

We fabricated YBCO film using a TFA-MOD method. In order to enhance the reaction kinetics and to control the formation of the second phases, $Y_2Ba_1Cu_1O_x$ and $Ba_3Cu_5O_8$ powders were used as precursors (the so called "211 process"). The films were calcined at $460^{\circ}C$ and then fired at $750^{\circ}C-800^{\circ}C$ in a 12.1% humidified $Ar-O_2$ atmosphere. We found that the microstructure varied significantly with the firing temperature. The textures of all of the films were similar and mainly biaxial. For the film fired at $775^{\circ}C$, the critical current was obtained to be 39 A/cm-width (corresponding critical current density is 2.0 MA/$cm^2$).

• Progress in Superconductivity
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• 제6권2호
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• pp.118-123
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• 2005

A low cost YBCO oxide powder was employed as a starting precursor for MOD process. YBCO oxide is advantageous over metal acetates or TFA salts which are popular starting precursors for conventional MOD-TFA process because that YBCO oxide precursor is cheap and easy to control molar ratio. YBCO thin films were prepared by this oxide-precursor-based MOD process and annealing condition was optimized. The YBCO thin film annealed at below $780^{\circ}C$ shows no transport $I_c$ and poor microstructure. Raman spectroscopic study of YBCO thin film indicates that YBCO thin film prepared at below $780^{\circ}C$ contains a number of imperfections such as non-superconducting $BaCuO_2$ phase, cation disorder, etc. However, the YBCO thin film treated at above $800^{\circ}C$ shows improvement in microstructure and current transport properties. This research was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea.

• 한국초전도ㆍ저온공학회논문지
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• 제5권3호
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• pp.23-25
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• 2003

Effect of chemically modified precursor solution on YBCO coated conductor prepared by MOD-TFA method was investigated. YBCO thin films were deposited on (l00)-oriented single crystalline LaAlO$_3$ substrates by conventional MOD-TFA process. The microstructures of YBCO thin films contain maze-like patterns. The origin of this microstructure was delineated by compositional inhomogeneity during the pyrolysis process and it was shown that addition of diethanolamine (DEA) improve the microstructure of grown YBCO films. In addition, it was demonstrated that the chemical modification of precursor solution makes no harmful effect on biaxial texture of YBCO thin films.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2005년도 High Temperature Superconductivity Vol.XV
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• pp.91-91
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• 2005

• 한국초전도ㆍ저온공학회논문지
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• 제6권4호
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• pp.5-8
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• 2004

A low cost MOD processing using YBCO oxide powder as a starting precursor was employed for fabrication of YBCO thin films. YBCO oxide is advantageous over metal acetates or TFA salts which are popular starting precursors for conventional MOD-TFA process. YBCO thin films were prepared by oxide-precursor-based MOD process and annealing condition was optimized. The YBCO thin film annealed at 78$0^{\circ}C$ shows no transport $I_c$ and poor microstructure. However, the YBCO thin film annealed at higher temperature shows improvement in microstructure and current transport property. In order to improve critical current, YBCO thin film was prepared by double coating method. YBCO thin film prepared with double coating approach shows enhanced superconducting performance ($I_c$>100A/cm-w).

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2006년도 High Temperature Superconductivity Vol.XVI
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• pp.43-43
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• 2006

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2006년도 High Temperature Superconductivity Vol.XVI
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• pp.97-97
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• 2006