• 한국산학기술학회논문지
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• 제7권5호
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• pp.801-804
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• 2006

[ $YBa_2Cu_3O_{7-{\delta}}(YBCO)$ ]계 초전도 선재용 $GdAlO_3(GAO)$ 버퍼층을 졸-겔(sol-gel) 공정에 의해 제조하였다. 전구체 용액은 Gd 질산염과 Al 질산염을 1:1 화학양론비로 하여 메탄올에 용해하여 준비하였다. 전구체 용액을 $SrTiO_3(STO)$ (100) 단결정 기판위에 스핀 코팅하고, 수분이 포함된 $N_2-5%\; H_2$ 분위기에서 $1000^{\circ}C$에서 2시간 열처리 하였다. 열처리 후 GAO 층의 표면에 대한 주사전자현미경 관찰에 의해 GAO 층이 에피택셜의 특징인 각면 형상을 갖는 것을 알 수 있었다. X-선 회절분석에 의하면 GAO 버퍼층은 c-축으로 우선 배향된 에피택셜 박막으로써 반가폭이 각각 (002)면에서 $0.29^{\circ}(out-of-plane)$, {112}지면에서 $1.10^{\circ}(in-plane)$의 우수한 배향성을 나타내었다.

• 센서학회지
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• 제8권2호
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• pp.195-201
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• 1999

$Al_2O_3$ (알루미나 및 R-면 사파이어)기판 위에 c-축 $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) 박막을 펄스레이저 증착법을 이용하여 성장하였다. 완충층으로 사용하기 위해 $Al_2O_3$ 기판 위에 증착한 $CeO_2$ 박막의 결정성은 기판온도에 많은 영향을 받았다. $CeO_2$ 박막은 $800^{\circ}C$의 기판온도에서 $\alpha$-축방향으로 잘 성장하였으며, $CeO_2$ 완충층의 두께에 따라 YBCO/$CeO_2/Al_2O_3$ 박막의 초전도 특성은 큰 변화를 나타내었다. 알루미나 기판 위에서 $CeO_2$ 완충층의 두께는 약 $1200\;{\AA}$이하, 사파이어 기판의 경우 $100{\sim}1000\;{\AA}$ 범위에서 YBCO 박막은 양호한 초전도 특성을 나타내었으나, 그 보다 두껍게 성장시킬 경우 초전도 특성이 급격하게 나빠졌다. 알루미나 기판 위에 성장된 YBCO 박막의 임계온도는 83 K였으며, R-면 사파이어 기판 위에 성장된 YBCO 박막의 임계온도는 ${\geq}89.5\;K$였고, 임계전류밀도는 77K에서 $3{\times}10^6\;A/cm^2$로 나타났다.

• 한국세라믹학회지
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• 제27권3호
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• pp.355-360
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• 1990

One of the possible ways to make a flexible wire of high-Tc superconductiong ceramics is the extrusion of a mixture slurry of superconducting powder with an appropriate polymer binder. The fabrication procedure for $YBa_2Cu_3O_{7-{\delta}}$ superconducting coils with this plastic mass is described. The major factors limiting the formation of extruded wire are the binder content, powder size, and entrapped gas in the mixture slurries. The optimum content of binder for both good flexbility and strength of wire was estimated to be 30wt%. The finer the powder size is, the more homogeneous structure the extruded wire has. The vacuum degassing before extrusion was necessary to remove the entrapped gas in as-extruded wire. The formability of wire depends greatly on the wire radius and binder content. After burning out the binder and the successive sintering, the contacts between the superconducting grains could be made. The resistivity vs. temperature behavior measured in the final wire showed the transition temperature of 90K with narrow transition width. However, the critical current densities of these wires are much lower in comparison to those of conventional bulk specimens.

• Progress in Superconductivity
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• 제6권2호
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• pp.95-98
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• 2005

We present results of Raman spectroscopic studies of superconducting $YBa_2Cu_3O_7$ (YBCO) coated conductors. Raman scattering is used to characterize optical phonon modes, oxygen content, c-axis misalignment, and second phases of the YBCO coated conductors at a micro scale. A two-dimensional mapping of Raman spectra with transport properties has been performed to elucidate the effect of local propertied on current path and superconducting phase. The information taken from the local measurement will be useful for optimizing the process condition.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.287-290
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• 1989

Single-phase $YBa_2Cu_3O_{j-g}$ (YBC) ceramic samples were annealed at $700^{\circ}C$ under a flowing $O_2$ atmosphere for 0, 18, 36, 54 and 72. hours after sintering. The resistivities(p) and the critical current densities($J_c$) of the samples were measured in a temperature range 77 to 300 K by a four probe method, using silver paint contacts. The variations of the electrical properties with annealing time are explained in terms of flux pinning, percolation probability and randomness, and alignment of grains and twins.The anomalous increases in $J_c$ and $T_c$ observed in sample annealed for a relatively long time possibly due to alignment of grains and twins, may imply the occurrence of superconducting glass state in high-$T_c$ superconducting ceramic.

• Progress in Superconductivity
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• 제2권2호
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• pp.92-96
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• 2001

We have fabricated a modified hairpin-type YBa$_2$Cu$_3$O$_{7-{\delta}}$ (YBCO) 2-pole microstrip bandpass filter with the center frequency of 5.8 GHz. We designed a hairpin-type filter with interdigital-coupled inner poles to improve the filter performance. Compared to a typical hairpin-type filter of the same size, the center frequency, the bandwidth and the insertion loss appeared smaller by 14.5% ,29.6%, and 0.55 dB, respectively. The dimensions of the filter were 13.7mm ${\times}$3.3 mm. YBCO films deposited on r-cut sapphire buffered with a CeO$_2$thin layer were used fur making the filter.

• Bulletin of the Korean Chemical Society
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• 제10권1호
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• pp.23-26
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• 1989

EPR spectra of the high-temperature superconductor YBa_2Cu_3O_{7-x}$ doped with ytterbium have been measured at 77-300K. The superconducting, orthorhombic phase shows a spectrum at g = 2.08 (Spectrum O). As the temperature is lowered, another line ascribable to $Yb^{3+}$ grows gradually at g = 3.31. The intensity of Spectrum O was determined using Yb as the internal reference. The semiconducting, tetragonal phase shows a spectrum at g = 2.06 (Spectrum T), different from Spectrum O. The origins of these spectra are discussed.

• 한국세라믹학회지
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• 제26권1호
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• pp.91-99
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• 1989

The concentrations of hydroxide, carbonate and oxalate for Y(III), Ba(II) and Cu(II) ions in an aqueous solution have been theoretically calcuated with respect to pH and their solubility diagram could be obtained. The optimum pH ofr oxalate coprecipitates at room temperature was estimated as<4, which was not influenced by carbonates and hydroxides in H2O solvent. The yield is dependent on the concentration of added oxalic acid, but the concentration of oxalic acid was fixed as 0.1M in this calculation for simplicity.

• Bulletin of the Korean Chemical Society
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• 제13권6호
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• pp.663-665
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• 1992

The superconducting $YBa_2Cu_4O_8$ was synthesized in oxygen condition at 1 atm. The starting material with 1 : 2 : 4 composition was obtained by pyrolysis of EDTA complex, which was converted to 1-2-3 phase during densification, followed by the 1-2-4 phase recovery at $810^{\circ}C$ . The phase presents were identified by XRD, TG, DTA and AC magnetic susceptibility. Our data indicated that considerable amounts of 1-2-4 phase formed but with the 1 : 2 : 3 phase or possibly 2-4-7 as visible. As the P($O_2$) increased with temperature, impurity peak, CuO ($2{\Theta}$ = 38.8), gradually decrease, and we conclude that the 1-2-4 phase is predominant bulk superconductor under the high oxygen pressure.

• Progress in Superconductivity
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• 제4권1호
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• pp.10-13
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• 2002

We report the effect of Ca doping in $YBa_2Cu_3O_{7-\delta}$ (YBCO) thin films grown on the Rolling- Assisted, Biaxially Textured Substrates (RABiTS) with the architecture of $CeO_2/YSZ/CeO_2/Ni$. Critical currents of bilayer and trilayer structures of $YBCO/Y_{0.7}Ca_{0.3}Ba_2Cu_3O_{7-\delta}$/(YCaBCO) as well as undoped YBCO for comparison have been measured in a wide range of temperatures and fields. For $6-8^{\circ}$ grain boundaries, 30% Ca-doping in bilayer structure enhances $J_c$ as high as 35%. The enhancement is larger at low temperatures and at magnetic fields. On the other hand, 30% Ca-doping in trilayer structure reduces $J_c$ as high as 60%. Combined with slightly lower $T_c$, this indicates that Ca is overdoped in this structure and degrades GBs.