• 한국재료학회:학술대회논문집
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• 한국재료학회 1994년도 춘계 학술발표 강연 및 논문 개요집
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• pp.22-23
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• 1994

• 한국세라믹학회지
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• 제27권5호
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• pp.702-704
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• 1990

• 한국세라믹학회지
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• 제27권6호
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• pp.829-830
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• 1990

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.499-504
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• 1991

EPR spectra of the high $T_c$ superconductor $YBa_2Cu_3O_{7-y}$ (YBCO) doped with $Pd^{2+} or Zn^{2+}$ have been measured at several temperatures and dopant concentrations. The spectral intensity of $YBa_2({Cu_{1-x}}{Pd_x})_3O_{7-y}$ is proportional to the dopant concentration. The behavior of $YBa_2(Cu_{1-x}Zn_x)_3O_{7-y}$ is quite different: the spectral intensity remains almost constant up to x=0.10 and then increases rapidly above x=0.10. The results are interpreted in terms of localized and antiferromagnetically spin-paired d holes in both CuO chain and planes. The $Pd_{2+}$ ion substitutes on the CuO chain consisting of "CuOCu dimers", and a $Cu_{2+}$ ion with an unpaired spin is gene rated for each $Pd_{2+}$ ion substituted. On the other hand, $Zn_{2+}$ substitutes on the CuO planes, and all or most of the spins in the two-dimensional plane manage to pair up in the region of low dopant concentration. When the dopant concentration exceeds a certain limit, it becomes more difficult for the spins to find partners, and the number of unpaired spins increases rapidly with increasing dopant concentration. The $Zn_{2+}$ ion is more effective than the $Pd_{2+}$ ion in suppressing the superconductivity of YBCO. This is attributed to the fact that $Zn_{2+}$ substitutes on the CuO planes which are mainly responsible for the superconductivity, while $Pd_{2+}$ substitutes on the CuO chain which is of secondary importance in the superconductivity.

• 한국세라믹학회지
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• 제27권1호
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• pp.48-54
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• 1990

YBa2Cu3O7-x(=YBCO) single crystals were grown by flux method and the growing process of crystals was investigated. YBCO and 3BaO-7CuO composition powders were mixed by the ratio of 25 : 75(wt%), and the mixtures were melted at 105$0^{\circ}C$ in a electric furnace with no temperature-gradient. Then the melt was cooled at a rate 2-1$0^{\circ}C$/h in the above furnace. YBCO single crystal plate with average size of $1.5\times$2.0$\times$0.1㎣ were obtained in the cavities between crucible and solidified ingot, and the single crystals were oriented to <001> direction. The ingots of flux parts were analyzed by XRD and EDS for the purpose of presuming the growing process of the crystals. It was assumed that the divorced eutectic reaction, by which YBCO crystals were grown first and then BaCuO2 and CuO crystals, occured in the case of cooling rate faster than 2$^{\circ}C$/h. When the cooling rate was 2$^{\circ}C$/h, it was assumed that quasi-equilibrium eutectic reaction occured, so that YBCO, BaCuO2 and CuO crystals were grown at the same time.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.913-916
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• 2001

From 1994 the cooperation between NEU of China and MJU of South Korea for study of ReBaCuO (Re=Rare earth elements) superconductors has been carried out. The progress has been got in following projects. Critical current density ($J_c$) of YBaCuO superconductor prepared by Melting Textured Growth (MTG) was improved. In the preparation of textured YBaCuO, 20 wt.% of YBaCuO 211 phase was added, which would be climactic for the microcracks in the textured YBaCuO. The effects of the 211 phase and Ag content on the superconductivity were studied and discussed in detail. The improved $J_c$ value was reached to 8$\times$10^4 A/cm^2 (77K,0T). Single phase $YbBa_{2}Cu_{3}O_{x}$ superconductor was sintered by the traditional powder metallurgical method, and its reaction process was studied. In recent years, NdBaCuO superconductor is being performed. The behavior of $Nd_{4}Ba_{2}Cu_{2}O_{10}$(Nd422 phase) and the solid solubility, x in the superconductor $Nd_{1+x}Ba_{2-x}Cu_{3}O_{y}$ by the heat treatment in the low oxygen partial pressure (1%) or Ar at $950{\circ}C$ were investigated. The zone-melting process was used to make oriented NdBaCuO superconductor in order to increase the critical current density.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.179-183
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• 2000

For a ground plane in high-temperature superconducting ramp-edge junction devices, YBa$_2$Cu$_3$O$_{7-{\delta}}$/SrTiO$_3$/YBa$_2$Cu$_3$O$_{7-{\delta}}$ multilayer structures were fabricated using pulsed laser deposition and ECR ion milling. Various process parameters were adjusted to enhance the device characteristics. By etching the STO layer to form a tapered edge of about 15$^{\circ}$ and in-situ RF plasma treatment of bottom YBCO surface prior to deposition of top YBCO, the top-to-bottom YBCO showed T$_c$ of 75${\sim}$80 K and I$_c$ of about 40 mA through holes. It was found that the deposition of bottom YBCO at a reduced laser repetition rate of 1Hz increased the T$_c$ of top YBCO to 79.9 K. The resistivity of 570 layer was about 10$^6$ ${\Omega}$cm at 60 K, which ensures good electrical isolation between successive YBCO layers.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.83-86
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• 2003

YBa$_2$Cu$_3$$O_{7-x}$ thin films for coated conductor application were deposited on a MgO single crystalline substrate by a metal organic chemical vapor deposition (MOCVD) system of a vertical type using a single liquid source. The film uniformity was enhanced by controlling the gas shower head structure, the distance between the shower head and substrate, and the rotation of the substrate. The source mole ratio of Y(thd)$_3$: Ba(thd)$_2$: Cu(thd)$_2$ was changed for obtaining stoichiometric film. The phase formation, crystal orientation, surface morphology and film composition were investigated with different source mole ratios, and the critical temperature (T$_{c}$) was measured.red.

• Bulletin of the Korean Chemical Society
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• 제10권1호
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• pp.5-8
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• 1989

Conventional ceramic method has been used to prepare the green phase, $Y_2BaCuO_5$, commonly observed in 90-K superconductor $YBa_2Cu_3O_P{7-{\delta}}$as an impurity phase. The powder X-ray diffraction analysis indicates that $Y_2BaCuO_5$ has an orthorhombic symmetry with lattice parameter of a = 12.2 $\AA$, b = 5.61 $\AA$, and c = 7.14 $\AA.$ The average g-value 2.13 observed in ESR spectrum is attributable to Cu2+ stabilized in $C_{4v}$ field. From the magnetic susceptibility ($\mu$eff = 2.29 BM) and the ESR measurements, it is confirmed that Cu(II) $3d^9$ electrons in $Y_2BaCuO_5$ are localized and can be characterized by Curie-Weiss behavior. Optical reflectance spectrum shows a broad absorption peak around 680 nm due to dxy ${\rightarrow}$ $dx^2-y^2$ eletronic transition.

• 대한전기학회논문지
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• 제41권5호
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• pp.525-532
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• 1992

Fluorine-doped YBaS12TCuS13TOS17-xTFS1yT superconducting materials with y varing two orders of magnitude form 0.02 to 2.0 have been prepared by a sol-gel process by using metal nitrate salts, sodium hydroxide and sodium fluoride. Fluorine contents have been measured using an ion-selective electrode. All fluorine doped as reactant were found to be present in the resulted samples. From the observation of XRD it has been concluded that the samples with y 0.2 formed simply the single phase of perovskite structure, whereas those with y 0.5 yielded together some compounds such as BaFS12T, YFS13T and CuO in the resulted samples. The observation of solid state S019TF NMR has been carried out in order to check whether fluorine was actually incorporated into the lattice sites, and the experimental results revealed that the mole ratio of fluorine incorporated into the lattice sites of YBaS12TCuS13TOS17-xT was approximately 0.2 per mole of the compound. Also electrical resistivity measurement indicated that onset transition temperature has the tendency to increase slightly with increasing y in the dilute region as y 0.2.