• Bulletin of the Korean Chemical Society
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• v.29 no.12
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• pp.2540-2542
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• 2008

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.388-391
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• 1999

Well oriented Bi2212 superconductor thick films were formed successfully on a copper substrate by liquid reaction between a Cu-free precursor and Cu tape method in which Cu-free BSCO powder mixture was' printed on copper plate and heat-treated. And we examined the effect of heat-treatment atmosphere for the superconducting properties and microstructure of Bi2212. The composition of Cu-free BSCO powder mixture was Bi$_2O_3$ : SrCO$_3$ : CaCO$_3$ = 1.2~2 : 1 : 1 and the heat-treatment for the superconducting formation reaction was performed in air, oxygen, nitrogen and low oxygen pressure. At heat-treatment temperature, the printing layer partially melt by reacting with CuO of the oxidizing copper plate, and the nonsuperconducting phases present in the melt are typically Bi-free phases and Cu-free phases. Among the nonsuperconducting phases, it is known that the (Sr,Ca)CuO$_3$ phase restrain the formation of the Bi2212 superconducting phase. Because a kind of the nonsuperconducting phases is controled by the oxygen partial pressure, the optimum condition in which the remnants of the second phases don't leave in the fully processed conductor was determined by XRD and the critical tempera to re (Tc) analysis.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.353-355
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• 2004

YBaCuO thick films were fabricated by plasma enhanced chemical vapor deposition, and the crystallinity and the superconducting properties were investigated. The growth temperature to obtain the thick films was decreased by around $150^{\circ}C$ due to plasma enhancement. The zero resistivity temperatures for films grown at $590^{\circ}C$ and $620^{\circ}C$ were 55 and 80 K, resistively.

• Progress in Superconductivity and Cryogenics
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• v.9 no.2
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• pp.23-26
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• 2007

The influence of water partial pressure in Metal-organic Deposition (MOD) method was investigated on the texture and the morphology of $YBa_2Cu_3O_{7-x}$ (YBCO) films grown on the buffered metal tapes. The water partial pressure was varied from 4.2% up to 10.0% with the other process variables, such as annealing temperature and oxygen partial pressure, kept constant. In this work, the fluorine-free Y & Cu precursor solution added with Sm was synthesized and coated by the continuous slot-die coating & calcination step. The next annealing step of the YBCO films was done by the reel-to-reel method with the gas flowed vertically down. From the x-ray diffraction analysis, the un-reacted phase like $BaF_2$ peak was found at the water partial pressure of 4.2%, but $BaF_2$ peak intensity is much reduced as the water partial pressure is increased. However, the higher water partial pressure of about 10% in this experiment leads to the poor crystallinity of YBCO films. The morphologies of the YBCO films were not different from each other when the water partial pressure was varied in this work. The maximum critical current density of 3.8MA/$cm^2$ was obtained at the water partial pressure of 6.2% with the annealing temperature of 780$^{\circ}C$ and oxygen partial pressure of 500ppm.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.300-304
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• 1999

To tap the feasibility of exploiting the 2$^{nd}$ phases as flux-pinning centers in the (Bi,Pb)$_2Sr_2Ca_2CuO_{10}$ superconductor, the size and the distribution of the precipitates have been controlled by changing reaction temperature and time, oxygen partial pressure Po$_2$ and annealing condition. Various annealing heat treatments were also conducted on the as-received 61 filament Bi-2223 tapes with Bi$_{1.8}Pb_{0.4}Sr_2Ca_{2.2}Cu_3O_8$ starting composition and annealed specimen were analyzed with XRD, SEM, EDS and TEM.. The grain size of (Ca,Sr)$_2$(BiPb)O$_4$ or Bi$_{0.5}Pb_3Sr_2Ca_2CuO_{\delta}$ was controllable by optimizing the heat treatment condition and critical current density (J$_c$) showed dependence on the size of the 2$^{nd}$ phases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.25-28
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• 2002

Contact type Ic measurement system is needed to measure Ic continuously for long Bi-2223 tapes. Voltage and current terminals were designed several shapes for 4-probe method Ic measurement. Voltage terminals were made with brass and current terminals were made with Cu. We used 2 kinds of Bi-2223 tapes with different strength. When we measured Ic of Bi-2223 tape with Ag-Mg sheath, The proper weight was 0.3 kg and sharp pin type was better. according to voltage terminal shape and load. In case of Bi-2223 tape with Ag-Mn sheath, the proper terminal weight was 4 kg and sharp pin type was bad. It was possible to make continuous contact type Ic measurement system because We could get proper data - terminal shapes and loads - through these experiments.

• Progress in Superconductivity and Cryogenics
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• v.12 no.2
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• pp.9-12
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• 2010

A lamination system using reflow soldering was developed to enhance the mechanical properties of high temperature superconductor (HTS) tape. The laminated coated conductor tape was fabricated using the continuous lamination process. The mean, maximum, and minimum tensile loads in a T-peel test of the laminated coated conductor were 9.9 N, 12.5 N, and 7.6 N, respectively. The critical current ($I_c$) distributions of the non-laminated and laminated coated conductor were compared using anon-contact Hall probe method. The transport $I_c$ nearly matched the non-contact $I_c$; however, some degraded Ic regions were found on the length of 800 cm of laminated coated conductor. We confirmed that the cause of the partially degraded $I_c$ was due to an increase in line tension by (1) solidification induced by a change of composition that usually occurs in molten brass (Cu, Zn) in solder, or (2) non-homogeneity of the thickness of the coated conductor or metal tapes. We suggest that reflow soldering is a promising method for reinforced HTS tape if the controlling solder thickness and lamination guide are modified.

• Progress in Superconductivity and Cryogenics
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• v.20 no.4
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• pp.26-30
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• 2018

The turn-to-turn contact resistance of 2G high temperature superconducting (HTS) coils with metal insulation (MI) is closely related to the stability of the coils, current charging rate and delay time [1]. MI coils were fabricated using five kinds of metal tapes such as aluminum (Al) tape, brass tape, stainless steel (SS) tape, copper (Cu)-plated tape and one-sided Cu-plated SS tape. The turn-to-turn contact surface resistances of co-winding model coils using Al tape, brass tape, and SS tape were 342.6, 343.6 and $724.8{\mu}{\Omega}{\cdot}cm^2$, respectively. The turn-to-turn contact resistance of the model coil using the one-sided Cu-plated SS tape was $ 248.8{\mu}{\Omega}{\cdot}cm^2$, which was lower than that of Al and brass tape. Al or brass tape can be used to reduce contact resistance and improve the stability of the coil. Considering strength, SS tape is recommended. For strength and low contact resistance, SS tape with copper plating on one side can be used.

• Progress in Superconductivity and Cryogenics
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• v.9 no.4
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• pp.24-27
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• 2007

The purpose of this work is to develop, integrate, and implement an optical characterization method to evaluate physical properties in coated conductors and investigate the local distribution of the causes of degraded performance. The method that we selected at this moment is Raman scattering spectroscopy, which is accompanied with measurements of local supercurrent transport, phase composition, microstructure, and epitaxy quality for coated conductors that range in size up to multi-meter-length tapes and that embrace the entire tape embodiment (substrate through cap layer). The establishment of Raman spectroscopy as an on-line process monitoring tool is our eventual goal of research, but it requires very robust and cost-effective equipments. We analyzed $YBa_2Cu_3O_7(YBCO)$ thin films grown at various substrate temperatures by using Raman spectroscopy. YBCO films were grown by a high-rate electron-beam co-evaporation method. Raman spectra of YBCO films with lower-transport properties exhibit additional phonon modes at ${\sim}300cm^{-1}$, ${\sim}600cm^{-1}$ and ${\sim}630cm^{-1}$, which are related to second-phases such as $Ba_2Cu_3O_{5.9}$ and $BaCuO_2$. We propose a new method to characterize Raman spectra of coated conductors for an in-line quality control.

• Progress in Superconductivity
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• v.8 no.2
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• pp.175-180
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• 2007

High temperature superconductor $YBa_2Cu_3O_{7-x}$ (YBCO) films have been grown by in-situ electron beam evaporation on artificial metal tapes such as ion-beam assisted deposition (IBAD) and rolling assisted biaxially textured substrates (RABiTS). Deposition rate of the YBCO films is $10{\sim}100{\AA}/sec$. X-ray diffraction shows that the films are grown epitaxially but have inter-diffusion phases, like as $BaZrO_3\;or\;BaCeO_3$, at their interfaces between YBCO and yttrium-stabilized zirconia (YSZ) or $CeO_2$, respectively. Secondary ion mass spectroscopy depth profile of the films confirms diffused region between YBCO and the buffer layers, indicating that the growth temperature ($850{\sim}900^{\circ}C$) is high enough to cause diffusion of Zr and Ba. The films on both the substrates show four-fold symmetry of in-plane alignment but their width in the -scan is around $12{\sim}15^{\circ}$. Transmission electron microscopy shows an interesting interface layer of epitaxial CuO between YBCO and YSZ, of which growth origin may be related to liquid flukes of Ba-Cu-O. Resistivity vs temperature curves of the films on both substrates were measured. Resistivity at room temperature is between 300 and 500 cm, the extrapolated value of resistivity at 0 K is nearly zero, and superconducting transition temperature is $85{\sim}90K$. However, critical current density of the films is very low, ${\sim}10^3A/cm^2$. Cracking of the grains and high-growth-temperature induced reaction between YBCO and buffer layers are possible reasons for this low critical current density.