• Korean Journal of Materials Research
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• v.23 no.6
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• pp.309-315
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• 2013

$GdBa_2Cu_3O_{7-y}$(Gd123) powders were synthesized by the solid-state reaction method using $Gd_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The synthesized Gd123 powder and the Gd123 powder with $Gd_2O_3$ addition ($Gd_{1.5}Ba_2Cu_3O_{7-y}$(Gd1.5)) were used as raw powders for the fabrication of Gd123 bulk superconductors. The Gd123 and Gd1.5 bulk superconductors were fabricated by sintering or a top-seeded melt growth (TSMG) process. The superconducting transition temperature ($T_{c,onset}$) of the sintered Gd123 was 93 K and the transition width was as large as 20 K. The $T_{c,onset}$ of the TSMG processed Gd123 was 82 K and the transition width was also as large as 12 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Gd123 and TSMG processed Gd123 were as low as a few hundreds A/$cm^2$. The addition of 0.25 mole $Gd_2O_3$ and 1 wt.% $CeO_2$ to Gd123 enhanced the $T_c$, $J_c$ and magnetic flux density (H) of the TSMG processed Gd123 sample owing to the formation of the superconducting phase with high flux pinning capability. The $T_c$ of the TSMG processed Gd1.5 was 92 K and the transition width was 1 K. The $J_cs$ at 77 K (0 T and 2 T) were $3.2{\times}10^4\;A/cm^2$ and $2.5{\times}10^4\;A/cm^2$, respectively. The H at 77 K of the TSMG-processed Gd1.5 was 1.96 kG, which is 54% of the applied magnetic field (3.45 kG).

• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.9-13
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• 2014

Effects of neutron irradiation on the superconducting properties of the undoped $MgB_2$ and the carbon(C)-doped $MgB_2$ bulk superconductors, prepared by an in situ reaction process using Mg and B powder, were investigated. The prepared $MgB_2$ samples were neutron-irradiated at the neutron fluence of $10^{16}-10^{18}n/cm^2$ in a Hanaro nuclear reactor of KAERI involving both fast and thermal neutron. The magnetic moment-temperature (M-T) and magnetization-magnetic field (M-H) curves before/after irradiation were obtained using magnetic property measurement system (MPMS). The superconducting critical temperature ($T_c$) and transition width were estimated from the M-T curves and critical current density ($J_c$) was estimated from the M-H curves using a Bean's critical model. The $T_cs$ of the undoped $MgB_2$ and C-doped $MgB_2$ before irradiation were 36.9-37.0 K and 36.6-36.8 K, respectively. The $T_cs$ decreased to 33.2 K and 31.6 K, respectively after irradiation at neutron fluence of $7.16{\times}10^{17}n/cm^2$, and decreased to 22.6 K and 24.0 K, respectively, at $3.13{\times}10^{18}n/cm^2$. The $J_c$ cross-over was observed at the high magnetic field of 5.2 T for the undoped $MgB_2$ irradiated at $7.16{\times}10^{17}n/cm^2$. The $T_c$ and $J_c$ variation after the neutron irradiation at various neutron fluences were explained in terms of the defect formation in the superconducting matrix by neutron irradiation.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.740-743
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• 1992

Effects of powder sintering and 2nd, pressing on the superconducting characteristics in the (Bi,Pb)SrCaCuO system have been studied. The sample prepared by the powder sintering process had a porous microstructure with a $T_c$ below 77 K, while the sample prepared by 2nd. pressing process had highly oriented microstructure with a $T_c$ above 100 K. The critical current density($J_c$) was relatively improved in the sample prepared by the 2nd. pressing process. But the value of $J_c$ is cosiderably low in practical use.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.18-24
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• 2019

This study was carried out to investigate the effect of milling of boron (B), which is one of raw materials of $MgB_2$, on the critical current density ($J_c$) of $MgB_2$. B powder used in this study is semi-amorphous B (Pavezyum, Turkey, 97% purity, 1 micron). The size of B powder was reduced by planetary milling using $ZrO_2$ balls (a diameter of 2 mm). The B powder and balls with a ratio of 1:20 were charged in a ceramic jar and then the jar was filled with toluene. The milling time was varied from 0 to 8 h. The milled B powders were mixed with Mg powder in the composition of (Mg+2B), and the powder mixtures were uniaxially pressed at 3 tons. The powder compacts were heat-treated at $700^{\circ}C$ for 1 h in flowing argon gas. Powder X-ray diffraction and FWHM (Full width at half maximum) were used to analyze the phase formation and crystallinity of $MgB_2$. The superconducting transition temperature ($T_c$) and $J_c$ of $MgB_2$ were measured using a magnetic property measurement system (MPMS). It was found that $B_2O_3$ was formed by B milling and the subsequent drying process, and the volume fraction of $B_2O_3$ increased as milling time increased. The $T_c$ of $MgB_2$ decreased with increasing milling time, which was explained in terms of the decreased volume fraction of $MgB_2$, the line broadening of $MgB_2$ peaks and the formation of $B_2O_3$. The $J_c$ at 5 K increased with increasing milling time. The $J_c$ increase is more remarkable at the magnetic field higher than 3 T. The $J_c$ at 5 K and 4 T was the highest as $4.37{\times}10^4A/cm^2$ when milling time was 2 h. The $J_c$ at 20 K also increased with increasing milling time. However, The $J_c$ of the samples with the prolonged milling for 6 and 8 h were lower than that of the non-milled sample.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.140-144
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• 1997

The effects of the particle size of precursor powder on the microstructure and Jc of Ag-sheathed Ri-2223 tapes were investigated. The calcined powder with overall composition of $Bi_{1-89}Pb_{0-41}Sr_{2-01}Ca_{2-23}Cu_{3-03}O_{y}$ was milled for various times using planetary ball mill. The transport property of the tapes were found to depend strongly on the particle size of the precursor powder Enhanced reactivity of the milled powder facilitated the formation of 2223 phase and resulted in an increase of Jc. Excessive milling, however, led to the amorphisation of the powder and degraded the electrical property of the tapes.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.315-318
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• 1999

Bi$_{2}Sr_{2}CaCu_{2}O_{\delta}$ superconducting films were rapidly fabricated on copper tape by liquid reaction between a Cu-free precursor and Cu tape (LiReac-PreCu) method. Those thick films were well oriented along the c-axis. The precursor was made by melt-quenched technology using twin roller. The melt-quenched films were transparent and glossy yellow in appearance. These films which were the compostion of Bi$_2SrCaO_y$, Bi$_3Sr_2CaO_z$ were placed on copper tape and then heated at various temperatures for several minutes in air. They were analyzed using X-ray powder diffraction, SEM, a DC four-probe method. The mechanism of superconducting phase formation . from the melt-quenched precursor on Cu tape was studied

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1516-1518
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• 1998

$YBa_2Cu_3O_x$(Yl23) Superconducting thick films on $Y_2BaCuO_5$(Y211) substrate were Prepared by surface diffusion process between $BaCuO_2$+CuO composite coating powder and a Y2ll substrate. X-ray diffraction shows that the Yl23 layer onto Y2ll substrate is the orthorhombic crystal structure. The specimen heated at $940^{\circ}C$ for 2h showed the maximum $J_c$ fo 500A/$cm^2$. Based on optimal condition, the superconducting fault current limiter(FCL) having a current limiting area 1mm wide and 66mm long was fabricated on Y211 substrate. A typical current limiting waveform was measured. When a voltage of 3V was applied, the fault current with a peak of 15A was limited to about 0.11A.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05b
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• pp.82-85
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• 2003

This dissertation describes an optimization method for fabricating thick films with superconducting YBCO powders by electrophoresis technique. The lateral alternating applied voltage caused to shake the superconducting powder vertically to the deposition field during the process of the oriented deposition so that it was deposited along the c-axis on the silver tape with shaky-aligned EPD. As the result, the optimized thin film fabrication method was obtained to get more dense and uniform surface morphology as well as the improved critical current density. For commercial utilization and efficiency, in this dissertation, alternating voltage of 25-120 V/cm in frequency of 60Hz was proposed to apply it as a subsidiary source for shaky-flow deposition so that the fabricated thin film showed uniform surface morphology with less voids and cracks and $T_{c.zero}$ of 90 K and the critical current density of $3419A/cm^2$.

• Korean Journal of Materials Research
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• v.1 no.2
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• pp.71-76
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• 1991

The superconducting powders in $YBa_2Cu_3O_{7-x}$ and Bi-Pb-Sr-Ca-Cu-O system were easily prepared from water in oil type emulsion by loading each cation into the aqueous phase. In $YBa_2Cu_3O_{7-x}$ system, the superconducting orthorhombic phase was formed by calcining at $750^{\circ}C$ for 10h in $O_2$. The size of the superconducting phase powders was submicron. The density of the sintered specimen using this powders was about 95% of the theoretical density and the resistance sharply decreases at about 90K, In Bi-Pb-Sr-Ca-Cu-O system the low Tc phase($(Bi, Pb)_2Sr_2Ca_1Cu_2O_y$) was formed by calcining at $800^{\circ}C$ for 10h in a low oxygen partial pressure of 1/20 atm The shape of clacined powder is thin plate of which size is about $2\mu\textrm{m}$ and thickness is smaller than $\mu\textrm{m}$. It was observed that the high Tc phase ($(Bi, Pb)_2Sr_2Ca_2Cu_3O_y$) was formed by sintering at $850^{\circ}C$ for 30h in oxygen pressure of 1/20 atm without intermediary grinding. The above sintered sample exhibited superconductivity with a Tc(zero)=105K.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.69-72
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• 1999

A Well oriented Bi$_2$re$_2$CaCu$_2$O$\sub$8/(Bi2212) superconductor thick films were formed successfully on a copper substrate by liquid reaction between a Cu-free precursor and Cu tape using method in which Cu-free BSCO powder mixture was printed on copper plate and heat-treated. And we examined the mechanism for the rapid formation of Bi2212 superconducting films from observing the surface microstructure with heat-treatment time. At heat-treatment temperature, the printing layer partially melt by reacting with CuO of the oxidizing copper plate, and the nonsuperconducting phases present in the melt are typically Bi-free phases and Cu-free phases. Following the partial melting, the Bi$_2$Sr$_2$CaCu$_2$O$\sub$8/ superconducting phase is formed at Bi-free phase/liquid interface by nucleation and grows. It was confirmed that the phase colony from the phase diagram of Bi$_2$O$_3$-(SrO+CaO)/2-CuO system is similar to the observed result.