• Electrical & Electronic Materials
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• v.6 no.6
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• pp.514-522
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• 1993

본 연구에서는 Ag/ 첨가에 의한 YB $a_{2}$C $u_{3}$ $O_{7-{\delta}}$산화물의 초전도 특성 변화를 조사하였다. Ag가 첨가된 YB $a_{2}$C $u_{3-x}$A $g_{x}$ $O_{7-{\delta}}$ 산화물 시료를 만들고 이 시료들에 대한 X-ray 회절분석, IR흡수 스펙트럼분석, 임계온도(Tc)측정 및 자화(M-H)특성 측정등을 통하여 제조된 시료의 물리적 성질을 조사하였다. X-ray 회절실험 결과로 부터 x.leq.0.03인 경우에는 YB $a_{2}$C $u_{3-x}$A $g_{x}$ $O_{7-{\delta}}$가 단일상의 물질로 존재하고 x가 증가함에 따라 불순물상( $Y_{2}$ $O_{3}$, 순Ag)이 나타남을 알 수 있었다. IR흡수의 실험결과에서 Cu와 치환되어 들어간 Ag의 Ag-O 결합에 의한 흡수 스펙트럼(670$cm^{-1}$ /)이 관측되었다. 실험 결과로 부터 치환된 Ag의 양 x가 증가함에 따라 Tc가 조금씩 낮아지는 경향이 있었으며 자화의 세기 및 임계자장( $H_{C2}$)은 급격히 감소함을 알 수 있었고 또 M-H특성곡선에는 히스테리시스 특성이 나타났다.났다..났다.다.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.141-144
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• 2000

We report on the influence of d-wave pairing symmetry in high-T$_c$ superconductor by tunneling spectroscopy. The zerobias conductance peak(ZBCP) which is produced by tunneling through the ab-plane is observed on both of metal Au/YBa$_2$Cu$_3$O$_y$(N/S) tunnel junctions and ferromagnet Co/Au/ YBa$_2$Cu$_3$O$_y$(F/N/S) tunnel junctions. The effects of Andreev reflection on the differential conductance of each junctions are dependent on the tunnel direction. For the S/N/F junction, it appears the suppression of the ZBCP due to the suppression of Andreev reflection at the interface between a ferromagnetic material and a d-wave superconductor. By comparing these experimental results with recent theoretical works on Andreev reflection, the existence of Andreev bound state is verified in high-T$_c$ superconductor, due to the d-wave symmetry of the pair potential.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.71-74
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• 1999

We have fabricated high-T$_c$ superconducting YBa$_2Cu_3O_{7-{\delta}}\;/SrTiO_3/\;YBa_2Cu_3O_{7-{\delta}}$ (YBCO/STO/YBCO) multilayer structure on (001) $SrTiO_3$ substrate by using pulsed laser deposition technique for applying to ground plane of single flux quantum digital circuits. In this structure, the top and bottom YBCO layers were connected through the holes in the STO insulating layer. The critical temperature of the two YBCO layers connected each other was 86 K after annealing at 500 $^{\circ}C$ in $O_2$ atm for about 60 hr. This result shows that the annealing process is very important fabricating YBCO/STO/YBCO multilayer structure An experiment to optimize the fabrication process of YSCO/ST0/YBCO multilayer structure with good quality is in progress.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.384-387
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• 1999

A new multi-seeding process for the growth of YBa$_2Cu_3O_x$ single crystals was developed. This process introduces an additional heating step to peritectic temperature and a subsequent slow cooling step to the growth temperature following the point when the crystals contacted. The crystal growth was resumed thereafter. The results obtained with this new process were compared with those of the conventional growth process, in which materials were only kept at the growth temperature. There was significant improvement in trapped magnetic field over the conventional multi-seeding process, which is believed to be due to complete elimination of liquid phase between crystals.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1345-1348
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• 1997

$YBa_2Cu_3O_x$ samples were fabricated by MPMG(Melt Powder Melt Growth). The effects of the $Y_2BaCuO_5$ and Ag addition on $YBa_2Cu_3O_x$ were studied throuth the Jc, Tc and magnetization. For the application of the bulk HTSC to current limiter, fly wheel and current lead and so on, the critical charateristics were investigated and compared with the solid sintering method.

• Journal of the Korean Ceramic Society
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• v.26 no.1
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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.

• Progress in Superconductivity
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• v.13 no.2
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• pp.133-138
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• 2011

To reduce the processing cost of the single grain REBCO (RE: Rare-earth elements) bulk superconductors, a cost-effective process should be developed. One possible way of developing the cost-effective process is the use of low-cost precursor powders. In this study, the single grain YBCO superconductors were fabricated using a home made powder. $YBa_2Cu_3O_{7-y}$ (Y123) powders were synthesized at $850-900^{\circ}C$ in air by the powder calcination method with repeated crushing and heat treatment steps. The processing parameters for the fabrication of single grain Y123 bulk superconductors, $T_{max}$ (maximum temperature), $T_p$ (peritectic temperature) and a cooling rate through $T_p$ were optimized. To enhance the flux pinning capacity of the single grain Y123 samples, $Y_2BaCuO_5$ (Y211) particles were dispersed in the Y123 matrix by adding $Y_2O_3$ powder to the calcined Y123 powder. Applying the optimized processing condition, the single grain Y123 superconductors with $T_c=91\;K$ and $J_c=1.5{\times}10^4\;A/cm^2$ at 2 T were successfully fabricated using a home made powder. The levitation forces and trapped magnetic field at 77 K measured using a Nd-B-Fe permanent magnet of 5300 G were 47 N and 3000 G, respectively, which are comparable to those obtained for the samples fabricated using a commercial grade Y123 powders.

• Progress in Superconductivity
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• v.5 no.2
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• pp.114-117
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• 2004

We fabricated large single grain YBa$_2$Cu$_3$O$_{x}$ (Y-123) superconductors. The single grain Y-123 was grown by top seeded melt growth (TSMG) method. In a conventional box furnace with uniform temperature distribution, it was very difficult to grow large single grain Y-123 superconductors due to the size limitation in growth. To overcome the size limitation, we applied a radial thermal gradient (lower temperature at sample center and higher temperature on the sample edge) to the TSMG process. In this case, large single grain Y-123 could be easily grown. This is attributed that the liquid of the sample edge was maintained at the high temperature compared to the growth front. Using this method, we successfully fabricated a large single grain Y-123 of 6.4 cm X6.4 cm

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.217-217
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• 2003

초전도체 선재를 제작하기위해 YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) 와 Ni substrates사이의 계면 문제를 해결하기 위한 buffer layer로써 CaRuO$_3$ (CRO) thu film이 제안되었는데, 이런 buffer layer의 조건으로는Ni metal과 YBCO superconductor사이의 화학적 반응이 없어야 하고 metal component가 YBCO로 diffusion되는 것을 막아주어야 하며 substrates의 산화를 막아주어야 한다. 이런 조건을 만족시키는 것 중에서 CRO thin film이 가장 적절하였지만, CRO의 orthorhombic구조의 distortion에 의만 lattice mismatch 문제가 발생하였다. 이러한 문제를 해결하기 위해 이론적인 구조 분석을 통한 CRO의superconductor buffer layer로써의 가능성을 검토해 보는 것이 목적이다.

• Progress in Superconductivity and Cryogenics
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• v.5 no.3
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• pp.1-5
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• 2003

The effect of CeO$_2$ coating on the surface nucleation of the top-seeded melt-growth processed YBCO superconductors was studied. It was effective that the coating of Y123 compact surfaces by CeO$_2$ powder suppressed the undesirable subsidiary YBa$_2$Cu$_3$O$_{7-y}$ (Y123) nucleation during melt processing. BaCeO$_3$ was formed in the CeO$_2$-coated layers, which might cause a CuO-excessive liquid at the partial melt stage of $Y_2$BaCuO$_{5}$(Y211) plus liquid, and thus the Y123 nucleation at the YBCO compact surfaces could be suppressed during the melt growth of Y123 grain. In addition, the CeO$_2$ refined the Y211 particles near the compact / coating interface. While the levitation forces of the top surfaces with and without CeO$_2$ coating were similar to each other, the levitation force of the interior of the CeO$_2$ coated sample was higher than that of the interior of the sample without CeO$_2$ coating, which was attributed to the suppression of subsidiary Y123 nucleation at the compact walls.s.s.