• Progress in Superconductivity
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• v.6 no.1
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• pp.41-45
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• 2004

Polycrystalline Tl-1223 superconductors with a chemical composition of (Tl, Pb, Bi)TEX>$ (Sr, Ba)<_2$$Ca_2$$Cu_3$$O_{x}$ were synthesized by the solid state reaction method. The optimum chemical composition was $Tl_{0.8}$ $Pb_{0.2}$ $Bi_{0.2}$ $Sr_{1.8}$ $Ba_{0.2}$ $Ca_{2.2}$ $Cu_3$$O_{x}$ And the optimum sintering temperature and time were $905^{\circ}C$ and 7.5h, respectively. The sample was evaluated for their superconducting properties by magnetization measurement. The critical temperature $T_{c}$ is 120 K and the critical current density $J_{c}$ (T=5K, 0T) is estimated to be ∼ $10^{5}$ A/$\textrm{cm}^2$ for $Tl_{0.8}$ $Pb_{0.2}$ $Bi_{0.2}$ $Sr_{1.8}$ $Ba_{0.2}$ $Ca_{2.2}$$Cu_3$$O_{x}$ .

• Progress in Superconductivity
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• v.1 no.2
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• pp.89-94
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• 2000

A YBCO superconductor was prepared in a short time by a melt infiltration process that utilizes meting of $Ba_3Cu5O_8$ powder and the infiltration into a porous $Y_2BaCuO_5$ compact. The processing parameters such as a reaction temperature and time, and atmosphere (air and $O_2$) were controlled to establish the fabrication condition. The formation of a $YBa_2Cu_3O_x$, phase and the developed microstructure are reported.

• Journal of Powder Materials
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• v.20 no.2
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• pp.142-147
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• 2013

$YBa_2Cu_3O_{7-y}$ (Y123) powders for the fabrication of bulk superconductors were synthesized by the powder reaction method using $Y_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The raw powders were weighed to the cation ratio of Y:Ba:Cu=1:2:3, mixed and calcined at $880^{\circ}C-930^{\circ}C$ in air with intermediate repeated crushing steps. It was found that the formation of Y123 powder was more sensitive to reaction temperature than reaction time. The calcined Y123 powder and a mixture of (Y123 + 0.25 mole $Y_2O_3$ + 1 wt.% $CeO_2$, $Y_{1.5}Ba_2Cu_3O_x$ (Y1.5)) were used as raw powders for the fabrication of poly-grain or single grain superconductors. The superconducting transition temperature ($T_{c,onset}$) of the sintered Y123 sample was 91 K and the transition width was as large as 11 K, whereas the $T_{c,onset}$ of the melt-grown Y1.5 sample was 90.5 K and the transition width was 3.5 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Y123 was 700 $A/cm^2$, whereas the $J_c$ of the top-seeded melt growth (TSMG) processed Y1.5 sample was $3.2{\times}10^4\;A/cm^2$. The magnetic flux density (H) at 77 K of the TSMG-processed Y123 and Y1.5 sample showed the 0.53 kG and 2.45 kG, respectively, which are 15% and 71% of the applied magnetic field of 3.5 kG. The high H value of the TSMG-processed Y1.5 sample is attributed to the formation of the larger superconducting grain with fine Y211 dispersion.

• Progress in Superconductivity and Cryogenics
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• v.19 no.3
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• pp.27-32
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• 2017

The effects of artificial holes on the trapped magnetic fields and magnetic levitation forces of very large single-grain $Y_{1.5}Ba_2Cu_3O_{7-y}$ (Y1.5) bulk superconductors were studied. Artificial holes were made for Y1.5 powder compacts by die pressing using cylindrical dies with a diameter of 30 mm or 40 m, or rectangular dies with a side length of 50 mm. The single grain Y1.5 bulk superconductors (25 mm, 33 mm in diameter and 42 mm in side length) with artificial holes were fabricated using a top-seeded melt growth (TSMG) process for the die-pressed Y1.5 powder compacts. The magnetic levitation forces at 77 K of the 25 mm single grain Y1.5 samples with one (diameters of 4.2 mm) or six artificial holes (diameters of 2.5 mm) were 10-17% higher than that of the Y1.5 sample without artificial holes. The trapped magnetic fields at 77 K of the Y1.5 samples with artificial holes were also 9.6-18% higher than that of the Y1.5 sample without artificial holes. The 33 mm and 42 mm single grain Y1.5 samples with artificial holes (2.5 mm and 4.2 mm in diameter) also showed trapped magnetic fields 10-13% higher than that of the Y1.5 samples without artificial holes in spite of the reduced superconducting volume fraction due to the presence of artificial holes. The property enhancement in the large single grain Y1.5 bulk superconductors appears to be attributed to the formation of the pore-free regions near the artificial holes and the homogeneous oxygen distribution in the large Y123 grains.

• Korean Journal of Materials Research
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• v.30 no.7
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• pp.343-349
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• 2020

NKN [(Na,K)NbO₃] is a candidate lead-free piezoelectric material to replace PZT [Pb(Zr,Ti)O₃]. A single crystal has excellent piezoelectric-properties and its properties are dependent of the crystal orientation direction. However, it is hard to fabricate a single crystal with stoichiometrically stable composition due to volatilization of sodium during the growth process. To solve this problem, a solid solution composition is designed (Na,K)NbO₃-Ba(Cu,Nb)O₃ and solid state grain growth is studied for a sizable single crystal. Ceramic powders of (Na,K)NbO₃-M(Cu,Nb)O₃ (M = Ca, Sr, Ba) are synthesized and grain growth behavior is investigated for different temperatures and times. Average normal grain sizes of individual specimens, which are heat-treated at 1,125 ℃ for 10 h, are 6.9, 2.8, and 1.6 ㎛ for M = Ca, Sr, and Ba, respectively. Depending on M, the distortion of NKN structure can be altered. XRD results show that (NKN-CaCuN: shrunken orthorhombic; NKN-SrCuN: orthorhombic; NKN-BaCuN: cubic). For the sample heat-treated at 1,125 ℃ for 10 h, the maximum grain sizes of individual specimens are measured as 40, 5, and 4,000 ㎛ for M = Ca, Sr, and Ba, respectively. This abnormal grain size is related to the partial melting temperature (NKN-CaCuN: 960 ℃; NKN-SrCuN: 971 ℃; NKN-BaCuN: 945 ℃).

• Journal of the Korean Vacuum Society
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• v.1 no.3
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• pp.389-394
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• 1992

용액분무법으로 (100) MgO 단결정 기판위에 YBa2Cu3O7-x 초전도박막을 제조하 였다. YBa2Cu3O7-x 초전도 박막의 Y, Ba, Cu 원자의 상대적인 비는 EDX의 검출 한계내에 서 1 : 2 : 3이었고, 이는 분무 용액속의 금속이온의 비와 같았다. YBa2Cu3O7-x 초전도 박 막의 결정구조는 단일 상의 사방구조였으며, 기판에 수직인 c축의 방향으로 grain이 성장되 었고, 격자상수 c0는 11.678$\AA$였다. 95$0^{\circ}C$의 공기중에서 10분간 열처리한 박막의 Tc-on=100K, Tc-zero=80K, Jc=2.5 $\times$ 104A/cm2였고, 95$0^{\circ}C$의 흐르는 산소분위기에서 10분간 열처리한 박막의 Tc-on=103K, Tc-zero=80K, Jc=1.0 $\times$ 105A/cm2였다. 초전도 박막의 미세구 조, grain 크기와 grain 경계폭은 제조후 열처리(post-annealing) 시간과 가스 분위기에 강 한 영향을 받았다.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.21-24
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• 2001

A series of superconducting Hg$Ba_{2}$Cu$O_{4+7}$ materials, containing $Ag_{x}$ additions with molar fraction x = 0, 0.05, 0.1, 0.3, and 0.5, have been studied. This study has showed that Ag additions lead to changes in superconducting properties of Hg-1201 materials. In addition, according to the amount of $Ag_{x}$ additions with molar fraction x up to 0.5, both $T_{c}$ and $J_{c}$ of Hg-1201 materials generally decrease with Ag-content. These and other results are discussed in this paper.

• 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.

• Electrical & Electronic Materials
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• v.4 no.4
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• pp.330-337
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• 1991

y의 크기가 0.02에서부터 2.0까지의 두 차수만큼 변하게 불소가 첨가된 YBa$_{2}$Cu$_{3}$$O_{7-x}$F$_{y}$ 초전도물질을 금속질산염과 수산화나트륨 및 불화나트륨을 써서 졸-겔법으로 제조하였다. 불소함유양들을 이온-선택 전극을 사용하여 측정하였다. 반응물질로 첨가된 불소전부가 최종시료속에 존재한다는 것을 알았다. XRD 관측으로부터 y.leq.0.2인 시료들은 단지 단상 페로브스카이트 구조로 되었고 반면 y.geq.0.5인 것들은 최종시료속에 BaF$_{2}$ YF$_{3}$및 CuO와 같은 화합물들과 함께 생성되어져 있다고 결론지을 수가 있다. 더구나 고체 $^{19}$ F 핵자기공명관측이 불소가 정말로 격자위치들 속에 혼입되어 있는지 여부를 확인하기 위하여 행해졌는데 실험결과로부터 YBa$_{2}$Cu$_{3}$$O_{7-x}$ 격자위치속에 혼입된 불소의 몰비는 화합물 1몰당 약 0.2라는 것을 보여주었다. 또한 전기저항률의 측정은 개시감계온도가 y.leq.0.2와 같이, 지정된 첨가율이 적은 영역에서는 y의 증가에 따라 약간씩 증가하는 경향이 있음을 보여주고 있다.

• Progress in Superconductivity and Cryogenics
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• v.13 no.4
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• pp.22-25
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• 2011

A single-coat $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) film of high critical currents ($I_c$) could be successfully fabricated by optimizing the viscosity of the coating solution in the metal-organic deposition (MOD) process. From a Ba-deficient coating solution (Y: Ba: Cu = 1: 1.5: 3) having the viscosity of 212 $mPa{\cdot}sec$, 0.9 ${\mu}m$-thick single coat YBCO film with the $I_c$ value of 289 A/cm-width ($J_c$ = 3.2 MA/$cm^2$) at 77 K was achievable on the $SrTiO_3$ (STO) substrate, which was superior to that of our previous report for 0.8 ${\mu}m$-thick single coat YBCO film from a stoichiometric coating solution (Y: Ba: Cu = 1: 2: 3) on the $LaAlO_3$ (LAO) substrate. This result might be attributed to denser and more homogeneous microstrcuture in the case of the YBCO film from the Ba-deficient coating solution.