• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.93-95
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• 2003

YBa$_2$Cu$_3$O$_{x}$ (Y123) single crystal was grown by TSMG (top seeded melt growth) method. Physical properties of Y123 single crystal were dependent on the shape and distribution of Y2BaCuOx (Y211) in it and on the oxygenation temperature and the holding time. In this work, It was investigated to an optimal oxygenation condition and a dependence of melting temperature and holding time on physical properties. The optimal oxygenation condition was found that it was heat-treated for 30 hours at 45$0^{\circ}C$, Also it was found that the critical current density and the size of Y211 were increased with the melting temperature and the holding time.e.

• Progress in Superconductivity
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• 제5권2호
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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

• Progress in Superconductivity
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• 제8권1호
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• pp.119-121
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• 2006

We studied the mechanical and magnetic properties of Y-Ba-Cu-O superconductor with and without resin and Ag impregnation. Bulk YBCO superconductor was manufactured with the top-seeded melt-growth method. Typical sample of 40mm X 20mm X 3mm was made and then 8 holes with 0.5mm diameter were drilled arbitrally. Epoxy resin and $AgNO_3$ were systematically added into the holes to compare the mechanical and magnetic properties of YBCO superconductor before and after reinforcement of resin and Ag. Based on the result of 3 point bending, bending strength increased with increasing amounts of resin and carbon nano-tube. However, it was found that the levitation force decreased after making hole, compared with virgin sample without hole.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.247-248
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• 2006

Bulk YBCO 초전도체는 top-seeded melt-growth 방법으로 제조되었다. YBCO bulk는 Epoxy resin과 $AgNO_3$를 보강해 초전도체의 기계적 강도를 향상하고자 하였다. Epoxy resin은 보강 재료인 STYCAST 2850-FT와 경화제인 CATALYST 24LV 를 100:5 비율로 혼합하여 제조한 후 mould에 넣고 $66^{\circ}C$에서 2시간 열처리 하였다 (rotary pump로 진공 분위기 조성). $AgNO_3$는 $350^{\circ}C$에서 2시간, $450^{\circ}C$에서 1시간 열처리 하여 Ag와 $NO_3$의 분리 후 YBCO bulk에 Ag가 보강되도록 하였다. Epoxy resin 과 분리된 Ag는 YBCO bluk의 crack과 void에 침투되는 것을 SEM과 광학현미경을 통해 관찰할 수 있었다. Three point bending test를 이용하여 보강 전후의 YBCO bulk의 기계적 강도를 측정하였다. 보강 후의 YBCO bluk의 기계적 강도는 보강 전에 비해 향상된 결과를 확인할 수 있었고, Epoxy resin과 $AgNO_3$를 보강한 YBCO는 기계적 강도 향상에 높은 신뢰성을 보이고 있다.

• 한국재료학회지
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• 제22권11호
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• pp.569-574
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• 2012

Large single grain $Gd_{1.5}Ba_2Cu_3O_{7-y}$ (Gd1.5) bulk superconductors were fabricated by a top-seeded melt growth (TSMG) process using an $NdBa_2Cu_3O_{7-y}$ seed. The seeded Gd1.5 powder compacts with a diameter of 50 mm were subjected to the heating cycles of a TSMG process. After the TSMG process, the diameter of the single grain Gd1.5 compact was reduced to 43 mm owing to the volume contraction during the heat treatment. The superconducting transition temperature ($T_c$) of the top surface of the single grain Gd1.5 sample was as high as 93.5 K. The critical current densities ($J_cs$) at 77 K and 1T and 1.5 T were in ranges of 25,200-43,900 $A/cm^2$ and 10,000-23,000 $A/cm^2$, respectively. The maximum attractive force at 77 K of the sample field-cooled using an Nd-B-Fe permanent magnet (surface magnetic field of 0. 527 T) was 108.3 N; the maximum repulsive force of the zero field-cooled sample was 262 N. The magnetic flux density of the sample field-cooled at 77 K was 0.311T, which is approximately 85% of the applied magnetic field of 0.375 T. Microstructure investigation showed that many $Gd_2BaCuO_5$ (Gd211) particles of a few ${\mu}m$ in size, which are flux pinning sites of Gd123, were trapped within the $GdBa_2Cu_3O_{7-y}$ (Gd123) grain; unreacted $Ba_3Cu_5O_8$ liquid and Gd211 particles were present near the edge regions of the single grain Gd1.5 bulk compact.

• 한국분말재료학회지
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• 제20권2호
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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.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.363-368
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• 1999

Multiseeding 방법을 사용하여 Y-Ba-Cu-0 초전도_ 시료를 제조하였다. Multiseeding은 여러개의 종자를 동시에 사용함으로써 단시간에 큰 size의 시료를 제조하고자 하는 의도에서 시도되었다. 또한 field-cooled 상태에서 포획 자기장의 크기를 측정함으로써 입자간 결합 상태와 시료의 품질을 평가하였다. 일반적인 방법으로 제조할 경우 포획 자기장 값은 입계를 지나면서 크게 감소하였는데, 이는 입계에 존재하는 잔류액상 및 미반응 211 입자 등에 기인한 결과이다. 입계를 따라 미반응상들이 잔류하는 현상을 억제하기 위해 본. 연구에서는 종자들간의 간격을 조절하였다. 그 결과 종자결정들간의 간격을 최대한 좁게 배열하였을 때 포획자기장의 크기가 입계에서 감소하지 않는 결과를 얻었다. 이와 같이 종자간의간격이 충분히 가까울 경우에는, 결정성장 초기에 두 입자가 하나로 결합될 수 있으므로 입계에 미반응 액상이 잔류하는 현상을 억제할수 있었던 것으로 생각된다.

• 한국초전도ㆍ저온공학회논문지
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• 제14권3호
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• pp.1-4
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• 2012

Effects of artificial holes on the cooling efficiency of single grain YBCO bulk superconductors were studied. Single grain YBCO bulk superconductors without artificial holes, with six 2.4 mm holes and six holes filled with Bi-Pb-Cd-Sn metal solder were fabricated by a top-seeded melt growth process for powder compacts with/without holes. Simulation for the cooling rate to a liquid nitrogen temperature (77 K) of YBCO samples was carried out using a finite element method (FEM) and the results are compared with the actual cooling rates of samples in liquid nitrogen. The simulated cooling times for the YBCO sample without holes, with six holes and with six holes filled with the metal solder were 80, 47 and 75 sec. respectively, which are similar to the actual cooling times of 84, 52 and 78 sec. estimated for the same samples cooled in liquid nitrogen. The shorter cooling time of the sample with artificial holes are attributed to the increased surface areas associated with the presence of artificial holes. The metal filling into the holes did not give any remarkable effect on the cooling efficiency.

• 한국초전도ㆍ저온공학회논문지
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• 제19권3호
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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.

• 한국재료학회지
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• 제23권6호
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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).