• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1241-1242
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• 2006

Electromagnetic properties of $CeO_2$ doped and undoped YBaCuO superconductors were evaluated to investigate the effect of pinning center on the magnetization and magnetic shielding. The variation $\DeltaM$ with doping was maximum for 3% doping and decrease with further doping. The magnetic shielding was evaluated by measuring the induced voltage in secondary coil and the voltage initially set to 0.5V, decreased to 0.17V and 0.28V respectively for the undoped and 3% $CeO_2$ doped sample. The much less change in the induced voltage for the 3% doped sample is attributed to the increased flux shielding by shielding vortex current. The $CeO_2$ was converted to fine $BaCeO_3$ particles which were trapped in YBaCuO superconductor during the reaction sintering. The trapped fine particles, $BaCeO_3$ may be acted as a flux pinning center.

• 한국초전도ㆍ저온공학회논문지
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• 제1권1호
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• pp.1-6
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• 1999

The microstructures of top seed mult processde $\textrm{YBa}_2\textrm{Cu}_3\textrm{O}_7$.$\delta$ single crystal were studied. Although shape of the seed was not faceted. the growth shape of Y123 single crystal was faceted. It was observed that Y211 phases were trapped in specific spaces of the faceted region. From the microstructural investigation. it was suggested that the segregation of Y211 is due to the difference of growth rates in crystal direction. When a single crystal was grown by the single seed with stepped multi surfaces. a microstrue was grown from multi-seed. The microstructure show the possibility of multi-seed growth. Corn kernel like structure without Y211 phase was observed and seemed to be formed by the diffusion reaction between Y211 phase in crystal and liquid wetted on the crystal. the diagonal line on Y123 crystal was observed that it was formed by the corn kernel like structure.

• 한국초전도ㆍ저온공학회논문지
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• 제22권1호
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• pp.1-6
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• 2020

This is a parameter study for the direct fabrication of a large grain YBCO bulk superconductors using Y₂O₃, BaCO₃ and CuO powders without any grinding step. The cracks, which have been formed due to volume contraction during calcination step, have been prevented by controlling the heating rate at 930~950 ℃. It has been observed that multi-grain growth has occurred due to the dissolution of Sm123 seed due to the retention of carbon in Ba-Cu-O melt. In order to accelerate the carbon release in prior calcination heat treatment, the reduction of pellet thickness and the drilling of artificial holes have been applied. Single-grain YBCO bulk superconductor has been successfully fabricated by stacking multiple thin slab. However, the crack formation has been rather prominent for the compact with artificial holes. The use of buffer pellet, which is supposed to act as diffusion barrier, has prevented the dissolution of Sm123 seed crystal and has led to the growth of single grain of high content of carbon containing specimen.

• Progress in Superconductivity
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• 제8권2호
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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.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2007년도 High Temperature Superconductivity Vol.XVII
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• pp.82-82
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• 2007

• 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.

• 한국초전도ㆍ저온공학회논문지
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• 제5권3호
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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.

• E2M - 전기 전자와 첨단 소재
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• 제3권3호
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• pp.215-223
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• 1990

Y-Ba-Cu-O계 고온 초전도체를 소결, 소결+HIP encapsulation방법으로 각각 제작하였다. 소결은 900.deg.C~960.deg.C에서 하였으며 소결시편의 일부는 HIP처리 하였는데 이때 HIP조건은 150MPa Ar압력에서 800.deg.C, 30min이었다. HIP시편의 상대밀도는 90%~93%의 밀도를 갖는 소결시편보다 5%~8% 증가하였다. 열처리 조건에 따른 x-ray 회절분석은 사방정-정방정 상변태를 보여주었다. 임계온도(Tc)는 91.deg.k 에서 전기비정항이 급격히 감소하기 시작하여 89.deg.k에서 완전히 0이 되었으며 전이폭은 3.deg.k내로 매우 좁았다. 임계전류밀도(Jc)는 소결시편의 경우 전형적인 ~159A/$cm^{2}$의 값을 보였으나 HIP처리 후 ~89A/$cm^{2}$로 감소했기 때문이라 생각하였다. 경도와 인성은 각각 38GPa과 2.9MPam$^{1}$2/로 증가하였다.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2009년도 Korea Superconductivity Society Meeting 2009
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• pp.50-50
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• 2009

• 한국진공학회:학술대회논문집
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• 한국진공학회 2001년도 창립10주년 제20회 학술발표회
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• pp.87-87
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• 2001