• 한국결정성장학회지
• /
• 제4권2호
• /
• pp.169-177
• /
• 1994

결정성장된 시편의 농도분포를 제어하기 위해서는 초기융액의 농도를 균일하게 하여야 한다. 용질농도가 초기융액에 있어서 균일하지 않다면, 성장된 시편에 예측한 것과 다른 거시편석이 발생할 수 있다. 위 쪽의 온도가 높은 온도 구배를 갖고 아래로부터 응고를 진행시키는 Bridgman 방법으로 Al-Cu 합금을 성장시키는 경우, 성장된 시편의 어용질 농도분포가 초기응고 부분이 높고 을고가 진행됨에 따라 감소하는 경향을 갖는 것으로 관찰되었다. 이런 현사은 주괴가 녹으면서 도가니와 주괴의 틈으로 스며나온 Cu의 농도가 높은 융액이 주괴가 완전히 녹은 후의 대류에 의해 아래부분에 축적됨으로 발생했다. Al-Mg 합금의 경우 도가니와 주괴의 틈으로 스며나온 Mg의 농도가 높은 융액이 주괴가 완전히 녹은 후의 대류에 의해 떠오르면서 용질 농도분포가 성장중에 최소값을 가지는 것으로 나타났다. 이러한 거시편석을 억제하기 위하여, 균질화 처리 또는 도가니와 주괴의 틈을 없게 함으로 균일한 농도의 초기유액을 얻었다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
• /
• pp.243-243
• /
• 2007

We have studied the electrical properties and microstructure of $(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_2Cu_3O_y[(YNS)-123]$ Oxides by rod-type seeded melt growth process(RSMG) in air atmosphere. Rod-type $NdBa_2Cu_3O_y${Nd-123) seed crystals made a extrusion process method, were used for achieving the ab-plane alignment having large grains perpendicular to the center of (YNS)-123 samples. The observations using SEM and TEM micrographs of the melt-textured (YNS)-123 samples revealed that the nonsuperconducting $(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_2Cu_3O_y[(YNS)-211]$ inclusions are uniformly distributed in the superconducting matrix. The microstructure and electrical properties were investigated by XRD, SEM, TEM and DC SQUID magnetometer. The sample showed a sharp superconducting transition at 90 K. The magnetization values of the (YNS)-123 sample exhibited the enhanced electrical properties, compared with $YBa_2Cu_3O_y$(Y-123) sample.

• Applied Microscopy
• /
• 제26권2호
• /
• pp.235-241
• /
• 1996

Amophization and decomposition behaviour in $Mg_{62}Cu_{26}Y_{12}$ alloy prepared by melt spinning method and wedge type metal mold casting method have been investigated by a detailed transmission electron microscopy. Amorphous phase has formed in melt-spun ribbon. In the case of the wedge type specimen, however, the amorphous phase has formed only around the tip area within about 2 mm thickness. The remaining part of the wedge type specimen consists of crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$. The supercooling for crystallization behaviour of the amorphous $Mg_{62}Cu_{26}Y_{12}$ alloy, ${\Delta}T_x$ has been measured to be about 60 K. Such a large undercooling of the crystallization bahaviour enables formation of the amorphous phase in the $Mg_{62}Cu_{26}Y_{12}$ alloy under the cooling rate of $10^{2}K/s$. The amorphous $Mg_{62}Cu_{26}Y_{12}$ has decomposed into crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$ after heat treatment at $170^{\circ}C\;and\;250^{\circ}C$.

• 한국초전도ㆍ저온공학회논문지
• /
• 제5권3호
• /
• pp.1-5
• /
• 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.

• 한국결정성장학회지
• /
• 제13권2호
• /
• pp.83-87
• /
• 2003

부유대역용융성장법을 이용한 $(Nd/Y)_{1.8}Ba_{}2.4Cu_{3.4}O_{7-x}$[이하 (Nd/Y)1.8]계 고온초전도체를 대기 중에서 용융성장실험을 하였다. 용융성장에 사용된 (Nd/Y)1.8 시편은 rubber 몰드를 이용해 냉간정수압성형(CIP) 과정을 거쳐 길이방향 원통 형상으로 제조되었다. 용융성장 된 (Nd/Y)1.8 초전도체는 SEM, TEM 그리고 SQUID magnetometer를 이용해 미세구조 및 초전도특성을을 평가하였다. 특히 용융성장 된 (Nd/Y)1.8 초전도체의 SEM에 의한 미세구조 관측 결과 초전도상인 (Nd/Y)123 matrix 내에 비초전도상인 (Nd/Y)211 inclusions이 균질하게 분포되어 있는 것이 관측되었다. 또한 용융성장 된 (Nd/Y)1.8 초전도체는 90K에서 임계온도가 시작되어 77K 이상의 온도에서 포화되는 특성을 보였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제48권4호
• /
• pp.221-225
• /
• 1999

This paper shows the parameters to affect the critical characteristic of YBaCuO superconducting bulk fabricated by MPMG (Melt Powdered Melt Growth)process. In order to investigate proper processing variables, the effect of the holding time at the melting temperature and that of the slow cooling time in $O_2\; ambient\; on\; the\; J_c$ were experimented. And then with the above obtained heat treatment conditions, the effects of addition of $Y_2BaCuO_5\; and\; Ag\; on\; the\; J_c$ were also investigated. A proper slow cooling time yields phase transformation from Tetragonal $(YBa_2Cu_3O_6)$ to Orthorhombic $(YBa_2Cu_3O_7)$ during an annealing time in $O_2$. Ag addition plays a role in increasing the $T_c\; and\; the J_c$, but the magnetization decreases. The $J_c$ and the magnetization increase with addition of Y211. $J_c$ of the sample added Ag 10wt% is superiorover 3000 G. Proper holding time, slow cooling time and amount of impurity addition are important parameters in fabricating the YBaCuO bulk by MPMG process with high $J_c$.

• 한국분말재료학회지
• /
• 제8권2호
• /
• pp.117-123
• /
• 2001

Formation of pores in melt-processed $YBa_2Cu_3O_{7-x}$ (123) oxides and its effect on the microstructure were studied. Spherical pores with a size of a few tens of microns were formed due to the evolution of oxygen gas during melting of a 123 oxide. Some of pores were converted into liquid pockets by liquid filling, but others remained unfilled. The liquid pockets were converted into spherical 123 regions with a lower $Y_2BaCuO_5$ (211)density through the peritectic reaction during subsequent cooling, while the pores were entrapped into the periteictically grown 123 grains. The spherical 123 regions often consists of a residual melt due to the unbalanced peritectically reaction.

• Progress in Superconductivity
• /
• 제1권2호
• /
• pp.89-94
• /
• 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.

• Transactions on Electrical and Electronic Materials
• /
• 제6권6호
• /
• pp.284-288
• /
• 2005

We have systematically studied the superconducting properties and flux pinning enhancement of $(Y_{0.33}Sm_{0.33}Nd_{0.33})\;Ba_2Cu_3O_y$ [(YSN)-123] composite oxides by melt growth process in air. A sample prepared by this method showed well-textured microstructure, and $(Y_{0.33}Sm_{0.33}Nd_{0.33})\;BaCuO_5$ [(YSN)211] nonsuperconducting particles were uniformly dispersed in large (YSN) 123 superconducting matrix. The sample showed a sharp superconducting transition at 91 K. The magnetization measurements of the (YSN)-123 sample exhibited the enhanced flux pinning, compared with $YBa_2Cu_3O_y$ (Y-123) sample without Sm and Nd. Critical current densities of (YSN)-123 sample was $2.5{\times}10^4 A/cm^2$ at 2 T and 77 K.

• Transactions on Electrical and Electronic Materials
• /
• 제5권2호
• /
• pp.81-85
• /
• 2004

High T$\_$c/ (Sm/Y)$\_$1.8/Ba$\_$2.4/Cu$\_$3.4/O$\_$7-$\delta$/ ［(Sm/Y)］ superconductor, a combination of Y and Sm(50% each), was systematically investigated by the zone melt growth process. A sample prepared by this method showed well-textured microstructure, and (Sm/Y)$_2$BaCuO$\_$5/［(Sm/Y)211］inclusions were uniformly dispersed in large (Sm/Y)Ba$_2$Cu$_3$O$\_$y/ ［(Sm/Y)123］matrix. The sample showed a sharp superconducting transition at 91 K. The magnetization measurements of the (Sm/Y)1.8 sample exhibited the enhanced flux pinning, compared with Y$\_$1.8/Ba$\_$2.4/Cu$\_$3.4/O$\_$7-$\delta$/(Y1.8) sample without Sm. Critical current densities of (Sm/Y) 1.8 sample was 3.5${\times}$10$^4$A/$\textrm{cm}^2$ at 1 T and 77 K.