• KIEE International Transactions on Electrophysics and Applications
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• 제5C권6호
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• pp.251-256
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• 2005

Directionally melt-textured high $T_c\;(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_{2}Cu_{3}O_y$ [(YNS)-123] superconductor was systematically investigated by the zone melt growth process in air. A sample prepared by this method showed well-textured microstructure, and $(Y_{0.5}Nd_{0.25}Sm_{0.25})_{2}BaCuO_5$[(YNS)211] inclusions were uniformly dispersed in large $(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_{2}Cu_{3}O_y$ [(YNS)123] matrix. High irreversibility field and magnetization hysteresis loop of the zone melt-textured (YNS)-123 sample exhibited the enhanced flux pinning, compared with $YBa_{2}Cu_{3}O_y$ (Y-123) sample without RE(rare earth). Critical current density of (YNS)-123 sample was $2.5{\times}10^4\;A/cm^2$ at 2 T and 77 K.

• 한국세라믹학회지
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• 제56권6호
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• pp.589-595
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• 2019

The top-seeded solution growth (TSSG) method is an effective approach for the growth of high-quality SiC single crystals. In this method, the temperature gradient in the melt is the key factor determining the crystal growth rate and crystal quality. In this study, the effects of the aperture at the top of the hot-zone on the growth of the SiC single crystal obtained using the TSSG method were evaluated using multiphysics simulations. The temperature distribution and C concentration profile in the Si melt were taken into consideration. The simulation results showed that the adjustment of the aperture at the top of the hot-zone and the temperature gradient in the melt could be finely controlled. The surface morphology, crystal quality, and polytype stability of the grown SiC crystals were investigated using optical microscopy, high-resolution X-ray diffraction, and micro-Raman spectroscopy, respectively. The simulation and experimental results suggested that a small temperature gradient at the crystal-melt interface is suitable for growing high-quality SiC single crystals via the TSSG method.

• 한국결정성장학회지
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• 제3권2호
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• pp.117-124
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• 1993

연속성장법은 crystal growth chamber의 상부에 있는 reservoir에서 원료 분말을 연속적으로 공급하면서 도가니 하부에 용융대를 형성시킨 후, 종자결정을 용융대에 dipping하여 회전시키면서 아래로 끌어내려 단결정을 성장시키는 방법이다. 본 연구에서는 연속 성장법을 이용하여 silicon 단결정을 육성시켰으며 연속성장에 영향을 미치는 인자는 critical melt level, 원료공급속도, 성장속도, graphite crucible과 gruphite susceptor의 형태, work coil의 위치에 따른 graphite susceptor의 수직온도구배, 중력과 종자결정의 회전에 의한 원심력이 용융대의 안정화에 미치는 영향과 용융액 표면에서 일어나는 소결현상에 관해 고찰하였다.

• 한국결정성장학회지
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• 제15권5호
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• pp.188-192
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• 2005

High $T_c(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_2Cu_3O_y[(YNS)-123]$ superconductors with/without $CeO_2$ additive were systematically investigated by the zone melt growth process in air. Cylindrical green rods of (YNS)-123 oxides were fabricated by cold isostatic pressing (CIP) method using rubber mould. A sample prepared by this method showed well-textured microstructure, and $(Y_{0.5}Nd_{0.25}Sm_{0.25})_2BaCuO_5[(YNS)211]$ nonsuperconducting inclusions were uniformly dispersed in large $(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_2Cu_3O_y$[(YNS)123] superconducting matrix. In this study, optimum melting temperature and growth rate were $1100^{\circ}C$ and 3 mm/hr, respectively. The directionally melt-textured (YNS)-123 sample with $CeO_2$ additive showed an onset critical temperature $(T_c)\;T_c{\geq}93K$ and sharp superconducting transition.

• 한국전산유체공학회지
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• 제3권1호
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• pp.100-107
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• 1998

A numerical analysis of thermal stress over temperature variations near the crystal-melt interface is carried out for a floating-zone growth of Cadmium Telluride (CdTe). Thermocapillary convection determines crystal-melt interfacial shape and signature of temperature in the crystal. Large temperature gradients near the crystal-melt interface yield excessive thermal stresses in a crystal, which affect the dislocations of the crystal. Based on the assumption that the crystal is elastic and isotropic, thermal stresses in a crystal are computed and the effects of operating conditions are investigated. The results show that the extreme thermal stresses are concentrated near the interface of a crystal and the radial and the tangential stresses are the dominant ones. Concentrated heating profile increases the stresses within the crystal, otherwise, the pulling rate decreases the stresses.

• 한국결정성장학회지
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• 제4권3호
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• pp.325-335
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• 1994

Floating zone법으로 Spinel$(MgO.Al_2O_3)$을 성장시켰다. $MgO.Al_20_3$ spinel의 용융점은 $2135^{\circ}C$ 정도이고, 용융액으로부터 단결정을 성장시키는 방법에 있어서 매우 중용한 사항이다. Verneuil법과 RF-유도가열법을 이용한 czochralski법으로 성장시킨 경우가 보고된 바 있으나, 본 공법으로는 처음이라 사료된다. 본 연구에서는 halogen적외선 lamp를 이용한 image fur-nace에서 용융하여 아래쪽으로 하강함으로 인해 단결정을 육성시키는 floating zone법을 사용하여, $MgAl_2O_4$ spinel 단결정을 성장하였다. 또한 전이금속 이온을 doping하여 용융점의 하강 효과와 함께 적색, 녹색을 띈 단결정을 성장시켰다. 결론으로 성장계면과 용융대의 안전성에 주목하여 spinel 단결정 성장 기구를 규명하려 하였으며 성장계면이 오목함(결정쪽으로)에서 비롯되는 성장시의 양상에 대해 고찰하였다.

• 한국결정성장학회지
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• 제14권2호
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• pp.68-72
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• 2004

Sm 원소가 첨가된 $(Sm/Y)_{1.8}Ba_{2.4}Cu_{3.4}O_{7-x}$[이하 (Sm/Y)1.8] 고온초전도체를 국부용융성장법을 이용해 대기 중에서 용융성장실험을 하였다. 초기 (Sm/Y)1.8 초전도체 시편은 rubber 몰드를 이용해 냉간정수압성형(CIP) 과정을 거쳐 길이 방향 원통형상으로 제조되었다. 이렇게 얻어진 (Sm/Y)1.8 초전도체는 용융온도 및 성장속도에 따라 광학현미경, TEM그리고 SQUID magnetometer를 이용해 미세구조 및 초전도특성을 평가하였다. 이 결과 (Sm/Y)1.8 초전도체의 최적의 용융온도 및 성장속도는 $1085^{\circ}C$에서 3.5mm/hr로 나타났다. 특히 일방향으로 용융성장된 (Sm/Y)1.8 초전도체의 광학현미경 및 TEM에 의하 미세구조 관측 결과, 초전도상인 (Sm/Y)123 matrix내에 비초전도상인 (Sm/Y)211 inclusions이 균질하게 분포되어 있는 것이 관측되었다. 초전도특성을 평가한 결과 용융성장된 (Sm/Y)1.8초전도체는 90K에서 임계온도가 시작되어 77K이상의 온도에서 포화되는 특성을 보였다.

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

• 대한기계학회논문집B
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• 제20권10호
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• pp.3322-3333
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• 1996

A numerical analysis has been conducted to investigate a modified floating-zone crystal growth process in which most of the melt surface is covered with a heated ring. The crystal rod is not only pulled downward but rotated around its axisymmetric line during crystal growth process in order to produce the flat interface of crystal growth and the single crystal growth of NaNO3 is considered in 6mm diameter. The present study is made from a full-equation-based analysis considering a pulling velocity in all of solid and liquid domains and both of solid-liquid interfaces are tracked simultaneously with a governing equation in each domain. Numerical results are mainly presented for the comparison of the surface shape of rotational crystal rod with that of no-rotational crystal rod and the effects of revolution speeds of the crystal rod. Results show that the rotation of crystal rod produces more its flat surface. In addition, the shape of crystal growth near the centerline is more concaved with the increase in the revolution speed of crystal rod. The flow pattern and temperature distribution is analyzed and presented in each case. As the pulling velocity of crystal rod is increasing, the free surface of the melt below the heated ring is enlarged due to the crystal interface migrating downward.

• 한국결정성장학회지
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• 제13권2호
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• pp.83-87
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• 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.