• Proceedings of the Materials Research Society of Korea Conference
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• 1996.11a
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• pp.170-170
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• 1996

• Analytical Science and Technology
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• v.5 no.2
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• pp.223-228
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• 1992

$Bi_2Sr_2Ca_2Cu_3Oy$-based superconductor phases were synthesized by the wet process using acetate precursors. Superconducting transition temperature ($T_c$) was determined from both measurements of electrical resistivity and magnetic susceptibility for the samples which were sintered at the temperatures of $850^{\circ}C$, $860^{\circ}C$, and $870^{\circ}C$ for 40 hours, respectively. The values of carrier concentration from Hall measurements were compared with $T_c$ data as a function of the sintering temperature. The formation mechanism of the superconducting phase was tentatively discussed on a basis of the distribution profile concept of the carrier concentration and the amount of superconducting phases in a ceramic bulk. This explanation may be supported by the experimental results of correlation between the relative amount of superconducting phases and the difference of $T_c$ values between superconducting onset temperature and cutoff temperature at each sintering temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.2
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• pp.61-70
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• 2023

This paper examines the way of thinking and limitations of physicists regarding the phenomenon of superconductivity and outlines how room-temperature and ambient-pressure superconductors can be developed through the statistical thermodynamic background of the liquid state theory. In hypothesis, the number of electron states should be limited by confining them to a state close to one-Dimension. Simultaneously, the electron-electron interactions should be frequent enough for the electrons to have liquid-like properties. As an example of implementing the hypothesis, our team reports the development of room-temperature and ambient-pressure superconductivity of a material named LK-99 (superconducting compound name developed in the research), whose structure was revealed through numerous experiments with a clue found by chance. Moreover, we summarize the theoretical and experimental basis for the characteristics and discovery of the world's first superconducting material surpassing the critical temperature of 97℃ at atmospheric pressure.

• Korean Journal of Materials Research
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• v.4 no.7
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• pp.828-836
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• 1994

In order to investigate the high temperature deformation characteristics in YBaiCu307-, oxide superconductor, the compression test was performed at temperatures from $890^{\circ}C$ to $930^{\circ}C$ at initial strain rate between $1.0 x 10^{-5}s^{-1}\; and \; 1.0^{-4}s^{-1}$. As the temperature increased and the initial strain rate decreased, the flow stress decreased. The strain rate sensitivity exponent measured as 0.41-0.46, supporting occurence of a superplastic deformation. The activation energy for superplastic deformation was calculated as 500-580KJ/mol, which decreased with increasing Ag content. Microstructure of the superplastically-deformed specimens showed that a grain growth occurred during deformation, and it appeared to be considerable when Ag content increased, but most grains still remained equiaxed after deformation. In this study, the deformation mechanism of YBCO superconductor was the grain boundary sliding with the diffusional accommodation and the contribution of the gram boundary sliding to the total strain was estimated to be 65%.

• Korean Journal of Materials Research
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• v.5 no.3
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• pp.371-378
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• 1995

YBCO 산화물 초전도체의 초소성 변형에 대한 최적 변형조건을 파악하고자 80$0^{\circ}C$~93$0^{\circ}C$의 온도범위에서 1.0 $\times$ $10^{-3}$s^{-1}$!1.0 $\times$ $10^{-7}$s^{-1}$의 초기변형속도로 압축시험을 수행하였다. 변형속도 민감지수는 m=0.50 $\pm$ 0.1로 나타났다. 이는 결정립계 미끄러지\ulcornerㄹ 주 변형기구로 하는 초소성임을 의미한다. 결정립크기에 따른 유동응력과의 관계는 $\sigma$\propto$d^{1.8 $\pm$ 0.3}$의 지수함수식을 이루고 있으며 Nabarro-Hering 크\ulcorner과 상응하는 격자확산이 확산경로임을 보였다. 초소성 변형에 대한 활성화에너지는 Q=571 $\pm$ 30 kJ/mole이었다. 본 실험온도 구간에서 압축 변형시 변형속도, 변형응력 및 결정립크기에 따른 고온 변형거동 관계식은 $\varepsilon$=A$\sigma$^{2.00 $\pm$ 0.04 - 1.8 $\pm$ 0.3}$ exp(-571 $\pm$ 30kJ/RT)와 같이 유도 되었다. 본 실험조건에서 최적 초소성 변형조건은 86$0^{\circ}C$ 부금, 초기변형속도 ~1.0 $\times$ $10^{-4}$S^{-1}$이었다.

• Journal of the Korean Vacuum Society
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• v.4 no.2
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• pp.194-200
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• 1995

2-3nm의 공간분해능을 갖는 전자에너지손실분광법(Electron Energy Loss Spectroscopy, EELS)을 이용하여, 전기적 특성조사된 YBa2Cu3O7-$\delta$ 고온초전도체 쌍결정의 결정경계(grain boundary)에서 산소의 조성변화를 조사하였다. Misorientation angle이 $14^{\circ}$, $28^{\circ}$,$ 30^{\circ}$인 3개의 쌍결정 중에서 Josephson junction 특성을 보인 $28^{\circ}$ 및 $30^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서의 oxygen 1s absorption edge와 매우 다름을 알 수 있었다. 이는 결정경계에서의 산소조성이 결정내부에 비해 낮음을 의미하며, 그 영역이 결정경계 부근 20-40nm로, coherence length에 비해 큼을 알 수 있다. 반면에, flux pinningxmr성을 보인 $14^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서와 별 차이를 보이지 않았다. 따라서 일반적으로 관찰되어온, misorientation angle이 큰 결정경계에서의 Josephson junction 특성은 결정경계 부근에서 산소의 조성이 낮아지는데에 기인하며, 그 원인은 결정경계면을 통해 산소가 out-diffusion되기 때문인 것으로 생각된다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.744_745
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• 2009

고해상도의 NMR 연구 개발을 위해서는 고자장의 마그넷연구가 선행되어야 한다. 고자장을 구현하기 위해서는 저온초전도체를 이용한 마그넷뿐만이 아니라 고온초전도체를 이용한 인서트 코일의 연구가 필요하다. 연세대학교에서는 국가지정연구실사업으로 단백질 구조 규명의 초고자장 NMR 실현을 위한 고온초전도 인서트 코일 기술연구를 진행하고 있다. 본 논문에서는 고온초전도 인서트 코일 연구를 위해 제작할 LTS background magnet과 HTS 인서트 코일에 대한 전자장 해석을 진행하였다. 균일도나 선재 사양 등의 주요 변수 등을 고려하여 LTS background magnet과 HTS 인서트 코일에 적합한 사양을 결정하도록 하였다.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.04a
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• pp.85.2-85
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• 2003

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.9-12
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• 2001

The microstructure evolution and the peritectic solidification of Sm$Ba_{2}$$Cu_{3}$ $O_{7-\delta}$ superconducting materials during the isothermal annealing were studied over the temperature range 1030-$1060^{\circ}C$ The faceted growth of the peritectic phase and its dependence upon Sm-diffusion in the liquid phase are discussed. A growth model is proposed to explain the growth shape of Sm123 crystals.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.4
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• pp.165-165
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• 2023