• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.3
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• pp.679-685
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• 2004

Although the electrophoretic deposition method has the advantage of simple processing procedure, less fabrication facilities, and easier control for deposition thickness and wire length, providing economical and technical merits, it also has the disadvantages of cracking and porosity phenomena, requiring an improved processing method for higher particle density and constant particle orientation. we have developed an optimization method to increase the particle density and to unify its orientation, and have performed a study to overcome the cracking and porosity problems in the fabricated superconductor. In order to improve the surface uniformity and the conduction properties of the fabricated YBCO thick films, a system that applies alternate voltage vertically has been developed for the first time and applied to the electrophoretic deposition process. The applied alternate electric field caused a force to be exerted on each YBCO particle and resulted in a rotation of the particle in the direction of applied electric field, accomplishing a uniform particle orientation. We name this process as the shaky-aligned electrophoretic deposition method. For commercial utilization and efficiency, in this dissertation, alternating voltage of 60 Hz and 25 ∼ 120 V/cm was proposed to apply it as a subsidiary source for shaky-flow deposition so that the fabricated thin film showed uniform surface morphology with less voids and cracks and Tc,zero of 90 K and the critical current density of 3419 A/$cm^2$.

• Korean Journal of Materials Research
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• v.9 no.8
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• pp.849-853
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• 1999

In the study, superconducting properties of $Bi_2$-x(sub)$LSr_2$Ca(sub)1+x(sub)$LCu_2$O(sub)8+d (x(sub)L=0, 0.05, 0.1, 0.2) films prepared by the LPE method was investigated. The peak decompositions of Sr3d and Ca2p XPS spectra, together with the EPMA results, elucidated the occupancies of Bi, Sr and Ca atoms on the SrO- and Ca-layers. The lattice parameter c monotonically increased with increasing x(sub)L for $0\leq$x(sub)L$\leq$0.2. The superconducting critical temperature T(sub)c showed a maximum value around x(sub)L=0.1. The x(sub)L dependence of the superconducting critical temperature T(sub)c and the lattice parameter c are explained by the changes of the excess oxygens in the BiO-layer. Since distribution and deficiency of the atoms in SrO-layer have influenced on superconducting properties and crystal structure.

• 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.

• Progress in Superconductivity and Cryogenics
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• v.8 no.1
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• pp.39-44
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• 2006

Before applying HTS power cable to the real utility. system analysis should be carried out by some simulation tools . Hereby the electrical power system analysis is very important for practical use of HTS devices. Nowadays PSCAD/EMTDC simulation tool is one of the most popular and useful analysis tool for the electrical power system analysis. Unfortunately the model component for HTS power cable is not provided in the PSCAD/EMTDC simulation tool In this paper. the EMTDC model component for HTS power cable has been developed considering critical current, critical temperature and recovery time constant that depend on the sorts of HTS wire. The numerical model of HTS Power cable in PSCAD/EMTDC was designed by using the real experimented data obtained from the real HTS 1G wire test. The utility application analysis of HTS power cable was also performed using the developed model component and the parameters of the real utility network in this study. The author's got good results. The developed model component for HTS power cable could be variously used when the power system includes HTS power cable, especially it will be readily analyzed by PSCAD/EMTDC in order to obtain the data for the level of fault current power flow, and power losses, and so on.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.274-277
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• 2003

Critical current(Ic) degradation of HTS tapes after bending is one of the hottest issues in HTS development and application studies. Many people are measuring Ic degradations for effect of bending radius. However even if the bending radius is larger than the breaking radius a HTS tapes can be damaged by repetitive bending, which is unavoidable in the winding processes. Therefore, We studied the Ic degradation after repetitive bending. at 77K with self-field, of Bi-2223 tapes processed by "Powder-in-Tube" technique, which was made by America Superconductor Corporation(AMSC) and superconductiing tapes that strain is imposed measured critical current by temperature difference of L$N_2$ and normal temperature. Like this, critical current could measure that degradation about 1~3％ by temperature difference. These results will amount the most important basis data in power electric machine of superconductivity cable, magnet, etc that winding work is require.

• Electrical & Electronic Materials
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• v.7 no.4
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• pp.306-311
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• 1994

In this study, the influence of the powder sintering, the 2nd sinteiing and the grinding time on the Superconducting properties in the Bi(Pb)SiCaCuO Superconductor has been studied. From the analysis of SEM and XRD patterns, it was known that the sample prepared by the process of powder sintering has a porous microstructure with the critical temperature(Tc) below 77K, while the sample prepared by the 2nd sintering has a highly oriented microstructure with the Tc above 100K. The Critical Current Density(Jc) of the sample prepared by the 2nd sintering was better than the sample prepared by the process of powder sinteiing, but it's Jc, was low in practical use. Also, the effect of grinding time from 0[min] to 120[min] was investigated. As the grinding time is increased, the samples degraded from high-Tc phase to low-Tc phase and nonsuperconducting phases.

• Journal of the Korean Ceramic Society
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• v.34 no.10
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• pp.1083-1091
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• 1997

As one of the chemical powder fabrication methods, the powder preparation method by using oxalate has the following advantages; (1) easy to control the chemical stoichiometry, (2) easy to fabricate homogeneous and fine particles, and (3) easy to be thermaly decomposed at low temperature. In the present study, the initial morphology and size distribution of the powder were controlled and the homogeniaty was improved. By carefully controlling the pH with NH4OH, the Bi(Pb)-Sr-Ca-Cu-O superconducting powders were prepared and investigated for their properties. The microstructures and the superconducting properties of the pelletized samples were investigated. Also, the microstructures and electrical properties of the samples prepared by tape casting method were investigated. The fabricated powders were spherical with less than 400 nm, but most of them were agglomerated to be 1~3 ${\mu}{\textrm}{m}$ in size. The critical temperature of the pelletized sample annealed at 84$0^{\circ}C$ for 72 hours in air was 110K. And the critical currents of annealed samples in air prepared by tape casting process for 24 hours and 72 hours were 0.6 A (Jc=600A/$\textrm{cm}^2$) and 1.9A (Jc=1, 900A/$\textrm{cm}^2$) respectively.

• Korean Journal of Materials Research
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• v.4 no.1
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• pp.37-43
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• 1994

Y-Ra-Cu-0 oxide superconductors were fabricated by the sinter-forging method to make the critical current density improve through controlling of microstructure and crystal texture. The grain alignment of oxide superconductor was formed by the sinter-forging process and it's c-axis orientation was parallel to the press direction.The orientation factor of texture increased with sinking temperature and pressure, and also grain alignment was improved by the addition of Ag. As for the sinterforged Y-Ba-Cu-O/Ag sample, the $T_c$(on-set) was not almost varied with the sinter-forging temperature, but $T_c\;^{zero}$ decreased more or less at high sinter-forging temperatures. In addition, it was observed that added-Ag was mainly distributed along the grain boundar~es in the (123) matrix, resulting in the densification of microstructure. From these results, i t was thought that the improvement of $J_c$ over 2000A/$\textrm{cm}^2$ was attributed to the texture, densification of microstructure, and (123) grain growth due to the Ag addition.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.631-632
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• 2008

본 논문은 2.5MJ의 저장용량을 가지는 SMES 용 고온초전도 마그넷의 설계에 관한 연구 결과이다. 선재는 2세대 고온초전도 선재인 YBCO CC를 2단으로 적층하여 사용하였다. 운전전류는 전도냉각 방식을 사용하는 것을 가정해 22K의 운전온도에서 선재의 임계전류를 고려하여 600A 이상으로 결정하였다. 마그넷의 형상은 싱글 솔레노이드와 토로이드 형태로 각각 설계하였고 싱글 솔레노이드는 더블 팬케이크 모듈코일을 적층하여 구성 토로이드는 싱글팬케이크 모듈코일을 배열하여 모듈러 토로이드로 구성하였다. 각 형상별 설계결과를 통해 저장에너지와 선재사용량 그리고 누설자장의 크기를 각각 비교하였다.

• Progress in Superconductivity
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• v.12 no.1
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• pp.17-22
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• 2010

Distribution of local critical temperature and current density in $YBa_2Cu_3O_{7-\delta}$ (YBCO) coated conductors was analyzed using a Low-temperature Scanning Laser Microscopy (LTSLM). We prepared YBCO coated conductors of various bridge types to study the spatial distribution of critical temperature and current density in single and multi bridges. An LTSLM system was modified for a detailed two-dimensional scan without shifting of the sample. We observed a spatial distribution of the critical temperature from the bolometric response, which arises from a focused laser beam at the sample near the superconducting transition. Also we studied the relation between the critical temperature and the current density.