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Progress in superconductivity 14건

  1. [국내논문]   $MgB_2$박막의 혼합상태에서의 홀 효과  

    김보연 (Department of Physics, Pukyong National University ) , 정순길 (Department of Physics, Pukyong National University ) , 문경희 (Department of Physics, Pukyong National University ) , 강원남 (Department of Physics, Pukyong National University ) , 최은미 (National Creative Research Initiative Center for Superconductivity, Department of Physics, Pohang University of Science and Technology ) , 김헌정 (National Creative Research Initiative Center for Superconductivity, Department of Physics, Pohang University of Science and Technology ) , 이성익 (National Creative Research Initiative Center for Superconductivity, Department of Physics, Pohang University of Science and Technology ) , 김형진 (National Creative Research Initiative Center for Semiconductor Nanorods, Department of Materials Science and Engineering, Pohang University of Science and Technology)
    Progress in superconductivity v.7 no.2 ,pp. 103 - 108 , 2006 , 1229-4764 ,

    초록

    We have measured the Hall resistivity ( ${\rho}_{xy}$ ) and the longitudinal resistivity ( ${\rho}_{xy}$ ) on superconducting $MgB_2$ thin films in extended fields up to 18 T. We found a universal scaling behavior between the Hall resistivity and the longitudinal resistivity, which is independent of the temperature and the magnetic field. At a wide magnetic field region from 1 to 18T, a universal power law of ${\beta}=2.0{\pm}0.1$ in a scaling relation, ${\rho}_{xy}={A{\rho}_{xx}}^{\beta}$ , was observed in c-axis-oriented $MgB_2$ thin films. These results can be well interpreted by using recent models.

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  2. [국내논문]   초전도 Pipelined Multi-Bit ALU에 대한 연구  

    김진영 (University of Incheon ) , 고지훈 (University of Incheon ) , 강준희 (University of Incheon)
    Progress in superconductivity v.7 no.2 ,pp. 109 - 113 , 2006 , 1229-4764 ,

    초록

    The Arithmetic Logic Unit (ALU) is a core element of a computer processor that performs arithmetic and logic operations on the operands in computer instruction words. We have developed and tested an RSFQ multi-bit ALU constructed with half adder unit cells. To reduce the complexity of the ALU, We used half adder unit cells. The unit cells were constructed of one half adder and three de switches. The timing problem in the complex circuits has been a very important issue. We have calculated the delay time of all components in the circuit by using Josephson circuit simulation tools of XIC, $WRspice^{TM}$ , and Julia. To make the circuit work faster, we used a forward clocking scheme. This required a careful design of timing between clock and data pulses in ALU. The designed ALU had limited operation functions of OR, AND, XOR, and ADD. It had a pipeline structure. The fabricated 1-bit, 2-bit, and 4-bit ALU circuits were tested at a few kilo-hertz clock frequency as well as a few tens giga-hertz clock frequency, respectively. For high-speed tests, we used an eye-diagram technique. Our 4-bit ALU operated correctly at up to 5 GHz clock frequency.

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  3. [국내논문]   YBCO 박막을 이용한 배전급 저항형 초전도 한류기  

    이방욱 (Elecrotechnology R&D center, LS Industrial Systems ) , 박권배 (Elecrotechnology R&D center, LS Industrial Systems ) , 강종성 (Elecrotechnology R&D center, LS Industrial Systems ) , 김호민 (Elecrotechnology R&D center, LS Industrial Systems ) , 오일성 (Elecrotechnology R&D center, LS Industrial Systems ) , 심정욱 (Korea Electric Power Research Institute ) , 현옥배 (Korea Electric Power Research Institute)
    Progress in superconductivity v.7 no.2 ,pp. 114 - 119 , 2006 , 1229-4764 ,

    초록

    High critical current density, high n value, multiple faults endurances, and fast recovery characteristics of YBCO thin films are very attractive characteristics for developing resistive type superconducting fault current limiters. But due to the limited current and voltage ratings of one YBCO module, it is needed to construct series and parallel module connections for high capacity electric networks. Especially for distribution network, more than 30 units should be connected in series to meet voltage level. So in order to construct distribution-level superconducting fault current limiter, simultaneous quench in one YBCO thin films should be realized, and furthermore, quench should be occurred in all fault current limiting units equally to avoid local heating and failures. In this paper, we proposed optimum design of YBCO thin films for fault current limiting module and technical method using shunt resistor to achieve simultaneous quench between multi current limiting units. From the analytical and the experimental results, optimal current path and thickness of shunt material was determined for YBCO thin films and shunt resistor between modules was developed. Finally, 14 kV one phase resistive fault current limiter using multi YBCO thin films was constructed and it was possible to get satisfactory test results.

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  4. [국내논문]   이축정렬된 Ni 금속모재에 RF 마그네트론 스퍼터링에 의해 증착된 $CeO_2$$Y_2O_3$ 완충층 박막 특성  

    오용준 (Hanbat National University ) , 라정석 (Hanbat National University ) , 이의길 (Hanbat National University ) , 김찬중 (Korea Atomic Energy Research Institute)
    Progress in superconductivity v.7 no.2 ,pp. 120 - 129 , 2006 , 1229-4764 ,

    초록

    We comparatively studied the epitaxial growth conditions of $CeO_2$ and $Y_2O_3$ thin buffers on textured Ni tapes using rf magnetron sputtering and investigated the feasibility of getting a single mixture layer or sequential layers of $CeO_2$ and $Y_2O_3$ for more simplified buffer architecture. All the buffer layers were first deposited using the reducing gas of $Ar/4%H_2$ and subsequently the reactive gas mixture of Ar and $O_2$ , The crystalline quality and biaxial alignment of the films were investigated using X-ray diffraction techniques ( ${\Theta}-2{\Theta},\;{\phi}\;and\;{\omega}\;scans$ , pole figures). The $CeO_2$ single layer exhibited well developed (200) epitaxial growth at the condition of $10%\;O_2$ below an $450^{\circ}C$ , but the epitaxial property was decreased with increasing the layer thickness. $Y_2O_3$ seldom showed optimum condition for (400) epitaxial growth. The sequential architecture of $CeO_2/Y_2O_3/CeO_2$ having good epitaxial property was achieved by sputtering at a temperature of $700^{\circ}C$ on the initial $CeO_2$ bottom layer sputtered at $400^{\circ}C$ . Cracking of the sputtered buffer layers was seldom observed except the double layer structure of $CeO_2/Y_2O_3$ .

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  5. [국내논문]   MOCVD 법에 의해 제조된 $CeO_2$ 버퍼층 증착 거동의 기판 의존성  

    전병혁 (Nuclear Nanomaterials Development Lab., Korea Atomic Energy Research Institute (KAERI) ) , 최준규 (Nuclear Nanomaterials Development Lab., Korea Atomic Energy Research Institute (KAERI) ) , 정우영 (Nuclear Nanomaterials Development Lab., Korea Atomic Energy Research Institute (KAERI), Korea University of Technology and Education ) , 이희균 (Korea Polytechnic University ) , 홍계원 (Korea Polytechnic University ) , 김찬중 (Nuclear Nanomaterials Development Lab., Korea Atomic Energy Research Institute (KAERI))
    Progress in superconductivity v.7 no.2 ,pp. 130 - 134 , 2006 , 1229-4764 ,

    초록

    Buffer layers such as $CeO_2\;and\;Yb_2O_3$ films for YBCO coated conductors were deposited on (100) $SrTiO_3$ single crystals and (100) textured Ni substrates by a metal organic chemical vapor deposition (MOCVD) system of the hot-wall type. The substrates were moved with the velocity of 40 cm/hr. Source flow rate, $Ar/O_2$ flow rate and deposition temperature were main processing variables. The degree of film epitaxy and surface morphology were investigated using XRD and SEM, respectively. On a STO substrate, the $CeO_2$ film was well grown epitaxially above the deposition temperature of $450^{\circ}C$ . However, on a Ni substrate, the XRD showed NiO (111) and (200) peaks due to Ni oxidation as well as (111) and (200) film growth. For the films deposited with $O_2$ gas as oxygen source, it was found that the NiO film was formed at the interface between the buffer layer and the Ni substrate. The NiO layer interrupts the epitaxial growth of the buffer layer. It seems that the epitaxial growth of the buffer layer on Ni metal substrates using $O_2$ gas is difficult. We are considering a new method avoiding Ni oxidation with $H_2O$ vapor instead of $O_2$ gas.

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  6. [국내논문]   TFA-MOD법에 의한 YBCO 박막의 열처리변수 효과  

    장석헌 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 임준형 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 김규태 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 이진성 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 윤경민 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 주진호 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 이희균 (The department of Electronic Engineering, Korea Polytechnic University ) , 홍계원 (The department of Electronic Engineering, Korea Polytechnic University)
    Progress in superconductivity v.7 no.2 ,pp. 135 - 139 , 2006 , 1229-4764 ,

    초록

    We fabricated YBCO coated conductors (CCs) by TFA-MOD process and evaluated microstructure, texture formation, and critical temperature ( $T_c$ ) and current ( $I_c$ ). YBCO precursor solution was synthesized using metal-trifluoroacetates and dip coated on $LaAlO_3$ (LAO) substrate. The phase formation and microstructure was characterized by X-ray diffraction and scanning electron microscopy (SEM) and the degree of texture was evaluated by pole-figure analysis. The CC was heat-treated in various calcining temperatures ( $370^{\circ}C-460^{\circ}C$ ) and firing temperatures ( $750^{\circ}C-800^{\circ}C$ ). As fired at $775^{\circ}C$ for 4h, the CC had the highest $T_c$ of 89.5 K and $I_c$ of 40 A/cm-width ( $J_c=2.0\;MA/cm^2$ ). Microstructural observation indicated that the YBCO film was dense and homogeneous and had a strong cube texture without formation of second phase and its in-plane full-width at half-maxima; $5.2^{\circ}$ under optimum condition.

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  7. [국내논문]   211 공정을 이용한 새로운 TFA-MOD YBCO 박막 선재 제조  

    임준형 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 장석헌 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 김규태 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 이진성 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 윤경민 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 박의철 (School of Advanced Materials Science and Engineering, Sungkyunkwan University ) , 주진호 (School of Advanced Materials Science and Engineering, Sungkyunkwan University)
    Progress in superconductivity v.7 no.2 ,pp. 140 - 144 , 2006 , 1229-4764 ,

    초록

    We fabricated the YBCO films on single crystal $LaAlO_3$ substrates via a metal organic deposition (MOD) process. In the process, $Y_2Ba_1Cu_1O_x$ and $Ba_3Cu_5O_8$ powders were dissolved in trifluoroacetic acid (TFA) followed by calcining and firing heat treatments. To evaluate the effects of the firing temperature on YBCO phase formation and critical properties, the films were fired at $750^{\circ}C,\;775^{\circ}C\;and\;800^{\circ}C$ after calcining at $430^{\cric}C$ . Microstructure observation indicated that a crack-free surface formed and a strong biaxial texture was developed. The FWHM of out-of-plane texture was measured to be in the range of $4.3^{\cric}-7.0^{\circ}$ for all the films. When the YBCO film was fired at $775^{\cric}C$ , it had the highest critical properties: 88.5 K of critical temperature and 16 A/cm-width of critical current ( $1MA/cm^2$ as critical current density). On the other hand, those properties were degraded as firing at $750^{\circ}C\;and\;800^{\circ}C$ . It is considered that the improved critical values are partly owing to dense and homogeneous microstructure, strong texture, and high oxygen content.

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  8. [국내논문]   구리 기판에 전착시킨 니켈과 니켈합금의 집합조직 형성  

    김재근 (Korea Polytechnic University ) , 이선왕 (Korea Polytechnic University ) , 김호진 (Korea Polytechnic University ) , 홍계원 (Korea Polytechnic University ) , 이희균 (Korea Polytechnic University)
    Progress in superconductivity v.7 no.2 ,pp. 145 - 151 , 2006 , 1229-4764 ,

    초록

    Nickel and nickel-tungsten alloy were electroplated on a cold rolled and heat treated copper(Cu) substrate. 4 mm-thick high purity commercial grade Cu was rolled to various thicknesses of 50, 70, 100 and 150 micron. High reduction ratio of 30% was applied down to 150 micron. Rolled texture was converted into cube texture via high temperature heat treatment at $400-800^{\circ}C$ . Grain size of Cu was about 50 micron which is much smaller compared to >300 micron for the Cu prepared using smaller reduction pass of 5%. 1.5 km-long 150 micron Cu was fabricated with a rolling speed of 33 m/min and texture of Cu was uniform along length. Abnormal grain growth and non-cube texture appeared for the specimen anneal above $900^{\circ}C$ . 1-10 micron thick Ni and Ni-W film was electroplated onto an annealed cube-textured Cu or directly on a cold rolled Cu. Both specimens were annealed and the degree of texture was measured. For electroplating of Ni on annealed Cu, Ni layer duplicated the cube-texture of Cu substrate and the FWHM of in plane XRD measurement for annealed Cu layer and electroplated layer was $9.9^{\circ}\;and\;13.4^{\irc}$ , respectively. But the FWHM of in plane XRD measurement of the specimen which electroplated Ni directly on cold rolled Cu was $8.6^{\circ}$ , which is better texture than that of nickel electroplated on annealed Cu and it might be caused by the suppression of secondary recrystallization and abnormal grain growth of Cu at high temperature above $900^{\circ}C$ by electroplated nickel.

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  9. [국내논문]   REBCO 초전도 박막제조를 위한 Fluorine-free MOD 전구체 용액 개발  

    김병주 (Korea Polytechnic University ) , 임선원 (Korea Polytechnic University ) , 김호진 (Korea Polytechnic University ) , 홍계원 (Korea Polytechnic University ) , 이희균 (Korea Polytechnic University)
    Progress in superconductivity v.7 no.2 ,pp. 152 - 157 , 2006 , 1229-4764 ,

    초록

    New precursor solution with dichloroacetic acid (DCA) was developed for fabricating high $J_c$ REBCO film. DCA based-precursor solution was coated on $LaAlO_3$ (001) substrate by dip coating method. Processing parameters such as oxygen partial pressure, water vapor, ramping rate and pyrolysis temperature were controlled in order to obtain a good epitaxial film. The film with thickness of 0.5 micrometer was obtained by single coating and no crack was observed at calcined films. Oxygen partial pressure was controlled in the range of $100{\sim}1,000$ ppm and conversion heat treatment was carried out at the temperature range of $705-765^{\circ}C$ . A critical transition temperature ( $T_c$ ) of 90 K and a critical transport current density ( $J_c$ ) of $>0.5\;MA/cm^2$ (77 K and self-field) were obtained for the GdBCO film. It is thought that fluorine-free MOD solution using DCA is promising precursor solution for fabricating high quality REBCO films.

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  10. [국내논문]   화학적으로 변형된 전구용액을 이용한 YBCO 박막 제조  

    김영국 (Korea Institute of Machinery and Materials ) , 유재무 (Korea Institute of Machinery and Materials ) , 정국채 (Korea Institute of Machinery and Materials ) , 고재웅 (Korea Institute of Machinery and Materials ) , 김영준 (Iljin Electric Co. Ltd. ) , 한봉수 (Iljin Electric Co. Ltd.)
    Progress in superconductivity v.7 no.2 ,pp. 158 - 161 , 2006 , 1229-4764 ,

    초록

    Superconducting YBCO films were successfully fabricated by MOD process using chemically modified precursor solution. In this study, a chemically modified precursor solution for MOD processing was synthesized using metal-organic salts and organic additives. It was shown that crack-free and uniform precursor films were formed after calcination in humidified Oxygen atmosphere. Less than 3 hours are required to finish the calcination process. XRD measurement shows that $BaF_2,\;CuO,\;Y_2O_3$ are major constituent of precursor films. Furthermore, YBCO films without any secondary phases were successfully fabricated after annealing in wet $Ar/O_2$ atmosphere. The YBCO film prepared on a $LaAlO_3$ single crystal substrate ( $10mm{\times}10mm$ ) gives transport $I_c$ of 10A at 77K. This chemical modification approach is a possible candidate for improving MOD-processing of YBCO coated conductor.

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