MgB₂ 초전도체

송규정 ( Kyu Jeong Song ) 전북대학교 과학교육연구소 2017 과학과 과학교육 논문지 Vol.42 No.1

MgB₂ 초전도체는 중간금속성 초전도체이다. 2001년 처음으로 MgB₂ 물질에서 초전도성이 발견된 후, 지금까지 17년 동안 MgB₂ 초전도체에 대하여 수많은 연구들이 진행되었다. 초전도메커니즘 규명을 위한 MgB₂ 초전도특성 연구들이 수행되어, 기존의 저온 및 고온초전도체의 특성들과 구별되는 MgB₂ 고유의 초전도특성들이 발견되었고, 또한 산업적인 응용을 위한 MgB₂ 초전도선재 연구들이 수행되어, 경제적인 MgB₂ PIT(powder in tube) 초전도선재들이 개발되었다. 현재, MgB₂ 초전도체는 초전도연구의 핵심 분야로서 한 부분을 차지하고 있으며, MgB₂ 초전도특성 향상과 MgB₂ 초전도마그넷처럼 MgB2 PIT 초전도선재의 초전도전력기기 응용을 위해 많은 연구자들이 활발히 참여하고 있다. 따라서 아직도 많은 연구자들의 관심 속에 있는 MgB₂ 초전도체의 본 리뷰 논문에서는 저자가 지금까지 수행해온 MgB₂ 초전도관련 연구 결과들을 중심으로 MgB₂ 초전도체의 최근 연구동향들과 미래 연구경향들을 논의하고자 한다. The MgB₂ superconductor is an inter-metallic superconductor. Since the discovery of superconductivity in MgB₂ materials in 2001, a number of studies have been conducted on MgB₂ superconductor for 17 years. MgB₂ superconductivity studies have been carried out to elucidate the superconducting mechanism. MgB₂ inherent superconducting properties are differentiated from those of conventional low-Tc and high-Tc superconductors. For industrial applications, MgB₂ superconducting wire has been developed, and economical MgB₂ PIT superconducting wires have been commercialized. In these days, the MgB₂ superconductor is one of the core fields in superconducting area. Many researchers vigorously participate in the fields of the enhancement of MgB₂ superconductivity and the MgB₂ superconducting power application, such as MgB₂ superconducting magnet. Therefore, on the basis of MgB₂ superconductivity studies performed by the present author on MgB₂ superconductor, recent research trends and future research trends of MgB₂ superconductors, which are in the interest of many researchers, will be discussed in this review paper.

3 T급 대면적 YBCO 초전도 벌크자석 개발

한상철,정세용,박병준,한영희,Han, S.C.,Jeong, S.Y.,Park, B.J.,Han, Y.H. 한국초전도학회 2012 Progress in superconductivity Vol.14 No.1

For the practical application of a YBCO superconductor bulk magnet, the superconductor bulk magnet with strong and stable magnetic field on a large area surface should be fabricated. To satisfy these requirements, we have designed a conduction-cooled bulk magnet system using six single grain YBCO bulk superconductors. Six rectangular-shaped YBCO bulk superconductors with a dimension of $38{\times}38{\times}15mm^3$ were field-cooled at 20 K using a superconductor magnet with maximum operating magnetic field of 4 T. The magnetic flux of 3.0 T and 2.8 T were achieved on the surface of bulk superconductors and over the vacuum chamber surface of the refrigerator, respectively.

Bi/CNT 화합물과 Resin/CNT를 보강한 YBCO 초전도체의 기계적, 자기적 특성 변화

오원석,장건익,한영희,성태현,Oh, W.S.,Jang, G.E.,Han, Y.H.,Sung, T.H. 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1

Bi/CNT composite and resin/CNT were chosen to improve the mechanical properties of $YBa_2Cu_3O_7$(YBCO) superconductor. In order to elucidate the effects of Bi/CNT composite and resin/CNT in YBCO superconductors, melt texture superconductor were impregnated by mixed compound of Bi and CNT into the artificial holes parallel to the c-axis, which were drilled on the YBCO superconductor. Various amount of Bi/CNT and resin/CNT were impregnated to YBCO superconductor with different holes diameters. Typical artificial holes diameters were 0.5, 0.7, and 1.0 mm respectively. Result of three-point bending test measurement, the bending strength with resin/CNT impregnation was improved up to 59.64 MPa as compared with 50.79 MPa of resin/CNT free bulk. Resin/CNT impregnation has been found to be one of the effective ways in improving the mechanical properties of bulk superconductor.

Critical Behavior and Spectrum of Holographic Superconductors

Hyo Chul AHN,홍덕기,박천수 한국물리학회 2017 New Physics: Sae Mulli Vol.67 No.1

We study a minimal gravity dual of planar superconductivity at finite temperature to estimate the Meissner and Debye masses of photons in a planar superconductor, which are the characteristic properties of superconductors. We also study the temperature dependences of those masses to find their critical behavior near the critical temperature to see if the behaviors of holographic superconductors deviate from those of the usual conventional BCS superconductors because high-temperature superconductors exhibit properties very different from those of the usual BCS superconductors, as they are strongly correlated. We find that the critical exponents to be 0.49 and 0.92 for the Debye mass and the Meissner mass, respectively. Finally, we study the critical behavior of the radial excitations of the order parameter.

Direct fabrication of a large grain YBCO bulk superconductor without intermediate grinding step

Hong, Yi-Seul,Kim, Chan-Joong,Lee, Hee-Gyoun The Korea Institute of Applied Superconductivity a 2019 한국초전도저온공학회논문지 Vol.21 No.3

Large grain YBCO bulk superconductors are fabricated by the top-seeded melt growth (TSMG) or top-seeded infiltration growth (TSIG) method. Both growth methods use at least one of $YBa_2Cu_3O_{7-{\delta}}$, $Y_2BaCuO_5$, $BaCuO_3$ pre-reacted precursor powders. However, the synthesis of the pre-reacted powders includes multiple calcination runs which are cost-bearing and time-consuming. In this work, we report the successful growth of single-domain YBCO bulk superconductors directly by using the powder compact that has been pressed from the mixture of $Y_2O_3$, $BaCuO_3$ and CuO powders without any intermediate grinding step. Single-domain YBCO bulk superconductor has been also prepared by using $Y_2O_3$, $BaO_2$ and CuO powders without intermediate grinding step. Investigations on the trapped magnetic field and microstructure of the melt-processed specimen show that the elimination of the repeated processes of calcinations and pulverization has hardly affected on the crystal growth and the magnetic properties of the grown YBCO bulk superconductors. However, it is thought that the presence of residual carbon affects on the size of Y211 particles in melt-processed YBCO bulk superconductor.

Josephson Effect in a Singlet Superconductor-Ferromagnet-Triplet Superconductor Junction

최치훈 한국물리학회 2017 New Physics: Sae Mulli Vol.67 No.12

We study the current-phase relation of a ballistic SIFIT junction, consisting of a spin-singlet superconductor (S), an insulating ferromagnetic interface (I), a weak ferromagnetic metal (F), another insulating ferromagnetic interface (I), and a spin-triplet superconductor (T). We use the generalized quasiclassical formalism developed by Millis $et al.$ to compute the current density and the free energy of the junction for arbitrary orientations of the magnetizations of the junction barrier. We investigate in detail the effect of the distribution of magnetization on the various harmonics of the current-phase relation and the transition of the ground state of the junction. A magnetization parallel to the d-vector of the triplet superconductor can lead to an anomalous Josephson current and a transition of the ground state from the $\pi/2$-state to the $3 \pi/2$-state. The $\phi$-state junction can be realized for a noncollinear orientation of the barrier magnetizations in the plane perpendicular to the d-vector.

Direct fabrication of a large grain YBCO bulk superconductor without intermediate grinding step

Yi-Seul Hong,Chan-Joong Kim,Hee-Gyoun Lee 한국초전도.저온공학회 2019 한국초전도저온공학회논문지 Vol.21 No.3

Large grain YBCO bulk superconductors are fabricated by the top-seeded melt growth (TSMG) or top-seeded infiltration growth (TSIG) method. Both growth methods use at least one of YBa2Cu3O7−δ, Y2BaCuO5, BaCuO3 pre-reacted precursor powders. However, the synthesis of the pre-reacted powders includes multiple calcination runs which are cost-bearing and time-consuming. In this work, we report the successful growth of single-domain YBCO bulk superconductors directly by using the powder compact that has been pressed from the mixture of Y2O3, BaCO3 and CuO powders without any intermediate grinding step. Single-domain YBCO bulk superconductor has been also prepared by using Y2O3, BaO2 and CuO powders without intermediate grinding step. Investigations on the trapped magnetic field and microstructure of the melt-processed specimen show that the elimination of the repeated processes of calcinations and pulverization has hardly affected on the crystal growth and the magnetic properties of the grown YBCO bulk superconductors. However, it is thought that the presence of residual carbon affects on the size of Y211 particles in melt-processed YBCO bulk superconductor.

Preparation of Yba₂Cu₃O_x Superconductor Prepared with Additives of PbO and Ag₂O

Chu, Soon-Nam,Park, Jung-Cheul,Jeon, Yong-Woo The Korean Institute of Electrical and Electronic 2009 Transactions on Electrical and Electronic Material Vol.10 No.1

The improvement of preparation process of ${YBa_2}{Cu_3}{O_x}$ superconductor and its conducting properties is important for practical applications. In this study, the additives such as $Ag_{2}O$ and PbO were used to improve the preparation conditions of ${YBa_2}{Cu_3}{O_x}$ superconducting bulk samples and the properties of ${YBa_2}{Cu_3}{O_x}$ superconductors prepared with powders using sol-gel method and solid state reaction method were studied. The effects of the different powders and the additives to the density, grain alignment, and porosity of samples, that affect the critical current density of superconductor, also have been investigated. It is found that the properties of ${YBa_2}{Cu_3}{O_x}$ prepared with sol-gel synthesized powder and the additives showed better superconductivities than those of conventionally prepared superconductors.

Preparation of YBa2Cu3Ox Superconductor Prepared with Additives of PbO and Ag2O

추순남,박정철,전용우 한국전기전자재료학회 2009 Transactions on Electrical and Electronic Material Vol.10 No.1

The improvement of preparation process of YBa2Cu3Ox superconductor and its conducting properties is important for practical applications. In this study, the additives such as Ag2O and PbO were used to improve the preparation conditions of YBa2Cu3Ox superconducting bulk samples and the properties of YBa2Cu3Ox superconductors prepared with powders using sol-gel method and solid state reaction method were studied. The effects of the different powders and the additives to the density, grain alignment, and porosity of samples, that affect the critical current density of superconductor, also have been investigated. It is found that the properties of YBa2Cu3Ox prepared with sol-gel synthesized powder and the additives showed better superconductivities than those of conventionally prepared superconductors.

Ni₂X₂ (X=pnictide, chalcogenide, or B) based superconductors

Ronning, F.,Bauer, E.D.,Park, T.,Kurita, N.,Klimczuk, T.,Movshovich, R.,Sefat, A.S.,Mandrus, D.,Thompson, J.D. Elsevier 2009 Physica. C, Superconductivity Vol.469 No.9

<P>We review the properties of Ni-based superconductors which contain Ni2X2 (X = As, P, Bi, Si, Ge, B) planes, a common structural element found also in the recently discovered FeAs superconductors. Strong evidence for the fully gapped nature of the superconducting state has come from field dependent thermal conductivity results on BaNi2As2. Coupled with the lack of magnetism. the majority of evidence suggests that the Ni-based compounds are conventional elect ron-phonon mediated superconductors. However, the increase in T-c in LaNiAsO with doping is anomalous, and mimics the behavior in LaFeAsO. Furthermore, comparisons of the properties of Ni- and Fe-based systems show many similarities, particularly with regards to structure-property relationships. This suggests a deeper connection between the physics of the FeAs superconductors and the related Ni-based systems which deserves further investigation. (C) 2009 Elsevier B.V. All rights reserved.</P>