• Journal of the Korean Ceramic Society
• /
• v.33 no.6
• /
• pp.718-724
• /
• 1996

Deformation mechanism map of Langdon-Mohammed type for YBa2Cu3O7-x superconducting ceramic was constructed by considering mechanisms of Nabarro-Herring Coble and powder-law creep and grain boundary sliding (GBS) with an accommodation by grain boundary diffusion. The map was found consistent with experi-mental results not only of the creep the also of the superplastic deformation. It showed the transition from interface reaction-controlled to the grain boundary diffusion-controlled GBS mechanism at about 1 ${\mu}{\textrm}{m}$ grain size and 100 MPa flow stress in agreement with the experimental results.

• Progress in Superconductivity and Cryogenics
• /
• v.18 no.4
• /
• pp.30-34
• /
• 2016

In this study, a SFCL-combined DC circuit breaker system was proposed by applying the current-limiting technology for DC circuit breaking. The SFCL-combined circuit breaker system consists of a mechanical DC circuit breaker combined with superconductors. To ensure the reliable structure and operation of the SFCL-combined circuit breaker system, a simulation grid was designed using the EMTDC/PSCAD program, and simulation was conducted. The results showed that the SFCL-combined DC circuit breaker system with superconductors limited the maximum fault current by 37%. In addition, the burden on the DC circuit breaker was decreased by 87%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.07b
• /
• pp.1270-1273
• /
• 2004

The combination of methane-chemical activation and Self-propagating High-temperature synthesis (SHS) has widened the possibilities for both methods. For YBCO systems the investigation showed that a short-term mechano-chemical activation of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors of YBCO composition with a grain size d < $1{\mu}m$ is developed. The specific feature of the technique is formation of the $YBa_2Cu_3O_{7-x}$ crystalline lattice directly from an X-ray amorphous state arising as a result of mechanical activation of the original oxide mixture. The technique allows the stage of formation of any intermediate reaction products to be ruled out. X-ray and magnetic studies of ultra-fine high temperature superconductors (HTS) are carried out. Dimension effects associated with the microstructure peculiarities are revealed. A considerable enhancement of inter-grain critical currents is found to take place in the ultra-fine samples investigated.

• 한국초전도학회:학술대회논문집
• /
• v.10
• /
• pp.9-14
• /
• 2000

We report on the novel nonequilibrium nlicrowave emission from quasiparticle-injected high-Tc superconductors. The phenomena have been observed for the current-injected YBCO/I/Au or BSCCO/I/Au thin-film tunnel junctions and BSCCO single-crystal intrinsic Josephson mesa junction samples. For the thin-film tunnel junctions, the emitted radiation appears as broadband. For the intrinsic BSCCO mesa samples, the radiation appears as three different modes of emissions depending on the bias point in the hysteretic current-voltage characteristics; Josephson-emission, nonequilibrium broad emission and sharp coherent microwave emission. The results were interpreted by the Josephson plasma excitation model due to quasiparticle injection.

• Progress in Superconductivity
• /
• v.11 no.2
• /
• pp.112-117
• /
• 2010

We examine phase transition of the spin density wave and $\pi$ phase shifted superconductivity in the Fe pnictide superconductors. The phase diagram is described in the plane of the temperature T and the doping x with the combination of Ginzburg-Landau expansion of the free energy near the multi-critical temperature $T_c$ and the self-consistent numerical iterations of the gap equations. The phase separation or coexistence is determined by computing the 4-th order terms of the free energy which is confirmed by the numerical calculations. We can show the phase coexistence when the spin density wave is incommensurate. And the first order phase transition is observed near the boundary between commensurate and incommensurate spin density wave.

• Progress in Superconductivity
• /
• v.13 no.3
• /
• pp.146-150
• /
• 2012

We solve the momentum resolved d-wave Eliashberg equation employing the magnetic excitation spectrum from the inelastic neutron scattering on the LSCO superconductors reported by Vignolle et al. The magnetic excitation spectrum exhibits 2 peaks: a sharp incommensurate peak at 18 meV at momentum (${\pi}$, ${\pi}{\pm}{\delta}$) and (${\pi}{\pm}{\delta}$, ${\pi}$) and another broad peak near 40~70 meV at momentum (${\pi}$, ${\pi}$). Above 70 meV, the magnetic excitation spectrum has a long tail that is shaped into a circle centered at (${\pi}$, ${\pi}$) with ${\delta}$. The sign of the real part of the self-energy is determined by the momentum position of the peaks of the magnetic excitation spectrum and bare dispersion. We will discuss the effects of the each component of the magnetic excitation spectrum on the self-energy, the pairing self-energy.

• 한국초전도학회:학술대회논문집
• /
• 2007.07a
• /
• pp.63-63
• /
• 2007

• 한국초전도학회:학술대회논문집
• /
• 2007.07a
• /
• pp.64-64
• /
• 2007

• Progress in Superconductivity and Cryogenics
• /
• v.6 no.2
• /
• pp.1-6
• /
• 2004

It is important to estimate the total AC loss which is the total energy, or power, dissipated in the superconductor in the simultaneous application of AC transport current and an AC external magnetic field. Experimental and numerical works on AC loss estimation of high $T_c$ superconductors in the author's group are reviewed. The method and the set-up for total AC loss measurements are described. The experimental results for a twisted Bi-2223 multifilamentary tape and a Y-123 mm conductor are given. A general theory for numerical electromagnetic field analysis of superconductor by the finite element method is explained. The numerical results for twisted Bi-2223 multifilamentary tapes and a rectangular superconductor simulating coated conductors are presented.

• Progress in Superconductivity
• /
• v.3 no.2
• /
• pp.183-187
• /
• 2002

In this paper we analyzed the electromagnetic behavior of high $-T_{c}$ superconductor under the quench state using finite element method. Poisson equation was used in finite element analysis as a governing equation and was solved using algebra equation using Gallerkin method. We first investigate d the electromagnetic behavior of U-type superconductor. Finally we applied our analysis techniques to 5.5 kVA meander-line superconducting fault current limiters (SFCL) which are currently developed by many power-system researcher in the world. Meshes of 14,600 elements were used in analysis of this SFCL. Analysis results show that the distribution of current density was concentrated to inner curvature in meander-line type-superconductors and maximum current density 14.61 $A/\m^2$ and also maximum Joule heat was 6,420 W/㎥. We concluded that this meander line-type SFCL was not pertinet fur uniform electromagnetic field distribution.n.