• Korean Journal of Materials Research
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• v.21 no.2
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• pp.73-77
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• 2011

Specific heat of a crystal is the sum of electronic specific heat, which is the specific heat of conduction electrons, and lattice specific heat, which is the specific heat of the lattice. Since properties such as crystal structure and Debye temperature do not change even in the superconducting state, the lattice specific heat may remain unchanged between the normal and the superconducting state. The difference of specific heat between the normal and superconducting state may be caused only by the electronic specific heat difference between the normal and superconducting states. Critical temperature, at which transition occurs, becomes lower than $T_{c0}$ under the influence of a magnetic field. It is well known that specific heat also changes abruptly at this critical temperature, but magnetic field dependence of jump of specific heat has not yet been developed theoretically. In this paper, specific heat jump of superconducting crystals at low temperature is derived as an explicit function of applied magnetic field H by using the thermodynamic relations of A. C. Rose-Innes and E. H. Rhoderick. The derived specific heat jump is compared with experimental data for superconducting crystals of $MgCNi_3$, $LiTi_2O_4$ and $Nd_{0.5}Ca_{0.5}MnO_3$. Our specific heat jump function well explains the jump up or down phenomena of superconducting crystals.

• Journal of the Korean Ceramic Society
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• v.35 no.2
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• pp.137-144
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• 1998

High-temperature superconducting joints between 61 filaments of Bi-2223 tapes were fabricated by chem-ical corrosion and repeated thermomechanical process. The silver sheath of the superconducting tape was chemically removed using chemical etchant(NH4OH:H2O2=1:1) from one side of each tape without altering the form of lap joint. The joined region was formed by uniaxial pressing and a series of thermomechanical process and then subjected to properties measurement and microstructural analysis. The critical current(Ic) variation and I-V characteristics along the joint were mesured with several configuration of proble points. Ic value of the transition region of the joint inthe multifilament tape which limit the total current carring capacity of the superconducting tape was higher than that of monofilament tape. But the transition ex-ponent n-value of the multi-filament tape was lower than that of monofilament wire due to the interaction of the individual superconducting core of the multi-filament. The critical current through the joint area was improved by respeated press and reaction annealing treatment.

• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.6-8
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• 2014

The influence of quenching temperature, heating atmosphere and annealing time on superconducting characteristics has been studied for $LuBa_2Cu_3O_{7-z}$ compound which has been recently synthesized in a nearly phase-pure form. Resistivity measurements for the as-prepared sample heated at $300^{\circ}C$ in oxygen and subsequently quenched into liquid nitrogen revealed that there is no significant change in $T_c$. On the other hand, $T_c$ of the sample slightly increased when the sample was heated at $300^{\circ}C$ either in air or in $N_2$ atmosphere. It was also found that $T_c$ of the sample decreased when the annealing temperature in $N_2$ atmosphere increased above $400^{\circ}C$. The experimental results indicated that the as-prepared sample is under overdoped state. The enhanced superconducting transition observed in the samples after heating at $300^{\circ}C$ in air or $N_2$ atmosphere was discussed in conjunction with a slight removal of oxygen and ordering of oxygen atoms in the as-prepared sample.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1858-1860
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• 1999

To fabricate superconducting multiplexers with narrow pass band characteristics and reduce the physical size of device, we have designed multiplexer using hair-pin type filters with the center frequency of 13.6 GHz. Multiplexers have been fabricated superconductor(HTS), because It has low surface resistance. The $YBa_2Cu_3O_{7-{\delta}}$(YBCO) films were deposited on MgO substrates$(20{\times}20{\times}0.5mm^3)$ by using pulsed laser deposition and conventional photo-lithographic methods were used to pattern the multiplexer. Epitaxial YBCO films were grown on(100) MgO substrates and showed strongly c_axis orientations observed by X-ray diffraction technique. Superconducting transition temperatures were measured to be about 89K. Simulated results of superconducting multiplexer consisting of hair-pin type filters show the insertion loss of about 1.2dB. The measured frequency response will be compared with the simulated results.

• Progress in Superconductivity and Cryogenics
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• v.7 no.1
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• pp.25-31
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• 2005

Since the discovery of the high temperature superconductors many researches have been performed for the practical applications of superconductivity technologies in various fields. As results, significant progress has been achieved. Especially, Superconducting Fault Current Limiter (SFCL) offers an attractive means In limit fault current in power systems. HTS resistive type SFCL is based on the ultra fast transition from the superconducting (non resistive) state to the normal (resistive) state by overstepping the critical current density, In this study, the simulation method of resistive type superconducting fault current limiter using EMTDC is proposed and the developed EMTDC model of SFCL is applied to the modeled power network using the Parameters of real system.

• Progress in Superconductivity and Cryogenics
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• v.17 no.4
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• pp.21-24
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• 2015

We report optical spectra of underdoped $BaFe_{1.89}Co_{0.11}As_2$ that hosts both of magnetic and superconducting orders. The temperature dependent evolution of optical conductivity shows finger prints of the magnetic order and the s-wave nature of the superconducting gaps. Careful inspection on the superconducting state reveals that the two orders compete but coexist in the ground state.

• Transactions on Electrical and Electronic Materials
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• v.6 no.6
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• pp.284-288
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• 2005

We have systematically studied the superconducting properties and flux pinning enhancement of $(Y_{0.33}Sm_{0.33}Nd_{0.33})\;Ba_2Cu_3O_y$ [(YSN)-123] composite oxides by melt growth process in air. A sample prepared by this method showed well-textured microstructure, and $(Y_{0.33}Sm_{0.33}Nd_{0.33})\;BaCuO_5$ [(YSN)211] nonsuperconducting particles were uniformly dispersed in large (YSN) 123 superconducting matrix. The sample showed a sharp superconducting transition at 91 K. The magnetization measurements of the (YSN)-123 sample exhibited the enhanced flux pinning, compared with $YBa_2Cu_3O_y$ (Y-123) sample without Sm and Nd. Critical current densities of (YSN)-123 sample was $2.5{\times}10^4 A/cm^2$ at 2 T and 77 K.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.71-74
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• 2006

Transport and tunneling measurements of nanostructured superconducting thin films are presented. To understand the effects of film morphology on their superconducting properties, thermal annealing experiments have been performed. The transition temperature increases with thermal annealing temperature towards the bulk value. Also, thermal annealing results in a shift of transverse phonon mode. These can be understood with changes in film morphology and suggest its importance on the superconducting state properties.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.2
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• pp.352-354
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• 2010

The effects of Au addition on the structure and the superconducting properties of Bi system bulk have been investigated. Au exists in the metalic form in above materials. It does not affect the formation and structure of the BiSrCaCuO(2223) phase. The superconducting transition temperature Tc does not change for $Bi_{1.7}Pb_{0.3}Sr_2Ca_2Cu_3O$ composite However Au doping can make the grains smaller. Metallic Au can make gathers on the grains boundary and lead to the increment of critical transport current density. The current density of $Bi_{1.7}Pb_{0.3}Sr_2Ca_2Cu_3Au_{0.5}O$ was 1000A/$cm^2$ at liquid nitrogen temperature.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.98-100
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• 1998

This paper presents the fluid characteristics simulation and design guide line of the fluid path inside the rotor, which has an high-Tc superconducting field winding using Ag sheathed BSCCO-2223. The analysis was conducted with an equivalent model of the high-Tc superconducting synchronous motor under transition condition that occurs during the load varying from 250watt to 500watt. The results show that the designed fluid circulation system performs adequately in maintaining the superconducting state in the winding.