• 한국초전도학회:학술대회논문집
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• v.9
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• pp.388-391
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• 1999

Well oriented Bi2212 superconductor thick films were formed successfully on a copper substrate by liquid reaction between a Cu-free precursor and Cu tape method in which Cu-free BSCO powder mixture was' printed on copper plate and heat-treated. And we examined the effect of heat-treatment atmosphere for the superconducting properties and microstructure of Bi2212. The composition of Cu-free BSCO powder mixture was Bi$_2O_3$ : SrCO$_3$ : CaCO$_3$ = 1.2~2 : 1 : 1 and the heat-treatment for the superconducting formation reaction was performed in air, oxygen, nitrogen and low oxygen pressure. At heat-treatment temperature, the printing layer partially melt by reacting with CuO of the oxidizing copper plate, and the nonsuperconducting phases present in the melt are typically Bi-free phases and Cu-free phases. Among the nonsuperconducting phases, it is known that the (Sr,Ca)CuO$_3$ phase restrain the formation of the Bi2212 superconducting phase. Because a kind of the nonsuperconducting phases is controled by the oxygen partial pressure, the optimum condition in which the remnants of the second phases don't leave in the fully processed conductor was determined by XRD and the critical tempera to re (Tc) analysis.

• Progress in Superconductivity
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• v.1 no.1
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• pp.1-8
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• 1999

The magnetization and/or resistivity of high $T_c$ superconductors ($YBa_2Cu_3O_{7-\delta}$(YBCO) single crystal, $Bi_2Sr_2CaCu_2O_8$ (Bi-2212) single crystal, $Tl_2Ba_2CaCu_2O_8$ (Tl-2212) film, $HgBa_2Ca_2Cu_3O_8$ (Hg-1223) film) have been measured as a function of magnetic field H and temperature T. The extracted fluctuation part of the magnetization and conductivity exhibits a critical behavior consistent with the three-dimensional XY model. The dynamic critical exponent z does not sensitively vary with a type of the superconductors. The value of z ranges from 1.5 to $1.8{\pm}0.1$. However, the static critical exponent ${\nu}$ is the most largely increased in Tl-2212 that has a weaker interlayer coupling strength than YBCO; the value of ${\nu}$ is 0.669, 0.909, 1.19, and 1.338 for YBCO, Bi-2212, Hg-1223, and Tl-2212 respectively. The results indicate that the weak interlayer coupling along the c-axis of high $T_c$ superconductors near $T_c$ does not influence the dynamic critical exponent z (the same value of superfluid $^4He$), but significantly increases the static critical exponent ${\nu}$.

• Journal of the Korean institute of surface engineering
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• v.39 no.2
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• pp.57-63
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• 2006

In this study, In-base solder was applied to the interface between $Bi_2Sr_2Ca_1Cu_2O_x(Bi_{2212})$ superconductor and Cu-Ni shunt metal at the temperature lower than $150^{\circ}C$. Most of the cases, $Bi_{2212}$ superconductor was precoated with Ag by electroplating in order to improve the contact properties of the solder layer. When the superconductor was directly soldered on to the superconductor, the solder was easily separated without external force. The shear strength of the contact between superconductor and shunt metal increased from 69.2 kgf to 74.4 kgf and 80.1 kgf, as the current density of the Ag electroplating was changed from 63 mA to 96 mA and 126 mA, respectively. The contact strength also increased to 49.9 kgf and 69.2 kgf when thickness of the electroplated Ag layer increased to $5{\mu}m$ and $10{\mu}m$, reapectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.4
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• pp.343-350
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• 2003

Using Bi$_2$Sr$_2$Ca$_2$.$_2$Cu$_3$ $O_{x}$ powders prepared by solid state reaction and spray drying method, the nucleation and growth behaviors of superconducting and second phases were investigated during isothermal heat treatment. When the spray drying power was used in contrast with solid state reaction powder, Bi$_2$Sr$_2$Ca$_2$.$_2$Cu$_3$ $O_{x}$ (2223) phase could be formed at the relatively shot time and second phases were much bigger. Quantitative analysis showed that as the heat treatment time increased, more Bi$_2$Sr$_2$Ca$_2$.$_2$Cu$_3$ $O_{x}$ (2212) changed to 2223 and the major second phase was changed from (Sr,Ca)$_{14}$Cu$_{24}$ $O_{x}$(14:24) to (Sr,Ca)$_2$Cu$_1$ $O_{x}$ (2:l). The superconducting phase formed at the relatively short time 14:24 phase. Following the Bi-free phase of 14:24 Phase, but long time was needed in places far from the 14:24 phase. Following the formation of the 2212 phase near the 14:24 phase, the 2223 phase nucleated preferentially at the interface between the 2212 and 14:24 phases. The preferential nuclcation of 2223 was explained by its structural similarity and low Interfacial energy with both the Bi-free and 2212 Phases.12 Phases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.259-260
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• 2006

This study was progressed to value of Bi2212 tubes uniformity depend on cooling conditions. The tube from 150 mm in length, 30 mm in O.D., 20 mm in I.D., 5 mm in thickness was combined with electrodes by 3 sections. The tube from 60, 70 mm in length, 30, 50 mm in O.D., 20.4, 40.4 mm in I.D., 4.8 mm in thickness was in controled of cooling rate by a heat exchanger. Bi2212 tubes were fabricated by Centrifugal Forming Process (CFP) and they were annealed at $840^{\circ}C$ for 80 h in oxygen atmosphere. The tube from 150 mm in length was analyzed by EFDLab of NIKA to show cooling rate and temperature distributions. When the tube was cooled for 100s, the temperature distributions was $663^{\circ}C$ in the middle, $500{\sim}647^{\circ}C$ in inlet, $598{\sim}647^{\circ}C$ in the other side. Electric characteristics from $I_c$ was 450 A in the middle, 650 A in inlet, 600 A in the other side. Electric characteristics by a heat exchanger showed the more fast cooling rate, the more high $I_c$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.152-156
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• 2000

Bi-thin films are fabricated by an ion beam sputtering, and sticking coefficients of the respective elements are evaluated. The sticking coefficient of Bi element exhibits a characteristic temperature dependence : almost a constant value of 0.49 below $730^{\circ}C$ and decreases linearly with temperature over $730^{\circ}C$. This temperature dependence can be elucidated from the evaporation and sublimation rates of bismuth oxide, $Bi_2O_3$, from the film surface. It is considered that the liquid phase of the bismuth oxide plays an important role in the Bi(2212) phase formation in the co-deposition process.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.22-25
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• 1999

A well oriented Bi-2212 superconductor thick films were fabricated by screen printing with a Cu-free Bi-Sr-Ca-Cu-O powder on a copper plate and heat-treating at 820- $880^{\circ}C$for several minute in low oxygen pressure or are. At minute in low oxygen pressure of air. At , the printing layer partially melted by reaction between the Cu-free precursor by reaction between the Cu-free$870^{\circ}C$ precursor and CuO of the oxidizing copper plate. It is believed that the solid phase is Bi : Sr : Ca : Cu = 2 : 2 : 0 : 1. It is likely that the Bi-2212 superconducting phase is formed at Bi-2212 superconducting phase is formed at Bi-free phase/liquid interface by nucleation and grows.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.17-20
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• 2001

Stress/strain dependencies of the critical current I$_{c}$ in AgMgNi sheathed multifilamentary Bi(2212) superconducting tapes were evaluated at 77K. The external reinforcement was accomplished by soldering Ag-Mg tapes to single side or both sides of the sample. With the external reinforcement, the strength of tapes increased but I$_{c}$ decreased. The I$_{c}$ degradation characteristic according to the external reinforcement was improved markedly in terms of the stress although it appeared less remarkable on the basis of the strain. Effects of external reinforcement were discussed in a viewpoint of monitoring sensitivity of cracking in superconducting filaments by considering n-value representing the transport behavior of the current, which is closely associated with the location of them relative to the voltage-monitoring region in the tape. tape.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.25-28
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• 2001

Bi-2212 HTS tube was fabricated by centrifugal forming process(CFP). As a variation of melt casting process(MCP) or centrifugal casting technique, the centrifugal forming process is a flexible method for manufacturing Bi-2212 bulk tubes and has been optimized to achieve smooth surface and uniform thickness. At this process, the slurry was prepared in the mixing ratio of 10:1 between Bi-2212 powder and binder and initially charged into the rotating mold under the speed of 300~450 rpm Heat-treatment was performed at the temperature ranges of 860 ~ $890^{\circ}C$ in air for partial melting. The HTS tube fabricated by centrifugal forming process at $890^{\circ}C$ under the rotating speed of 450 rpm was highly densified and the plate-like grains with more than 20$\mu$m were well oriented along the rotating axis. The measured Tc and Jc at 10K were around 85K and 3,000A/cm2 respectively.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.715-722
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• 1994

Off-axis supttering using shielder was used to efficiently prevent negative oxygen ions from resputtering deposited films. In this method, the substrate was located vertically to the target and shielded by the semicircled steel plate. By using this method, the resputtering could be reduced, and 2223 high-Tc phase could be formed at the lower substrate temperature and in the broader temperature region. As increasing the substrate temperature, 2212, 2223, 2212 superconducting phases were formed by turns. 2223 phase was formed above 2$\times$10-2 torr, and 2212 phase was formed above 4$\times$10-2 torr.