• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.8
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• pp.1063-1067
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• 1995

The superconducting properties of YBa$_{2}$Cu$_{3}$$O_{7-x}$(YBaCuO) thin films prepared by laser ablation have been investigated. The x-ray diffraction patterns and surface morphology of the films were substantially different from one another. The compositional ratios of YBaCuO films were controlled by the conditions of the target-substrate distance. The YBaCuO films manufactured on MgO(100) substrate were indicated T$_{c}$(zero)=91.2 K, T$_{c}$(onset)=93 K, and J$_{c}$=3.5*10$^{5}$ A/cm$^{2}$(at 77.3K). The optimum conditions were found to be a substrate temperature of 710 .deg. C, a energy density of 2 J/cm$^{2}$, and a target-substrate distance of 60 mm in an oxygen partial pressure of 200 mTorr.0 mTorr.

• Progress in Superconductivity and Cryogenics
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• v.23 no.3
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• pp.45-50
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• 2021

In this study, the effect of the size of B powder on the critical current density (J_c) of MgB₂ prepared by an in situ reaction process was investigated. Various combinations of B powders were made using a micron B, ball-milled B and nano B powders. Micron B powder was reduced by ball milling and the milled B powder was mixed with the micron B or nano B powder. The mixing ratios of the milled B and micron or nano B were 100:0, 50:50 and 0:100. Non-milled micron B powder was also mixed with nano powder in the same ratios. Pellets of (2B+Mg) prepared with various B mixing ratios were heat-treated to form MgB₂. T_c of MgB₂ decreased slightly when the milled B was used, whereas the J_c of MgB₂ increased with increasing amount of the milled B or the nano powder. The used of the milled B and nano B power promoted the formation MgB₂ during heat treatment. In addition to the enhanced formation of MgB₂, the use of the powders reduced the grain size of MgB₂. The use of the milled and nano B powder increased the J_c of MgB₂. The highest J_c was achieved when 100% nano B powder was used. The J_c enhancement is attributed to the high volume fraction of the superconducting phase (MgB₂) and the large grain boundaries, which induces the flux pinning at the magnetic fields.

• Progress in Superconductivity
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• v.12 no.1
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• pp.1-5
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• 2010

In this work we synthesized both MgB2 and Carbon doped MgB2 superconductor with Ag addition via high energy milling and substituent heat treatment. Heat treatments were performed at $900\;^{\circ}C$ for 30 min in flowing Ar gas. We varied amount of Ag powder. In a range of Ag powder was 0~5wt%. The effect of Ag was correlated with superconducting properties. The results show a slight decrease in critical temperature ($T_c$) and a reduction of critical current density ($J_c$) at high fields for the Ag-doped samples as compared to the un-doped samples. Reduction of $J_c$ may be due to the formation of MgAg compound.

• Progress in Superconductivity and Cryogenics
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• v.8 no.4
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• pp.8-11
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• 2006

High temperature superconducting coated conductor has various buffer structures on Ni-W alloy. We comparatively studied the growth conditions of a multi buffer layer $(CeO_2/YSZ/CeO_2)$ and a single buffer layer$(CeO_2)$ on textured Ni-W alloy tapes. XRD data showed that the qualities of in-plane and out-of-plane textures of the two type buffer structures were good. Also, we investigated the properties of SmBCO superconducting layer that was deposited on the two type buffer structure. The SmBCO superconducting properties on the single and multi buffer structure showed different critical current values and surface morphologies. FWHM of In-plane and out-of-plane textures were $7.4^{\circ},\;5.0^{\circ}$ in the top CeO2 layer of the multi-buffer layers of $CeO_2/YSZ/CeO_2$, and $7.3^{\circ},\;5.1^{\circ}$ in the $CeO_2$ single buffer layer. $1{\mu}m-thick$ SmBCO superconducting layers were deposited on two type buffer layer. $I_c$ of SmBCO deposited on single and multi buffer were 90 A/cm, 150 A/cm and corresponding $J_c$ were $0.9MA/cm^2,\;1.5MA/cm^2$ at 77K in self-field, respectively.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.41-46
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• 2022

The superconducting properties of high temperature superconducting (HTS) GdBCO coated conductor (CC) tape (Ag/GdBCO/Buffer-layers/Stainless Steel) were investigated, specifically a series of samples prepared by vacuum heat treatment (200℃ to 600℃), using a Quantum Design PPMS-14. The critical current density J_c value was obtained by applying the modified Bean model to the irreversible magnetization ∆M_irr(H) data which was estimated from the magnetization M(H) loop. The reduction rates of lnJ_c and T_c values according to the increase of the vacuum annealing temperature T_an were d(lnJ_c)/dT_an = - 0.016 A/(cm²∙℃) and dT_c/dT_an = - 0.24, respectively. We examined the effect of recovery temperature T_re (475℃ to 700℃) and recovery duration time t (0.5 h to 24 h) on the restoration of previously completely lost superconductivity in samples that subsequently received heat treatment in an O₂ gas flow space. All samples were fully restored to superconductivity by heat treatment in an O₂ gas flow space. The recovery temperatures T_re (475℃ to 700℃) and recovery duration times t (0.5 h to 24 h) were both independent of the superconductivity recovery characteristics.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.21-24
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• 2001

A series of superconducting Hg$Ba_{2}$Cu$O_{4+7}$ materials, containing $Ag_{x}$ additions with molar fraction x = 0, 0.05, 0.1, 0.3, and 0.5, have been studied. This study has showed that Ag additions lead to changes in superconducting properties of Hg-1201 materials. In addition, according to the amount of $Ag_{x}$ additions with molar fraction x up to 0.5, both $T_{c}$ and $J_{c}$ of Hg-1201 materials generally decrease with Ag-content. These and other results are discussed in this paper.

• Progress in Superconductivity and Cryogenics
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• v.25 no.3
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• pp.22-27
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• 2023

Magnetic properties of MgB₂ superconducting powder were investigated. M(H), the magnetic field H dependence of magnetization M, was measured and analyzed using a PPMS instrument. The MgB₂ superconducting powder showed high critical current density J_c > ~ 10⁷ A/cm² and clean limit superconducting properties. The equilibrium magnetization M_eq properties of MgB₂ powders exhibiting various superconducting properties were studied. We find that the equilibrium magnetization M_eq(H) properties of MgB₂ powders showing conventional BCS properties deviate from the predictions of the standard local-London theory at temperatures below T = 19 K and are in good agreement with the generalized nonlocal-London theory. Nonlocal-London analysis was used to determine and analyze the nonlocal parameters. The temperature dependence of the London penetration depth values λ(T) was studied.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.9-14
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• 2016

The effect of the size and shape of magnesium(Mg) powder on the formation of $MgB_2$ and the critical current density($J_{c,}$) of $MgB_2$ bulk was studied. As a precursor for the formation of $MgB_2$, Mg and $MgB_4$ powder, which was synthesized through the reaction of boron (B) with Mg powders, was used. $MgB_4$ was mixed with Mg powders of various sizes, pressed into pellets and heat-treated at $650^{\circ}C-750^{\circ}C$ in flowing argon gas. The XRD analysis of the heat-treated $MgB_2$ samples showed that the volume fraction of $MgB_2$ was the highest as 92.74 % when spherical Mg powder with an average size of $25.7{\mu}m$ was used, whereas the volume fraction was the lowest as 79.64 % when plate-like Mg powder with a size of $34.1{\mu}m$ was used. The superconducting transition temperature ($T_c$) of $MgB_2$ was not sensitive to the characteristics of the Mg powders used. All of the prepared $MgB_2$ samples showed a high $T_c$ of 38.3 K and a small superconducting transition width of 0.2 K-0.5 K. $J_c$ (5 K and 1 T) of $MgB_2$ was the highest as $3.93{\times}10^4A/cm^2$ when spherical Mg powder with a size of $25.7{\mu}m$ was used, whereas $J_c$ was the lowest as $2.18{\times}10^4A/cm^2$when plate-like Mg powder with a size of $34.1{\mu}m$ was used. The relationship between the $J_c$ of $MgB_2$ and the characteristics of the Mg powders used was explained in terms of the volume fraction of $MgB_2$ and the apparent density of the $MgB_2$ pellets.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.18-24
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• 2019

This study was carried out to investigate the effect of milling of boron (B), which is one of raw materials of $MgB_2$, on the critical current density ($J_c$) of $MgB_2$. B powder used in this study is semi-amorphous B (Pavezyum, Turkey, 97% purity, 1 micron). The size of B powder was reduced by planetary milling using $ZrO_2$ balls (a diameter of 2 mm). The B powder and balls with a ratio of 1:20 were charged in a ceramic jar and then the jar was filled with toluene. The milling time was varied from 0 to 8 h. The milled B powders were mixed with Mg powder in the composition of (Mg+2B), and the powder mixtures were uniaxially pressed at 3 tons. The powder compacts were heat-treated at $700^{\circ}C$ for 1 h in flowing argon gas. Powder X-ray diffraction and FWHM (Full width at half maximum) were used to analyze the phase formation and crystallinity of $MgB_2$. The superconducting transition temperature ($T_c$) and $J_c$ of $MgB_2$ were measured using a magnetic property measurement system (MPMS). It was found that $B_2O_3$ was formed by B milling and the subsequent drying process, and the volume fraction of $B_2O_3$ increased as milling time increased. The $T_c$ of $MgB_2$ decreased with increasing milling time, which was explained in terms of the decreased volume fraction of $MgB_2$, the line broadening of $MgB_2$ peaks and the formation of $B_2O_3$. The $J_c$ at 5 K increased with increasing milling time. The $J_c$ increase is more remarkable at the magnetic field higher than 3 T. The $J_c$ at 5 K and 4 T was the highest as $4.37{\times}10^4A/cm^2$ when milling time was 2 h. The $J_c$ at 20 K also increased with increasing milling time. However, The $J_c$ of the samples with the prolonged milling for 6 and 8 h were lower than that of the non-milled sample.

• Electrical & Electronic Materials
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• v.9 no.4
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• pp.357-363
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• 1996

The superconducting properties of YBa$_{2}$Cu$_{3}$$O_{7-x}$(YBaCuO) thin films prepared by laser ablation have been investigated. The x-ray diffraction patterns of the films were substantially different from one another. The Y and Ba oxides are formed by the collisions with oxygen molecules. On the other hand, the Cu oxide is mainly formed at initial stage of the laser irradiation. The YBaCuO films manufactured on MgO(100) substrate were indicated T$_{c}$(zero)=90 K, T$_{c}$(onset)=92 K, and J$_{c}$=3.5*10$^{5}$ A/cm$^{2}$(at 77.3K). The optimum conditions were found to be a substrate temperature of 710.deg. C, an energy density of 2 J/cm$^{2}$, and a target-substrate distance of 60mm in an oxygen partial pressure of 200 mTorr.0 mTorr.