• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.09a
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• pp.1-4
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• 2001

In electrophoresis, it is studied to get best condition of suspension media with alcoholic system for superconducting film. High-temperature superconductor films of $YBa_{2}Cu_{3}O_{7-x}$ were fabricated by electrophoretic deposition(EPD) from alcohol-based suspension. Maximum stability is observed for the suspension containing iso-alcohol as dispersion medium. However, for the formation of a dense and adherent coating of YBCO on a silver substrate by EPD. the best results were obtained in mixing PrOH and BuOH suspension. The superconducting critical current density($J_c$) was $1,200A/cm^2$ for the films deposited in 30% iso-PrOH and 70 % iso-BuOH suspension.

• Bulletin of the Korean Chemical Society
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• v.17 no.4
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• pp.324-330
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• 1996

We examined the formal oxidation states of Pb and Cu in the Pb2CuO4 slab of Pb2Sr2ACu3O8(A=Y1-xCaxor Nd1-xSrx) and their possible changes by oxygen incorporation in the Cu layer of the slab by performing tight-binding band electronic structure calculations on the Pb2CuO4+δ slab. Our results show that the most likely oxidation state of Pb is +2 and that of Cu is +1 for the Pb2CuO4 slab prior to oxidation. With small δ values, the oxygen incorporation occurs by the formation of such chain fragments as in YBa2Cu3O7-y along the a+b axis. The four-coordinate Cu atoms in the chain fragments are in the +3 oxidation states. For values of δ larger than 0.5, however, an additional oxygen (Oad) goes to the site along the b axis to form short Pb-Oad distances oxidizing Pb2+ to Pb4+. This change in the Pb oxidation state leads to the suppression of superconductivity due to the decrease of holes in the CuO2 layer.

• Journal of Powder Materials
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• v.15 no.1
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• pp.6-12
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• 2008

[ $YBa_2Cu_3O_{7-y}$ ](123) powders were synthesized by the solid state reaction method using two different purity $BaCO_3$ powders (99.75% and 99.7% purity) and $Y_2O_3$ (99.9%) and CuO (99.9%) powders. The effect of $BaCO_3$ purity on the formation of a 123 phase and the superconducting properties were investigated. The mixtures of raw powders were calcined at temperature ranges of $800^{\circ}C-880^{\circ}C$ in air and finally made into a single grain samples by a melt processing with top seeding. It was found that a 123 phase was well formed at temperature above $870^{\circ}C$, but the purity effect on the 123 formation was negligible. The single-grain 123 samples prepared from the different $BaCO_3$ powders showed the same $T_c$ value of 90.5 K and similar $J_c$ values about $10^4\;A/cm^2$ at 0 T and 77 K, and $10^3\;A/cm^2$ at 2 T and 77 K. This result indicates that the low purity, cheap price $BaCO_3$ powder can be used as a raw material for the fabrication of single-grain, high-$J_c$ superconducting levitator.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.2
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• pp.147-150
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• 2020

Relatively pure YBCO was first synthesized by heating a mixture of metal carbonates at temperatures between 1,000 and 1,300 K, resulting in the reaction: 4BaCO₃+Y₂(CO₃)₃+6CuCO₃+(1/2_-x)O₂ → 2YBa₂Cu₃O_7-x+1/3CO₂. Modern syntheses of YBCO use the corresponding oxides and nitrates. The superconducting properties of YBa₂Cu₃O_7-x are sensitive to the value of x, i.e., its oxygen content. Only those materials with 0≤x≤0.65 are superconducting below Tc, and when x ~ 0.07, the material superconducts at the highest temperature, i.e., 95 K, or in the highest magnetic fields, i.e., 120 T and 250 T when B is perpendicular and parallel to the CuO₂ planes, respectively. In addition to being sensitive to the stoichiometry of oxygen, the properties of YBCO are influenced by the crystallization methods applied. YBCO is a crystalline material, and the best superconductive properties are obtained when crystal grain boundaries are aligned by careful control of annealing and quenching temperature rates. However, these alternative methods still require careful sintering to produce a quality product. New possibilities have arisen since the discovery of trifluoroacetic acid, a source of fluorine that prevents the formation of undesired barium carbonate (BaCO₃). This route lowers the temperature necessary to obtain the correct phase at around 700℃. This, together with the lack of dependence on vacuum, makes this method a very promising way to achieve a scalable YBCO bulk.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.04a
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• pp.9-10
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• 2001

용융공정 $YBa_2Cu_3O_{7-x}$(123) 초전도체는 고자장 하에서도 통전특성이 우수하다 그러나 123 초전도체에는 미세균열이나 기공과 같이 초전도체의 통전특성에 유해 한 요인들도 다수 포함된다. 미세균열은 고온 정방정 상이 저온 사방정상으로 상변 태 시 발생하는 웅력에 의해 생성된다. 반면, 기공은 123 성형체를 녹이는 과정에서 123 상에 포함된 산소원자들이 격자로부터 이탈되고, 이 산소원자들이 모여 액상에서 기공을 형성한다. 제조공정에 따라 기공의 크기와 밀도가 다르지만 대략 수십 이크론 정도로 대단히 크다 생성된 기공 중 일부는 열처리 중에 소멸되나, 어떤 것들은 그대로 남아 초전도체의 치밀화를 방해한다. 본 연구에서는 123의 용융 및 $YBa_2Cu_3O_{7-x}$(211)과 액상으로의 분해 과정 및 포정반응과 관련된 미세조직을 조사하여 기공생성과 소멸과정을 조사하였고, 123의 최종 미세조직에 대한 기공의 영향에 대 하여 연구하였다. 열처리 스케쥴은 123-211-액상의 그림 l의 2원 상태도를 기초로 하여 결정하였다. 먼저 부분 용융상태에서의 기공의 분포를 알고자 시편을 105$0^{\circ}C$에서 0.5-1 시 간 유지한 후, 액체 질소통에 넣어 냉각하였다 (그림 2의 열처리 경로 CD)$\circled1$부분 용 융상태에서 급랭할 경우 211과 액상 상태가 그대로 유지되므로 액상에서의 기공분 포를 관찰할 수 있다. 또 다른 시편들은 그림 2의 @$\circled2$경로로 열처리하였다. 이 시편에서는 고온에서 생성된 211과 액상이 반웅하여 123 결정이 생성, 성장하므로 123 결정립 내의 기공분포를 알 수 있다. 그림 3은 시편에서의 기공과 액상포켓의 분포를 모식도와 각 부위의 미세조직 사진이다. 시편에는 산소가스 발생으로 인해 생성된 수형의 기공이 관찰된다. 기공은 시편의 중앙에 집중되며, 시편 바깥부분은 기공에 액상이 채워진 액상포켓이 관찰된다. 기공의 생성과 소멸과정은 다음과 같다. 출발물질인 123 분말이 211과 액상으로 분해될 때 산소가스가 배출되며, 이로 인해 액상에서 구형의 기공이 생성된다. 이들 중 일부는 액상으로 채워져 소멸되나, 나머지는 그대로 남는다. 특히, 시편 중앙에 서는 수십-수백 마이크론 크기의 커다란 기공이 다수 관찰된는데, 이는 기공의 합체로 만들어진 것이다. 포정반응 열처리 시 기공 소멸로 만들어진 액상포켓들은 주변 211 입자와 반응하여 123 영역으로 변한다. 이곳은 다른 지역과 비교하여 211 밀도 가 낮기 때문에, 미반응 액상이 남거나 211 밀도가 낮은 123 영역이 된다. 액상으로 채워지지 못한 구형의 기공들 중 다수가 123 결정 내로 포획되며, 그 형상은 액상/ 기공/고상 계면에너지에 의해 결정된다.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.357-362
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• 1996

Several applications of radio-frequency (RF) thermal plasma to film formation are reviewed. Three types of injection plasma processing (IPP) technique are first introduced for the deposition of materials. Those are thermal plasma chemical vapor deposition (CVD), plasma flash evaporation, and plasma spraying. Radio-frequency (RF) plasma and hybrid (combination of RF and direct current(DC)) plasma are next introduced as promising thermal plasma sources in the IPP technique. Experimental data for three kinds of processing are demonstrated mainly based on our recent researches of depositions of functional materials, such as high temperature semiconductor SiC and diamond, ionic conductor $ZrO_2-Y_2O_3$ and high critical temperature superconductor $YBa_2Cu_3O_7-x$. Special emphasis is given to thermal plasma flash evaporation, in which nanometer-scaled clusters generated in plasma flame play important roles as nanometer-scaled clusters as deposition species. A novel epitaxial growth mechanism from the "hot" clusters namely "hot cluster epitaxy (HCE)" is proposed.)" is proposed.osed.

• Progress in Superconductivity
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• v.2 no.1
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• pp.15-19
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• 2000

[ $YBa_2Cu_3O_{7-\delta}$ ] thin films were deposited by laser ablation using modified melt-textured grown targets. As the laser energy density was increased, the films showed an increasing c-axis orientation and an improvement of superconducting properties. However, at 4 $J/cm^2$, the degree of c-axis alignment and $J_c$ of the film were considerably reduced. These were attributed to the enhanced a-axis outgrowths. It was shown that the increased laser energy density resulted in the formation of $Y_2O_3$ inclusions during the c-axis film growth, and that these inclusions nucleated the a-axis outgrowths.

• Progress in Superconductivity
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• v.8 no.1
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• pp.27-32
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• 2006

[$YBa_2Cu_3O_{7-x}$] thin films were deposited on various buffered-templates by a metal organic chemical vapor deposition(MOCVD). Three different templates of $CeO_2/YSZ/CeO_2/pure-Ni(CYC),\;CeO_2/YSZ/Y_2O_3/Ni-3at.%W(YYC)$ and $CeO_2/IBAD-YSZ$/stainless steel were used. The Ni and Ni-W alloy tapes were biaxially textured by cold rolling and annealing heat treatment. The dense YBCO films were grown on both the IBAD and YYC templates with no microcrack, while the YBCO films on the CYC templates were grown with the formation of microcracks and NiO. The YBCO film on the YYC template showed the higher $I_c$ than that on CYC template. Especially, the IBAD templates with a thin $CeO_2$(type I) and thick $CeO_2$(type II) top layer were used to compare the deposition nature of the YBCO on them. Comparing the current property of the YBCO films on IBAD templates, the YBCO film deposited on thick $CeO_2$ layer was better than the film on thin $CeO_2$ layer.

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

• Journal of the Speleological Society of Korea
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• no.78
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• pp.1-8
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• 2007

The combination of mechano-chemical activation (MCA)and Self-propagating High-temperature Synthesis (SHS) has widened the technical possibilities for both methods. For YBCO systems the investigation showed that a short-term MCA of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors (HTS) of YBCO composition with a grain size d <1m is developed using combination of MCA and SHS. The specific feature of the technique is formation of the $YBa_2Cu_3O_7-$ 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 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.