• Bulletin of the Korean Chemical Society
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• v.10 no.6
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• pp.504-509
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• 1989

The effect of oxygen-deficiency on the charge distributions and orbital energies for small copper oxide clusters representing the superconducting materials $YBa_2Cu_3O_x (6{\leq}x{\leq}7)$ were investigated by the extended Huckel molecular orbital (EHMO) method with the tight-binding model. Our calculations show +3 oxidation state of Cu(1) in the $CuO_3$ chain and +2 or +1 of Cu(2) in the $CuO_2$ layers for $YBa_2Cu_3O_7$ with the nominal charge of $Cu_3$ = +7 (or +5), while for $YBa_2Cu_3O_6$ +1 oxidation state of Cu(1) and +3 (or +2) of Cu(2) in the $CuO_2$ layers with the nominal charge of $Cu_3$ = +7 (or +5). For $Cu_3O_{12}$ cluster representing $YBa_2Cu_3O_7$ with the nominal charge of $Cu_3$ = +7 the Cu(2) $d_{{x^2}-{y^2}}$ orbitals in the $CuO_2$ layers is a typical Jahn-Teller $d^9$ system with the partial hole and the Cu(1) $d_{{_z2}-{_y2}}$ orbital in the $CuO_3$ chain contains hole occupancy. For $Cu_3O_{10}$ cluster representing $YBa_2Cu_3O_6$ with the nominal charge of Cu = +5 the orbital character of the highest partially occupied MO (HPOMO) and the lowest completely unoccupied MO (LCUMO) of $Cu_3O_{12}$ representing $YBa_2Cu_3O_7$ with the nominal charge of $Cu_3$ = +7 is reversed, and the character of Cu(1) $d{{x^2}-{y^2}}$ orbital of LCUMO of the $Cu_3O_{12} $cluster is vanished. It is suggested that the local crystal field environment of Cu(1) by the oxygens in the Cu(1) chain may play a vital role in conductivity and superconductivity, either alone or through cooperative electronic coupling with the Cu(2) layers in $YBa_2Cu_3O_7.$.

• Progress in Superconductivity and Cryogenics
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• v.1 no.1
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• pp.15-21
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• 1999

Textured bulk $YBa_2Cu_3O_x$ superconductors samples were grown directionally using different precursors of $YBa_2Cu_3O_x$ power. and a mixture of $YBa_2Cu_3O_5, BaCuO_2 and CuO$ powder. The microstructures and superconducting properties of the samples were compared. The mixture powder produced better microstructures i.e. dense and crack-free so that a higher critical current density was achieved at the same hot-zone temperature of 115$0^{\circ}C$ than the reacted powder does. When the reacted powder used as a precursor, as the hot-zone temperature increased upto 1215$^{\circ}C$, the texture of the sample improved and the critical current density increased. The amount of melt in the sample is of secondary importance for the growth of superconducting $YBa_2Cu_3O_x$ grains. The microstructures and superconductivity of good quality superconductors grown directionally were more strongly influenced by the kind of precursor rather than the amount og melt in a sample.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05a
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• pp.42-45
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• 2003

The phase transformation of $REBa_2Cu_3O_{7-x}$ (RE=Nd, Gd, Dy) was investigated using isothermal heat-treatment and continuous cooling in air. During continuous cooling, the $REBa_2Cu_3O_{7-x}$ (RE=123) superconducting phase with well-distributed $REBa_2Cu_3O_{7-x}$ (RE-211) was obtainde at a cooling rate of $0.001^{\circ}C$/s. Single phase RE-123 (Nd, Gd, Dy) was stable at $1050^{\circ}C$, $1050^{\circ}C$, and $950^{\circ}C$ during isothermal heat-treatment, respectively. Above these temperatures the RE-211 phase existed within the RE-123 grains. The RE-123, RE-211, $BaCu_2Od_2$, and CuO phases coexisted at $50^{\circ}C$ below the partial melting temperature for each respective rare-earth RE-123.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.63-66
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• 1996

The method for calculation of $Y_2$BaCuO$_{5}$ contents was set up. It was estimated that the optimum value of 211 contents in the textured YBCO superconductor as flux pinning center was about 20wt.%. Ag contents have no influence on the critical temperature, but have large influence on the critical current density of the textured YBCO. When Ag contents over 15wt.%, which was the solubility of condensed YBCO, the critical current densities tend to a stable value.e.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.218-221
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• 1999

Magnetization measurements have been carried out on grain aligned Hg-1223 with the applied field parallel to the c-axis. The temperature dependence of the lower critical field H$_{cl}$(T) was determined by considering the effect of the surface barrier on the magnetization. H$_{cl}$(T) have been determined .from magnetic hysteresis loops within the framework of the modified Kim-Anderson critical-state model, where the surface barrier and the lower critical field are explicitly considered. At high temperature, H$_{cl}$(T) is identified as H$_p$(T). This results are agreed with the theory of Bean-Livinston surface barriers.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.41-41
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• 2004

• 한국초전도학회:학술대회논문집
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• v.16
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• pp.94-94
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• 2006

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.91-99
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• 1989

The concentrations of hydroxide, carbonate and oxalate for Y(III), Ba(II) and Cu(II) ions in an aqueous solution have been theoretically calcuated with respect to pH and their solubility diagram could be obtained. The optimum pH ofr oxalate coprecipitates at room temperature was estimated as<4, which was not influenced by carbonates and hydroxides in H2O solvent. The yield is dependent on the concentration of added oxalic acid, but the concentration of oxalic acid was fixed as 0.1M in this calculation for simplicity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.362-363
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• 2006

In this study, the filter was designed for tuning center frequency and fabricated using ($Sr,Ba)TiO_3$ ferroelectrics and $YBa_2CuO_7$ high temperature superconductor thin film. The best result in figure of merit was 35 when the $Ba_{0.5}Sr_{0.5}TiO_3$ thin film deposition temperature was $600^{\circ}C$, the post anneal condition was $600^{\circ}C$, 10min in 1atm, $O_2$. When using $20{\mu}m$ IDC pattern gap. The higher tunability was obtained than using $30{\mu}m$ pattern gap.

• Progress in Superconductivity
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• v.13 no.1
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• pp.7-11
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• 2011

The effects of Sm:Ba:Cu composition ratio in SmBCO coated conductor on their superconducting properties were investigated. The SmBCO coated conductors were fabricated by reactive co-evaporation method using EDDC(Evaporation using Drum in Dual Chamber) system. In this system, we could obtain various samples with different composition ratios in a batch by the technique providing composition gradient at deposition zone. From the specimens prepared by EDDC system, we found that composition ratio is uniform parallel to the drum axis, but gradient along the circumferential direction of the drum. We installed a shield having parallelogram open area between the deposition chamber and the evaporation chamber in EDDC system, and attached a 30 cm long template, which is parallel to drum axis, onto the drum surface. In this configuration, we could obtain SmBCO coated conductors having a gradient composition along the length of template. We measured the composition ratios and surface morphologies with periodic interval by SEM and EDAX, and confirmed the profile of composition ratio. We also measured critical current using non-contact Hall probe critical current measurement system and thereby could plot composition ratio vs. critical current. The maximum critical current was obtained, and the surface morphology with the shape of roof tile was observed at the corresponding composition ratio of Sm:Ba:Cu = 1.01:1.99:4.87. It was also found that composition ratio had an effect on not only critical current but also surface morphology.