• Bulletin of the Korean Chemical Society
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• 제10권6호
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• pp.551-554
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• 1989

Quadrupole coupling constants of $^{63}$CU in the high $T_c$ superconductor $YBa_2Cu_3O_7_{-x}$, as determined by NQR or NMR studies, are compared with the values for representative Cu(Ⅱ) complexes determined by analyzing the forbidden lines in their EPR spectra. It is shown that the two NQR lines at 22 and 31 MHz correpsond to the quadrupole coupling constants of a square planar Cu(Ⅱ) complex and a square pyramidal Cu(Ⅱ) complex, respectively.t This result is in agreement with the assignment of these lines to Cu(1) and Cu(2) sites in YBCO based on the NMR spectra of oriented single crystals.

• Progress in Superconductivity
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• 제8권2호
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• pp.175-180
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• 2007

High temperature superconductor $YBa_2Cu_3O_{7-x}$ (YBCO) films have been grown by in-situ electron beam evaporation on artificial metal tapes such as ion-beam assisted deposition (IBAD) and rolling assisted biaxially textured substrates (RABiTS). Deposition rate of the YBCO films is $10{\sim}100{\AA}/sec$. X-ray diffraction shows that the films are grown epitaxially but have inter-diffusion phases, like as $BaZrO_3\;or\;BaCeO_3$, at their interfaces between YBCO and yttrium-stabilized zirconia (YSZ) or $CeO_2$, respectively. Secondary ion mass spectroscopy depth profile of the films confirms diffused region between YBCO and the buffer layers, indicating that the growth temperature ($850{\sim}900^{\circ}C$) is high enough to cause diffusion of Zr and Ba. The films on both the substrates show four-fold symmetry of in-plane alignment but their width in the -scan is around $12{\sim}15^{\circ}$. Transmission electron microscopy shows an interesting interface layer of epitaxial CuO between YBCO and YSZ, of which growth origin may be related to liquid flukes of Ba-Cu-O. Resistivity vs temperature curves of the films on both substrates were measured. Resistivity at room temperature is between 300 and 500 cm, the extrapolated value of resistivity at 0 K is nearly zero, and superconducting transition temperature is $85{\sim}90K$. However, critical current density of the films is very low, ${\sim}10^3A/cm^2$. Cracking of the grains and high-growth-temperature induced reaction between YBCO and buffer layers are possible reasons for this low critical current density.

• 한국세라믹학회지
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• 제26권2호
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• pp.267-275
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• 1989

YBa2Cu3O7-x oxide superconductors were fabricated by sintering and hotisostatic pressing (HIP), and their microstructures and properties were compared with each other. Thougha part of the second phase was observed along grain boundaries, their structures were consisted of single (123) phase and they had many porosities. But, porosities were remakably reduced by Hiping and the densification was brought about. The structure of (123) compound also showed a number of twins, which are typical of high Tc superconductors. The on-set temperature of YBa2Cu3O7-x compound sintered at 96$0^{\circ}C$ in oxygen and hipped at 88$0^{\circ}C$ was highest, but that shwoed 0 resistance at 87$^{\circ}$K, which is a little lower than the compound sintered at 96$0^{\circ}C$. HIP treatment also increased the critical current density of as-sintered compound. However, its value was low, which may be ascribed to the many pores of starting-sintered compact and partially to the second phase along grain boundaries.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.117-119
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• 2003

YBa$_2$Cu$_3$O$_{7-{\delta}}$(YBCO) high temperature superconducting thin films were grown on SrTiO$_3$single crystal substrates by pulsed laser deposition(PLD). The texture and lattice parameter of the YBCO films were analysed using the GADDS (general area detector diffraction system) which enables XRD analyses to be done faster and with fewer sample movement than with the XRD system with point detector. The XRD results of the films grown in different deposition conditions are reported together with the SEM microstructure analysis results.ysis results.

• E2M - 전기 전자와 첨단 소재
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• 제6권6호
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• pp.514-522
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• 1993

본 연구에서는 Ag/ 첨가에 의한 YB $a_{2}$C $u_{3}$ $O_{7-{\delta}}$산화물의 초전도 특성 변화를 조사하였다. Ag가 첨가된 YB $a_{2}$C $u_{3-x}$A $g_{x}$ $O_{7-{\delta}}$ 산화물 시료를 만들고 이 시료들에 대한 X-ray 회절분석, IR흡수 스펙트럼분석, 임계온도(Tc)측정 및 자화(M-H)특성 측정등을 통하여 제조된 시료의 물리적 성질을 조사하였다. X-ray 회절실험 결과로 부터 x.leq.0.03인 경우에는 YB $a_{2}$C $u_{3-x}$A $g_{x}$ $O_{7-{\delta}}$가 단일상의 물질로 존재하고 x가 증가함에 따라 불순물상( $Y_{2}$ $O_{3}$, 순Ag)이 나타남을 알 수 있었다. IR흡수의 실험결과에서 Cu와 치환되어 들어간 Ag의 Ag-O 결합에 의한 흡수 스펙트럼(670$cm^{-1}$ /)이 관측되었다. 실험 결과로 부터 치환된 Ag의 양 x가 증가함에 따라 Tc가 조금씩 낮아지는 경향이 있었으며 자화의 세기 및 임계자장( $H_{C2}$)은 급격히 감소함을 알 수 있었고 또 M-H특성곡선에는 히스테리시스 특성이 나타났다.났다..났다.다.

• 한국진공학회지
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• 제4권2호
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• pp.194-200
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• 1995

2-3nm의 공간분해능을 갖는 전자에너지손실분광법(Electron Energy Loss Spectroscopy, EELS)을 이용하여, 전기적 특성조사된 YBa2Cu3O7-$\delta$ 고온초전도체 쌍결정의 결정경계(grain boundary)에서 산소의 조성변화를 조사하였다. Misorientation angle이 $14^{\circ}$, $28^{\circ}$,$ 30^{\circ}$인 3개의 쌍결정 중에서 Josephson junction 특성을 보인 $28^{\circ}$ 및 $30^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서의 oxygen 1s absorption edge와 매우 다름을 알 수 있었다. 이는 결정경계에서의 산소조성이 결정내부에 비해 낮음을 의미하며, 그 영역이 결정경계 부근 20-40nm로, coherence length에 비해 큼을 알 수 있다. 반면에, flux pinningxmr성을 보인 $14^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서와 별 차이를 보이지 않았다. 따라서 일반적으로 관찰되어온, misorientation angle이 큰 결정경계에서의 Josephson junction 특성은 결정경계 부근에서 산소의 조성이 낮아지는데에 기인하며, 그 원인은 결정경계면을 통해 산소가 out-diffusion되기 때문인 것으로 생각된다.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.71-74
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• 1999

접지면을 가지는 정사형 조셉슨 결합을 제작하기 위한 기본 단계로 YBCO/STO/YBCO 구조의 다층 박막을 제작하였다. 상하부 YBCO 박막은 그 사이에 존재하는 STO 절연층에 형성된 홀을 통해 서로 연결되어 있으며 이것의 저항-온도 특성을 측정한 결과 임계 온도가86 K로 나타났다. 이 결과는 시편을 매우 장시간동안 열처리한 후 얻은 결과로서 YBCO/STO/YBCO 다층 구조의 박막 제작시 하부 YBCO 박막의 특성이 많이 저하되고 이를 복원하기 위해서는 열처리 공정이 매우 중요함을 알 수 있었다. 현재 우수한 특성을 가지는 YBCO/STO/YBCO 다층 구조의 제작 공정을 최적화하기 위한 연구를 계속 수행 중에 있다.

• Progress in Superconductivity
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• 제7권1호
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• pp.87-91
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• 2005

[ $YBa_{2}Cu_{3}O_{7-x}$ ] thin films were fabricated on $LaAlO_3$(100) substrate by TFA-MOD process. Yttrium-excess (0, 2.5, 5, 10, 15, 20 $at\%$) coating solution was prepared by adding extra amount of yttrium into a stoichiometric(Y:Ba:Cu=1:2:3) TFA precursor solution. Results are presented concerning the influence of excess yttrium additions on the microstructure development and superconducting properties of $YBa_{2}Cu_{3}O_{7-x}$ film. Large sized CuO particles was observed by SEM EDS investigation. The addition of excess yttrium affected little on $T_c$ of $YBa_{2}Cu_{3}O_{7-x}$ film. $J_c$ of YBCO film was enhanced with excess yttrium addition. Jc maximum of $2.21\;MA/cm^2$ (77 K, self field) appeared with the $15\;at\%$ addition of excess yttrium. With further yttrium addition up to $20\;at\%$, Jc decreased down to $0.9\;MA/cm^2$.

• Progress in Superconductivity
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• 제11권1호
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• pp.62-66
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• 2009

Introduction of proper impurity into $YBa_2Cu_3O_{7-x}$ (YBCO) thin films is an effective way to enhance its flux-pinning properties. We investigate effect of $Y_2O_3$ nanoparticles on the critical current density $J_c$ of the YBCO thin films. The $Y_2O_3$ nanoparticles were created perpendicular to the film surface (parallel with the c-axis) either between YBCO and substrate or on top of YBCO, YBCO/$Y_2O_3$/LAO or $Y_2O_3$/YBCO/STO, by pulsed laser deposition. The deposition temperature of the YBCO films were varied ($780^{\circ}C$ and $800^{\circ}C$) to modify surface morphology of the YBCO films. Surface morphology characterization revealed that the lower deposition temperature of $780^{\circ}C$ created nano-sized holes on the YBCO film surface which may behave as intrinsic pinning centers, while the higher deposition temperature produced much denser and smoother surface. $J_c$ values of the YBCO films with $Y_2O_3$ particles were either remained nearly the same or decreased for the samples in which YBCO is grown at $780^{\circ}C$. On the other hand, $J_c$ values were enhanced for the samples in which YBCO is grown at higher temperature of $800^{\circ}C$. The difference in the effect of $Y_2O_3$ can be explained by the fact that the higher deposition temperature of $800^{\circ}C$ reduces intrinsic pinning centers and $J_c$ is enhanced by introduction of artificial pinning centers in the form of $Y_2O_3$ nanoparticles.

• Bulletin of the Korean Chemical Society
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• 제11권5호
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• pp.460-463
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• 1990

The normal and fluorinated high-Tc superconducting materials, $YBa_2Cu_3O_{7-x}F_y$with $0.25{\leq}x{\leq}0.55\;and\;0.00{\leq}y{\leq}0.30$, were synthesized to investigate the dopping effect of fluorine atom on the superconductivity of Y123 and studied by X-ray diffraction analysis and electron probe microanalysis, resistivity and thermopower measurements, and polarized micro-Raman spectroscopy. The reproducible micro-Raman spectra were recorded and analyzed. The coherent assignments could be suggested for the spectra of normal and fluorinated samples. The fluorine atoms introduced were found to be substituted for oxygen in pyramidal Cu-O units rather than in Cu-O chains. The unit cell parameters were decreased upon the substitution of oxygen by fluorine atom. From the decreasing cell parameters and Tc, the increasing thermopower, and the possible assignments of the vibrational modes, it could be suggested that the dopping of fluorine atom localizes the superconducting electrons in Y123.