• 한국초전도학회:학술대회논문집
• /
• v.16
• /
• pp.57-57
• /
• 2006

• Progress in Superconductivity and Cryogenics
• /
• v.13 no.4
• /
• pp.22-25
• /
• 2011

A single-coat $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) film of high critical currents ($I_c$) could be successfully fabricated by optimizing the viscosity of the coating solution in the metal-organic deposition (MOD) process. From a Ba-deficient coating solution (Y: Ba: Cu = 1: 1.5: 3) having the viscosity of 212 $mPa{\cdot}sec$, 0.9 ${\mu}m$-thick single coat YBCO film with the $I_c$ value of 289 A/cm-width ($J_c$ = 3.2 MA/$cm^2$) at 77 K was achievable on the $SrTiO_3$ (STO) substrate, which was superior to that of our previous report for 0.8 ${\mu}m$-thick single coat YBCO film from a stoichiometric coating solution (Y: Ba: Cu = 1: 2: 3) on the $LaAlO_3$ (LAO) substrate. This result might be attributed to denser and more homogeneous microstrcuture in the case of the YBCO film from the Ba-deficient coating solution.

• Progress in Superconductivity
• /
• v.2 no.1
• /
• pp.27-32
• /
• 2000

A prototype for a highly sensitive, automated measurement system for the microwave surface resistance of high-$T_c$ superconductor films was set up, and tested by measuring the microwave surface resistances of high-$T_c$ $YBa_2Cu_3O_{7-\delta}$ (YBCO) films at the frequency of about 19.6 GHz and the temperature of 30 K $\sim$ 90 K. An open-ended $TE_{011}$ mode sapphire-loaded cylindrical cavity resonator was used as the measurement probe, where YBCO films were used as the endplates of the cylindrical cavity. The characteristics of the measurement system include functions to display the unloaded Q and the resonant frequency of the $TE_{011}$ mode resonator as well as the microwave surface resistance of the YBCO films, all simultaneously as a function of temperature. Applicability of the measurement system for investigating the homogeneity in the microwave properties of large high-$T_c$ superconductor films is discussed.

• 한국초전도학회:학술대회논문집
• /
• v.10
• /
• pp.173-178
• /
• 2000

A prototype for a highly sensitive, automated measurement system for the microwave surface resistance of high-T$_c$ superconductor films was set up, and tested by measuring the microwave surface resistances of high-T$_c$ YBa$_2$Cu$_3$O$_{7-{\delta}}$(YBCO) films at the frequency of about 19.6 GHz and the temperature of 30 K ${\sim}$ 90 K. An open-ended TE$_{011}$ mode sapphire-loaded cylindrical cavity resonator was used as the measurement probe, where YBCO films were used as the endplates of the cylindrical cavity. The characteristics of the measurement system include functions to display the unloaded ${\varrho}$ and the resonant frequency of the TE$_{011}$ mode resonator as well as the microwave surface resistance of the YBCO films, all simultaneously as a function of temperature. Applicability of the measurement system for investigating the homogeneity in the microwave properties of large high-T$_c$ superconductor films is discussed.

• Progress in Superconductivity
• /
• v.7 no.1
• /
• pp.92-96
• /
• 2005

YBCO thin films on metal substrates were prepared by the metal-organic deposition using trifluoroacetates (TFA-MOD). To compensate the loss of Ba element from the precursor films due to the reaction with $CeO_2$ cap layer, we have employed Ba-excessive precursor solutions of $YBa_{2+x}Cu_{3}O_{7-{\delta}}$ ($0{\le}x{\le}0.1$). The precursor solutions were dip-coated on the metal substrates with $CeO_2$ cap layer, initially heated up to $400^{\circ}C$, and finally fired at the various high temperatures for 2 h in a reduced oxygen atmosphere. With this approach, YBCO films possessing critical temperature over 85 K could be successfully prepared on the metal substrates. The highest $T_{c,zero}$ value of 86 K was obtained from the Ba-excessive YBCO film of x=0.005 in $YBa_{2+x}Cu_{3}O_{7-{\delta}}$ fired at $750^{\circ}C$ for 2 h. However, unexpected $T_c$ suppression even in Ba-excessive YBCO samples requires further identification.

• Progress in Superconductivity
• /
• v.9 no.1
• /
• pp.91-95
• /
• 2007

[ $YBa_2Cu_3O_{7-{\delta}}$ ] films have been prepared on $LaAlO_3$ (100) single-crystal substrates by the metal organic deposition using dichloroacetate precursors (DCA-MOD). DCA precursor solutions with different composition such as; Yttrium-excess(15 at%), barium-poor(25 at%), and a stoichiometric(Y:Ba:Cu=1:2:3) were prepared in order to investigate the effects of precursor composition on the properties of YBCO films prepared by DCA-MOD method. Coated films were calcined at low temperature up to $500^{\circ}C$ in flowing humid oxygen atmosphere. Conversion heat treatment was performed $800^{\circ}C$ for 2 h in flowing Ar gas containing 1000 ppm oxygen with a humidity of 9.45%. For the film prepared using excess yttrium composition, high critical current density ($J_c$) of $>2MA/cm^2$ was obtained whereas, for the films prepared using barium-poor composition, $J_c$ was lower than $1MA/cm^2$.

• Proceedings of the KIEE Conference
• /
• 1999.11d
• /
• pp.873-875
• /
• 1999

We have fabricated good quality superconducting $YBa_{2}Cu_{3}O_{7-\delta}$ thin films on Hastelloy(Ni-Cr-Mo alloys) metallic substrate with $CeO_2$ and $BaTiO_3$ buffer layers in-situ by pulsed laser deposition in a multi-target processing chamber. We have chosen $CeO_2$ as a buffer layer which has cubic structure of $5.41{\AA}$ lattice parameter and only 0.2% of lattice mismatch with YBCO. $CeO_2$ layer may be helpful for power transmission due to its conducting property. In order to enhance the crystallization of YBCO films on metallic substrates. we deposited $CeO_2$ and $BaTiO_3$ buffer layers at various temperatures. The YBCO superconducting tape fabricated with $BaTiO_3$ and $CeO_2$ buffer layers shows 85K of transition temperature and about $8.4{\times}10^4A/cm^2$ of critical current density at 77K.

• 한국초전도학회:학술대회논문집
• /
• v.9
• /
• pp.392-396
• /
• 1999

Superconducting YBa$_2Cu_3O_{7-{\delta}}$(YBCO) thin films were grown on Hastelloy(Ni-Cr-Mo alloys) with CeO$_2$ buffer layer in-situ by pulsed laser deposition in a multi-target processing chamber. To apply superconducting property on power transmission line, we have deposited YBCO thin film on flexible metallic substrate. However, it is difficult to grow the YBCO films on flexible metallic substrates due to both interdiffusion problem between metallic substrate and superconducting overlayers and non-crystallization of YBCO on amorphous substrate. It is necessary to use a buffer layer to overcome the difficulties. We have chosen CeO$_2$ as a buffer layer which has cubic structure of 5.41 ${\AA}$ lattice parameter and only 0.2% of lattice mismatch with 3.82 ${\AA}$ of a-axis lattice parameter of YBCO on [110] direction of CeO$_2$ In order to enhance the crystallization of YBCO films on metallic substrates, we deposited CeO$_2$ buffer layers with varying temperature and 02 pressure. By XRD, it is observed that dominated film orientation is strongly depending on the deposition temperature of CeO$_2$ layer. The dominated orientation of CeO$_2$ buffer layer is changed from (200) to(111) by increasing the deposition temperature and this transition affects the crystallization of YBCO superconducting film on CeO$_2$ buffered Hastelloy.

• Progress in Superconductivity
• /
• v.8 no.2
• /
• pp.143-151
• /
• 2007

Accurate measurements of the microwave surface resistance (Rs) of high temperature superconductor (HTS) films are important with regard to applications of HTS materials for wireless communications. As the surface resistance values of HTS films are usually extracted from the measured unloaded quality factor ($Q_0$) of resonators made of HTS films, it is essential to measure the resonator $Q_0$ with accuracy. The $TE_{011}\;mode\;Q_0$ of sapphire resonators with the endplates made of $YBa_2Cu_3O_{7-{\delta}}$(YBCO) film on $LaAlO_3$ is measured by using the S-parameter circle-fit method at a frequency of about 19.6 GHz and temperatures of 30 K to 90 K, which is compared with the measured values by using the Lorentzian-fit method. Good agreements are found between the two sets of $Q_0$ values measured by using the two different methods whether the resonator is used in a weak-coupling scheme or a strong-coupling scheme, showing reliability of both methods fur measuring the resonator $Q_0$ accurately. The $Q_0$ of sapphire resonators with a gap between the top plate and the rest of the resonator is also discussed.

• Proceedings of the KIEE Conference
• /
• 1997.07d
• /
• pp.1298-1300
• /
• 1997

금속기판상 초전도 $YBa_2CU_3O_{7-{\delta}}$ (YBCO) 박막을 yttria-stabilized zirconia (YSZ) 완충막을 이용하여 in situ 펄스 레이저 증착법에 의해 증착하였다. YBCO 박막을 직접 금속기판에 증착하게 되면 YBCO 박막과 금속기판 사이의 계면에서 상호확산현상이 발생하기 때문에 이를 방지하기 위해 YSZ 완충막이 사용되었다. YSZ 완충막의 증착온도가 박막의 결정성과 전기적 특성에 미치는 영향을 알아보기 위해 YSZ 완충막은 여러 가지 온도로 증착되었다. YBCO 박막의 증착온도와 같은 온도로 YSZ 완충막을 증착했을 때보다 YBCO 박막의 증착온도보다 높은 온도로 YSZ 완충막을 증착했을 경우, 증착된 YBCO 박막은 x선 회절에 의해 c 축 방향으로 성장하였음을 알 수 있었고, 저항이 0이 되는 임계온도가 83K가 되는 실험 결과를 얻었다.