YBa2Cu3O7-x Research Articles

Yttrium-enriched YBa2Cu3Ox thin films for coated conductors fabricated by pulsed laser deposition

The effects of excess yttria on the structural and electrical properties of the YBa2Cu3Ox (YBCO) thin films are studied. The films were deposited on (LaAlO3)0.3–(Sr2AlTaO8)0.7 substrates by pulsed laser ablation from targets with different elemental composition. An increase of yttrium content of the target leads to formation of porous films with significantly improved current-carrying capabilities. Structural studies of these films reveal presence of yttria nanoparticles embedded into the YBCO matrix. The highest obtained critical current density in an external magnetic field of 5T was 2.6MA/cm2 at 50K and 9.4MA/cm2 at 20K. The fabricated Y-enriched YBCO films remain c-oriented at least up to 600nm thickness with no significant suppression of the critical current density.

Studies on Ni/ZrO<sub>2</sub> Catalyst in YBCO Membrane Reactor by TG on Methane Partial Oxidation to Syngas

We investigated the Ni/ZrO2 catalyst performance of YBa2Cu3O7-x (YBCO) membrane reactor in the process of partial oxidation of methane (POM) to syngas by TG. The activity of the catalyst effected not only on the methane conversion but also CO selectivity. The effect of temperature on CO selectivity was little and could be neglected.The change of CH4 conversion along time was caused by the deactivation of catalyst or/and the decay of membrane reactor. The loss of catalysts increase with temperature accoding to the carves of TG .

Fabrication of YBCO Small Test Coils for Accelerator Magnet Development

A research program for studying coil winding technologies using YBa2Cu3Ox (YBCO) coated conductors is now in progress. In this program, we are attempting to develop high-Tc superconducting magnets for highly functional, efficient, and compact accelerator systems. In designing superconducting coils with thin tape conductors, we must be concerned about magnetization of the superconducting layer. In order to experimentally evaluate the influence of the additional field resulting from the magnetization current, prototype racetrack coils were constructed with YBCO coated conductors. A 62 m length of coated conductor was wound to form each of the coils, which were then impregnated with epoxy resin. For precise analysis of the additional magnetic field, it is essential to fabricate superconducting coils without degradation because the voltage generated at such a degraded part would affect the behavior of the additional magnetic field. In a liquid nitrogen environment, the racetrack coils were energized to evaluate the voltage-current (V-I) characteristics. It was found that there was no degradation in the superconductivity. The V-I characteristics showed sufficiently high index values of 28 and 34 throughout an electric field range of 10-9 V/cm. Magnet design derived from accelerator design, as well as construction of an experimental reduced-scale coil in a typical shape, are also discussed.

Interfacial defects distribution and strain coupling in the vertically aligned nanocomposite YBa2Cu3O7-X/ BaSnO3 thin films

Abstract

Ratchet Effect of Single Vortex Motion in Superconducting Asymmetrical Nanobridges

We have successfully obtained asymmetrical current–voltage (I–V) characteristics in YBa2Cu3O7-x (YBCO) nanobridges patterned with asymmetrical geometry. These asymmetrical nanobridges (ANBs) are shown to control vortices one at a time. The critical current Ic, of 200-nm-wide and 100-nm-thick ANB changes by a maximum of 9% when a magnetic field of 2.4 mT is applied. The Ic variation ΔIc increases monotonically with increased magnetic field from -2.2 to 2.4 mT. The asymmetrical I–V characteristics obtained in our experiment are due to the restriction of vortex motion by the asymmetrical surface barrier (the so-called vortex ratchet effect). The width and thickness dependencies of the I–V asymmetry are also studied, and indicate that the bias current and the Meissner screening current, determined by the relative width compared to the effective penetration depth of the YBCO film, dominates the I–V asymmetry characteristics.

Properties of SFS heterostructures prepared by a focused-ion-beam technique

We present a study of superconductor-ferromagnet (SF) bilayers and superconductor-ferromagnet-superconductor (SFS) heterostructures of nanometer dimensions prepared by a gallium focused-ion-beam (FIB) technique. The SFS heterostructures were implemented on the basis of high-Tc superconducting YBa2Cu3Ox (YBCO) and ferromagnetic La0.67Sr0.33MnO3 (LSMO) thin films deposited by magnetron sputtering on SrTiO3 (100) single crystal substrates. SFS weak link junctions require weak link dimensions in the range of nanometer size realizable by FIB patterning. On the other hand, the focused gallium ion beam might cause unacceptable degradation of the superconducting and ferromagnetic thin film properties. Our results confirm such influence of the FIB technology. However, protection of the structures by a gold thin film may effectively solve this problem, as is presented in the paper.

Comparison of AC Transport Current Loss in Different YBCO Coated Conductor Tapes Measured at 4.2K

Abstract The YBa2Cu3O7-x (YBCO) superconducting tapes are promising candidates for using in applications at liquid helium temperature. Their parameters have not been adequately explored in these conditions by now. This work deals with AC transport current loss comparison of different YBCO coated conductors in self field in liquid helium (LHe). For experiments we used YBCO tapes of different widths, both with and without ferromagnetic substrate and stabilizing layer. The measurements are based on the lock-in technique using a special measurement device working on the principle of a current transformer. The device enables to measure up to high currents (order of kA). The heating of current leads and LHe evaporation is minimized. The experimental data show very good transport properties of YBCO tapes in LHe (high critical currents and corresponding transport current loss). This contribution is completed by AC transport current losses of used YBCO samples measured in liquid nitrogen (LN2)

Growth process of BaZrO3 doped YBCO films by TFA-MOD method

Crystal growth process of YBa2Cu3O7-X (YBCO) films with BaZrO3 (BZO) pinning centers were investigated to enhance JC property by controlling microstructure of the films. The YBCO films were fabricated by a metal organic deposition (MOD) method using solutions with trifluoroacetates (TFA) and Zr-salts. Quenched films were prepared by cooling them rapidly during crystallization process and crystallized phases were identified by an X-ray diffraction (XRD) measurement. It is indicating that BZO forms at lower temperature than that of YBCO formation and that BZO and BaF2 are crystallized at the similar temperature range around 700°C. Then, we kept the heating temperature which is under 600°C before crystallization temperature of YBCO and investigated the effect of temperature keeping on film growth. In the film kept for more than 3 hours, BZO peak was detected by XRD measurement. However, BZO particles were not observed in the film even kept for 9 hours by transmission electron microscopy (TEM) and energy dispersive X-ray (EDS) analyses. It is indicated that growth rate of BZO is slow at 600°C. On the other hand, smaller YBCO particles and decreasing of surface roughness (Ra) were observed for the film which were kept at 600°C for 3 hours and then crystallized. This result suggests the density of YBCO film is higher than that for YBCO without that process. In summary, it can be considered that YBCO film density become high by temperature keeping process below 600°C before YBCO crystallization and that size of BZO particles are determined by heat treatment at the temperature of above 600°C

Combinatorial Synthesis of (YxGd1-x)Ba2Cu3Ox Superconducting Thin Films

Environmentally friendly water-based YBa2Cu3Ox (YBCO) and GdBa2Cu3Ox (GdBCO) precursor solutions were synthesized to realize thin films by chemical solution deposition. Pure YBCO and GdBCO precursor solutions were used for ink plotting on SrTiO3 substrates and subsequent thermal treatment at the corresponding crystallization temperature. Phase formation of Gd123 requires a higher crystallization temperature of 840 ¡C compared to the Y123 phase. The critical temperature of YBCO films is about 92 K with a sharp transition into the superconducting state. Micro liter sized ink volumes of YBCO and GdBCO were successfully mixed for two-dimensional ink plotting of a (YxGd1-x)Ba2Cu3Ox film library. A homogeneous surface and no indication of a-axis growth were found in all mixed films.

Comparison in Tribological Properties of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>X</sub>/Ag and Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>X</sub>/Ag Self-Lubricating Composites

The YBa2Cu3Ox/Ag and Bi2Sr2CaCu2Ox/Ag self-lubricating composites were prepared using powder metallurgic method. The crystal structure and morphology of the as-synthesized samples were characterized by XRD and SEM. The YBa2Cu3Ox/Ag and Bi2Sr2CaCu2Ox/Ag self-lubricating composites were found to compose of superconductor phase and Ag phase. The tribological properties from ultra-low temperature to room temperature of the composites were studied by pin-on-disk friction test. It was found that the friction coefficients of pure YBa2Cu3Ox(YBCO) and Bi2Sr2CaCu2Ox(BSCCO) were both dropped abruptly when the temperature cooled below the superconducting transition temperature. At room temperature, the friction coefficient of pure YBa2Cu3Oxis 0.68~0.95, when mixing 15wt% Ag, the friction coefficient of the sample decreased to the lowest value 0.11. The friction coefficient of pure Bi2Sr2CaCu2Ox is 0.15~0.17, When Ag content reach 10wt%, the coefficient was lowest (average value is 0.13). The addition of appropriate amount of Ag obviously improve the tribological property of YBCO, while only slightly meliorate that of BSCO. On the other hand, the YBCO/Ag composites exhibit better tribological properties than BSCCO/Ag composites at higher load under the same experimental condition.

Effect of Oxygen Depletion on the Pinning Properties of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{\rm x}$ Films With Nanoinclusions

Applications of YBa2Cu3Ox (YBCO) coated conductors require strong vortex pinning to ensure a non-dissipative state over a large range of temperatures and magnetic field values. Incorporations of nanoparticles and nanorods have generally resulted in a substantial increase of pinning, but the actual mechanism producing this increase is not fully understood. This report addresses the origin of the enhanced pinning through comparative resistive measurements in the mixed state of thin films of YBCO, YBCO doped with Y2O3 nanoparticles, and YBCO doped with BaSnO3 nanorods. In order to study the effect of oxygen, all three kinds of samples have been annealed in air at 420°C. We have extracted and compared the resistive irreversibility lines before and after annealing. Our results indicate that while the nanoinclusions in the fully-oxygenated samples improve the pinning strength over that in the pure YBCO sample, the pinning enhancement essentially vanishes upon oxygen depletion. This is true for both pinning structures, nanorods and nanoparticles.

Optimization of the ${\rm BaCeO}_{3}$ Concentration in YBCO Films Prepared by Pulsed Laser Deposition

A series of studies has been carried out on thin films prepared by pulsed laser deposition (PLD) from micro-grained targets of YBa2Cu3O7-x (YBCO) to determine the effect of doping them with BaCeO3 (BCO) in concentrations between 0-10 wt%. BCO has been found to increase Jc in e.g. melt-textured and bulk samples, but no systematic study with PLD thin films has been performed. Magnetometric measurements up to 8 T and down to 10 K as well as structural measurements with XRD and AFM were performed. Jc increased with doping and the highest Jc 's were achieved with low dopant levels (2% and 4%), which varied according to the external field and temperature. Tc decreased when the dopant concentration was increased, similarly as in BaZrO3 (BZO) doped films. However, the BCO growth process in the films was found to be different from the BZO and, furthermore, an interesting effect where the YBCO twin structure is altered was found around 6 wt% of BCO. The Jc results and a comparison with structural properties with increasing dopant level and optimally BZO-doped YBCO thin films are presented.

Annealing Temperature Effects on ${\rm YBCO/LaAlO}_{3}$ and ${\rm YBCO/CeO}_{2}/{\rm Al}_{2}{\rm O}_{3}$ for Microwave Applications by TFA-MOD

YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) superconducting films can be used for microwave applications due to their low surface resistance. Both LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> can be considered as applicable substrates since their excellent properties for the preparation of high-quality YBCO films and for the design of microwave elements. In order to optimize the annealing temperature, the microstructure and properties were investigated for YBCO/LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and YBCO/CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /r-cut Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films prepared by trifluoroacetates metal organic deposition (TFA-MOD). The results show that the annealing temperature window is broader for YBCO films on LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrates; while, the window is relative narrower for YBCO films on CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrates. The reasons were also discussed. The surface resistivity (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) was measured for the samples with highest critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ). The results will provide useful information about processing effects on YBCO films using TFA-MOD for microwave applications.

Pinning Enhancements in YBCO Films via Nanoengineered ${\rm LaMnO}_{3}$:${\rm MgO}$ Composite Cap Layer

In the present work, composite LaMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :MgO (LMO:MgO) cap buffer layers with varying MgO contents 5 vol% up to 75 vol% have been grown on homo-epi MgO/IBAD(MgO) substrates to enhance the performance of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) films. Results showed formation of phase separated MgO nanocolumns within the LMO matrix. The impact of these nanocolumns on the superconducting properties of YBCO films deposited using pulsed laser deposition (PLD) on the nanostructured layer was investigated by electrical transport measurements. Such YBCO films showed better in-field performance compared to that of YBCO films on standard LMO cap films. In particular, measurements of the field-angle dependence revealed <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis correlated pinning for YBCO films on these composite cap layers. The present results demonstrate a practical approach to obtain high performance superconducting wires.

Transport Properties of YBCO Nanowires

We have carried out transport studies of YBa2Cu3O7-x (YBCO) nanowires. By exposing nanowires with microwaves, we see that short wires which have a flux-flow like current-voltage characteristic (IVC) clearly manifest current steps in the IVC (Shapiro steps). On the contrary, the longer wires exhibiting a resistively and capacitively shunted junction (RCSJ) model like current-voltage characteristic do not feature any Shapiro steps. The second case can be explained by taking into consideration the longer wire lengths where the wires loose coherency of flux flow due to inhomogeneity along the wire.

Effect of substrate topography for YBa2 Cu3 O7-x coated conductors on the nucleation mechanism of buffer layer

The surface condition of substrate tape is an important factor to obtain epitaxial buffer layer on biaxially textured Ni tape for YBa2Cu3O7-x coated conductors. We prepare ceria films on Ni single crystal, biaxially textured Ni tape and sulfured Ni substrates by direct current magnetron sputtering. The results show that the ceria films prepared on Ni single crystal and sulfured Ni substrates each have a poor-textured grain structure. However, the ceria film fabricated on rolling assisted biaxially textured substrate (RABiTS) exhibits a good c-axis texture and desirable surface morphology. Reflection high-energy electron diffraction analysis indicates that the c(22) superstructure on the RABiTS Ni surface has a dramatic effect on the heteroepitaxial growth of oxide buffer layer.

AFM Nano-Plough Planar YBCO Micro-Bridges: Critical Currents and Magnetic Field Effects

The critical current (Ic) of YBa2Cu3O7-x (YBCO) AFM plough micro-constrictions is measured as a function of temperature, width and the magnetic flux density (B), which was applied perpendicular to the YBCO ab-plane and surface of the bridges. C-axis oriented thin films of YBa2Cu3O7-x were deposited on MgO substrates using an inverted cylindrical magnetron (ICM) sputtering technique. The films were then patterned into 8-10 micron size strips, using standard photolithography and dry etching processes. Micro-bridges with widths between 1.9 microm to 4.1 microm were fabricated by using atomic force microscope (AFM) nanolithography techniques. Critical current versus temperature data shows a straight-line behavior, which is typical of constriction type Josephson junctions. The Ic versus B characteristics exhibited a modulation, and a suppression of the critical current of up to 84%. It was also found that the critical current increases with increasing constriction width.

Nano Techniques for Enhancing Critical Current in Superconducting YBCO Films

A range of nano techniques is explored in order to increase the critical current in pulsed laser deposited (PLD) superconducting YBa2Cu3Ox (YBCO) thin films. The structural measurements are linked with magnetic and transport measurements of the films. The effectiveness of PLD techniques is analyzed from the point of view of the dimensionality of nanostructures formed prior to and during the film growth. It is shown that a combination of two-dimensional substrate decoration with nanoparticles before the film deposition and one-dimensional growth of external phase nanorods during the deposition offers a high critical current in magnetic field both along the c-axis and in the ab-plane of YBCO.

ChemInform Abstract: Plasma-Sprayed-Yttria Layers for Corrosion Resistance.

Crucible corrosion in the growth of YBa2Cu3O7-x (YBCO) superconducting single crystals is one of the major obstacles in obtaining high-quality crystals. Both metallic and ceramic crucibles have shown significant corrosion that affects the size and properties of YBCO crystals. Plasma spraying has been successfully used to produce yttria coatings on alumina substrates. Yttria coatings with thicknesses between 30 and 100 μm have shown corrosion rates of 3 to 4 μm/h; these rates are 5 to 10 times lower than that of the alumina substrate.

Study on deposition of YBCO for coated conductor using pulsed laser deposition

YBa2Cu3Ox (YBCO) superconductors were coated on the CeO2/YSZ/Y2O3 buffered Ni5W tape by reel-to-reel pulsed laser deposition (PLD). To achieve high current carrying capacities, combinations of various deposition conditions were explored. X-ray diffraction measurements showed good in-plane and out-plane texture in YBCO films. The transition temperature of the coated YBCO was typically 89 K. The critical current is over 50 A at 77 K in meter-long YBCO tapes with a width of 1 cm. Their surface morphology was found being thickness-dependent. Further research work is under way.