Pure YBCO Research Articles

Over–current carrying characteristics of rectangular–shaped YBCO thin films prepared by MOD method

A fault current limiter (FCL) may be manufactured at competitive qualities and prices by using rectangular-shaped YBCO films which are prepared by metal-organic deposition (MOD) method, because the MOD method can produce large size elements with a low-cost and non-vacuum technique. Prior to constructing a superconducting FCL (SFCL), AC over-current carrying experiments were conducted for 120 mm long elements where YBCO thin film of about 200 nm in thickness was coated on sapphire substrate with cerium oxide (CeO2) interlayer. In the experiments, only single cycle of the ac damping current of 50 Hz was applied to the pure YBCO element without protective metal coating or parallel resistor and the magnitude of the current was increased step by step until the breakdown phenomena occurred in the element. In each experiment, current waveforms flowing through the YBCO element and voltage waveform across the element were measured to get the voltage-current characteristics. The allowable over-current and generated voltage were successfully estimated for the pure YBCO films. It can be pointed out that the lower n-value trends to bring about the higher allowable over-current and the higher withstand voltage more than tens of volts. The YBCO film having higher n-value is sensitive to the over-current. Thus, some protective methods such as a metal coating should be employed for applying to the fault current limiter.

Study on the formation of YBCO phase and texture transformation of Ag substrate during the heat treatment of TFA-MOD process

The YBCO films were directly deposited on cold-rolled Ag substrates by MOD (metal-organic deposition) method. The formation of YBCO phase and change of Ag textures were studied during firing precursor films. It was found that YBCO phase starts to be formed at 800°C when Ag {110}<110>texture (most suitable texture for YBCO epitaxial growth) appears. With the increase of firing temperature, pure YBCO phase is obtained and Ag {110}<110>texture gradually becomes stronger. The textures of both {110}<110>texture in Ag substrate and biaxial orientation in YBCO film were optimized after holding the film at 900°C for 30 minutes. Finally, the YBCO film deposited directly on cold rolled Ag substrate has a good biaxial texture, a smooth and dense surface as well as high critical current density of 1.5×104A/cm2. The results show that cold-rolled Ag can be used as a substrate material to directly deposit YBCO film without any buffer layers by MOD method.

Superconducting properties of chromium Cr-YBCO grown by pulsed laser deposition

Thin superconducting films of type Chromium incorporated YBa2Cu3CrxO6+δ have been grown by Pulsed Laser Deposition (PLD). The prepared films have been characterized using X-ray powder diffraction (XRD) and Energy Dispersive X-Ray (EDS) analysis. The superconducting transition temperature Tc determined from electrical resistivity measurements was found to slightly increase for low Cr-content (x) and decreases when x > 0.05. Furthermore, the surface morphology of the Cr doped and the pure YBCO films were investigated by Scanning Probe Microscope (SPM).

Incorporation of double artificial pinning centers inYBa2Cu3O7−d films

YBa2Cu3O7−x+BaZrO3+Y2O3 (YBCO+BaZrO3+Y2O3) mixed filmswere prepared on SrTiO3/MgO substrates by pulsed-laser deposition, with anYBCO+BaZrO3 targetwith a thin Y2O3 sector stuck on the top. The pinning properties for the double-dopedYBCO+BaZrO3+Y2O3 thin film were enhanced in comparison with those of a pure YBCO sample preparedin the same experimental conditions. The maximum global pinning forcesFp for the double-dopedsample are 12.8 GN m−3 near3 T at 77 K, 46.3 GN m−3 near4 T at 65 K, and 122 GN m−3 near 9 T at 40 K. In the double-doped sample the angular dependence ofJc showed a broad peak at , due to the flux pinning by c-axis correlated defects, combined with a plateau, due to the flux pinning by isotropic pinning centers. BothBaZrO3 nanorodsparallel to the c-axis and Y2O3 nanoparticles randomly dispersed inside the YBCO matrix were consistently observed inthe cross sectional transmission electron microscopy images.

Magnetic pinning‐effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 bilayer

AbstractThe vortex lines of superconductor can be driven by electrical currents, which are often coupled with a reliable control of flux quanta movement by defects or magnetic domains. In this work, the magnetic pinning‐effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers is investigated. It is found that by increasing the field from 0 to 5 Tesla, the critical current Ic of pure YBCO film at 50 K is suppressed by three orders of magnitude. However, in the NCMO/YBCO bilayer Ic is less sensitive to the field and maintains at the level of 100 mA at high field. This result indicates that the magnetic pining effect of NCMO is much more efficient than the conventional routes, which maybe related to the fine domain structure of NCMO film. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Epitaxial Growth of High-J c NdBa2Cu3O7−δ Films on RABiTS by Pulsed Laser Deposition

NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (NdBCO) films were grown on rolling-assisted biaxially textured substrates (RABiTS) via pulsed laser deposition. c-Axis-oriented epitaxial NdBCO films with high performance were obtained under optimal deposition conditions. Transmission electron microscopy analysis shows that the NdBCO film grown on RABiTS has a clear interface with a CeO{sub 2} cap layer and a nearly perfect lattice structure. The NdBCO film exhibits higher {Tc} of 93.7 K and better in-field J c in magnetic fields and at all field orientations, compared to pure YBCO films.

Flux pinning in MOD YBCO films by chemical doping

A novel nanomaterial synthesis technique has been developed to introduce 0D (particles),1D (columnar defects) and 3D (domains) nanoscale pinning centres in MODY1Ba2Cu3O7 (YBCO) coated conductors. We have succeeded in introducing nanoscale Y enriched particles, nanoscale90° rotated Y1/3Sm2/3Ba2Cu3O7 domains and nanoscale Zr enriched columnar defects into YBCOlayers by different chemical doping. The pinning force density inY2O3-doped YBCO film is found to be larger than that of pure YBCO film atall fields. Also it was found that YBCO films with Sm substituting for Yhave yielded improved critical current density characteristics over a widerange of magnetic fields. Maximum pinning force densities exceeding 7 and8 GN m−3 are obtained in 5% BZO-doped and Sm substituted YBCO films, respectively. Additionally,TEM studies revealed nanoscale Zr enriched columnar defects distributing in the matrix of thec-oriented YBCO film throughout the whole cross section. This indicates that chemicaldoping is a promising fabrication technique to create specific pinning landscapes in YBCOcoated conductors.

Fabrication of YBCO Films on ${\rm SrTiO}_{3}$ and Textured Ag Substrates by TFA-MOD Method

In this paper, we presented the results of YBCO films deposited epitaxially on both SrTiO3 single crystal and textured Ag substrates by a TFA-MOD method. The growing conditions and forming mechanisms of the YBCO films on these two kinds of substrates was investigated systematically. It was found that the precursor film coated on Ag substrate took less time to completely decompose to an amorphous precursor film during the first stage of the calcination than that on SrTiO3 substrate. Moreover, the higher temperature was needed to obtain pure YBCO phase on Ag substrate during the second annealing stage. A possible growing mechanism for this difference was described. A transport jc value of 1.5 x 104 A/cm2 (at 77 K) was obtained for the YBCO film deposited on Ag substrate, while the film on SrTiO3 substrate exhibited an a Tc onset of 92 K and a high jc value of 2.3 MA/cm2 at 77 K in self-field was measured.

YBa2Cu3O7−x + YSZ mixed films with enhanced critical current densities in magnetic field

YBa2Cu3O7−x+YSZ (YBCO+YSZ) mixed films were prepared on SrTiO3/MgO substrates by pulsed laser deposition (PLD) from a YBCO target with thin YSZ sector on the top of the target. In comparison with a pure YBCO film, the Jc at 77K for mixed YBCO+YSZ thin film was enhanced from 1.46MA/cm2 to 1.95MA/cm2 (self-field) and from 0.09MA/cm2 to 0.28MA/cm2 (B∥c, B=5T) even when both films were prepared on the same deposition conditions. In the YSZ-added sample, the angular dependence of Jc shows a broad peak at B∥c, due to the flux pinning by c-axis correlated defects. Consistently, elongated nanorods grown in the direction parallel to c-axis were observed in cross-sectional TEM images.

Current enhanced magnetic proximity in Nd0.7Ca0.3MnO3∕YBa2Cu3O7 bilayer

The Nd0.7Ca0.3MnO3∕YBa2Cu3O7 (NCMO/YBCO) bilayer is fabricated with the method of pulsed laser deposition, and the current dependent proximity effects are investigated. Our experimental data show that the suppression rate of superconducting transition temperature (Tc) with respect to the applied current (&amp;gt;1mA) is enhanced by one order of magnitude in NCMO/YBCO compared with that in pure YBCO. The enhanced Tc suppression is attributed to pair breaking via the interactions with the spin-polarized quasiparticles and the magnetic exchange, in association with a current-induced melting of the charge-order state in NCMO.

Angular properties of pure and Ca-substituted YBa 2Cu 3O 7− δ superconducting thin films grown on SrTiO 3 and CeO 2 buffered Al 2O 3 substrates

In this work transport properties of superconducting 10 at.% Ca-substituted YBCO thin films grown on (1 0 0)-SrTiO 3 single crystal substrate (STO) and superconducting pure and 10 at.% Ca-substituted YBCO thin films grown on CeO 2 buffered Al 2O 3 substrates (CAO) have been analyzed as a function of the temperature, applied magnetic field and angle between magnetic field direction and the direction normal to the film surfaces. Particularly, the angular analysis provides an easy way to discriminate between isotropic point defects and correlated pinning sites. Despite the intragrain pinning mechanisms remained unaffected by Ca substitution, a detrimental effect on grain boundary properties clearly emerged for 10 at.% Ca concentration. This effect is enhanced in sample grown on CeO 2 buffered sapphire where a more disturbed grain boundary is expected resulting in an enhancement of the correlated pinning, already observed in pure YBCO films grown on CAO, and in a reduction of the intrinsic pinning efficiency.

Enhancement of critical current density of YBa 2Cu 3O 7 − δ thin films by self-assembly of Y 2O 3 nanoparticulates

YBa 2Cu 3O 7 − δ (YBCO) thin films, possessing high critical current density ( J c), have been synthesized by embedding a homogeneous array of Y 2O 3 non-superconducting nanoclusters/nanoparticles using a pulsed laser deposition technique. The size, interparticle spacing, and density of Y 2O 3 nanoparticles in YBCO thin films were tailored by varying the number of laser pulses in order to determine the optimum size for effective immobilization of vortices. Scanning transmission electron microscopy with atomic number contrast and X-ray diffraction techniques were used to determine the size and structure of the nanoparticles. Both techniques indicate that the Y 2O 3 particles are epitaxial with respect to the surrounding YBCO matrix. The information about pinning of vortices by the nanoparticles was obtained by investigating the behavior of critical current density as a function of temperature and applied field, which in turn determines the vortex density in the sample. The superconducting transition temperature ( T c) of YBCO films with the inclusion of nanoparticles was observed to remain almost the same or decrease marginally (1–2 K) with respect to T c of pure YBCO films deposited under identical conditions. However, J cs of YBCO films embedded with self-assembled nanoparticles were found to be significantly higher than that of pure YBCO films. The J c enhancement was up to five times in high magnetic field, which is a key requirement for practical application of high- T c materials.

Flux Pinning Enhancement of YBCO Films by Y and Ba Site Doping at Minute Concentrations

AbstractYBa2Cu3O7-x (Y123) superconducting thin films can maintain high critical current densities in applied magnetic fields up to a few Tesla at 77 K. Even so, this does not preclude the intentional addition of alternate flux pinning centers in the Y123 films to further optimize their in-field Jc. Unfortunately, many methods to incorporate flux pinning centers into Y123 thin films introduce additional steps and/or re-optimization of the deposition parameters for a given addition. Identifying potential additions that can optimize the performance of YBCO films without changing the deposition conditions would be ideal. The work presented here is an extension of earlier work and demonstrates new dopants and possibilities for introducing pinning centers by the route of minute doping or nanodoping. Preliminary results of a study to determine if minute doping can be performed with smaller lanthanide atoms (Tm, Lu), non-lanthanide atoms (Sc) and Ba-site substitution (Sr) are presented. All samples were deposited under identical conditions as pure YBCO. The new dopants will be discussed in addition to those previously presented (Tb, Pr, Ce, Nd, and La). Critical current density data will be presented for 65 K and 77 K in fields up to 9T in addition to new structural data obtained by cross-sectional TEM.

Magnetic field dependence of the critical current and the flux pinning mechanism inYBa2Cu3O6+xfilms doped withBaZrO3

Dependence of the critical current on applied magnetic field ${j}_{c}({B}_{a})$ is investigated in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ (YBCO) films prepared by pulsed laser deposition from pure YBCO target and from those doped with 2.9 or $9.0\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ ${\mathrm{BaZrO}}_{3}$. All targets were sintered from nanophase powders made by a citrate-gel process. Transmission electron microscopy images show distributions of ${\mathrm{BaZrO}}_{3}$ particles with typical diameters of $5--10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the doped films. In comparison with the pure YBCO film the value of ${j}_{c}(0)$ is slightly smaller in the film deposited from the target doped with $2.9\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ ${\mathrm{BaZrO}}_{3}$ and only half in case of $9.0\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ doping. Two interesting phenomena in the behavior of ${j}_{c}({B}_{a})$ are observed for the doped films. First, the low-field plateau of ${j}_{c}$ is significantly lengthened and second, in fields above the accommodation field ${B}^{*}$ marking the end of this plateau the rate of decrease of ${j}_{c}$ is strongly reduced. These results are well fitted with a critical state model of superconductors taking into account the self field effects at low applied magnetic fields.

Fabrication of YBCO coated conductor by TFA-MOD using the “211 process”

YBCO film was fabricated by the TFA-MOD method based on the “211 process” in which precursors of Y2Ba1Cu1Ox (Y211) and Ba3Cu5O8 powders, instead of Y-, Ba-, and Cu-based acetates, were dissolved in trifluoroacetic acid (TFA) in order to explore its possible application in coated conductors. We evaluated the effects of the humidity and firing temperature on the phase formation, texture formability, and critical temperature (Tc) and current (Ic) of the YBCO film. We successively synthesized pure YBCO films of which those fired in 12.1–20.0% humidified Ar gas showed the highest critical properties, viz. a Tc-zero of 88.6K and Ic of 30A/cm width. These improvements in the critical properties were attributed to the formation of pure YBCO phase, to the improved density and the large grain size. In addition, we observed that the Ic varied significantly with the firing temperature. The variation of the Ic with the firing temperature was correlated with the microstructural evolution.

Critical current enhancement in PLD YBa2Cu3O7−x films using artificial pinning centers

We introduced high-density columnar defects as artificial pinning centers (APCs) for quantized vortices into YBa2Cu3O7−x (YBCO) films during the film deposition procedure. APCs were introduced perpendicular to the film surface using nano-sized Y2O3 islands prepared on SrTiO3(100) substrates. Varying the deposition parameters and the substrate annealing conditions allowed strong changes in the shape and density of the Y2O3 islands to be induced. Compared to a pure YBCO film, the best performance among the APCs samples was obtained on the Y2O3-deposited substrate with 5 laser pulses, corresponding to a nominal thickness of 0.2nm. Even when the APC films were prepared using the same deposition conditions, the columnar defects enhanced Jc at 77K from 1.8 to 2.7MA/cm2 (self field) and from 0.06 to 0.10MA/cm2 (H=5T, H∥c-axis).

The effects of the firing temperature of YBCO coated conductors fabricated by TFA-MOD process

We fabricated YBCO films on LAO substrates using the TFA-MOD method and evaluated the effects of the heat treatment temperature on the microstructure, degree of texture, and critical properties. The phase formation and microstructure were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM) and the degree of texture was evaluated by pole-figure analysis.The firing was performed in the temperature range of 750–800°C and we found that the phase purity, grain size and orientation, degree of texture, and oxygen content varied with the firing temperature. The films fired at 775°C showed the highest critical temperature (TC-onset) of 89.5K and critical current (IC) of 40A/cm-width, which corresponds to a critical current density (JC) of 1.8MA/cm2. According to the results of the XRD, pole-figure, SEM and Raman analyses, these optimum critical properties can probably be attributed to the formation of a pure YBCO phase, stronger c-axis orientation and higher oxygen content.

Structural and magnetotransport properties of YBa2Cu3O7−δ∕Y2O3 quasimultilayers

A series of quasimultilayers of YBa2Cu3O7−δ(YBCO)∕Y2O3, namely, 70×[YBCO(m)∕Y2O3(n)] (m=40 pulse, and n=2, 5, 10, and 20 pulse) were prepared on single-crystal SrTiO3 using pulsed-laser deposition. X-ray diffraction measurements revealed that both in-plane and out-of-plane textures of YBCO in the present quasimultilayers are as good as in pure YBCO films. Nanoscale Y2O3 precipitates grow epitaxially inside YBCO. With increasing Y2O3 pulse number, Tc decreases slightly, while ΔTc remains less than 1.5K. As well, the YBCO lattice parameter c has an increasing trend with increasing n. This can be attributed to the effect of epitaxial strain induced by lattice mismatch. The flux pinning force density in films with lower Y2O3 content (such as n=2), is improved in large ranges of field and temperature. In contrast, films with high Y2O3 content show enhanced flux pinning only at low temperature, which is understandable from the temperature dependence of irreversibility fields.

Tuning of the critical current inYBa2Cu3O7−x thin films by controlling the size and density ofY2O3 nanoislandson annealed SrTiO3 substrates

We introduced high density columnar defects, as artificial pinning centres (APCs) for quantized vortices,into YBa2Cu3O7−x (YBCO) films during the film deposition procedure. APCs wereintroduced perpendicular to the film surface using nanosizedY2O3 islandsprepared on SrTiO3(100) substrates by pulsed laser deposition. Varying the deposition parameters and thesubstrate annealing conditions allowed strong changes in the shape and density of theY2O3 islands to be induced. The best performance among the APC samples ascompared to the pure YBCO film was obtained for that grown on theY2O3-deposited substrate with five laser pulses, corresponding to 0.2Y2O3 monolayers (ML). Even when the 0.2 ML APC films were preparedusing the same deposition conditions, the columnar defects enhancedJc at 77 K from 1.8to 2.7 MA cm−2 (self-field)and from 0.06 to 0.10 MA cm−2 (H = 5 T).

Raman spectra, microstructure and superconducting properties of Sb(III)–YBCO composite superconductor

The pure YBCO (YBa 2Cu 3O 7) and its variant antimony containing composites with general formula; Y 1+ x Sb x Ba 2Cu 3O z , where x = 0.1, 0.2, 0.4 and 0.6 mol%, respectively, were prepared by the solid-state reaction route. X-ray measurements indicated that Sb 3+ ions have a negligible effect on the main crystalline structure and substitutes Y-sites successfully in lattice structure of 123-YBCO at low concentrations of doping ( x = 0.1 → 0.2). From SE-microscopy mapping and EDX elemental analysis, Sb 3+ was detected qualitatively with good approximation to the actual molar ratio but not observed at 123-YBCO grain boundaries which confirm that antimony (III) has diffused regularly into material bulk of superconducting 123-YBCO-phase at low concentrations. Additions of Sb(III) affected sharply on the main vibrating modes of YBCO regime particularly, on the apical oxygen (O 4) vibrational mode A 1g. Magnetic susceptibility measurements proved that antimony oxide additions have slight effect on the transport properties of YBCO-composites regime.