Critical Current Density In YBCO Research Articles

Effectiveness of Two Pinning Profiles in Controlling Magnetic Critical Current Density in YBCO + YCMO Composites

Effectiveness of Two Pinning Profiles in Controlling Magnetic Critical Current Density in YBCO + YCMO Composites

Large enhancement of the in-field critical current density of YBCO coated conductors due to composite pinning landscape

YBa2Cu3O7-based coated conductors (CCs) achieve the highest critical current densities (J c) of any known superconductor and are a key technology for applications such as rotatory machines, high-field magnets and power transmission. Incorporation of nano-sized non-superconducting second phases as additional vortex pinning centers has been considered the most amenable route to further enhance J c at an industrial scale, and has been successfully used in commercial CCs. The resulting pinning landscape is quite complex, with both synergistic and competing interactions among the various types of defects. Particle irradiation, on the other hand, allows for a controlled post-processing incorporation of a well-defined defect morphology. We have previously shown that irradiation with protons and other light ions can further enhance the in-field J c in commercial state-of-the-art CCs. Here we develop a combined irradiation process that increases J c above values previously achieved by irradiating with only one species. Our new approach involves sequentially irradiating with 250 MeV Au ions and 4 MeV protons. For example, at T∼ 27 K (liquid neon) and µ 0 H∼ 4 T, a region of interest for rotatory machines applications, we obtain J c ∼ 5 MA cm−2, which is about 40% higher than the values produced by the individual irradiations. Finally, we conclude that this is due to the synergistic pinning effects of the introduced splayed, non-uniform columnar defects and small clusters.

The effect of Y2O3 and YFeO3 additions on the critical current density of YBCO coated conductors

The pinning mechanism of MOCVD-grown YBCO coated conductors with Y2O3 precipitates was investigated by angle-resolved transport measurement of Jc in a wide range of temperature and magnetic fields. Aside from the Y2O3 nanoprecipitates, a-axis grains and threading dislocation along the c-axis were found in the YBCO layer. The Y2O3 precipitates are less effective pinning centers at lower temperature. The tapes with precipitates show a higher anisotropy with larger Jc at H || ab than H || c. This behavior was attributed to the preferred alignment of the nanoprecipitates along the ab-plane.

Fabrication of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> Superconducting Film on NiW Alloy Using Electrophoretic Deposition

This work reported on exploring a low cost preparation technology for coated conductor. The epitaxial of La0.4Sr0.6TiO3 conductive buffer layer on NiW substrate was achieved by metal organic deposition. Excellent in-plane and out of plane alignment is confirmed via XRD. YBCO film was fabricated by electrophoretic deposition (EPD). We used buffered (LSTO) Ni-W substrate and Ni plate as cathode and anode respectively. The critical current density of YBCO coating is more than 1000A/cm2 (0T, 77K).

The Influence of Surface Morphology of Buffer Layer on the Critical Current Density in YBCO Coated Conductors

1 μm-thickYBa2Cu3O7-δ(YBCO) films were grown on the Y2O3/yttria stabilized zirconia (YSZ)/CeO2buffer layers with different surface morphologies using direct-current sputtering. The critical current density (Jc) value of YBCO was 1.1 MA/cm2when the root mean square surface roughness (Rrms) of the buffer layer was 2.5 nm. As theRrmsof the buffer layer increased to 15 nm, theJcdecreased to 0.3 MA/cm2. X-ray diffraction and scanning electron microscopy showed the strong relevance of the evolution of the structure and surface morphologies of YBCO films with the buffer layer of differentRrms. A model was proposed to explain the influence of surface morphology on the superconducting properties of YBCO films.

The Decrease of the Critical Current of Coated Conductors When a Perpendicular Magnetic Field is Applied: A Josephson Effect Point of View

Abstract A large decrease is observed in the critical current density of YBCO coated conductors (CC) and related compounds when a strong perpendicular magnetic field is applied. While measurements are generally carried out at 77K only, here we present a magnetic technique permitting to determine the critical current per unit width of conductor (Icr/w) in a large temperature range with and without applied field. We report measurements carried out on various CCs that show that, in addition to the reduction in the critical temperature that can be attributed to the low value of the irreversibility field near Tc, the field application results in a large decrease of Icr/w at all temperatures. We ascribe this reduction to the Josephson behaviour of the twin boundaries included in the YBCO layer.

Application of shock waves for the improvement of current-carrying properties of YBCO(123) and Bi(2223) HTSC tapes in magnetic fields

Shock waves with a leading-edge pressure of ∼1011 Pa, which were produced in a plasma focus setup, were used to increase the critical current density in YBCO(123) and Bi(2223) HTSC tapes. It was shown that the effect of chemically inactive high-temperature high-density plasma on the HTSC tapes leads to an irreversible increase in the critical current in high magnetic fields. The improvement of the current-carrying properties of the YBCO(123) HTSC tape is confirmed also by the results of scanning Hall magnetometry at 77 K. In particular, in a field of 8 T applied perpendicular to the c axis (H ⊥ c), the increase in the critical current after shock-wave treatment is ∼60%. In the case of the Bi(2223) tape, the critical current in a zero field in the sample portion subjected to shock-wave action was found to be twice as high as that in the untreated portion (100 and 50 A, respectively). The increase in the critical current can be related to a number of possible structural transformations of the superconducting core. First of all, an increase in the density of current-carrying core, which leads to an increase in weak bonds at grain boundaries, is possible. In this case, the formation of nanosized defects, which are responsible for an increase in the force of pinning of Abrikosov vortices, is also possible.

Spatial distribution of the local resistive transition and the critical current density in YBCO coated conductors using Low-temperature Scanning Laser Microscopy

Low-temperature Scanning Laser Microscopy (LTSLM) was carried out to reveal the spatial distribution of the local resistive transition temperature and the local current density in commercial YBCO coated conductors near the superconducting transition. The result of the sample with an array of holes of various sizes shows that the signal δV is proportional to the current density. The distribution of the critical temperature of the sample with two parallel bridges is quite homogeneous and the transport current flows mainly along the outer edge of the sample. Using LTSLM we directly image the current path in YBCO coated conductors of different patterns.

Temperature and Magnetic Field Dependence of Critical Current Density of YBCO With Varying Flux Pinning Additions

The critical current density (Jc) of YBa2Cu3O7-z films doped with varying flux pinning nanoparticle additions was systematically studied, for applied magnetic fields of H = 0-9 T and operation temperatures T = 20-77 K. Films were prepared with pulsed laser deposition by (M/YBCO)N multilayer or (YBCO)1-xMx single-target methods, for different M phases including Y2O3, Y2BaCuO5 (Y211) green-phase, and BaZrO3. Very significant differences of Jc(H//c,20-77 K) were measured for optimized M phase additions, that are difficult to model or predict at present. Multilayer films with Y211 and Y2O3 nanoparticle additions had the highest Jc (20-77 K) for H 4 T and 65-77 K, however not for T 2 T) had the strongest properties increasing 70% compared to YBCO+nanoaddition films and increasing 400% compared to YBCO.

Pinning centres and enhancement of critical current density in YBCO doped with Pr, Caand Ni

Substitutional studies have been carried out on sintered bulk samples of YBCOto determine the effect of doping it with Pr, Ca (at Y site) and Ni (at Cusite) in small concentrations on the formation of effective pinning centres forjc enhancement. The results show Pr and Ca substitutions to be far more effective than Ni substitution.The former two give rise to formation of rows of oxygen vacancies with pronounced strain fields inCuO2 planeswhere superconductivity resides. The defects thus formed seem to be analogous to arrays of normal nanodotsin CuO2 planes which are expected to have strong intragrain pinning interactions with pancake vortices ofCuO2 planes forming the mixed state structure. Both these substitutions tend tomarginalize the adverse effects of grain boundaries. The superconductingvolume fraction of the pristine sample is significantly raised by both thesesubstitutions. These special features are, however, absent with Ni substitution. Thispaper brings out the importance of Pr substitution in significantly enhancingjc(B).

Critical current properties in high-temperature superconducting wires and tapes

The hot topics of the critical current properties in YBCO coated conductors and Bi-2223 silver-sheathed tapes are discussed. The dependence of the critical current density in YBCO coated conductors on the superconducting layer thickness is partly associated with the defects nucleated in thicker films and is also caused by the thickness dependent influence of the flux creep. Experimental results on PLD processed conductors with different thicknesses are compared with the theoretical analysis based on the flux creep-flow model. A discussion will also be given for the optimum layer thickness for applications.In Bi-2223 tapes introduction of CT-OP (ConTrolled Over Pressure) process has significantly improved the critical current properties. This progress can be attributed to the improvement of the mean value of the flux pinning strength and the decrease in its distribution width. The possibility of further improvement of the critical current properties is discussed using the flux creep-flow model.

Superconducting and normal state transport properties of epitaxial 10 at.% Ca substituted YBCO thin films

The improvement of the critical current density in YBCO coated conductor tapes necessarily concerns the study of grain boundary (GB) properties and the study of different pinning mechanisms involving both GB and the interior of the grain (IG). Recently, it has been proposed that the introduction of Ca substituting Y enhances Jc in YBCO grain boundaries (GB). On the other hand enhanced correlated pinning, as observed in YBCO thin films grown on CeO2 buffered substrates, has been ascribed to elongated defects along the c-axis of the film. In order to evaluate the role of calcium and CeO2 buffer layer on the superconducting transport properties of YBCO films, critical current density measurements as a function of temperature, magnetic field and angle between magnetic field direction and c-axis of the film have been performed on epitaxial thin films of unsubstituted and 10at.% Ca substituted YBCO grown on CeO2 buffered Al2O3 single crystal substrates. Results are compared with data obtained on 10at.% Ca substituted YBCO grown on SrTiO3 single crystal substrate.

Thermal stress analysis for the meander-shape YBCO fault current limiter

A thermal stress in a meander-shape YBCO fault current limiter has been calculated numerically. The FEM code combining the thermal stress analysis, temperature analysis and current distribution analysis has been developed. From the comparison between the results of simulation and the measurement results of thermal expansion in a small piece of stainless steel, it has been found that the our code is useful for the estimation of thermal stress. The thermal stress and temperature distribution in the meander-shape YBCO fault current limiter under a normal operating condition have been calculated in two conditions; the critical current density of YBCO degrades at the inside of corner and at the middle part of straight section. In both cases, the thermal stress is concentrated around the inside of corner. In the former case, there is high possibility that YBCO bulk is cracked around the corner because the maximum thermal stress exceeds fracture strength of YBCO. On the contrary, in the latter case, there is high possibility that YBCO bulk burns out around the straight section because the maxim thermal stress in YBCO is lower than the fracture strength at the temperature enough to melt YBCO bulk.

High critical current density in YBCO coated conductors prepared by thermalco-evaporation

We report on the in situ preparation ofY Ba2Cu3O7−δ films uniformly depositedover large areas,>20 × 20 cm2, at 690 °C by thermal co-evaporation onto Ni–5 at.% W biaxially textured tapes buffered with e-beam evaporatedCeO2. Typically, the thickness of the YBCO andCeO2 layerswas 0.9 and 0.1 µm, respectively. Deposition rates were 0.2 and2.5 nm s−1, respectively.X-ray diffraction θ–2θ Bragg–Brentano and pole figure measurements, and Nomarsky opticaland SEM microscopy analysis show good biaxial texture of both layers,sharp interfaces and the absence of cracks. Midpoint critical temperatures,Tc, fall reproducibly in the 87–88 K range with transition widthsΔTc = 1 K. Remarkably high transport critical current densities,Jc, in the2.0–2.5 MA cm−2 range are achieved at 77 K in 1 cm long samples. The above deposition route appears to bepromising for the development of long-length YBCO coated conductors thanks to therelatively low deposition temperature, the high degree of uniformity over large areas andthe simple single buffer layer architecture.

High critical current density of YBCO coated conductors fabricated by inclined substrate deposition

Inclined substrate deposition (ISD) has great potential for rapid production of high-quality template layers for YBCO-coated conductors. We have grown biaxially textured magnesium oxide (MgO) films on metallic substrates by ISD at deposition rates, 20–100 Å/s. Scanning electron microscopy of the ISD MgO films showed columnar grain structures with a roof-tile-shaped surface. X-ray diffraction and pole figure analysis revealed that the c-axis of the ISD MgO is tilted at an angle with respect to the substrate normal. A full width at half maximum (FWHM) of ≈10° was observed in the φ-scan for MgO films. Yttria-stabilized zirconia (YSZ) and ceria (CeO 2) buffer layers were epitaxially grown on ISD MgO by pulsed laser deposition (PLD) prior to YBCO deposition by PLD. The YBCO films grown on YSZ/CeO 2 buffered ISD MgO substrates were biaxially aligned with the YBCO c-axis normal to the substrate surface. A critical current density of J c>1.2×10 6 A/cm 2 was measured at 77 K in self-field.

Approaches to improving critical current density of YBCO superconducting thick films deposited by electrophoresis

Fabrication of YBCO superconducting thick films by electrophoresis has been widely reported. However, the value of critical current density (J c) is far from what the practical application requires. The superconducting thick films are obtained using top-seeded melt growth method with different proportional Y2BaCuO5 (Y211) addition. High-pressure oxygen has been used in the annealing process to improve the uniformity of the oxygen content in the superconducting thick films. When 40mol% Y211 powder is added to the YBa2Cu3O7–5 (Y123) powder,J c for the superconducting thick film by approaches described above reaches 7.008×103 A/cm2 (77 K, 0 T), which is greater than the value ever reported.

Hysteresis of the critical current density in YBCO, HBCCO and BSCCO superconducting polycrystals: a comparative study

The hysteresis of the transport critical current of YBa 2Cu 3O 7− δ (Hg,Re)Ba 2Ca 2Cu 2O 8+ δ and (BiPb) 2Sr 2Ca 2Cu 3O 10+ δ polycrystals was studied. While the first two systems display qualitatively similar hysteretical patterns, the third one behaves differently. The experimental results are interpreted in terms of a phenomenological model which considers the effects of the magnetization in the grains on the intergranular weak links as responsible for the observed hysteresis. The hysteresis of the transport critical current is discussed on the light of the microstructural features of the samples, concluding that the shape and disposition of the grains do not account in a straightforward fashion for the differences in the hysteretical behavior.

Temperature and magnetic field dependence of the critical current density of YBCO with fine grains

Abstract We measured the critical current of thin strips of sintered YBCO deposited by electrophoresis or sedimentation on an Ag substrate. The typical granulometry of deposited samples was about 1 μm. The critical current of the samples was measured as a function of the temperature (from the transition temperature down to LHe) and of the magnetic field. The current density versus temperature and magnetic field behavior shows a number of interesting features. The current increases quadratically on decreasing temperature and the half width of the I versus B curves increases slightly, with a value in agreement with the junction size. We show that these effects can be explained in the framework of BCS theory, by modelling the material as a network of weak links with small dimensions having a normal barrier.

Effects of Ag-doping on critical current densities in high T c superconducting materials of YBa 2Cu 3O 7−x

To enhance the critical current density of YBCO superconductors the attempt to add Ag, Ag 2O, AgNO 3 into the materials has been made. No obvious difference on microstructures, such as grain size, orientations, twins, boundaries, microcracks, were observed between pure and doped YBCO specimens. ALCHEMI was used to locate the impurity atoms inside YBCO unit cells. Most of Ag in YBCO Ag-system doped specimens to be found filling in the sinter pores contributes to strengthening the materials and purifying the YBCO matrices. Some Ag + cations entering YBCO lattices and occupying the Cu 2+ or Cu 3+ sites were detected by ALCHEMI. The Ag + substitution for Cu 2+ or Cu 3+ will deteriorate the superconductivity due to the decrease of oxygen absorption abilities of YBCO crystals. The total effect of Ag-doping depends on the competition of the Ag dopants with two kinds of distributions.