Critical Current Density Of YBa2Cu3O7 Research Articles

Geometric and compositional factors on critical current density in YBa2Cu3O7−δ films containing nanorods

Critical current density (Jc) was investigated in YBa2Cu3O7−δ films containing nanorods prepared with various nanorod materials, with variation of nanorod content, substrate temperature, and oxidization condition. Three types of compositional situation were realized: films containing strain induced oxygen vacancies; fully oxidized films containing cation compositional deviation; and oxygen deficient films. Normalized Jc−B behavior was determined via the matching field, which is a geometric factor, regardless of the compositional details. A Jc−critical temperature (Tc) relation depending on distribution and fraction of compositional deviation (cation compositional deviation and strain induced oxygen vacancies) was found: the Jc values decreased with decreasing Tc due to the effect of Tc on nanorod pinning strength in the fully oxidized films; Jc decreased with decreasing oxygen pressure in the film cooling process after film deposition in spite of Tc remaining almost the same, due to reduction of the effective area for current flow in the oxygen deficient films. Thus, a Jc landscape based on geometric and compositional factors was obtained. The study highlights the importance of the Jc−Tc analysis in the understanding of Jc in YBa2Cu3O7−δ films containing nanorods.

High Critical Current Density of YBa2Cu3O7-x Superconducting Films Prepared through a DUV-assisted Solution Deposition Process.

Although the solution deposition of YBa2Cu3O7−x (YBCO) superconducting films is cost effective and capable of large-scale production, further improvements in their superconductivity are necessary. In this study, a deep UV (DUV) irradiation technique combined with a low-fluorine solution process was developed to prepare YBCO films. An acrylic acidic group as the chelating agent was used in the precursor solution. The acrylic acidic group was highly sensitive to DUV light at 254 nm and significantly absorbed UV light. The coated gel films exposed to DUV light decomposed at 150 °C and copper aggregation was prevented. The UV irradiation promoted the removal of the carbon residue and other by-products in the films, increased the density and enhanced the crystallinity and superconductivity of the YBCO films. Using a solution with F/Ba = 2, YBCO films with thicknesses of 260 nm and enhanced critical current densities of nearly 8 MA/cm2 were produced on the LaAlO3 (LAO) substrates.

Atomic interface sequence, misfit strain relaxation and intrinsic flux-pinning defects in different YBa2Cu3O7−δ heterogeneous systems

To explore the interface effects on enhancing critical current density in YBa2Cu3O7−δ (YBCO) thin films, four heterogeneous systems, of which two have small opposite lattice misfits (i.e., the YBCO/STO (∼1.6%) and the YBCO/LAO (∼−1.6%)), and the other two have relatively large opposite mismatch (i.e., the YBCO/MgO (∼8.9%) and the YBCO/YSZ (∼−5.9%)), were selected and synthesized by pulsed-laser deposition. A detailed microstructure analysis including XRD, TEM and the state-of-the-art Cs-corrected STEM imaging, and a thorough superconducting property characterization including critical transition temperature (Tc) and critical current density ( and (H ‖ c) at various temperatures), were conducted for all four heterogeneous systems. The results reveal that the YBCO intrinsic defects, driven by the interface mismatch of different strain states, present a diverse nature in their distribution and density, and thus different flux-pinning performances under various measurement conditions. This study provides an in-depth insight into the microstructure–property correlation in a strongly correlated electronic system, the YBCO heterogeneous structures.

Enhanced critical current density in YBa2Cu3O7−δ thin film deposited on La0.67Sr0.33MnO3 decorated SrTiO3 substrates

Thin films of YBa2Cu3O7−δ (YBCO) have been deposited on undecorated and La0.67Sr0.33MnO3 (LSMO) nanoparticles decorated single crystal SrTiO3 (STO) substrate using laser ablation technique and their flux pinning characteristics have been compared using temperature dependent magnetization studies. Significant improvement in the critical current density of YBCO thin film has been observed even at higher applied magnetic field (∼7T). The improved flux pinning properties of YBCO thin films deposited on LSMO decorated STO substrate has been attributed to the presence of ferromagnetic LSMO nanoparticles at the substrate/film interface which seem to be acting as artificially generated magnetic pinning centres leading to improved flux pinning properties.

Eliminating thickness dependence of critical current density in YBa2Cu3O7−x films with aligned BaZrO3 nanorods

The thickness dependence of critical current density (Jc) has been investigated in YBa2Cu3O7−x films with BaZrO3 (BZO) nanorods (YBCO/BZO) aligned along the film normal. With the presence of linear defects in the YBCO/BZO films, the thickness dependence of Jc becomes negligible at self field and weak applied magnetic field (H), suggesting these linear defects playing a key role to the elimination of the thickness dependence of Jc. The effect of temperature (T) and H on Jc thickness dependence have been investigated and comparisons have been made between YBCO and YBCO/BZO samples. Since BZO nanorods alignment is greatly influenced by growth temperature, the quantitative difference in terms of nanorod’s density and average length is reflected on Jc angular dependence of H and Jc thickness dependence as thermally assisted flux motion (TAFM) becomes important above a threshold H determined by the BZO nanorod density. With further increasing H, a monotonically increasing Jc vs. thickness trend was observed in YBCO/BZO films, in contrast to an opposite trend when collective pinning is dominant. This result suggests the thickness dependence of Jc is dictated by the microstructure and hence pinning mechanism in YBCO films.

Improved Critical Current Densities in YBa2Cu3O7−δ Multilayer Films Interspaced with Palladium Nano-dots

Power applications of superconducting coated conductors in high magnetic fields require thick films with high critical current density Jc and strong artificial pinning centers. Here, we report on the artificial pinning centers induced in YBCO quasi-multilayer films interspaced with palladium (Pd) nano-dots. Quasi-multilayered (QM) YBa2Cu3O7−δ (YBCO) films composed of YBCO layers interspaced with quasi-layers of palladium nano-dots were grown by pulsed laser deposition on SrTiO3(100) substrates. DC magnetization and frequency-dependent measurements showed high Jc comparable with best YBCO films in thin quasi-multilayers and significant improvement of Jc in thick quasi-multilayers. TEM study shows regions of planar defects, stacking faults, and pore formations suitable for immobilizing vortices. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films.

Enhancement of Critical Current Density in YBa2Cu3O7−y HTS Through Boron Addition

The effect of B2O3 addition on the superconducting transition and grain boundary critical current density of the boron free (control) and boron doped HTS ceramics with nominal composition YBa2Cu3BxO7−y (x=0, 0.025, 0.05, 0.075, 0.1 and 0.15) has been investigated. For the lowest-level boron doping (x=0.025) an increase by nearly 1.5 times was observed in the critical current density Jc compared to the control sample. The small additives of boron in YBa2Cu3BxO7−y (x=0.025 and 0.05) do not essentially affect the critical temperature Tc=92.5 K of nominally pure Y123. Higher-level boron added compounds revealed a decrease in both Tc and Jc values. The data obtained indicate the possibility of boron dopant being inserted either into interstitial or into substitutional sites of the lattice.

The effect of strain on grains and grain boundaries inYBa2Cu3O7−δ coated conductors**Work partially supported by NIST, a US government agency, not subject to US copyright.Certain commercial materials are referred to in this paper to foster understanding.Such identification does not imply recommendation or endorsement by NIST, nordoes it imply that the materials identified are necessary the best available for thepurpose.

The role of grains and grain boundaries in producing reversiblestrain effects on the transport current critical current density (Jc) ofYBa2Cu3O7−δ (YBCO)coated conductors that are produced with metal–organic deposition (MOD) was investigated. The strain (ε) dependenceof Jc for full-width coated conductors is compared with that for samples in which the currenttransport was limited to a few or single grain boundaries by cutting narrow tracks with alaser or focused ion beam, as well as with thin films deposited on bicrystallineSrTiO3 substrates by use of pulsed-laser deposition (PLD). Our results show that the dependences ofJc onε for the grains and for the grain boundaries from the two kinds of YBCO samples can beexpressed by the same function, however with a greater effective tensile strain at thegrain boundaries than in the grains. The really striking result is that the grainboundary strain is 5–10 times higher for grain boundaries of in situ PLD grownbicrystals as compared to the aperiodic, meandered, nonplanar grain boundaries thatdevelop in ex situ grown MOD-YBCO in the coated conductor of this study.

The role of interfacial defects in enhancing the critical current density ofYBa2Cu3O7−δ coatings

The critical current density (Jc) of very thin YBa2Cu3O7−δ (YBCO) filmscan approach 10 MA cm−2 at 77 K inself-field, but for such films Jc drops sharply as the film thickness is increased. We have shown previouslythat this strong thickness dependence results from an enhancement ofJc near the film–substrate interface. In the present paper we investigateinterfacial enhancement using laser-deposited YBCO films onNdGaO3 substrates, and find that we can adjust deposition conditions to switch the enhancement onand off. We find that the ‘on’ state is accompanied by a dense array of interfacial misfitdislocations, while we do not observe dislocations in films prepared in the ‘off’state. This result appears to be but one of many examples in which interfacialproperties of electronic film materials are profoundly affected by stress-induced defectsat the film–substrate interface; however, to our knowledge the present work isthe only case in which electronic properties are shown to be enhanced by suchdefects.

Thickness dependence of critical current density inYBa2Cu3O7−δ filmswith BaZrO3 and Y2O3 addition

We report the thickness dependence of critical current density (Jc) inYBa2Cu3O7−δ (YBCO) films with5 mol% BaZrO3 (BZO) and5 mol% Y2O3 additionsgrown on single crystal SrTiO3 substrates by pulsed laser deposition (PLD). The results show that addingBZO+Y2O3 has reduced the thickness dependence of the self-field critical current density (Jcsf), compared to that observed in optimized YBCO films, with a significant enhancement ofJcsf in the thickfilm region (>2 µm). The so-called ‘dead layer’ did not appear until the film thickness was greater than 6.4 µm. We attribute this improvement to the additional pinning centers introduced in the bulkby the addition and a decrease in microstructure degradation with thickness. As a result,Jcsf remains as highas 2.3 MA cm−2 in a 6.4 µm thick film. Thecombination of this high Jcsf value and the enhancement of the in-fieldJc induced by the additions, which was observed in the wholethickness range, leads to a critical current per centimeter width (Ic−w) in excess of400 A cm−1 at 1 T and75.5 K and 530 A cm−1 at 3 T and 65 K under all field directions.

Flux pinning in YBa2Cu3O7−δ thin film samples linked to stacking fault density

In this paper, we report a strong correlation between the stacking fault (SF) density and the critical current density of YBa2Cu3O7−δ (YBCO) thin films in applied field (Jcin-field). We found that the Jcin-field (H∥c) increases as a clear linear dependence of the density of SF identified in the as-grown samples deposited on both SrTiO3 (STO) and LaAlO3 substrates. Detailed microstructural studies including cross-section transmission electron microscopy (TEM) and high resolution TEM were conducted for all the films deposited on STO substrates. This work suggests that the YBCO SF density plays an important role in the YBCO in-field transport performance.

Performance enhancement in high-T c ceramics through melting by Joule heating, infrared lamps, and laser radiation

We have analyzed experimental data on the effect of short-term melting followed by recrystallization on the microstructure and critical current density of YBa2Cu3O7 − x , Bi2Sr2CaCu2O8 − x , and Bi2Sr2Ca2Cu3O10 − x high-T c ceramics. The ceramics were melted using different heat sources: infrared lamps, laser radiation, and electric current. A significant increase in the critical current density of Bi2Sr2Ca2Cu3O10 − x ceramics (by a factor of 40 at 20 K and by a factor of 8 at 77 K) was achieved using cw CO2 laser irradiation. Melting TiC-doped (0.1%) Bi2Sr2Ca2Cu3O10 − x ceramics with a CO2 laser, followed by annealing, insured an even larger increase in critical current density: by a factor of 35 at 77 K. We have calculated the thickness of the molten layer produced by laser heating of high-T c ceramics.

Combined effect of a single grain boundary and artificial pinning centers on the critical current density in a YBa2Cu3O7−δ thin film

The combined effect of a single grain boundary and artificial pinning centers (APCs) on the critical current density (Jc) in YBa2Cu3O7−δ thin films was investigated. The authors decorated the surface of a 5°-tilt bicrystal SrTiO3 substrate with Y2O3 nanoislands to introduce APCs into the film. Jc of the bicrystal YBa2Cu3O7−δ film with APCs was measured in various magnetic fields. The APCs improved Jc in high magnetic fields, but not in low magnetic fields due to the existence of the grain boundary. The limiting mechanism of Jc in the bicrystal film containing APCs is discussed based on the experimental results.

Minute doping with deleterious rare earths in YBa2Cu3O7−δ films for flux pinning enhancements

To enhance the critical current density of YBa2Cu3O7−δ films, flux pinning centers are intentionally added to inhibit flux flow in applied magnetic fields. Here we provide an initial demonstration that the incorporation of very minor additions (⩽1% of Y as opposed to the 10%–40% in standard substitutions) of typically deleterious rare earths into high quality YBa2Cu3O7−δ thin films provides significant improvement of the film’s in-field current density. This is accomplished without reoptimization of the deposition parameters. Instead of site substitution for Y as might be expected, the deleterious rare earths potentially result in the formation of nanoparticulates.

High critical current densities in YBa2Cu3O7−x films grown at high rates by hybrid liquid phase epitaxy

Liquid-mediated growth of YBa2Cu3O7−x has the potential to be high rate and low cost. However, the reported critical current densities (Jc) are generally lower than for films deposited by physical vapor deposition processes. We report the deposition of thick high-Jc films (1.2MAcm−2 in self-field) on (001) SrTiO3 by high-rate hybrid liquid phase epitaxy, and show angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy.

The identification of grain boundary networks of distinct critical current density inYBa2Cu3O7−x coated conductors

Evidence for the existence of grain boundary (GB) networkswith different critical current densities has been obtained inYBa2Cu3O7−x coated conductor tapes, through distinct magnetic responses in AC susceptibilitymeasurements. Percolating currents through GB networks of different quality may bedistinguished by the appearance of modified dissipation contributions in the imaginarycomponent of the AC susceptibility. The application of the Bean critical-state model to theAC susceptibility response of finite size samples has allowed us to properly quantify thesecritical current densities. AC susceptibility appears as a unique direct measurement of thetemperature-dependent intergrain critical current densities with additional informationabout the current networks, which cannot be reached by transport measurements.

Enhancement of critical current density in YBa2Cu3O7−δ thin films grown using PLD on YSZ (001) surface modified with Ag nano-dots

Y123 thin films were grown by pulsed laser deposition (PLD) on YSZ (001) substrate. Prior to the film deposition, a discontinuous layer of Ag was deposited on the substrate, also using PLD, in the form of separate islands. Atomic force microscopy (AFM) investigation of the Ag layer showed that its morphology consisted of self-assembled islands of nanometre size, randomly distributed on the surface of the substrate, called nano-dots. The Y123 superconducting films grown on such a surface were characterized using AFM, x-ray diffraction, secondary electron microscopy, ac susceptibility and dc magnetization. The results show that there is no significant difference in surface morphology, crystallographic orientation, phase composition or superconducting transition temperature between the Y123 films grown on YSZ (001) with an Ag nano-dots layer and a control Y123 film grown on a virgin YSZ (001) surface. On the other hand, at 77 K, the magnetic critical current density () was three times higher for the Y123 film grown on YSZ with the modified (001) surface than for the film grown on YSZ with a virgin (001) surface. At 5 K the enhancement of was approximately seven times, at both low and high fields. This suggests an increase in pinning, caused presumably by point defects formed in the Y123 film above the Ag islands.

Critical current density of YBa2Cu3O7−δ low-angle grain boundaries in self-field

A study has been perfomed on the superconducting critical current density Jc flowing across low-angle grain boundaries in epitaxial thin films of YBa2Cu3O7−δ. The materials studied were dual grain boundary rings deposited on SrTiO3 and containing 2°, 3°, 5°, and 7° tilt boundaries. The current density in self-field was determined by magnetometric methods at temperatures from 5 K to Tc. We conclude that at the higher temperatures of coated conductor applications, there is limited potential for improving Jc by reducing the grain boundary angle below ∼3°.

Screening technique measurement of ac imaginary susceptibility and critical current density of YBa2Cu3O7−δ films

The screening technique was used to study systematically the ac susceptibility of superconducting YBa2Cu3O7−δ thin films in the temperature range of 32–83 K. We used the Fourier transform of the pick-up signal, coming from the secondary coil, to estimate the critical current density. From the experimental data we observed regularities in the imaginary part of ac susceptibility, and confirmed that the flux creep mechanism is dominant.

Critical current density of thin YBCO films on buffered sapphire substrates

The critical current density of YBa2Cu3O7- films dc magnetron sputtered onto buffered (CeO2) sapphire substrates is measured. The peculiarities of these dependences are interpreted by taking into account the crystal defect (edge dislocations) film structure which in turn is determined by the film growth mode.