Maximum Critical Current Density Research Articles

Enhanced performance of GdBCO bulk superconductors by doping a new kind of YGdBa4CuNbO y nanoparticles

In this work, a new kind of YGdBa4CuNbO y (YGdNb-11411) nano-particles was designed and sintered using a solid-state reaction method, whereas their impact on the performance of GdBCO bulks was investigated for the first time. From the acquired x-ray diffraction data and scanning electron microscopy imaging results, it was proved that the YGdNb-11411 particles were of excellent chemical stability and did not react with other phases during the crystal growth process. The YGdNb-11411 particles ranged from 80 to 130 nm and they were uniformly distributed in the well-textured GdBCO bulk superconductors. The maximum critical current density (J c-max) of the samples was enhanced from 3.48 × 104 A cm−2 to 8.63 × 104 A cm−2 (77 K) in the self-field as the doping amount increased from 0 wt% to 7 wt%. In addition, the GdBCO sample with YGdNb-11411 particles also showed an enhanced flux pinning force density and relatively high J c around the magnetic flux density range of 1 T–2 T (77 K). These results clearly indicated that the YGdNb-11411 particles could effectively enhance the properties of the GdBCO bulk superconductors.

Interfacial reactions and critical current density of Cu-sheathed Cu-doped MgB2 wire with Ti diffusion barrier

Development of reaction zones at the core Mg(Cu) – boron (B) and barrier (Ti) – sheath (Cu) interfaces of an internal magnesium diffusion (IMD) manufactured MgB2 composite wire has been studied at varying temperatures of 560–665 °C for 30 min and varying time periods of 30–180 min at 560 °C. MgB2 has predominantly formed at the Mg(Cu) – B interface with little solubility of Cu of 1–3 at%. A second phase enriched with Cu, Mg2Cu, has also formed at random locations within the MgB2 phase matrix, indicating the advantage of doping Cu in the Mg rod. However, a layer of another B-rich phase, MgB4, has also formed at a higher temperature of 665 °C with negligible solubility of Cu at the MgB2 – B interface. At the Ti – Cu interface, the formation of CuTi2, CuTi, Cu4Ti and Cu4Ti3 intermetallic phases took place. However, the Cu4Ti and Cu4Ti3 phases develop after annealing the wire at a relatively higher temperature of 620 °C and at 560 °C with progress in annealing time. Critical current density (Jc) decreases with annealing time; however, the sensitivity of Jc towards annealing time is low. Critical current density is found to be strongly dependent on the annealing temperature of the composite wires for the formation of the MgB2 superconductor phase. A maximum critical current density of ∼ 2.5 × 104 A/cm2 at 5 T and 4.2 K is attained for the Cu-doped MgB2 composite wire when annealed at 665 °C for 30 min. A maximum shift of only 0.5 K is measured for MgB2 when formed at the highest annealed temperature compared to the lowest one in this study.

Critical Current Density in d-Wave Hubbard Superconductors.

In this work, the Generalized Hubbard Model on a square lattice is applied to evaluate the electrical current density of high critical temperature d-wave superconductors with a set of Hamiltonian parameters allowing them to reach critical temperatures close to 100 K. The appropriate set of Hamiltonian parameters permits us to apply our model to real materials, finding a good quantitative fit with important macroscopic superconducting properties such as the critical superconducting temperature (Tc) and the critical current density (Jc). We propose that much as in a dispersive medium, in which the velocity of electrons can be estimated by the gradient of the dispersion relation ∇ε(k), the electron velocity is proportional to ∇E(k) in the superconducting state (where E(k)=(ε(k)-μ)2+Δ2(k) is the dispersion relation of the quasiparticles, and k is the electron wave vector). This considers the change of ε(k) with respect to the chemical potential (μ) and the formation of pairs that gives rise to an excitation energy gap Δ(k) in the electron density of states across the Fermi level. When ε(k)=μ at the Fermi surface (FS), only the term for the energy gap remains, whose magnitude reflects the strength of the pairing interaction. Under these conditions, we have found that the d-wave symmetry of the pairing interaction leads to a maximum critical current density in the vicinity of the antinodal k-space direction (π,0) of approximately 1.407236×108 A/cm2, with a much greater current density along the nodal direction (π2,π2) of 2.214702×109 A/cm2. These results allow for the establishment of a maximum limit for the critical current density that could be attained by a d-wave superconductor.

Improving critical current density of Nb3Sn by optimizing pinning potential of grain boundary and grain size

Nb3Sn superconductor is of significant interest for applications in constructing high-field magnets beyond the limit of NbTi. However, its critical current density decreases rapidly at high magnetic fields (12 T) and the state-of-the-art level of Nb3Sn superconductors still cannot meet the requirements of the planned future accelerator magnets. The primary flux pinning centers for Nb3Sn wire mainly arise from the grain boundaries (GBs). In the present paper, we theoretically investigate, through time-dependent Ginzburg-Landau theory and with graphics-processing unit parallel technique, the vortex pinning and the critical current density in large-scale polycrystalline Nb3Sn superconductor by varying the pinning potential of GB and grain size at various magnetic fields. Unlike the conventional dot-like pinning systems, it is found that the critical current is not a monotonous function by suppressing the superconductivity of the GBs. The optimal pinning potential of GB for maximum critical current density strongly depends on magnetic fields. Furthermore, we find that the critical current density can be significantly enhanced by reducing grain size at low magnetic fields, while increase of critical current density cannot always be observed at high magnetic fields. Actually, critical current density even decreases by reducing grain size, which depends on the superconductivity of GBs. The findings in the paper provide theoretical foundations to achieve further improvement of Nb3Sn with optimizing the flux pinning.

Growth and Characterizations of Iron-based Superconductor (Ba1-x Rb x ) Fe2As2 Single Crystals

Novel nematic states as well as remarkable superconducting properties were reported in iron-based superconductors. We synthesized high-quality single crystals of (Ba1-x Rb x )Fe2As2 close to the optimal composition of x ≈ 0.4, and have characterized normal state and superconducting properties for pristine and proton irradiated samples. The highest Tc was found to be ∼36.6 K for pristine samples. A maximum critical current density of 12 MA/cm2 was achieved in a proton irradiated sample, which is comparable to that in irradiated (Ba0.6K0.4) Fe2As2. Twin boundaries were observed optically in both non-doped and under-doped samples. We also attempted local magnetic field measurements induced by transport current in a sample with twin boundaries for future exploration of nematic states in different regions of doping.

Relationship between anion height and superconducting properties for Fe1+x Te0.6 Se0.4 bulk single crystals

We have synthesized Fe1+xTe0.6Se0.4 large bulk single crystals by the melting method with a homogenization heat treatment. The relationship between the crystal structures and the superconducting properties was investigated. Critical temperature Tc onset reached the highest value of 14 K for the crystal with x = - 0.005. The maximum critical current densities Jc in the a-b plane at 4.2 K achieved 1.53 and 0.83×105 A/cm2 at 0 T and 5 T for the crystal with x = 0, respectively. The crystal lattice and structural parameters were refined by Rietveld analysis. The anion height was estimated by using the obtained parameters. The anion height dependence of Tc and Jc were investigated. The Tc decreased as the anion height increased, and it showed the same tendency as other Fe-based superconductors. On the other hand Jc increased initially and then decreased with the increase in the anion height. We believe that it comes from the trade-off between the increase in flux pinning centres of excess Fe sites and the deterioration of superconductivity.

Partially-oriented MgB2 superconducting bulks with addition of B4C and cubic BN obtained by slip casting under high magnetic field and spark plasma sintering

Partially-oriented MgB2 bulk discs (13 and 9 %) with the starting compositions of (MgB2)0.99(B4C)0.01 and (MgB2)0.99(c-BN)0.01 were fabricated by slip casting under an H0 = 12 T magnetic field (perpendicular to the disc surface) and subsequent spark plasma sintering. The maximum critical current density and irreversibility field are for H//H0 (H=applied field). These values are higher or similar to the randomly-oriented samples with the same composition. The maximum volume pinning force (Fp) is lower in the partially-oriented ones than in the randomly-oriented samples. The pinning-force-related parameters depend on the additive and orientation. Assessment of the major pinning mechanism within the scaling and percolation models considering these parameters shows significant limitations. A method to scale Fp is proposed; for the randomly and partially-oriented samples (that show an extra peak in Fp), the single and double Gaussian functions fit well. The results suggest an anisotropic influence of carbon substituting for boron in the MgB2.

Magnetic levitation force performance of benzil added bulk MgTi0,06B2 superconductors

MgB2 superconductors can be proposed as a good candidate for Maglev systems due to their superior structural and superconducting properties. Besides, magnetic levitation and guidance force properties of these superconductors should be increased for commercial applications of Maglev systems. Therefore, the critical current density and magnetic levitation and guidance force properties of MgTi0.06B2 superconducting samples were investigated in this study, at measurement temperatures of 20 K and 25 K, depending on benzil (C14H10O2) addition in different adding amounts of 0, 1.5, 3, 4.5, 6 and 9 wt%. In addition to benzil, nanometer-sized silver particles were added to the samples in a constant ratio of 2 wt% to enhance the structural properties. The maximum critical current density values increased from 67 kA/cm2 for pure sample to 92 kA/cm2 with benzil adding amount of 3 wt% at T = 20 K, indicating an increment of 37%. In addition, the levitation force in ZFC (zero field cooling) regime and the guidance force in FC (field cooling) regime at 20 K increased at an amount of 46% and 57%, respectively, with 3% benzil addition. It can be said that the suitable amount of benzil addition as a carbon source produces additional pinning centres inside the MgTi0.06B2 and thus structural properties, critical current density and therefore, magnetic levitation properties of the samples are increased.

Experimental Study on Quasi-Isotropic Critical Current of an HTS Conductor With High Engineering Current Density

It is well known that the critical current of the second generation (2G) high temperature superconducting (HTS) wire strongly depends on magnetic field and its orientation. An HTS conductor with high engineering current density considering the effect of quasi-anisotropy of critical current has been proposed, and its configuration is a combination of a quasi-isotropic strand (Q-IS) on which winding HTS wires similar with winding method of cable layer. In this paper, the dependence of the critical current density of inner Q-IS on twisting pitch of Q-IS and winding pitch of cable layer was analyzed by both of simulation and experiment. Experimental results are good agreement with the simulation ones, and show that the critical current density of Q-IS increases as decreasing winding pitch of cable layer and twisting pitch of Q-IS. The achieved maximum critical current density is about 7%more than the one of Q-IS in self-field. It is predicted that the critical current density of inner Q-IS will increase further if the 2G HTS wire is narrower or the current in outer cable layer bigger. The variation of n-value of inner Q-IS with winding pitch of cable layer and twisting pitch of Q-IS is also measured, and the trend of n-value is similar to the trend of critical current density.

Changes of Superconducting Properties Due to the Unidirectional Tensile Deformation on Bronze-Processed Nb3Sn Multifilamentary Wires Using Various Cu–Sn–Zn Ternary Alloy Matrices

The degradation of transport current property by the mechanical strain on the practical Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire is a serious problem for the future fusion magnet operated under higher electromagnetic force. Recently, we developed various Zinc (Zn) solid solution ternary Cu-Sn alloy (Cu-Sn-Zn) matrices for the internal strengthened matrix and Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn multifilamentary precursor wires using various Cu-Sn-Zn matrices through the conventional bronze process. After the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn synthesis heat treatment, the additional Zn remained in the matrix and it may act as a solid solution strength factor of the matrix. We carried out the unidirectional tensile test under 4.2 K and 15 T on the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires using various Cu-Sn-Zn matrices in order to investigate the remaining Zn effect on the mechanical property. The peak tensile stress in the maximum critical current density on the 10 mass%Zn additional sample was obtained to approximately 200 MPa and it became remarkably higher compared with conventional bronze processed Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire. This tensile stress was similar to the CuNb and ODS-Cu reinforced Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires. The internal strengthened matrix due to the solid solution was one of the most effective methods for improving mechanical property of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire.

Water-vapor assisted photochemical fabrication of YBa2Cu3O7-x superconducting films with high critical current density

A novel water-vapor assisted photochemical solution deposition method was put forward to fabricate high-performance YBa2Cu3O7-x (YBCO) superconducting films. The dip-coated gel films derived from YBCO solution with Y:Ba:Cu:F = 1:2:3:4 were exposed to deep UV light at a low temperature of 150 °C. During the UV exposure, water-vapor was artificially introduced to produce hydroxyl radicals (*OH) with strong oxidizing ability. After that, photon-activated amorphous oxide precursor films were obtained. It was found that the high-energy photons and *OH species promoted the cleavage of organic groups, enhanced the removal of residual organics, and improved the density of the YBCO films. Thus, YBCO superconducting films with improved superconducting properties were obtained after the crystallization process. The YBCO superconducting film that was UV-irradiated for 100 min with water vapor had a maximum critical current density (Jc) of 8.69 MA/cm2 (77 K and 0 T).

The influence of re-pelletization and heat treatment on physical, superconducting, magnetic and micro-mechanical properties of bulk BSCCO samples prepared by ammonium nitrate precipitation method

Abstract The influence of re-pelletization and annealing time on the structural, magnetic, electrical and mechanical properties of Bi-based high temperature bulk superconductor have been investigated. All samples used in this study have been prepared by a wet technique denoted as ammonium nitrate precipitation method. The samples have been characterized by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), resistance vs. temperature ( R-T ), magnetic hysteresis ( M-H ) and hardness vs. applied load ( Hv-F ) measurements. Bi-2223 and Bi-2212 peaks as major phases have been observed with small amounts of impurities from XRD results. The microstructures of most samples show a plate-like granular form. The grain sizes have been investigated by SEM and XRD. The critical transition temperature ( Tc ) has been obtained from resistivity measurements in the range of 99–110 K, depending on the annealing time and re-pelletization. The calculated maximum critical current density (Jc), using Beans’ model, is around 12,000 A/cm2 at 10 K ∼ 0.2 T. Moreover, all prepared samples exhibit reverse indentation size effect (RISE) behavior and hardness increased with re-pelletization according to results obtained from mechanical measurements.

Numerical Stress Analysis During Cooldown and Compressive Loading in an Imperfect Nb3Sn Wire

High field superconductors are critical to the success of next step magnetic fusion confinement devices such as ITER and DEMO. The low-temperature superconducting material that is currently favored for these applications, Nb3Sn, is susceptible to performance due to its brittleness and high strain-sensitivity. Under extreme loads, an irreversible degradation in the maximum critical current density has been shown to occur and believed to be strongly influenced by two factors: plasticity and cracked filaments. Cracks in filaments are induced when sufficiently high stress concentrations occur in the wire. In this paper, we explore using finite element analysis the impact that voids have on the stress distributions and peak stresses under two loading conditions: transverse compressive loading in a 2D model, and a full cool down phase in a 3D model.

Effect of Y2BaCuO5 Nanoparticle Doping on Critical Current Density of YBa2Cu3 O 7-δ Bulk Superconductor

This study presents the effect of Y2BaCuO5 (Y211) nanoparticle doping on critical current density and critical temperature of YBa2Cu3 O 7-δ (YBCO) superconductor. Y211 nanoparticles with different particle sizes ranging from 34 to 455 nm were synthesized by a sol-gel method, then doped into the YBCO superconductor by 0.5, 1, and 2 wt.%. Samples were characterized using X-ray diffraction and scanning electron microscope measurements. The standard four-probe technique was used to measure the critical current density at 77 K. The results showed that in the all-doped samples, critical current density was higher than that of the pure sample. It was found that in the samples containing 1 and 2 wt.% of Y211 nanoparticles, by increasing the size of nanoparticles, the J c was increased, but in samples containing 0.5 wt.%, the J c decreased. The maximum critical current density of 64 A/cm 2 was obtained for the samples doped with 2 wt.% of 455 nm Y211 nanoparticles. Also, it was observed that the critical temperature slightly decreased with nanoparticle doping.

Influence of Cu Content in Precursor Powders on the Phase Evolution and Superconducting Properties of Bi-2212 Superconductors

Precursor powders of Bi 2.1 Sr 1.96 CaCu x O 8+δ (Bi-2212) high temperature superconductors with different nominal Cu ratios of x =2.0, 2.1, 2.2, 2.4 were fabricated by a modified co-precipitation process. The influences of Cu ratios on the phase evolution process during sintering were investigated. Bi-2212 thick films and single filament tapes were fabricated with dip-coating process and powder in tube process, respectively. Obvious influences of Cu ratios on the phase compositions, microstructures and superconducting properties were discussed. Results show that the initial Cu ratio can affect the thermodynamic properties of Bi-2212 phase, thus changing phase evolution process. With the increase of Cu ratio, the phase content of Bi-2201 decreases, while the content of AEC phase increases. The maximum critical current density is obtained in the x =2.2 film and tape simultaneously due to the proper phase composition and better texture structures.

Preparation of Gd2Zr2O7 buffer layers for coated conductor by polymer-assisted chemical solution deposition

Gd2Zr2O7 (GZO) buffer layers with a thickness of about 300nm have been directly deposited on bi-axially textured Ni-5at%W (NiW) alloy substrate and the Y2O3 buffered NiW substrate by a newly developed polymer-assisted chemical solution deposition (PA-CSD) method. The solution prepared from metal nitrate precursor has been achieved by a simple, low cost, and effective method. The Y2O3 thin film was deposited as the seed layer by dc reactive sputtering technique. The films have been studied with X-ray diffraction (XRD) and AFM analyses. It is found that only GZO buffer layer on Y2O3/NiW can be grown with highly c-axis oriented. Highly epitaxial 500-nm-thick YBa2Cu3O7−x (YBCO) thin film, deposited on GZO/Y2O3/NiW, reaches a maximum self-field critical current density (Jc) of 1.5 MA/cm2 at 77K the possible reasons are discussed in detail.

A Study of Calcination Conditions for Synthesizing Fine Particles of (Nd0.33Eu0.33Gd0.33)Ba2Cu3O y and (Nd0.33Eu0.33Gd0.33)2BaCuO5

The calcination temperature was studied for optimum processing conditions for preparing (Nd0.33Eu0.33Gd0.33) Ba2Cu3Oy (NEG-123) and (Nd0.33Eu0.33Gd0.33)2BaCuO5 (NEG-211) powders with good quality and fine size. This study used commercially available raw powders of Nd2O3, Eu2O3, Gd2O3, BaO2, and CuO in a purity of 99.9 % with 3–5- μm particle size. These raw powders were carefully weighed to have the compositions of NEG-123 and NEG-211 and pressed into pellets 25 g in weight. The samples were placed in a box furnace under ambient atmosphere and heated to temperatures of 820, 840, 860, and 880 ∘C at a rate of 100 ∘C/h, held there for 24 h, followed by cooling at 100 ∘C/h. X-ray diffraction analyses showed that almost all the samples are single phase except NEG-123 processed at 820 ∘C. The average particle size of NEG-123 powders increased with increasing processing temperatures, while that of NEG-211 remained in the same range below 5 μm irrespective of the treatment temperature. Since the particle size of NEG-123 powders was around 10 mm, one need to refine the particle size below 5 μm with a technique like mechanical grinding for the production of high Jc NEG-Ba-Cu-O bulk super conductors. NEG-211 powders will be suitable for such a use in the present form. The homemade powders were used to fabricate NEG-Ba-Cu-O bulk by cold top seeding melt growth with MgO seed following by oxygen annealing treatment. The characterization of bulk demonstrated critical temperature at 65 K with maximum critical current density of 70,000 kA/cm 2 at 10 K with H//c-axis.

Asymmetry in the effect of magnetic field on photon detection and dark counts in bended nanostrips

Current crowding in the bends of superconducting nano-structures not only restricts measurable critical current in such structures but also redistributes local probabilities for dark and light counts to appear. Using structures from strips in the form of a square spiral which contain bends with the very same curvature with respect to the directions of bias current and external magnetic field, we have shown that dark counts as well as light counts at small photon energies originate from areas around the bends. The minimum in the rate of dark counts reproduces the asymmetry of the maximum critical current density as function of the magnetic field. Contrary, the minimum in the rate of light counts demonstrate opposite asymmetry. The rate of light counts become symmetric at large currents and fields. Comparing locally computed absorption probabilities for photons and the simulated threshold detection current we found the approximate locations of areas near bends which deliver asymmetric light counts. Any asymmetry is absent in Archimedean spiral structures without bends.

The influence of critical current density of Bi-2212 superconductors by defects after Yb-doping

Bi2Sr2Ca1−xYbxCu2O8+δ (Bi-2212) single crystals with x = 0.000, 0.005, 0.010 and 0.020 have been prepared by self-flux method. The influences of Yb doping on the formation of the dislocations in the lattice structures, as well as the related current carrying capability are investigated. Due to the SQUID measurement and the Bean model calculation, the maximum critical current density (Jc) is obtained when the Yb doping content is x = 0.010, though the Tc and the carrier concentration are not in the optimal region. Based on the HRTEM analyses of the Ca–O and Cu–O2 layers, the optimal dislocation density in the Cu–O2 layers is deduced according to the number of the dislocations per unit area. Besides, the sizes of the dislocations also prove the effectiveness of Yb substitution on the enhancement of the current carrying capability in Bi-2212 single crystals.

Effect of Secondary Annealing Process on Critical Current Density in Highly Textured Bi-2212 Superconducting System

Bi-2212 samples prepared by a solid-state reaction technique have been grown from the melt using the laser floating zone method. After annealing the as-grown bars, the samples showed a good grain alignment and a high transport critical current density. Secondary annealing processes were performed on the annealed samples with the aim of producing Bi-2212 phase controlled decomposition. Hence, the Bi-2201 phase and the secondary phases, which act as effective pinning centers, were obtained with the secondary annealing process. After these thermal treatments, the transport critical current densities of samples significantly increased, when compared to the annealed ones. The maximum critical current density was achieved when the samples were subjected to secondary annealing at 680°C for 168 h with an improvement of ~80%, compared to the annealed ones. Moreover, it was found that magnetization of the secondarily annealed samples was also increased. The magnetic critical current densities in these secondary annealed samples were about 3 times higher than the values obtained for the annealed ones. These results clearly indicate that the secondary annealing processes lead to the formation of effective pinning centers in the bulk material.