Transport Critical Current Density Research Articles

Effect of metallic particle addition to the filling powders on the superconducting properties of ex situ processed MgB2 tapes using milled powders

Various metallic particles A were added to the filling powder in ex situ processed MgB2 tapes. The superconducting properties such as critical temperature (Tc) and transport critical current density (Jc) of those sintered tapes depend on the additives. Some additives such as Te can enhance the Jc property, whereas the others such as Mo, Nb and W can cause a Jc deterioration. The Jc enhancement is due to the improved grain connectivity and the enhancement in both upper critical field (Hc2) and irreversibility field (Hirr), whereas the origin of the Jc deterioration is the Tc reduction which is probably brought about by the reaction of the additives with MgB2. The detrimental additives possibly substitute the Mg site, Mg1−yAyB2. In contrast, the other additives which do not cause significant Jc deterioration neither form borides, ApBq, nor cause substitution reaction influencing the superconducting properties. Thus, neither reduction of superconducting phase MgB2 in the core layer nor Tc reduction occurs. Te addition reduces the optimal sintering temperature (Tsin) at which best performance in transport Jc at 4.2 K and 10 T is obtained by only 30 °C, from 710 °C to 680 °C. This Tsin reduction is much smaller than that for Sn addition, about 100 °C. Nevertheless, when sintered at temperatures of 530–560 °C, the Jc values of the tapes with Te addition are around 150 A/mm2, which is comparable to those with Sn addition and twice as large as those of the tapes without addition. Thus, Te is effective for improving the Jc property over a wide range of Tsin among various additives.

The Successful Incorporation of Nd Into Ba Site of Y0.9Ho0.1Ba2-yNdyCu3O7-δ Bulk Superconductors

Abstract: This inclusive study reports the effect of the Nd atoms on the mechanical, microstructural, electrical and superconducting characteristics of Y0.9Ho0.1Ba2-yNdyCu3O7-δ superconductors with the aid of standard characterization methods, including X-ray diffraction, scanning electron microscopy, the bulk density, dc resistivity, and transport critical current density. The experimental results such as the degree of granularity, hole localization effect, room temperature resistivity, critical transition temperature, degree of the broadening, thermodynamic fluctuations, crystallinity, crystal plane alignments, crystal structure, grain size, phase purity and lattice parameters, the appearance of flux pinning centers, grain boundary weak-links, surface morphologies elemental compositions and distributions belonging to Y-site Ho and Ba-site Nd substituted Y-123 superconducting samples are discussed in detail for the first time. All the experimental findings show that the microstructural, electrical, mechanical and superconducting properties regularly improve with the increment in the HcN (Ho constant+Nd changeble) until a certain value of y=0.100, beyond which the characteristics tend to retrograde rapidly. This is attributed to the fact that excess penetration of the Nd damages the crucial properties given above.

Fabrication of superconducting coils and (Ba,A)Fe2As2 (A:Na, K) long round wires with large superconducting cores

We fabricated superconducting coils using 10-20 m-class round wires of 122-type iron-based superconductors (IBSs). Round wires and coils are fabricated by powder-in-tube method and hot-isostatic-press technique. Transport critical current (I c) of the whole (Ba,K)Fe2As2 coil is 46 A under the self-field at 4.2 K, and magnetic field at the center of the coil reaches 0.3 T. Although the edge of the long wire in the coil is damaged, the rest of the part is relatively homogeneous. Furthermore, the largest transport critical current density (J c) and I c in (Ba,K)Fe2As2 wires picked up from the coil reach 49 kAcm−2 and 44 A at 4.2 K under a magnetic field of 10 T, respectively. This value exceeds the previous highest transport J c of (Ba,K)Fe2As2 round wires. We also fabricated a (Ba,Na)Fe2As2 coil using long round wire with large superconducting core by react and wind method. Transport I c of the coil is significantly low due to cracks perpendicular to electric current flow direction, although magnetic J c in the round wire picked up from the coil reaches 40 kAcm−2 at 4.2 K under 4 T.

Thermally activated flux flow and inter-granular coupling properties in superconducting (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1−x (ZnO NPs)x composites

In high-temperature ceramic superconductors, vortices motion is induced by the strong thermal fluctuations because of the thermally activated flux flow (TAFF). The TAFF impedes the transport properties and critical current density of superconductors. It has been reported that adding nano-scale impurities can induce artificial pining centers that may improve inter-granular connections and flux pinning strength in ceramic superconductors. Here, the effects of different amounts (0.0–1.0 wt%) of ZnO nanoparticles on the TAFF behavior and zero temperature activation energy of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconducting phase have been studied using the modified TAFF model. Moreover, the impacts of the additive on the inter-granular traits and the Josephson coupling energy of the superconducting phase have been investigated using AC susceptibility measurements. Vortex phases analysis indicates that all composites show a vortex glass to vortex liquid phase transition at Tg. The vortex liquid phase is divided into the critical region existing in a finite temperature region just above Tg and the TAFF region present in the finite temperature region above it. It was found that the TAFF region is shifted to the higher temperatures and gets narrower, as the ZnO nanoparticles concentration enhances from 0.0 to 0.2 wt%. The vortex glass to vortex liquid transition temperature, Tg, increases from 93.8 K for the sample without additive to 101.0 K for the composite with 0.2 wt% ZnO nanoparticles. In addition, the zero-temperature activation energy (U0/KB) increases from ~0.4 × 105 K for the sample without additive to ~1.4 × 105 K for the composite with 0.2 wt% ZnO nanoparticles and then decreases for more ZnO concentrations. Moreover, it was found that the Josephson coupling energy Ej increases from ~0.039 eV for the sample without additive to ~0.136 eV for the composite with 0.2 wt% ZnO nanoparticles. These results point out a significant enhancement of the activation energy, flux pinning capability, and inter-granular coupling of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconducting phase with the addition of the 0.2 wt% ZnO nanoparticles.

Progress in the development of the 122-type IBS wires

Profit from their low anisotropy and high upper critical field, iron-based superconductors (IBSs) have great potential for high magnetic fields applications. Significant progress has been made for the current density improvement of (Sr,Ba) 0.6 K 0.4 Fe 2 As 2 (122-type) IBS wires over the past fourteen years. In this article, an overview of the preparation procedures and key issues affecting the critical current performance of 122-type IBS wires is given, to provide a fundamental understanding of what controls the transport critical current density of 122-type IBS wires. Additionally, the recent developments for 122-type IBS wires are presented and future prospect and challenges in the development of 122-type IBS wires for practical applications are discussed.

The structural, magnetic, and pinning features of Bi-2223 superconductors: Effects of SiC nanoparticles addition

In this research, the influence of Silicon Carbide nanoparticles (SiC-NPs) addition on the microstructure, superconducting, and pinning properties of (Bi, Pb)2Sr2Ca2Cu3O10+θ (Bi-2223) superconductors is comprehensively studied. The superconductors are synthesized by the sol-gel method and SiC-NPs are added up to 0.8 wt%. The X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) measurements are carried out for structural and morphological investigations. The superconductivity parameters such as intra-granular critical current density (JC, intra), inter-granular current critical density (JC, inter), transport critical current density (JC, t), and pinning force density (FP) are detected through DC- and AC-susceptibility, hysteresis loop, and transport measurements. The obtained results show that the 0.4 wt% addition of SiC-NPs improves the microstructure and the connectivity of grains as well as JC, inter, JC, intra, JC, t, and FP in the Bi-2223 superconductor. This research opens notable avenues for the use of synthesized Bi-2223 ceramics for electrical and industrial applications such as high-current energy storage, wires, and tapes.

Critical Current Density and Meissner Effect of Smart Meta-Superconductor MgB2 and Bi(Pb)SrCaCuO.

The smart meta-superconductor MgB2 and Bi(Pb)SrCaCuO increase the superconducting transition temperature (TC), but the changes in the transport critical current density (JC) and Meissner effect are still unknown. Here, we investigated the JC and Meissner effect of smart meta-superconductor MgB2 and Bi(Pb)SrCaCuO. The use of the standard four-probe method shows that Y2O3:Eu3+ and Y2O3:Eu3++Ag inhomogeneous phase significantly increase the JC, and JC decreases to a minimum value at a higher temperature. The Meissner effect was measured by direct current magnetization. The doping of Y2O3:Eu3+ and Y2O3:Eu3++Ag luminescent inhomogeneous phase causes a Meissner effect of MgB2 and Bi(Pb)SrCaCuO at a higher temperature, while the non-luminescent dopant reduces the temperature at which samples have Meissner effect. The introduction of luminescent inhomogeneous phase in conventional MgB2 and copper oxide high-temperature Bi(Pb)SrCaCuO superconductor increases the TC and JC, and Meissner effect is exerted at higher temperature. Therefore, smart meta-superconductivity is suitable for conventional and copper oxide high-temperature superconductors.

Comparative study of Tl-1223 superconductors prepared by the sol-gel route and solid-state reaction

This paper presents sol-gel (SG) and solid-state reaction (SSR) pathways to produce multiphase ceramic precursors of BCCO and then the superconducting phase of Tl-1223. The heat treatments showed that to obtain high-purity precursors prepared by SG and SSR methods are sufficient to heat treatments at 915 and 945 °C, respectively. Furthermore, the diamagnetic onset temperature of the superconducting transition for the Tl-1223 samples prepared by precursors SG at 915 °C and SSR at 945 °C is approximately 120 K, and complete screening of applied ac magnetic fields observed at T ≈ 102 and ≈ 94 K, respectively. In addition, the value of the transport critical current density Jc for SSR was 128 A/cm2, whereas for the SG sample it was precisely 174 A/cm2. Thus, we could conclude that using wet chemistry offers some advantages over classical solid-state ceramic processing, significantly better chemical homogeneity, and higher reactivity of the precursor powder.

Improved critical current density property in ex situ processed MgB2 tapes using filling powders with metallic particle addition

MgB2 powders milled with low-melting-point metallic particles, Bi and In, and Fe-sheathed tapes using those milled powders were sintered at various temperatures. With increasing the amount of those additives, the wear of WC jar and balls during milling process is promoted. Compared with In addition, Bi addition clearly causes the formation of some amorphous or poor crystalline phase in the as-milled state. Concerning the sintered tape samples, the optimal sintering temperature (Tsin), at which best performance in transport critical current density (Jc) at 4.2 K in 10 T is obtained, is 680 °C for the tapes using the milled powders with In addition. This temperature is lower than that by 30 °C for the tapes without additives. Furthermore, In addition promotes the reaction at the interface between the MgB2 core and the Fe sheath. In contrast, Bi addition appreciably causes neither reduction of the optimal Tsin nor the promoted reaction at the interface. Although both additives hardly bring about critical temperature (Tc) reduction, only Bi addition can improve the transport Jc property. This Jc enhancement is mainly attributed to improved grain connectivity. In addition itself can be effective for grain connectivity improvement as well. However, reduced upper critical and irreversibility fields (Hc2 and Hirr) brought about by the addition degrade the Jc property.

Effect of Heat Treatments under High Isostatic Pressure on the Transport Critical Current Density at 4.2 K and 20 K in Doped and Undoped MgB2 Wires.

Annealing undoped MgB2 wires under high isostatic pressure (HIP) increases transport critical current density (Jtc) by 10% at 4.2 K in range magnetic fields from 4 T to 12 T and significantly increases Jtc by 25% in range magnetic fields from 2 T to 4 T and does not increase Jtc above 4 T at 20 K. Further research shows that a large amount of 10% SiC admixture and thermal treatment under a high isostatic pressure of 1 GPa significantly increases the Jtc by 40% at 4.2 K in magnetic fields above 6 T and reduces Jtc by one order at 20 K in MgB2 wires. Additionally, our research showed that heat treatment under high isostatic pressure is more evident in wires with smaller diameters, as it greatly increases the density of MgB2 material and the number of connections between grains compared to MgB2 wires with larger diameters, but only during the Mg solid-state reaction. In addition, our study indicates that smaller wire diameters and high isostatic pressure do not lead to a higher density of MgB2 material and more connections between grains during the liquid-state Mg reaction.

Fabrication of small superconducting coils using (Ba,A)Fe2As2 (A: Na, K) round wires with large critical current densities

We report the fabrication of small (Ba,A)Fe2As2 (A: Na, K) coils using 10 m-class long round wires, fabricated by the powder-in-tube method. Coils are sintered using the hot-isostatic-press technique after glass-fiber insulations are installed. Critical current (I c) of the whole coil using (Ba,Na)Fe2As2 and (Ba,K)Fe2As2 are 60 A and 66 A under the self-field, and the generated magnetic fields at the center of the coil reach 2.6 kOe and 2.5 kOe, respectively. Furthermore, the largest transport critical current density (J c) and I c in (Ba,Na)Fe2As2 wires picked up from the coil reach 54 kA cm−2 and 51.8 A at T = 4.2 K under a magnetic field of 100 kOe, respectively. This value exceeds transport J c of all previous iron-based superconducting round wires. Texturing of grains in the core of the wire due to the improvement of the wire drawing process plays a key role for the enhancement of J c.

Enhanced Transport Critical Current Density of Tl-1212 Bulk Superconductor Added with Nickel-Zinc Ferrite Nanoparticles

High temperature superconductor Tl-1212 with nominal starting composition (Tl0.85Cr0.15)Sr2CaCu2O7-δ was prepared with high purity oxide powders using a solid state reaction method. Small amounts of nickel-zinc ferrite nanoparticles (Ni0.5Zn0.5Fe2O4) at compositions 0.01, 0.02, 0.05 and 0.10 wt. % were added into Tl-1212 superconductors. The effect of Ni0.5Zn0.5Fe2O4 nanoparticles’ addition on the critical temperature (Tc), transport critical current density (Jc), phase formation, and morphology was studied. The samples were characterized using electrical resistance measurement, transport critical current density measurement, powder X-ray diffraction method (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Zero-resistance critical temperature (Tc-zero) was found to rise from 97 K to 99 K with increasing Ni0.5Zn0.5Fe2O4 nanoparticles concentration. The highest value recorded for transport critical current density (Jc) was 3,120 mA/cm2 at 77 K, which exhibited by sample with 0.02 wt. % of Ni0.5Zn0.5Fe2O4 nanoparticles. All samples showed a dominant Tl-1212 phase and exhibited tetragonal lattice structure in the P4/mmm space group. SEM micrographs showed close-packed microstructure with low porosity. EDX mapping showed that Ni0.5Zn0.5Fe2O4 nanoparticles were well distributed in the Tl-1212 samples. This study demonstrated that Ni0.5Zn0.5Fe2O4 nanoparticles have functioned as effective flux pinning centers to Tl-1212 superconductors and thus significantly enhanced its Jc.

Enhancing Transport Performance in 7-filamentary Ba0.6K0.4Fe2As2 Wires and Tapes via Hot Isostatic Pressing

Iron-based superconductors (IBS) are considered as potential materials for manufacturing high-field magnets, for which developing multi-filamentary conductors with high performance and high strength is essential. Herein, 7-filamentary Cu/Ag composite sheathed Ba0.6K0.4Fe2As2 (Ba122) round wires and tapes were successfully prepared through the ex situ powder-in-tube (PIT) method and treated by hot isostatic pressing (HIP) process. Pure Ba122 phase with roughly homogeneous element distribution was obtained in the superconducting filaments. The wires and tapes show very small low-temperature normal-state resistivity of 0.12 μΩ cm and 0.17 μΩ cm respectively owing to the high electrical conductivity of copper and silver. The HIP process greatly enhances the mass density of the superconducting filaments and promotes the formation of well-grown plate-like Ba122 grains. Vickers hardness measurements on the cross sections of these filaments reveal a rather good uniformity of the mass density. The transport critical current density (Jc) in the 7-filamentary Ba122/Ag/Cu round wires and tapes reached 1.3 × 104 A cm−2 and 4.8 × 104 A cm−2 at 4.2 K in 10 T respectively. These results indicate that hot isostatic pressing is advantageous in developing high-performance multi-filamentary iron-based superconductors.

Visualization of the grain structure in high-performance Ba1−x K x Fe2As2 superconducting tapes

122 type iron-based superconductors (IBSs) are potential for high-field applications, and the fabrication of high-performance IBS wires and tapes is essential. By using the powder-in-tube method, transport critical current density (J c) of hot-pressed (HP) silver-sheathed Ba1−x K x Fe2As2 (Ba-122) tapes have reached 1.5 × 105 A cm−2 at 4.2 K and 10 T. However, the J c of flat-rolled (FR) tapes is 6.2 × 104 A cm−2 (4.2 K, 10 T), less than half of the former. The grain orientation, grain size, and grain shape are important parameters for the understanding of the superconducting properties of IBS tapes. Such grain structure data can be provided by the electron backscatter diffraction (EBSD) technique. In this work, we extensively adopted EBSD to visualize the microstructure of state-of-the-art HP and FR Ba-122 tapes. The grain orientation, grain connectivity, grain size, and grain shape aspect ratio of these two types of tapes are quantitatively analyzed. The c-axis texture is commonly found in both HP and FR tapes, but no in-plane texture is discovered. The texture and grain connectivity in HP tapes are better than that in FR tapes. The grain size of FR tapes is smaller than that of HP tapes, and the hot-pressing processes can promote the growth of grains along the ab plane. We recommend that strong texture will promote the growth of grains, while the small-sized grains will return to limit the formation of texture. Therefore, finding a balance point that plays a synergistic promote effect of grain orientation and grain size is a strategy to improve the transport properties of IBS tapes further. The present results demonstrate that there is still margined to enhance the properties of IBS tapes.

Application of Neutron Flux from PUSPATI TRIGA Mark II Research Reactor in Enhancing Superconducting Properties of BSCCO Superconductor

The PUSPATI TRIGA Mark II Research Reactor is currently been used in various applications such as Neutron Activation Analysis (NAA), Delayed Neutron Activation Analysis (DNAA), radioisotope production for medical, industrial and agricultural purposes, Neutron Radiography and Small Angle Neutron Scattering (SANS). However, there are not much research activities on utilizing neutron flux from the reactor to study properties of superconducting materials. For superconductors to be fabricated into components of electrical and magnetic devices, the sustainability of the transition temperature, TC and the transport critical current density, JC of the materials is vital to ensure the durability and effectiveness of the devices. A strong superconducting flux pinning capability of superconductors is necessary to maintain high TC and larger JC. Meanwhile, exposure of superconductors to neutron flux is able to create the self-organization of defects that are responsible in producing higher TC and JC in superconductors where the defects act as the flux pinning centres. In this paper, we report the utilization of neutron flux from the PUSPATI TRIGA Mark II research reactor in enhancing the TC and JC of bismuth-strontium-calcium-copper oxide (BSCCO) superconductor. Appropriate sample holder and shielding was fabricated as protection from radiation effect. In this work, 2212-phase BSCCO superconductor (Bi-2212 phase) samples were synthesized using the conventional solid-state reaction method. The samples underwent fast neutron irradiation with neutron flux of 2.0 × 1011 neutrons/(cm2.s) for 6 hours. Results showed that the TC of the samples improved slightly, and the JC was found to increase by more than 3 folds.

High transport critical current density in high magnetic fields at Mg11B2 wires made with nano 11B

In this work, we show the transport current results and structural analysis for Mg11B2 wires for the first time made with high purity, nano-size and amorphous boron 11 (11B). Irradiation has a weak effect on the MgB2 material made of 11B. Therefore, it is important for future applications to fusion reactors. This type of reactor will produce clean and cheap energy. We report for first time that high-fields pinning centers and dense layered structure lead to high transport critical current density (Jtc) in high magnetic fields. This allows to obtain highest Jtc value in the world (100 A/mm2 at 4.2 K and 8.5 T). We show that lack of dense layered structure and high-fields pinning centers lead to lower Jtc in high magnetic fields. Our research shows that high isostatic pressure (HIP) promotes high-field pinning centers.

Superconducting properties of sintered ex situ MgB2 tapes through ball milling process as a function of crystallite size in the as-milled and sintered states

Ball milled MgB2 powders and ex situ processed tapes using those milled powders were sintered at various temperatures. Critical temperature (Tc) increases moderately with increasing sintering temperature (Tsin) up to 705 – 735 °C, at which best performance in transport critical current density (Jc) at 4.2 K in 10 T for the tape samples is obtained. In contrast, the Tc rapidly increases when sintered above that temperature. Although the transport Jc property is improved with increasing the Tsin up to this optimal Tsin, further increase of the Tsin degrades the Jc property in the high-field region. These behaviors of the superconducting properties are attributed to the crystallite growth. The reduced crystallite size brought about through milling process recovers by sintering, and this recovery is remarkable above the optimal Tsin. With increasing the crystallite size, the Tc increases, whereas both upper critical field (Hc2) and irreversibility field (Hirr) decrease. While MgB2 decomposition is promoted above the optimal Tsin, grain connectivity is improved with increasing the Tsin. Thus, high-temperature sintering not only improves the grain connectivity and hence the Jc property in the low-field region, but also brings about large Jc degradation in the high-field region due to the decrease in Hc2 and Hirr at 4.2 K. Since the crystallite size in the as-milled and sintering states are linked with one another, those superconducting properties of the optimally sintered tapes in which MgB2 decomposition is ignorable are easily deduced from the crystallite size of MgB2 in the filling powders.

The Influence of Wire Bending and Wire Diameter on Transport Critical Current Density in Small MgB2 Superconducting Coils for Applications in Multi-Section Coils

This article presents the impact of MgB2 wire bending and diameter on transport critical current density and irreversible magnetic field of a resultant coil. Unreacted MgB2 wires 500 mm in length and 0.63 or 0.83 mm in diameter have been used in the fabrication of small diameter (14 mm) superconducting coils. The coils were subsequently annealed under isostatic pressure of 1 GPa for 15 min at 700 °C and 725 °C. Our results indicate that larger wire diameter, higher annealing temperature, and bending lead to slight reduction of critical current density and irreversible magnetic field in the coil.

Influence of Dysprosium Addition on the Phase Formation and Transport Properties of Hg-1223 Superconductor

We study the influence of dysprosium (III) oxides on the superconductivity properties of Hg-1223 material. Dysprosium-free Hg-1223 and dysprosium-doped HgBa2Ca2Cu3DyxO8+δ (x = 0.00–0.075 wt%) superconductors are synthesized by sealed quartz tube technique. Our results demonstrate that a presence of dysprosium oxide not only makes the Ba2Ca2Cu3Oy multiphase precursor more reactive and enhances the kinetics of the reaction, but also leads to the promotion of the high-Tc phase and enhancement of the transport critical current densities Jc.

Effect of Ni<sub>0.5</sub>Zn<sub>0.5</sub>Fe<sub>2</sub>O<sub>4</sub> Nanoparticles Addition on Tl-1212 High Temperature Superconductor

The effects of Ni0.5Zn0.5Fe2O4 nanoparticle addition on the superconducting and transport properties of (Tl0.85Cr0.15)Sr2CaCu2O7 (Tl-1212) superconductor were investigated in this paper. The Tl-1212 samples were produced by mixing high purity oxide powders through a solid-state reaction method. Nano Ni0.5Zn0.5Fe2O4 particles with compositions of 0.001 wt.%, 0.003 wt.%, 0.005 wt.%, 0.01 wt.% and 0.02wt.% with average size of 60 nm were added into the Tl-1212 powders. The transition temperatures (Tc-zero and Tc-onset) were measured using a four-point probe method. The highest Tc-zero recorded was 97 K which was exhibited by the pure Tl-1212 sample. The transport critical current, Ic, of the Tl-1212 samples were found through the 1 µV/cm criterion with temperature ranging from 30 K to 77 K. The sample with a composition of 0.003 wt.% displayed the highest value of Jc at 77 K with a value ranging up to 1780 mA/cm2. The Tl-1212 samples were characterised using scanning electron microscopy (SEM), powder X-ray diffraction method (XRD), energy dispersive X-Ray analysis (EDX), electrical resistance measurements and transport critical current density measurements. The Jc of the Tl-1212 superconductor has been improved through the addition of Ni0.5Zn0.5Fe2O4 nanoparticles but adding an excessive amount has caused its Jc to degrade.