High Transport Critical Current Density Research Articles

High transport Jc in 7-filament Cu/Ag sheathed Ba0.6K0.4Fe2As2 tapes manufactured by ambient pressure sintering

In regard to iron-based superconductors (IBS), the multi-filament Cu/Ag composite sheathed Ba-122 tape is particularly attractive for industrial high-field applications owing to its prominent properties. By a cost-effective and scalable way, ambient pressure sintering, a high transport critical current density (Jc) of 7-filament Cu/Ag sheathed Ba-122 tapes reached 4.5 × 104 A cm−2 at 4.2 K and 10 T, whose corresponding engineering critical current density (Je) has achieved to 104 A cm−2. An optimized powder-in-tube (PIT) method was adopted aiming at overcoming the difficulty of ambient pressure sintering to obtain high-density superconducting core and grain alignment. Improvements in the manufacturing process, such as drawing without intermediate annealing and rolling from larger initial diameter to thinner tapes, have resulted in high grain connectivity and good c-axis texture, which are the major factors contributing to high Jc. Our results demonstrate that the ambient pressure sintering process is a viable method to fabricate long-length multifilamentary Cu/Ag composite sheathed IBS tapes with high Jc for practical high-field applications.

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.

Effect of Nano-Sized Nickel Ferrite Addition on Superconducting Properties of (Tl<sub>0.85</sub>Cr<sub>0.15</sub>)Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>7-δ</sub> Superconductors

The effect of nanosized nickel ferrite (NiFe2O4) addition on (Tl0.85Cr0.15)Sr2CaCu2O7-δ superconductors has been investigated. (Tl0.85Cr0.15)Sr2CaCu2O7-δ high temperature superconductors was prepared via solid-state reaction method using high purity oxide powders. Nanosized NiFe2O4 was added to the compound at composition x = 0 - 0.003 wt.%. Samples were studied using scanning electron microscopy (SEM), X-ray diffraction method (XRD), electrical resistance versus temperature, transport critical current density Jc and AC susceptibility measurements. SEM micrographs showed close-packed microstructure with low porosity. XRD patterns showed a dominant phase of Tl-1212 with a minor phase of Tl-1201 for all samples. All of the samples displayed metallic normal state behavior before the onset transition temperature (Tc-onset) which was between 102 and 104 K. The transition temperature (Tcχ’) from AC susceptibility measurement also showed the similar results between 101 and 103 K. Tc-zero was slightly suppressed with the addition of nanosized NiFe2O4. The peak temperature Tp from the imaginary part of the susceptibility χ” was found between 77 - 91 K for all samples. The highest transport critical current density (Jc) at 77 K was shown by sample x = 0.001 wt.% at 2213 mAcm-2. Nanosized NiFe2O4 has significantly enhanced the Jc of (Tl0.85Cr0.15)Sr2CaCu2O7-δ superconductor.

High critical current density in Cu/Ag composited sheathed Ba0.6K0.4Fe2As2 tapes prepared via hot isostatic pressing

Iron-based superconductors (IBSs) with ultrahigh upper critical fields and low anisotropies have attracted significant attention in terms of the novel mechanism of superconductivity and high-field applications. A major concern for practical research is the fabrication of long wires with enhanced critical current density and low cost. In this paper, Cu/Ag composited sheathed Ba0.6K0.4Fe2As2 (Ba122) tapes were fabricated through a hot isostatic pressing method, which is feasible for long-wire manufacturing. The Cu/Ag composite sheath can lower the tape cost by reducing the use of expensive Ag. A high-transport critical current density (Jc) up to 5.8 × 104 A cm−2 under 10 T at 4.2 K was achieved in our tapes. Evidence has shown that these tapes have pure Ba122 phase, homogeneous element distribution, orientated grains and good grain connectivity. Our work shows that low-cost Cu/Ag-sheathed IBS tapes have great promise for practical applications in the future.

High transport current superconductivity in powder-in-tube Ba0.6K0.4Fe2As2 tapes at 27 T

The high upper critical field and low anisotropy of iron-based superconductors (IBS) make them particularly attractive for high-field applications, especially for the construction of next-generation nuclear magnetic resonance spectrometers, particle accelerators and high-field magnets. However, for practical use it is essential to make IBS materials into wire and tape conductors with sufficient current carrying capability, which is limited by misaligned grains inside the conductors. Here, based on a simple and low-cost powder-in-tube (PIT) method, we demonstrate a high transport critical current density (Jc) reaching 1.5 × 105 A cm−2 (Ic = 437 A) at 4.2 K and 10 T in Ba0.6K0.4Fe2As2 (Ba-122) tapes by texturing the grain orientation with optimized hot-press technique. The transport Jc measured at 4.2 K under high magnetic fields of 27 T is still on the level of 5.5 × 104 A cm−2. Moreover, at 20 K and 5 T the transport Jc is also as high as 5.4 × 104 A cm−2, showing a promising application potential in moderate temperature range which can be reached by liquid hydrogen or cryogenic cooling. All these Jc values are the highest ever reported for IBS wires and tapes. The high-performance PIT Ba-122 tapes in this work suggest IBS to be a strong potential competitor of cuprate superconductors for the race of high-field applications in the future.

Transport current density at temperatures up to 25 K of Cu/Ag composite sheathed 122-type tapes and wires

The fabrication of iron-based superconductors with high transport critical current density (Jc) and low cost is a crucial determinant of whether they can be used for practical applications. In this paper, Cu/Ag composite sheathed Sr0.6K0.4Fe2As2 (Sr122) tapes and Ba0.6K0.4Fe2As2 (Ba122) round wires were fabricated via an ex situ powder-in-tube method and heat-treated by the hot pressing and hot isostatic pressing process respectively. In order to thoroughly reveal the application potential of Cu/Ag composite sheathed ‘122’ iron pnictide superconductors, transport Jc of tapes and wires in high fields at temperatures up to 25 K was measured. High transport Jc of 4.4 × 104 A cm−2 at 4.2 K and 3.6 × 103 A cm−2 at 20 K in 10 T was achieved in Cu/Ag composite sheathed Sr122 tapes. Transport Jc of Ba122 wires is 9.4 × 103 A cm−2 at 4.2 K and 1.9 × 103 A cm−2 at 20 K in 10 T. These results demonstrate the great potential of Cu/Ag composite sheathed ‘122’ iron pnictide superconducting tapes and wires for high-field applications at intermediate temperatures around 20 K, which can be easily obtained by using cryocoolers.

Phase Formation and Transport Critical Current Density of Tl2Ba2CaCu2O8 Superconductor with Nano Bi2O3

The effect of nanosized Bi2O3 (150 nm) on the formation of the Tl2Ba2CaCu2O8 (Tl-2212) phase, transition temperature and transport critical current density has been studied. Samples with nominal starting composition Tl2Ba2CaCu2O8(Bi2O3)x (x = 0 to 0.5 wt. %) were prepared using the solid state reaction method. Most samples except x = 0.5 showed a mixed phase consisting of the Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 (Tl-2223). The x = 0.5 sample showed a single Tl-2212 phase. However, the transition temperature, Tc of the x = 0.5 was very much suppressed (Tonset = 106 K, Tc zero 88 K). All samples showed random grain size and orientation, with partial melting and high porosity. The x = 0.1 mixed phase sample showed the highest transport critical current density of 285 mA/cm2 at liquid nitrogen temperature (78 K).

Tailoring the critical current properties in Cu-sheathed Sr1−xKxFe2As2 superconducting tapes

Cu is an attractive metal to use as the sheath material for Sr1−xKxFe2As2 superconducting wires. However, unfavorable reactions between the Cu sheath and the superconducting core severely affect the superconducting performance. In this work, Cu-sheathed Sr1−xKxFe2As2 tapes are fabricated at a low temperature of 740 °C using a hot pressing method. A systematic correlation between the sintering holding time, reaction layer, microstructure, and superconducting properties is investigated. It is found that the samples that are hot pressed for 60 min exhibit the highest transport critical current density (Jc), i.e. 3.5 × 104 A cm−2 in 10 T and 1.6 × 104 A cm−2 in 26 T at 4.2 K, respectively. Furthermore, the engineering critical current density (Je) value of the samples is over 1.0 × 104 A cm−2 in 10 T at 4.2 K. This is by far the highest Jc reported for Cu-sheathed iron-based superconducting tapes.

Fabrication of FeSe 0 . 5 Te 0 . 5 Superconducting Wires by an Ex Situ Powder-in-Tube Method

We report the fabrication of Cu/Nb-sheathed FeSe0.5Te0.5 superconducting wires by an ex situ powder-in-tube method. After swaging and drawing, the as-drawn wires were heat-treated at different heat conditions. Subsequently, characterizations and transport critical current measurements were performed on the heat-treated FeSe0.5Te0.5 wires. Also, the results of the as-drawn wire are presented for comparison. The FeSe0.5Te0.5 cores reacted with the Nb sheaths when heat-treated at a high temperature or at a low temperature for a long time. Furthermore, according to our results, the highest transport critical current density (J c) at 0.5 and 0.75 T is about 1.6 × 10 4 and 1.5 × 10 3 A/cm 2, respectively.

Low-temperature synthesis to achieve high critical current density and avoid a reaction layer in SmFeAsO1−xFx superconducting tapes

A low-temperature (300–500 °C) heat treatment process under ambient pressure or uniaxial pressure was performed on Sn-added SmFeAsO1−xFx superconducting tapes fabricated by the ex situ powder-in-tube method. A highest transport critical current density (Jc) of 3.95 × 104 A cm−2 (at 4.2 K and self-field) was achieved by this process. The low-temperature process allows tapes to endure much longer heat treatment without Jc degradation than the high-temperature method. Microscopic analysis also revealed that this method could obtain a clear boundary without a reaction layer or interdiffusion between a superconducting core and sheath metal.

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.

Nanostructural Defects and Critical Current Densities in High-Quality <inline-formula> <tex-math notation="TeX">$\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{CaCu}_{2}\hbox{O}_{8+{\rm X}} $</tex-math></inline-formula> Epitaxial Thin Films Prepared by MOCVD

Nanostructural defects were investigated by transmission electron microscopy in c-axis-oriented epitaxial Bi 2 Sr 2 CaCu 2 O 8+X (Bi2212) thin films with high T c (R = 0) ≥ 83 K and high transport critical current density ofJ c >10 10 A/m 2 at 10 K. We observed misfit dislocations at twin boundaries, dislocations associated with stacking faults parallel to the a-b plane, and antiphase boundaries. We compared the magnetic-field dependent J c values at various temperatures in two Bi2212 films. About 110-nm-thick film A showed lower J c than ~280-nm-thick film B at low temperatures (≤ 20 K) or in low magnetic fields (≤ 0.1 T). However, the J c of film B decreased more rapidly in high magnetic fields, leading to a crossover of the two J c -B curves at temperatures of 30 K and above. This is probably because film B contained a higher density of antiphase boundaries, which caused stronger pinning and higher J c values at low temperatures but may have caused enhanced thermally activated motion of pancake vortices that eventually resulted in lower Jc values in high magnetic fields at moderate temperatures.

Enhancement of transport critical current density of SmFeAsO1−xFx tapes fabricated by an ex-situ powder-in-tube method with a Sn-presintering process

SmFeAsO1−xFx (Sm1111) tapes were prepared by an ex-situ powder-in-tube method with a Sn-presintering process. Scanning electron microscopy revealed apparent difference in microstructure between Sn-presintered tapes and the previously reported polycrystalline Sm1111 bulk, since Sn has reduced FeAs wetting phase and filled the voids between Sm1111 grains. The Sn-presintered tapes showed significant enhanced field dependences of transport Jc compared with Sn-added tapes. A highest transport critical current density (Jc) of 3.45 × 104 A cm−2 at 4.2 K and self-field is achieved. Magneto-optical imaging further confirmed large and well-distributed global and intergranular Jc in Sn-presintered Sm1111 tapes.

Improved superconducting properties of MgB2 thin films fabricated by ultrasonic spray pyrolysis method at high temperature

High quality MgB2 superconducting thin films have been successfully prepared by 2.4MHz ultrasonic spray pyrolysis (USP) system on single crystal Al2O3 (001) substrates. The microstructure, electrical and magnetic properties of approximately 500–600nm thick films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) in conjunction with the energy dispersive X-ray analysis (EDX), resistance versus temperature (R–T) and magnetization measurements (M–H) under different magnetic fields and transport critical current density (Jc). Films were first heat treated in situ in the spraying chamber with an extra Mg powder during deposition to compensate excess evaporation of Mg from the films and then additionally heat treated in Ar atmosphere at 700°C for a short time. According to the results obtained, orientation on any particular direction for the crystal growth was not seen. Homogeneous, highly dense and highly smooth surface morphology and low resistance have been achieved under optimum conditions. Optimally treated films exhibited relatively high transport critical current density of 2.37×105Acm−2. These results have been also compared with the Jcmag results calculated from the M–H curves. The electrical resistance property of the best samples was obtained to be 39.5 and 37.4K for Tc and Tzero, respectively.

Fabrication of binary FeSe superconducting wires by diffusion process

We report successful fabrication of multi- and mono-core FeSe wires with high transport critical current density Jc using a simple in-situ Fe-diffusion process based on the powder-in-tube (Fe-diffusion PIT) method. The seven-core wire showed transport Jc of as high as 1027 A/cm2 at 4.2 K. The superconducting transition temperature Tczero was observed at 10.5 K in the wire-samples, which is about 2 K higher than that of bulk FeSe. The Fe-diffusion PIT method is suitable for fabricating multi-core wires of the binary FeSe superconductors with superior properties.

Enhanced Inter-grain Connectivity in Nano-particles Doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ Superconductors

Polycrystalline (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors show strong composition variations at the termination ends of the crystals which compromise over-all superconducting properties of the final compound. These composition variations are one of the root causes of void formation which produces a poor quality material. The better inter-grain coupling suppresses the Josephson losses required for higher transport critical current density (J c ). The lower losses across the inter-grain Josephson junctions are essential for wire and microelectronic applications. We have fixed such inadvertent composition variation in (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors by doping them with nano-particles of CuO, BaO and CaO2. Nano-particles doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors were synthesized at 860 °C and characterized using X-ray diffraction (XRD), resistivity (ρ), ac-susceptibility (χ), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) measurements. The magnitude of superconductivity is significantly enhanced with the doping of nano-particles. The samples with 15 wt. % addition of CuO nano-particles have even shown textured elongated crystalline with extremely low population of voids.

High transport critical current densities in textured Fe-sheathed Sr1−xKxFe2As2+Sn superconducting tapes

We report the realization of grain alignment in Sn-added Sr1−xKxFe2As2 superconducting tapes with Fe sheath prepared by ex-situ powder-in-tube method. At 4.2 K, high transport critical current densities Jc of 2.5 × 104 A/cm2 (Ic = 180 A) in self-field and 3.5 × 103 A/cm2 (Ic = 25.5 A) in 10 T have been measured. These values are the highest ever reported so far for Fe-based superconducting wires and tapes. We believe the superior Jc in our tape samples are due to well textured grains and strengthened intergrain coupling achieved by Sn addition. Our results demonstrated an encouraging prospect for application of iron based superconductors.

Low-temperature synthesis of FeTe0.5Se0.5 polycrystals with a high transport critical current density

We have prepared high-quality polycrystallineFeTe0.5Se0.5 at temperatureas low as 550 °C. The transport critical current density evaluated from the current–voltage characteristics is over700 A cm − 2 at 4.2 K under zero field, which is several times larger than that forFeTe0.5Se0.5 superconducting wires. The critical current density estimated from magneto-optical images offlux penetration is also similar to this value. The upper critical field of the polycrystallineFeTe0.5Se0.5 atT = 0 K estimated using Werthamer–Helfand–Hohenberg theory is 585 kOe, which is comparableto that of single crystals. This study gives some insight into how to improve the performance ofFeTe0.5Se0.5 superconducting wires.

Low-temperature synthesis of SmFeAsO0.7F0.3 − δ wires with a high transport critical current density

Ag-sheathed SmFeAsO0.7F0.3 − δ (Sm-1111) superconducting wires were prepared by a one-step solid state reaction at temperatures as lowas 850–900 °C, instead of commonly used temperatures of 1150–1250 °C. The x-ray diffraction pattern of the as-sintered samples is well indexed on the basis of thetetragonal ZrCuSiAs-type structure. We characterized the transport critical current densityJc ofthe SmFeAsO0.7F0.3 − δ wires in increasing and subsequently decreasing fields, by a resistive four-probe method. A transportJc as highas ∼ 1300 A cm − 2 at4.2 K and self-field has been observed for the first time in Sm-1111 type polycrystalline superconductors.The Jc also shows a rapid depression in small applied fields as well as a magnetic-historydependence, indicating weak-linked grain boundaries. The low-temperature synthesismethod can be very beneficial for fabricating the RE-1111 iron oxypnictides in a convenientand safe way.

Large transport critical currents of powder-in-tube Sr0.6K0.4Fe2As2/Ag superconducting wires and tapes

We report the achievement of transport critical currents in Sr0.6K0.4Fe2As2 wires and tapes with a Tc = 34 K. The wires and tapes were fabricated through an in situ powder-in-tube process. Silver was used as a chemical addition as well as a sheath material. All the wire and tape samples have shown the ability to transport superconducting current. Critical current density Jc was enhanced upon silver addition, and at 4.2 K, a largest Jc of ∼1200 A/cm2 (Ic = 9 A) was achieved for 20% silver added tapes, which is the highest in iron-based wires and tapes so far. The Jc is almost field independent between 1 T and 10 T, exhibiting a strong vortex pinning. Such a high transport critical current density is attributed to the weak reaction between the silver sheath and the superconducting core, as well as an improved connectivity between grains. We also identify a weak-link behavior from the apparent drop of Jc at low fields and a hysteretic phenomenon. Finally, we found that compared to Fe, Ta and Nb tubes, Ag was the best sheath material for the fabrication of high-performance 122 type pnictide wires and tapes.