Enhancement Of Critical Current Density Research Articles

Evaluation of temperature dependent vortex pinning properties in strongly pinned YBa2Cu3O7-δ thin films with Y2BaCuO5 nanoinclusions

The pinning of quantized magnetic vortices in superconducting YBa2Cu3O7- δ(YBCO or Y123) thin films with Y2BaCuO5 (Y211) nanoinclusions have been investigated over wide temperature range (4.2–77 K). The concentration of Y211 nanoinclusions has been systematically varied inside YBCO thin films prepared by laser ablation technique using surface modified target approach. Large pinning force density values (Fp ∼ 0.5 TNm−3 at 4.2 K, 9 T) have been observed for the YBCO film with moderate concentration of Y211 nanoinclusions (3.6 area % on ablation target). In addition, uniform enhancement in critical current density (Jc) was observed in the angular dependent Jc measurement of YBCO+Y211 nanocomposite films. Y211 nanoinclusions have been found to be very efficient in pinning the quantized vortices thereby enhancing the in-field Jc values over a wide range of temperature. Increasing the concentration of Y211 secondary phase into Y123 film matrix results into agglomeration of Y211 phase and observed as increased Y211 nanoparticle size. These larger secondary phase nanoparticles are not as efficient pinning centers at lower temperatures as they are at higher temperatures due to substantial reduction of the coherence length at lower temperatures. Investigation of the temperature dependence of Jc for YBCO+Y211 nanocomposite films has been conducted and possible vortex pinning mechanism in these nanocomposite films has been discussed.

Thermal-driven gigantic enhancement in critical current density of high-entropy alloy superconductors

The high-entropy alloy (HEA) superconductor, Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 (Ta–Nb–Hf–Zr–Ti), is systematically studied to examine changes in superconducting critical properties, critical temperature (Tc), critical current density (Jc), and upper critical field (Hc2), concerning thermal treatment conditions. Annealing condition affects Jc more significantly than Tc and Hc2, with a large improvement of flux pinning force density (Fp). The Jc of bare sample is reduced to 10 A cm–2 at an applied magnetic field of approximately 1.5 T, whereas the sample annealed at 550 °C for 12 h exhibits Jc > 100 kA cm–2 up to around 4 T. Furthermore, the Vickers hardness (HVIT) of the Ta–Nb–Hf–Zr–Ti HEA superconductor notably increases from ∼384 to 528 HVIT following a 24-h annealing at 500 °C. These results demonstrate that thermal annealing is a powerful process to optimize both the superconducting and mechanical properties of high-entropy alloy superconductors.

Enhancement of irreversibility field and critical current density of rare earth containing V0.60Ti0.40 alloy superconductor by cold-working and annealing

β-V1−xTix alloy superconductors are considered to be promising materials for high magnetic field applications. So far, attempts to improve the critical current density (JC) of β-V1−xTix alloys have shown limited success. Improving JC requires a controlled generation of defects. Similar to the V0.6Ti0.4-RE (RE = Gd, Y) alloys, RE = Ce, Dy and Nd are also immiscible in the V0.6Ti0.4 matrix. The superconducting transition temperature (TC), upper critical field (HC2), irreversibility field (HIrr), and JC increase with the RE addition. However, the tensile strength of V0.6Ti0.4-Gd alloy is observed to be significantly lower than that of V0.6Ti0.4 alloy. Cold-working is found to further improve the TC, HC2, HIrr, and JC of all the V0.6Ti0.4-RE alloys. Successive cold-working (with 50% reduction of thickness each time) and annealing (SCA) at 450∘C for 5 hrs is found to significantly improve the HIrr, and JC of V0.6Ti0.4-RE (RE = Gd, Ce) alloys. The tensile strength is also found to increase to about 60–70% of the V0.6Ti0.4 alloy after the third annealing. It is observed that α′ and ω phases form at the defect sites at various stages of cold-working and annealing. JC(H = 0) and HIrr are about 840 Amm−2 and 7 T respectively for the as-cast V0.6Ti0.4-RE alloys. Cold-working on the V0.6Ti0.4-RE alloys further improves the JC(H = 0) and HIrr to about 1250 Amm−2 and 8.45 T respectively. SCA increases the JC(H = 0) and HIrr to about 4000 Amm−2 (or more) and 9 T respectively, and the JC(7 T) to about 500 Amm−2 in V0.6Ti0.4-RE alloy at 4 K. We present a detailed description of the defect structure in these alloys and its role in pinning the magnetic flux lines, thereby improving the overall JC.

Enhancement of Critical Current Density of Nb3Al Superconductors by B Doping

Boron (B)‐doped Nb3Al superconductors are prepared by mechanical alloying and subsequent sintering process in this work. Then, the critical current density (Jc) of Nb3Al with different amounts of B doping is studied. In the results, it is shown that Jc performance of Nb3Al is improved obviously after B doping. The best Jc value obtained in this work is 2.2 × 104 A cm−2 (4.2 K, 5 T) for Nb3(Al0.9B0.1) sample. Furthermore, the mechanism of enhanced Jc performance for Nb3(Al0.9B0.1) sample is comprehensively explored. It is found that B doping can significantly enhance the grain connectivity of Nb3Al superconductor, and the active cross‐sectional area fraction values increase from 0.11 for the undoped sample to 0.34 for Nb3(Al0.9B0.1) sample. In addition, the lattice distortion caused by the interstitially dissolved B may also serve as flux pinning centers, which strengthens the flux pinning force of Nb3(Al0.9B0.1).

Enhancement of critical current density and critical magnetic field of superconducting medium entropy alloy Nb2/5Hf1/5Zr1/5Ti1/5

We investigated the superconducting properties of medium entropy alloys (MEA) Nb2/5Hf1/5Zr1/5Ti1/5, synthesized by arc melting (AM) and powder metallurgical spark plasma sintering (SPS) methods. The samples exhibit superconducting transitions at Tc=7.99 K (AM) and 6.63 K (SPS) from the electrical resistivity measurements. The upper critical field at zero-temperature limit μoHc2(0) gives a relatively high value of 14.63 T (AM) and 11.68 T (SPS). The isothermal magnetic hysteresis of the SPS-MEA shows significantly enhanced vortex pinning, resulting in the enhancement of critical current density (Jc= 39,000 A/cm2) compared with the AM-MEA (Jc= 5,500 A/cm2) at 2 K (about seven times enhancement). The SPS-MEA shows a significant suppression of vortex avalanches compared with the previously reported SPS-HEA Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 superconductor. The SPS-MEA showed the secondary fishtail effect at a high magnetic field. There was a sizable specific heat jump ΔC(Tc)/γTc (3.3 for AM and 3.9 for SPS), significantly higher than the value of BCS prediction (1.43). Superconducting properties of MEA suggest the intermediate coupling of the electron-phonon coupling constant λ∼1 (λel−ph≃0.89 for AM and λel−ph≃0.78 for SPS) and the intermediate to strong coupling regime. The Kadowaki-Woods plot of the compounds is located on the line of the heavy fermion system. The Uemura plot indicates that the compounds are close to the conventional BCS superconductor. The contradictory property of strongly correlated and conventional BCS-type metallic superconductivity may come from the dirty superconducting regime with high Fermi velocity. Enhancing critical current density with significantly suppressed vortex avalanches on the SPS-MEA Nb2/5Hf1/5Zr1/5Ti1/5 compound suggests possible practical applications on the bulk superconductivity.

Effects of the oxygen source configuration on the superconducting properties of internally-oxidized internal-Sn Nb3Sn wires

We successfully manufactured 12-filament rod-in-tube Nb3Sn wires with oxide nanoparticles formed by the internal oxidation method. We employed Nb-7.5 wt%Ta-1 wt%Zr and Nb-7.5 wt%Ta-2 wt% Hf alloys along with oxygen sources (OSs) in two different configurations—in the core of Nb filaments (coreOS) and at the boundary between the filaments and the Cu tube (annularOS)—to assess the influence of the OS layout on the superconducting properties and grain size. The simultaneous presence of the OS and of Hf or Zr reduced the average Nb3Sn grain size to around 50 nm, leading to an enhancement of the layer critical current density (Jc ) up to 3000 A mm−2 at 4.2 K and 16 T for the Hf-annularOS wire. Samples manufactured with an OS show a shift toward higher reduced magnetic fields of the position of the maximum in pinning-force density, this shift being more pronounced when SnO2 is added in the annularOS configuration, and for the Hf-containing samples. This enhanced pinning at higher magnetic field is beneficial for high-field magnet applications. Moreover, we measured a very high upper critical field, reaching 29.3 T at 4.2 K in the Hf-annularOS samples.

Improvement of the critical current density of alkaline water electrolysis based on the hydrodynamic similarity between boiling and water electrolysis

Since water electrolysis is a pollution-free and economical method to produce hydrogen which has a great potential as an energy carrier, it is imperative to improve the performance of water electrolysis for efficient hydrogen production. Supposing that the analogy between boiling and water electrolysis holds, the next interesting question is whether the water electrolysis performance can also be significantly improved by using a method that improves the heat transfer coefficient and the critical heat flux (CHF). The critical current density (CCD), which is the upper operation limit of water electrolysis, is considered to be one of the keys for effective hydrogen generation. However, the study on the enhancement of CCD has rarely been conducted. It is known that the boiling CHF can be improved by a honeycomb porous plate (HPP) due to two effects, capillary force and path separation of gas-liquid. In this work, we applied a cooling method using an HPP which has succeeded in improving the boiling CHF to alkaline water electrolysis. For the first time, we have succeeded in improving the CCD to approximately 1.3 times (CCD: 6.6 A/cm2) compared to without capillary force case (CCD: 5.1 A/cm2). As regards the mechanism, the effect of the liquid supply by capillary action and the improvement of the bubble discharge by separating the gas–liquid flow path using the honeycomb structure of the HPP play an important role in increasing the CCD.

Enhancements of critical current density in Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconductors by additions of SnO2 nanoparticles

The impact of adding SnO2 nanoparticles on the enhancements of critical current density (Jc) of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconductors was studied. Polycrystalline superconductors with stoichiometry of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1−x(SnO2)x where was x was ranged from 0.000, 0.002, 0.004, 0.006, 0.008 to 0.010 were made through traditional solid state reaction technique. X-ray diffraction data revealed that all fabricated samples consisted of Bi-2223 and Bi-2212 superconducting phases. The volume fraction of the Bi-2223 phase decreased with SnO2 addition. Analyses of textural structure using scanning electron microscopy data evidenced a clear decrease in grain orientation and porosity with increased doping levels. SnO2 presence in connection to Bi-2223 deceleration reduced the critical temperature. Values of Jc deduced from the magnetization hysteresis loops measured at different temperatures of 35 K, 45 K, 55 K, 65 K were found to enhance for the SnO2 added samples. In the x = 0.002 samples, the field dependent Jc achieved its maximum values. In order to have a deeper understanding in the improvements of flux pinning properties, small and large bundle fields were determined by using the collective pinning theory. The obtained values indicate the expansion of the two corresponding regimes with appropriate. By analyzing the dependence of normalized Jc versus normalized critical temperature, the dominant flux pinning mechanisms in all samples were consistent with δl pinning. Besides, the addition of SnO2 nanoparticles was likely to produce pinning centers in form of core point as evidenced by using the Dew–Hughes model.

High-field critical current density enhancement in GdBCO coated conductors by cooperative defects

Irradiation can precisely control defects in, and improve the superconducting properties of, REBa2Cu3O7−δ (REBCO, RE: rare earth) coated conductors (CCs). Here we report an effective approach for enhancing the in-field performance of GdBCO CCs. The critical current density (J c) of GdBCO films was significantly improved through cooperative defects created by co-irradiation with O ions and protons, especially at low temperatures and high magnetic fields. Surprisingly, the in-field J c of commercial CCs can be nearly doubled. The cooperative irradiation-induced defects are uniformly distributed throughout the GdBCO layer, which promotes the overall performance of the CC. Moreover, the dimensions of these irradiation-induced defects closely match the coherence length of REBCO. This simple and efficient method is a practical post-production solution to improve the in-field performance of commercial REBCO CCs.

Self‐Formed Fluorinated Interphase with Fe Valence Gradient for Dendrite‐Free Solid‐State Sodium‐Metal Batteries

AbstractThe poor anode/electrolyte compatibility and dendrite growth have discouraged the development of solid‐state sodium‐metal batteries (SSSMBs). Here, a self‐formed interphase with a unique Fe valence gradient is designed to stabilize the anode interface of Na3Zr2Si2PO12 solid electrolyte. This interphase consists of a Fe‐ and NaF‐containing outer layer near the Na anode and a Fe2+/Fe3+‐rich inner layer, which are in situ formed upon contacting Na with a sodiophilic α‐Fe2O3‐xFx interlayer specially coated on Na3Zr2Si2PO12. The NaF and Fe prevents continuous reduction reactions and homogenize the electric filed, while the iron oxide gradient layer offers buffering Na storage during plating, further suppressing dendrite growth. Benefiting from the dynamically stable, low‐impedance and dendrite‐free interface, the symmetric cells achieve a 20‐fold reduction in interfacial resistance and a fourfold enhancement in critical current density (CCD) at 25 °C, and powered a high CCD of 1.9 mA cm‐2 and a 1000‐h cycle life at 1 mA cm‐2 at 80 °C. The corresponding SSSMBs based on Na3V2(PO4)3 cathodes deliver a capacity retention rate of 96% over 120 cycles at 1 C. This robust interface design supports one of the best electrochemical performances ever reported and offers a comprehensive solution to stabilize the Na3Zr2Si2PO12/Na interface toward practical SSSMBs.

Critical current density enhancement of Nb3Sn superconducting wires by incorporating oxygen through rapid-heating method

The critical current density (Jc) still has much room for improvement for Nb3Sn superconductors. In this paper, SnO2 is doped into powder-in-tube (PIT) Nb3Sn superconducting wires as the oxygen source through rapid heating, quenching and annealing (RHQA) process. The results show that the 1.5 wt% SnO2-doped Nb3Sn has much higher Jc@4.2 K,10 T than the pure sample after RHQ at 2150 °C in 2 s. This is not the case when the Nb3Sn wires RHQ at 1700 °C. The increase in Jc is related to a decrease in grain size and an enhancement of inter-grain connectivity.

Synthesis of Three-Dimensional Carbon Nanosheets and Its Flux Pinning Mechanisms in C-Doped MgB2 Superconductors.

Three-dimensional carbon nanosheets (3D-CNS) were synthesized by salt template spray-drying method in order to solve the agglomeration of 2D nanocarbon by a traditional mixing method. MgB2 bulks doped with 3D-CNS with molar ratio composition of MgB2-x(3D-CNS)x (x = 0, 0.1 and 0.2) have been prepared by in situ sintering process. The microstructure, critical current density and flux pinning of the sintered samples have been investigated. Differing from the structure in previous studies, the 3D-CNS doping is more efficient for the refinement of the MgB2 grains due to the 3D network structures. The results clearly show that more active C releasing from 3D-CNS at high temperature can provide effective flux pinning centers by the substitution of C for B in MgB2 lattice. Furthermore, the lattice distortion and increased grain boundaries should be responsible for the enhancement of critical current density (Jc) at high magnetic fields as well as the increased irreversible magnetic field (Hirr). However, the positive action in Jc at low field has been extremely offset by the concentration of impurities at MgB2 grain boundaries such as released extra C without substitution and MgO, which is considered to further deteriorate the grain connectivity.

Drastic enhancement of magnetic critical current density in Zn doped Bi-2212

At several temperatures (T) we have studied magnetization (M) as a function of magnetic field (H) in (i) the pure Bi-2212 and (ii) the Zn doped Bi-2212 below respective critical temperatures, Tc. An enhancement in ΔM(H) in Zn doped Bi-2212 has been observed. Based on the criterion, ΔM = constant the HT diagram is found. Shifting in the irreversibility line (IL) has also been investigated. An enormous enhancement of magnetic critical current density (Jcm) in the Zn doped Bi-2212 superconductor is observed. We have analysed Jcm(H) to understand the microscopic nature of vortex pinning. A possible crossover from the collective pinning regime at lower magnetic field to a single vortex pinning with the increase in H at several T is observed in both samples having almost similar granular nature. Pinning of pancake vortices is strongly affected by the localised magnetic moment induced by nonmagnetic Zn in Cu sites. Change in the pinning force density in doped Bi-2212 has been explained.

Vortex Dynamics and Critical Current Densities in 90 K-phase and 60 K-phase YBa2Cu3O7−δ with Splayed Columnar Defects

Enhancement of critical current density (J c) was observed in YBa2Cu3O7−δ with splayed columnar defects (CDs). In the case of 90 K-phase YBa2Cu3O7−δ with splayed CDs, the enhanced J c drops suddenly at the depinning temperature of vortices from CDs (T dp), which is interpreted to be caused by the excitation of double kinks traversing neighboring CDs. In addition to the optimal 90 K-phase, where the superconductivity dominates, there is another stable 60 K-phase and other phases with different T c. This study reports temperature dependence of J c and the step-like decrease of J c in YBa2Cu3O7−δ with CDs and with different T c. Results show that the T dp is strongly related to the T c. However, additional entropic reduction of T dp may depend on parameters other than T c.

Significant enhancement of critical current density in H+-intercalated FeSe single crystal

Superconducting transition temperature (T c) and critical current density (J c) are two key factors that are not only crucial for probing high temperature superconducting mechanism, but also for practical applications. The simple crystal structure of FeSe is very favorable for the fabrication of thin films and wires, but its application is limited by the relatively low T c and small J c. Previous studies have found that the T c of FeSe can be significantly enhanced over 40 K by using protonation method. Here, we present a systematic study of J c and vortex properties of H+-intercalated FeSe (H x -FeSe) single crystals. The value of J c for H x -FeSe single crystal is significantly enhanced, exceeding 1.3 × 106 A cm−2 at 4 K, which is more than two orders of magnitude larger than 1.1 × 104 A cm−2 of pristine FeSe. The vortex pinning mechanism of H x -FeSe is found to be surface pinning, which is different from the dominant strong point-like pinning in pristine FeSe. Moreover, the systematic study of the vortex phase transition and the underlying mechanism provides a wealth of information for the vortex phase diagram of H x -FeSe single crystal. Our results confirm that the introduction of H+ intercalations into FeSe not only enhance the T c but also significantly increases the value of J c, which is favorable for practical applications.

Enhancement of self-field critical current density by several-tens-MeV ion irradiation in YBa2Cu3O7 films prepared by fluorine-free metal-organic deposition

An up to 63% enhancement in critical current density (J c) was achieved for 1 μm thick YBa2Cu3O7 (YBCO) films at self-field at 77 K by irradiation with 24–84 MeV Au ions. This enhancement is highly unusual, since in YBCO films, J c at self-field (J c sf) is generally insensitive to ion irradiation, unlike J c in magnetic fields. Our observed film-thickness dependence of the irradiation effect and our microstructure imaging indicate that this rare observation is attributed to an extremely “clean” (i.e. less-disordered) microstructure in the top 700 nm of the layer of our 1 μm thick films prepared via fluorine-free metal-organic deposition. Our results directly indicate that discontinuous 1D vortex-pinning centers (pins) that have the following features effectively enhance MA cm−2-order J c sf at 77 K of YBCO films; namely, 5–10 nm in diameter, ∼20 nm in size along a pin track, have a ∼20 nm gap between the pins in a pin track, and are directed in the c-axis.

Impact of Ti-doping position on Nb3Sn layer formation in internal Sn-processed Nb3Sn superconducting wires

Further enhancement of critical current density of Nb3Sn superconductors is still of great interest and challenging towards realization of leading-edge magnets such as the future circular collider (FCC) and demonstration Power Station (DEMO) fusion reactors. In this study, the influence of the Ti-doping position on the Nb3Sn layer formation in internal Sn-processed Nb3Sn superconducting wires, which has not been sufficiently clarified yet, was investigated using the simplest diffusion pair structure that consists of a single Nb/Cu/Sn layer. Three types of specimens were prepared, in which Ti was doped into the Sn core, Nb, and Cu matrix (denoted as ST, NT, and CT, respectively). The NbCuSnTi compound phase appeared as a diffusion barrier at the boundary between the Nb3Sn and Cu–Sn phases in the ST and CT samples and remained during the Nb3Sn layer formation, although it was absent in NT. The electron backscatter diffraction analysis of the formed Nb3Sn grain morphologies showed no significant difference in terms of the average grain size and area fraction of the equiaxed grains regardless of the doping position. However, the average Nb3Sn layer thickness of NT was at least 1.6 times larger than that of ST and CT. The absence of the NbCuSnTi phase promotes Sn diffusion into Nb, which accounts for the thicker Nb3Sn layer and much higher Ic–B characteristics in NT.

Critical current improvement and resistance evaluation of superconducting joint between Bi2223 tapes

We improved the critical current (I c) of the superconducting joint between the Bi2223 tapes by introducing the two-step sintering process. The in-field transport I c of ∼300 A at 4.2 K and 1 T under a 10−9 Ω criterion was successfully demonstrated. The I c improvement can probably be attributed to the enhancement of the intergrain critical current density for a Bi2223 intermediate layer. Ultra-low in-field joint resistance below 10−14 Ω at 4.2 K and 1 T was also demonstrated using current decay measurement. To the best of our knowledge, this study is the first to demonstrate a practical level of in-field transport I c and ultra-low in-field joint resistance for the superconducting joint between Bi2223 tapes. We believe that this superconducting joint technology will facilitate development of persistent current mode Bi2223 superconducting magnets.

Anisotropic Critical Current Densities in Ba0.6K0.4Fe2As2 with Splayed Columnar Defects

Enhancement and non-monotonic field dependence of critical current density (Jc ), called anomalous peak effect, were observed in Ba1−x K x Fe2As2 with splayed columnar defects. In principle, anisotropy of in-plane Jc should be present in this superconductor since the introduced splayed columnar defects introduce anisotropy in the plane. This study reports in-plane anisotropy of Jc observed in 2.6 GeV U irradiated Ba0.6K0.4Fe2As2 with splay angles of ±15° and ±20°. Results show that Jc component parallel to the splay plane is larger than the perpendicular component, and the parallel component contribute to the anomalous peak effect at around B Φ/3 more.

Evolution of Superconducting Properties of Coexistent Bi-2212 and Bi-2223 phases in BSCCO

The evolution of superconducting properties of BSCCO superconductors, inadvertently hosting the two superconducting phases Bi-2212 and Bi-2223 have been investigated in pristine and Pb doped BSCCO. The superconducting transition temperature TC of Bi-2212 phase monotonically increases with increasing Bi-2223 phase fraction. On the other hand Bi-2223 phase exhibits depression in TC for its lower phase fractions (<24%) but attains its bulk value as Bi-2223 phase fraction is increased to 30%. This behavior has been rationalized by invoking the interplay of proximity effects between the two coexisting phases and establishment of Bi-2223 superconducting percolation path. In addition to aiding the formation of BSCCO with higher Bi-2223 phase fraction, the Pb substitution also leads to an enhancement of critical current density by the creation of pinning centres.