Intragranular Critical Current Density Research Articles

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.

Intergrain connectivity in YBa2Cu3O7-δ superconductor added with Dy2O3 nanoparticles: AC susceptibility investigation

YBa2Cu3O7-δ (or YBCO) superconductors added with various concentrations of dysprosium oxide nanoparticles (NP-Dy2O3) were prepared using the solid-state process. The additive NP-Dy2O3 has a size of about 10 nm and presents a para/ferromagnetic transition at about 300 K. The characterization of samples was probed via XRD, TEM, SEM, DC magnetization, and AC susceptibility measurements. Some models were employed to compute superconducting parameters like intragranular critical current density under a magnetic field (Jcm(H)), the density of intragranular pinning force for Abrikosov vortex (εg(0)), intergranular critical current density (Jc,inter), intergranular electrical character, superconductor grain volume fraction (fs). The correlation between these parameters and microstructure was discussed. The inclusion of NP-Dy2O3 does not alter the structural properties and the spatial growth of YBa2Cu3O7-δ. NP-Dy2O3 addition led to significant enhancements of Jcm(H) and εg(0). The decrement in Jc,inter was attributed to the change of grain boundary characteristics that transformed from SNS to SINS junction due to NP-Dy2O3 addition.

Effect of annealing conditions on the superconducting properties of nano-sized metallic Au-added Bi1.8Sr2Au0.2Ca1.1Cu2.1Oy (Bi-2212) ceramics

In this study, the effects of annealing process on the phase formation and electrical and magnetic properties of nano-sized metallic Au-added Bi-2212 ceramics have been investigated. The Bi1.8Sr2Au0.2Ca1.1Cu2.1Oy including x = 0.2 Au content as starting composition was chosen due to the improved transport properties in the Bi-2212 system, as known in the literature. The samples for the post-annealing technique were exposed at different dwell times (10 m, 30 m, 1 h, and 2.5 h) at a fixed temperature of 870 °C after the application of normal heat treatment of 850 °C for 120 h. The XRD diagrams clearly indicate that a significant part of the phases in all the samples belongs to Bi-2212 phase. SEM results show that all the samples have randomly oriented grain forms as the main characteristic of applied solid-state method. In all cases, the post-annealed samples showed better superconducting properties of Bi-2212 phase, indicating that the increases in the dwell time positively affect its granular polycrystalline character such as inter-connectivity of the grains, the nucleation, and growth of the Bi-2212 phase. Moreover, the sample with dwell time of 2.5 h at 870 °C reveals significant enhancement in the M–H loops compared to the sample with less dwell time, despite the fact that the Bi-2212 phase can easily decompose into secondary phases such as Cu-free and Bi-free due to thermodynamic instabilities of Bi-2212 at temperatures above 860 °C. Finally, the intragranular critical current density values (Jc) have been obtained by using the data from M-H measurements according to the critical Bean model. It has been found that the Jc value (16.5 × 104 A/cm2 in 0.15 T at 15 K) of the sample in the dwell time of 2.5 h at 870 °C is higher than that of the sample (13.4 × 104 A/cm2 in 0.15 T at 10 K) with the same starting composition reported in the literature.

Impact of planetary ball milling parameters on the microstructure and pinning properties of polycrystalline superconductor Y3Ba5Cu8Oy

We have reported the influence of planetary high energy ball milling parameters on morphology, microstructure and flux pinning capability of polycrystalline Y3Ba5Cu8Oy. Samples were prepared through the standard solid-state reaction by using two different milling methods, ball milling in a planetary crusher and hand grinding in a mortar. Phase analysis by X-ray diffraction (XRD) method, microstructural examination by scanning electron microscope (SEM), electrical resistivity, the global and intra-granular critical current densities measurements are done to characterize the samples. The processing parameters of the planetary milling have a considerable impact on the final product properties. SEM observations show the presence of nanoscale entities submerged within the Y3Ba5Cu8Oy crystallites. The results show that the fine grain microstructure of the Y3Ba5Cu8Oy bulk induced by ball milling process contributes to critical currents density enhancement in the magnetic field and promotes an optimized flux pinning ability.

Highly dense and textured superconducting (Bi,Pb)2Sr2Ca2Cu3O10+δ ceramic samples processed by spark-plasma texturing

Consolidated powders of the superconducting cuprate Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) by the spark-plasma texturing (SPT), spark-plasma sintering (SPS), and the traditional solid-state reaction method were investigated by several techniques and their features compared. The results show that SPT samples exhibit a higher degree of texture, as inferred by a Lotgering factor of ∼0.73 along the [00l] direction and a relative density of 96% of the theoretical value. From magnetic hysteresis loops M vs. H at 5K, the intragranular critical current densities along two applied magnetic field orientations, Jc0c and Jc0ab, relative to the compacting pressure direction, were determined. The anisotropy factor, γJ=Jc0ab/Jc0c, yielded an estimate of ∼2 in the SPS sample and ∼19 for samples obtained via the SPT method. In the latter samples, Jc0c at 5K is close to 1.3×108A/cm2, a value higher than others found for the same compound. The temperature dependence of the electrical resistivity, ρ(T), analyzed within the framework of a current conduction model for granular superconductors, supports the higher degree of texture of SPT samples and indicates changes in the oxygen content when samples are subjected to a post-annealing heat treatment. All the results reveal the promising capabilities of the SPT method for improving volume density, texture, and grain boundary connectivity of superconducting Bi-2223 materials.

Fabrication of Large and High-Performance FeSe Bulk Superconductors by a Simple Liquid–Solid Diffusion Method

FeSe polycrystalline superconductors with dimensions over 10 × 10 × 3 mm 3 were fabricated by diffusing liquid Se into an iron tablet at 650 °C. Scanning electron microscopy and X-ray diffraction analyses were performed on the FeSe samples, and they showed that the main phase throughout the bulk is tetragonal β-FeSe and the grains are well crystallized and connected. The critical transition temperature (onset) was determined to be 12 K, with a transition width of 3 K, by a resistivity measurement. The upper critical fields H c2 (0) was estimated to be 40 T, and the intragranular critical current density estimated from the Bean model is about 1.5 × 10 5 A/cm 2 at 4 Kin self-field. These results suggest that liquid-solid diffusion is a promising technique for fabricating large and high-quality FeSe bulk superconductors.

Effect of Silver Addition to Superconducting SmFeAsO1−x F x

We investigate the effect of silver addition to polycrystalline Sm-1111 superconductor. We show that Ag improves the phase homogeneity of the samples drastically reducing the weight of the low temperature, hence, leading to less fluorinated phases. The intragranular critical current density is enhanced by adding a small amount of Ag in all pinning regimes but a higher content of Ag leads to a decrease of this quantity. A tentative explanation for this dependence is proposed.

Biopolymer mediated synthesis of plate-like YBCO with enhanced grain connectivity and intragranular critical current

We present a biochemical synthesis protocol for the efficient production of strongly anisotropic, plate-like crystallites of YBa2Cu3O7–δ (YBCO) of typical dimension 6 μm × 6 μm × 1 μm. The hierarchical structure of these crystallites, revealed by transmission electron microscopy, is responsible for an unprecedented bulk intragranular critical current density reaching 0.1 MAcm−2 at 77 K—an order of magnitude higher than commercially sourced powder material. Further, we show that a naturally-occurring close alignment of adjacent plate-like grains leads to an electrical connectivity that allows an intergranular supercurrent to flow. This work provides an important starting point for an alternative route to the synthesis of YBCO conductors that has the potential to overcome many of the limitations of existing thin film based approaches.

Comparative Study on the Profiles of Intra-Granular Critical Current Density in SmBCO and YBCO Coated Conductors

We measured the magnetic hysteresis loops (M-H loop) of SmBCO coated conductor (CC) and YBCO-CC by using SQUID-magnetometer. These samples were fabricated by RABiTS method and IBAD method. We found the peak shifts of their M-B loops were qualitatively different. To understand this, we measured the magnetic field profiles, H(x), of SmBCO-CC and YBCO-CC by using scanning Hall probe method and calculated their current profiles, J(x). We found that the contrasting difference of M-B loops of the two types of CC was partly due to the inhomogeneous distributions of field and current, which depend on the sample shapes.

Bulk and Local Magnetic Properties of Iron-Based Oxypnictide Superconductor SmFeAsO1-xFx

We have characterized bulk and local magnetic properties of iron-based oxypnictide superconductor SmFeAsO 0.7 F 0.3 polycrystalline sample ( T c ∼53 K) synthesized at ambient pressure and NdFeAsO 0.7 ( T c ∼52 K) synthesized at high pressure by using SQUID magnetometer, micro-Hall probe, and magneto-optical imaging technique. Intragranular critical current densities evaluated from bulk magnetization and local magnetic profile give values of about 1×10 5 A/cm 2 at 10 K in both compounds. Magnetic field profiles of both samples are far from Bean-like, suggesting that intergrain connection is not strong. Low-field characteristics including flux-penetration field are measured by using a micro-Hall probe. Obtained results are compared with data on high temperature superconductors.

The Influence of Neutron Irradiation on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3O z Superconducting Phase: The Role of the Grain Edge

Using the transport and magnetization measurements the influence of neutron irradiation at a fluence of 5x10$^{17}$ n cm$^{-2}$ on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3Oz has been investigated. The neutron irradiation was found to decrease critical temperature and transport critical current density, increase the residual and normal state resistivity, and improve the intragranular critical current density with 1.6x10$^{57}$ A/cm$^{2}$ (at 77.3K and in the applied field up to 160 kA m) and \Delta Mirr/\Delta Mnonirr ratio (up to factor of 3) at highest field used for investigation. The field dependence of this ratio, which is below the unity at very low field but higher than 1 at high fields, correlated with the shape of the hystertic loops as well as with the change of the transport parameters after irradiation suggests the role of the irradiation induced effects on the grain edges. We discuss these effects in the framework of the Bean-Livingstone surface barriers and geometrical barriers.

The influence of neutron irradiation on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3O z superconducting phase: The role of the grain edge

Using the transport and magnetization measurements, the influence of neutron irradiation at a fluence of 5 × 1017 n cm−2 on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3O z has been investigated. The neutron irradiation was found to decrease critical temperature and transport critical current density, increase the residual and normal state resistivity, and improve the intragranular critical current density with 1.6 × 105 A/cm2 (at 77.3 K and in the applied field up to 160 kA m) and ΔM irr/ΔM nonirr ratio (up to factor of 3) at highest field used for investigation. The field dependence of this ratio, which is below the unity at very low field but higher than 1 at high fields, correlated with the shape of the hysteretic loops as well as with the change of the transport parameters after irradiation suggests the role of the irradiation-induced effects on the grain edges. We discuss these effects in the framework of the Bean-Livingstone surface barriers and geometrical barriers.

Spray Pyrolysis of<tex>$rm YBa_2rm Cu_3rm O_7-rm x$</tex>Coated Conductors on

YBa/sub 2/Cu/sub 3/O/sub 7-x/ films have been deposited using spray pyrolysis on (100) SrTiO/sub 3/ substrate. An extended study on the optimization of the composition, carrying gas flow, deposition temperature as well as annealing time was performed. It was found that these parameters are strongly correlated and affect the morphology, orientation and superconducting properties of the YBCO films. As grown films already exhibit J/sub c/ values of 10/sup 4/ A/cm/sup 2/, thus indicating that the correct structure is already formed during deposition. It was found that the temperature gradient in the pyrolysis zone played a fundamental role during the deposition. After modification of this heat gradient by adding a metallic susceptor, a noticeable improvement in the properties of the films was obtained. An in-plane orientation FWHM value of 0.70/spl deg/ was measured from the (102) pole figure. The films exhibited a T/sub c/ onset of 91 K (/spl Delta/T/sub c/=1.5 K), while the J/sub c/ value at 77 K in self-field approached 10/sup 5/ A/cm/sup 2/. Based on an assumed typical intragranular critical current density, we found a 40/spl times/40 /spl mu/m area in our best film where the assumed critical current density is well above 10/sup 6/ A/cm/sup 2/.

MO observation of flux penetration into high- Tc superconductors with grain boundaries

Effect of grain boundaries on the magnetic field distributions in YBCO was studied by use of magneto-optical (MO) imaging technique. The grain boundary was artificially introduced with a multi-seeded melt-growth process. The current distribution in the sample was obtained from the MO image using an inversion scheme based on the inverse-matrix method. With this technique, we could obtain intergranular and intragranular critical current densities. Large depression of the intergranular critical current was observed in the sample with large misorientation angles.

Anomalies of AC susceptibility losses in the doped[Bi(Pb)]2Sr2Ca2Cu3Ox superconductor

AC susceptibility measurements have been performed onBi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox (Bi-2223) samples doped with different Li-based compounds and prepared by thesolid-state method. As-prepared samples and/or samples annealed in oxygen or argon,ground or unground, have been investigated in detail in order to understandthe occurrence, nature and evolution of the anomalous peaks observed in curves versus the measuring parameters; we have detected up to four peaks instead of theusual two peaks observed in the non-doped samples. It was found that intrinsicphysical–chemical properties, such as the melting temperature of the doping compound, areno less important for the final properties of the superconductor than their insertionproperties into the crystal lattice of Bi-2223. Doping compounds with melting temperaturesbelow or close to the phase formation temperature of the Bi-2223 phase can act as flux,changing the growth conditions. Intensification of some processes against others(e.g. decomposition–recovery of the Bi-2223 phase, solubilization–precipitation of thesecondary phases, changes in the properties of the liquid phase, etc) can lead to theformation of the Bi-2223 phase with different properties than for the non-dopedsuperconductor. Generally, when using flux-type doping compounds, anomalous AC lossespeaks are detected and the intra-granular critical current density is enhanced.

Effect of the magnetic moments of Gd on the superconductivity in the infinite-layer superconductor Sr 0.9Gd 0.1CuO 2

We report the synthesis of Sr 0.9Gd 0.1CuO 2 and its superconducting properties. The low-field magnetization, the structural analysis, and the value of the paramagnetic moment of the Gd ion ( μ∼7.6 μ B/Gd) showed a homogeneous doping of the samples. By a comparison of Sr 0.9Gd 0.1CuO 2 with Sr 0.9La 0.1CuO 2, we found that the T c was not sensitive to the presence of the large magnetic moments due to the Ln ions sandwiched between two neighboring CuO 2 planes. This is rather contrasting with the large pair-breaking effect when the magnetic element Ni is between the CuO 2 planes. A correlation of the values of the T c and the tetragonal a-axis lattice constant was discussed between (Ln,Ce) 2CuO 4 and (Sr,Ln)CuO 2. The irreversibility field line and the intragranular critical current density were measured to probe the pinning properties and the pinning strength were nearly the same for Ln=La and Gd.

Magnetic properties of Bi 1.7Pb 0.4Sr 1.5Ca 2.5Cu 3.6O x/(LiF) y superconducting system

AC complex susceptibility (with and without a superimposed DC field) and DC magnetization measurements on (Bi,Pb)-2223 high-temperature superconductors with various amounts of LiF are presented. The results are discussed in the frame of the critical state model. The values of the intra- and inter-granular critical current density as well as of fields for full penetration are estimated. It can be seen that, in Bi 1.7Pb 0.4Sr 1.5Ca 2.5Cu 3.6O x /(LiF) y , various amounts of LiF change the superconducting properties of both the grains and the inter-grain matrix. The intra-granular critical current density has similar values from both AC susceptibility and DC magnetization measurements, its highest value being attained for y=0.15. For all LiF-doped samples, a split of the peak corresponding to the dissipation in the grains was observed.

Determination of inter- and intragranular currents in high temperature superconducting tapes and coated conductors

The inter- and intragranular critical current densities were determined for different types of coated conductors as well as mono- and multifilamentary (BiPb)2Sr2Ca2Cu3Ox tapes. Either the inter- or the intragranular critical current density was changed systematically by bending the tapes or by neutron irradiation, respectively. Thus, we are able to assess these two critical current densities, even in samples with very good grain connectivity.

The effects of crystallization on the magnetic properties and critical current in Bi–Sr–Ca–Cu–O glass–ceramics

We report on the influence of crystallization on the dc magnetization, the ac susceptibility, and the intergranular and intragranular critical current density of Bi4Sr3Ca3Cu4Ox crystallized glass. The samples, characterized by x-ray diffraction, contained mainly a Bi2Sr2Ca1Cu2O8 superconducting phase. The transition to the superconducting state was investigated by magnetic methods: dc magnetization and ac susceptibility. All the samples exhibited diamagnetic properties below 80 K, which is in agreement with the critical temperature of the Bi2Sr2Ca1Cu2O8 phase. The superconducting volume fraction and the values of critical current were evaluated from the magnetization measurements of the samples cooled in an applied magnetic field and the measurements of magnetization hysteresis. The values of critical current for all the samples were quite small, in the range of 50–100 A cm−2 for intergranular current, depending on the amount of superconducting phase in the sample.

The Influence of the Polycrystalline State and Partial Dy Substitution on the Superconducting Properties of YBCO

The influence of the quasi-equal partial substitution of non-magnetic (Y3+)/magnetic (Dy3+) ions in YBa2Cu3O7—y on the superconducting properties of the material has been investigated. To minimize the influence of the stress field induced by lattice mismatch, Dy-substituted YBa2Cu3O7—y was studied because Y3+ and Dy3+ ions have similar ionic radii. The investigation was performed on polycrystalline and powder samples with general formula DyxY1—xBa2Cu3O7—y (x = 0.4–0.6). Higher magnetic losses and intragranular critical current density Jc were observed for partially substituted samples in comparison with DyBCO. The strongest influence of magnetic substitution on the electrical resistivity properties was observed in the mixed state.