Jc Characteristics Research Articles

Three-dimensional characterization of BaHfO3 precipitates in GdBa2Cu3O7-y flim using STEM tomography.

IntroductionSince the discovery of REBa2Cu3O7-y (RE: Rare Earth element, REBCO) superconductors, they have been expected as the best candidates for the power cable application due to its high critical temperature (Tc) and critical current density (Jc). Among those REBCO superconductors, GdBa2Cu3O7-y (GdBCO) have been receiving great interest because they have higher Tc and Jc than YBa2Cu3O7-y [1].GdBCO with various types of precipitates as artificial pinning centers (APCs) have been proposed to minimize the anisotropy of Jc characteristics under the magnetic field. Among those precipitates, BaHfO3 (BHO) was found most effective precipitates as APCs in GdBCO film prepared by pulsed laser deposition (PLD) method [2]. It is therefore necessary to investigate not only the morphologies but also the dispersion of BHO precipitates within the GdBCO, to understand the role of BHO for the superconducting characteristics. In this study, morphologies and dispersions of BHO precipitates were characterized three-dimensional by scanning transmission electron tomography ExperimentalBHO dispersed GdBCO films were fabricated on Hastelloy C-276TM substrates with buffer layers of CeO2/LaMnO3/MgO/ Gd2ZrO7 by PLD method.To observe microstructure of GdBCO film with BHO precipitates, cross-section TEM specimens were prepared by FIB method using Quanta 3D-200 (FEI, USA) with acceleration voltage from 2 to 30 kV. Three-dimensional information such as morphology and dispersion, of BHO precipitates were characterized by electron tomography using STEM-HAADF. Result and discussionFigure1 shows three-dimensional reconstructed volume of BHO precipitates in GdBCO, which revealed that fine BHO precipitates have rod- and plate-like morphologies with homogeneous dispersion in GdBCO. In addition, growth directions of these precipitates were found with wide angular distributions from growth direction of GdBCO. Anisotropy of Jc in the magnetic fields was probably enhanced by various growth directions and homogeneous dispersion of nanosized BHO within GdBCO.jmicro;63/suppl_1/i26/DFU080F1F1DFU080F1Fig. 1.Three-dimensional reconstructed volume of BHO.

Current-carrying capacity of HTS DC cables with the reduced Lorentz force

The structure of superconducting DC cable made with high temperature superconducting tapes is designed to improve the current-carrying capacity by reducing the Lorentz force acting on flux lines. For this purpose an axial magnetic field is produced by the outer shield conductor. The analysis was performed for the optimum structure for various superconducting tapes with different Jc(B,θ) characteristics. It is found that the current-carrying capacity increases appreciably when the difference in the critical current density of the tape is large enough between normal and parallel magnetic fields.

Comparison of Jc characteristics in PIT wires based on BaFe2As2 with different substitutions

Three kinds of superconducting wires based on BaFe2As2 with different substitutions are fabricated using powder-in-tube method and characterized including magneto-optical imaging. In the case of (Ba,K)Fe2As2 wires processed by hot isostatic press, critical current density (Jc) of 32 kA/cm2 has been achieved at 4.2 K under self-field. Wires fabricated in a similar way with Ba(Fe,Co)2As2 resulted in much lower Jc of 7.8 kA/cm2 at 4.2 K under self-field. In the case of BaFe2(As,P)2, Jc of ambient-pressure processed wire has Jc of only 1.0 kA/cm2 at 4.2 K under self-field. Origins of these differences are discussed.

In-field performances of commercial REBCO tapes below liquid nitrogen temperatures

We investigated critical current density (Jc) characteristics of commercial REBCO tapes of four manufacturers at temperatures between 30 and 77K in magnetic fields up to 5T. We first examined variation in the Jc characteristics of two Zr-doped REBCO tapes (SuperPower) of the same specifications, which are found to be quite different, indicating that the in-field Jc characteristics due to artificial pinning centers vary among spools or along the length of tape.We then investigated in-field performances of four different commercial REBCO tapes (AMSC, Fujikura, SuNAM, SuperPower), calculating performances of coils using their magnetic-field angle dependences of Jc. The REBCO tapes are found to give very different in-field performances depending on the strength and direction of field they experience, and their relative superiority is observed to vary with temperature.

Flux Pinning Properties and Microstructures of Multilayered Films Consisting of Sm1.04Ba1.96Cu3Oy Layers and BaSnO3-Doped Sm1.04Ba1.96Cu3Oy Layers

In order to enhance Jc in magnetic fields for all applied angles, we fabricated multilayered films consisting of Sm1.04Ba1.96Cu3Oy (SmBCO) layers and BaSnO3 (BSO)-doped SmBCO layers on MgO substrates (multilayered SmBCO) by the pulsed laser deposition (PLD) method. We varied the numbers of layers (8, 16, 32, and 64). In the magnetic field angle dependence of Jc (B = 1 T, 77 K), only in the 8-layer sample was Jc higher than that of pure SmBCO thin films for all applied angles. The other sample showed different Jc characteristics.

Trapping Effect on Electrical Behavior of Polyester Film. II: Bipolar Injection

The time evolution of conduction current Jc(t) determined experimentally, in polyethylene terephthalate, at 373 K, was simulated by using a bipolar charge (electrons and holes) model with injecting electrodes including dipoles with the relaxation time τ and a discrete set of localized levels with a density Nt. The numerical calculation showed that the Jc(t) characteristics are significantly affected by the carrier charge motion and depend on the model parameters.

Numerical Simulation of MgB<sub>2</sub> Superconducting Magnetic Energy Storage Coil

A coupled thermal electromagnetic finite element analysis has been used to numerically simulate the electromagnetic characteristics of an MgB2 SMES coil. Magnetic field distribution data and current density predictions of the numerical model were compared with the literature and with the superconducting properties of explosively consolidated MgB2 samples measured experimentally. The material Jc characteristics were determined by applying Bean’s critical state model on the material magnetisation measurements conducted on a superconducting quantum interference device (SQUID).

OS7-2-2 溶液法によりBaZrO_3を導入したYBa_2Cu_3O_7薄膜の磁束ピンニング特性(OS7 最先端材料が拓くマイクロ・ナノ工学の新展開(2))

We have investigated the crystallization process of YBa_2Cu_3O_7 (YBCO) films with BaZrO_3 (BZO) to enhance critical current density, Jc. In order to control and optimize the microstructures of YBCO films during the crystallization process, the precursor films were heated up to 600℃ for 0, 60, 180, 540 min before YBCO crystallization. From XRD results, the peak intensity of BZO (110) was found increased with the film kept 600℃ for the longer period, which suggested that BZO was crystallized lower than at 600℃. Moreover, the film kept at 600℃ for 180 min showed improved Jc characteristics of 7.77×10^4 A/cm^2 at 3 T (B//c) at 77.3 K, which was 2.5 times higher than the film without keeping as 3.04×10^4 A/cm^2. These results suggest that microstructures and Jc characteristics could be improved greatly by controlling the heat treatment during the crystallization process.

Nanorod Self-Assembly in High Jc YBa₂Cu₃O₇-x Films with Ru-Based Double Perovskites.

Many second phase additions to YBa2Cu3O7−x (YBCO) films, in particular those that self-assemble into aligned nanorod and nanoparticle structures, enhance performance in self and applied fields. Of particular interest for additions are Ba-containing perovskites that are compatible with YBCO. In this report, we discuss the addition of Ba2YRuO6 to bulk and thick-film YBCO. Sub-micron, randomly oriented particles of this phase were found to form around grain boundaries and within YBCO grains in bulk sintered pellets. Within the limits of EDS, no Ru substitution into the YBCO was observed. Thick YBCO films were grown by pulsed laser deposition from a target consisting of YBa2Cu3Oy with 5 and 2.5 mole percent additions of Ba2YRuO6 and Y2O3, respectively. Films with enhanced in-field performance contained aligned, self-assembled Ba2YRuO6 nanorods and strained Y2O3 nanoparticle layers. A 0.9 µm thick film was found to have a self-field critical current density (Jc) of 5.1 MA/cm2 with minimum Jc(Θ, H=1T) of 0.75 MA/cm2. Conversely, Jc characteristics were similar to YBCO films without additions when these secondary phases formed as large, disordered phases within the film. A 2.3 µm thick film with such a distribution of secondary phases was found to have reduced self-field Jc values of 3.4 MA/cm2 at 75.5 K and Jc(min, Θ, 1T) of 0.4 MA/cm2.

Comparison on Effects of ${\rm B}_{4}{\rm C}$, ${\rm Al}_{2}{\rm O}_{3}$, and SiC Doping on Performance of ${\rm MgB}_{2}$ Conductors

Several MgB2 monofilamentary samples are prepared to evaluate the effects that the doping compounds B4C, Al2O3, and SiC have on critical current density (Jc) and the Jc dependency of magnetic flux density (B) of the sample. All of the samples in this study have Nb sheaths and are manufactured using in situ precursor powders and the Powder-in-Tube fabrication method. The amounts of added impurities are 10 wt.% for B4C and Al2O3, and 3, 10, and 20 wt.% for SiC. A reference sample without any doping is also prepared. All of the samples are heat treated between 650 and 800°C for 30 minutes. The transport Jc(B) characteristics are measured at 4.2 K and the magnetic Jc(B) behavior is obtained in varied temperatures up to 30 K. The changes in connectivity, or effective cross-section, are also evaluated by performing resistivity measurements on the samples after removal of the sheath. Furthermore, the pinning forces of the samples are evaluated from the magnetic measurements.

Effect of fabrication route on density and connectivity of MgB2 filaments

Series of samples was manufactured to test the effect of fabrication route on the density of the polycrystalline core, the connectivity between MgB2 grains and also the critical current density of undoped MgB2 conductors. All the samples had titanium sheaths and were manufactured using the Powder-in-Tube method. The Ti tubes were filled with either in situ, ex situ, or 60%–40% mixture of in situ and ex situ powders. After powder packing, the samples went through different deformation steps such as rotary swaging, two-axial rolling, pressing, cold isostatic pressing, or some combination of these, to form monofilamentary tapes. The core density was qualitatively estimated by measuring the Vickers microhardness from several locations of the ceramic filament. The changes in connectivity, or effective cross-section, were evaluated by performing resistivity measurements on the MgB2 cores after removal of the metallic sheath. The Jc characteristics were measured at 4.2 K and at variable external magnetic flux densities.

Burned Rice Husk: An Effective Additive for Enhancing the Electromagnetic Properties of MgB2Superconductor

We investigated the effect of doping of burned rice husk which contains ultrafine SiO2 and highly reactive carbon, on the crystal lattice and superconducting properties of MgB2 superconductor prepared by an in situ powder in sealed tube method. XRD, TEM, and magnetic measurements confirm the substitution of carbon atoms at boron sites in the MgB2 lattice and the formation of intragrain nanoinclusions in MgB2. From JC (H) characteristics, doped samples show a drastic enhancement of JC compared with pure MgB2. The enhancement of in-field JC values is due to the flux pinning on lattice defects produced by C substitution and nanoscale inclusions of impurity phases.

Dependence of the Pinning Property on the Superconducting Layer Thickness of CVD-processed YBCO Tape

The dependence of the transport and magnetization critical current density (Jc) characteristics on the superconducting layer thickness (d) was investigated for IBAD/CVD-processed, YBCO-coated conductors. It is believed that the decrease in Jc with increasing d in the low magnetic-field region is caused by degradation of the superconducting layer structure. The irreversibility field (Bi) increased in the low electric-field region as the thickness increased, whereas it decreased in the usual electric-field region. The apparent pinning potential (U0*) estimated using magnetic relaxation measurement also showed a complicated dependence on thickness. The results observed were approximately explained by the prediction of the flux creep-flow model.

Effect of Dy Substitution at the Sr Site on the Critical Current Density and Flux-Pinning Properties of (Bi, Pb)-2212 Superconductor

The effect of substitution of the rare earth Dy on the critical current density and flux-pinning properties of (Bi, Pb)-2212 system prepared by a solid-state synthesis in bulk polycrystalline form was studied. Phase analysis, microstructural investigation, and superconducting characterization were performed to evaluate the relative performance of the samples. The XRD and EDS analyses show that Dy atoms are successfully substituted in place of Sr in the system. The critical temperature (TC), critical current density (JC), and field dependence of JC of the Dy-substituted samples are found to be highly enhanced for optimum doping levels. The flux-pinning force (FP) calculated from the field-dependent JC values shows that the irreversibility lines (IL) of the Dy-substituted (Bi, Pb)-2212 shift toward higher fields to different extents depending on the value of Dy stoichiometry (x). The samples with x=0.2 show a maximum FP of 135.1 × 104 N/m3 and the peak position of FP shifts to higher fields (0.80 T) as against 2.0 × 104 N/m3 and 0.12 T for the pure sample. Also, the values of the self-field JC and pinning potential (U0) are maximum for this sample (x=0.2). The enhancements of JC(B) characteristics, and the values of U0 and FP are explained on the basis of the hole optimization and formation of point defects due to the substitution of Dy into the (Bi, Pb)-2212 system.

Enhancement of critical current density and flux pinning properties of Gd-doped (Bi, Pb)-2212 superconductor

The enhanced critical current density (JC) and flux pinning properties of Bi1.7Pb0.4Sr2-xGdxCa1.1Cu2.1O8+δ (where x=0.0, 0.1, 0.2, and 0.3) system prepared by solid-state synthesis in bulk polycrystalline form were studied. Phase analysis, microstructural investigation, and superconducting characterization were performed to evaluate the relative performance of the samples. The x-ray diffraction and energy dispersive spectroscopy analyses show that Gd atoms are successfully doped in place of Sr in the system. It is found that Gd in (Bi, Pb)-2212 enhances the critical temperature (TC), JC, and flux pinning strength of the system. The flux pinning force (FP) calculated from the field dependant JC values shows that the irreversibility line of the Gd-doped (Bi, Pb)-2212 shift toward higher fields to different extents depending on the value of x. The samples with x=0.2 show maximum FP of 645 kN m−3 and the peak position of FP shifts to higher fields (0.68 T) as against 26 kN m−3 and 0.12 T for the pure sample. Also, the values of self-field JC and pinning potential (U0) are maximum for this sample (x=0.2). The enhancements of TC, self-field JC, JC(B) characteristics, U0, and FP are explained on the basis of the hole optimization and formation of point defects due to the doping of Gd in (Bi, Pb)-2212 system.

Transient Stability Characteristics of a 1-m Single-Layer YBCO Cable

YBCO tapes are expected to be used in future high temperature superconductor (HTS) applications as they have better Jc characteristics at high temperatures and in high magnetic fields. For power applications such as transmission cables, YBCO tapes and a copper former are connected in parallel and they might be subjected to a short-circuit fault current that is 10 to 30 times the normal operating current. Therefore, the over-current behavior, including the hot-spot and the distribution of transport current between the copper-laminated YBCO tapes and the copper former, is very important to examine the stability and feasibility of the cable. This paper describes the experimental results for over-current pulses of a 1-m single-layer cable fabricated with five copper-laminated YBCO tapes and a copper former. Further, we performed numerical simulations by using a newly developed computer program based on the 3D finite element method.

Full penetration current variation of a superconducting tube

It is well known that the critical current density Jc of a superconducting material depends on the magnetic field B. If magnetic independent Jc is chosen for analytical calculation of current distribution, the critical current Ic0 corresponds to full penetration current Ip. Ic0 is a measured current with 1μV/cm criterion and Ip is a calculated current. The aim of this paper is to present Ip variation of superconducting tube. To calculate Ip, which is depending on the material itself, a linear function Jc(B) is sufficient to obtain realistic values by analytic way. We need to have a linear Jc(B) law (Jc(B)=JC0.(1-|B|/BJ0) that is close to the measured Jc(B) characteristics presented in this paper. The linear Jc(B) law chosen was used for the calculation of the distribution of both magnetic field B(r, t) and the current density J(r, t). These distributions allow the analytical calculation of Ip. We present the variation of Ip with material characteristics and geometric parameters of the tube. The two main results are presented. Ip decreases when BJ0 increases for same JC0. Ip increases when the tube internal radius Rin increases for same tube section. For AC losses versus current curves, Ip is the frontier between low and high losses. So the present results, allow designing future transport current superconducting cable.

Degradation of YBCO coated conductors caused by over-current pulses

YBCO tapes are expected to be used in future high temperature superconductor (HTS) applications because they have excellent Jc characteristics at high temperatures and in high magnetic fields. For application to electric power devices such as transmission cables, transformers, and fault current limiters, the YBCO tapes might be subjected to a short-circuit fault current that is 10–30 times the normal operating current. In a worst-case scenario, YBCO tapes may degrade and burn. Therefore, it is important to clarify the mechanism of the degradation caused by an over-current pulse. This paper describes the experimental results of the degradation of the YBCO tapes through a series of over-current pulse tests. We focussed on the degradation temperature and carried out the experiments with different bending strains. Measurements were performed as a function of the amplitude of an over-current pulse for an operating temperature of 80 K (Gifford-McMahon cryocooler was adopted) in a self-field. We also examined a tape after the experiments with magneto-optical (MO) imaging, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction patterns.

Influence of reactivity of sheath materials with Mg/B on superconducting properties of MgB2

We investigated the influence of reactivity of commonly used sheath materials (Fe, SS, Cu, and Ni) with Mg/B, processed by in situ powder in sealed tube method on superconducting properties of MgB2. X-ray diffraction characterization of samples yields quantitative data of the volume fraction of MgB2 core, whereas magnetic measurements show the influence of added sheath materials on TC , JC(H), Hirr, and flux pinning behavior of MgB2. Our comparative study gives better phase purity, JC(H) characteristics, and flux pinning behavior for Fe and SS added samples, which shows the suitability of Fe and SS as sheath materials in MgB2 wire/tape fabrication.

Doping and effect of nano-diamond and carbon-nanotubes on flux pinning properties of MgB2

Doping effects of two types of nano-carbons: nano-diamond and carbon-nanotubes (CNTs), on the flux pinning properties of MgB2 bulk materials have been studied. Compared with nano-diamond, CNTs is prone to be doped into MgB2 lattice. Nano-diamond doping improves Jc(H) characteristics more significantly than CNTs doping in MgB2. TEM analysis reveals a unique microstructure in diamond-doped MgB2, which consists of tightly packed MgB2 nanograins (50–100nm) with dense distribution of diamond nanoparticles (10–20nm) inside the grains. Relatively, such a unique microstructure is not easy to form in CNTs-doped MgB2 due to an active reaction between CNTs and MgB2.