Critical Current Density Of Samples Research Articles

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.

Effect of Yb substitution in Bi-2212 ceramics prepared by laser floating zone technique

In the present work, the influence of Yb substitution for Bi on the structural, electrical and magnetic properties of textured Bi-2212 ceramics has been investigated. X-ray diffraction studies indicated that the major peaks correspond to the Bi-2212 phase. The SEM images clearly show that there is an increase in the number of secondary phases with raising Yb content while all samples maintain similar grain morphology. Magnetic analysis of all samples has been done by magnetic hysteresis measurements, indicating that an enhancement in the M-H loops is obtained by a low Yb doping. The critical current density of samples was calculated from the M-H curves by using Bean’s critical state model, indicating that sample with 0.05 Yb substitution possesses the highest J c values.

Intergranular Coupling, Critical Current Density, and Phase Formation Enhancement of Polycrystalline Bi1.6Pb0.4Sr2Ca2Cu3O10−y Superconductors by α-Al2O3 Nanoparticle Addition

In this work, the effect of alumina (α-Al2O3) nanoparticle addition on the phase formation and superconducting properties of Bi1.6Pb0.4Sr2Ca2Cu3O10−y ((Bi,Pb)-2223) system has been investigated. Six samples with different alumina nanoparticle contents (0.0, 0.1, 0.2, 0.3, 0.5, and 1 wt % of the sample’s total mass) were prepared by conventional solid-state reaction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods have been used to study phase formation and microstructure of the prepared samples, respectively. Also, electrical resistivity and critical current density of the prepared samples were measured by four-probe technique. AC susceptibility of the samples has been measured by an LCR meter. XRD results showed that addition of small amounts of the alumina nanoparticles improves (Bi,Pb)-2223 phase formation significantly. Temperature dependency of AC susceptibility measurements revealed that addition of α-Al2O3 nanoparticles improves the intergranular coupling. The I-V measurements show that critical current density of samples increased from about 36 A/cm 2 for the alumina nanoparticle-free sample to about 107 A/cm 2 for the sample with 0.5 wt % α-Al2O3 nanoparticles.

Jc enhancement and flux pinning of Se substituted YBCO compound

Y2/3 Se1/3Ba2Cu3Ox compound was fabricated by using solid state fabrication technique. Optimum heat treatments conditions for Y0.77Se0.33Ba2Cu3Ox were investigated. It was determined that the XRD results of these samples were similar to Y-123 phase with some impurities. Magnetization dependence of applied magnetic fields was measured in the range of 0–9 T at 10–50 K. The symmetric and asymmetric M–H loops were obtained for the samples. Magnetization loops obtained from measurements were successfully described by the extended Valkov–Khrustalev model. The temperature and applied magnetic field dependencies of magnetization of sample were estimated and critical current density of samples was calculated by Bean model and pinning force of samples was calculated by using Lorentz force. It is found from critical current density values that Se additions were acted as a pinning center which increased critical current density.

Microstructure and critical current of bimetallic sheathed Bi-2223 tapes

To reduce the cost of Bi-2223 superconducting tapes, we prepared Bi-2223 tapes by the powder-in-tube process using a bimetallic sheath consisting of Ag and Ni. Ag was in contact with the superconducting ceramic core and acted as a protective layer against reaction between the external Ni sheath and the internal superconducting core. We remove Ni on one edge of the tape in order to provide a path for oxygen diffusion. After two step heat treatments, the critical current density of sample is 9307Acm−2. SEM photographs and XRD results show that there are some Bi-2212 phase in samples conducted two step heat treatments. It is suggested that the heat treatment process should be optimized in the future research in order to decrease the thickness of NiO layer, to reduce the fraction of Bi-2212 phase, and to improve superconducting performance of Bi-2223/Ag/Ni tape.

The Magnetic and Structural Properties of SiC-Doped MgB2 Bulks Prepared by the Standard Ceramic Processing

According to general formula MgB2−xSiCx (x = 0, 0.05, 0.1, 0.2), MgB2 and SiC-doped bulk superconduc- tors were prepared by the standard ceramic processing. The mixtures of the corresponding powders were sintered at 750 °C for 0.5 h under pressure of 8 bar Argon. X-ray dif- fraction patterns show that all the samples have MgB2 as the main phase with a very small amount of MgO; further, with SiC-doped, the presence of Mg2Si is also noted. The magnetization-temperature measurements showed a transi- tion temperature of 37.5 K for the undoped sample which indicates the typical transition temperature of MgB2. When the content of SiC increased in the sample, the transition temperatures decreased to the lower temperatures system- atically. The M-H loops measured using a VSM showed very large magnetization value at low temperature for SiC doped samples. The largest M-H loops were taken from the sample contains 5% SiC. The critical current density of samples calculated from M-H loops indicated a value of around 4 × 10 5 A/cm 2 , which is in good agreement with the literature.

Properties of seven-filament in situMgB2/Fe composite deformed by hydrostatic extrusion, drawing and rolling

Seven-filament MgB2/Fe wires and tapes were made by in situ processing using hydrostatic extrusion, rolling and drawing.Microhardness measurements have shown that the density of as-deformed cores reflects theapplied deformation and follows the iron sheath hardness. The filament size was reduced from245 µm downto 19 µm by rolling and the critical current densities of samples with different coresizes and deformation routes were compared. The highest current density wasmeasured for the tape deformed by two-axial rolling and a filament size of60 µm. Thinner filamentsshow lower Jc values due to hard inclusions present in low-purity boron powder (boron oxide), whichreduce the transport current substantially. The obtained results show that a propercombination of extrusion and rolling deformations leads to high filament density in wiresand tapes, which results in high transport current density.

The study of phonon modes of Cu 1− xTl xBa 2Ca 3Cu 4O 12− y superconductor thin films by FTIR absorption spectroscopy

The superconducting properties of Cu 1− x Tl x Ba 2Ca 3Cu 4O 12− y thin films prepared by amorphous phase epitaxial (APE) method have been studied, by resistivity measurements, critical current density measurements, infrared spectroscopy and X-ray diffraction. The resistivity measurements of all the samples have shown metallic variation down to onset of superconductivity and T c in the range of 95–112 K. The critical current densities of samples were also measured and it was observed that the samples with higher thallium contents in the unit cell have low critical current density, J c (∼10 3 A/cm 2) while lower thallium contents in the material give, higher critical current density J c (∼10 6 A/cm 2). The XRD measurements showed the material to be single phase and oriented along c-axis. The φ-scan of (1 0 3) reflection of Cu 1− x Tl x -1234 material showed the crystal to be a-axis oriented. The main emphasis of this research work is on the study of phonon modes of vibration of different atoms in the unit cell of Cu 1− x Tl x Ba 2Ca 3Cu 4O 12− y superconductor. The effects of post-annealing, of the samples in air atmosphere, on the phonon modes absorption is also studied. Three major phonon modes around 450–475, 900 and 1200 cm −1 in Cu 1− x Tl x -1234 have been observed. These modes are assigned to the vibrations of apical oxygen, O 3 and C–O respectively. The apical oxygen mode at 464 cm −1 is hardened to 474 cm −1 when the preparation temperature is increased from 905 to 920 °C while these modes substantially reduce in intensity after the post-annealing in air at 650 °C. The 945 cm −1 O 3 mode is softened to 880 °C when the synthesis temperature is above 910 °C. The softening of O 3 mode increases the critical temperature of the material, which also showed that the presence of O 3 atoms provide maximum stability to T1 atoms of the unit cell. The post-annealing of the materials in air atmosphere at 650 °C substantially reduces the intensity of 465–475 and 850 cm −1 mode. The reduced intensity of these modes shifts the material towards highly resistive regime and superconductivity is destroyed.

超伝導体 Ａｇシース法によるＮｄＢａ２Ｃｕ３Ｏｙ超電導テープ線材の超電導特性

We prepared Ag-sheathed Nd system tape by the compression molding powder-in-tube method. Ag sheathed tapes of Nd system superconductors were studied for sample with nominal composition of NdBa2Cu3Oy(Nd123). The critical current density of sample apparently depended on the thickness of the tape and temperature gradient, and increased markedly with decreasing the tape thickness. The maximum value of the critical current density of sample reached 2.0×105 A/cm2 at 6.7 K in zero magnetic field for a tape with 0.3 mm thickness and 1.1×104A/cm2 at 77K in zero magnetic field.

圧縮成型試料を詰めたＢｉ‐２２２３テープの超電導特性

We prepared Ag-sheathed Bi system tape by the stuff with compression molding powder-in-tube method. Ag-sheathed tape of Bi system superconductors were studi-ed for sample with nominal composition of Bi1.8Pb0.4Sr2Ca2.2Cu3Oy. The critical current density of sample apparently depended on the thickness of the tape and increased markedly with decreasing tape thickness. The maximum value of the critical current density of sample 6.1×105A/cm2 at 6 K in zero magnetic field was achieved in a tape with 0.3 mm thickness and at 77K were 1.4×104A/cm2 in zero magnetic field.

Enhancing of weak links in polycrystalline superconductor YBa 2Cu 3O 7− δ

A method of enhancing the superconducting coupling between grains in polycrystalline YBa 2Cu 3O 7− δ by combined addition of Sn and F is discussed. The addition of appropriate amounts of Sn and F can remove the impurity phases from the grain boundaries and thus evidently strengthen the weak links among superconducting grains. As a result, the critical current densities of samples with Sn and F dopants are increased significantly.

An investigation of the superconducting properties of the system Bi-Sr-Ca-Cu-O

The critical current density of samples of the system Bi-Sr-Ca-Cu-O with different nominal compositions is investigated. The highest temperature at which zero resistivity was achieved is Tc.off approximately=80 K for the sample with nominal composition BiSr1.2Ca0.8Cu2Oy. The maximum critical current density value in grains at T=60 K and H=2*103 Oe is 8.6*105 A cm-2.