Effect of Ag2O addition on the intergranular properties of the superconducting Bi–(Pb)–Sr–Ca–Cu–O system

The effect of Ag2O addition on the Bi–(Pb)–Sr–Ca–Cu–O system has been investigated in terms of ac susceptibility, phase evolution, critical current density and critical temperature. It was found that as the amount of Ag2O addition increases, the intergranular critical current density decreases in our samples (Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10) fabricated by ammonium nitrate technique. The analysis for comparison is based on the suppression degree of the diamagnetic behaviour with respect to fields, rapid or slow shift of the summit in χ'(T) to lower temperature with increasing field amplitude and the sharpness of the transition of χ'(T) for intergranular component for the same field amplitude. We also qualitatively discuss experimental results in the framework of the critical state model. The room temperature XRD diagram indicates the presence of large amount of high-Tc (2223) phase. The percentage of Bi-2223 phase in the phase mixture was estimated from the intensities of high-Tc (2223) and low-Tc (2212) phase peaks as 78% for the pure BSCCO sample. Among the Ag2O-added BSCCO samples studied, the one in which 5 wt%Ag2O was added shows the highest rate of Bi-2223 formation as 92%. The SEM analysis reveals some morphological changes induced by silver addition

Fabrication and Transport Critical Current Densities of MgB 2

We have fabricated superconducting 6 and 7 filaments $MgB_2//Fe//Cu$ tapes by ex situ powder-in-tube method using Cu-sheath without any intermediate annealing. Properties of two different multicore $MgB_2//Fe//Cu$ tapes annealed at 900C for 2 h in high purity argon gas atmosphere were compared. The samples were characterized using scanning electron microscope, X-ray diffraction, electron dispersive spectroscopy, optical microscopy, critical transition temperature, transport critical current density, and magnetic measurements. Transport critical current densities of the 6 and 7 filaments tapes were found to be 450 A/cm^2 and 190 A/cm^2 at 20 K, respectively. From X-ray diffraction measurements, lattice parameters a and c were determined. From dc resistivity measurements, the connectivity between grains was investigated by using Rowell's connectivity analysis

Production of BiPbSrCaCuO thin films on MgO and Ag/MgO substrates by electron beam deposition techniques

WOS: 000179783200022Superconducting BiPbSrCaCuO thin films were prepared on MgO(001) and Ag/MgO substrates using an electron beam (e-beam) evaporation technique. The effects of annealing temperature and Ag diffusion on the crystalline structure and some superconducting properties, respectively, were investigated by X-ray diffraction, atomic force microscopy, and by measurements of the critical temperature and the critical current density. It was shown that an annealing of both types of films at 845 or 860 degreesC resulted in the formation of mixed Bi-2223 and Bi-2212 phases with a high degree of preferential orientation with the c-axis perpendicular to the substrates. The slight increase of the critical temperature from 103 K to 105 K, the enhancement of the critical current density from 2 x 10(3) to 6 x 10(4) A/cm(2), and the improved surface smoothness are-due to a possible silver doping from the substrate

Influence of annealing temperature on the microstructure and mechanical properties of MgB2

We have investigated the effect of annealing temperature on the microstructure, magnetic and mechanical properties of MgB2 superconducting samples employing X-ray diffraction (XRD), scanning electron microscopy (SEM), ac susceptibility and Vickers microhardness measurements. XRD patterns and SEM micrographs are used to obtain information about lattice parameters and grain size, respectively. These measurements indicate that MgB2 grain size, lattice parameters, and critical temperature are increased, and grain connectivity is improved, with increasing the sintering temperature up to 850°C. It is also observed that the Vickers microhardness of the samples is dependent of the sintering temperature and applied load. In addition, we calculate the load dependent mechanical properties of MgB 2 samples such as the Young's modulus, yield strength, and fracture toughness. The possible reasons for the observed improvements in microstructure, superconducting and mechanical properties due to annealing temperature are discussed. © 2009 IOP Publishing Ltd

Effects of annealing temperature on the structural and optical properties of ZnO hexagonal pyramids

ZnO thin films were deposited on quartz substrate at 550 degrees C by using spray pyrolysis method and subsequently annealed between 600-900 degrees C with a step of 100 degrees C. The characterizations of the structural and optical properties of the films have been carried out by means of X-ray diffraction, scanning electron microscopy (SEM) and optical transmittance measurements. XRD ans SEM images indicated that annealing temperature did not play a great role on the microstructure of ZnO films. ZnO thin films are all in hexagonal crystallographic phase and have (0 0 2) preferred orientation, regardless of the annealing temperature. However, SEM studies showed that there exist a high density of micro-rods in the shape of hexagonal pyramid with the width in the order of about 1 mu m and height in range of 1-3 mu m and the adjacent hexagonal crystals to start fusing with each other along their boundaries at high temperatures. As a result of the optical measurements, it was observed that the films show the low transmittance and optical band gap decreases from 3.15 to 3.10eV with the increasing of the annealing temperatures up to 800 degrees C and followed by an increase to 3.20 eV upon further annealing at 900 degrees C

Fabrication and Transport Critical Current Densities of MgB2//Fe//CuMgB_2//Fe//Cu Multifilament Tapes without Any Intermediate Annealing

We have fabricated superconducting 6 and 7 filaments $MgB_2//Fe//Cu$ tapes by ex situ powder-in-tube method using Cu-sheath without any intermediate annealing. Properties of two different multicore $MgB_2//Fe//Cu$ tapes annealed at 900C for 2 h in high purity argon gas atmosphere were compared. The samples were characterized using scanning electron microscope, X-ray diffraction, electron dispersive spectroscopy, optical microscopy, critical transition temperature, transport critical current density, and magnetic measurements. Transport critical current densities of the 6 and 7 filaments tapes were found to be 450 A/cm^2 and 190 A/cm^2 at 20 K, respectively. From X-ray diffraction measurements, lattice parameters a and c were determined. From dc resistivity measurements, the connectivity between grains was investigated by using Rowell's connectivity analysis

The effect of cooling rates on properties of Bi1.7Pb0.35Sr1.9Ca2.1Cu3Oy superconductors produced by solid-state reaction method

Yegen, Dincer/0000-0003-3180-600X; Ozturk, Ozgur/0000-0002-0391-5551WOS: 000243735700007We have investigated the effect of the cooling rates in the Bi-2223 superconducting samples prepared by standard solid-state reaction method using electrical resistivity, transport critical current density, and XRD (X-ray diffraction) measurements. We estimated the transition temperature values from the DC resistivity measurements. We observed that transition temperature, T-c, and transport critical current density, J(c)(trans), depend on the cooling rates of the samples. They both increase with increasing cooling rates. We estimated the peak temperature, T-P, from our previous ac susceptibility measurements. The pinning force density increased with increasing the cooling rate. XRD patterns are used to calculate lattice parameter c and obtain information about Bi-2223 phase ratio. (c) 2006 Elsevier B.V. All rights reserved

Investigation of Lu effect on YBa2Cu3O7-delta superconducting compounds

Turkoz, Mustafa Burak/0000-0002-4127-7650WOS: 000314773800010This study reports the effect of Lu addition on the microstructural and superconducting properties of YBa2LuxCu3O7-delta (Y123) superconducting samples with x = 0, 0.1, 0.3, 0.5 and 0.7 by means of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), electron dispersive X-ray (EDX), electrical resistivity and transport critical current density (J(c)) measurements. The samples prepared by the liquid ammonium nitrate and derivatives are exposed to various annealing time (20, 40 and 60 h) and temperature (950, 960 and 970 A degrees C), and the best ambient for the sample fabrication is determined to be 970 A degrees C for 20 h. Zero resistivity transition temperatures (T-c), critical current densities (J(c)), variation of transition temperatures, hole-carrier concentration, grain size, lattice parameter, surface morphology, element distribution, crystallinity and resistivity (at room temperature) values of the bulk superconducting samples prepared at 970 A degrees C for 20 h are compared with each other. T-c and J(c) values of the samples are inferred from the dc resistivity and the critical current measurements, respectively. The results show that the T-c value of the pure sample is about 90.6 K while the sample doped with 0.1 wt% Lu has the maximum T-c value (92.5 K). However, beyond x = 0.1, the T-c value is observed to decrease toward to 83.5 K with increment in the Lu addition. Similarly, the J(c) values measured are found to reduce from 142 to 76 A/cm(2) with the addition. Moreover, XRD measurements show that both pure and Lu-doped samples exhibit the polycrystalline superconducting phase with the changing intensity of diffraction lines and contain Y123 and Y211 phase, confirming the incorporation of Lu atoms into the crystalline structure of the samples studied. At the same time, comparing of the XRD patterns of samples, the intensity ratio of the characteristic (110) and (013) peaks on the sample doped with 0.1 wt% Lu is more than that on the other samples prepared. Additionally, SEM images display that the sample doped with 0.1 wt% Lu obtains the best crystallinity, grain connectivity and largest grain size whereas the worst surface morphology is observed for the maximum doped sample (x = 0.7). Further, EDX results demonstrate that the Lu atoms doped are successfully introduced into the microstructure of the Y123 samples studied and the maximum Cu element level is observed for the sample doped with 0.1 wt%, explaining that why this sample obtains the best superconducting properties compared to others. According to all the results obtained, it is concluded that the 0.1 wt% Lu addition into the Y123 system improves the microstructural and superconducting properties of the samples studied

Flux pinning by regular nanostructures in

Periodic pinning effects in indented \chem{Nb} films and \chem{Nb} films with rectangular arrays of submicrometric \chem{Ni} dots were studied. The indented samples consisted of \chem{Nb} film deposited on top of \chem{Si} substrates patterned with rectangular arrays of nanoholes. Pinning effects can be observed in the evolution of resistivity and critical current with the applied magnetic field, showing the same qualitative behavior, for both types of samples. The main difference between them is that the matching effects are more pronounced in the samples with magnetic dots. The analysis and comparison of these results allows determining the pinning as due to superconductivity suppression around the nanostructures (indentations or dots) due to a thickness reduction. For the samples with magnetic dots, this suppression of superconductivity is reinforced by the magnetic proximity effect