Papers by Keyword: Superconductor

Abstract: The Tl_2-xTe_xBa₂CaCu₂O_8-δ (Tl-2212) high temperature superconductors with x = 0.0-0.5 have been prepared by the standard solid-state reaction method. The precursor powder were sintered at 900°C for 24 h with several grindings and heating. The powder were then pressed into pellets and heated at 910°C in oxygen flow for 4 min followed by furnace cooling. The electrical resistance versus temperature dependence measurements showed metallic normal state behavior for all samples. Substitution of Te at the Tl-site led to multi-phasic samples. The x = 0.4 sample showed the highestT_{c zero}= 98 K and T_conset= 111K. The Tl-2212 phase increased from 50% for x=0 up to 92% in the x= 0.4 sample.

Abstract: We have succeeded in synthesizing new arsenic-based filled skutterudite compounds CaFe₄As₁₂ and BaOs₄As₁₂ under high pressure. These compounds have lattice constants of 8.3288 and 8.5809 Å, respectively. The magnetic properties of CaFe₄As₁₂ and BaOs₄As₁₂ have been studied by means of electrical resistivity, magnetic susceptibility and magnetization measurements. The electrical resistivity and magnetic measurements indicate that CaFe₄As₁₂ is a nearly ferromagnetic metal with spin fluctuations of Fe 3d electrons and BaOs₄As₁₂ is a new superconductor with a transition temperature around 3 K.

Abstract: MgB₂ superconductor with relatively high critical temperature (Tc=40 K) has been developed for possibilities utilization in various practical applications such as Magnetic Resonance Imaging. In order to enhance the process, the material was prepared by Powder-In-Tube (PIT) method, while the superconducting properties was improved by incorporating 0 wt.%, 10 wt.% and 20 wt.% SiC nanoparticles into MgB₂ structure. This study aimed at analyzing the effect of sintering temperature on the microstructure, resistivity and phase of Fe-sheathed MgB₂ superconducting wires. Three different compositions of MgB₂ powders were inserted into Fe tube with inner ø of 4 mm and outer ø of 6 mm. This tube was then rolled and drawn into a ø 2.5 mm wire. Wire samples with three different compositions of SiC were heat treated at 600°C and 800°C respectively. All samples were characterized to analyze the morphology, resistivity and crystal structure. X-ray diffraction (XRD) analysis showed that some Mg may react with SiC to form MgSi and with oxygen to form MgO. Scanning electron microscope (SEM) images revealed that with no addition of SiC, MgB₂ was formed and dispersed uniformly in wire, but with 10 wt.% and 20 wt.% SiC nanoparticles, the whisker morphology was observed resulting in degradation of the superconducting properties.

Abstract: We investigated some properties of Y134 superconductor doped Ti superconductor. The series of samples of Y134 doped Titanium (YBa₃Cu₄Ti_xO_9-δ) which x=0, 0.05, 0.10, 0.15, 0.20, 0.25 were prepared by solid state reaction method with calcinations and sintering temperature at 980 °C. The porosity was reduced and the melting area were found for all Ti-doped samples. There was a little effect of Ti-doped on Tc onset but the lower of Tc offset were found that agree with the melting found on surface of sample with Ti-doped. The peritectic temperature of Y134 powder, and Y134 + 0.10Ti were on the same range about with more peak area of pure Y134 than Y134 with Ti-doping.

Abstract: FeSe superconducting bulks were prepared with high energy ball milling (HEBM) aided sintering process, within which process, tetragonal β-FeSe superconducting phase could be formed directly with one step sintering process, and the formation of hexagonal δ-FeSe non-superconducting phase was effectively avoided. The influences of HEBM time on the sintering process of FeSe bulks were systematically investigated. With different HEBM time, the phase composition and morphology of precursor powders changed correspondingly, which thus influenced the final phase composition and superconducting properties of FeSe superconducting bulks. Due to the formation of FeSe bulks with larger tetragonal phase content and higher superconducting transition temperature, HEBM time of 6.0 h was recognized as the optimal parameter. Shorter HEBM time could lead to the insufficient decrease of particle size and low density. While longer HEBM time caused the formation of amorphous hexagonal δ-FeSe, which crystallized during sintering process. Thus no more tetragonal FeSe could be obtained. The FeSe superconducting bulk with the critical temperature T_c(onset) of 8.0 K was obtained with the HEBM time of 6 h, and sintering temperature of 700 ^oC for 12 h.

Abstract: YBa₂Cu₃O_7-δ (YBCO) coated conductors have wide-ranging potential in large scale applications, such as, superconducting maglev trains and superconducting electric cables, but low current carrying capability restrains the practical application of YBCO coated conductors at high temperatures and high magnetic fields. It is crucial to develop YBCO coated conductors with high flux pinning capability. In this paper, epitaxial, dense, smooth and crack-free YDy_xBa₂Cu₃O_7-δ (x = 0~0.5) films were prepared on a LaAlO₃ (LAO) single crystal substrate via a fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The effects of Dy addition on the microstructure and superconducting character of YBCO films were investigated. The all films show a strong c-axis orientation and good texture in-plane and out of plane. The Dy addition to the YBCO film hardly affects the critical temperature of YBCO superconductor. The irreversibility fields of YBCO films can be improved with the Dy addition x = 0.5 compared to the pure YBCO film but decreased in the x = 0.3 sample.

Abstract: The effect of Ca substitution on the electrical and structural properties in high and low density Y(Ba_1-xCa_x)₂Cu₃O_δ where x = 0.00, 0.10, 0.20 and 0.30 via solid state reaction method has been investigated. The electrical properties, elemental analysis, and structural identification were measured by the four-point probe technique, energy dispersive x-ray (EDX) and X-ray diffraction (XRD) respectively. The electrical properties such as critical temperature (T_c) and critical current density (J_c) were found to be strongly dependent in both high and low densities Y(Ba_1-xCa_x)₂Cu₃O_7-δ. These parameters were decreased monotonously with the increasing of Ca substitution. An obvious results of the Ca-doped samples can be seen in x = 0.20 where T_{c zero} of high density sample is 77 K, which is higher than that of the low density sample that occurred at 73 K. Meanwhile, J_c at 60 K for high density is 1.842 A/cm² compared to 1.410 A/cm² in low density sample. EDX analysis confirmed the existence of Ca in all doped samples. The crystallographic structure remained orthorhombic and the volume of unit cell increased towards further increased of Ca concentration.

Abstract: The influences of cerium doped on low density Bi-2223 superconductor have been studied and this study examines the significant changes in the structural and superconducting properties. The nominal compositions of low density Bi_1.6Pb_0.4Sr₂Ca_2-xCe_xCu₃O_y (where x =0.000, 0.025, 0.05, 0.1 and 0.2) ceramic superconductor were prepared by solid state method. The effects of different Ce doping levels on the superconductor structure and superconducting properties has been investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction analysis (XRD), electrical resistance and transport critical current density (J_C) measurements. The results show that T_{C zero} and J_C of the samples reduced gradually with the increase in the Ce addition. It has been observed that, the J_C of low density Bi-2223 for Ce-free was measured to be 12.120 A/cm² and 0.448 A/cm² in x=0.025 at 60 K under zero magnetic field. As for XRD analysis showed the doping of Ce reduced the volume fraction of the 2223 phase and increased the volume fraction of the 2212 phase. FESEM results showed the surface morphology not homogenous and weak links between superconducting grains of the samples due to increase of the Ce doping.

Abstract: High temperature superconductor ceramic of low density Bi_1.6Pb_0.4Sr₂(Ca_2-xEu_x)Cu₃O_y both doped and non-doped, have been produced by the method of conventional solid state reaction synthesis. The effects of rare earth doping on the low density superconducting compound have been studied by considering Eu substitution at Ca site to stoichiometric of Bi (Pb)-2223 with x ranging from 0.000 to 0.2000. The experimental works in this study consist of direct-current (DC) electrical resistance-temperature and critical current density measurements for both electrical and superconducting properties, and powder X-ray diffraction (XRD) for phase analyses and lattice parameters while Field Emission Scanning Electron Microscopy (FESEM) for surface morphology. All the Eu-doped samples consist of both low-Tc Bi (Pb)-2212 and High-Tc Bi (Pb)-2223 phases. The substitution of Eu at the Ca site induced the decrease of volume fraction for the Bi (Pb)-2223 phase and the increase of the volume fraction for Bi (Pb)-2212 phase. Eu doping does not enhance the Tc zero but gradually decrease its value and become semiconducting at higher dopant concentration with x=0.200. From FESEM investigation, the grain size started to degrade from x=0.000 to x=0.0100 and form smaller plate-like grain which belong to Bi (Pb)-2212 phase and the grain particles are seem to be coagulated to form clusters for x=0.200.

Abstract: It was investigated the influence of Ca substitution by Zn on the fluctuations of specific resistivity, thermal power and exsess conductivity of Bi₂Sr₂Ca_0.6Zn_0.4Cu₂O_X and Bi₂Sr₂Ca₁Cu₂O_X in the 70-300К temperature interval. Experimental results explained taking into account strong anisotropy and multiband character of superconducting state in these compounds. The microscopic parameters such as dimensional crossover temperature (T_cr), interlayer coupling strength (J), and zero temperature coherence length along c axis (ξ₀) are estimated.