24 research outputs found
Casting of superconducting composite materials (M-4)
An aluminum-lead-bismuth alloy is a flexible alloy and is promising for easily workable embedded-type, filament-dispersed superconducting wire material. It is difficult to produce homogeneous ingots of this material because it is easily separated into elements when melted on Earth due to the large specific gravity differences. In this experiment, a homogeneous alloy will first be produced in molten state in microgravity. It will then be returned to Earth and processed into a wire or tape form. It will then be dispersed as the second phase in micro texture form into the primary phase of aluminum. Superconducting wire material with high-critical-magnetic-field characteristics will be produced. The texture of the material will be observed, and its performance will be evaluated. In addition to the above alloy, a four-element alloy will be produced from silver, a rare Earth element, barium, and copper. The alloys will be oxidized and drawn into wire after being returned to Earth. The materials are expected to be forerunners in obtaining superconducting wire materials from oxide superconductors
Fabrication of Bi2212 Cross Whiskers Junction
An intrinsic Josephson junction has been successfully fabricated without any
micro-fabrication technique. Two Bi2212 whiskers were crossed with one another
and joined by post-annealing. The inter-whisker electrical transport properties
were measured by the four-probe method. The temperature dependence of
resistance exhibited metallic behavior above TC. The resistance decreased to
zero around 80K, corresponding to the superconducting transition. The
current-voltage characteristics at 5K exhibited a small hysteresis and voltage
jump, which can be explained by the intrinsic Josephson effect.Comment: 3 page PDF fil
A Cross-Whiskers Junction as a Novel Fabrication Process for Intrinsic Josephson Junction
A Bi2Sr2CaCu2O8+d cross-whiskers junction has been successfully discovered as
a novel intrinsic Josephson junction without using any technique for
micro-fabrication. Two Bi2Sr2CaCu2O8+d whisker crystals were placed crosswise
on a MgO substrate and heated at 850C for 30 min. They were electrically
connected at their c-planes. The measurement terminals were made at the four
ends of the whiskers. The I-V characteristics of the cross-whiskers junction at
5K were found to show a clear multiple-branch structure with a spacing of
approximately 15 mV that is a feature of the intrinsic Josephson junction. The
critical current density Jc was estimated to be 1170 A/cm2. The
branch-structure was strongly suppressed by the magnetic field above 1kOe.Comment: 4 pages, PDF fil
Large Transport Critical Current Densities of Ag Sheathed (Ba,K)Fe2As2+Ag Superconducting Wires Fabricated by an ex-situ Powder-in-Tube (PIT) Process
We report large transport critical current densities observed in Ag-added
(Ba,K)Fe2As2 superconducting wires prepared by an ex-situ powder-in-tube (PIT)
process. The wire has a simple composite structure sheathed only by Ag. A
precursor bulk material prepared by a melting process was ground into powder
and put into a Ag tube. The composite was then cold worked into a wire and heat
treated at 850C for sintering. Transport critical current densities,
Jc, at 4.2 K are 1.0\times104 A/cm2 (Ic = 60.7 A) in self field and
1.1\times103 A/cm2 (Ic = 6.6 A) in 10 T. These are the highest values reported
so far for the Fe-based superconducting wires.Comment: in press for Appl. Phys. Expres
Superconducting Properties of Combustion Synthesized MgB2
We have successfully prepared the MgB2 superconducting bulk and powdered
materials by the method of combustion synthesis. The starting materials used in
this study were powders of Mg and B. X-ray powder diffraction pattern was well
assigned to the P6/mmm MgB2 phase. The temperature dependence of magnetization
shows sharp superconducting transition around 38K. The critical current density
can be estimated from the hysteresis of the magnetization curvature using the
Bean's model. The powdered sample shows a high critical current density of
2x10^6 A/cm2 at 5K under the magnetic field of 1T.Comment: 5 pages, 7 figures, PDF fil
Synthesis of YNi2B2C thin films by magnetron sputtering
Thin films of YNi2B2C superconductor by the magnetron sputtering technique have been synthesized. The YNi2B2C phase was found to crystallize very uniformly after annealing at 1050 °C in vacuum. The structure was investigated and the electric and magnetic properties were characterized. The films were c-axis oriented and showed a Tc onset of ~15 K by both magnetization and resistivity measurements. The results of the critical current measurement suggested the existence of anisotropies of pinning force and an upper critical field Bc2