R eesearch Highlights
Prototype Fe-based
Superconducting Wire
Using Fe(Se,Te)
Nano Frontier Materials Group,
Advanced Superconducting Wires Group†,Superconducting Materials CenterGroup Leader

Managing Director†

Yoshihiko Takano, Yoshikazu Mizuguchi, Hiroaki Kumakura
Materials which show zero electrical resistance at low
temperatures are called superconductors. In the superconducting state, it is possible to transmit electrical energy overgreat distances with no loss. If it were possible to circle theplanet with wire manufactured from a superconductor, generating solar power on the sunny side of the globe during daytime and transmitting it to areas on the nighttime side would
not be a dream.
Recently, Fe-based superconductors have been a topicof great interest as a new type of high temperature superconductor. Our groups has been working to develop wire materials using these Fe-based superconductors. The test material
used in this research is a Fe(Se,Te) material, which has thesimplest crystallographic structure among the Fe-based
superconductors and has a superconducting transition temperature (Tc) of approximately 14K. Because iron, which isits main component, is an element which exists on Earth ingreat abundance, we devised a unique superconducting wire
manufacturing method in which Fe is used as the sheathmaterial (material forming the outer shape of the wire) and, atthe same time, also serves as a raw material for the Fe-based
superconducting substance which is formed in the interior.
Fig.1 shows a schematic diagram of the wire material
manufacturing process. First, an SeTe compound is preparedby reacting Se and Te in advance. These are the non-Fe components of the Fe-based superconductor. This SeTe compound is then filled into an iron pipe, which will form thesheath material. The filled pipe is then rolled into a long,thin, tape-shaped wire material with a width of 4.3mm andthickness of 0.55mm using grooved rolls and flat rolls. The
wire material obtained in this manner is sealed in a quartz
glass tube so as to prevent reaction with the air, and heat
treatment is performed. When this was done, the SeTe compound in the tube reacts with the Fe sheath, and a Fe(Se,Te)superconductor is synthesized inside the sheath. A scanningelectron microscope image of the cross section of theobtained wire material is shown in Fig.2. A satisfactory
filling condition, in which the superconductor was in close
contact with the sheath, with no crevices or spaces, wasobtained on both sides of the wire material.
Electrodes were attached to the wire material and a current test was performed. As a result, a superconducting current was successfully passed through a wire material using anFe-based superconductor for the first time in the world.
Although the critical current density still shows a small valueof Jc=12.4A/cm2, various efforts to achieve higher values areplanned, including increasing the filling rate and improving
the bonding between the sheath and the superconductor, useof a multicore design, introduction of flux pinnig, etc. This is
expected to result in further improvement in the superconducting critical current value in the future.

Sheath (Fe)Roll

Superconductor Fe (Se, Te)

SeTeRoll
Fe sheath

Filling

RollingFig.1 Schematic diagram of the wire manufacturing
process.

0.1 mm
Fig.2 Scanning electron microscope image of crosssection of superconducting wire.

International 2009. Vol.7 No.10

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