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| Figure 3 Critical current density of the developed fullerene
nanowhisker superconductor (5K). The critical current density
remains constant over a wide range of field intensities, showing
that this material has excellent superconducting properties. |
| Copyright : NIMS |
The National Institute for Materials Science (NIMS; President:
Sukekatsu Ushioda) succeeded in realizing superconductivity in
fullerene nanowhiskers, which are a nanosized carbon material that
is lightweight and has a fine fibrous shape. Among the conventional
superconducting materials, superconductors with comparatively high
superconducting transition temperatures were mainly intermetallic
compounds or ceramics, and those were often heavy, hard
materials.
This research will enable development of new thread-like and
cloth-like superconducting materials called “Flexible,
lightweight superconductors.” This research result was
achieved through joint research by Dr. Yoshihiko Takano, Group
Leader of the NIMS Nano Frontier Materials Group, Dr. Hiroyuki
Takeya, a Chief Researcher of the same group, and a team headed by
Dr. Kun'ichi Miyazawa, Group Leader of the NIMS Fullerene
Engineering Group.
Superconductivity is expected to play a key role in solving many
environmental and energy problems, as electrical energy can be
transported with no loss. Fullerenes have attracted attention as a
substance that may make it possible to realize this with
lightweight carbon. The fullerene C60, which was discovered in
1985, is a carbon material in which carbon atoms are arranged in a
shape resembling a soccer ball. It was also found that fullerenes
display superconductivity when doped with a small amount of
potassium. Because fullerenes are composed of carbon, high
expectations are placed on this material as a “lightweight
superconductor.” However, it was difficult to obtain good
quality superconductors with the reaction process used until now,
as the percentage of the fullerene feedstock which displayed
superconductivity was extremely small, at less than 1% with
treatment for one day.
In this research, the NIMS team succeeded for the first time in the
world in realizing superconductivity in a fullerene-based material
by adding potassium to fullerene nanowhiskers, which are a
nano-sized thread-like substance that can be synthesized from
fullerenes, and heat-treating the resulting nanowhiskers. Even when
the material manifests superconductivity, it retains its fine,
fibrous structure. Furthermore, substantially 100% of the specimen
material becomes a superconductor with heat treatment for one day.
From the results of magnetization measurements, the superconducting
transition temperature is approximately 17K. The critical current
density is extremely high, at 105A/cm2, even in a magnetic field,
and the decrease in the critical current density accompanying
increased field strength is slight. From these results, it is clear
that this is an outstanding superconducting material.
Many materials with high superconducting transition temperatures,
beginning with high temperature superconductors, MgB2, etc. are
hard and brittle, and a high level of technology was necessary to
process those materials into wire form, for example, for
superconducting electrical wire. However, because the fullerene
nanowhisker superconductor obtained in this research is
lightweight, has a fine fiber-like shape from the initial stage,
and maintains that fine, fibrous shape even after the appearance of
superconductivity, it is considered that superconducting materials
with diverse forms, such as a bundled fiber form, cloth-like form,
and the like will be produced in the future. Thus, this achievement
is a great advance toward the realization of lightweight, flexible
superconductors.
This research result was achieved as part of the research topic
“Research on Carbon-based Materials” (Research
Representative: Yoshihiko Takano) of the Grant-in-Aid for
Scientific Research on Priority Areas Program (Research Supervisor:
Katsumi Tanigaki) of the Ministry of Education, Culture, Sports,
Science and Technology (MEXT) and the NIMS project,
“Development of Novel Nanocarbon Materials and Their
Functionalization” (Sub-theme Leader: Kun’ichi
Miyazawa). It is scheduled to be announced officially at the
Meeting of the Project on Priority Research Areas (“New
Materials Science Using Regulated Nano Spaces”) to be held at
NIMS beginning January 5, 2012. |
