Scene in which stress is applied to a high temperature superconducting nanowire. |
A
team headed by Dr. Kazunari Yamaura, a principal researcher in the
Strongly Correlated Materials Group at Japan’s National Institute for
Materials Science, has succeeded in the development of strong, tough
high temperature superconducting nanowires containing iron and arsenic
that offer advantages over other
Iron-based
superconductors, which have recently been developed in Japan, contain
iron and arsenic as essential elements, and are known to achieve the
highest superconducting transition temperature when they contain two or
more other additional elements. In the general whisker crystal
manufacturing method, the raw material elements are vaporized and
transported by the reaction gas or a carrier gas, and crystals are grown
on a substrate by a vapor phase reaction. However, when crystals with a
whisker shape having a high aspect ratio (L/d) of length (L) and
diameter (d), which is important for industrial applications, were
manufactured by this method, toxicity was difficult to control, as the
arsenic raw material element diffused widely in the crystal growth
device. The fact that the superconducting properties of iron-based
superconductors are sensitive to the crystal composition was also a
problem. For example, an iron-based superconductor in which the
superconducting transition temperature is an absolute temperature of 30 K
(-243 C) or higher comprises four or more types of elements, including
iron and arsenic, but with the conventional method, it was difficult to
synthesize whisker crystals in which four or more constituent elements
including Fe and As were arbitrarily controlled. As a result, whisker
crystals of iron-based superconductors had not been manufactured until
now.
In
this research, the desired whisker crystals of an iron-based
superconductor were successfully manufactured by mixing an additive that
promotes crystal growth in the raw material, filling this mixed powder
in a capsule-shaped metal reaction vessel, mechanically applying the
proper pressure, decompressing the material after achieving the optimum
high densification of the mixed power, and then performing appropriate
heat treatment. The fact that the obtained whisker crystals undergo
transition to the superconducting state at an absolute temperature of 33
K (-240 C) was confirmed. It was also found that the crystals have a
rod-like needle shape with an aspect ratio of 200 or more, and their
diameter is on the order of 1 micrometer or less (nanowire).
Whisker
crystals of copper oxide-based superconductors with similar or higher
superconducting transition temperatures have been manufactured. However,
due to the inherent brittleness of ceramics, their applications are
limited. Fullerene superconducting whiskers have also been manufactured,
but their aspect ratio is approximately 10 or less. In contrast to
these materials, the iron-based superconductor whisker crystals have
properties closer to alloys than to ceramics, being strong and tough,
and also have a large aspect ratio, and thus can expand the range of
possible applications.
This
result was achieved as part of the “Search for New Materials with
Superconducting and Related Functions and Application of Industrial
Superconducting Wire Materials” (Central Researcher: Hideo Hosono) of
the Funding Program for World Leading Innovative R&D of Science and
Technology (FIRST Program) of the Japan Science and Technology Agency
(JST), and was published in the Journal of the American Chemical Society on March 7, 2012.
Growth of Single-Crystal Ca10(Pt4As8)(Fe1.8Pt0.2As2)5 Nanowhiskers with Superconductivity up to 33 K
Source: NIMS
