Xavier Obradors & Teresa
Puig talk with ScienceWatch.com and answer a few
questions about this month's New Hot Paper in the field of
Xavier Obradors &
coauthor Teresa Puig
Article Title: Strong isotropic flux pinning in
solution-derived YBa2Cu3O7-x nanocomposite superconductor
Authors: Gutierrez, J;Llordes, A;Gazquez, J;Gibert, M;Roma,
N;Ricart, S;Pomar, A;Sandiumenge, F;Mestres,
Puig, T;Obradors, X
Journal: NAT MATER
Year: MAY 2007
* CSIC, Inst Ciencias Mat Barcelona, Campus UA Barcelona,
Bellaterra 08193, Catalonia, Spain.
(addresses have been truncated)
Why do you think your paper is highly
The development of high-temperature superconductors (HTS) with high
performances has been an outstanding problem of the physics and materials
sciences over the past 20 years. For power applications of superconductors,
the outstanding property is the critical current density, i.e., the total
amount of current that you can transport without dissipation.
The achievement of high-critical current density is actually a
nanotechnology issue, exactly the opposite than in semiconductor materials.
A "good" superconductor is one which has an optimal concentration of
non-superconducting defects or secondary phases, and these defects should
have dimensions smaller than 10nm. But not all defects can be beneficial,
for instance, grain boundaries could completely destroy their high
Our work has described a new chemical methodology used to prepare
nanocomposite superconductors, which fulfills all the stringent demands for
a superconductor with high performance at high temperature under high
The record performances achieved with these new materials have strongly
stimulated further research in this area because their theoretical limit is
still much higher and hence there remains room for improvement.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Our paper has described a new methodology used to prepare epitaxial
superconducting nanocomposites, which has resulted in new physical
discoveries. One important hindrance of HTS is that they have a layered
structure which results in anisotropic physical properties, particularly
the critical current. This characteristic causes a lot of trouble for power
devices design such as cables, magnets, or motors.
The materials that we have developed include randomly distributed and
randomly oriented nanodots which deeply decrease the effective anisotropy
of the superconducting YBa2Cu3O7 matrix.
This was an unexpected result which we have learned to quantify, but which
still requires much more investigation, even if it has already raised a
Would you summarize the significance of your paper
in layman’s terms?
As we have mentioned a "good" superconductor is an "imperfect" material,
about 10% of a non-superconducting phase should be mixed with the
superconducting phase with its size in the nanometric scale; while it
should, in addition, generate a massive density of nanodefects in the
superconducting matrix. This segregation process should happen
spontaneously in order to be able to produce conductors with kilometric
Three years ago, a collaboration between the University of Cambridge in the
UK and Los Alamos National Laboratory in US (J. MacManus-Driscoll et
al., Nature Materials 3: 439, 2004) showed that indeed this natural
separation process occurs if you carefully select a material which can not
mix up with the superconducting matrix.
This work was based on the use of a vacuum deposition method—"pulsed
laser deposition" or PLD—while our work uses chemical solutions. The
consequences of using this alternative methodology are straightforward
because it turned out that the nanodots are growing in a different way,
resulting in a different crystallographic orientation, and this has deep
consequences within the physical properties. It is a good example to show
that sometimes new methodologies open new avenues in the field of materials
How did you become involved in this research, and
were there any problems along the way?
We have been involved in the problem of understanding the mechanisms
controlling critical currents in superconductors for about 20 years. It is
a very complex physical problem involving vortex behavior—a
collection of supercurrent whirlpools crossing the materials—and
During the past seven years, we have been the leader in EU projects. Two of
these studies are: "Novel sol gel technology for long length
superconducting coated tapes" or "SOLSULET," and "High-performance
nanostructured coated conductors by chemical processing" or "HIPERCHEM,"
which is an effort to use a low-cost methodology in preparing the second
generation of superconductors through "chemical solution deposition" or
Our effort in understanding the materials science and physical properties
has been essential to our achievement and this interdisciplinary approach
has been essential. It is quite unusual to find physicists, chemists, and
experts in microstructure working closely together. The achievement of our
core group in Barcelona has been a key factor in our success.
Where do you see your research leading in the
There is a still a long road ahead in this field. First, we need to
understand more clearly the influence of the nanostructure on
superconducting properties while also exploring new ideas about those
physical mechanisms which pin vortices in superconductors. We are convinced
that these performances can be deeply improved. We're also deeply involved
in transferring our discoveries to practical conductors and this means
gaining much more in reproducibility and strict control of those relevant
parameters involved in the process.
Do you foresee any social or political implications
for your research?
High-temperature superconductivity is a key enabling technology for the
development of efficient electrical energy delivery and management to
society, and hence we are convinced that the impact of these materials in
achieving a sustainable energy use will be very high.
The goal of our EU project HIPERCHEM is to develop low-cost fabrication
methodologies and this is why we are closely cooperating with industry to
make reality the development of conductors carrying 100 times more current
than copper. Prototypes of cables, magnets, and "fault-current limiters" or
"FCL," based on the new YBa2Cu3O7
superconductors have already been demonstrated and we expect that its full
engineering potential will be confirmed very soon.
Prof. Xavier Obradors
Institut de Ciència de Materials de Barcelona
Dr. Teresa Puig
Institut de Ciència de Materials de Barcelona
Keywords: high-temperature superconductors, high-critical
current density, vortex behavior, nanotechnology, grain boundaries,
non-superconducting defects, nanocomposite superconductors, power
devices design, epitaxial superconducting nanocomposites, nanodefects in
the superconducting matrix, pulsed laser deposition, nanodots, chemical
solution deposition, fault-current limiters.