Superconducting wire with unprecedented performance

Just add nanocolumn defects


Nanotubes imagesThe ability to control nanoscale imperfections in superconducting wires results in materials with unparalleled and customized performance, according to a new study from the Department of Energy’s Oak Ridge National Laboratory.
Applications for superconducting wires, which carry electricity without resistance when cooled to a critical temperature, include underground transmission cables, transformers and large-scale motors and generators. But these applications require wires to operate under different temperature and magnetic field regimes.
A team led by ORNL’s Amit Goyal demonstrated that superconducting wires can be tuned to match different operating conditions by introducing small amounts of non-superconducting material that influences how the overall material behaves. Manipulating these nanoscale columns — also known as defects — allows researchers to exert control over the forces that regulate the wires’ superconducting performance. The team’s findings are published in Nature Publishing Group’s Scientific Reports.
“Not only can we introduce these nanocolumn defects within the superconductor and get enhanced performance, but we can optimize the performance for different application regimes by modifying the defect spacing and density,” Goyal said.
A wire sample grown with this process exhibited unprecedented performance in terms of engineering critical current density, which measures the amount of current the wire can carry per unit cross-sectional area. This metric more accurately reflects the real-world capabilities of the material because it takes into account the wire’s non-superconducting components such as the substrate and the buffer and stabilizer layers, Goyal said.
“We report a record performance at 65 Kelvin and 3 Tesla, where most rotating machinery applications like motors and generators are slated to operate,” he said.
The paper reports a minimum engineering critical current density at all applied
magnetic field orientations of 43.7 kiloamperes/cm2, which is more than twice the performance level needed for most applications. This metric assumes the presence of a 50-micron-thick copper stabilizer layer required in applications. Generating defects in the superconductor is accomplished through an ORNL-developed self-assembly process, which enables researchers to design a material that automatically develops the desired nanoscale microstructure during growth.
The mechanism behind this process, which adds very little to the production cost, was the subject of a recently published study by a team led by Goyal in Advanced Functional Materials. “When you’re making the wires, you can dial-in the properties because the defects self-assemble,” Goyal said. “You change the composition of the superconductor when you’re depositing the tape.” Goyal, who has collaborated with multiple superconducting technology companies, hopes the private sector will incorporate the team’s findings to improve upon existing products and generate new applications.
The study is published as “Engineering nanocolumnar defect configurations for optimized vortex pinning in high temperature superconducting nanocomposite wires.” Co-authors are ORNL’s Sung Hun Wee and Claudia Cantoni and the University of Tennessee’s Yuri Zuev.
This story is reprinted from material from Oak Ridge National Lab, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

Graphene on its way to conquer Silicon Valley

QDOTS imagesCAKXSY1K 8Nanowerk News) The remarkable material graphene  promises a wide range of applications in future electronics that could  complement or replace traditional silicon technology. Researchers of the  Electronic Properties of Materials Group at the University of Vienna have now  paved the way for the integration of graphene into the current silicide based  technology. They have published their results in the new open access journal of  the Nature Publishing group, Scientific Reports (“Controlled assembly of graphene-capped nickel, cobalt and iron  silicides”).
graphene layers
The  above images were taken with the spectroscopy method ARPES while NiSi was formed  under the graphene layer. In the final image (d) scientists can identify a  particular spectrum (the linear Dirac-like spectrum of grapheme electrons)  indicating that the graphene interacts only weakly with the metal silicides and  therefore preserves its unique properties.
The unique properties of graphene such as its incredible  strength and, at the same time, its little weight have raised high expectations  in modern material science. Graphene, a two-dimensional crystal of carbon atoms  packed in a honeycomb structure, has been in the focus of intensive research  which led to a Nobel Prize of Physics in 2010. One major challenge is to  successfully integrate graphene into the established metal-silicide technology.  Scientists from the University of Vienna and their co-workers from research  institutes in Germany and Russia have succeeded in fabricating a novel structure  of high-quality metal silicides all nicely covered and protected underneath a  graphene layer. These two-dimensional sheets are as thin as single atoms.
Following Einstein’s footsteps
In order to uncover the basic properties of the new structure  the scientists need to resort to powerful measurement techniques based on one of  Einstein’s brilliant discoveries – the photoelectric effect. When a light  particle interacts with a material it can transfer all its energy to an electron  inside that material. If the energy of the light is sufficiently large, the  electron acquires enough energy to escape from the material. Angle-resolved  photoemission spectroscopy (ARPES) enables the scientists to extract valuable  information on the electronic properties of the material by determining the  angle under which the electrons escape from the material.
“Single-atom thick layers and hybrid materials made thereof  allow us to study a wealth of novel electronic phenomena and continue to  fascinate the community of material scientists. The ARPES method plays a key  role in these endeavours”, say Alexander Grueneis and Nikolay Verbitskiy, members of the  Electronic Properties of Materials Group at the University of Vienna and  co-authors of the study.
Graphene keeping its head up high
The graphene-capped silicides under investigation are reliably  protected against oxidation and can cover a wide range of electronic materials  and device applications. Most importantly, the graphene layer itself barely  interacts with the silicides underneath and the unique properties of graphene  are widely preserved. The work of the research team, therefore, promises a  clever way to incorporate graphene with existing metal silicide technology which  finds a wide range of applications in semiconductor devices, spintronics,  photovoltaics and thermoelectrics.
The work on graphene related materials is financed by a Marie  Curie fellowship of the European commission and an APART fellowship of the  Austrian Academy of Sciences.
Source: University of Vienna

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