Forum für Wissenschaft, Industrie und Wirtschaft

Hauptsponsoren:     3M 
Datenbankrecherche:

 

Why Calcium Improves a High-Temperature Superconductor

08.06.2004


Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have found evidence to prove why adding a small amount of calcium to a common high-temperature superconductor significantly increases the amount of electric current the material can carry. This research may be a first step toward developing commercial applications for high-temperature superconducting materials. The results appear in the May 15, 2004 issue of Physical Review Letters.


Yimei Zhu (left) and Marvin Schofield, in front of the transmission electron microscope they used to perform the research



“Many materials classified as high-temperature superconductors exhibit good properties only in single-crystal form and are actually unsuitable for practical applications, such as high-efficiency electrical wire, because their bulk composition – individual crystalline grains – disrupts the flow of electrons,” said Yimei Zhu, a Brookhaven physicist who led the research.

... mehr zu:
»Science »Why »YBCO


“But for practical applications in which large electric currents need to be transported, such as power cables, the polycrystalline forms must be used. These polycrystalline materials carry a very low current compared to their single-crystal counterparts,” he said.

This is due to the problem of grain boundaries – the interfaces created between adjacent grains. At grain boundaries, incoming electrons slow down or change direction, thus losing momentum and releasing the lost energy as heat. This results in low electron flow across the boundaries – exactly the opposite of “good” superconductor behavior.

Researchers theorized that electric voltage barriers at the grain boundaries are the cause of this problem. Now, the Brookhaven scientists have found evidence to support this theory.

“We discovered why grain boundaries are the predominant factor that limits the current flow in these materials,” said Brookhaven physicist Marvin Schofield, the paper’s principle author.

“By understanding grain boundary behavior, we can engineer grain boundaries with improved properties. This is a major challenge in superconductor research, which may lead to the commercialization of high-temperature superconducting materials that could revolutionize our daily lives in the near future.”

Scientists worldwide have studied YBCO, a high-temperature superconductor named for the elements it contains – yttrium, barium, copper, and oxygen. They know that it conducts significantly better when it is “doped” with calcium, but have not known, until now, why this is true. The Brookhaven scientists determined this by comparing calcium-doped YBCO to undoped YBCO.

The evidence lies in the areas within grain boundaries in which adjacent grains are most mismatched. To visualize this, picture a centimeter-based ruler next to an inch-based one, where the tick marks on each ruler represent the positions of atoms in the crystal structure of two adjacent, slightly different grains. The marks will match in some cases, nearly match in others, and misalign completely in the rest.

In undoped YBCO, the scientists found, the electrons encounter the most electrical resistance at the most misaligned regions, where the voltage barrier is wide and high. Doping YBCO with calcium causes these regions to shrink, both in width and height. As a result, Schofield and his colleagues determined that calcium doping increases the current across the grain boundary by 35 percent.

To perform the research, the Brookhaven scientists used a YBCO “bicrystal,” a type of crystal grown to contain just one grain boundary, much like two very large grains merged together. The electromagnetic properties of bicrystals are well characterized, allowing the researchers to pinpoint what happens to the electrons at the boundary upon calcium doping, using the results as a model for the overall material. Bicrystals eliminate the impossible task of isolating one boundary out of thousands in the material sample.

To closely examine the bicrystal grain boundary, the scientists used a transmission electron microscope (TEM), a device that uses electrons as tiny probes to “see” inside materials. A sample is placed inside the TEM and bombarded with electrons. As the electrons pass through the sample, they are scattered away from the charged regions of the material. When they emerge, they carry information about the electric and magnetic fields within the sample. This information is then retrieved by a method known as electron holography.

“With electron holography,” Schofield explained, “we can see exactly what the electrons in the material see at the grain boundary. Thus, this method takes us a tremendous step closer to understanding the role grain boundaries play in the properties of real materials.”

Additional collaborators instrumental in this research were Marco Beleggia, of Brookhaven Lab, and Karsten Guth and Christian Jooss, both of the University of Gottingen in Germany. The work was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy’s Office of Science and the German Research Foundation.

Karen McNulty Walsh | BNL
Weitere Informationen:
http://www.bnl.gov/bnlweb/pubaf/pr/2004/bnlpr060704.htm

Weitere Berichte zu: Science Why YBCO

Weitere Nachrichten aus der Kategorie Materialwissenschaften:

nachricht Quantenanomalien: Das Universum in einem Kristall
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

nachricht Projekt »ADIR«: Laser bergen wertvolle Werkstoffe
21.07.2017 | Fraunhofer-Institut für Lasertechnik ILT

Alle Nachrichten aus der Kategorie: Materialwissenschaften >>>

Die aktuellsten Pressemeldungen zum Suchbegriff Innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Molekulares Lego

Sie können ihre Farbe wechseln, ihren Spin verändern oder von fest zu flüssig wechseln: Eine bestimmte Klasse von Polymeren besitzt faszinierende Eigenschaften. Wie sie das schaffen, haben Forscher der Uni Würzburg untersucht.

Bei dieser Arbeit handele es sich um ein „Hot Paper“, das interessante und wichtige Aspekte einer neuen Polymerklasse behandelt, die aufgrund ihrer Vielfalt an...

Im Focus: Das Universum in einem Kristall

Dresdener Forscher haben in Zusammenarbeit mit einem internationalen Forscherteam einen unerwarteten experimentellen Zugang zu einem Problem der Allgemeinen Realitätstheorie gefunden. Im Fachmagazin Nature berichten sie, dass es ihnen in neuartigen Materialien und mit Hilfe von thermoelektrischen Messungen gelungen ist, die Schwerkraft-Quantenanomalie nachzuweisen. Erstmals konnten so Quantenanomalien in simulierten Schwerfeldern an einem realen Kristall untersucht werden.

In der Physik spielen Messgrößen wie Energie, Impuls oder elektrische Ladung, welche ihre Erscheinungsform zwar ändern können, aber niemals verloren gehen oder...

Im Focus: Manipulation des Elektronenspins ohne Informationsverlust

Physiker haben eine neue Technik entwickelt, um auf einem Chip den Elektronenspin mit elektrischen Spannungen zu steuern. Mit der neu entwickelten Methode kann der Zerfall des Spins unterdrückt, die enthaltene Information erhalten und über vergleichsweise grosse Distanzen übermittelt werden. Das zeigt ein Team des Departement Physik der Universität Basel und des Swiss Nanoscience Instituts in einer Veröffentlichung in Physical Review X.

Seit einigen Jahren wird weltweit untersucht, wie sich der Spin des Elektrons zur Speicherung und Übertragung von Information nutzen lässt. Der Spin jedes...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: Das Proton präzise gewogen

Wie schwer ist ein Proton? Auf dem Weg zur möglichst exakten Kenntnis dieser fundamentalen Konstanten ist jetzt Wissenschaftlern aus Deutschland und Japan ein wichtiger Schritt gelungen. Mit Präzisionsmessungen an einem einzelnen Proton konnten sie nicht nur die Genauigkeit um einen Faktor drei verbessern, sondern auch den bisherigen Wert korrigieren.

Die Masse eines einzelnen Protons noch genauer zu bestimmen – das machen die Physiker um Klaus Blaum und Sven Sturm vom Max-Planck-Institut für Kernphysik in...

Alle Focus-News des Innovations-reports >>>

Anzeige

Anzeige

IHR
JOB & KARRIERE
SERVICE
im innovations-report
in Kooperation mit academics
Veranstaltungen

Den Nachhaltigkeitskreis schließen: Lebensmittelschutz durch biobasierte Materialien

21.07.2017 | Veranstaltungen

Operatortheorie im Fokus

20.07.2017 | Veranstaltungen

Technologietag der Fraunhofer-Allianz Big Data: Know-how für die Industrie 4.0

18.07.2017 | Veranstaltungen

 
VideoLinks
B2B-VideoLinks
Weitere VideoLinks >>>
Aktuelle Beiträge

Pharmakologie - Im Strom der Bläschen

21.07.2017 | Biowissenschaften Chemie

Verbesserung des mobilen Internetzugangs der Zukunft

21.07.2017 | Informationstechnologie

Blutstammzellen reagieren selbst auf schwere Infektionen

21.07.2017 | Biowissenschaften Chemie