electronic growth of quantum alloys aids superconductivity

UT-ORNL professor's discovery leads to $1.2 million hydrogen grant

KNOXVILLE -- A unique discovery being published this week by University of Tennessee Knoxville scientists has led to a $1.2 million grant to help overcome roadblocks facing the wide-scale use of hydrogen as a national energy source.

Hanno Weitering, a professor of physics and joint faculty member between UT and Oak Ridge National Laboratory, found that by adding small amounts of the element bismuth to an extremely thin film of lead atoms, he could fine-tune the stability and physical properties of the newly made "quantum alloy."

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The research appears in this week's issue of the journal Science. In this instance, Weitering's experiment revealed that by varying the amount of bismuth in the lead film, he could vary the lead's superconductivity, a highly studied trait of metals that allows them to conduct electricity, usually at very low temperatures, without losing energy. Weitering and co-authors Zhenyu Zhang, a UT-ORNL research professor, and Jim Thompson, UT professor of physics, call the process "electronic growth" because the formation and properties of the film can be controlled based on the number of free electrons it contains. Lead and bismuth differ only by one electron, so adding bismuth to the mix adds electrons. The significance of the research comes from the fact that it is extremely difficult to control a physical trait like superconductivity at such a small scale in a precise manner without suppressing or destroying it, according to Weitering. "You could consider this a proof of principle," said Weitering. "Plus, if we can change physical properties in this manner, it raises the question of whether we could also tune a material's chemical properties." In fact, that is the question Weitering will address with a $1.2-million grant from the U.S. Department of Energy to study how electronic growth might influence the efficiency of hydrogen fuel cells. Instead of mixing bismuth with lead, in this study, Weitering will mix aluminum and/or sodium with magnesium. Weitering will modify magnesium by adding different amounts of sodium and aluminum to see if doing so makes it easier for hydrogen atoms to travel in and out of an incredibly thin sheet of magnesium. Learning how best to store hydrogen and then easily remove it presents a major hurdle to the use of hydrogen as an energy source. "Bulk magnesium is a promising storage material but right now, the process only works at high temperatures -- 300 degrees Celsius or so," he said. "We'd like to lower that temperature. We're aiming to show that the chemistry can be much better controlled at a very small scale." Weitering's work is part of a field known as nanophysics. He deals with materials in incredibly small amounts, on a nearly atom-by-atom basis.

In such small quantities, materials take on a very different set of qualities than they might in a bulk size, opening a number of avenues of study.

While Weitering points out that his findings are not guaranteed to work on bulk levels, he noted that the research sheds critical light on the nature of the materials being studied.

The grant is part of $11.2 million given to universities and national laboratories around the U.S. as part of the DOE's effort to apply science to the challenges of wide-scale hydrogen use.

Weitering's co-principal investigators on the grant are Ward Plummer, a UT-ORNL distinguished professor of physics, and Zhang. Weitering and Zhang both hold chairs of excellence in the UT-ORNL Joint Institute for Advanced Materials, currently led by Plummer.

Weitering pointed to the energy research as a logical area of study as a joint UT-ORNL researcher.

"This is a great way to contribute to the mission of the university and of the lab as joint faculty," he said. ###

Contact: Jay Mayfield jay.mayfield@tennessee.edu 865-974-9409 University of Tennessee at Knoxville

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