11-10 :: October 2011

nanotimes News in Brief

Caltech Engineers Reveal How Scandium Trifluoride Contracts with Heat

They shrink when you heat ‘em. Most materials expand when heated, but a few contract. Now engineers at the California Institute of Technology (Caltech) have figured out how one of these curious mate- rials, scandium trifluoride (ScF3

), does the

trick – a finding, they say, that will lead to a deeper understanding of all kinds of materi- als. Materials that don‘t expand under heat aren‘t just an oddity. They‘re useful in a variety of applications – in mechanical ma- chines such as clocks, for example, that have to be extremely precise. Materials that contract could counteract the expansion of more conventional ones, helping devices remain stable even when the heat is on.

“When you heat a solid, most of the heat goes into the vibrations of the atoms,” explains Brent Fultz, professor of materials science and applied physics and a coauthor of the paper. In normal materials, this vibration causes atoms to move apart and the material to expand. A few of the known shrinking materials, however, have unique crystal structures that cause them to contract when heated, a property called negati- ve thermal expansion. But because these crystal structures are complicated, scientists have not been able to clearly see how heat – in the form of atomic vibrations – could lead to contraction.

Image/Video: Heat causes the atoms in ScF3 to vibrate, as captured in this snapshot from a simulation. Fluorine atoms are in green while scandium atoms are in yellow. © Caltech/C. Li et al.

Chen W. Li, Xiaoli Tang, J. A. Muñoz, J. B. Keith, S. J. Tracy, D. L. Abernathy, and B. Fultz: Structural Relationship between Negative Thermal Expansion and Quartic Anharmonicity of Cubic ScF3

, In: Physical Review Letters, Volume

107(2011), Issue 19, November 04, 2011, Article 195504 [5 pages], DOI:10.1103/PhysRevLett.107.195504: http://dx.doi.org/10.1103/PhysRevLett.107.195504

http://www.youtube.com/user/caltech#p/u/0/l46Kgm5u3Nw

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