Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Unusual material that contracts when heated is giving up its secrets to physicists

19.11.2004


Most solids expand when heated, a familiar phenomenon with many practical implications. Among the rare exceptions to this rule, the compound zirconium tungstate stands out by virtue of the enormous temperature range over which it exhibits so-called "negative thermal expansion," contracting as it heats up and expanding as it cools, and because it does so uniformly in all directions.



While engineers are already pursuing practical applications in areas ranging from electronics to dentistry, physicists have had a hard time explaining exactly what causes zirconium tungstate to behave in such a bizarre manner. Now, a team of researchers at the University of California, Santa Cruz, and other institutions has reported new insights into the atomic interactions underlying this phenomenon. A paper describing their findings will be posted online on November 22 and will appear in the December 26 issue of the journal Physical Review Letters. "We have shown that a combination of geometrical frustration and unusual atomic motions are likely to be important to the negative thermal expansion in zirconium tungstate," said Zack Schlesinger, a professor of physics at UCSC.

Geometrical frustration sounds like something a high-school math student might feel, but is actually a rich area of research in physics and material science. In simple terms, geometrical frustration is like trying to tile a floor with pentagons--the shapes just won’t fit together. In the case of zirconium tungstate, geometrical frustration comes into play during certain temperature-related vibrations of the compound’s crystal lattice structure, the configuration of atomic bonds that holds the atoms together in a crystal.


The normal thermal expansion of solids results from changes in the atomic motions that make up these lattice vibrations. As heating adds more kinetic energy to the system, the lattice structure expands (in most solids) to accommodate the increasingly energetic atomic motions.

To study the atomic motions involved in lattice vibrations, physicists separate the vibrations into discrete "modes" or types of vibrations. In their investigation of zirconium tungstate, Schlesinger and his collaborators found evidence for a rotational ("twisting") mode that, due to geometrical frustration, occurs together with a translational ("back-and-forth") mode. This mixing of rotational and translational motion has the effect of pulling the overall structure together as heating puts more energy into the vibrations.

In other materials that show negative thermal expansion, the vibrational modes that pull the solid together create instabilities that eventually lead to rearrangements in the atomic structure. As a result, the negative thermal expansion only occurs over a narrow temperature range. In zirconium tungstate, however, geometrical frustration appears to block any such instability.

At least, that is the researchers’ current thinking, Schlesinger said. "To understand a complex system like this is not trivial. You have to break it down into all the different components of the atomic motions, and our work is making progress in that direction," he said. "It involves both mathematical analysis and experimental measurements, and ultimately you need to be able to visualize it."

The experiments themselves are relatively simple, he said. They involve shining infrared light on a sample of zirconium tungstate and measuring the reflectivity, which can be transformed mathematically into optical conductivity. These measurements reveal the frequencies of light that are absorbed by coupling with the lattice vibrations, and the researchers studied how these measurements changed with temperature.

Schlesinger said he initially gave the project to an undergraduate working in his lab, Chandra Turpen. When she began finding anomalous results, graduate student Jason Hancock used mathematical modeling to help figure out what the results meant. "It started out as a senior thesis project that just became a lot more interesting as we went along," Schlesinger said. In addition to Schlesinger, Turpen, and Hancock, who is the first author of the paper, the other coauthors are Glen Kowach of the City College of New York and Arthur Ramirez of Bell Laboratories, Lucent Technologies, in New Jersey.

Schlesinger said the findings are interesting with respect to both pure physics and practical applications. On the pure physics side, they seem to provide a new and unusual example of geometrical frustration, which is most often studied in the realm of magnetism and disordered systems such as spin glasses. "This material is not disordered--it is a perfect stoichiometric crystal--so we are seeing geometrical frustration manifested in a whole new system," Schlesinger said.

On the practical side, thermal expansion is a big problem in many different areas. In dentistry, most cracked fillings are the result of uneven expansion and contraction--the so-called "tea-to-ice-cream problem." And engineers working on everything from electronics to high-performance engines must cope with the effects of thermal expansion. A material that did not expand or contract with changing temperatures would have broad applications. "If you could create the right mix of materials to neutralize thermal expansion, that would be quite a significant technological advance," Schlesinger said.

Tim Stephens | EurekAlert!
Further information:
http://www.ucsc.edu

More articles from Physics and Astronomy:

nachricht Major discovery in controlling quantum states of single atoms
20.02.2018 | Institute for Basic Science

nachricht Observing and controlling ultrafast processes with attosecond resolution
20.02.2018 | Technische Universität München

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

'Lipid asymmetry' plays key role in activating immune cells

20.02.2018 | Life Sciences

MRI technique differentiates benign breast lesions from malignancies

20.02.2018 | Medical Engineering

Major discovery in controlling quantum states of single atoms

20.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>