Triple point: Physicists pinpoint key property of material that both conducts and insulates

Aug 21, 2013
The lines of data points are where two of the three solid-state phases of vanadium dioxide can exist stably together, and the point where the three lines meet -- the triple point -- is where all three phases can exist together. Credit: David Cobden/University of Washington

It is well known to scientists that the three common phases of water – ice, liquid and vapor – can exist stably together only at a particular temperature and pressure, called the triple point.

Also well known is that the solid form of many materials can have numerous phases, but it is difficult to pinpoint the temperature and pressure for the points at which three solid phases can coexist stably.

Scientists now have made the first-ever accurate determination of a triple point in a substance called vanadium dioxide, which is known for switching rapidly – in as little as one 10-trillionth of a second – from an to a conductor, and thus could be useful in various technologies.

"These solid-state triple points are fiendishly difficult to study, essentially because the different shapes of the solid phases makes it hard for them to match up happily at their interfaces," said David Cobden, a University of Washington physics professor.

"There are, in theory, many triple points hidden inside a solid, but they are very rarely probed."

Cobden is the lead author of a paper describing the work, published Aug. 22 in Nature.

In 1959, researchers at Bell Laboratories discovered vanadium dioxide's ability to rearrange and shift from an insulator to a , called a metal-insulator transition. Twenty years later it was discovered that there are two slightly different insulating phases.

The new research shows that those two insulating phases and the conducting phase in solid vanadium dioxide can coexist stably at 65 degrees Celsius, give or take a tenth of a degree (65 degrees C is equal to 149 degrees Fahrenheit).

To find that triple point, Cobden's team stretched vanadium dioxide under a . The team had to build an apparatus to stretch the tiny wires without breaking them, and it was the stretching that allowed the observation of the triple point, Cobden said.

It turned out that when the material manifested its triple point, no force was being applied – the wires were not being stretched or compressed.

The researchers originally set out simply to learn more about the phase transition and only gradually realized that the triple point was key to it, Cobden said. That process took several years, and then it took a couple more to design an experiment to pin down the triple point.

"No previous experiment was able to investigate the properties around the triple point," he said.

He regards the work as "just a step, but a significant step" in understanding the metal-insulator transition in . That could lead to development of new types of electrical and optical switches, Cobden said, and similar experiments could lead to breakthroughs with other materials.

"If you don't know the triple point, you don't know the basic facts about this phase transition," he said. "You will never be able to make use of the transition unless you understand it better."

Explore further: Pseudoparticles travel through photoactive material

More information: Nature paper: dx.doi.org/10.1038/nature12425

Related Stories

Scientists crack materials mystery in vanadium dioxide

Nov 23, 2010

(PhysOrg.com) -- A systematic study of phase changes in vanadium dioxide has solved a mystery that has puzzled scientists for decades, according to researchers at the Department of Energy's Oak Ridge National ...

Recommended for you

Pseudoparticles travel through photoactive material

Apr 23, 2015

Researchers of Karlsruhe Institute of Technology (KIT) have unveiled an important step in the conversion of light into storable energy: Together with scientists of the Fritz Haber Institute in Berlin and ...

From metal to insulator and back again

Apr 22, 2015

New work from Carnegie's Russell Hemley and Ivan Naumov hones in on the physics underlying the recently discovered fact that some metals stop being metallic under pressure. Their work is published in Physical Re ...

Electron spin brings order to high entropy alloys

Apr 22, 2015

Researchers from North Carolina State University have discovered that electron spin brings a previously unknown degree of order to the high entropy alloy nickel iron chromium cobalt (NiFeCrCo) - and may play ...

Expanding the reach of metallic glass

Apr 22, 2015

Metallic glass, a class of materials that offers both pliability and strength, is poised for a friendly takeover of the chemical landscape.

Electrons move like light in three-dimensional solid

Apr 22, 2015

Electrons were observed to travel in a solid at an unusually high velocity, which remained the same independent of the electron energy. This anomalous light-like behavior is found in special two-dimensional ...

Quantum model helps solve mysteries of water

Apr 20, 2015

Water is one of the most common and extensively studied substances on earth. It is vital for all known forms of life but its unique behaviour has yet to be explained in terms of the properties of individual ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.