Windows that block heat only on hot days: New research brings us closer

April 8, 2011
UB's Sarbajit Banerjee with a scanning electron microscopy image of tungsten-doped vanadium-oxide nanowires, which have a phase transition temperature close to room temperature.

( -- New materials science research from the University at Buffalo could hasten the creation of "smart" windows that reflect heat from the sun on hot summer days but let in the heat in colder weather.

The findings concern a unique class of synthetic chemical compounds that are transparent to at lower temperatures, but undergo a phase transition to begin reflecting infrared when they heat up past a certain point.

An article detailing some of these discoveries appears today (April 7) on the cover of the Journal of Physical Chemistry Letters. Additional papers have appeared online or in print in CrystEngComm, the Journal of Materials Chemistry and Physical Review B.

In the papers, UB researchers report that they have managed to manipulate the trigger temperature for vanadium oxide, one such material. The advance is a crucial step toward making the compound useful for applications such as coatings for energy-saving windows.

By preparing vanadium oxide as a nanomaterial instead of in bulk, the scientists managed to lower the compound's trigger point from 153 degrees Fahrenheit to 90. Doping vanadium oxide with tungsten brought the temperature down further, to 7 degrees Fahrenheit. doping had a similar but smaller effect.

Researchers also found that they were able to induce a phase transition using an electric current instead of heat.

UB chemist Sarbajit Banerjee led the studies, collaborating with Sambandamurthy Ganapathy, an assistant professor of physics, to head the Physical Review B research on the use of the electric current.

"Definitely, we are closer than we've ever been to being able to incorporate these materials into window coatings and other systems that sense infrared light," said Banerjee, an assistant professor. "What we found is an example of how much of a difference finite size can make. You have a material like vanadium oxide, where the phase is too high for it to be useful, and you produce it as a nanomaterial and you can then use it right away."

Banerjee and Ganapathy previously led research projects demonstrating that, in nanoscale form, two additional synthetic compounds -- copper vanadate and potassium vanadate -- exhibit akin to those in vanadium oxide.

Banerjee's work has caught the attention of the National Renewable Energy Laboratory, which has contacted him to discuss developing window coatings that could improve the energy efficiency of buildings with heating or air conditioning systems. The technology could be particularly useful in places like Phoenix and Las Vegas that experience extreme summer temperatures.

Besides smart windows, could also be useful in products including computer chips, night-vision instruments and missile guidance systems, Banerjee said.

Two major awards are funding Banerjee's research on the material: A Cottrell Scholar Award from the Research Corporation for Science Advancement, announced this year, and a National Science Foundation CAREER award, the foundation's most prestigious award for junior investigators.

Explore further: Scientists Formulate Intelligent Glass That Blocks Heat Not Light

More information:
The research is described in a video at

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1 / 5 (1) Apr 08, 2011
Blocks heat on hot days, lets all the heat out during winter. You can't explain that
not rated yet Apr 08, 2011
Modern windows are bilayered with a vacuum between the panes to stop ambient heat from escaping.
1 / 5 (1) Apr 08, 2011
Blocks heat on hot days, lets all the heat out during winter. You can't explain that

Um, convection and conduction do not work through a vaccuum or nobel gas insulated window.

Infrared radiation passes through both glass and vaccuum.
not rated yet Apr 08, 2011
Bread, windows do not use vacuum to block conduction. The pressure is far too high for any reasonable thickness of flat glass.

QC - argon gas only reduces conduction, it doesn't eliminate it, as does a vacuum, because conductivity depends inversely on the molecular weight of the gas. Uranium hexifloride be even better.

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