Vanadium oxide nanowires enable windows to block the heat on hot days

New findings in materials science research from the University at Buffalo (UB) could accelerate the creation of “smart” windows. UB researchers managed to manipulate the trigger temperature for vanadium oxide, in order to make it transparent to infrared light at lower temperatures, but it goes through a phase transition to begin reflecting infrared light once it heats up past a certain point.

By preparing vanadium oxide as a nanomaterial instead of in bulk, the scientists managed to lower the compound’s trigger point from 67.2°C (153°F) to 32.2°C (90°F). Doping vanadium oxide nanowires with tungsten brought the temperature down further, to -13°C (7°F). Molybdenum 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, while Sambandamurthy Ganapathy heads the Physical Review B on the use of the electric current in the research.

“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. “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 transition temperature 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 phase transitions 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, vanadium oxide could also be useful in products including computer chips, night-vision instruments and missile guidance systems.

For more information, read the article published in Journal of Physical Chemistry Letters named: “Microscopic and Nanoscale Perspective of the Metal−Insulator Phase Transitions of VO2: Some New Twists to an Old Tale”.