Windows That Block Heat Only On Hot Day

Scientists from University of Buffalo have invented a material for window glass that reflects back heat from sun in summer but allows it during winter. These materials are transparent to infrared light at low temperatures but higher temperature causes them to undergo phase transition (change in internal structure) which improves reflection.

Researchers have basically found the temperature for Vanadium Oxide at which this change happens. 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 nanowires with tungsten brought the temperature down further, to 7 degrees Fahrenheit. 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.

Applications

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