Windows that block heat only on hot days.

• Position: Physics - Brief article

The creation of "smart" windows that reflect heat from sun on hot summer days but let in the warmth in colder weather could be hastened by new materials research, suggests an article in the Journal of Physical Chemistry Letters. The findings concern a unique class of synthetic chemical compounds that is transparent to infrared light at lower temperatures, but undergoes a phase transition to begin reflecting infrared when heated past a certain point. 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 have managed to lower the compound's trigger point from 153[degrees]F to 90[degrees]. Doping vanadium oxide nanowires with tungsten brings the temperature down even further. Molybdenum doping has a similar, but smaller, effect.

Researchers also found that they were...