Smart glass' can switch from transparent to opaque at the flick of a switch and is increasingly used in cars, aircraft and homes to reduce the Sun's glare and filter out infrared light and heat. Masaki Nakano and colleagues from the RIKEN Center for Emergent Matter Science have now used vanadium dioxide to make a transparent material that can be activated to block infrared light without affecting its transparency for visible light.
Vanadium dioxide is a well-known thermochromic material that is transparent below about 30 °C and reflects infrared light above 60 °C. This transition is related to a change in crystal structure that also results in a shift from electrically insulating properties at lower temperatures to conductive properties at higher temperatures.
For the first time, Nakano and colleagues have been able to trigger this change using a static voltage rather than heat. Previous attempts were unable to create a large enough electric field to completely switch the material from an insulator to a conductor.