In the recent article, ”No More Curtains” by Jesse Emspak Big windows provide light, and a view, but they don't always do much for energy efficiency or privacy. The glass transmits heat to the outside in winter and traps it inside during the summer. The only real solution: curtains or blinds. But now there's a glass that changes, chameleon-like, from opaque to transparent, and can be adjusted for different wavelengths of light. It could boost energy efficiency in buildings with large glass facades, freeing homeowners from the chore of picking window treatments. The glass is the brainchild of scientists at Lawrence Berkeley National Laboratory (LBNL) in California and the Autonomous University of Barcelona. It's made of niobate, a compound composed of the element niobium and oxygen. The ingredients get mixed together with nanometer-sized crystals of indium tin oxide, or ITO, which is used in touch screens to register when a finger contacts the display. The scientists' experiments appear online in the Aug. 14 issue of the journal Nature.
The resulting material is called a glass because it has the characteristic structure of a glass: the molecules are all jumbled around, without a clear pattern, like in a liquid. But unlike a liquid, glass doesn't flow. Ordinary window glass is made of silicon dioxide mixed with other chemicals, such as sodium oxide (Na2O), magnesia (MgO), lime (CaO) and alumina (Al2O3), which give it extra strength. To make their smart glass, the researchers dissolved the niobate in water, and then add the nanocrystals of indium tin oxide. The niobate molecules linked up to the ITO, forming tiny clusters. "The art was making the nanocrystals," said Delia J. Milliron, a materials scientist at LBNL, who led the study. Otherwise, Milliron said, the chemistry is relatively straightforward, and all done at room temperature. The researchers then let the solution evaporate while heating it, which transformed the niobate-ITO mixture into an amorphous...