Smart window material efficiently blocks heat and light

A new smart window material based on amorphous nanomaterials can control the transmission of heat and light with unprecedented efficiency.

The material, developed by a team from the Cockrell School of Engineering at the University of Texas, Austin, USA, can be deposited on plastic surfaces, which makes it cheaper and easier to apply than other materials that usually require glass.

The material enables turning the window or a glass roof darker or lighter, based on the needs of the building. The switching between clear and tinted opacity is carried out more quickly and using less power than in previously developed technologies.

"There's relatively little insight into amorphous materials and how their properties are impacted by local structure," said Delia Milliron, who led the team that devised the low-temperature process for coating the new smart material on plastics.

"We were able to characterise with enough specificity what the local arrangement of the atoms is, so that it sheds light on the differences in properties in a rational way."

The flexible coating material, described in an article to be published in the September issue of the journal Nature Materials, requires a charge of four volts to lighten or darken. When the smart window is light, heat-producing near-infrared radiation is allowed in, resulting in heating of the interior. Darkening of the window blocks the radiation and thus the heating, increasing comfort of the inhabitants and possibly reducing the cost of air-conditioning.

The new material is amorphous, which means it lacks any long-range organisation typical for crystals. Instead, the atoms in the material are organised in a linear, chain-like manner.

The material is unlike other amorphous materials, which are usually produced at very high temperatures. Conventional amorphous materials usually have a denser three-dimensionally bonded structure. However, the structure of the new material, based on condensed niobium oxide, allows ions to flow more freely, which in turn offers a two-fold improvement in the efficiency of the smart window.

During the development, the team gained in depth insight into the behaviour of amorphous materials in relation to their atomic structure. The researchers hope they will be able to use this knowledge to develop novel applications. They believe that by engineering the nanostructure of the materials, they will be able to achieve a wide range of useful properties. One of the possible applications is using the amorphous materials as supercapacitors capable of rapidly storing and releasing electrical energy. 

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