ESRF hard X-rays help in developing disordered materials for "smart windows"


An international team of researchers has invented a new flexible smart window material that, when incorporated into windows, sunroofs, or even curved glass surfaces, will have the ability to control both heat and light from the sun. The ESRF was key in providing an insight into the structure of the new material.

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The advancement is a new low-temperature process for coating the new smart material on plastic, which makes it easier and cheaper to apply than conventional coatings made directly on the glass itself. The team created a flexible electrochromic device, which means a small electric charge (about 4 volts) can lighten or darken the material and control the transmission of heat-producing, near-infrared radiation. Such smart windows are aimed at saving on cooling and heating bills for homes and businesses. 

The research team is led by researchers at the University of Austin Texas (US) and it includes scientists at the ESRF and CNRS, Grenoble Alpes Université, Institut des Sciences de la Terre (France), and Ikerbasque (Spain).

 The new electrochromic material, like its high-temperature processed counterpart, has an amorphous structure, meaning the atoms lack any long-range organization as would be found in a crystal. “There is relatively little insight into amorphous materials and how their properties are impacted by local structure,” Delia Milliron, leader of the investigation, said.

The role of the ESRF was instrumental in the characterisation of this new material. It showed a unique local arrangement of the atoms in a low-dimensionality, chain-like structure. Whereas conventional amorphous materials produced at high temperature have a denser three-dimensionally bonded structure, the researchers’ new linearly structured material, made of chemically condensed niobium oxide, allows ions to flow in and out more freely. As a result, it is twice as energy efficient as the conventionally processed smart window material.


Linear structural model of chemically condensed niobium oxide determined by combined experimental and theoretical approach (green balls represent Nb while red balls represent O). Credits: Cockrell School of Engineering.


"The characterisation of this type of low-dimensionality materials is challenging. The use of high-energy X-rays in combination with the molecular modelling effort was crucial. We are looking forward to the new opportunities that the new ID15 beamline will open for in operando studies when it opens later this year", Alejandro Fernandez-Martinez, from the Institut des Sciences de la Terre, said.

Apart from using the ESRF, the researchers combined other of techniques and measurements to determine an atomic structure that is consistent in both experiment and theory. They carried out Pair Distribution Function analysis on ID15 at the ESRF, as well as Raman Spectroscopy and theoretical calculations in the US.

Milliron believes the knowledge gained here could inspire deliberate engineering of amorphous materials for other applications, such as supercapacitors that store and release electrical energy rapidly and efficiently.


Llordés A. et al, Nature Materials, DOI: 10.1038/NMAT4734.

Top image: A darkened electrochromic film on plastic prepared by chemical condensation. Credits: Cockrell School of Engineering.