New ‘camera’ with shutter speed of 1 trillionth of a second sees through dynamic disorder of atoms

At slow shutter speeds, GeTE’s atomic structure looks ordered but blurry. Faster exposures reveal a distinctly intricate pattern of dynamic movement. Credits: Jill Hemman / ORNL, US Department of Energy

Researchers are beginning to understand that the best-performing materials in renewable energy applications, such as converting sunlight or waste heat into electricity, often exploit collective fluctuations of clusters of atoms within a much larger structure. This process is often referred to as “dynamic disorder.”

Dynamic disorder

Understanding dynamic disorder in materials can lead to more energy-efficient thermoelectric devices, such as solid-state refrigerators and heat pumps, as well as better recovery of usable energy from waste heat, such as car exhausts and power station exhausts, by directly convert to electricity. A thermoelectric device was able to extract heat from radioactive plutonium and convert it into electricity to power the Mars Rover when there wasn’t enough sunlight.

When materials function in a working device, they can behave as if they were alive and dancing – parts of the material react and change in amazing and unexpected ways. This dynamic disorder is difficult to study because the clusters are not only so small and disordered, but also fluctuate over time. In addition, there is a “dull” non-fluctuating disorder in materials that researchers are not interested in because the disorder does not improve properties. Until now it was impossible to see the relevant dynamic disorder against the background of a less relevant static disorder.

New “camera” has an incredibly fast shutter speed of about 1 picosecond

Researchers from Columbia Engineering and Universit√© de Bourgogne report developing a new kind of “camera” that can see local disorder. Its main feature is a variable shutter speed: because the disordered atom clusters move, the dynamic disorder faded when the team used a slow shutter, but when they used a short shutter they could see it. The new method, which they call variable shutter PDF or vsPDF (for atomic pair distribution function), doesn’t work like a conventional camera. atomic positions with a shutter speed of about one picosecond, or a million million (a trillion) times faster than normal camera shutters. The study was published on February 20, 2023 by Natural materials.

“Only with this new vsPDF tool can we really see this side of materials,” said Simon Billinge, professor of materials science and applied physics and applied mathematics. “It gives us a whole new way to untangle the complexities of what’s going on in complex materials, hidden effects that can amplify their properties. This technique allows us to look at a material and see which atoms are in the dance.” and they’re out.”

Revealing atomic structures with a “neutron camera”. Credit: Oak Ridge National Laboratory

New theory on stabilizing local fluctuations and converting waste heat into electricity

The vsPDF tool enabled the researchers to find atomic symmetries that are broken in GeTe, an important thermoelectricity material that converts waste heat into electricity (or electricity into refrigeration). They had previously been unable to see the movements, or show the dynamic fluctuations and how fast they fluctuated. As a result of vsPDF’s insights, the team has developed a new theory showing how such local fluctuations can form in GeTe and related materials. Such a mechanistic understanding of the dance will help researchers search for new materials with these effects and apply external forces to influence the effect, leading to even better materials.

Research group

Billlinge co-led this work with Simon Kimber, who was at the University of Bourgogne in France at the time of the research. Billinge and Kimber teamed up with colleagues from ORNL and the Argonne National Laboratory (ANL), also funded by the DOE. The inelastic neutron scattering measurements for the vsPDF camera were made at ORNL; the theory was done at ANL.

Next steps

Billinge is now working to make his technique easier to use for the research community and apply it to other dynamic disorder systems. At the moment the technique is not ready, but with further development it should become a much more standard measurement that could be used on many material systems where atomic dynamics are important, from watching lithium move in battery electrodes to studying dynamic processes during water splitting with sunlight.

The study is titled “Dynamic Crystallography Reveals Spontaneous Anisotropy in Cubic GeTe.”

More information:
Simon AJ Kimber et al, Dynamic crystallography reveals spontaneous anisotropy in cubic GeTe, Natural materials (2023). DOI: 10.1038/s41563-023-01483-7

Provided by Columbia University School of Engineering and Applied Science

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