New ‘camera’ with shutter speed of 1 trillionth of a second glimpses dynamic disruption of atoms

At slow shutter speeds, the atomic structure of GeTE looks ordered but blurred. Faster exposures reveal a clearly intricate pattern of dynamic displacements. Credit: Jill Hemman/ORNL, US Department of Energy

Scientists are realizing that the best-performing materials in sustainable energy applications, such as converting sunlight or waste heat into electricity, often use collective fluctuations of clusters of atoms within a much larger structure. This process is often referred to as “dynamic suffering”.

Dynamic disorder

Understanding dynamic disorder in materials can lead to more energy-efficient thermoelectric devices, such as solid-state refrigerators and heat pumps, and also to better recovery of useful energy from waste heat, such as car exhaust and power plant exhaust, by converting it directly into electricity. A thermoelectric device was able to take heat from radioactive plutonium and convert it into electricity to power the Mars Rover when there was not enough sunlight.

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

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

Researchers at Columbia Engineering and the Université de Bourgogne report that they have developed a new kind of “camera” that can see the local disorder. Its key feature is a variable shutter speed: because the disordered atomic clusters move, when the team used a slow shutter the dynamic disturbance was blurred, but when they used a fast 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—it uses neutrons from a source at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) to measure atomic positions at a shutter speed of about a picosecond, or one million million (one trillion) times faster than normal camera shutters. The survey was published on February 20, 2023 by Natural materials.

“It’s only with this new vsPDF tool that we can really see this side of materials,” said Simon Billinge, professor of materials science and applied physics and applied mathematics. “It gives us a completely new way of unraveling the complexity of what is going on in complex materials, hidden effects that can overshadow their properties. With this technique, we will be able to see a material and see which atoms are in the dance and who endures it.”

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

New theory on stabilization of local fluctuations and conversion of waste heat into electricity

The vsPDF tool allowed the researchers to find atomic symmetries that are broken in GeTe, an important material for thermoelectricity that converts waste heat into electricity (or electricity for cooling). They had not previously been able to see the displacements or show the dynamic fluctuations and how fast they were swinging. As a result of the insights from vsPDF, the team 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 to look for new materials with these effects and to apply external forces to influence the effect, leading to even better materials.

Research team

Billinges co-led this work with Simon Kimber, who was at the University of Burgundy in France at the time of the study. Billinge and Kimber worked with colleagues at ORNL and 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 made at ANL.

Next step

Billinge is now working to make his technique easier to use for the research community and apply it to other systems with dynamic disorder. Currently, the technique is not turnkey, 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 around 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

Journal information:
Natural materials

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