Scientists led by a team from Columbia University and the Université de Bourgogne have developed an innovative “camera” with a shutter speed of 1 trillionth of a second that can see through the dynamic disorder of atoms. Intrinsic local structural effects were found not to be that unusual and can really determine properties, and the energy-resolved variable shutter PDF (pair distribution function) approach also demonstrated these effects are dynamic and the atoms are dancing.
The most effective materials for sustainable energy applications tend to use collective fluctuations of clusters of atoms within a much larger structure, a process called “dynamic disorder”. When materials are functioning inside an operating device, they can act strangely with parts responding and changing in different ways, which is not easy to analyze since the clusters are not just small and disordered, but also fluctuate over time.
As reported in Nature Materials [Kimber et al. Nat. Mater. (2023) DOI: 10.1038/s41563-023-01483-7], understanding this dynamic disorder in materials could lead to improved energy-efficient thermoelectric devices, such as solid-state refrigerators and heat pumps with high energy efficiencies, as well as offering better recovery of useful energy from the waste heat from car exhausts and power station exhausts.
As standard crystallography can’t distinguish between static disorder and atomic motions, the technique was used to collect structural snapshots with different exposure times. At slow shutter speeds the atomic structure of germanium telluride (GeTE) looks ordered but is blurred, while faster exposures show an intricate pattern of dynamic displacements, revealing the complex nature of its local structure.
This approach uses neutrons to measure atomic positions, allowing a view of which atoms are dancing and which are not that provides a new way to untangle the complexities of what is going on in complex materials, and which can supercharge their properties. It also meant it was possible to locate atomic symmetries being broken in GeTe, a key material for thermoelectricity that converts waste heat to electricity or electricity into cooling.
The technique also showed that atom dynamics are very anisotropic, so the material is stiff in some directions but soft in others. This atomic dance takes place in a confined space and the atoms have to move cooperatively to accommodate this, which could be important in driving such behavior in related systems. As Simon Billinge told Materials Today, “Such understanding is transformative because when you have a better understanding of what is driving interesting effects, you have a better chance to predict and engineer materials to do it better.”
The team are also extending the type of materials to investigate quantum materials with emergent behaviors like superconductivity and insulator metal transitions, and think there is a need for quantum mechanical calculations to be developed to correctly capture these non-long-range-ordered phenomena.
“Such understanding is transformative because when you have a better understanding of what is driving interesting effects, you have a better chance to predict and engineer materials to do it better.”Simon Billinge
An artists’ representation of how atoms look when they are blurred out by taking the picture with a slow shutter, and what they look like frozen when taken with a fast shutter (credit: Jill Hemman/ORNL, US Dept. of Energy)