Novel neutron camera reveals atomic structure of future green technology
According to researchers, the best materials for sustainable energy uses, like turning sunlight or waste heat into electricity, frequently use collective fluctuations of clusters of atoms within a much larger structure.
Called "dynamic disorder," understanding it in materials may help create thermoelectric devices like solid-state refrigerators and heat pumps that are more energy-efficient and improve the direct conversion of waste heat from power plants and automobile exhausts into usable energy.
For example, when there wasn't enough sunlight to power the Mars Rover, a thermoelectric device could turn the heat from the radioactive plutonium into electricity.
Materials can act as though they are living and dancing while working inside an operating device; various sections of the material can react and change in unique and unexpected ways.
However, "dynamic disorder" is hard to study because the small, disorganized clusters change over time. Also, researchers aren't interested in "boring" non-changing disorders in materials because they don't improve their qualities.
To help solve this, a new study by researchers from the Université de Bourgogne and Columbia Engineering claims to have created a brand-new type of "camera" that can detect local chaos. Its essential feature is a variable shutter speed: because the disordered atomic clusters are moving, when the team used a slow shutter, the "dynamic disorder" blurred out, but when they used a fast shutter, they could see it.
The new process, called variable shutter atomic pair distribution, or vsPDF, measures atomic positions with a shutter speed of about one picosecond, or a 'million million' (a trillion) times faster than typical camera shutters.
Professor of materials science, applied physics, and applied mathematics Simon Billinge said, "It gives us a whole new way to untangle the complexities of what is happening in complex materials—hidden effects that can supercharge their properties. With this technique, we can watch a material and see which atoms are dancing and which are sitting it out.”
In the future, Billinge is making it easier for scientists to understand and use his method on more dynamically chaotic systems. The technique still needs to be fully automated, but with more work, it should become more common and can be used in many material systems where the movement of atoms is significant.
For example, it can be used to watch lithium move in battery electrodes or study the movement of particles when sunlight splits water.
You can view the study for yourself in the journal Nature Materials.
"Cubic energy materials such as thermoelectrics or hybrid perovskite materials are often understood to be highly disordered. In GeTe and related IV–VI compounds, this is thought to provide the low thermal conductivities needed for thermoelectric applications. Since conventional crystallography cannot distinguish between static disorder and atomic motions, we develop the energy-resolved variable-shutter pair distribution function technique. This collects structural snapshots with varying exposure times on timescales relevant for atomic motions. In disagreement with previous interpretations, we find the time-averaged structure of GeTe to be crystalline at all temperatures, but with anisotropic anharmonic dynamics at higher temperatures that resemble static disorder at fast shutter speeds, with correlated ferroelectric fluctuations along the <100>c direction. We show that this anisotropy naturally emerges from a Ginzburg–Landau model that couples polarization fluctuations through long-range elastic interactions. By accessing time-dependent atomic correlations in energy materials, we resolve the long-standing disagreement between local and average structure probes and show that spontaneous anisotropy is ubiquitous in cubic IV–VI materials."