HOUSTON – (August 1, 2024) – Materials behave differently in different size regimes, and researchers tend to cluster their efforts either at the nanoscale, examining materials in atom-level detail, or at the microscale, looking at structures between three and five orders of magnitude greater.
However, less is known about what happens in the "in-between" realm spanning from 10 billionths to 1 millionth of a meter.
"We call this the mesoscale," said Rice University materials scientist Lane Martin, who together with collaborators at the U.S. Department of Energy's (DOE) Argonne National Laboratory and Lawrence Berkeley National Laboratory, focused on this overlooked interval for insight into how a piezoelectric material transforms a voltage into a change in shape and vice versa.
"We examined a piezoelectric material called a relaxor ferroelectric and uncovered an exciting connection between the nanoscale features of its atomic structure and its macroscopic material properties," said Martin, who is a corresponding author on a study about the research published in Science. "Our insights into the mesoscale structures provide a new approach to the design of smaller electromechanical devices that work in ways not thought possible."
The research could inform applications in high-efficiency energy storage and conversion, next-generation electronics, lasers and sensors.
The focus of the study is an oxide made of a complex mixture of lead, magnesium, niobium and titanium, and it is characterized by tiny pairs of positive and negative charges, or dipoles, that group into clusters called polar nanodomains. Under an electric field, these dipoles align in the same direction, causing the material to change shape, or strain. Similarly, applying a strain can alter the dipole direction, creating an electric voltage.
"If you analyze a material at the nanoscale, you only learn about the average atomic structure within an ultrasmall region," said Yue Cao, an Argonne physicist who is also a corresponding author on the study. "But materials are not necessarily uniform and do not respond in the same way to an electric field in all parts. This is where the mesoscale can paint a more complete picture bridging the nano- to microscale."
To test the material under operating conditions, Martin, Rice's Robert A. Welch Professor, professor of materials science and nanoengineering and director of the Rice Advanced Materials Institute, developed a fully functional relaxor device composed of a thin film (55 nanometers) of the material sandwiched between nanoscale layers that served as electrodes used to apply a voltage and generate an electric field.
Using beamlines in sectors 26-ID and 33-ID of Argonne's Advanced Photon Source (APS), Argonne team members mapped the mesoscale structures within the relaxor. Key to success was a specialized capability called coherent X-ray nano-diffraction, available through the Hard X-ray Nanoprobe (Sector 33-ID) operated by the Center for Nanoscale Materials at Argonne and the APS. Both are DOE Office of Science-user facilities.
The results showed that under an electric field, the nanodomains self-assemble into mesoscale structures consisting of dipoles that align in a complex tilelike pattern (see image). The team identified the strain locations along the borders of this pattern and the regions responding more strongly to the electric field.
"These submicroscale structures represent a new form of nanodomain self-assembly not known previously," noted John Mitchell, an Argonne Distinguished Fellow. "Amazingly, we could trace their origin all the way back down to underlying nanoscale atomic motions; it's fantastic!"
"The brighter and more coherent X-ray beams now possible with the recent APS upgrade will allow us to continue to improve our device," said Hao Zheng, the lead author of the research and now a beamline scientist at the APS. "We can then assess whether it has application for energy-efficient microelectronics such as neuromorphic computing modeled on the human brain."
Low-power microelectronics are essential for addressing the ever-growing power demands from electronic devices around the world, including cell phones, desktop computers and supercomputers.
The research was supported by the DOE (DE-AC02-06CH11357, DE-AC02-06CH11357, DE-SC-0012375), the Army Research Laboratory (W911NF-24-2-0100), the Army Research Office (W911NF-21-1-0118) and the National Science Foundation (2329111).
Content adapted from an article by Joseph E. Harmon, Argonne National Laboratory. The content in this press release is solely the responsibility of the authors and does not necessarily represent the official views of the supporting institutions.
