Miniaturizing Ferroelectrics Improves Performance Before Degradation

In a recent study published in Nature Nanotechnology, researchers from Rice University examined the behavior of relaxor ferroelectric materials, which are widely used in sensors, actuators, and nanoelectronics due to their energy-conversion properties. The findings indicate that when these materials are reduced to thin films at a scale comparable to their internal polarization structures, their fundamental properties can change in unexpected ways.

The study focused on lead magnesium niobate-lead titanate (PMN-PT), a widely used ceramic material found in gas sensors, energy harvesting systems, and medical imaging applications such as ultrasound.

While investigating how the internal polarization structure of PMN-PT changes at extremely small scales, the researchers observed an unexpected effect: the material exhibited enhanced performance before ultimately losing its unique properties. This previously unknown "sweet spot" could inform the development of next-generation nanoelectronic devices.

PMN-PT is a ferroelectric relaxor known for its ability to convert energy efficiently. When an external voltage is applied, the material changes shape, and when subjected to mechanical pressure, it generates a voltage. Its atomic structure consists of positive and negative atoms that can shift relative to one another, forming local dipoles.

These dipoles do not align uniformly across the material. Instead, they are influenced by competing forces—one that promotes random orientation and another that encourages alignment. This competition leads to the formation of polar nanodomains, microscopic clusters in which dipoles align in a common direction.

These self-assembled structures of polarization inside the material are highly responsive to external stimuli due to the chemical complexity of the material and the size of these regions at their smallest, PMN-PT nanodomains are only 5-10 nm. Nobody really knew what would happen if we shrunk the whole material down to their size.

Jieun Kim, Assistant Professor and Study First Author, Korea Advanced Institute of Science and Technology

Understanding material behavior at nanoscale dimensions is critical for advancing miniaturized electronics and related technologies. As devices continue to shrink, ultrathin films of materials like PMN-PT become increasingly necessary. However, according to Kim, a comprehensive study of the physics governing relaxors at these extremely small scales “has never been done before.”

We hypothesized that as PMN-PT films got thinner, their polar nanodomains would shrink and eventually disappear along with the material’s desirable properties. The research confirmed this expectation, but we also found something unexpected.

Lane Martin, Robert A. Welch Professor, Materials Science and Nanoengineering, Rice University

Lane Martin is the Director of the Rice Advanced Materials Institute.

Instead of degrading immediately, PMN-PT exhibited improved performance when reduced to a specific thickness of 25–30 nm, approximately 10,000 times thinner than human hair. At this scale, the material's phase stability—its ability to maintain structure and function under varying conditions—was significantly enhanced.

To uncover this behavior, the researchers used advanced scientific tools. Ultrabright X-ray beams at Argonne National Laboratory's Advanced Photon Source allowed them to examine the material’s atomic structure. A technique called synchrotron-based X-ray diffraction enabled them to track how the nanodomains evolved as the material became thinner.

We correlated these findings with measurements of dielectric properties we performed in our lab and rounded out the picture using scanning transmission electron microscopy to map out polarization with atom-level resolution. For the thinnest films, we also performed molecular-dynamics simulations basically recreating the thin films in a computer to study the structural evolution of the polar nanodomains.

Jieun Kim, Assistant Professor and Study First Author, Korea Advanced Institute of Science and Technology

Kim began the project four years ago as a doctoral student under Martin at the University of California, Berkeley.

These methods provided the most detailed analysis of PMN-PT’s nanoscale behavior to date. Unlike many materials that lose functionality when reduced in size, PMN-PT displayed a “Goldilocks zone” effect, where its properties first improved before eventually deteriorating.

This discovery could enable advanced applications in low-voltage magnetoelectrics, pyroelectric energy conversion, capacitive energy storage (pulsed power), and nanoelectromechanical systems.

Next, the researchers plan to explore stacking ultrathin layers of PMN-PT with related materials, creating engineered structures similar to a "pancake stack" of functional layers. These materials could lead to innovations in next-generation sensors, low-power computing, and energy harvesting.

“Now we know that we could make devices that are smaller and better,” Kim said.

The study was funded by the Army Research Office, the Office of Naval Research, the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Army Research Laboratory, the Air Force Office of Scientific Research, and the Advanced Photon Source, a U.S. Department of Energy Office of Science user facility operated by Argonne National Laboratory.

Journal Reference:

Kim, J., et al. (2025) Size-driven phase evolution in ultrathin relaxor films. Nature Nanotechnology. doi.org/10.1038/s41565-025-01863-x.