A research team from Kumamoto University has successfully visualized how microscopic structures inside one of these crystals react to electric fields in real time, a first for the world, according to a study published in Applied Physics Letters. This study provides insight into the dynamics of nanostructure in materials used in ultrasound probes.
Change of domain structure by AC poling. A transmission electron microscopy (TEM) image (top left) and the corresponding domain structure (bottom left) before applying an AC electric field. The top right and bottom right are TEM images, and the corresponding domain structure after applying an AC electric field for 0.05 seconds. In the bottom panels, domain boundary is indicated by black and colored lines. Red and blue hatches in the right bottom panel indicate newly generated and laterally shrunk domains, respectively. Direction of the electric fields is shown in the top right panel. Image Credit: Kumamoto University
One of the most used diagnostic techniques in contemporary medicine is ultrasound imaging. A class of materials called piezoelectric single crystals, which have the ability to transform electrical signals into mechanical vibrations and vice versa, is responsible for its non-invasive magic.
Under the direction of Professor Yukio Sato of the Research and Education Institute for Semiconductors and Informatics (REISI), the group concentrated on PMN-PT, a crystal that is valued for its remarkable piezoelectric performance and is a solid solution of lead titanate and magnesium niobate.
Applying alternating current (AC) electric fields, or AC poling, has been shown to improve these materials' performance. However, the precise processes underlying this enhancement and how excessive use can actually impair performance were yet unknown.
Using a specific in situ electron microscopy technique created at Kumamoto University, the team could see microscopic domain formations, known as ferroelectric nanodomains, as they reacted to AC electric fields to conduct their investigation.
They observed a remarkable phenomenon: the domain structure was drastically altered by a single cycle of an AC electric field at a strength of 12 kV/cm and 20 Hz. Some domain walls grew and merged over time as a result of shorter AC treatments, which would have improved the material's qualities. However, long-term treatments resulted in the development of vertically aligned microdomain bands, which are consistent with over-poling and could impair performance.
This is the first time we’ve been able to watch these nanoscale domains react in real time. Understanding these changes is essential for refining the poling process and developing more efficient and longer-lasting medical imaging devices.
Yukio Sato, Professor, Research and Education Institute for Semiconductors and Informatics
Journal Reference:
Li, N.-H., et al. (2025) Response of ferroelectric nanodomain to alternative-current electric fields in morphotropic-phase boundary Pb(Mg1/3Nb2/3)O3−PbTiO3. Applied Physics Letters. doi.org/10.1063/5.0232904