By Cameron Chai
A team of researchers, led by Albina Borisevich from the Oak Ridge National Laboratory (ORNL) of the Department of Energy, has proposed a new theory to elucidate the unusual properties of a material that find possible use in actuators and capacitors.
The research, a part of the ORNL’s Shared Research Equipment User Program, investigated bismuth samarium ferrite or BSFO thin films. BSFO, which demonstrates intriguing properties at its transition between two different phases, shows promise to be used as a zero-lead replacement for lead zirconium titanate or PZT used in various technologies such as ultrasound devices and sensors. BSFO and PZT are known as ‘materials on the brink’ due to their unusual behavior that is closely related to the phase transition.
In the study, the research team investigated the changes in the local structure of the BSFO films during their transition from ferroelectric to antiferroelectric phase by mapping the position of atoms in the films with the help of the scanning transmission electron microscope. Borisevich informed that the material demonstrates best properties at its transition. However, the team discovered that current theories were not able to explain the behavior of the material at the atomic level.
Some theorists have hypothesized that a nanocomposite is formed by the material at the transition. To achieve this, the boundary energy between phases must approach zero. However, the team discovered that the boundary energy was a negative value. Based on its findings, the team confirmed that flexoelectricity, a comparatively weak interaction was responsible for the material’s behavior.
Borisevich commented that different systems that have similar phase boundaries can be studied using the team’s method. She also highlighted the significance of atomic-level mapping of materials. Since the BSFO films are periodic structures, only electron microscopy can be used to study the local changes, she added.
The study findings have been reported in the journal, Nature Communications.