Microscopy inspires flexoelectric theory behind 'material on the brink'

Electron microscopy, conducted as part of the Shared Research Equipment (ShaRE) User Program at the Department of Energy's Oak Ridge National Laboratory, has led to a new theory to explain intriguing properties in a material with potential applications in capacitors and actuators.

A research team led by ORNL's Albina Borisevich examined thin films of bismuth samarium ferrite, known as BSFO, which exhibits unusual physical properties near its transition from one phase to another. BSFO holds potential as a lead-free substitute for lead zirconium titanate (PZT), a similar material currently used in dozens of technologies from sensors to ultrasound machines.

Materials such as BSFO and PZT are often called "materials on the brink" in reference to their enigmatic behaviour, which is closely tied to the transition between two different phases. These phases are characterized by structural changes in the material that produce different electrical properties.

"The best properties of the material are found at this transition," Borisevich said. "However, there has been a lot of discussion about what exactly happens that leads to an enhancement of the material's properties."

Using scanning transmission electron microscopy, the team mapped the position of atoms in BSFO films to find what happens to the local structure at the transition between ferroelectric and antiferroelectric phases. The team's results are published in Nature Communications.

"We discovered that neither of the two dominant theories could describe the observed behaviour at the atomic scale," Borisevich said.