Scientists from the University of Arkansas have recently achieved a major breakthrough in ferroelectric materials. They found a lead-free replacement that has the potential to improve performance in a wide range of electronic applications. This advance centers on a very thin film of sodium niobate (NaNbO3), which has remarkable qualities resulting from its shift between different crystalline phases caused by strain. Their discovery may lead to the development of electronic devices that are both safer and more efficient.
Ferroelectric materials have an intrinsic electrical polarization, which can be switched by an external electric field. Scientists initially discovered these materials in 1920. Since then, they have become indispensable for a variety of applications, including infrared focal plane arrays, medical ultrasounds, dynamic random access memories and actuators. Actuators turn electric energy into mechanical energy and vice versa, and thus ferroelectric materials are crucial components of advanced technology today.
The unusual properties of ferroelectric materials are closely tied to their atomic arrangements. They can show quite a few different crystalline forms, the places where these forms meet are called phase boundaries. Researchers have been seeking the qualities that make ferroelectric materials particularly functional. These properties are particularly pronounced at phase boundaries.
Laurent Bellaiche, a Distinguished Professor of Physics at the University of Arkansas, underscored that there is a worldwide push to discover lead-free ferroelectric materials. This effort has developed significant momentum in the last ten years. He stated, “For the last 10 years, there has been a huge initiative all over the world to find [ferroelectric materials] that do not contain lead.” This push is largely motivated by a desire to limit health risks associated with lead-based materials.
The research team, which includes Kinnary Patel, a research consultant in the Department of Physics, successfully created a sodium niobate thin film where strain induced three different phases simultaneously. Bellaiche remarked on this phenomenon: “What is quite remarkable with sodium niobate is if you change the length a little bit, the phases change a lot.” This surprising outcome indicates that we can improve the ferroelectric quality of the material. We just have to make more of phase boundaries available.
Bellaiche further expressed surprise at the findings, stating, “What I was expecting, to be honest, is if we change the strain, it will go from one phase to another phase. But not three at the same time.” The special activity of sodium niobate brings exciting possibilities. For example, it might enable property improvements in electronic devices requiring fine-tuned control of electrical properties.
The research team is now preparing to investigate the effects of strain on sodium niobate. They will perform experiments within severe temperature conditions, ranging from minus 270°C up to 1,000°C. Ruijuan Xu of North Carolina State University, who led this investigation, is still working to understand the material’s potential applications.