Researchers Discover New, Controllable State in Ferroelectric Nanowires

FAYETTEVILLE, Ark. – Researchers at the University of Arkansas and their colleagues have discovered a new phase in ferroelectric nanowires that could be controlled to optimize important properties for future electronic devices.

Lydie Louis and Laurent Bellaiche of the University of Arkansas; P. Gemeiner, G. Geneste and B. Dkhil of the École Centrale Paris; Inna Ponomareva of the University of South Florida; and W. Ma and N. Setter of the Swiss Federal Institute of Technology reported their findings in Nano Letters.

Ferroelectric materials are used in medical ultrasound to examine fetuses and internal organs, in military sonar for underwater navigation and detection, and in cell phones. These materials have a spontaneous charge separation that allows them to generate an electric field when their shape is changed — thus mechanical energy becomes electrical energy. Potential applications for ferroelectric nanowires include data storage memories and energy harvesting devices.

“Industry wants materials to be multifunctional, to have many different properties at the same time,” said Louis. “Therefore we have to understand the properties that arise under different conditions.”

Louis and her colleagues performed theoretical calculations and conducted experiments and found that the ferroelectric nanowires went through different structural phases at different temperatures, including a new phase not seen before.

“We also found out we could control the phase with a certain screening parameter,” she said. The scientists could alter the direction of polarization within this phase by changing the magnitude of the depolarization field and the size of the nanostructure itself, implying that one can “tune” the physical properties of these nanowires.

The researchers used X-ray diffraction and Raman spectroscopy to examine ferroelectric nanowires made from one material, potassium niobate, and performed first-principles-based calculations on nanowires based on another ferroelectric material with similar properties, barium titanate, by using the Star of Arkansas, a supercomputer at the University of Arkansas.

The theoretical calculations and experimental findings complemented one another.

“This shows the reliability of our computations,” Louis said.

Louis is a graduate student in a joint doctoral program between the University of Arkansas and École Centrale de Paris in France, which is sponsored by the National Science Foundation. Bellaiche is the Twenty-First Century Professor in Nanotechnology and Science Education in the J. William Fulbright College of Arts and Sciences.