Understanding the relaxing ferroelectric properties could lead to many advances

A fundamental new understanding of the ferroelectric behavior of polymeric relaxants could lead to advancements in flexible electronics, actuators and transducers, energy storage, piezoelectric sensors, and electrocaloric cooling, according to a team of researchers at Penn State and North Carolina State.

Researchers have debated the theory behind the mechanism of relaxing ferroelectrics for more than 50 years, said Qing Wang, a professor of materials science and engineering at Penn State. While relaxing ferroelectrics are recognized materials, fundamentally fascinating and technologically useful, a Nature The article commented in 2006 that they were a heterogeneous and hopeless disaster.

Without a fundamental understanding of the mechanism, little progress has been made in the design of new relaxing ferroelectric materials. The new understanding, which is based on both experiments and theoretical models, shows that relaxing ferroelectricity in polymers comes from chirality-induced chain conformation disorders. Chirality is a characteristic of many organic materials in which the molecules are mirror images of each other, but not exactly the same. The relaxation mechanism in polymers is very different from the proposed mechanism for ceramics whose relaxation behavior originates from chemical disorders.

“Unlike ferroelectrics, relaxants do not show large long-range ferroelectric domains, but rather messy local polar domains,” said Wang. “Research into relaxing polymeric materials has been challenging due to the presence of multiple phases such as the crystalline interfacial area , amorphous and crystalline-amorphous in polymers. “

In energy storage capacitors, relaxants can deliver a much higher energy density than normal ferroelectrics, which have a high ferroelectric loss that is converted to residual heat. Additionally, relaxants can generate higher voltage under applied electric fields and have much better energy conversion efficiency than normal ferroelectrics, making them preferred materials for actuators and sensors.

Penn State has a long history of discoveries in ferroelectric materials. Qiming Zhang, a professor of electrical engineering at Penn State, discovered the first relaxing ferroelectric polymer in 1998, when he used an electron beam to irradiate a ferroelectric polymer and found that it had become a relaxant. Zhang together with Qing Wang also made seminal discoveries in the electrocaloric effect using relaxant polymers, allowing solid state cooling without the use of harmful gases and using much less energy than conventional cooling.

“The new understanding of relaxant behavior would open up unprecedented opportunities to design relaxing ferroelectric polymers for a range of energy storage and conversion applications,” said Wang.

His work, “Relaxing Properties Induced by Chirality in Ferroelectric Polymers,” appears today, June 29, in the journal Natural materials.