The origin of ultrahigh piezoelectric response

January 10, 2017
Illustration of the polar directions in relaxor-ferroelectric solid solutions where a small amount of polar nanoregions embedded in a long-range ferroelectric domain leads to dramatically enhanced piezoelectric and dielectric properties. Credit: Xiaoxing Cheng/ Penn State

All ferroelectric materials possess a property known as piezoelectricity in which an applied mechanical force can generate an electrical current and an applied electrical field can elicit a mechanical response. Ferroelectric materials are used in a wide variety of industrial applications, from ultrasound and sonar to capacitors, transducers, vibration sensors and ultrasensitive infrared cameras. Now, an international team of scientists led by Penn State may have solved the 30-year-old riddle of why certain ferroelectric crystals exhibit extremely strong piezoelectric responses.

In 1997, a relaxor-ferroelectric solid solution crystal with the highest known piezoelectric response was reported at Penn State by Thomas R. Shrout, currently senior scientist and professor of materials science and engineering at Penn State, and the late Seung-Eek Park. It has a piezoelectric response five to ten times higher than any other known ferroelectric material.

"There have been a number of mechanisms proposed to explain its ultrahigh piezoelectric responses, but none of them offer a satisfactory explanation for all the experimental observations and measurements associated with the high response. Without a firm understanding of the underlying mechanism, it would be difficult to design new materials with even higher piezoelectric response," said Fei Li, a postdoctoral scholar in materials science and engineering at Penn State and lead author of a recent article in the journal Nature Communications attempting to explain the phenomenon.

However, the scientific community has reached a general consensus that something called polar nanoregions contributed to the high piezo response of relaxor crystals, Li said.

A polar nanoregion is a spatial region within a crystal. It has a nanoscale size (5-10 nm) and possesses a net electric polarization. There are many such tiny regions randomly distributed in space in a relaxor crystal. Other well-known piezoelectric materials, like lead zirconate titanate (PZT), do not have polar nanoregions, but instead have much larger ferroelectric domains in which the polarization is uniform. The team set out to prove that the polar nanoregions were indeed responsible for the huge responses, and more importantly, to determine the mechanism by which they help to generate such huge responses.

The experiments were carried out at ultralow cryogenic temperatures (50-150 K). This enabled the researchers to separate the responses from the polar nanoregions, which remain active within that temperature range, from those high piezoelectric responses that typically takes place near a ferroelectric phase transition.

"We experimentally observed a significant enhancement of piezoelectric response of relaxor-ferroelectric crystals in the temperature range of 50-150 K. This enhancement accounts for 50-80% of room-temperature piezoelectricity," said Shujun Zhang, a senior author and professor of materials science and engineering at Penn State (currently at University of Wollongong).

"We attributed the experimentally observed enhancement to the existence of the polar nanoregions. Using phase-field modeling, we first proved that this significant enhancement originated from the polar nanoregions, i.e., the enhancement is absent without the presence of these polar nanoregions, and then demonstrated how the polar nanoregions help generate ultrahigh responses," said Long-Qing Chen, a senior author and Donald Hamer professor of and engineering, Penn State. "Our proposed mechanism is able to successfully explain all the experimental measurements and observations associated with the high responses. This work is an important step in realizing the dream of discovering new piezoelectric materials by design.

A note of caution

"However, it should be noted that our proposed model is a mesoscale model, which is an intermediate scale. The atomistic origin of PNRs is still an open question, so further in-depth research is still required to clarify the contribution of polar nanoregions at the atomic scale. And in fact, our ongoing work is focused on understanding the atomic-scale mechanisms of polar nanoregions in piezoelectric responses," said Chen.

Explore further: Study yields new knowledge about materials for ultrasound and other applications

More information: Fei Li et al. The origin of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution crystals, Nature Communications (2016). DOI: 10.1038/ncomms13807

Related Stories

Possible Mechanism for Enormous Electromechanical Response

May 12, 2008

Scientists at the U.S. Department of Energy's Brookhaven National Laboratory and collaborators at Stony Brook University, Johns Hopkins University, and the National Institute of Standards and Technology have discovered that ...

Researchers provide answers to questions about relaxors

August 7, 2012

(Phys.org) -- University of Arkansas physicists and their colleagues have determined important information about the nanoscale properties of materials called relaxors, which can be used in electronic devices to change temperature ...

Recommended for you

Scientists discover superconductor with bounce

October 23, 2017

The U.S. Department of Energy's Ames Laboratory has discovered extreme "bounce," or super-elastic shape-memory properties in a material that could be applied for use as an actuator in the harshest of conditions, such as outer ...

Scientists update four key fundamental constants

October 23, 2017

Paving the way for transforming the world's measurement system, an international task force has determined updated values for four fundamental constants of nature. The updated values comprise the last scientific piece of ...

Experiment provides deeper look into the nature of neutrinos

October 23, 2017

The first glimpse of data from the full array of a deeply chilled particle detector operating beneath a mountain in Italy sets the most precise limits yet on where scientists might find a theorized process to help explain ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Macksb
not rated yet Jan 11, 2017
Good work.

But the "randomly distributed" sentence cries out for further attention.

This sentence: "There are many such tiny regions randomly distributed in space in a relaxor crystal."

Random is rarely the answer in physics, particularly for key facts strongly associated with causation of any type, let alone causation stimulating a higher form of order, such as this "ultrahigh piezoelectric response."

I suggest a closer look at an image in the scholarly paper itself, which can be found by clicking on the bold face DOI reference at the bottom of the Physorg article. Figure 3 in that article is the image that attracts my attention.
Macksb
not rated yet Jan 11, 2017
Perovskite. That's another point of interest bearing further discussion. This research involves a perovskite ferroelectric, as noted in the scholarly article.

The ultra high piezoelectric response is associated with perovskite ferroelectrics, to the best of my knowledge. Not with non-perovskite structures.

Perovskite structure is also associated with another surprising phenomenon: cuprate (high temp) superconductivity.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.