Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New acoustic technique reveals structural information in nanoscale materials

29.12.2015

Understanding where and how phase transitions occur is critical to developing new generations of the materials used in high-performance batteries, sensors, energy-harvesting devices, medical diagnostic equipment and other applications. But until now there was no good way to study and simultaneously map these phenomena at the relevant length scales.

Now, researchers at the Georgia Institute of Technology and Oak Ridge National Laboratory (ORNL) have developed a new nondestructive technique for investigating these material changes by examining the acoustic response at the nanoscale. Information obtained from this technique - which uses electrically-conductive atomic force microscope (AFM) probes - could guide efforts to design materials with enhanced properties at small size scales.


This is a schematic representation of the atomic force microscope interacting with the material surface.

Credit: Rama Vasudevan, ORNL

The approach has been used in ferroelectric materials, but could also have applications in ferroelastics, solid protonic acids and materials known as relaxors. Sponsored by the National Science Foundation and the Department of Energy's Office of Science, the research was reported December 15 in the journal Advanced Functional Materials.

"We have developed a new characterization technique that allows us to study changes in the crystalline structure and changes in materials behavior at substantially smaller length scales with a relatively simple approach," said Nazanin Bassiri-Gharb, an associate professor in Georgia Tech's Woodruff School of Mechanical Engineering. "Knowing where these phase transitions happen and at which length scales can help us design next-generation materials."

In ferroelectric materials such as PZT (lead zirconate titanate), phase transitions can occur at the boundaries between one crystal type and another, under external stimuli. Properties such as the piezoelectric and dielectric effects can be amplified at the boundaries, which are caused by the multi-element "confused chemistry" of the materials. Determining when these transitions occur can be done in bulk materials using various techniques, and at the smallest scales using an electron microscope.

The researchers realized they could detect these phase transitions using acoustic techniques in samples at size scales between the bulk and tens of atoms. Using band-excitation piezoresponse force microscopy (BE-PFM) techniques developed at ORNL, they analyzed the resulting changes in resonant frequencies to detect phase changes in sample sizes relevant to the material applications. To do that, they applied an electric field to the samples using an AFM tip that had been coated with platinum to make it conductive, and through generation and detection of a band of frequencies.

"We've had very good techniques for characterizing these phase changes at the large scale, and we've been able to use electron microscopy to figure out almost atomistically where the phase transition occurs, but until this technique was developed, we had nothing in between," said Bassiri-Gharb. "To influence the structure of these materials through chemical or other means, we really needed to know where the transition breaks down, and at what length scale that occurs. This technique fills a gap in our knowledge."

The changes the researchers detect acoustically are due to the elastic properties of the materials, so virtually any material with similar changes in elastic properties could be studied in this way. Bassiri-Gharb is interested in ferroelectrics such as PZT, but materials used in fuel cells, batteries, transducers and energy-harvesting devices could also be examined this way.

"This new method will allow for much greater insight into energy-harvesting and energy transduction materials at the relevant length sales," noted Rama Vasudeven, the first author of the paper and a materials scientist at the Center for Nanophase Materials Sciences, a U.S. Department of Energy user facility at ORNL.

The researchers also modeled the relaxor-ferroelectric materials using thermodynamic methods, which supported the existence of a phase transition and the evolution of a complex domain pattern, in agreement with the experimental results.

Use of the AFM-based technique offers a number of attractive features. Laboratories already using AFM equipment can easily modify it to analyze these materials by adding electronic components and a conductive probe tip, Bassiri-Gharb noted. The AFM equipment can be operated under a range of temperature, electric field and other environmental conditions that are not easily implemented for electron microscope analysis, allowing scientists to study these materials under realistic operating conditions.

"This technique can probe a range of different materials at small scales and under difficult environmental conditions that would be inaccessible otherwise," said Bassiri-Gharb. "Materials used in energy applications experience these kinds of conditions, and our technique can provide the information we need to engineer materials with enhanced responses."

Though widely used, relaxor-ferroelectrics and PZT are still not well understood. In relaxor-ferroelectrics, for example, it's believed that there are pockets of material in phases that differ from the bulk, a distortion that may help confer the material's attractive properties. Using their technique, the researchers confirmed that the phase transitions can be extremely localized. They also learned that high responses of the materials occurred at those same locations.

Next steps would include varying the chemical composition of the material to see if those transitions - and enhanced properties - can be controlled. The researchers also plan to examine other materials.

"It turns out that many energy-related materials have electrical transitions, so we think this is going to be very important for studying functional materials in general," Bassiri-Gharb added. "The potential for gaining new understanding of these materials and their applications are huge."

###

This research was supported by the National Science Foundation (NSF) through grant DMR-1255379. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility at ORNL. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NSF or DOE.

CITATION: Rama K. Vasudevan, et al., "Acoustic Detection of Phase Transitions at the Nanoscale," (Advanced Functional Materials, 2015). http://dx.doi.org/10.1002/adfm.201504407

Media Contact

John Toon
jtoon@gatech.edu
404-894-6986

 @GeorgiaTech

http://www.gatech.edu 

John Toon | EurekAlert!

More articles from Materials Sciences:

nachricht New materials: Growing polymer pelts
19.11.2018 | Karlsruher Institut für Technologie (KIT)

nachricht Why geckos can stick to walls
19.11.2018 | Jacobs University Bremen gGmbH

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nonstop Tranport of Cargo in Nanomachines

Max Planck researchers revel the nano-structure of molecular trains and the reason for smooth transport in cellular antennas.

Moving around, sensing the extracellular environment, and signaling to other cells are important for a cell to function properly. Responsible for those tasks...

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Optical Coherence Tomography: German-Japanese Research Alliance hosted Medical Imaging Conference

19.11.2018 | Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

 
Latest News

Nonstop Tranport of Cargo in Nanomachines

20.11.2018 | Life Sciences

Researchers find social cultures in chimpanzees

20.11.2018 | Life Sciences

When AI and optoelectronics meet: Researchers take control of light properties

20.11.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>