Theory helps boost performance of piezoelectric material

Guided by a theoretical understanding of ultrahigh piezoelectricity in ferroelectric materials, an international team of researchers has developed a new material with twice the piezo response of any existing commercial ferroelectric ceramics.

Piezoelectricity is the material property at the heart of medical ultrasound, sonar, active vibration control, and many sensors and actuators. A piezoelectric material has the ability to mechanically deform when an electric voltage is applied or to generate electric charge when a mechanical force is applied.

In a paper in Nature Materials, the researchers report that adding small amounts of a carefully selected rare earth material, samarium, to a high-performance piezoelectric ceramic called lead magnesium niobate-lead titanate (PMN-PT) dramatically increases its piezo performance. This materials-by-design strategy will be useful in designing materials for other applications as well, the team believes.

"This is not the typical way to develop new materials," said the team's co-corresponding author Long-Qing Chen, professor of materials science and engineering, professor of mathematics, and professor of engineering science and mechanics at Penn State. "The majority of existing useful materials are discovered by trial-and-error experiments. But here we designed and synthesized a new piezoelectric ceramic guided by theory and simulations."

The team first analyzed the impact of adding various chemical dopants on the local structure of an existing ferroelectric ceramic. This allowed them to reduce the pool of effective dopants by comparing the measured dielectric losses with the signatures obtained from phase-field simulations. After screening the dopants, they focused on optimizing both the doping process and composition of the ceramic to achieve ultrahigh piezoelectricity.

"This work is based on an understanding of the origin of ultrahigh piezoelectricity in the ferroelectric crystals that was developed 30 years ago. Our new understanding suggested that local structure heterogeneity plays an important role in piezoelectricity in ferroelectrics, which also can be extended to other functionalities," said co-corresponding author Shujun Zhang, a professor of materials science, formerly at Penn State and now at the University of Wollongong in Australia.

Local structure heterogeneity refers to nanoscale structural distortions within a host material created by doping it with a small amount of a chemical species. In this case, the researchers doped the PMN-PT ceramic with samarium as a way to modify its thermodynamic energy landscape. This increased the ceramic’s dielectric properties – the ability of a material to respond to an electrostatic field – and its piezoelectric properties.

"This material is a good choice to use in transducers, such as those used in medical ultrasound," said lead author Fei Li, a research associate at Penn State. "We already have a device made from our material by a group at the University of Southern California."

This device is called a needle transducer and uses a submillimeter element of the piezoelectric ceramic, fitted into a standard needle or catheter, to perform minimally invasive procedures, image inside the body or to guide precision surgery. The device has better performance than existing devices with the same dimensions, Li said.

This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.