Lead-free piezoceramic materials could help usher in safer and more environmentally friendly ultrasonic sensors.

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Ultrasound imaging, the green way

9 Nov 2020

Lead-free piezoceramics sacrifice performance for lower toxicity, but A*STAR researchers have developed a method to overcome that.

From the insides of your body to the deepest foundations of a building, ultrasound is an important way to visualize what the human eye can’t. The key to each of these ultrasound imaging devices is a little component—called an ultrasonic transducer—that generates ultrasound waves with electrical signals and also converts the mechanical pressure exerted by ultrasound waves into electrical signals that the imaging devices can read.

For this reason, ultrasonic transducers must be made of special materials, such as piezoceramics, which can change their shape when an electric field is applied. However, commercial piezoceramics can contain more than half their weight in lead, such as in the form of the widely used lead zirconate titanate (PZT).

“Commercial piezoelectric ceramics contain a large amount of toxic lead, typically more than 50 percent by weight,” explained study co-corresponding author Kui Yao, a Principal Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE).

“For environmental concerns starting from material manufacturing to waste disposal, it is desirable to be able to obtain lead-free alternatives to replace existing lead-based materials in devices.”

Concerns over lead toxicity have driven the need to find lead-free piezoelectric materials and transducers, but current lead-free alternatives are both unstable at high temperatures and perform poorly. Yao and colleagues in Singapore and China have now discovered a new lead-free piezoceramic material that is suitable for practical use in devices, made from potassium sodium niobate (KNN).

“KNN-BNZ-AS-Fe is a ceramic with a complex lead-free composition that can achieve coexistence of multiple crystalline phases,” Yao said. “This is an important structural feature for a piezoelectric material to have because it makes the material highly responsive to external stimuli, including ultrasound waves or electric fields.”

On top of that, the engineered piezoceramic performed well, displaying both a strong piezoelectric response and stability under high temperature. These results indicate that the strategy of appropriately engineering the piezoceramic’s structure to allow for multiple-phase coexistence can improve its piezoelectric performance and stability, the team noted.

Thanks to its stability and impressive piezoelectric properties even at high temperatures, an ultrasonic transducer using this new KNN-BNZ-AS-Fe ceramic could be a promising lead-free alternative to be used in piezoelectric-dependent devices such as ultrasonic transducers.

“We have demonstrated that the KNN-BNZ-AS-Fe ceramic has excellent and stable piezoelectric properties, and its performance as an ultrasonic transducer is competitive to those of PZT–based transducers,” Yao shared.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).

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Zheng T., Zhang Y., Ke Q., Wu H., Liew W. H., et al. High-performance potassium sodium niobate piezoceramics for ultrasonic transducer. Nano Energy 70 (2020) | article

About the Researcher

Kui Yao is a Principal Scientist at A*STAR’s Institute of Materials Research and Engineering in Singapore. His research covers smart materials, with a focus on piezoelectric and ferroelectric materials, as well as the sensors and transducers they enable. Together with his colleagues and collaborators, he is actively exploring how these sensors and transducers can be used for structural and condition monitoring, ultrasonic and photoacoustic testing, noise and vibration mitigation and other applications.

This article was made for A*STAR Research by Wildtype Media Group