Waste Energy Could be Harvested Using KNN Piezoelectric Materials

By fine-tuning the chemistry and grain structure of potassium sodium niobate, researchers at Pennsylvania State University have created a lightweight, thermally stable ceramic that can harvest waste energy from human activities. 

The vibrations created by human activities, such as moving on dance floors, exercising on gym machines, and using engines in cars or planes, generate a large amount of potential energy. Using a class of ceramic materials called piezoelectrics, which release electrical charges when trodden on or handled, some tech companies have already started to harness waste vibrations to power lights and replenish batteries.

A team led by materials scientists at Penn State has expanded these early efforts by improving the structure and chemistry of a piezoelectric material made of potassium sodium niobate (KNN). The improved ceramic samples are thermally stable, fatigue-resistant, and less dense, outperforming conventional lead-based piezoelectric materials, according to the researchers. The findings were reported in Small.

The researchers suggest that their findings may help replace the harmful lead-based materials currently used in piezoelectric devices.

Mechanical vibrations are everywhere, produced by people or engines. We can place a piezoelectric energy harvester under dance floors and corridors, or under bridges and parking decks, to harvest the energy from those mechanical sources. Because of the lightweight design of our KNN material, we could also include them in aircraft – which wasn’t previously possible with lead-based materials – to harvest the vibrations during flights, even at high altitudes.

Aman Nanda, Study First Author and Doctoral Student, Pennsylvania State University

These energy harvesters have a cantilever design, with a rigid component fastened to one end. Ceramic materials are fragile, and as a result require extra attention during innovation and development to ensure they can withstand mechanical stress in real-world settings.

When pressed, the cantilever vibrates and creates electricity due to the piezoelectric effect of the material, which turns mechanical energy into power.

Looking to substitute lead, the researchers created a lighter piezoelectric ceramic by altering the chemical composition and structure of KNN. They initially added manganese, a magnetic element, to the chemical composition.

Aman optimized the material with specific elements to improve the properties. These materials have been around a while in terms of chemistry, but he has done a lot more work in making the chemistries better by changing the composition and synthesis procedures, such as experimenting with different heat times, temperatures, and structures of the material.

Mike Lanagan, Study Co-Corresponding Author and Professor, Pennsylvania State University

Grains usually grow from point centres randomly in all directions. In this study, however, the researchers employed heat and particular manufacturing techniques to regulate grain growth, ensuring that they all grew in the same way.

“With the appropriate synthesis temperature range, we achieved unidirectional grain growth. This resulted in enhanced functional properties, such as mechanical strength and toughness, in the direction of the grain alignment, as well as improved piezoelectric response,” Nanda added.

According to the researchers, this was the first lead-free piezoelectric material to perform competitively compared to lead-based materials in terms of the voltage generated by mechanical vibration. In laboratory experiments, the enhanced KNN material produced a similar amount of energy as a typical lead-based substance.

Next, the researchers will investigate the material’s possible applications. In addition to energy harvesting, the scientists suggest that this novel material might be used in sensors that sense weight, sound waves, position, air pressure, and light.

Since lead-free materials are biocompatible, our new KNN-based material also opens the possibility to integrate the devices made from these materials in biomedical applications, such as self-powered pacemakers or neural stimulating devices.

Bed Poudel, Study Co-Corresponding Author and Research Professor, Pennsylvania State University

Journal Reference:

Nanda, A. et.al. (2025) Textured Lead-Free Ceramic with High Thermal Stability and Electrical Quality Factor. Small. doi.org/10.1002/smll.202505193.