Piezoelectricity Made Simple

You may not think it, but there’s a good chance that there’s electricity running through your wristwatch. Quartz watches run on piezoelectricity—the electric charges that accumulate in solid materials when mechanical stress or pressure is applied to them—hence its name, which stems from the Greek word to squeeze or press.

Whether it is the tiny quartz crystal helping your watch keep time or the precision actuator controlling the deposit of ink in a printer, piezoelectric devices are highly dependent on the materials used to make them. For over 60 years, the main way to boost the performance of piezoelectric materials has been to construct multiphase boundaries by tuning their chemical composition. However, this strategy usually involves complex chemical compositions and results in materials that are not stable at high temperatures.

Now, an international team of researchers, including scientists and engineers from A*STAR’s Institute of Materials Research and Engineering (IMRE) and Institute of High Performance Computing (IHPC), has found a simpler way to induce a piezoelectric response.

“With just three elements—sodium, niobium and oxygen—we obtained a much larger effective piezoelectric response compared to the complex compositions designed using conventional strategy,” said Kui Yao, the study corresponding author and Principal Scientist at IMRE.

The secret to their success was the nanopillar structures that spontaneously formed in the material during the deposition process. Structural distortions in these nanopillar regions lowered the symmetry of the resulting crystal, significantly enhancing the material’s piezoelectric performance.

“Using our new films, we observed a giant effective piezoelectric coefficient which is more than twice that of the market-dominant lead zirconate titanate (PZT) films, with an applied electric field of 125 kV/cm at 1 kHz,” said Yao, adding that the material had the additional benefit of being more environmentally friendly since it does not contain toxic lead unlike PZT.

Furthermore, the results showed that the material remained piezoelectric even at temperatures up to 450°C, making it suitable for electromechanical devices that are required to operate at a wider range of temperatures. Yao suggests that the material, which IMRE has filed a provisional patent for, could be used to create micro-actuators that have lowered driving voltage and micro-sensors that have improved sensitivity.

According to Yao, this strategy of modifying a material’s properties through self-assembling nanopillars could also be used to design and optimize other functional materials.

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