Advanced Ceramics

MATERIAL INNOVATIONS: Exploring Piezoelectric Ceramics

Lead-free piezoelectric ceramics can be used to help detoxify electronic gadgets.

Crystal structure of KNBT before the application of an electric field (here) and after (below). The purple spheres are either sodium or potassium atoms, the red spheres are oxygen atoms, and the small blue sphere is titanium. The figures show the arrangement of the atoms changing from rhombohedral, where the a, b and c axes are of the same length and the rhombohedral angle is less than 90, to tetragonal symmetry, where the a and b axes are of the same length and the c axis is longer.

Crystal structure of KNBT after the application of an electric field.

Scientists are using Diamond Light Source, the UK's national synchrotron facility, to discover how we can detoxify our electronic gadgets. Results published in Applied Physics Letters on October 1, 2010, reveal the potential for new artificial materials that could replace lead-based components in everyday products from inkjet printers to digital cameras.

Researchers from the Institute for Materials Research at the University of Leeds' Faculty of Engineering used the Diamond Light Source synchrotron to investigate the structure and properties of piezoelectric ceramics in order to develop more environmentally friendly alternatives to the widely used but toxic lead zirconium titanate (PZT). The team used the I15 Extreme Conditions beamline to probe the interior crystal structure of the ceramics with a high-energy pinpoint X-ray beam and saw changes in the crystal structure as an electric field was applied. The results demonstrate that a new material, potassium sodium bismuth titanate (KNBT), shows the potential to perform the same job as its lead counterpart.

"These results are very encouraging," said Tim Comyn, Ph.D., of the University of Leeds. "Although harmless when in use, at the end of their lifetime, these PZT gadgets have to be carefully disposed of due to their lead content and, as a consequence, there is significant interest in developing lead-free ceramics."

Potential Applications

Piezoelectric materials generate an electrical field when pressure is applied, and vice versa. For example, in gas igniters like those used on ovens, a piezoelectric crystal creates sparks when hit with the hammer. In an electrical field, it undergoes a phase transition and changes occur in the crystal structure. The team will continue to work at Diamond Light Source to study the electric field-induced transformation at high speed (1000 times per second) and under various conditions using state-of-the-art detectors.

"Not only could a lead-free solution mean safer disposal of electronic equipment, by virtue of the absence of lead, these new materials are far lighter than PZT," said Adam Royles of the University of Leeds. "The piezoelectric market has applications in many fields, where a lighter lead-free alternative could make quite a difference."

In the medical field, PZT is used in ultrasound transducers to generate sound waves and send the echoes to a computer to convert into a picture. Piezoelectric ceramics also hold great potential for efficient energy harvesting, a possible solution for a clean sustainable energy source in the future. Lead-based electronic ceramics are one of only a few exemptions to the European directive on the restriction of the use of certain hazardous substances in electrical and electronic components (2002/95/EC). This exemption will be reviewed again in 2012.

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