By: Tina Casey
A team of researchers from UC Berkeley and the U.S. Department of Energy’s Lawrence Berkeley Lab have discovered a new lead-free material that produces an electrical current when exposed to stress. The phenomenon, called piezoelectricity, sounds exotic but it could some day become as common as backyard grills.
Piezoelectricity is a sustainable way to generate energy. It works by applying pressure or stress to certain crystalline materials, including certain ceramics and even bone, so it’s a green alternative to burning fossil fuels. Up to now, though, the most popular piezoelectric materials contain lead, a notorious neurotoxin. The discovery of a lead-free material could open the door to a piezoelectric energy future in which people generate significant amounts of electricity just by moving through the civic infrastructure, from highways to flooring and revolving doors.
Piezoelectricity in Daily Life
Piezoelectricity actually is as common as backyard grills. Push-button grill starters, and likewise pushbutton cigarette lighters, both use piezoelectric materials to strike a spark. Microphones and quartz watches are two other common products that use the piezoelectric effect. Piezoelectricity also has numerous medical and engineering applications, especially in ultrasound equipment and testing devices for roads and bridges. However, the severe health risks associated with lead in the environment make it clear that a more widespread application of lead-based piezoelectric materials is not a sustainable path to pursue.
By removing the lead hazard, the Berkeley discovery could prompt the use of piezoelectric materials not only in infrastructure and buildings, but also in common consumer products that are exposed to stress, such as shoes or even T-shirts. The researchers found that thin films of bismuth ferrite, an inorganic crystalline material associated with magnetic-electric phenomena, produce a piezoelectric effect when subjected to large amounts of properly focused strain. Bismuth ferrite consists of crystal planes that alternate between oxygen and iron atoms, and oxygen and bismuth atoms (bismuth is a heavy, brittle metal used in cosmetics and medicines, and it is becoming more common as a replacement for lead in manufacturing). Putting strain on the films causes the “exotic behavior” described by one researcher, in which the planes to move relative to each other and then revert to their former position when the strain is relaxed. The researchers also note that in principle bismuth ferrite is just one among other crystalline lead-free materials that could be used to produce a piezoelectric effect.
Image: Nrbelex on flickr.com.