Piezoelectricity is one of those great advantages of physics that allows certain materials to generate an electric charge when subjected to mechanical stress, or to deform when an electric field is applied.
Engineers take advantage of this piezoelectric effect all the time to convert mechanical energy into electrical energy (as in sensors or generators) or to convert electrical energy into mechanical energy (as in speakers or actuators). Piezo is a Greek term for “pressure.”
Given how valuable piezoelectric sensors can be in modern technology applications, researchers have studied new ways to fabricate the solid piezo materials, made from ceramics or crystals.
Scientists in England have lately been researching the use of bismuth iodide, an inorganic salt with low toxicity, to create a soft material sensitive to movement that they say rivals the performance of lead-based ceramics for use in piezoelectric applications. Their discovery was published Nov. 26 in the Journal of the American Chemical Society. The research teams hail from the universities of Birmingham, Oxford and Bristol.
Dr. Dominik Kubicki from the University of Birmingham said the discovery opens a new pathway to environmentally responsible technologies to power sensors, medical implants and flexible electronics. Acuators that depend on piezoelectricity are used in camera autofocus and inkjet printer pumps Energy-harvesting sensors are built into wearables like fitness trackers and smart clothes and car airbags.
The bismuth iodide material has no lead, compared to existing PZT (lead zirconate titanate), which is 60% lead. Also, bismuth iodide can be produced at room temperature, while existing materials require temperatures of 1000 degrees C. Those conditions suggest
“a new pathway toward low-cost, low-toxicity mechanical energy harvesting and actuating devices,” the researchers wrote in the journal.
Using single-crystal X-ray diffraction and solid-state nuclear magnetic resonance, researchers discovered the way the organic and inorganic parts of the material bond together, which can be used to change its structure and improve piezoelectric performance.
“By fine-tuning the interactions between the organic and inorganic components, we were able to create a delicate structural instability that breaks symmetry in just the right way, “ said Dr. Esther Hung from the University of Oxford’s Physics Department.
“This interplay between order and disorder is what gives the material its exceptional piezoelectric response. It’s a different approach to piezoelectricity than in traditional materials such as lead zirconate titanate (PZT), and that’s what’s led to these big improvements.”