SusChEM: Nanoscale Insight into Electric Fatigue of Lead-Free Piezoelectric Ceramics

Iowa State University, Ames IA

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: Lead interferes with many body processes, including the development of the nervous system, and therefore is particularly toxic to children, and can cause permanent learning and behavior disorders. Regulations restricting lead use, such as enforced recycling of lead-acid batteries of automobiles and the ban of leaded gasoline and lead paint, have greatly reduced lead exposure in the developed world since the 1970s. However, lead is one of the most produced metals in the world and is still widely used in various products. Even today, lead poisoning remains one of the largest environmental medicine problems in terms of numbers of people exposed and the public health toll it takes. In electronic devices and medical instruments, lead is primarily used in piezoelectric elements. These elements convert electrical signals into acoustic signals and are critical for underwater communications and ultrasound medical imaging. To further reduce lead contamination and create a sustainable environment for future generations, currently used lead-containing piezoelectric materials must be replaced by lead-free ones. This project on fundamental research aims to identify environmentally-friendly compositions for the multi-billion dollar piezoelectrics industry. The outcome has the potential to greatly benefit both human health and the environment. TECHNICAL DETAILS: The core elements in piezoelectric devices are made of lead zirconate titanate ceramics, which contain more than 60 wt.% of lead. The toxicity of lead has raised serious environmental concerns and legislations on restriction of its use have driven extensive worldwide research on the development of lead-free piezoelectric materials. Significant progress has been made in the past decade in composition design and processing control and the research community is now being prompted to move these scientific achievements into fruitful environmentally safe products. As such, fundamental issues related to performance stability and device reliability need to be addressed thoroughly and immediately. In real devices during service, these ceramics are almost invariably driven by cyclic electric or mechanical forces, and eventually their performances deteriorate due to fatigue. Electric fatigue degradation is the major concern for stability and reliability of piezoelectric devices utilizing lead-free ceramics. In this project, the researchers at Iowa State are investigating the microstructural mechanisms of electric fatigue through electrically cycling lead-free ceramic specimens inside the transmission electron microscope for the first time. Such innovative in situ studies can identify the primary microstructural feature that leads to fast fatigue degradation and therefore, will help find ways to alleviate the property degradation. Lead-free compositions can then replace lead zirconate titanate in a wide range of engineering and medical technologies, which greatly help to create a sustainable future for children. This project is also designed to have a broad impact on graduate and undergraduate education by training students in cutting-edge materials research techniques. Furthermore, an App for iPads on the toxicity of lead is under development for demonstrations to high school students and undergraduate students.