Lead-free Piezoelectric Ceramics

Throughout the world, demand is growing for materials that are benign to the environment and human health. Many government regulations have been enacted in response to this demand, such as the Restriction of Hazardous Substances (RoHS) directives in Europe and China. The European RoHS directive (2006) restricts hazardous substances used in electrical and electronic equipment, including lead (Pb). Other related legislative acts passed by the European Union include End-of-life Vehicles (ELV) in 2003 and Waste from Electrical and Electronic Equipment (WEEE) in 2004.

Structure of PZT: Ti and Zr ions in center of perovskite unit displace above the Curie temperature, inducing polarity.

Lead oxide based ferroelectric materials such as lead zirconate titanate (PZT) are the most widely used materials for electronic devices such as actuators, sensors and transducers, because of their excellent piezoelectric properties. However, the environmental and health hazards of lead are well-known, and recycling and disposal of devices containing lead-based piezoelectric materials is of great concern, especially those used in consumer products such as cars, sound systems, and medical devices. Thus, interest is high for development of lead-free piezoelectric materials that are biocompatible and environmentally friendly. Another motivation for seeking lead-free alternatives is the need for piezoelectric ceramics (or piezoceramics) suitable for high temperature operations. Three major families of lead-free piezoceramic materials have been actively researched, based on perovskite, tungsten-bronze, and bismuth layered structures. However, none of these lead-free piezoelectric material types is ready to replace the PZT-based materials. Moreover, the processing and properties of lead-free piezoceramics under different conditions of pressure, frequency, and temperature are not well understood compared to PZT systems. Due to the lack of comparable alternative materials, electronic components and devices made from PZT piezoceramics have been exempted from European RoHS regulation. The exempt status will be re-evaluated by 2011.

Yazaki Corporation is strongly committed to environmental concerns, and its utmost corporate responsibility is to help ensure a viable planet for future generations. YTC America has confronted the technical challenge to replace environmentally harmful PZT materials and initiated an effort to develop lead-free piezoceramics, utilizing our substantial technology base in solution synthesis of highly pure metal oxide materials. The initial application target is high-power actuator-type products that offer long-term stability at operating temperatures greater than 100C.

© 2008 YTC America Inc.