Origin of the Electric Field-induced Strain in Lead-free Piezoelectric Ceramics

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NON-TECHNICAL DESCRIPTION: Piezoelectric materials change their dimensions when subjected to electric fields, consequently their applications range from gas igniters, speakerphones, to medical ultrasonic imaging systems. In current commercial piezoelectric devices these materials contain ~60 wt.% of lead. Due to the toxicity of lead, recent legislation in many countries restricts its use. This project aims to uncover the fundamental mechanism of the piezoelectric deformation in lead-free ceramics. The research findings will ultimately lead to the production of ceramics that will replace lead-containing piezoelectric materials. Therefore, a significant impact on health and the environment is anticipated. In addition to getting graduate and undergraduate students from underrepresented groups involved, this project will also directly benefit the K-12 education in local schools in Ames, Iowa through the lectures on piezoelectric devices to the Science Olympiad (http://soinc.org/) team students. TECHNICAL DETAILS: The environmental concerns about lead in Pb(Zr1-xTix)O3 (PZT) have currently stimulated extensive worldwide researches on the development of lead-free piezoelectric ceramics. Previous researchers suggest that the two best systems, ceramics based on (K0.5Na0.5)NbO3 and those based on (Bi0.47Na0.47Ba0.06)TiO3, have completely different piezoelectric deformation mechanisms from those in PZT. Limited evidence indicates that the strain from the electric field-induced phase transition becomes significant. With the PI's unique in situ transmission electron microscopy technique, this project seeks to uncover the origin of the strain that develops under applied electric fields in these lead-free ceramics. Integrated with the experimental work, computational modeling based on density functional theory methods is also planned. The outcome of this project is expected to provide critical guidelines in the development of new lead-free compositions with high and yet temperature-stable piezoelectric properties. This project is designed to have a broad impact on graduate and undergraduate materials science education. Undergraduate students, especially those from underrepresented groups, will be integrated into research at Iowa State University through various educational programs. In addition, through existing connections with the Ames Middle School science teachers, the PI plans to give lectures on piezoelectric devices and demonstrate the piezoelectric effect to the Ames Middle School Science Olympiad team students.