SusChEM: Defect Mechanisms in Bismuth Perovskites

Oregon State University, Corvallis OR

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: Research on bismuth-containing perovskite materials has grown steadily over the last decade due in part to energy efficiency considerations and environmental standards such as the Reduction of Hazardous Substances (RoHS) directive. These same regulations were the motivation for the development of Pb-free solders that were broadly implemented across the electronics industry. While interest in bismuth perovskites as a potential materials replacement for Pb-based electronic materials has grown in recent years, there have been few studies on the role of point defects (e.g. cation and anion vacancies) in these materials. This project contributes to the fundamental understanding of the role of defects in bismuth perovskites to help guide the development of these sustainable materials for emerging applications. This research is critical because point defects ultimately have a profound influence on phenomena (such as piezoelectric fatigue, aging, reliability, and high temperature resistivity). Fatigue behavior can be a limiting factor in high performance microelectromechanical systems (MEMS) devices, such as ink jet printers, accelerometers, and actuators. This work also impacts the development of capacitor materials for high temperature and high electric field applications because robust electrical properties are important for devices for down hole drilling electronics for geothermal systems, high temperature SiC-based passive components, and others. TECHNICAL DETAILS: This project combines synthesis, analysis and computational approaches to investigate the dominant defect species and relevant defect equilibrium conditions for bismuth-containing perovskites to help guide the development of these materials for emerging applications. Point defects are prevalent in these systems given that many Bi-based perovskites feature tetravalent Ti on the B-site which has been shown to exhibit oxygen non-stoichiometry at high temperatures from a reduction reaction. Furthermore, the common A-site cations of Bi3+, Na+ and K+ are all known to be volatile under the typical processing conditions of both ceramics and thin films. This project involves three experimental tasks including synthesis of ceramics with controlled cation and anion non-stoichiometry, characterization techniques to identify the nature and concentration of the defect species, and establishing the linkage between the defect chemistry and the materials properties through measurements of the dielectric and piezoelectric properties and electrical resistivity. Finally, computational (first principles) efforts are integrated throughout this project to complement and verify the experimental results and to help guide future experiments. In addition to training and mentoring undergraduate and graduate students in materials research, this project incorporates a high-impact K-12 outreach activity by hosting two high school students into the laboratory at OSU each summer as part of the Summer Experience in Science and Engineering for Youth (SESEY).