SusChEM: Defect Mechanisms in Bismuth Perovskites

非技术描述：含铋钙钛矿材料的研究在过去十年中稳步增长，部分原因是能源效率考虑和环境标准，如减少危险物质(RoHS)指令。这些法规也是无铅焊料发展的动力，这种焊料在整个电子行业得到了广泛应用。近年来，人们对铋钙钛矿作为铅基电子材料的潜在替代材料的兴趣与日俱增，但关于点缺陷(如阳离子和阴离子空位)在这些材料中的作用的研究还很少。该项目有助于从根本上理解铋钙钛矿中缺陷的作用，以帮助指导这些可持续材料的开发，以用于新的应用。这项研究是至关重要的，因为点缺陷最终会对现象(如压电疲劳、老化、可靠性和高温电阻率)产生深远的影响。疲劳行为可能是高性能微电子机械系统(MEMS)设备的限制因素，例如喷墨打印机、加速计和执行器。这项工作还影响了高温和高电场应用电容器材料的开发，因为坚固的电学性能对于地热系统的井下钻探电子设备、高温碳化硅基无源元件和其他设备非常重要。技术细节：该项目结合合成、分析和计算方法来研究含铋钙钛矿的主要缺陷种类和相关的缺陷平衡条件，以帮助指导这些材料的开发，以满足新兴应用。点缺陷在这些体系中很普遍，因为许多铋基钙钛矿在B位上具有四价钛，这已被证明在高温下通过还原反应表现出氧的非化学计量比。此外，在陶瓷和薄膜的典型工艺条件下，Bi3+、Na+和K+中常见的A位阳离子都是挥发性的。该项目涉及三个实验任务，包括合成阳离子和阴离子非化学计量比可控的陶瓷，鉴定缺陷种类的性质和浓度的表征技术，以及通过测量介电、压电性能和电阻率来建立缺陷化学与材料性能之间的联系。最后，计算(第一原理)的努力被整合到整个项目中，以补充和验证实验结果，并帮助指导未来的实验。除了对本科生和研究生进行材料研究方面的培训和指导外，该项目还结合了一项影响很大的K-12外联活动，每年夏天在俄亥俄州立大学的实验室接待两名高中生，作为青年科学和工程暑期体验(SESEY)的一部分。

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).