SusChEM: Defect Mechanisms in Bismuth Perovskites

非技术描述：对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的考虑和环境标准，如减少有害物质（RoHS）指令。这些相同的法规是在整个电子行业广泛实施的无铅焊料开发的动机。近年来，人们对铋钙钛矿作为替代铅基电子材料的潜在材料的兴趣越来越大，但对这些材料中点缺陷（如阳离子和阴离子空位）的作用的研究却很少。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，用于新兴应用。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。在高性能微机电系统（MEMS）器件中，如喷墨打印机、加速度计和执行器，疲劳行为可能是一个限制因素。这项工作还影响了用于高温和高电场应用的电容器材料的发展，因为强大的电性能对于地热系统、高温sic基无源元件等井下钻井电子设备非常重要。技术细节：该项目结合了合成、分析和计算方法，研究含铋钙钛矿的主要缺陷种类和相关缺陷平衡条件，以帮助指导这些材料的开发，用于新兴应用。点缺陷在这些体系中普遍存在，因为许多铋基钙钛矿在b位上具有四价Ti，在高温下从还原反应中表现出氧非化学计量。此外，已知Bi3+， Na+和K+的常见a位阳离子在陶瓷和薄膜的典型加工条件下都是挥发性的。本项目包括三个实验任务，包括合成具有控制阳离子和阴离子非化学计量的陶瓷，鉴定缺陷种类的性质和浓度的表征技术，以及通过测量介电和压电性能以及电阻率建立缺陷化学与材料性能之间的联系。最后，计算（第一性原理）的努力整合在整个项目中，以补充和验证实验结果，并帮助指导未来的实验。除了在材料研究方面对本科生和研究生进行培训和指导外，该项目还结合了一个高影响力的K-12外展活动，每年夏天邀请两名高中生进入俄勒冈州立大学的实验室，作为青少年科学与工程暑期体验（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).