Ferroelasticity and Hysteresis in Mixed Conducting Perovskites

在这项提议中，我们的目标是建立在我们最近发现的混合离子-电子导电(MIEC)钴镧(LaCoO_3)钙钛矿中铁弹性和磁滞的基础上，并对这种行为的起源有一个基本的理解。外载荷对钙钛矿材料的弹性滞后和铁弹性行为的影响将通过压缩试验来表征。主要的障碍是要明确地证明，在压缩加载中，压力引起的磁畴重新定向，随后发生相变。利用独特的电子显微镜和X射线衍射原位技术，分析了钙钛矿结构钙钛矿La-Co的晶格扭曲和缺陷结构、磁区和磁区壁微结构以及超弹性-铁弹性相变过程中的空位有序化/聚集现象。因此，拟议的研究将使我们能够研究不同的一阶或二阶相变、有序-无序相变、非金属-金属相变和马氏体相变，这些相变可能导致钙钛矿相的增韧，并增加这些材料在室温和高温下的稳定性和可靠性。随后将更全面地了解压力、温度和组成对钙钛矿相和微结构稳定性的影响。由于目前还没有对这些材料的铁弹性性质的基本了解，这些研究对于理解用于高温合成气反应堆、氧传感器、催化剂和固体氧化物燃料电池(SOFC)的MIEC材料的弹性不稳定性的来源和机械性能是必不可少的。预计拟议的研究结果将涉及对混合离子电子导电钙钛矿材料的铁弹性和磁滞的新的基本见解。建议的项目也将是材料工程专业学生积极参与基于项目的学习的理想基础。本科生和研究生都将进行研究，并在技术会议上展示他们的成果。预计本科生和研究生的研究都将产生引人注目的出版物和享有盛誉的会议报告。将特别努力吸引代表性不足的学生投身材料科学和工程领域。

In this proposal we aim to build on our recent discovery of ferroelasticity and hysteresis in mixed ionic-electronic conducting (MIEC) lanthanum cobaltite (LaCoO3) perovskites and generate a fundamental understanding of the origin of this behavior. The effect of the external loading on the elastic hysteresis and ferroelastic behavior of perovskites will be characterized by the compression tests. The main hurdle is to demonstrate unambiguously that pressure induced domain reorientation, followed by phase transformation, occurs in a compression loading. Unique in situ techniques in electron microscopy and x-ray diffraction will be employed to analyze the lattice distortions and defect structures, domain and domain wall microstructures, and vacancy ordering/clustering that occurs during the paraelastic to ferroelastic phase transition in lanthanum cobaltite perovskites as a function of pressure, temperature and composition. Therefore, the proposed research will allow us to investigate different first or second order phase transitions, order-disorder transitions, nonmetal-metal transitions, and martensitic transitions, which could lead to the possible toughening of perovskites and an increase in the stability and reliability of these materials both at room and high temperatures. A more complete understanding of the effect of pressure, temperature, and composition on the phase and microstructural stability of perovskites will subsequently be achieved. As a basic understanding of the ferroelastic properties of these materials is not currently available, such research is essential to understand the origin of elastic instabilities and the mechanical properties of MIEC materials used for high-temperature syngas reactors, oxygen sensors, catalysts, and solid oxide fuel cells (SOFCs).It is anticipated that the results of the proposed research will involve new fundamental insights into ferroelasticity and hysteresis in mixed ionic electronic conducting perovskite materials. The proposed project will also be an ideal basis for Materials Engineering students to actively participate in project-based learning. Both undergraduate and graduate students will undertake research and present their results at technical meetings. It is expected that both undergraduate and graduate students' research will result in high-profile publications and prestigious conference presentations. Special efforts will be made to attract underrepresented students to careers in materials science and engineering.