Ferroelasticity and Hysteresis in Mixed Conducting Perovskites

在本提案中，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）镧钴酸盐（LaCoO3）钙钛矿中的铁弹性和迟滞，并对这种行为的起源产生基本的理解。外载荷对钙钛矿弹性迟滞和铁弹性性能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压力诱导的畴重定向，然后是在压缩加载中发生的相变。利用电子显微镜和x射线衍射等独特的原位技术，分析了钴酸镧钙钛矿在准弹性到铁弹性相变过程中晶格畸变和缺陷结构、畴和畴壁微观结构以及空位有序/聚类等随压力、温度和成分的变化。因此，所提出的研究将使我们能够研究不同的一阶或二阶相变、有序-无序转变、非金属-金属转变和马氏体转变，这些转变可能导致钙钛矿的增韧，并增加这些材料在室温和高温下的稳定性和可靠性。对压力、温度和成分对钙钛矿相和微观结构稳定性的影响将有更全面的了解。由于目前对这些材料的铁弹性性质还没有基本的了解，因此这类研究对于了解用于高温合成气反应器、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和机械性能的起源至关重要。预计所提出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迟滞的新的基本见解。本项目也将成为材料工程专业学生积极参与项目学习的理想基础。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成果将在高知名度的出版物和著名的会议上发表。将作出特别努力，吸引代表性不足的学生从事材料科学和工程方面的职业。

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.