Ferroelasticity and Hysteresis in Mixed Conducting Perovskites

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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.