CAREER: Tuning Complexity in Rare-Earth Transition Metal Oxides

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). NON-TECHNICAL SUMMARY Materials called “complex oxides” are essential for technologies such as cell phone batteries, capacitors in all kinds of electronic devices, and catalysts that clean up industrial pollutants. These materials contain oxygen and two or more types of metal ions. This configuration allows for highly variable composition (which ions are present) and structure (how the ions are arranged), which can be harnessed to improve the technologies that rely on these families of compounds. With this CAREER award, Professor Katharine Page at the University of Tennessee Knoxville will study “High Entropy Oxides” (HEOs) that contain five or more ions of rare-earth elements or transition metals, which can provide an extremely vast array of compositions and structures. By using novel techniques to uncover and influence how the various HEO atoms interact, this research will reveal how to combine multiple desirable physical properties into a single material. These insights will lead to more efficient, more powerful, and more diverse fuel cells, catalysts, sensors, and electronics. Additionally, this project will produce a middle school workshop series that will promote careers in materials chemistry and related fields through hands-on activities that celebrate the creative exploration process of materials engineering and crystallography. Professors, graduate students, and undergrads involved in the research will teach and mentor participants in the workshop series at economically disadvantaged schools in rural East Tennessee and Appalachian communities. TECHNICAL SUMMARY With this CAREER award, Professor Katharine Page at the University of Tennessee Knoxville aims to uncover the rules for enabling hierarchical and tailored design in pyrochlore and layered perovskite-based rare earth transition metal complex oxide families featuring two to five atom types per lattice site. Relatively little is currently known about the classifications separating traditional complex oxide phases from the emerging class of High Entropy Oxides (materials involving five or more ions per lattice site), including the extent to which new design paradigms are needed to understand and control their physical properties. High entropy and kinetic reaction controls will be examined for their potential to produce single-phase materials and specific crystal-chemical conditions in the pyrochlore family, seeking to improve ionic conductivity at lower working temperature for potential applications in solid oxide fuel cells and catalysts. Similar approaches will seek to tune magnetic, electronic, and multiferroic responses in the layered perovskite family. Sophisticated scattering probes, theoretical tools, and multi-modal modeling methods will be combined to evaluate the impact of local to long-range structure traits on the electronic and magnetic properties of the respective series. The extent to which specific defects, distortions, and chemical short-range order may be achieved and tuned to impact the stability and respective properties of the structural classes will be determined. This fundamental materials chemistry approach will lead to the foundational insights necessary to design HEO materials with desired combinations of traits. Relationships governing the stability, local to global symmetry, and overall tunability in HEOs emerging from this work will impact the broader exploration of complex oxide chemistries unfolding across multiple disciplines and applications. Concurrently, this project will promote a new generation of scientists through outreach, teaching, and mentoring activities that celebrate the creative exploration process of materials chemistry and crystallography approaches as part of a workshop series for traditionally marginalized groups at economically disadvantaged middle schools in rural East Tennessee and Appalachian communities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.