Pushing the Boundaries of Kinetic Stability in Metastable Perovskite Oxides

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Part 1. Non-Technical Summary One of the major limitations in the discovery and design of new materials is the capability of predicting which compounds can potentially be synthesized. The underlying fundamental principles are not well understood and have historically required extensive trial and error. This project, supported by the Solid State and Materials Chemistry program within the Division of Materials Research, investigates and pushes the boundaries of synthesizability of crystalline solids, enabling the development of new strategies for preparing future technological materials. Discoveries stemming from the research efforts can provide new methods to prepare, for example, less toxic or more energy-efficient compounds that are critically important to the nation’s semiconductor and electronic ceramics industries. More generally, the advancement of strategies to synthesize materials over a wider attainable range of compositions and structures enables the rapid acceleration of their technological development. An in-depth characterization of the local and long-range structural features is aimed at understanding the impacts on the local structure and/or disorder of materials that occur at the edges of synthesizability. The inspiration and training of the next generation of scientists is facilitated within these technologically relevant basic research activities, including professional experiences at national laboratories and the development of research experiences for high school and community college teachers. The educational activities also emphasize the recruitment and participation of research students from underrepresented groups in STEM disciplines. Part 2. Technical SummaryMetastable crystalline solids are ubiquitous and can be commonly found as a result of either synthetic or naturally occurring processes, such as in the formation of crystalline diamond or in the synthesis of austenite stainless steel. The synthesis of metastable solids with technologically relevant properties, but that are extremely difficult or impossible to prepare, is a growing limitation in many research fields. The central objective of the research project is to elucidate and exploit the underlying factors that can govern the kinetic stabilization of metastable phases. Research thrusts specifically focus on metastable Sn(II)-containing perovskites that have potential applications as new lead-free ferroelectrics and as small bandgap semiconductors. The synthetic component is directed toward the discovery of new pathways to increase the range of synthesizability that can be experimentally achieved with the use of reaction conditions that can, for example, drive product formation while controlling ion diffusion and phase segregation in order to inhibit decomposition. Structural characterization by X-ray and neutron scattering techniques is aimed at answering key questions regarding the formation and decomposition pathways of these compounds. The extent and distribution of local and long-range structural disorder is probed at the precipices of energetically downhill decomposition pathways and the resulting new insights can help to push the limits of kinetic stabilization. Experimental efforts are complemented with quantification of thermodynamic relationships using open materials databases and density functional theory. Educational initiatives within this project, which is supported by the Solid State and Materials Chemistry program in the Division of Materials Research, include research training of undergraduate and graduate students, involvement of high school and community college teachers in research, and offering of an annual workshop on Rietveld methods for learners at a range of stages in their education.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.