Basic Research in Antiferroelectric Perovskites

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9988853ChenThe objective of this proposal is to investigate fundamental materials problems concerning antiferroelectric perovskites. Antiferroelectric perovskites are a small subclass of ferroic perovskites. Compared to prototypical ferroelectric perovskites, they have relatively limited applications to date and have been much less studied in the past. Nevertheless, theoretical considerations indicate that the antiferroelectric states are energetically similar to the ferroelectric states, and that in many large-response ferroelectrics there is a strong antiferroelectric/ferroelectric competition that is central to latter's outstanding properties. Moreover, several physical and chemical features common to nearly all of the antiferroelectric perovskites, e.g., a negative transformation volume and a very weak isotope effect, are anomalous and not found in any ferroelectric perovskites. This suggests that new basic research on antiferroelectric perovskites will have a fundamental impact on ferroelectrics that are used for important technological and biomedical applications. It also has the potential of discovering novel ferroelectrics and antiferroelectrics with attractive physical and chemical properties. In this research project, the PI will determine mechanical and electrical field effects on antiferroelectric-ferroelectric transitions, interrogate local atomic and electronic structures of antiferroelectric perovskites, and investigate antiferroelectric thin films and heterostructures. Using concepts in crystal chemistry and statistical physics, experiments will be designed to optimize antiferroelectric interactions and tune their competition with ferroelectric interactions. Synchrotron x-ray and other scattering and imaging techniques will be used to probe the cation couplings and electronic transitions that may give rise to the anomalous features observed in antiferroelectricity. This study will be further complemented by property characterization of bulk and thin film antiferroelectrics to understand the thermodynamics and kinetics of phase transitions, interface motion, interface-defect interactions, and antiferroelectric/ferroelectric competition at the smallest length scale. Antiferroelectric perovskites are a type of perovskites that have had relatively limited applications to date and have been much less studied in the past. Nevertheless, theoretical considerations indicate that these materials may have unique properties and thus basic research on them will have a fundamental impact on ferroelectrics that are used for important technological and biomedical applications. The project will train Ph.D. students as well as offering training to undergraduates and high school teachers. This effort will be integrated into the research project to attract traditional and non-traditional students and to provide them laboratory and research opportunities.