Complex Perovskites: Chemical & Structural Complexity as a Route to New Functional Materials

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TECHNICAL SUMMARY: Chemical substitutions that increase the compositional complexity of the perovskite structure are known to give rise to properties that cannot be realized in simpler materials. However, as the compositional complexity increases detailed knowledge of the bonding interactions that drive atoms to assemble into homogeneous single phase materials is needed to rationally approach the synthesis and design of such materials. The proposed research involves synthesis of new perovskites and the use of advanced structural characterization tools, and property measurements to study these materials. The specific research objectives involve: (1) Synthesis and characterization of new perovskites with useful dielectric, magnetic and ionic conduction properties by simultaneously ordering A- and B-site cation arrays. (2) Studies of perovskites where octahedral tilting disrupts the corner sharing connectivity of the octahedral framework. (3) Studies of phase transitions in oxyfluoride double perovskite, coupled with use of cation bonding preferences to control the orientational ordering of anionic oxyfluoride polyhedra. Variable temperature Raman spectroscopy studies will be used to follow changes in local and long range structure that occur in response to changes in temperature or composition. New materials with attractive dielectric, magnetic, nonlinear optical and electrical properties are anticipated. NON-TECHNICAL SUMMARY: Perovskite materials play a central role in many important technologies including: dielectric materials for electronic applications, ion conductors for batteries and fuel cells, superconductivity and magnetoresistance to name a few. This grant will advance our understanding of how to control atomic scale ordering of elements to produce new materials for these important technologies. The research involves collaborations with internationally renowned electron microscopy centers in Australia and Spain. To disseminate this knowledge Web based resources will be developed that will positively impact teaching and research across several disciplines. An upper level laboratory experiment that teaches the principles of X-ray powder diffraction and crystal packing forces will be created, implemented and disseminated. Finally the project will provide important opportunities for graduate and undergraduate students to learn skills that are needed for modern materials chemistry research. Students will create important contacts through national and international collaborations supported by this project.