CAS: Design and discovery of lead-free hybrid layered perovskite dielectrics

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Non-Technical Abstract:Dielectric materials find widespread application in modern society. Ferroelectrics are used to make circuit elements such capacitors, antennas and filters; piezoelectrics are used in sonar and ultrasound imaging technologies; pyroelectrics are used in infrared imaging devices among other applications. The vast majority of dielectric materials are inorganic oxides, many of which contain lead. With support from the Solid State and Materials Chemistry Program and the Electronic and Photonic Materials Program in the Division of Materials Research the principle investigator and his group discover and develop new dielectric materials within the emerging family of hybrid layered perovskites, materials that are made up of alternating layers of positively charged organic cations and negatively charged, corner-connected metal-halide octahedra. Through an iterative program of synthesis and characterization the rules governing the complex crystal chemistry of these materials are studied. The new knowledge is then used to design new dielectric and magnetic materials that can serve as alternatives to the lead-based oxide dielectrics that are widely used today. In addition, authentic in-class research experiments are developed and implemented in general chemistry courses at Ohio State University that impact hundreds of students per year, introducing them to research and key materials chemistry concepts at an early stage of their college education. Finally, the graduate and undergraduate students supported by this project gain training that prepares them for successful careers in academia and industry. Technical Abstract:The research, supported by the Solid State and Materials Chemistry Program and the Electronic and Photonic Materials Program in the Division of Materials Research, can be divided into two thrust areas. The first thrust involves synthesis and characterization of layered double perovskites that contain a checkerboard pattern of 1+ and 3+ cations on the octahedral sites of the inorganic layers. When paired with the appropriate organic cations these materials are able to mimic the promising dielectric properties that have recently been seen in lead-based hybrid layered perovskites, while avoiding incorporation of toxic elements such as lead and cadmium. Phase transitions are studied to understand the structure directing forces in these materials and reveal the mechanisms by which various distortion mechanisms couple to one another. The second thrust brings a similar approach to compounds that contain magnetic cations, like Cu2+, Mn2+ and Fe2+. The research leverages the interactions between organic and inorganic layers to amplify the electrical polarization seen in polar crystals and enhance the coupling between magnetic and ferroelectric order parameters. The overarching theme of the research program is to develop an understanding of the complex crystal chemistry of these hybrid materials and use that knowledge to design and develop new ferroelectrics, antiferroelectrics, piezoelectrics, multiferroics, ferroelectric semiconductors, and related classes of multifunctional dielectric materials.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.