Solid State Oxyfluorides

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The focus of this project is on the rational design of crystal structures based on the chemical nature of molecular components in noncentrosymmetric structures based on acentric transition metal oxyfluorides. Robust synthetic methods used to prepare metal oxyfluorides from metal oxides allow many reactions to be carried out simultaneously, which greatly enhances reaction yields, controlled purity, and single crystal growth. Acentric molecules and solids are those that lack inversion symmetry. A major goal is to understand how to optimize geometries and the electrostatic potential of the individual oxyfluoride anions to create order and avoid disorder in the metal-oxygen and metal-fluoride bonds. Crystal symmetries of the oxyfluorides are determined by the network of contacts the surrounding lattice provides which are controlled to create chiral, polar or chiral-polar three-dimensional solids. Structures lacking inversion symmetry are a requirement for important current and future technologies that are being created by numerous inventions based on piezoelectricity, pyroelectricity, ferroelectricity and second harmonic generation (SHG). The goal is to provide is to provide a new class of solids for studies in basic science associated with the noncentrosymmetric space groups. %%%Enhancing the infrastructure of research and education is a key objective. Strong ties are maintained with the Materials Research Science and Engineering Center (MRSEC) and the Center for Catalysis and Surface Science (CCSS) at Northwestern University. These centers encourage, support and operate multi-user facilities and provide training for the students which facilitate a high level of scientific achievement and professional development. Undergraduate, graduate and post-graduate students benefit from the significant advances that can be made in the discovery of new materials and from the cross-disciplinary experiences gained from the characterization of these new structures and their properties. Students are given every opportunity to give presentations at scientific meetings where they can interact with industrial and academic colleagues. The determination of structure/property relationships is ongoing with basic structural studies (X-ray, neutron and electron diffraction and microscopy), thermo-dynamic properties (thermogravimetric analysis and differential scanning calorimetry), and optical and magnetic properties (IR, Raman and SQUID). Strong ties are also maintained with National Laboratories especially Argonne National Laboratory, and in particular with scientists at the Intense Pulsed Neutron Source (IPNS) and the new Spallation Neutron Source (SNS) under development at Oak Ridge National Laboratory. New materials classes exhibiting piezoelectricity, pyroelectricity, ferroelectricity and second harmonic generation (SHG) are of significant interest as applied materials and students trained in these and related areas are very competitive in the job market.***