Solid-State Oxides and Oxide-Fluorides

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Non-Technical SummaryLasers were discovered in 1960 by scientists at Bell Laboratories. A year after the initial discovery, a group of researchers demonstrated that the high electric fields produced by a laser pulse converted the light passing through a quartz crystal from one color to another (red to green) via a nonlinear optical (NLO) process called second-harmonic generation. Since then, NLO materials like quartz have played a key role in advancing frontiers in laser science. NLO activity and other exciting properties are allowed in materials where inversion symmetry in broken, which are known as noncentrosymmetric (NCS) solids. Through this project, which is supported by the Solid State and Materials Chemistry program at NSF, Prof. Poeppelmeier's group at Northwestern University advances the understanding how chemistry can be used to create materials with broken inversion symmetry and connect atomic structure to properties. A variety of synthetic approaches are used to control the alignment of the building blocks that make up a crystal structure. Their growth of large, high-quality crystals of NCS materials enables detailed investigation of the connection between atomic structure and properties in NCS materials. The research is carried out by undergraduate and graduate students, who in the process of this project are trained in state-of-the-art solid state chemistry. Additionally, the students are encouraged to participate in a myriad of outreach activities that the PI himself is involved in.Technical SummaryAdvances in laser technology have led to a significant increase in the application of laser systems in areas ranging from eye surgery to particle acceleration. Emerging laser technologies require high-performance materials that can efficiently convert the frequency of laser radiation through nonlinear optical (NLO) processes, such as second-harmonic generation and parametric amplification. The NLO properties necessary for applications in tunable laser systems, as well as other technologically useful properties such as piezoelectricity, ferroelectricity, and pyroelectricity, are available in crystalline materials lacking inversion symmetry, known as noncentrosymmetric (NCS) solids. This project, which is supported by the Solid State and Materials Chemistry program at NSF, develops targeted synthesis methods for NCS materials using hydrothermal, solvothermal, and solid-state methods to control the alignment of anionic basic building units such that useful properties can be realized. These synthetic efforts are guided by chemical knowledge as well as machine learning methods that elucidate important trends from large amounts of experimental data. The growth of large, high-quality crystals enables structural characterization with single crystal and powder x-ray diffraction along with NLO and other property measurements to determine structure-property relationships. Examination of the syntheses, structures, and properties of NCS materials is expected to lead to discovery of new NCS materials and new strategies for future NCS materials synthesis.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.