Solid-State Oxides and Oxide-Fluorides

Northwestern University, Evanston IL

Investigators

Abstract

Non-Technical Abstract Highly-efficient non-linear optical (NLO) materials are essential to act as waveguides for electrooptic applications. Such materials are used in ultrafast laser spectroscopy and, more recently, to generate ultraviolet laser light for nanolithographic applications. Current research and engineering activities in the field of NLO materials typically concern synthesis of NLO crystals; however, research is needed for understanding how to design NLO materials and why materials exhibit a particular NLO response. While exploring the fundamental driving factors for creation of new NLO materials, research will be performed to grow large (on the order of one cubic centimeter) single crystals to allow a quantitative understanding of the interaction of light with the NLO material. These analyses of basic principles by graduate students and postdoctoral associates -- who are also engaged in local education, teaching, mentoring, and leadership -- will enhance scientific progress and promote commercial expansion of this technologically important field. Technical Abstract Emerging technologies require high-performance nonlinear optical (NLO) materials that exhibit enhanced optical properties at the microscopic and macroscopic level. The rational design of crystal structures, in particular noncentrosymmetric materials, and how to target polar, polar-chiral, and chiral structures, is an ongoing theme in crystal engineering. A new class of potentially high performance NLO inorganic materials, solid-state oxide-fluorides, has been identified. These studies demonstrate that i) the use of fluoride ligands with early-transition metals enhances the second-order Jahn-Teller distortion in comparison to pure oxide compounds, ii) the synthesis of noncentrosymmetric materials can be promoted with the use of polar basic-building units, and iii) the synthesis of compounds that contain two separate anionic building units is likely to result in a noncentrosymmetric compound. These materials comprise a large and new class of solids with properties associated with piezoelectricity, pyroelectricity, ferroelectricity and second harmonic generation (SHG). The structure-property relationships that give rise to high, low, or null nonlinearities of the NLO materials will be examined. Finally, the growth of large crystals (on the order of one cubic centimeter) allows detailed analysis with measurements of the NLO tensor and phase-matchability properties, and other properties of interest such as piezoelectricity. The materials synthesized will have potential use in relaxor ferroelectrics and non-linear optics. These materials will have a high damage threshold and the potential to fabricate large, single crystals suitable for optical use and technical applications. The project is supported by the Solid State and Materials Chemistry Program in the Division of Materials Research.