Lattice Properties of Crystalline Solids with Glasslike Properties: Ultrasound Studies of Inclusion Compounds and Quasicrystals

University Of Mississippi, University MS

Investigators

Abstract

This proposal is designed to investigate the elastic response and ultrasonic attenuation of a wide variety of "glasslike crystals" (materials that simultaneously reflect both crystalline and glasslike properties). The scientific issues that will be addressed include: (a) the relationship between inclusion compounds, quasicrystals, and structural glasses, (b) are tunneling states (which are typically found in glasses at low temperatures) intrinsic to inclusion compounds and/or quasicrystals, and (c) structure-property relationships - to what extent can various structural features be used to predict the elastic properties of a given material? This research project will use Resonant Ultrasound Spectroscopy (RUS) to probe the elastic properties of the materials under investigation. RUS is a novel technique for determining the elastic moduli of solids, based on the measurement of the resonances of a freely vibrating body. The ultrasonic attenuation of the materials will be measured using a standard pulse-echo technique. This proposal will contribute toward the development of a strong solid-state program at The University of Mississippi. Both advanced undergraduate and graduate students will gain in-depth experience in ultrasound experiments and the techniques of low temperature physics. "Ordinary" materials are either crystals (with long-range order, i.e., the atoms are arranged in a periodic array) or glasses (with no long-range order). This proposal will investigate the properties of some "extraordinary" materials such as inclusion compounds and quasicrystals. These are materials that simultaneously display both crystalline and glasslike properties. The project will focus on the elastic properties of these remarkable solids, using a relatively new technique, Resonant Ultrasound Spectroscopy (RUS). A study of materials that display the unusual combination of glasslike and crystalline features is expected to have an impact on two fronts. First, the investigation of the glasslike properties found in these materials is expected to lead to a better understaanding of the origin of glassy behavior. Since these materials are of interest for technological (thermoelectric) applications, a better understanding of their properties is essential for the design of materials with superior properties. Secondly, this research will contribute to the training of young scientists at the undergraduate and graduate level in Mississippi, who will gain in-depth experience in the field of condensed-matter physics.