The primary purpose of this grant is to develop a better understanding of the role of local structure and long-range diffusion on glass formation and crystallization. Representative glasses will be chosen from four technologically important families (Al-based, Ti/Zr-based, Fe-based and Mg-based). Amorphous structures will be studied with wide-angle x-ray scattering, 3D atom probe, EXAFS, and variable coherence (or fluctuation) dark-field transmission electron microscopy (TEM). Plausible amorphous structures will be constructed from a Reverse Monte Carlo analysis of the measured x-ray structure factor. The influence of long-range diffusion on nucleation and growth will be studied with energy filtered TEM, atom probe and small angle scattering, and the kinetics will be determined from differential scanning calorimetry and TEM measurements. These data will be fit to a new model for diffusion-influenced nucleation developed at Washington University. A second goal of the grant is to continue hydrogenation studies of Ti/Zr/Hf/Mg-based quasicrystals and glasses that have technologically relevant features, such as a high storage to weight ratio. %%% The insight gained from the coordinated measurements and modeling in glasses will clarify the mechanisms responsible for nanostructure formation during glass crystallization that will lead to improved control of nanostructure production. In addition to producing new information of basic and technological interest, this research has a significant educational importance. Both graduate and undergraduate students will receive training in theoretical and experimental methods in materials science and condensed-matter physics. Presentations of this and related research will be given in local secondary schools, providing information for potential scientific careers and allowing opportunities for graduate and undergraduate students to help with science education. ***
