Collections > Electronic Theses and Dissertations > Dynamics and Structure in Metallic Supercooled Liquids and Glasses Studied by NMR
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In this dissertation, we used high temperature NMR to study the dynamic behavior of metallic liquids and glasses from completely molten state to temperatures well below the glass transition. We found that there are different processes in the system that have distinct effects to NMR probing methods, so we employed several NMR techniques to study these processes separately. A dramatic temperature dependence of Knight shift was recorded and it was attributed to the fast vibration and rattling processes. A transition was directly observed at Tc which is about 100K above the glass transition temperature. The result was shown to be consistent with MCT, mode coupling theory. Nuclear quadrupolar relaxation, 1-d lineshape analysis and stimulated echo techniques were utilized to study the slow processes. At high temperatures, the dynamics follow the MCT predictions. Starting from Tc and below, a decoupling in diffusion behavior between the light/small atoms and heavy/big ones was discovered. We discussed possible dynamic and thermodynamic explanations. In the second part of the dissertation, we used NMR to study the primary crystallization in some Aluminum-based metallic glasses. A precursor for crystallization was found even in as-quenched samples. A common metastable state was discovered at low temperatures. We also presented some studies on the electronic structure and short-range order of some metallic glasses and possible correlations of such properties with the glass forming ability.