| By employing the technique of electrostatic levitation, coupled with high-energy x-ray diffraction and rapid data acquisition, this study obtained high quality structural data in the supercooled regime of liquids. The experimental x-ray diffraction data for supercooled liquids such as Si, Ti, Ni and Zr were analyzed using the Reverse Monte Carlo method to determine realistic atomic structures. No change in the coordination number of supercooled liquid Si was observed over the measured temperature range of supercooling. This result calls into question previous experimental claims of structural evidence for the existence of a liquid-liquid phase transition. Instead, based on the Honeycutt Andersen index and bond orientational order parameter analyses of the RMC structure, the fraction of regions with white-tin (A5) and diamond cubic (A4) order remain nearly constant with supercooling; however, the coherence length of the A5 order increases. This study proposes local structural models for supercooled liquid transition metals (Ti, Ni and Zr). All analyses suggest that an icosahedral short-range order is present in these supercooled liquids, but this short-range order is distorted in liquid Ti. These results support the observed evolution of the high-q shoulder on the second peak in the structure factor, S(q).; The structures of metallic glasses (such as the Zr-based glasses) were investigated by the same techniques to provide further insight into the atomic structure of liquids. The relation between glass forming ability and the local structure of these metallic glasses was explored. Interestingly, Zr-based metallic glasses with different glass forming abilities showed similarly strong icosahedral order in liquid and glassy states. An investigation of the structural behavior near the glass transition temperature (Tg) in these glasses demonstrated an evolution of icosahedral order with supercooling. The evolution was arrested on approaching the Tg and thereafter became constant below the Tg.; The local structures of Ti-Zr-Ni liquids that form quasicrystal phases and TiFeSiO liquids that form crystal approximant phases were studied as a function of supercooling. This study found similarities between the supercooled liquid and quasicrystal structures in Ti-Zr-Ni and the liquid and approximant structures in TiFeSiO. |
