Structural studies of liquids and glasses using aerodynamic levitation

In this thesis aerodynamic levitation and laser heating has been combined with neutron diffraction, X-ray absorption spectroscopy (XAS), and computer simulations to investigate the structure of liquids and glasses. In order -to determine the structure of BaTi205 glass and RE0.3Ba0.7Ti2O5.15 glass the complementary techniques of neutron diffraction and XAS were combined. Molecular dynamics models based on simple empirical potentials were generated and then refined using Reverse Monte Carlo (RMC) simulations fitting to the neutron diffraction data. From these structural models the glasses were determined to consist of a network of 4, 5, and 6 coordinated Ti-O polyhedra, which was found to be consistent with the X-ray absorption near edge spectra. A decrease in the rare earth oxygen bond length with increasing rare earth atomic mass was observed in both the RMC models and the rare earth edge XAS. The contentious issue of the apparent iso-compositional liquid-liquid phase transition in the (Y203)x(AI203)1-x system was investigated using in situ aerodynamic levitation and small angle neutron scattering (SANS). Samples of x = 0.2, 0.25, 0.3, and 0.375 were studied across a temperature range of 1300-1900K, with detailed measurements at the reported liquid-liquid transition temperature of 1788K (Greaves et al., 2008). There was no observed increase in SANS intensity consistent with the nucleation of a second liquid phase at any temperature. In situ aerodynamic levitation and neutron diffraction with isotopic substitution was used to determine the atomic structure of liquid Invar (Fe65Nh5) at -1800K. Although the introduction of Ni is substitutional, a small degree of chemical was apparent in the Bhatia-Thornton (1970) partial structure factors. Significant magnetic correlations were detected -l300K above the Invar Curie temperature. Anomalous neutron scattering was undertaken on the unusual semiconducting liquid InSe. A first peak coordination number of 3 suggested that the underlying cause of the unusual behaviour is not related to In-In homopolar bonding.