## Arts & Sciences Electronic Theses and Dissertations

#### ORCID

http://orcid.org/0000-0002-1812-0559

#### Date of Award

Winter 12-15-2018

#### Author's School

Graduate School of Arts and Sciences

Physics

#### Degree Name

Doctor of Philosophy (PhD)

Dissertation

#### Abstract

A major outstanding problem in condensed matter physics is the nature of the glass transition, in which a rapidly cooled liquid can bypass the transition into a crystalline state and the liquid structure is "frozen-in" due to kinetic arrest. To characterize the fundamental features behind this transition the liquid, both in the high temperature (equilibrium) and supercooled state, needs to be better understood. By examining the relationship between structure and dynamics a better characterization of the liquid state and a determination of the mechanisms that are ultimately important for the formation of the glass can be gained. In this dissertation, elastic X-ray and inelastic neutron diffraction measurements (made using the electrostatic levitation technique), coupled with both reverse Monte Carlo (RMC) and molecular dynamics (MD) simulations are presented. These studies detail important connections between the structure and dynamics that may aid in the understanding of the glass transition. The RMC technique, which is a common method for obtaining plausible atomic configurations from diffraction data, is examined to determine the properties that are reliable when using few diffraction measurements as constraints. The liquid bond length, obtained from X-ray diffraction measurements and associated RMC simulations, is examined using the nearest-neighbor distance distribution. These studies demonstrate that the local structure is related to the liquid fragility, a measure of temperature dependence of viscosity, through the thermal expansion coefficient. An analysis of the X-ray diffraction data also demonstrates that a crossover from Arrhenius to super-Arrhenius temperature dependence of the viscosity at a temperature ($T_A$) can be related to the onset of an accelerated development of a well-defined next-nearest neighbor length scale. Finally, new measurements of the dynamic pair correlation function obtained from inelastic neutron scattering studies of a $\mathrm{Pt}-\mathrm{Zr}$ metallic liquid, combined with molecular dynamics simulations, show that above $T_A$ the viscosity is controlled by atoms leaving or joining a local cluster. Taken together, these three results give a coherent picture that relates structure and dynamics in equilibrium supercooled liquids.

English (en)

#### Chair and Committee

Kenneth F. Kelton

#### Committee Members

Rohan Mishra, Zohar Nussinov, James S. Schilling, Li Yang,