Dissertation/Thesis Abstract

The Structure and Dynamics of Monatomic Liquid Polymorphs; Case Studies in Cerium and Germanium
by Cadien, Adam, Ph.D., George Mason University, 2015, 140; 3706976
Abstract (Summary)

The study of liquid polymorphism is at the frontier of fundamental thermodynamics and materials science. Liquid polymorphism occurs when a single material has multiple structurally unique liquid phases. Water was the first substance suggested to exhibit multiple liquid phases, a number of monatomic semiconductors and metals have been found to exhibit similar characteristics since then. A better understanding of the liquid-liquid phase transition is needed to tackle problems in glass sciences, it is also relevant to geophysical studies of the Earth's core and mantle and has applications in nanotechnology.

Computational methods are critical to developing a better understanding of liquids. Through simulation thermodynamic obstacles that hamper experiments can be artificially bypassed, metastable regions outside the equilibrium phase diagram can be accessed and all of the properties of the system are directly recorded. Computationally it is much simpler to iterate over a range of environmental variables such as temperature, pressure and composition, and measure a system's response. In this thesis ab-initio and semi-empirical approximations are used to accurately describe the complex many body interactions that take place in liquids.

Two independent case studies of liquid polymorphism are presented here. The first is a stable liquid-liquid phase transition was found to occur in Cerium which was initially discovered through X-Ray diffraction experiments and later confirmed through simulation. This phase transition is predicted to end at a critical point.

The second is a comprehensive study of the structure and dynamics of Germanium's many metastable amorphous and liquid phases. This is currently the largest ab-initio based study of the dynamics of Germanium's metastable liquid phases. Methods ranging from the mean square displacement to the van Hove function and intermediate scattering function are introduced and analyzed. The micro-structural characteristics are quantified and correlated with the mobility in the material revealing dynamical heterogeneity.

Indexing (document details)
Advisor: Sheng, Howard
Commitee: Blaisten-Barojas, Estela, Papaconstantopoulos, Dimitrios, Shehu, Amarda
School: George Mason University
Department: Computational Sciences and Informatics
School Location: United States -- Virginia
Source: DAI-B 76/10(E), Dissertation Abstracts International
Subjects: Condensed matter physics, Materials science, Computer science
Keywords: Diffraction, Dynamics, Liquid, Polyamorphism, Simulation, Structure
Publication Number: 3706976
ISBN: 9781321812336
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