Molecular Dynamics Simulations of Structural Transitions in Crystalline and Amorphous Inorganic Compounds

Using MD simulations I have (i) gained detailed insights into the transformation mechanisms of crystalline silica, (ii) discovered the structure of high-density C-III cristobalite (a phase that has been known to exist but was never indexed), (iii) revealed a ubiquitous tendency for oxygen ordering in various high-density crystalline phases of silica, and (iv) used the knowledge gained concerning structural transitions in crystalline silica to explain the nature of polyamorphism in the non-crystalline counterparts of this material. I observed both reversible and irreversible polyamorphic transitions in silica glass, depending on the thermo-mechanical condition at which the transitions take place. Macroscopically, reversible transitions are manifest in the anomalous thermo-mechanical behaviors of silica glass, such as an increase of the mechanical moduli upon expansion. Irreversible polyamorphic transitions occur under large compressive stresses provided adequate thermal activation for the necessary bond exchanges to take place. This leads to a permanent densification of silica glass. In addition to tetrahedral SiO 2, I also investigated vitreous B2O3, representative of network glasses that exhibit mixed coordination states under pressure. My MD simulations show that cation coordination change plays a crucial role in the polyamorphic transitions in B2O3 glass, whereas in silica it does not. Through this research, I gained a fundamental understanding of the atomistic origin of various anomalous behaviors in materials, such as negative thermal expansion, increase of elastic moduli with temperature, amorphization of crystals under compression, and polyamorphic transitions.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science and Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Huang, Liping

Contributors dc:contributor

• Kieffer, John

• Engineering, Materials Science

Language dc:language

eng

Identifier

(MiAaPQ)AAI3130937

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/82750