The Complex Behavior of Nitrogen Under Pressure: Ab Initio Simulation of the Properties of Structures and Shock Waves

"I report ab initio simulations of nitrogen as a function of temperature and pressure that reveal new structures and basic features of the phase diagram. In particular, the simulations show there are many structures with competitive ground state energies at the volumes that a non-molecular phase is predicted. This most favorable new structure consists of hexagonally packed zig-zag metallic chains. I show several structures to be very stable, implying large barriers to transitions. Furthermore, if there are competing structures with large barriers, it is possible for nitrogen to be transformed by pressure and temperature to an amorphous glassy structure. I investigate such amorphous glassy structures and find them to have similarities with the experimental data. I suggest a way to passivate defects in our amorphous structure leading to increased range of metastability, even to zero pressure at low T. I find characteristics of both the cubic gauche and hexagonally packed chain structure in the amorphous structure, and conclude that the experimental structure may be an amorphous collection of small clusters of these two structures. I have also carried out simulations as a function temperature that, in addition to qualitatively reproducing the experimental principle Hugoniot, predict the anomalous behavior of nitrogen under shock wave conditions, including ""double-shock-induced cooling"". I show quenching from these high temperature phases also reveals the tendency toward structures including chains and cubic-gauche-like bonding."

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Mattson, William David

Contributors dc:contributor

• Martin, Richard M.

• Physics, Condensed Matter

Language dc:language

eng

Identifier

(MiAaPQ)AAI3101918

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/80496