Dynamic Compression to Ultrahigh Pressures

Abstract

In this dissertation, different experimental techniques are employed and developed in order to study the physical properties of geologically important materials to extreme conditions relevant to the Earth's interior and beyond.

Iron and magnesium oxide are the two key minerals of the Earth's interior and planetary bodies, each representative of the major composition of the core and mantle. Understanding the structure and dynamics of planetary bodies requires measurements of the equation of state to ultra-high pressures. A new experimental platform for dynamic ramp compression (or shockless compression) on iron and magnesium oxide has been developed and tested on both materials up to as high as 273 GPa. The new findings provide a method to study these materials in the solid phase to ultrahigh pressure and bridge the gap between traditional shock compression (adiabatic path) and static compression (isothermal path).

Modeling the interior of a planetary body also requires determination of phase boundaries of the constituent materials at high pressure. Theoretical calculation using density functional theory can predict the solid-solid and solid-liquid transition pressures. However, there is poor agreement among different theoretical approaches and experiments, especially for transition metals. Molybdenum is an important transition metal used as a high-pressure standard material. The structure of solid molybdenum and its melting point under shock loading are here determined up to 1000 GPa with a newly developed x-ray diffraction technique combined with ramp/shock compression, which now provides the ability to determine the solid-solid and solid-liquid transition to extremely high pressure. This enables us to test theoretical calculations and resolve the discrepancies between theory and experiments.

Quartz is a geologically abundant and technically important mineral. It is one of the most common minerals in the Earth's crust and SiO2 is the major oxide component of Earth's interior. The elasticity of single-crystal quartz was measured up to 10 GPa under hydrostatic conditions using the diamond anvil cell (DAC) and Brillouin spectroscopy. The new results provide measurements of the elastic tensor at high pressure and resolve the long-standing discrepancy between previous experimental data and theoretical calculations at high pressure.