Static High Pressure Instrumentation, Metallic Xenon, and Band-Overlap Metallization of Thallium-Iodide

The thesis is divided essentially into three parts: the first part deals with high pressure instrumentation and includes an analysis of the problems associated with the use of a small diameter collimators to illuminate samples in a diamond anvil cell with polychromatic x-rays in an energy dispersive x-ray diffraction experiment. Computer codes for the analysis of x-ray diffraction data and optical reflectivity and absorption data are presented. Formulae that simplify the analysis of hexagonal, tetragonal, and orthorhombic powder diffraction patterns are derived. Two optical systems, one for the collection of reflectivity and absorption data and the other for the collection of Raman spectra, are described. The second focus of the thesis is on solid xenon. A high resolution energy dispersive x-ray diffraction spectrum of the so-called intermediate phase is presented and the possibility of this phase being a mixture of HCP and FCC with stacking faults is discussed. A high pressure equation of state for HCP xenon is measured and used to measure the pressure of the xenon insulator-metal transition (150 GPa). The equation of state was constructed using the rhenium gasket as the pressure marker. This represents the first time such a measurement has been made. The x -ray data are correlated to the optical absorption data and band structure calculations to form a complete picture of the transition of solid xenon to the metallic state. Finally, optical work on thallium iodide is presented and correlated with the unpublished x-ray work of Chen showing that this material undergoes an insulator-metal transition by band-overlap metallization at 15 GPa.