Pressure-induced structural modifications in dioxides of group IVB elements: Titanium dioxide, zirconium dioxide and hafnium dioxide.

Abstract

Four specific studies are presented in this thesis, regarding the high-pressure phases of the three compounds. ZrO$\sb2$ was studied at pressures of up to 73 GPa using energy dispersive X-ray (EDX) diffraction techniques. The quenched phase was analysed using angle dispersive X-ray (ADX) diffraction with imaging plates, and was identified as having a cotunnite-type structure (space group Pnma) by Rietveld refinement. HfO$\sb2$ was also studied to 72 GPa using EDX diffraction measurements, and its quenched phase was also identified as having a cotunnite-type structure, based on the simularities of its EDX and Raman spectra with those of the quenched phase of ZrO$\sb2$. TiO$\sb2$ was involved in two separate studies. The first is a Raman spectroscopic study up to 73 GPa, starting with anatase. Some EDX diffraction measurements were also taken to pressures up to 105 GPa. Additionally, EDX diffraction measurements of TiO$\sb2$ up to 28 GPa were taken to determine the equations of state of its high-pressure phases, starting with anatase and furtile at atmospheric pressure. (Abstract shortened by UMI.)