Abstract The present thesis focused on the synthesis and phase transformation of tohdite and alumina via static compression of gels at high temperature-pressures and dynamic laser ablation condensation of metal target under oxygen background gas. In part I, hydrous Al2O3-TiO2 (78:22 in molar ratio) gel was fired at various PT conditions using a piston-cylinder apparatus and identified by XRD, FTIR, optical microscopy and electron microscopy. Below 675oC, the sample remained amorphous at ambient pressure, yet transformed at 1.5 kbar to Ti-doped tohdite, which is elongated along the crystallographic c-axis, with well-developed (0001) base and {10 0} faces. Tohdite has a significant water/hydroxy content and is therefore susceptible to pore coalescence parallel to the basal layer upon electron dosage. Tohdite also contains Ti4+ up to 3 at.%, which replaces Al3+ in tetrahedral and/or octahedral sites to form superstructures and defect microstructures. In contrast, a higher T-P condition (above 675oC and 8 kbar) caused the formation of more stable Ti-doped corundum, which is hexagonal-rhombohedral crystal form and in epitaxial association with rutile nuclei. Ti-doped tohdite and corundum shed light on a sol-gel route for their occurrence in peraluminous metamorphic rock. The nanoporous and nanodelaminated tohdite may have potential catalytic applications (Part I). In part II, amorphous Al2O3 nanocondensates were synthesized via very energetic Nd-YAG laser pulse irradiation of oxygen-purged Al target for a very rapid heating/cooling effect. The nanocondensates above a critical diameter of 20 nm were phase separated as

Pulsed laser ablation ¡]PLA¡^in single shot on polycrystalline Ti thin foil ca. 20

The specific surface area reduction and pore size distribution coupled with N2 adsorption-desorption hysteresis isotherm were studied in the temperature range of 1400-1550¢J for periclase MgO powder having 0.1£gm in size and with face-centered cubic structure. The apparent activation energy of such a rapid coarsening-coalescence process for MgO powder was estimated as 181¡Ó3kJ/mol. The minimum temperature for sintering/coarsening/coalescence of submicron MgO particles was estimated to be near 1300¢J based on the extrapolation of steady specific surface area reduction rates to zero. Pulsed laser ablation (PLA) of periclase MgO powders in water was conducted under Q-switch mode and specified water height and water depth (10 mm) for an accumulation time of 5 and 20 minutes at 10 Hz. Such a PLA process has successfully synthesized nanosized and protonated MgO particles from Mg(OH)2 and lamellar precusors, implying the three phases may co-exist at high pressure and temperature conditions upon dynamic shock loading. A significant internal compressive stress up to 10 GPa was built up for the MgO but not the readily relaxed Mg(OH)2 nanocondensates. The lamellae-derived Mg(OH)2 tended to undergo a dehydroxylation process to become MgO following a specific crystallographic relationship, i.e. lamellar basal layer parallel to Mg(OH)2(0001) and MgO(111). The minimum band gap of the colloidal solution of MgO/Mg(OH)2/lamellae was lowered to ca. 5.2eV after the PLA process.

This research deals with the synthesis and characterization (transmission electron microscopy and optical spectroscopy) of composite nanocondensates produced by pulse laser ablation (PLA) on Zn, Zn-Cu and Cu-Au targets in liquid or vacuum. First, wurtzite-type (W)-ZnO and