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

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