Titania gels in liquid media crystallized from amorphous to anatase at temperatures as low as 120 °C, while the onset of crystallization in air was 370 °C. The crystallization rate in water was much faster than in methanol and n-hexane, and the crystallite size of anatase prepared in water was larger than of those prepared in organic solvents. The crystallized powders were capable of efficient hydrogen evolution following band gap irradiation in the presence of a sacrificial hole acceptor such as methanol. The photocatalytic activity of powder crystallized in methanol was superior to those prepared in water and air.

The substitution of fluorine for oxygen in TiO2 was investigated by the reaction of Ti2O3, TiO2, and TiF3 under conditions of 4–6.5 GPa and 700–1400°C. The single phase of TiO2−x Fx solid solution was obtained in the region of 0≤x≤0.7. According to the x-ray diffraction data, the a and c axes of the rutile-type structure linearly increased with increasing fluorine content. The electrical resistivities of TiO2−x Fx were in the range from 10 Ω cm for x = 0.3 to 850 Ω cm for x = 0.7 at 300 K and the relationship between In ρ and 1000/T was linear. The activation energies were estimated to be from 0.17 eV at x = 0.3 to 0.28 eV at x = 0.7. Also, the thermoelectric powers at room temperature changed from 250μV/K to + 50 μV/K. The mechanism of electric conduction was discussed on the basis of the extended band model of rutile.