The preparation and electrical properties of TiO_2−xF_x

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 TiO_2−x F_x 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 TiO_2−x F_x 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.