Preparation and characterization of nanocrystalline doped TiO₂

Nanocrystalline TiO₂ powders, doped in range of 0.05-5 mol% Nb and Ta, have been prepared using a chemical method. Synthesized powders have an anatase crystal structure and a fine particle size of 10-20 nm. Energy-dispersive X-ray microanalysis shows uniform dopant distribution in the powder. Temperature dependence of resistivity for both the Nb- and Ta-doped TiO₂ sintered at 1300°C exhibits n-type conductivity in the range 100-500°C with an activation energy of about 0.2 eV. It was found by transmission electron microscope analysis that the dopants in the doped TiO₂ sintered samples are segregated on grain boundaries after repeated high temperature treatment regardless of doping ranges. Addition of Zr in small amount (about 1 wt%) sufficiently suppresses such phase segregation, improving the high temperature stability.