Thick films of nanostructured TiO2 and tantalum--doped TiO2 have based fabricated by screen--printing technology starting from pure titania and tantalum--doped titania powders prepared by sol--gel method. The titania powders, obtained via sol--gel, show crystalline anatase structure and the particles are homogeneous and nanosized (30 ÷ 50 nm). Two series of films each one composed by pure and Ta--doped titania samples have been obtained by firing the pastes in air atmosphere at the temperatures of 650°C and 850°C, respectively. SEM observations and electrical characterizations showed that the firing temperature strongly influences the nanostructure and the gas response of the pure titania samples. The addition of tantalum inhibits the grain sintering at the higher temperature. Moreover the electrical data show that the tantalum addition (10 at.%) does not affect the conductance of the films in air while significantly enhances the response towards CO and leaves almost unaltered or enhances its ability to sense NO2 depending on the thermal treatments
