The influence of Fe2O3 in the humidity sensor performance of ZrO2:TiO2-based porous ceramics

ZrO2:TiO2 ceramics were prepared with different porosity values by two methods: (a) sintering at 1150, 1300 and 1500 °C, corresponding to the temperatures of the first, second and third sintering stages, according to dilatometry results; (b) adding Fe2O3 (2.0 and 5.0 mol%) to ZrO2:TiO2 powders before sintering. The ZrO2:TiO2 specimens were characterized by X-ray diffraction, mercury porosimetry, scanning electron microscopy and impedance spectroscopy. The impedance spectroscopy analysis was carried out under different relative humidities. The bulk electrical resistivity in the low frequency region (10–100 Hz) decreases for increasing relative humidity. Increasing the sintering temperature from the first to the third sintering stage promoted grain growth, as expected, with consequent decrease of the intergranular porosity. The use of Fe2O3 as sintering aid reduced the porosity of the specimens, but increased the electrical response under humid environments in comparison with specimens sintered without Fe2O3.