Application of Nanocrystalline Pseudobrookite (Fe2TiO5) Thick Films for Humidity Sensing

Pseudobrookite nanocrystalline thick films were screen printed on alumina substrate with small interdigitated PdAg electrodes (width 6 mm, length 12 mm, electrode spacing 0.2 mm) and fired at 600°C for 30 minutes. Scanning electron microscopy (SEM) of the thick film surface confirmed the formation of a porous structure consisting of agglomerated nanocrystalline grains of pseudobrookite. Impedance response of pseudobrookite thick film samples was measured in a humidity chamber at operating temperatures of 25 and 50°C in the relative humidity (RH) range 40-90% and frequency range 42 Hz-1 MHz. At the lowest frequency of 42 Hz at 25°C the impedance reduced ~7 times (from 35.74 MΩ for RH 40% to 4.91 MΩ for RH 90%) and at 50°C~ 33 times (from 30.98 MΩ for RH 40% to 0.944MΩ for RH 90%). Low hysteresis (1.82 and 3.65%) was obtained at 25 and 50°C, respectively. Complex impedance was analyzed using an equivalent circuit consisting of parallel impedance and constant phase (CPE) element showing the dominant influence of grain boundaries.