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 degrees 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 degrees 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 degrees C the impedance reduced. 7 times (from 35.74 MO for RH 40% to 4.91 MO for RH 90%) and at 50 degrees C. 33 times (from 30.98 MO for RH 40% to 0.944 MO for RH 90%). Low hysteresis (1.82 and 3.65%) was obtained at 25 and 50 degrees 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.