Humidity sensing properties of nanocrystalline pseudobrookite (Fe2TiO5) based thick films

Pseudobrookite based nanopowder was obtained by solid state synthesis of starting hematite and anatase nanopowders in the weight ratio 55:45. Structural and morphological properties were analyzed using X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV/Vis diffuse reflectance spectroscopy, Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM) confirming the formation of nanocrystalline pseudobrookite. The obtained powder was mixed with a binder (ethyl cellulose), dispersant (alpha-terpinol) and adhesion agents (acetic acid and distilled water) to obtain a thick film paste. It was screen printed on alumina substrate with interdigitated PdAg electrodes and fired at 600 degrees C for 30 min. Formation of a porous nanocrystalline thick film structure was shown using Scanning electron microscopy (SEM), while Hall measurements enabled determination of carrier mobility. Change of impedance response in the frequency range 42 Hz-1 MHz with humidity was analyzed at room temperature (25 degrees C) and 50 degrees C in the relative humidity range 30-90% and 40-90%, respectively. At 42 Hz, and room temperature the impedance reduced similar to 28 times, while at 50 degrees C it reduced similar to 147 times in the relative humidity range 40-90%. The sensor showed rapid response (16 s) and relatively low hysteresis (8.39% at 25 degrees C and 2.64% at 50 degrees C) showing that this is a promising material for application in humidity sensing