Structural, morphological and textural properties of iron manganite (FeMnO3) thick films applied for humidity sensing

Abstract

Iron manganite (FeMnO3) powder with a cubic (bixbyite, Ia (3) over bar) crystal structure was obtained by a solid state reaction. Thick film paste (powder + organic vehicles) was screen printed on alumina substrate with test interdigitated PdAg electrodes. Significant porosity (60.6%) composed of macropores (larger than 100 nm) was determined by Hg porosimetry, changing only slightly from the first extrusion run indicating a stable pore system. Hg porosimetry evaluation of thick film samples enabled estimation of true textural parameters of the thick film compared to powder. Impedance response of the thick film sensor was monitored in a humidity chamber in the relative humidity (RH) range 30-90%, at room temperature (25 degrees C) and frequency range from 42 Hz to 1 MHz. At 100 Hz the impedance reduced from 10.41 M Omega for RH 30% to 0.68 M Omega for RH 90%. Analysis of complex impedance using an equivalent circuit showed the dominant influence of grain boundaries. The sensor response and recovery was fast (several seconds) and a relatively low hysteresis value of 2.8% was obtained.