Abstract
Characteristics of H3PMo12O40 and its salts used as humidity sensor has been studied at 20°C. Comparatively rapid response was obtained for thin-films of Cs3PMo12O40 and {(CH3) 2NH0} 3PMo12O40. As the relative humidity changed from 0 to 90%, the impedance decreased by a factor of 103. The resistance-humidity correlation is greatly changed by cation-substitution. Based on the comparison of these resistance-humidity correlations and adsorption (absorption) properties, it was revealed that the resistance depends on the amount of the adsorbed (absorbed) water and that there are three different mechanisms of water adsorption (absorption) : (1) Capillary condensation in micro and mesopores (e. g., Cs3PMo12O40 and {(CH3) 2NH2} 3PMo12O40). (In this case the logarithm of impedance changed almost linearly with the relative humidity). (2) Adsorption without capillary condensation on hydrophilic surface (e.g., (NH4) 3PMo12O40). (3) Absorption into the bulk (e. g., H3PMo12O40 and Na3PMo12O40).
