Fabrication and characterisation of nanocrystalline composites of Ca<inf>1−x</inf>Co<inf>x</inf>MoO<inf>4</inf> (x = 0, 0.3, 0.5, 0.7, 1) prepared by co-precipitation method as a humidity sensor

The effect of substitution of scheelite structure of calcium–cobalt molybdate (CaCM, Ca1−xCoxMoO4; x = 0, 0.3, 0.5, 0.7, 1) for humidity sensor application was studied. The composites were prepared using a co-precipitation method with different mole ratios. As-prepared composites were studied by TG/DTA analyses to find out the sintering temperature of the prepared the composites. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed in order to identify phase composition and crystallite structure. The composites were characterised by Fourier Transform-Infrared spectroscopy, Fourier Transform-Raman spectroscopy, transmission electron microscopy (TEM) and UV–visible absorption spectroscopy. Surface area of composites was studied using Brunauer–Emmett–Teller (BET) analysis. The composites were subjected to solid-state dc electrical conductivity for humidity sensing at room temperature. The resistance measurements as a function of relative humidity (RH) in the range of 5–98% were carried out and the sensitivity factors (Sf = R5%/R98%) were calculated. Our results showed high sensitivity (Sf) of Ca0.7Co0.3MoO4 (CaCM-2) as 5252 ± 157 compared with that of the end composites CaMoO4 (CaM-1) and CoMoO4 (CoM-5). The response and recovery times of CaCM-2 showed 150 and 110 s, respectively.