Fabrication and characterisation of nanocrystalline composites of Ca_1−xCo_xMoO₄ (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, Ca_1−xCo_xMoO₄; 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 (S _f = R _5%/R _98%) were calculated. Our results showed high sensitivity (S_f) of Ca_0.7Co_0.3MoO₄ (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.