Fabrication and characterisation of nanocrystalline composites of Ca_(1-x)Co_xMoO_4 (x = 0, 0.3, 0.5, 0.7, 1) prepared by co-precipitation method as a humidity sensor

摘要

The effect of substitution of scheelite structure of calcium-cobalt molybdate (CaCM, Ca_(1-x)Co_xMoO_4; 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_(0.7)Co_(0.3)MoO_4 (CaCM-2) as 5252 ±157 compared with that of the end composites CaMoO_4 (CaM-1) and CoMoO_4 (CoM-5). The response and recovery times of CaCM-2 showed 150 and 110 s, respectively.