Structural, electrical and humidity sensing properties of nano-structured nickel oxide prepared by sol–gel method

In this paper, we have presented the synthesis of nickel oxide (NiO) nanoparticles using sol–gel method and measured its structural, electrical and humidity sensing properties using different measurement tools after annealing at three different temperatures of 200 °C, 400 °C and 700 °C for 1 h in air. Structural and morphological properties of nickel oxide nanoparticles were measured by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. XRD analysis shows the crystallographic nature of prepared NiO nanoparticles. The result shows that the average crystallite size increases with increase in annealing temperature which reveals a fine nanocrystalline grain structure. The Williamson–Hall and size-strain plots were used to study the individual contribution of crystallite size and strain on the peak broadening of NiO nanoparticles. The parameters including stress and strain were also calculated from the XRD corresponding to the cubic phase of NiO. The FESEM images confirm the mesoporous surface morphology of a nickel oxide with an increase in particle size on increasing annealing temperature. The effect of annealing on the activation energy of the pellets is also discussed in the paper. Samples in the form of pellets were exposed to humidity in the range from 10 to 90% relative humidity (RH). NiO sample annealed at 700 °C has demonstrated the highest sensing response of 47.09% at 90% RH.