Electrical and optical properties of ZnO–WO3 nanocomposite and its application as a solid-state humidity sensor

This study reports the humidity sensing characteristics of ZnO–WO3 nanocomposite. Pellet samples of 0–5 weight% ZnO in WO3 were sintered from 300 to 600∘C. When exposed to humidity, the resistance of the sensing samples was found to decrease with increase in relative humidity (RH). Five percent ZnO-doped WO3 showed maximum sensitivity of 20.95 M Ω/%RH in 15–95% RH range. Sensor parameters like reproducibility, aging, hysteresis, response and recovery times were also studied. Sensing mechanism is discussed in terms of sintering temperature, composition and crystallite size of the sensing element. It was observed that sensing mechanism is strongly based on annealing temperature and percentage of doping. The sensing samples have also been investigated by X-ray diffraction, scanning electron microscope (SEM) and Raman spectroscopy. The crystalline size of the sample was identified by powder X-Ray Diffraction data. The SEM analysis was used to study the surface morphology. The structure, phase and the degree of crystallinity of the materials were examined by Raman spectroscopy.