Influence of Annealing Temperature on Structural, Morphological and NH3 Sensing Properties of Nanostructured WO3 Porous Films

The tungsten trioxide (WO3) precursor was prepared by sol-gel method with tungsten powder as the raw material, and the WO3 gas sensing films were obtained by a dip coating method and annealing precursor in air. X-ray diffraction (XRD) spectra indicate that with increasing annealing temperature the triclinic structure of as-prepared sample was transformed into monoclinic or orthorhombic phase. The images of scanning electron microscopy (SEM) exhibit that the WO3 grain sizes increase from less than 100 nm to several micrometers with increasing annealing temperature. The influences of applied frequency, annealing and operating temperature on NH3 gas sensing properties of the nanostructured WO3 porous films were investigated. The results indicate that the gas sensing film annealed at 500°C express high sensitivity, fast response and recovery speed to NH3 at operating temperature 250°C.