In this report, the structures, morphologies, optical, electrical and gas sensing properties of ZnO and ZnO: Na spin-coated films are studied. X-ray diffraction (XRD) results reveal that the films are of a single phase wurtzite ZnO with a preferential orientation along (002) direction parallel to c-axis. Na doping reduces the crystalline quality of the films. The plane surface of ZnO film turned to be wrinkle net-work structure after doping. The reflectance and the optical band gap of the ZnO film decreased after Na doping. The wrinkle net-work nanostructured Na-doped film shows an unusually sensitivity, 81.9% @ 50 sccm, for CO₂ gas at room temperature compared to 1.0% for the pure ZnO film. The signals to noise ratio (SNR) and detection limit of Na-doped ZnO sensor are 0.24 and 0.42 sccm, respectively. These enhanced sensing properties are ascribed to high surface-to-volume ratio, hoping effect, and the increase of O- vacancies density according to Kroger VinK effect. The response time increased from 179 to 240 s by the incorporation of Na atoms @50 sccm. This response time increased as the CO₂ concentration increased. The recovery time is increased from 122 to 472 s by the incorporation of Na atoms @50 sccm.

Nano-sized chromium oxide (Cr₂O₃) was synthesized by sol-gel method and mixed with polyvinyl alcohol (PVA) to produce nanocomposite films. Scanning electron microscopy (SEM) was used to observe the morphology and dispersion of Cr₂O₃ on the surface of the PVA films. X-ray diffraction (XRD) was performed on nano-sized Cr₂O₃, pure PVA, and Cr₂O₃/PVA composites. Based on the results of both XRD and high-resolution transmission electron microscopy (HR-TEM), the average particle size of the Cr₂O₃ was ≈ 46 nm. Differential scanning calorimetry (DSC) showed that the thermal stability and degree of crystallinity of the PVA were reinforced by the addition of Cr₂O₃ nanoparticles. The absorbance and extinction coefficients of the composites were studied in the UV-vis range and compared with those of pure PVA. The optical energy band gap, E_g, was calculated. Dielectric constant, ε′, dielectric loss modulus, M″, and ac conductivity, σ_ac, of all samples were measured within temperature and frequency ranges of 300–468 K and 10 kHz-2 MHz, respectively. According to the frequency and temperature dependence of the dielectric loss modulus, M″, the observed α-relaxation peak was due to the micro-Brownian motion of the polymer main chains. The behavior of σ_ac(f) for the composite films indicated that the conduction mechanism was correlated barrier hopping (CBH). The results of this work were discussed and compared with those of previous studies of PVA composites.