Concentration dependent dielectric, AC conductivity and sensing study of ZnO-polyvinyl alcohol nanocomposite films

The dielectric properties of polyvinyl alcohol (PVA) - zinc oxide (ZnO) hybrid nanocomposite films for different concentrations of nano ZnO (5 mol%-20 mol%) have been studied at ambient temperature in the frequency range 10 Hz-10 MHz. These studies indicate that the dielectric constant is maximum for 10 mol% ZnO-PVA hybrid film. An unusual low intensity loss peak is observed around 2.5-5 MHz in all the samples and this peak is more pronounced in the 10 mol% ZnO film. Impedance and modulus spectroscopy have been used to understand the dielectric and conductivity behaviour of these samples. These samples exhibit high bulk resistance and the Cole-Cole plot shows only the onset of the semicircles at room temperature. AC conductivity is found to obey Jonscher's power law and the enhancement in the conductivity is found to be highest for 10 mol% ZnO doped PVA nanocomposite film suggesting its suitability for use in sensing applications. The gas sensing performance of the hybrid films for detection of various gases such as NO2, H2S, NH3, LPG, and C2H5OH was studied and compared with that of pure PVA film. It was found that the hybrid sensor can complement the drawbacks of pure PVA as porous surface morphology and surface area of interface of nano-ZnO plays a vital role in sensing applications. At ambient temperature, 100 ppm concentration of both NO2 gas and H2S gas exhibit maximum response of 7.1% and 4.1% respectively for the 10 mol% hybrid sensor, whereas at 50 ppm concentration of H2S gas the 20 mol% ZnO-PVA sensor was found to be more sensitive with a reasonable response of 7%.