Structural, optical and excellent humidity sensing behaviour of ZnSnO₃ nanoparticles: effect of annealing

The chemi-resistive humidity sensing behaviour of as prepared and annealed fcc-ZnSnO₃ nanoparticles synthesized using wet chemical synthesis method is reported here. The effect of annealing on the evolution of varied nano-morphology of ZnSnO₃ is in accordance to Ostwald’s ripening law. The optical energy bandgap energy change from 4.64 to 3.84 eV for annealed samples confirms the role of annealing over improved sensing performance. At room temperature, an excellent humidity sensitivity of 4155% and response/recovery time of 19/22 s. is observed for 500 °C annealed ZnSnO₃ sample within 08–97% relative humidity range. The experimental data observed over the entire range of RH values well fitted with the Freundlich adsorption isotherm model, and revealing two distinct water adsorption regimes. This indicates that with an increase in annealing temperature the samples show improved adsorption capacity and strength. The excellent humidity sensitivity observed in the annealed nanostructures is attributed to Grotthuss mechanism considering the availability and distribution of available adsorption sites. This present result proposes utilization of low cost synthesis technique of ZnSnO₃ holds the promising capabilities as a potential candidate for the fabrication of next generation humidity sensors.