Impedance spectroscopy of undoped and Cr-doped ZnO gas sensors under different oxygen concentrations

► Cr doped ZnO is tested for gas sensing applications and for the best of our knowledge have not been studied previously. ► Cr doped ZnO can detect different oxygen concentration at low operating temperature. The operating temperature of the Cr doped ZnO gas sensor was shifted to 250 °C, and showed an enhancement towards oxygen gas. ► From impedance spectroscopy analysis, it showed that the resistance due to grain boundaries contributed significantly to the response behavior of the gas sensor.