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Description
Ag-doped CaCu3Ti4O12 (CCTO) thin films with different doping concentrations were prepared by a sol-gel technique. Films were grown by depositing four layers of CCTO on alumina substrates followed by sputtering Au/Cr interdigitated electrodes to fabricate gas sensors. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). The films have predominantly the perovskite CCTO crystal phase with very small amount of TiO2 secondary phases. In this work, both undoped CCTO and Ag-doped CCTO thin films were tested for selective sensing to H2S gas relative to NH3, H2, NO2 and ethanol vapor. For characterizing gas sensing properties of the films, gas concentrations in the range of 0.2-10 ppm were used with operating temperatures ranging from 150 to 350 °C. When compared to undoped CCTO sensor, the Ag-doped CCTO sensors presented much higher response. The best sensitivity towards H2S was found in 0.9 wt% Ag-doped CCTO film and at the optimum operating temperature of 250 °C. The highest response of the sensor based on the 0.9 wt% Ag-doped CCTO film to 10 ppm of H2S is approximately ten times than that of a sensor based on undoped CCTO film. The doped film sensor also showed stability and relatively short response and recovery times. Therefore, Ag-doped CCTO films with small doping concentration constitute an excellent candidate for developing H2S sensors operating at low-temperatures.
