Enhancement of H2S-sensing performances with Fe-doping in CaCu3Ti4O12 thin films prepared by a sol–gel method

In this work, the effects of Fe-doping on structural and gas-sensing properties of CaCu3Ti4O12 (CCTO) thin film prepared by a sol–gel method were systematically studied. Sol–gel-derived CCTO thin films with different Fe-doping concentrations were deposited on alumina substrates by spin-coating and Au/Cr interdigitated electrodes were patterned onto the films by photolithography, sputtering and lift-off processes. Characterizations by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and X-ray absorption near edge structure confirmed the perovskite CCTO phase with TiO2 and CuO secondary phases and suggested the substitution of Fe3+ ions at Ti4+ sites of CCTO structure. From gas-sensing measurements, Fe dopants greatly enhance H2S response, response time and H2S selectivity against NH3, CO, C2H2, CH4, ethanol and NO2. In particular, 9 wt% (∼3 at%) Fe-doped CCTO sensor exhibited the highest response of ∼126 to 10 ppm H2S, which was more than one order of magnitude higher than that of the undoped CCTO sensor at a low optimum operating temperature of 250 °C. The roles of Fe-dopant on gas-sensing mechanisms of CCTO sensor were proposed.