GAS SENSING RESPONSE OF NICKEL DOPED CALCIUM COPPER TITANATE THIN FILMS SYNTHESIZED BY SOL-GEL METHOD

Abstract

Nickel-doped calcium copper titanate (Ni-doped CCTO) thin films prepared by nickel oxide (NiO) and nickel (II) acetate (C4H6NiO4) have been synthesized using sol-gel method. Four layers of Ni-doped CCTO films with various nickel dopant concentrations including undoped film were deposited by a spin coating technique on silicon and alumina substrates. Each film layer was annealed at a fixed annealing temperature of 800 °C. All samples were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) field emission scanning electron microscope (FESEM). Only the doped films prepared by NiO were analyzed by Raman spectroscopy. Moreover, the CCTO films were fabricated as gas sensors to measure gas sensing properties. XRD patterns showed that the main phase of undoped and Ni-doped CCTO were a cubic perovskite structure and there is only a small amount of impurity phase of rutile TiO2. The XPS signals confirmed that Ni2+ was found in Ni-doped CCTO films. Moreover, FESEM images presented the films thickness of approximately 400-600 nm for four-layered films on silicon and the surface of the films contained granular particles. In case of gas sensing property measurements, the obtained films were tested towards different types of gases (NO2, H2, NH3, H2S and ethanol). All films exhibited the best selectivity towards H2S compared to other gases. In addition, the sensor response of the films increases with increasing Ni-doping concentrations. The 7 wt% Ni-doped CCTO sensor prepared by NiO exhibited the highest sensor response of 112 under 10 ppm H2S at 250 °C while the highest sensor response of 5 wt% Ni-doped CCTO sensor prepared by nickel (II) acetate was 175 at 300 °C. In both cases, the sensor response of Ni-doped CCTO films is more than that of the undoped indicating that Ni-dopants in the films acting as a catalyst improve much better sensor responses.