Investigation of Sm1-xCaxFe0.7Co0.3O3 films (x=0.0-0.3) prepared by modified sol-gel spin-coating method for carbon monoxide and propane gas sensing

Sm1-xCaxFe0.7Co0.3O3 thin film gas sensors with different calcium concentrations (x = 0.0-0.3) were prepared using a modified sol-gel spin-coating method and then annealed at 650 A degrees C for 2 h in air. The thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrical resistance measurements at concentrations from 1 to 200 ppm for carbon monoxide (CO) and from 1 to 500 ppm for propane (C3H8) in the temperature range of 25-300 A degrees C for both gases. The resulting XRD data reveal that a pure phase with perovskite structure was obtained for each substitution in x and corresponds to the orthorhombic system with a Pbnm space group. Topography and roughness of the coating were obtained by AFM; roughness results of the sample do not significantly affect the response of the sensor, but the Ca2+ content does. Morphology of the nanoparticles and the thickness of each doping in calcium were observed by SEM, and the thickness was around 300 nm. The gas-sensing characteristics of the Sm-Ca-Fe-Co-O system were investigated in CO and C3H8 gases. It was found that the electrical resistance and gas-sensing characteristics were influenced by the substitution of Sm2+ by Ca2+ ions. When x was greater than or equal to 0.2 and CO concentration was 200 ppm and operating temperature was 300 A degrees C, there was a higher response of the sensor, reaching up to 100%. For operating temperatures below 100 A degrees C, the response of the Sm1-xCaxFe0.7Co0.3O3-based sensors to CO or C3H8 was < 5% regardless of the degree of substitution of Ca. On the other hand, at temperatures above 100 A degrees C, the response depended on the gas to be sensed. In addition, the partial substitution of Ca in the structure increased the response of the sensor in relation to CO and C3H8 concentrations. It is suggested that this is due to the process of electric valence compensation.