Selective SO2 detection at low concentration by Ca substituted LaFeO3 chemiresistive gas sensor: A comparative study of LaFeO3 pellet vs thin film

Abstract

Abstract A comparative study of La1-xCaxFeO3 (0.4 ≤ x ≤ 0.8) pellets and La0.6Ca0.4FeO3 thin films for the selective detection of low concentration SO2 gas has been performed. The La0.6Ca0.4FeO3 thin films exhibited superior gas sensing performance than La1-xCaxFeO3 (0.4 ≤ x ≤ 0.8) pellets in terms of sensitivity, operating temperature, detection limit, response, and recovery time. The HRTEM images confirm the nanoparticle nature of the La1-xCaxFeO3 (0.4 ≤ x ≤ 0.8) samples. The material crystallizes in the orthorhombic crystal system with the Pbnm space group. Further, occupancy refinement of neutron diffraction data indicates the presence of oxygen vacancies which was also supported by XPS analysis. Among the various compositions of La1-xCaxFeO3 (0.4 ≤ x ≤ 0.8), the x = 0.4(La0.6Ca0.4FeO3) was found to exhibit the best gas sensing performance and chosen for thin film preparation. The gas sensing studies of thin films, prepared by the DC magnetron sputtering method, confirm the enhanced gas sensitivity towards 3 ppm SO2 gas at a low operating temperature of 120 °C. The selectivity studies show that La1-xCaxFeO3 (0.4 ≤ x ≤ 0.8) preferentially detects SO2 gas at the given operating condition over other gases such as CH4, CO2, and CO. The gas sensing mechanism and high sensitivity of the La1-xCaxFeO3 sensor towards the detection of SO2 gas were explained by DFT calculations which give evidence for the strong binding of SO2 molecules on the 121 surface of the sensor.