Investigation on electrical transport, CO sensing characteristics and mechanism for nanocrystalline La1−xCaxFeO3 sensors

The appropriate doping of Ca in nanocrystalline LaFeO3 not only reduces the electrical resistance, but also enhances the sensing response. A minimum of resistance for nanocrystalline La1−xCaxFeO3 (x = 0-0.35) occurs at about x = 0.3 with a value of Fe4+/Fe3+≈1. The electrical conduction of La1−xCaxFeO3 (x = 0-0.35) can be well described by the mechanism of small polaron hopping. Results of X-ray photoelectron spectroscopy (XPS) show that the proportion of adsorbed oxygen Oads enhances monotonously with Ca doping from x = 0-0.35. However, there exists an optimal Ca content (about x = 0.2) for obtaining highest response to 200 ppm CO among La1−xCaxFeO3-based sensors (0≤x≤0.35). Such results indicate that some parts of adsorbed oxygen species do not effectively release their electrons to the surface of La1−xCaxFeO3 at higher Ca dopants. The gas sensing response to CO for La1−xCaxFeO3 sensors depends not only upon the amount of adsorbed oxygen on grain surfaces of sensors, but also upon the desorption capabilities of adsorbed oxygen species through reacting with CO.