Impedancemetric acetylene gas sensing properties of Sm-Fe-based perovskite-type oxide-based thick-film device

Perovskite-type Sm1−xCaxFeO3 (x = 0, 0.05, 0.20, 0.50, 0.75, 1.0) powders as sensor materials were prepared by a wet-chemical route using a polymer precursor method at 750 °C. A perovskite-type oxide thick-film device prepared by a screen-printing method was used for an acetylene (C2H2) sensor for which outputs were measured by AC impedance spectroscopy at 400 °C. Although sensitivities of the devices using oxides with Ca2+ substitution were decreased because of reduction in the amount of impedance change between air and sample gas, the device without Ca2+ substitution showed extremely high response at a low frequency. According to Nyquist's plots of the SmFeO3 device, this is attributed to the fact that impedance of charge transfer from the surface reaction was taken at a low frequency. It was also found that the sensor devices showed good selectivity to interference gases.