Effect of 3d transition metals on gas sensing characteristics of perovskite oxides LaFe1-xCoxO3

Nano-crystalline powders of LaFe1-xCoxO3 (with x = 0.0; 0.1; 0.2; 0.3 and 0.4) were synthesized by the sol-gel technique. By X-ray diffraction examination, it was concluded that Fe in octahedra (BO6) of the perovskite LaFe1-xCoxO3 oxides could be replaced by Co. The gas-sensing characteristics of LaFe1-xCoxO3 based thick-film sensors were investigated in various gases including carbon monoxide (CO), methane (CH4), propane (C3H8), n-hexane (C6H14) and nitrogen dioxide (NO2). It was found that the electrical conductance and gas-sensing characteristics of the LaFe1-xCoxO3 oxides were strongly influenced by the ions of 3d transition metals, particularly Co ions, with the possibility to exist in different valence states (Co2+ and Co3+). It was also observed that the LaFe1-xCoxO3 sensors had high sensitivity and selectivity to CO with Co contents (x) of around 0.1. The decrease in stability of the LaFe1-xCoxO3 sensors upon increasing the Co content was discussed in relation to the stability and reversibility of the valence states of Co and Fe ions.