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

Abstract

Nano-crystalline powders of LaFe_1−xCo_xO₃ (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 LaFe_1−xCo_xO₃ oxides could be replaced by Co. The gas-sensing characteristics of LaFe_1−xCo_xO₃ 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 LaFe_1−xCo_xO₃ 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 LaFe_1−xCo_xO₃ sensors had high sensitivity and selectivity to CO with Co contents (x) of around 0.1. The decrease in stability of the LaFe_1−xCo_xO₃ sensors upon increasing the Co content was discussed in relation to the stability and reversibility of the valence states of Co and Fe ions.