Synthesis and characterization of perovskite-type BaMg0.33Nb0.67-xFexO3-δ for potential high temperature CO2 sensors application

Mixed ionic-electronic conducting BaMg0.33Nb0.67-xFexO3-delta was successfully synthesized by conventional solid state method in air at elevated temperature. Fe-doping helped to increase the total conductivity, while the chemical stability under CO2 at elevated temperatures and under H2O vapour at boiling conditions decreased with increasing Fe content above x = 0.17 in BaMg0.33Nb0.67-xFexO3-delta. Maximum total conductivity of 10(-3) S cm(-1) at 300 degrees C was obtained for BMNF33 in air, and further increase in Fe content lowered the electrical conductivity, particularly at low temperatures. Activation energy, in the range of 300-700 degrees C, for total electrical conduction was found to decrease in air by the incorporation of Fe in BaMg0.33Nb0.67O3 (BMN) (BMN: 0.96 eV; BMNF17: 0.72 eV; BMNF33: 0.25 eV). Furthermore, the x = 0.17 composition demonstrated excellent CO2 sensing characteristics at 700 degrees C. The investigated perovskite-type metal oxides seem to be promising candidates for monitoring CO2 (ppm level in air) at elevated temperatures.