CO₂ and SO₂ tolerant Fe-doped metal oxides for solid state gas sensors

Perovskite-type BaMg_0.33Nb_0.34Fe_0.33O _{3 - δ} (BMNF) and double perovskite-type Ba₂Ca _0.66Nb_0.68Fe_0.66O_{6 - δ} (BCNF) were prepared by conventional solid-state reaction at 1400 °C in air. Ex-situ powder X-ray diffraction (PXRD) and high temperature PXRD (30-700 °C) of BCNF and BMNF under CO₂ and SO₂ exhibited excellent chemical stability. Chemical stability under SO₂ was further confirmed by scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX), where no sulfur-containing compounds were detected within the detection limit of the equipment. BCNF and BMNF were tested for their sensing properties in CO₂ and SO₂ at 500-700 °C by applying constant DC voltage (0.1 V). Ag and Pt current collectors were employed as electrodes for BCNF and showed similar response at 600 °C (t₉₀ = 7 min) for ppm level of CO₂ in dry synthetic air. BCNF sensor was found highly stable and very selective toward CO₂ in presence of SO₂ (0 - 20 ppm)