High-T NO_x Sensing Elements Using Conductive Oxides and Pt

Development of NO_x sensing elements intended for operation at T ∼600 °C are described. The elements were fabricated by depositing co-planar La_1-x Sr_x BO₃ (B = Cr, Fe) and Pt electrodes on yttria-stabilized zirconia substrates. Characterization of the elements included response to NO₂ and NO as well as the [O₂] dependence of the NO₂ response. Much stronger (∼ 40 mV for 450 ppm NO₂ in 7 vol% O₂ at 600 °C) sensing responses were observed for NO₂ than NO, indicating these elements are best suited for detection of NO₂. Pronounced asymmetries were observed between the NO₂ step response and recovery times for the elements, with temperature being the primary variable governing the recovery times in the temperature range 500–700 °C.