Mechanism of NOx Sensing by the Variation of Conductivity of La2CuO4 (特集環境ガスセンサ)

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In order to make clear the mechanism of the variation in the conductivity of La2CuO4 with a small amount of NOx (x=1, 2) in oxygen atmosphere, measurements were made on the conductivity of La2CuO4 in the stream of NOx-02-N2 gas mixtures at temperatures 773-1023K and the outlet gas was analyzed by a zirconia sensor. The conductivity and the EMF of the zirconia sensor were analyzed in relation to P(NOx). P(O2) and T. When NO2 was applied to La2CuO4, catalytic reaction of NO2→NO+(1/2)O2 was found to take place. In the catalytic reaction process, excess oxygen was considered to be incorporated into La2CuO4. Under the steady state. the oxygen potential in La2CuO4 was kept much higher than that in the gas phase. resulting in the increase in the p-type conduction of La2CuO4. Numerical calculations were made for the oxygen potential enhanced in La2CuO4 as a function of P(NO2) and T to make clear the detection limits of La2CuO4-type NO2 sensors in relation to the gas phase P(O2) and T. Under the condition studied, NO affects very little to reduce the conductivity of La2CuO4. The reason was discussed based on the catalytic reaction kinetics to show the direction to enhance the NO effect in La2CuO4.
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