Mechanism of NO_x Sensing by the Variation of Conductivity of La₂CuO₄

抄録

In order to make clear the mechanism of the variation in the conductivity of La₂CuO₄ with a small amount of NO_x (x=1, 2) in oxygen atmosphere, measurements were made on the conductivity of La₂CuO₄ in the stream of NO_x-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(NO_x). 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.