JPH05332969

PURPOSE:To obtain a nitrogen oxide detecting sensor having a relatively simple and inexpensive structure and durability, by providing a gas detecting part of which the main constituent is a specific composite oxide and electrodes which are connected electrically with the gas detecting part. CONSTITUTION:A nitrogen oxide detecting sensor includes a gas detecting part of which the main constituent is a composite oxide having electric conductivity or semiconductivity and expressed by a formula A2-XA'XMO4-delta and electrodes 4 and 5 which are connected electrically with the detecting part 3. In the formula, A is a group IIIa element, A' is a group IIa element, M is a transition metal element which can be bivalent, (x) is a number smaller than 2, and delta is 0 to 0.2. In this composite oxide, a nitrogen oxide gas reacts reversibly with M of the surface thereof by a vapor-solid phase reaction. When this adsorptive reaction occurs, the detecting part 3 shows a change in an electric resistance value in accordance with the concentration of a nitrogen oxide in a vapor phase. This change in the electric resistance value is detected by using the electrodes 4 and 5 provided for the sensor and thereby the concentration of the nitrogen oxide gas contained in the air, a combustion exhaust gas or the like can be detected easily.