JPH05332971

PURPOSE:To obtain a nitrogen oxide detecting sensor being inexpensive and durable 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 base 2 provided with a gas detecting part 3 which is formed in a thin film of a composite oxide having electric conductivity or semiconductivity and expressed by a formula Bi2-XAXSr2CanCun+1O2n+6-delta and by providing current applying electrodes 4 and voltage detecting electrodes 5 which are connected electrically with this gas detecting part 3. In the formula, A is a group IVb element, (x) is 0 to 2, (n) is 1 or greater and delta is 0 to 0.2. The composite oxide has a layer-shaped oxygen lattice defect structure in a crystal structure and a nitrogen oxide molecule is made to coordinate with and eliminated from a portion of an oxygen defect reversibly. When this reaction occurs, the gas 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 is detected by using the electrodes 4 and 4 and thereby the concentration of a nitrogen oxide gas contained in the air, a combustion exhaust gas or the like can be detected.