Mixed Oxide Capacitor of CuO—BaTiO 3 as a New Type CO 2 Gas Sensor

An oxide capacitor consisting of BaTiO 3 and an oxide is studied as a new type CO 2 sensor based on capacitance change. Sensitivity to CO 2 , as well as the optimum operating temperature, was strongly dependent on the particular oxide mixed with BaTiO 3 . Among the elements investigated in this study, CuO–BaTiO 3 exhibited the highest sensitivity to CO 2 . In particular, the CuO–BaTiO 3 mixed oxide at the equimolar composition is highly sensitive to CO 2 . The optimum operating temperature and frequency for CuO–BaTiO 3 are 729 K and 100 Hz, respectively, and the 80% response time to 2% CO 2 is within 25 s. The equimolar mixture of CuO and BaTiO 3 can measure the CO 2 concentration from 100 to 60 000 ppm. Carbonation of oxide seems to play a key role for the detection of CO 2 on these mixed oxide capacitors. The optimum operating temperature of these mixed oxide capacitors for CO 2 detection, therefore, correlates with the decomposition temperature of the carbonate corresponding to the oxide mixed with BaTiO 3 . The capacitance increase of CuO–BaTiO 3 upon exposure to CO 2 seems to result from the elevated height of the potential barrier at the grain boundary between CuO and BaTiO 3 . Carbonation of CuO in the element seems to bring about the elevation in the height of the potential barrier.