A GAS SENSOR WITH POROUS FILMS OF BI2SR2CACU2O8+X - AN ANALYSIS OF THE RESPONSE

A systematic investigation has been carried out on the time dependence of the response to NO and CO of a gas sensor with a thick porous film of Bi2Sr2CaCu2O8+x (BSCCO). The oxidation of reducing gases such as NO and CO by lattice oxygen occurs in parallel with desorption of NO2 and CO2, respectively, in the whole range of temperatures investigated. An extension of a reported model has been proposed in order to describe the response of the sensor. The time dependence of the electrical resistivity can be interpreted by assuming a conductivity dominated by Schottky barriers at grain boundaries. A kinetic model underlying the temperature dependence of the sensitivity to NO and the selectivity against CO is discussed. The high sensitivity to NO as compared to that to CO is attributed to the high adsorption rate of NO at low temperatures. The good selectivity at high temperatures is attributed to the rapid increase of the desorption rate of CO and/or CO2 with increasing temperature. The response time increases with increasing equilibrium sensitivity S-0. The recovery time decreases with increasing S-0. They both decrease with increase of the desorption rate of CO(NO) and CO2(NO2).