Influence of CO2 in dry and wet atmospheres on the response of Mg-doped SrTiO3 ceramic oxygen sensors

The effect of CO2 on the response of Mg-doped SrTiO3 oxygen sensors both under dry and wet conditions is investigated. The results show that the Mg-doped SrTiO3 sensor exhibits p-type conducting characteristics and good oxygen-sensing properties in dry atmospheres containing O2, N2 and even CO2. CO2 gas can be thus regarded as a non-influential gas in dry atmospheres and the resistance of the sensor follows the oxygen partial pressure according to the standard expression irrespective of pCO2 changes. If CO2 coexists with water vapour, the oxygen sensor can only operate properly at CO2 concentrations below 70% and its resistance starts to deviate from the oxygen partial pressure dependence at CO2 concentrations of more than 80%. A model based on defect chemistry, grain structures and conduction mechanism of this material is developed to explain the experimental results satisfactorily. 18 refs.