CO Sensing Properties of TiO2 Based on the p-n Transition Induced by Carbon Monoxide at High Temperatures

Rutile TiO2 based semiconductor-type sensors were investigated for sensing CO within the temperature range from 600℃ to 800℃. The sensor showed p-type behavior to CO (20−2000 mg/m 3 ) when tested in oxygen con- centrations varied from 10% to 2% between 600℃ and 700℃. The response of the sensor decreased significantly as the temperature increased from 600℃ to 700℃ approaching to one. However, when the temperature was above 750℃, an n-type behavior of the sensor to CO was observed. This n-type response further increased when the temperature in- creased to 800℃. AC impedance was employed to study the conduction behaviors of the TiO2 thick film in both varied oxygen concentrations and CO environment at 800℃. The results indicate that the change of the oxygen ion/vacancy concentrations in the bulk TiO2 is probably the reason for the p-n conduction transition induced by CO.