CROSS-SENSITIVITY OF VARIOUS DOPED STRONTIUM-TITANATE FILMS TO CO, CO2, H2, H2O AND CH4

Doped and undoped films made from SrTiO3 have proved to be promising m aterials for use in high-temperature oxygen sensors (600<T<1000-degree s-C). Studies on the cross-sensitivity of these materials constitute a n important basis for understanding sensor signals. Reactive gases suc h as CO and CO2 have only a reducing effect when present in concentrat ions of 1% in oxygen-containing gas mixtures (1% O2, the remainder bei ng N2). The strongest effect is seen at about 575-degrees-C, H-2, H2O and CH4 also have a reducing effect in oxygen-containing atmospheres b elow a temperature that is dependent on the reactive gas in question. However, above these temperatures such gases have an 'oxidizing' effec t. These effects can be explained on the basis of a surface model for SrTiO3 that assumes that the positive surface charge at the grain surf ace is at least partially counterbalanced by OH groups.