Effects of previous treatments on the electrical response of SnO2-thick films exposed to a CO atmosphere

The influence of CO on the electrical conductivity on SnO2 thick films is studied. Possible sensing mechanisms are discerned by measuring the conductivity as a function of temperature during heating and cooling, and the transient responses to step changes in CO pressure at constant temperature. Studies of samples with prior treatments confirm the proposed mechanisms responsible for the observed film responses. The film conductivity is affected by CO adsorption and by reaction with previously adsorbed oxygen. Also, the oxygen vacancy concentration in the grains can be altered and, as a consequence, the sample resistivity.