Factors influencing the electric conductance of SnO2 gas sensors

The ever increasing concern about air pollution, the need to monitor potentially hazardous gases and to improve the efficiency of combustion processes has stimulated during the past three decades an extensive research and development of gas sensors. Among various types of gas sensing devices, most popular became the chemoresistive sensors based on the surface characteristics of semiconducting oxides, most commonly termed semiconductor gas sensors SGS. They offer the advantages of small size, simple operation, high sensitivity and simple associated electronics. They detect small concentrations (up to a few ppm) of reducing gases (H₂, CO, NO_x, hydrocarbons, alcohol vapours) in oxygen containing atmospheres (usually air) by variations in their electrical conductance. Besides the atmospheric composition, however, and depending on the conditions of preparation of the semiconducting oxide (heat treatment, doping), other important factors which produce conductance variations are the temperature of operation and the electrical phenomena at the electrodes. In our laboratory we concentrated on the study of sintered SnO₂ thick-film samples, by means of electrical conductance measurements. In the following we shall try to point out some ways of exploiting such measurements for the explanation of some peculiarities observed in the operation of SnO₂ SGS