FT-IR CHARACTERIZATION OF TIN DIOXIDE GAS SENSOR MATERIALS UNDER WORKING-CONDITIONS

In this work self-supporting tin dioxide disks are characterized using FT-IR spectroscopy in the presence of a reducing gas in air, and in d ifferent O-2/N-2 mixtures at temperatures varying from room temperatur e up to 450 degrees C. Every factor inducing a change in the oxygen co ntent of the gas atmosphere above the tin dioxide, as for instance a t emperature change, a surface reaction or adsorption of another species , induces a broad, intense IR absorption band with discrete weak bands superimposed on it. This broad absorption is assigned to the electron ic transition from a native donor level, the oxygen vacancy in the bul k of the domain, to the conduction band of the tin dioxide material. F or the interpretation of the narrow, superimposed absorptions, two hyp otheses remain. The results demonstrate that FT-IR spectroscopy is an extremely suitable technique for the characterization of semiconductin g metal oxide sensors, since it allows to follow in situ the processes in the bulk, at the surface and in the surrounding gas atmosphere of the sensor material at working temperature as well as in the presence of reducing gases in air.