Defect Problems in the Filed of Chemical Sensors

A review of some of the problems in chemical gas sensors is presented which are related to defects and disorder in the material in the basic sensing element. The article is aimed at a readership which has a background in defect science but only a limited experience in sensors. Four types of gas sensor are discussed as illustrative examples; namely (i) catalytic sensors for detecting flammable gases (pellistors), (ii) oxygen monitors based on zirconia, (iii) semiconducting metal oxide sensors for detecting reducing gases and (iv) semiconducting organometallic films for monitoring oxides of nitrogen. For each type of sensor an outline of the principles of its operation is presented. This section is then followed by a detailed discussion of some of the problems encountered in the operation of these sensors. Emphasis is given to the role of the techniques that are described in other chapters in this Volume can play in the study of sensor materials. This is particularly important as the need for the careful characterization of sensor materials emerges as a dominant requirement in sensor development.